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

Abstract

The invention discloses a holographic photopolymerization material, a holographic photosensitive film, a holographic optical element and display equipment, and relates to the field of high polymer materials. The holographic photopolymerization material comprises a photosensitizer, a photopolymerization monomer and a polymer matrix. The photopolymerizable monomer and the photosensitizer are distributed within 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 the side chain of the polymer matrix comprises a secondary reaction functional group. And the conversion rate of the secondary reaction functional group under the first condition is less than or equal to 30%, so that the photopolymerization monomer can migrate in the polymer matrix with the linear structure under the first condition, and the holographic optical element with better optical performance is obtained. Furthermore, the holographic optical element can be placed under a second condition, so that the secondary reaction functional groups are crosslinked, the thermodynamic property of the holographic optical element is further improved, and the holographic optical element can still keep better optical performance in a higher-temperature environment.

Description

Technical Field

[0001] 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

[0002] Holographic technology is based on the principles of optical interference and diffraction. By introducing a reference light wave to interfere with the object light wave, the amplitude and phase information of the object light wave is recorded on the holographic recording medium in the form of interference fringes. Then, the original object light wave is reproduced by the diffraction of the light wave, thereby reproducing the three-dimensional image of the original object. Holographic technology can include: the holographic recording process. Among them, the holographic recording process can be understood as recording / storing the optical information of the object using the interference principle. Holography can include: optical information such as the amplitude and phase of the light wave.

[0003] Holographic technology usually uses holographic photosensitive film to record / store light information such as the amplitude and phase of light waves. The material used in holographic photosensitive film can be called holographic recording medium. Holographic photopolymer material is a commonly used holographic recording medium. As a holographic polymer material, holographic photopolymer material has attracted much attention due to its wide photosensitivity range, easy manufacturing and transportation, and good long-term storage stability.

[0004] In recent years, with the expansion of the application field of holographic technology, the application temperature is relatively high in some fields. For example, in-vehicle and airborne display applications. The holographic photopolymer materials disclosed in the related art are prone to random movement of polymer chain segments under high temperature environments, resulting in a decrease in the optical performance of the holographic optical element / holographic photosensitive film formed by the holographic photopolymer materials. The decrease in optical performance may include: decreased diffraction efficiency, decreased transmittance, increased haze, and diffraction peak drift, etc., which limits the application of holographic photopolymer materials in the fields of vehicle-mounted and airborne displays. Summary of the invention

[0005] The present 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 photopolymerization monomer, and a polymer matrix. The refractive index of the polymer matrix is ​​less than the refractive index of the photopolymerization monomer, and the side chain of the polymer matrix comprises: a secondary reaction functional group. The secondary reaction functional group can be cross-linked under a second condition to obtain a holographic optical element with good thermodynamic properties.

[0006] The first aspect of 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 chain of the polymer matrix comprises: a secondary reactive functional group, the secondary reactive functional group is cross-linked under the second condition, and the conversion rate of the secondary reactive functional group under the first condition is less than or equal to 30%.

[0007] 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 to the coherent bright area and polymerize. This ultimately results in the coherent bright area and the coherent dark area having monomer polymers with different concentrations. The refractive index of the photopolymerizable monomer is greater than the refractive index of the polymer matrix, and correspondingly, the refractive index of the monomer polymer is greater than the refractive index of the polymer matrix. Therefore, the coherent bright area and the coherent dark area have different refractive indices, thereby achieving holographic recording / storage.

[0008] The photopolymerizable monomer and the photosensitizer are distributed in the polymer matrix, and the photopolymerizable monomer is polymerized under the first condition. The molecular structure of the polymer matrix includes: a linear structure, and the side chain of the polymer matrix includes: a secondary reactive functional group. The conversion rate of the secondary reactive functional group under the first condition is less than or equal to 30%, thereby ensuring that the photopolymerizable monomer can migrate in the polymer matrix of the linear structure under the first condition to obtain a holographic optical element with better optical properties. Furthermore, the holographic optical element can be placed under the second condition to crosslink the secondary reactive functional groups, thereby improving the thermodynamic properties of the holographic optical element, so that the holographic optical element can still maintain better optical properties under a higher temperature environment.

[0009] 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.

[0010] In combination with an implementation of the first aspect, the side chain of the polymer matrix further includes: fluorine element. In this implementation, the side chain of the polymer matrix includes: fluorine element (F), and the presence of F can reduce the refractive index of the polymer matrix so that the holographic optical element obtained by the holographic photopolymer material has better optical properties.

[0011] In combination with an implementation of the first aspect, the polymer matrix includes: at least one monomer.

[0012] 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.

[0013] In this implementation, the side chain of the polymer matrix includes: F. The presence of F can reduce the refractive index of the polymer matrix so that the holographic optical element prepared by the holographic photopolymer material has a higher diffraction efficiency. The side chain of the polymer matrix also includes: secondary reaction functional groups. The conversion rate of the secondary reaction 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 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.

[0014] In combination with an implementation of the first aspect, 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.

[0015] 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 under the first condition is less than or equal to 30%, thereby ensuring that under the first condition, the photopolymerizable monomer can migrate within the polymer matrix of the linear structure 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.

[0016] 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.

[0017] In this implementation, the polymer matrix may include: the side chain of the fourth monomer includes: at least one of hydrogen and an alkyl substituent. The introduction of the fourth monomer can adjust the glass transition temperature of the holographic photopolymer material.

[0018] 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.

[0019] In this implementation, the secondary reaction functional group includes at least one of vinyl ether, allyl group, epoxy group, carboxyl group and thiol group. The conversion rate of the secondary reaction functional group is less than or equal to 30% under the first condition, and the secondary reaction functional group can be cross-linked under the second condition. This ensures that the photopolymerizable monomer can migrate in the polymer matrix of the linear structure under the first condition, thereby obtaining 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 group, thereby improving the thermodynamic properties of the holographic optical element.

