Photopolymer and film thereof, film preparation method, and printing substrate

Abstract

The present invention relates to the technical field of volume holographic display materials, and in particular to a photopolymer and a film thereof, a film preparation method, and a substrate. The invention discloses a method for preparing a photopolymer film, comprising the following steps: weighing methyl methacrylate, a low-Tg acrylic monomer, a cross-linked acrylic monomer, a rigid side group monomer, a fluorine-containing or silicon-containing acrylic monomer, and a free radical thermal initiator in proportion, by mass percentage, to form a matrix; wherein, by mass percentage, the methyl methacrylate comprises 40-85%, the low-Tg acrylic monomer comprises 0-50%, the cross-linked acrylic monomer comprises 0-20%, the rigid side group monomer comprises 5-20%, the fluorine-containing or silicon-containing acrylic monomer comprises 4-20%, and the free radical thermal initiator comprises 0.5-5%; heating the matrix under reflux in a solvent 1 for 1-8 hours to obtain a non-film-forming matrix; and weighing the non-film-forming matrix, a high-refractive index monomer, a visible light harvester, and a photoinitiator in proportion, to form a first raw material; wherein, by mass percentage, the non-film-forming matrix comprises 40-80%, the high-refractive index monomer comprises 10-45%, the visible light harvester comprises 0.01-5%, and the photoinitiator comprises 1-10%.

Description

Technical Field

[0001] The present invention relates to the technical field of volume holographic display materials, in particular to a photopolymer and a film thereof, a film preparation method and a printing substrate. Background Art

[0002] Current AR waveguide technology is divided into three generations: the first generation array waveguides, the second generation surface relief grating waveguides, and the third generation volume holographic waveguides. The third generation volume holographic waveguides are realized using a thin photosensitive coating that is exposed through laser interference to form a volume holographic grating. The refractive index difference between the bright and dark stripes of the volume holographic grating is called refractive index modulation.

[0003] Materials commonly used to make volume holographic gratings include silver salts, dichromated gelatin, and photosensitive polymers. Photosensitive polymers offer advantages such as high sensitivity, high resolution, high diffraction efficiency, wide spectral response, simple processing, wide tolerance, and stable storage, making them ideal materials for recording volume holographic image information. Photosensitive polymers can be divided into three categories: photopolymerizable, photocrosslinkable, and photodegradable. Photopolymers are a type of photopolymerizable material.

[0004] In current photopolymer production, unexposed photopolymer is coated on a protective film, dried, and then covered with a protective film. However, because existing photopolymers typically use polyvinyl acetate (EVA) or partially fluorinated polymers of EVA as a matrix to form the film, they adhere to the protective film after light curing, making it difficult to completely remove the protective film and transfer the printed image. This significantly limits the application of photopolymers. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide a method for preparing a photopolymer film, comprising the steps of:

[0006] The matrix comprises methyl methacrylate, a low Tg acrylic monomer, a cross-linked acrylic monomer, a rigid side group monomer, a fluorine-containing or silicon-containing acrylic monomer, and a free radical thermal initiator, which are weighed in proportion by mass; wherein, by mass, the methyl methacrylate comprises 40-85%, the low Tg acrylic monomer comprises 0-50%, the cross-linked acrylic monomer comprises 0-20%, the rigid side group monomer comprises 5-20%, the fluorine-containing or silicon-containing acrylic monomer comprises 4-20%, and the free radical thermal initiator comprises 0.5-5%;

[0007] The matrix is ​​heated under reflux in solvent 1 for 1-8 hours to obtain a non-film-forming matrix;

[0008] Weigh a non-film-forming matrix, a high-refractive index monomer, a visible light harvester, and a photoinitiator in proportion to obtain the first raw material; wherein, by mass percentage, the non-film-forming matrix comprises 40-80%, the high-refractive index monomer comprises 10-45%, the visible light harvester comprises 0.01-5%, and the photoinitiator comprises 1-10%;

[0009] The raw material 1 is stirred and dissolved in the solvent 2 to obtain a photopolymer solution;

[0010] Making a volume holographic grating master with positioning marks;

[0011] coating a photopolymer solution on a protective film and drying the solution to form a photopolymer coating, and covering the photopolymer coating with a protective film to obtain a photopolymer intermediate;

[0012] replicating the volume holographic grating on the volume holographic grating master to a photopolymer intermediate to obtain a photopolymer film with the volume holographic grating;

[0013] UV irradiation and heating of photopolymer films.