[0020] In combination with an implementation of the first aspect, the secondary reaction functional group further includes: isocyanate and hydroxyl.

[0021] In this implementation, the secondary reaction functional groups include: isocyanate and hydroxyl. The conversion rate of isocyanate and hydroxyl under the first condition is less than or equal to 30%, thereby ensuring that the photopolymerizable monomer can migrate within the polymer matrix of the linear structure, thereby obtaining a holographic optical element with better optical properties. Further, the holographic optical element can be placed under the second condition to crosslink the isocyanate and hydroxyl, thereby improving the thermodynamic properties of the holographic optical element.

[0022] In combination with an implementation of the first aspect, the number average molecular weight of the polymer matrix is ​​20,000-300,000.

[0023] 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.

[0024] In combination with an implementation of the first aspect, the glass transition temperature of the polymer matrix is: -20°C-120°C.

[0025] In combination with an implementation of the first aspect, the mass fraction of fluorine element in the polymer matrix is ​​5%-30%.

[0026] In this implementation, the mass fraction of fluorine element in the polymer matrix is ​​5%-30%. The holographic photopolymer material containing the polymer matrix can have both better film-forming performance and better optical performance.

[0027] In combination with an implementation of the first aspect, a refractive index of the polymer matrix is ​​less than or equal to 1.48.

[0028] The refractive index of the polymer matrix disclosed in the present implementation 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.

[0029]

[0030] In one implementation of the first aspect, the molecular structure of the polymer matrix includes: R4 R5 R6, wherein R1 includes: a hydrogen atom or a methyl group; R2 includes: a hydrogen atom or a methyl group; R3 includes: a hydrogen atom or a methyl group; 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.

[0031] The second aspect of the 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 adopts the holographic photopolymer material disclosed in the first aspect.

[0032] Among them, the effects that can be achieved by 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.

[0033] The third aspect of the embodiment of the present application discloses a holographic optical element, comprising: a protective layer and a second film layer covering the protective layer, the material used for the second film layer comprises: a polymer matrix and a monomer polymer, the molecular structure of the polymer matrix comprises: a cross-linked structure; the second film layer comprises: a coherent bright area and a coherent dark area, 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 photopolymerizable monomers.

[0034] 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, and the refractive index of the area where the monomer polymer is polymerized (coherent bright area) is relatively high, while the area without the monomer polymer or the area with less monomer polymer polymerization (coherent dark area) can be understood as the background, and the refractive index of the background is relatively low. The monomer polymer can be used together with the background to record the holographic information. The molecular structure of the polymer matrix in the second film layer is a cross-linked structure, so the holographic optical element has better heat resistance. The holographic optical element can still maintain better optical properties in a higher temperature environment.

[0035] The fourth aspect of the 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 chain of the polymer matrix comprising: a secondary reaction functional group, the secondary reaction functional group cross-linking under a second condition, the conversion rate of the secondary reaction functional group under the first condition being less than or equal to 30%; under the first condition, the photopolymerizable monomer forms a monomer polymer to obtain a second film layer, the second film layer comprising: a coherent bright area and a coherent dark area, the density of the monomer polymer in the coherent bright area being greater than the density of the monomer polymer in the coherent dark area; under the second condition, the secondary reaction functional groups cross-linking to form a cross-linked structure to obtain a holographic optical element.

[0036] 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.

[0037] The fifth aspect of the embodiments of the present application discloses a display device, including: a display screen and an optical element arranged on the display screen; the optical element includes: the holographic photosensitive film disclosed in the second aspect or the holographic optical element disclosed in the third aspect.

[0038] 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

[0039] Figure 1 is a flow chart of a process for preparing a holographic optical element;

[0040] Figure 2 The flowchart of the method for preparing a holographic photosensitive film disclosed in a feasible implementation mode is as follows;

[0041] Figure 3 A flowchart of a method for preparing a holographic optical element disclosed in a feasible implementation manner;

[0042] Figure 4 is a schematic diagram of a holographic recording system;

[0043] Figure 5 The present invention is a flow chart of a method for preparing a holographic optical element disclosed in a feasible implementation manner. DETAILED DESCRIPTION

[0044] 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 of the embodiments.

[0045] In the following, the terms "first", "second", etc. are used only for descriptive purposes to distinguish between identical or similar items with substantially identical functions and effects, and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features.

[0046] Also, in the description of the present application, unless otherwise specified, “plurality” means two or more than two.

[0047] Meanwhile, in the embodiments of the present 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 the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a concrete manner for ease of understanding.

[0048] First, the concepts involved in the embodiments of the present application are explained:

[0049] Interference is the phenomenon that when two or more waves meet in space, they superimpose or cancel each other out to form a new waveform.

[0050] Amplitude: The maximum value that a light wave can vibrate to.

[0051] Phase is the position of a light wave at a specific moment in its cycle.

[0052] A light beam is a form of light wave, specifically a beam of light wave.

[0053] Macromolecular compounds generally refer to compounds with a relative molecular mass of several thousand to several million and have excellent mechanical properties.

[0054] Linear structure is a type of structure of polymer compounds. The entire molecule of the linear structure is like a long chain.

[0055] Crosslinked structure, also known as network structure, is a three-dimensional network structure of polymer compounds.

[0056] 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.

[0057] 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.

[0058] The refractive index modulation degree is an important parameter of holographic photopolymer materials, which reflects the degree to which the holographic photopolymer materials are controlled by light wave signals.

[0059] Transmittance is an important parameter of holographic photopolymer materials, which can be expressed by the ratio of the light flux passing through the holographic photopolymer material to its incident light flux.

[0060] 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.

[0061] Holographic technology, also known as virtual imaging technology, uses the principles of interference and diffraction to record and reproduce the real three-dimensional image of an object. Holographic projection technology can include: the holographic recording process and the holographic reproduction process.

[0062] The holographic recording process can be understood as using the interference principle to record the optical information of an object. Specifically: a part of the light wave is irradiated on the object to be photographed to form an object beam related to the object to be photographed; another part of the light beam is projected onto the holographic film (the holographic film in the embodiment of the present application can 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 a spatially varying intensity, so that the contrast and interval between the interference fringes are used to record all the optical information of the object beam (referred to as hologram in the embodiment of the present application). Among them, the optical information may include: phase, amplitude. In the embodiment of the present application, the holographic film used to record the interference fringes can be referred to as a holographic photosensitive film, or a holographic film.

[0063] The holographic reproduction 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 photo, 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 can generally give two images, namely the original image (also called the initial image) and the conjugate image. The two images can provide users with a strong sense of three-dimensionality and a real visual effect. Each part of the hologram records the light information of each point on the object being photographed, so in principle, each part of it can reproduce the entire image of the object being photographed. Through multiple exposures, multiple different images can be recorded on the same film, and they can be displayed separately without interfering with each other.

[0064] Visible holographic technology can use holographic optical elements to store light information such as the amplitude and phase of light waves. Holographic optical elements can replace lenses, gratings, reflectors or more complex optical elements in optical systems, and are used in high-tech fields such as head-up display (HUD), augmented reality (AR) glasses, holographic 3D projection, high-end anti-counterfeiting, and high-density data storage.

[0065] For example, in vehicle-mounted head-up display devices, holographic optical elements are used to prepare holographic windshields. The high diffraction efficiency of holographic optical elements is used to project relevant information required for driving onto the vehicle's windshield, effectively improving the driving experience and driving safety. At the same time, its excellent heat resistance can meet the harsh use environment of the vehicle. In AR glasses, optical waveguide technology is used to guide the image light source diffracted by the holographic optical element into the glass or resin for total reflection, and finally diffracted by the holographic optical element into the human eye to form an image.

[0066] As a holographic polymer material, holographic photopolymer is often used as the material of holographic optical elements due to its wide photosensitivity range, easy manufacture and transportation, and good long-term storage stability.

[0067] Holographic photopolymer materials can be prepared based on coherent laser technology. They are structurally ordered polymer materials that can simultaneously store all information such as light wave amplitude and phase. Holographic photopolymer materials can include: photosensitizer, polymer matrix and photopolymer monomer.

[0068] The polymer matrix can provide mechanical support for the holographic photopolymer material, bond 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 referred to as 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 difference in refractive index between the photopolymer and the polymer matrix, forming a holographic optical element with periodic phase separation.

[0069] The following is a further description of the preparation process of the holographic optical element in conjunction with the accompanying drawings:

[0070] See also Figure 1 The holographic photopolymer material comprises: 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 .

[0071] See also Figure 1 (ii) in the figure. The holographic photopolymer material may be irradiated with light wave A, so that part of the holographic photopolymer material is exposed and part of the holographic photopolymer material is not exposed. The exposed area may be referred to as a coherent bright area 11, and the unexposed area may be referred to as a coherent dark area 12.

[0072] Usually, the coherent bright regions 11 and the coherent dark regions 12 are distributed alternately. 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.

[0073] 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.

[0074] Please continue reading Figure 1 (ii) in the coherent dark area 12. The photopolymerizable monomer 100 hardly polymerizes. The radiation energy of the light wave A in the coherent bright area 11 prompts the photosensitizer to generate active intermediates, that is, the active intermediates exist in the coherent bright area 11. The active intermediates cause the photopolymerizable monomer 100 located in the coherent bright area 11 to polymerize to form a photopolymer, causing the concentration of the photopolymerizable monomer 100 in the coherent bright area 11 to decrease.

[0075] 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 .

[0076] See also Figure 1 In (iii), the concentration difference of the photopolymerizable monomer 100 causes the photopolymerizable monomer 100 in the dark area 12 to migrate to the bright area 11.

[0077] The polymer matrix 200 is cured into a film, so that the photopolymerizable monomer 100 stops migrating, and the Figure 1 The holographic optical element shown in (iv) in FIG. In the holographic optical element, the refractive index of the coherent bright region 11 is close to the refractive index of the photopolymer, and the refractive index of the coherent dark region 12 is close to the refractive index of the polymer matrix 200, and the refractive index of the photopolymer is greater than the refractive index of the polymer matrix 200. Therefore, the holographic optical element has a grating structure with a periodic change in refractive index.

[0078] Based on the above description, it can be known that the role of the polymer matrix 200 in the holographic optical element includes: 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.

[0079] 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.

[0080] One way to increase the refractive index difference between the polymer matrix 200 and the photopolymer may be:

[0081] Large conjugated structures such as sulfur (S), selenium (Se), benzene ring, and naphthalene ring 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.

[0082] Another way to increase the refractive index difference between the polymer matrix 200 and the photopolymer may be:

[0083] 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 , so as to increase the refractive index difference between the polymer matrix 200 and the photopolymer.

[0084] Specifically, the related art discloses a holographic photopolymer material, which may include: a film-forming resin (which may be referred to as a polymer matrix 200 in the embodiment of the present application). The film-forming resin is obtained by polymerizing a fluorinated monomer and a vinyl monomer. The vinyl monomer is selected from vinyl ester, vinyl alcohol, vinyl ether, and vinyl acetal, and the fluorinated monomer is selected from perfluorinated monomers, vinyl fluoride, vinylidene fluoride, fluorinated olefins, and fluorinated alkyl esters of acrylic acid or methacrylic acid. The mass fraction of fluorine in the film-forming resin is about 3% to 25%.

[0085] 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 degree, and the holographic optical element has a higher diffraction efficiency.

[0086] 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.

[0087] 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.

[0088] 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 degree of the holographic optical element, so that the holographic optical element has a higher diffraction efficiency.

[0089] In the solution disclosed in the related art 1, the film-forming resin contained in the holographic photopolymer material has a linear molecular structure. The thermodynamic properties of the holographic photopolymer material are poor, resulting in poor stability of the grating structure of the holographic optical element, which affects the optical properties of the holographic optical element.