[0014] The present invention also discloses a photopolymer, which comprises 50-80% of a matrix and 20-50% of a complexing base, calculated by mass percentage; wherein the complexing base comprises:

[0015] High refractive index monomer 70-90%

[0016] Visible light harvester 0.1-10%

[0017] Photoinitiator 9-20%;

[0018] Wherein, by mass percentage, the matrix comprises:

[0019]

[0020] Optionally, the low Tg acrylic monomer is one or more of ethyl acrylate (EA), butyl acrylate (BA), isooctyl acrylate (2-EHA), lauryl acrylate, and dodecyl acrylate.

[0021] Optionally, the cross-linking acrylic monomer is one or more of hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA) and other hydroxy acrylic monomers, acrylamide (AAM), hydroxymethyl acrylamide (NMA), diacetone acrylamide (DAAM) and ethyl acetoacetate methacrylate (AAEM), glycidyl methacrylate (GMA), dimethylaminoethyl methacrylate (DMAEMA); and / or

[0022] The rigid side group monomer is one or more of isobornyl methacrylate (IBOA), dicyclopentadiene and its derivatives, and adamantyl acrylate.

[0023] Optionally, the fluorine-containing acrylic monomer is one or more of trifluoroethyl acrylate (TFEA), trifluoroethyl methacrylate (TFEMA), hexafluorobutyl acrylate (HFBA), and dodecafluoroheptyl methacrylate (DFMA);

[0024] The silicon-containing acrylic monomer is one or more of methylvinylchlorosilane, vinyltrichlorosilane, and vinyltriethoxysilane (VTES).

[0025] Optionally, the free radical thermal initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate, hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, dibenzoyl peroxide, N,N-dimethylaniline or dimethyl-β-thiophene propionate.

[0026] Optionally, the matrix comprises, by mass percentage:

[0027]

[0028] The present invention also discloses a non-film-forming matrix for photopolymer, which comprises 30-70% matrix and 130-70% solvent by mass, wherein the matrix comprises:

[0029]

[0030] The present invention also discloses a photopolymer film, comprising the above-mentioned photopolymer and two layers of protective films, wherein the two layers of protective films respectively cover two sides of the photopolymer.

[0031] The present invention also discloses a photopolymer substrate, comprising a substrate and the photopolymer as described above, wherein the photopolymer is solidified on the substrate and the photopolymer has a volume holographic grating.

[0032] Compared with the prior art, the beneficial effects of the photopolymer provided by the embodiment of the present invention are: the present invention changes the brittleness of the photopolymer coating formula so that it does not form a film. The photopolymer can not only meet the optical requirements of high transmittance, low refractive index, low haze, etc., but also has a higher Tg, low adhesion to the protective film, and does not stick to the protective film. The protective film is removed during transfer without damaging the photopolymer. The photopolymer itself is relatively brittle and can be transferred locally by hot stamping, cold transfer, etc., and by blunt cutting of the concave and convex parts of the die head. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, in which:

[0034] Figure 1 Schematic diagram of manufacturing a holographic master according to an embodiment of the present invention;

[0035] Figure 2 is a schematic diagram of a photopolymer and positioning marks on a volume holographic master according to an embodiment of the present invention;

[0036] Figure 3 is a schematic diagram of a photopolymer film according to an embodiment of the present invention;

[0037] Figure 4 Schematic diagram of coating of a photopolymer film according to an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of replicating a volume holographic grating through a volume holographic master using a photopolymer film according to an embodiment of the present invention;

[0039] Figure 6 Schematic diagram of a continuous photopolymer film having a volume holographic grating and positioning marks replicated in accordance with an embodiment of the present invention;

[0040] Figure 7 is a schematic diagram of a process for further enhancing the volume holographic grating according to an embodiment of the present invention;

[0041] Figure 8 is a schematic diagram of transferring a photopolymer film onto a substrate according to an embodiment of the present invention;

[0042] Figure 9 This is a physical picture of a photopolymer film with a volume holographic pattern after exposure according to an embodiment of the present invention;

[0043] Figure 10 This is another physical picture of a photopolymer film with a volume holographic pattern after exposure according to an embodiment of the present invention;

[0044] Figure 11 This is a real picture of the laser embossed holographic film currently on the market;

[0045] Figure 12 This is a real picture of the silver halide film currently on the market (observed under non-point light source);

[0046] Figure 13 This is a physical picture of the silver halide material film currently on the market (observed under point light source). DETAILED DESCRIPTION

[0047] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The preferred embodiments of the present invention are now described in detail.