[0090] Specifically, under high temperature conditions, the polymer chain segments of the film-forming resin are prone to movement, resulting in deformation of the grating structure of the holographic optical element. The deformation of the grating structure will cause an all-round decline in the optical properties of the holographic optical element, such as the refractive index modulation, light transmittance, and haze.

[0091] In order to further improve the optical properties 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.

[0092] For example, the related art 2 discloses a holographic photopolymer material, wherein the film-forming resin used in the holographic photopolymer material is obtained by reacting a polyisocyanate component with an isocyanate-reactive component such as a polyol, and the film-forming resin has a three-dimensional cross-linked structure. The photopolymerizable monomer 100 used in the holographic photopolymer material includes: an acrylate compound. The film-forming resin in the holographic photopolymer material disclosed in the related art 2 has a three-dimensional cross-linked structure, so that the holographic photopolymer material has better thermodynamic properties, and the holographic optical element obtained from the holographic photopolymer material has better optical properties.

[0093] For another example, Related Art 3 discloses a photopolymer composition (holographic photopolymer material) for forming a hologram recording medium, wherein the film-forming resin in the photopolymer composition is a polymer formed by cross-linking a siloxane polymer containing at least one silane functional group and an acrylic polyol, and the film-forming resin has a cross-linked structure. Related Art 3 further discloses that the temperature and humidity durability of the holographic photopolymer material can be further improved by optimizing the cross-linking density of the film-forming resin.

[0094] The cross-linking density of the cross-linked film-forming resin is relatively high, which inhibits the migration of the photopolymerizable monomer 100 during holographic recording, so that the refractive index difference between the coherent bright area and the coherent dark area of ​​the final holographic optical element is relatively small, and the diffraction efficiency of the holographic optical element is relatively low.

[0095] 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.

[0096] The polymer matrix can provide mechanical support for the holographic photopolymer material. The photopolymer monomer and the photosensitizer are dispersed in the polymer matrix. The photosensitizer can absorb light waves and produce active intermediates that polymerize the photopolymer monomer. During holographic recording (the first condition), the holographic photopolymer 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. The polymerization of the photopolymer monomer is initiated, and the concentration difference of the photopolymer monomer thus produced causes the photopolymer monomer to diffuse to 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 photopolymer monomer is greater than the refractive index of the polymer matrix, and accordingly, the refractive index of the monomer polymer is greater than the refractive index of the polymer matrix. Therefore, the coherent bright area and the coherent dark area have different refractive indices, thereby achieving holographic recording / storage.

[0097] The molecular structure of the polymer matrix includes: a linear structure, and the side chain of the polymer matrix includes: a secondary reaction functional group. The conversion rate of the secondary reaction functional group under the first condition is less than or equal to 30%, thereby ensuring that under the first condition, the photopolymerizable monomer can migrate in the polymer matrix of the linear structure, thereby obtaining a holographic optical element with a higher diffraction efficiency, that is, obtaining a holographic optical element with better optical performance. Further, the holographic optical element can be placed under the second condition to crosslink the secondary reaction functional groups, thereby improving the thermodynamic properties of the holographic optical element, so that the holographic optical element obtained from the holographic photopolymer material can have excellent optical properties at a higher temperature, and the holographic optical element obtained from the holographic photopolymer material can be applied to more fields.

[0098] Optionally, the conversion rate of the secondary reactive functional group under the first condition is less than or equal to 10%.

[0099] The components of the holographic photopolymer material are further described below:

[0100] In the embodiment of the present application, the holographic photopolymer material may include: a polymer matrix.

[0101] In the embodiment of the present application, the polymer matrix includes: a polymer compound formed by connecting at least one monomer. The polymer matrix can provide mechanical support for the holographic photopolymer material.

[0102] In the embodiment of the present application, the molecular structure of the polymer matrix includes: a linear structure, and the side chain of the polymer matrix may include: a secondary reactive group, and the secondary reactive group will be further described in the subsequent embodiments. Generally, the lower the refractive index of the polymer matrix, the higher the diffraction efficiency of the holographic optical element finally obtained.

[0103] In order to further improve the diffraction efficiency of the holographic optical element made of holographic photopolymer material, as a feasible implementation method, the side chain of the polymer matrix can include: fluorine element (F). The presence of F can reduce the refractive index of the polymer matrix so that the holographic optical element made of holographic photopolymer material has a higher diffraction efficiency.

[0104] In some feasible implementations, the polymer matrix may include: a homopolymer. A homopolymer may be understood as a high molecular compound polymerized from a 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).

[0105] As a possible implementation, the molecular structure of the polymer matrix may include:

[0106] Structural formula 1: Structural formula 2: wait.

[0107] 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.

[0108] It is worth noting that the embodiments of the present application are merely exemplary introductions of several homopolymers that the polymer matrix may contain, and the types of the above homopolymers do not constitute a specific limitation.

[0109] 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.

[0110] As a feasible implementation method, 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: a fluorine element. The side chain of the third monomer includes: a secondary reaction functional group.

[0111] As a feasible implementation, the molecular structure of the polymer matrix may include:

[0112] Structural formula three:

[0113] The second monomer is described below:

[0114] 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 may include: one of a fluoroalkyl group or a fluoroaryl group. Exemplarily, the fluoroalkyl group may include: -CH2F, -CH2CH2F, etc. Exemplarily, the fluoroaryl group may include: wait.

[0115] In the structural formula 3, b can be understood as the degree of polymerization of the second monomer. The embodiment of the present application does not specifically limit b, and the value of b can be set according to the requirements.

[0116] Considering that the thermodynamic properties of the polymer matrix are related to b. Specifically: the larger b 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 method, b can be greater than or equal to 1 so that the polymer matrix has better thermodynamic properties.

[0117] Considering that the migration resistance of the photopolymerizable monomer is related to b, specifically, the larger the b is, the larger the migration resistance of the photopolymerizable monomer in the polymer matrix is, and the larger 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.

[0118] In order to make the holographic photopolymer material form a holographic optical element with a large 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 a large diffraction efficiency.

[0119] 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.

[0120] 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 final holographic optical element.

[0121] 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%.

[0122] Considering that the film-forming properties of the holographic photopolymer material are related to the mass fraction of the fluorine element in the polymer matrix. Specifically, the lower the mass fraction of the fluorine element in the polymer matrix, the better the film-forming properties of the holographic photopolymer material. In order to obtain a holographic photopolymer material with better film-forming properties, as a feasible implementation method, the mass fraction of the fluorine element in the polymer matrix can be less than or equal to 30%.

[0123] 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%.

[0124] 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.

[0125] The polymer matrix provided by the present implementation has a relatively low refractive index, and 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.

[0126] The third monomer is described below:

[0127] In structural formula three, It can be understood as the third monomer. Wherein, R6 is a secondary reaction functional group. c can be understood as the degree of polymerization of the third monomer. The present application embodiment does not make a specific limitation on c, and the value of c can be set according to the requirements.

[0128] 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 method, c is greater than or equal to 1 so that the polymer matrix has better thermodynamic properties.

[0129] Considering that the migration resistance of the photopolymerizable monomer is related to c, specifically, the larger the c is, the larger the migration resistance of the photopolymerizable monomer is, and the larger the migration resistance of the photopolymerizable monomer is, the lower the diffraction efficiency of the holographic optical element finally formed is.

[0130] In order to make the holographic photopolymer material form a holographic optical element with a large diffraction efficiency, as a feasible implementation, c can 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 large diffraction efficiency.

[0131] 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.

[0132] In order to adjust the glass transition temperature of the holographic photopolymerizable material, in some feasible implementations, 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.

[0133] For example, as a feasible implementation, the molecular structure of the polymer matrix may include:

[0134] Structural formula 4: In structural formula 4, R1, R2, and R3 include: hydrogen atoms or methyl groups.

[0135] The second monomer and the third monomer may refer to the above embodiments and will not be described in detail here.

[0136] The fourth monomer is described below:

[0137] Structural formula four, 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.

[0138] Considering that the glass transition temperature of the holographic photopolymer material is related to the type of the fourth monomer and the content of the fourth monomer (which can be represented by a in structural formula 4). In some feasible implementations, the glass temperature of the holographic photopolymer material can be adjusted to -20°C-120°C by adjusting R1 and a in structural formula 4, so that the holographic photopolymer material can meet the needs of different application scenarios. Optionally, the glass temperature of the holographic photopolymer material is 0°C-80°C.

[0139] The polymer matrix is ​​further described below in conjunction with the number average molecular weight:

[0140] The embodiments of the present application do not specifically limit the number average molecular weight of the polymer matrix.

[0141] Considering that the thermodynamic properties and film-forming properties of the polymer matrix are related to the number average molecular weight of the polymer matrix. Specifically, the larger the number average molecular weight of the polymer matrix, the better the thermodynamic properties of the polymer matrix. As a feasible implementation method, the number average molecular weight of the polymer matrix can be greater than or equal to 20,000, so that the polymer matrix has better thermodynamic properties.

[0142] 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.

[0143] 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.

[0144] The molecular structure of the polymer matrix is ​​further described below:

[0145] The molecular structure of the polymer matrix disclosed in the embodiments of the present application is a linear structure. The polymer matrix has a side chain, and the side chain of the polymer matrix includes: a secondary reactive functional group. In the embodiments of the present application, the conversion rate of the secondary reactive functional group is less than or equal to 30% under the first condition, and a cross-linking reaction can occur under the second condition.

[0146] 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 polymer matrix with a linear structure has less resistance to the migration process of the photopolymer monomer. The photopolymer monomer can migrate to the coherent bright area faster and polymerize in the coherent bright area to form a monomer polymer. Therefore, there is a large refractive index difference between the coherent bright area and the coherent dark area of ​​the holographic optical element formed by the holographic photopolymer material disclosed in the embodiment of the present application, and the holographic optical element has a high diffraction efficiency.

[0147] After the holographic recording is completed, the holographic optical element can be placed under a second condition to allow the secondary reactive functional groups to cross-link, thereby improving the thermodynamic properties of the holographic optical element.

[0148] The secondary reactive functional groups are further defined below.

[0149] 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.

[0150] In the embodiment of the present application, the first condition can be understood as a condition that allows the photopolymerizable monomer to polymerize. The first condition can include: visible light. The wavelength of the visible light is in the range of 400nm-800nm.

[0151] The process of polymerization of photopolymerizable monomers is generally as follows: irradiation with visible light divides the holographic photopolymerizable material into coherent bright areas and coherent dark areas. Photosensitizers in the coherent bright areas can produce active intermediates, which trigger polymerization of photopolymerizable monomers, thereby forming a concentration difference between the coherent bright areas and the coherent dark areas, thereby promoting the diffusion of photopolymerizable monomers toward the coherent bright areas, and ultimately resulting in the coherent bright areas being dominated by high-refractive-index photopolymers and the coherent dark areas being dominated by low-refractive-index polymer matrices.

[0152] 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.

[0153] As a feasible implementation method, the second condition may include: ultraviolet radiation, wherein the wavelength of the ultraviolet light is less than or equal to 400 nm.

[0154] 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, and the like.

[0155] This completes the description of the first condition and the second condition.

[0156] The secondary reaction functional groups involved in the embodiments of the present application are introduced below.

[0157] The embodiments of the present application do not specifically limit the types of secondary reaction functional groups. Any functional group whose conversion rate is less than or equal to 30% under the first condition and which undergoes cross-linking under the second condition can be used as a secondary reaction functional group in the embodiments of the present application.