[0048] Photopolymers are typically exposed using visible light, using a monochromatic visible laser as the exposure source. The resulting volume holographic grating is internal to the photopolymer, and the refractive index modulation of the volume holographic grating relies on the refractive index difference between the photopolymerized portion and the supporting matrix. The equipment costs for photopolymer production are significantly lower than those for arrayed waveguides and surface relief grating waveguides. The largest expense is the laser, which costs only a few hundred thousand yuan. Exposure is performed using a laser light source, which is extremely fast, taking only a fraction of a second. Furthermore, the non-contact production process offers higher production efficiency and yield than arrayed waveguides and surface relief grating waveguides.

[0049] The photopolymer coating is very thin, requiring a transmittance exceeding 85%. The volume holographic grating is parallel to the coating surface and deeply embedded within the photopolymer, resulting in no visible roughness or discontinuities, making it an ideal material for optical waveguide lenses. However, due to limited photopolymer sources, demanding optical parameters, and immature manufacturing processes, volume holographic gratings have struggled to become a mainstream optical waveguide material, significantly limiting their application.

[0050] In current production processes, an unexposed photopolymer solution is applied to a substrate, such as an AR lens substrate, in a darkroom via screen printing, knife coating, or spin coating. After drying, the solution is covered with a protective film. Before use, the solution must be stored in a refrigerated environment at 4-8°C, away from light. Furthermore, to protect the soft, unexposed photopolymer coating, the solution cannot be simply stacked on a flat surface. The process used in the present invention, however, involves applying the unexposed photopolymer solution to a protective film, which is then covered with another protective film for protection. The solution is then exposed to form a volume holographic grating within the photopolymer. This grating is then transferred to a substrate, such as an AR lens, packaging, or anti-counterfeiting material, after post-processing.

[0051] Of the two processes mentioned above, in the first process, the unexposed photopolymer is configured into a photopolymer solution with a lower concentration in order to ensure the uniformity of dispersion and low migration difficulty of each component in the photochemical reaction. After coating, it is dried or air-dried to form a film. The viscosity of this unexposed material solution is very low and it is easy to flow when coated. When coating a curved surface, it cannot maintain the required thickness due to the influence of gravity. Therefore, this type of process is generally used for flat substrates such as flat AR lenses. In addition, the flat AR lenses are large in size after direct coating and are not suitable for stacking and storage before exposure. They also require refrigeration for storage, which places high demands on semi-finished product warehouses. During the exposure process, since the flat AR lenses are discontinuous and laser interference shooting has extremely high requirements for vibration, the loading and unloading actions on the production line will generate vibration. Therefore, a period of static table time is required in the production process (the time to wait for all shooting actions to completely stop after the laser interference shooting is completed), and the production efficiency is relatively low.

[0052] The process used in this invention involves coating an unexposed photopolymer on a protective film, drying it, and then covering it with another protective film to isolate oxygen and prevent oxygen inhibition of the photochemical reaction. The coated sandwich-structured photopolymer film is then fed into the exposure light path in a roll-to-roll manner. The volume holographic grating structure designed on the volume holographic grating master is then exposed onto the photopolymer using an interference method, thereby recording the volume holographic image information on the photopolymer film.

[0053] Photopolymer formulations typically consist of a photocuring system and a matrix. The photocuring system initiates a photocuring reaction at the bright fringes of the volume holographic grating, forming a high-refractive-index volume holographic grating structure. This creates a refractive index difference with the low-refractive-index matrix, known as refractive-index modulation, to achieve reflection and refraction of light within a fixed, narrow wavelength range. However, in previous photopolymer formulations, the matrix was typically polyvinyl acetate (EVA) or a partially fluorinated polymer of EVA. Their refractive index ranges from approximately 1.42 to 1.45. These film-forming resins have high transparency and a low refractive index, making them suitable as optical materials. However, they are brittle and have a low glass transition temperature (Tg), approximately 20-50°C. The photopolymer forms a film (i.e., a continuous, integrated layer) and adheres to the protective film after photocuring, making it difficult to completely remove the protective film. This makes it difficult to achieve partial coating transfer and complete transfer, forcing the transfer to be performed using die-cutting followed by lamination, whereby the protective film is transferred with a sharp blade. Based on this, it is also very difficult to ensure smooth lamination for curved surfaces. Because of this production method, the protective film must be a highly transparent, corrosion-resistant optical film. The daily used ones are PET (polyester) protective film and TAC (cellulose acetate) protective film. The PET protective film has a high yield strength and low stretchability. When laminating to a curved surface, if the curvature is large, wrinkles that cannot be smoothed out will appear. The TAC protective film has poor shear resistance and low tensile strength, and it is easily broken when a curved surface appears. In addition, since the thickness of the protective film is at least ten to one hundred microns, the transmittance is also affected to a certain extent after lamination with the protective film.