[0158] As a feasible implementation method, the secondary reaction functional group may include: vinyl ether (the structural formula can refer to structural formula five), N-vinyl (the structural formula can refer to structural formula six), allyl (the structural formula can refer to structural formula seven), etc.

[0159] Structural formula 5: Structural formula VI: Structural Formula VII Here, * indicates a bonding site.

[0160] The secondary reaction 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.

[0161] As a feasible implementation method, the secondary reactive functional group may include: epoxy group.

[0162] The embodiments of the present application do not specifically limit the number of atoms forming a ring in the epoxy group. Exemplarily, the secondary reactive functional group may include: a three-membered epoxy group (the structural formula can refer to the structural formula eight), a four-membered epoxy group (the structural formula can refer to the structural formula nine), and a five-membered epoxy group (the structural formula can refer to the structural formula ten). In the embodiments of the present application, the secondary reactive functional group containing the epoxy group may be referred to as an epoxy secondary reactive functional group.

[0163] Structural formula eight: Structural formula 9: Structural formula 10:

[0164] As a feasible implementation, the secondary reaction functional group may include: carboxyl (-COOH). The conversion rate of the carboxyl group under irradiation with a wavelength of 400nm-800nm ​​is less than or equal to 30%. The carboxyl group can undergo an acid condensation reaction under the action of a catalyst, so that the polymer matrix is ​​converted from a linear structure to a cross-linked structure.

[0165] As a feasible implementation, the secondary reaction functional groups may include: thiol (-SH) and double bond (-C=C-). The conversion rate of SH and -C=C- under irradiation with a wavelength of 400nm-800nm ​​is less than or equal to 30%. -SH and -C=C- can undergo addition reaction of thiol (reaction functional group is -SH) and olefin (reaction functional group is -C=C-) under the action of a catalyst, so that the polymer matrix is ​​converted from a linear structure to a cross-linked structure.

[0166] As a feasible implementation, the secondary reaction 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 of isocyanate (the reaction functional group is -N=C=O) and alcohol (the reaction functional group is -OH) under the action of a catalyst, so that the polymer matrix is ​​converted from a linear structure to a cross-linked structure.

[0167] This completes the description of the secondary reactive functional groups.

[0168] In practical applications, holographic photopolymer materials can be analyzed using materials characterization equipment such as gel permeation chromatography, differential scanning calorimeter, nuclear magnetic resonance spectrometer, high performance liquid chromatography-mass spectrometer, Abbe refractometer and elemental analyzer. Specifically:

[0169] Gel permeation chromatography can obtain information on the molecular weight and molecular weight distribution of polymers isolated from holographic photopolymerizable materials.

[0170] Differential scanning calorimetry can be used to obtain the glass transition temperature of polymers.

[0171] 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.

[0172] High performance liquid chromatography-mass spectrometry can obtain the molecular weight of each component substance separated from the holographic photopolymer material.

[0173] The refractive index of polymers can be obtained using an Abbe refractometer.

[0174] Elemental analyzers can obtain information on the ratio of each element in polymers.

[0175] In the embodiment of the present application, the holographic photopolymer material may include: a photosensitizer.

[0176] Photosensitizer can be understood as a substance that can undergo photochemical changes to produce active intermediates when stimulated by light waves.

[0177] The embodiments of the present application do not specifically limit the types of photosensitizers. Any substance that can produce active intermediates 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.

[0178] 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. The photosensitizer has a stable structure, is not easy to turn yellow, and is easy to bleach, thereby ensuring that the holographic photosensitive film / holographic optical element prepared by the holographic photopolymer material disclosed in the implementation has a large transmittance.

[0179] The above-mentioned photosensitizer can produce active intermediates under the light wave of 400-800nm. The photosensitizer located in the coherent bright area can be irradiated to produce active intermediates, and the photosensitizer located in the coherent dark area does not produce or produces less active intermediates. The active intermediates promote the diffusion of photopolymer monomers to the coherent bright area and polymerize to form monomer polymers. Ultimately, the coherent bright area and the coherent dark area have different concentrations of monomer polymers, and the coherent bright area and the coherent dark area have different refractive indices, thereby realizing holographic recording / storage.

[0180] 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.

[0181] Exemplarily, the free radical active species may include, but are not limited to, phenyl free radicals and alkyl free radicals.

[0182] 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).

[0183] 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.

[0184] 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.

[0185] The embodiments of the present application do not specifically limit the types of coinitiators. Any substance that can accelerate the rate at which a photosensitizer generates active intermediates under the stimulation of light waves can be used as a coinitiator in the embodiments of the present application.

[0186] Exemplarily, the coinitiator may include at least one of N-phenylglycine, triethanolamine, triisopropanolamine, methyldiethanolamine, diphenyliodonium chloride, and diphenyliodonium hexafluorophosphate. The coinitiator may accelerate the rate at which the photosensitizer generates active intermediates under the excitation of light waves, thereby increasing the migration rate of the photopolymerizable monomer in the polymer matrix, thereby improving the optical properties of the holographic optical element formed by the holographic photopolymerizable material.

[0187] This completes the description of the photosensitizer / coinitiator.

[0188] In the embodiment of the present application, the holographic photopolymerizable material may include: a photopolymerizable monomer.

[0189] 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.

[0190] In the embodiment of the present application, the compound formed by polymerization of the photopolymerizable monomers 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.

[0191] Under the irradiation of the coherent light beam, the photosensitizer located in the coherent bright area can produce active intermediates, which promote the polymerization of the photopolymerizable monomers to the coherent bright area to form monomer polymers. Ultimately, the coherent bright area and the coherent dark area have different concentrations of monomer polymers, and the coherent bright area and the coherent dark area have different refractive indices, thereby realizing holographic recording / storage.

[0192] The embodiments of the present application do not specifically limit the types of photopolymerizable monomers. Any material 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.

[0193] 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 higher refractive index contrast. The higher refractive index contrast makes it easier to simultaneously achieve high transmittance and high diffraction efficiency of the holographic optical element.

[0194] This completes the description of the holographic photopolymerizable material.

[0195] The embodiment of the present application also discloses a holographic photosensitive film, which includes: 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 embodiment of the present application. The first film layer may include: a polymer matrix, a photopolymerizable monomer and a photosensitizer. The polymer matrix can provide mechanical support for the first film layer. Under the first condition, the photosensitizer can absorb light waves and produce active intermediates that polymerize the photopolymerizable monomers. The active intermediates can promote the migration of the photopolymerizable monomers to the coherent bright area of ​​the first film layer, so that the coherent bright area and the coherent dark area of ​​the first film layer have different refractive indices.

[0196] In addition, the side chain of the polymer matrix 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. This ensures that the photopolymerizable monomer can migrate in the polymer matrix of the linear structure under the first condition, and the migration rate of the photopolymerizable monomer in the polymer matrix is ​​relatively large, so the holographic photosensitive film can obtain a holographic optical element with better optical performance.

[0197] After the holographic recording / storage is completed, the holographic photosensitive film is converted into a holographic optical element. 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. It can be seen that the holographic photosensitive film provided in the embodiment of the present application can have a higher information recording / storage efficiency. In addition, the holographic photosensitive film disclosed in the embodiment of the present application can obtain a holographic optical element with higher thermodynamic properties.

[0198] The embodiments of the present application do not specifically limit the protective layer, and any material that can support and protect the first film layer can be used as a protective layer in the embodiments of the present application. For example, the protective layer can include, but is not limited to: polyester film (PET), triacetyl cellulose film (TAC), glass, ceramic, and a composite material containing multiple of these materials.

[0199] 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, and the refractive index of the area where the monomer polymer is polymerized (coherent bright area) is relatively high, while the area without the monomer polymer or the area with less monomer polymer polymerization (coherent dark area) can be understood as the background, and the refractive index of the background is relatively low. The monomer polymer can be used together with the background for recording the complete hologram. The molecular structure of the polymer matrix in the second film layer is a cross-linked structure, so the holographic optical element has better heat resistance.

[0200] Based on the same technical concept, the present application also discloses a method for preparing a holographic photosensitive film. Figure 2 As shown, the preparation method includes: S201-S203:

[0201] S201: Mixing a polymer matrix, a photopolymerizable monomer, and a photosensitizer to obtain a holographic photopolymerizable material.

[0202] S202: coating a holographic photopolymer material on the protective layer.

[0203] 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.

[0204] S203: converting the holographic photopolymer material into a first film layer to obtain a holographic photosensitive film.

[0205] In some feasible implementations, the S203 processing method includes but is not limited to: oven heating and other curing methods.

[0206] It is worth noting that the above S201-S203 should be completed in the dark or under a safe light. In the holographic photosensitive film prepared by this implementation, the side chain of the polymer matrix includes: secondary reaction functional groups. The conversion rate of the secondary reaction 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 polymer matrix of the linear structure to achieve information recording / storage efficiency, that is, the holographic photosensitive film prepared by this implementation can have a higher information recording / storage efficiency. In addition, the secondary reaction functional groups in the holographic photosensitive film obtained in the embodiment of the present application are cross-linked under the second condition, and a holographic optical element with higher thermodynamic properties can be further obtained.

[0207] Based on the same technical concept, the present application also discloses a method for preparing a holographic optical element. Figure 3 As shown, the preparation method includes: S301-S305:

[0208] S301: Mixing a polymer matrix, a photopolymerizable monomer, and a photosensitizer to obtain a holographic photopolymerizable material.

[0209] S302: coating a holographic photopolymer material on the protective layer.

[0210] S303: Converting the holographic photopolymer material into a first film layer.

[0211] The specific implementation of the above S301-S303 can refer to the above embodiments and will not be repeated here.

[0212] 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.

[0213] 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;

[0214] 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.

[0215] 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.

[0216] The embodiment of the present application uses a holographic recording system to transform the first film layer into the second film layer. Figure 4 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 .

[0217] The laser 41 is used to generate a light beam that meets the coherence condition, and the shutter is used to control the holographic exposure time. The beam expander 42 can change the beam diameter and divergence angle. The lens 43 is used to collimate the beam after expansion. The reflector 44 is used to control the propagation direction of the light beam so that the light beam propagates along the set path. The beam splitter 45 is used to split the light beam into coherent lights with the same frequency, constant phase difference, and consistent vibration direction.

[0218] See also Figure 4 (a) in the reflective holographic recording system, the light beam emitted by the laser 41 is split into coherent lights in two directions by the beam splitter 45. The coherent lights in the two directions are respectively emitted from the two sides of the holographic photosensitive film to the first film layer B, forming coherent bright areas and coherent dark areas on the first film layer B, and the first film layer is converted into the second film layer, thereby realizing holographic storage / recording.

[0219] See also Figure 4 In (ii), in a transmission holographic recording system, when two coherent light beams (44 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 realizing holographic storage / recording.

[0220] Based on the same technical concept, the embodiment of the present application also discloses a display device, including the holographic optical element or holographic photosensitive film disclosed in the embodiment of the present application. The display device is, for example, a head up display (HUD) device.

[0221] 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.

[0222] 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.

[0223] The scheme disclosed in the embodiments of the present application is further described below in conjunction with specific embodiments:

[0224] Embodiment 1:

[0225] 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 referred to Figure 5 (a) in.

[0226] 0.1 mol % of thermal 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.

[0227] Nitrogen was passed through the flask for 15 min to expel oxygen from the flask.

[0228] The round-bottom flask from which oxygen was purged was placed at 70°C with stirring for 12 h.

[0229] After the reaction is completed, the intermediate solution is diluted and added dropwise to n-hexane to precipitate, and the process is repeated N times (N is greater than or equal to 1). The solvent is filtered off, 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 the present embodiment).

[0230] 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 of the fluorine-containing film-forming resin 1 is n=1.43.

[0231] Table 1

[0232] Reactants MMA BA GMA DFMA AIBN PGMEA Feeding amount 1.5g 8.3g 1.42g 4.0g 0.017g 20mL

[0233] Combine the following Figure 5 , the process of forming holographic photopolymer materials, holographic photosensitive films and holographic optical elements from polymer matrices is described as follows:

[0234] See also Figure 5 (a) The reactants disclosed in Example 1 are mixed to obtain a fluorine film-forming resin 200.

[0235] See also Figure 5 The fluorine-containing film-forming resin 200 in (ii) is weighed and mixed with the photopolymerizable monomer 100, the photosensitizer (not shown in the figure), the solvent (not shown in the figure) and other components according to Table 2 to obtain a holographic photopolymerizable material. The solvent may include: dichloromethane (

[0236] dichloromethane, DCM) and methanol.

[0237] The holographic photopolymer material is 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.

[0238] 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 and in the dark for future use.

[0239] The holographic photosensitive film is holographically exposed using reflective optical path A, with an exposure wavelength of 460nm (blue light), an exposure power of 2mW, and an exposure time of 60s to form a holographic grating. For details, please refer to Figure 5 Of (3).

[0240] After the exposure is completed, ultraviolet (UV) bleaching is first performed by a high-pressure mercury lamp, and the cationic photoinitiator initiates the ring-opening polymerization of the epoxy functional groups to form a cross-linked network and the unreacted photopolymerized monomers react completely, and then heated at 80°C for 10 minutes to achieve a thermal enhancement effect, and finally white light bleaching is used for 24 hours to obtain the holographic optical element 1. For details, please refer to Figure 5 (IV) in.

[0241] The 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.

[0242] Heat resistance test:

[0243] After the holographic optical element was placed in an oven at 85°C for 40 hours, the holographic optical properties were tested and listed in Table 3.

[0244] Table 2

[0245]

[0246] Table 3

[0247]

[0248] In the scheme disclosed in Example 1, the fluorine-containing film-forming resin 1 used forms a cross-linked structure, taking into account both excellent optical properties and heat resistance. The diffraction efficiency of the holographic optical element finally obtained can reach 81.2%, the overall transmittance can reach 88.1%, and the haze can reach 1.60. After the holographic optical element is baked at 85°C for 40 hours, the optical properties do not show a significant decrease.

[0249] Embodiment 2:

[0250] The fluorine film-forming resin 2 was obtained by using the formula shown in Table 4. The holographic photosensitive film 2 was prepared by using the fluorine film-forming resin 2 according to the method of Example 1.

[0251] The difference from Example 1 is:

[0252] The wavelength of the light source used for exposure is 640nm (red light), and the exposure power is 2mW, 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.

[0253] Table 4

[0254]

[0255] Table 5

[0256] Test time (h) Diffraction efficiency (%) Overall transmittance (%) Haze(%) 0 95.6 85.0 2.34 40 95.5 82.1 1.98 Change value -0.1 -2.9 -0.36

[0257] In the scheme 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%, the haze of the holographic optical element can reach 2.34, and after baking at 85°C for 40 hours, the optical properties of the holographic optical element did not show a significant decrease.

[0258] Embodiment 3:

[0259] As shown in Table 6, 80mmol GMA and 20mmol TFMA were weighed into a 100mL round-bottom flask, 0.1mol% AIBN and 30mL PGMEA were added, nitrogen was passed through for 15 minutes to remove oxygen, and then the mixture was reacted at 70°C with stirring for 12h. After the reaction, the polymer solution was diluted to an appropriate concentration, added dropwise to n-hexane to precipitate, and the reaction was repeated twice. The solvent was filtered out, and the precipitate was dried in a vacuum oven at 60°C for 24h to obtain the purified fluorine-containing film-forming resin 2. The molecular weight of the fluorine film-forming resin 2 is 78.3kg / mol, the molecular weight distribution of the fluorine film-forming resin 2 is 2.85, the glass transition temperature of the fluorine film-forming resin 2 is 52°C, and the mass fraction of fluorine in the fluorine film-forming resin 2 is 7.5%.

[0260] Table 6

[0261]

[0262] Using the formula shown in Table 7, the holographic photosensitive film 3 was prepared using the fluorine-containing film-forming resin 2 according to the method of Example 1. The difference from Example 1 is:

[0263] The wavelength of the light source used for exposure is 540nm (green light), and the exposure power is 2mW 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.

[0264] Table 7

[0265]

[0266] Table 8

[0267] Test time (h) Diffraction efficiency (%) Overall transmittance (%) Haze(%) 0 89.9 82.0 0.66 40 88.5 81.5 1.34 Change value -1.3 -0.5 +0.68

[0268] In the scheme disclosed in Example 2, 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 the optical properties of the holographic optical element 3 do not show obvious decline after being baked at 85°C for 40h.

[0269] Comparative Example 1:

[0270] Comparative Example 1: Film-forming resin 4 is obtained by using the holographic formula shown in Table 9, and holographic optical element 4 is prepared according to the method of Example 1. The difference from Example 1 is that film-forming resin 4 is a resin formed by 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 is 89.1%, the overall transmittance of holographic optical element 4 is 72.5%, and the haze of holographic optical element 4 is 3.31.

[0271] Table 9

[0272]

[0273] Table 10

[0274] Test time (h) Diffraction efficiency (%) Overall transmittance (%) Haze(%) 0 89.1 72.5 3.31 40 80.8 12.9 27.12 Change value -8.3 -59.6 +23.81

[0275] In the scheme disclosed in Example 4, 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 decrease, including a decrease of 8.3% in diffraction efficiency, a decrease of 59.6% in overall transmittance, and an increase of 23.81 in haze, making it impossible to be used as a heat-resistant optical film.

[0276] Those skilled in the art will readily appreciate other embodiments of the present disclosure 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 that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the following claims.

[0277] 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 may 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 structure 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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