[0054] An embodiment of the present invention provides a method for preparing a photopolymer film, comprising the steps of:

[0055] S100: methyl methacrylate, low Tg acrylic monomer, cross-linked acrylic monomer, rigid side group monomer, fluorine-containing or silicon-containing acrylic monomer and free radical thermal initiator are weighed in proportion by mass percentage to form a matrix; wherein, by mass percentage, methyl methacrylate is 40-85%, low Tg acrylic monomer is 0-50%, cross-linked acrylic monomer is 0-20%, rigid side group monomer is 5-20%, fluorine-containing or silicon-containing acrylic monomer is 4-20%, and free radical thermal initiator is 0.5-5%.

[0056] S200: heating the matrix in solvent 1 under reflux for 1-8 hours to obtain a non-film-forming matrix, wherein, by weight, the solvent 1 comprises 30-70% and the matrix comprises 30-70%. Solvent 1 may be butanone.

[0057] S300: weighing a non-film-forming matrix, a high-refractive index monomer, a visible light harvester, and a photoinitiator in proportion to obtain raw material 1; wherein, by mass percentage, the non-film-forming matrix comprises 40-80%, the high-refractive index monomer comprises 10-45%, the visible light harvester comprises 0.01-5%, and the photoinitiator comprises 1-10%.

[0058] S400: Stirring and dissolving the raw material 1 in the solvent 2 to obtain a photopolymer solution. The solvent 2 can be added in an amount of 15-25%, with the remainder being the raw material 1. The solvent 2 can be butanone, ethyl acetate, methanol, or dichloromethane.

[0059] S500: Producing a volume holographic grating master with positioning marks.

[0060] S600: coating the photopolymer solution on the protective film and drying it to form a photopolymer coating layer, and covering the photopolymer coating layer with the protective film to obtain a photopolymer intermediate.

[0061] S700: copying the volume holographic grating on the volume holographic grating master to a photopolymer intermediate to obtain a photopolymer film with the volume holographic grating.

[0062] S800: UV irradiation and heating of photopolymer film.

[0063] In the method for preparing a photopolymer film of the present invention, a non-film-forming matrix is ​​used as a base material, wherein the non-film-forming matrix includes methyl methacrylate, a low-Tg acrylic monomer, a cross-linked acrylic monomer, a rigid side group monomer, a fluorine-containing or silicon-containing acrylic monomer, and a free radical thermal initiator. Such a photopolymer can not only meet optical requirements such as high transmittance, low refractive index, and low haze, but also has a high Tg, low adhesion to the protective film, and does not stick to the protective film. The protective film is removed during transfer without damaging the photopolymer. The photopolymer itself is relatively brittle and can be locally transferred by hot stamping, cold transfer, etc., and by blunt cutting of the concave and convex parts of the die head.

[0064] Specifically, the preparation method of the present invention modifies the brittleness of the photopolymer coating formula, preventing it from forming a film during the preparation process (i.e., due to its high brittleness, it cannot form a continuous film layer and exist independently as a film, but must adhere to other surfaces, such as a protective film, to form a thin layer structure). Therefore, in step S600, the protective film is not adhered to the protective film. In terms of process, the photopolymer is coated on the protective film, dried, and then covered with the protective film to obtain a roll of unexposed photopolymer, which is suitable for assembly line production. This also reduces the difficulty and space required for refrigerated storage of semi-finished products, significantly saving production costs.

[0065] Specifically, in step S100 and step S300, the specific proportions, compositions, functions, etc. of the components are the same as those described below and will not be described in detail herein.

[0066] In step 200, an appropriate amount of butanone solvent can be selected, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, and the matrix can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. Alternatively, the amounts shown in Table 1 can be used, and the heating reflux time can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, or 8 h.

[0067] The obtained non-film-forming matrix is ​​clear and transparent and has a certain viscosity, which is used for the subsequent preparation of the photopolymer, wherein the viscosity can be adjusted by adjusting the amount of the butanone solvent added. In the subsequent processing step S600, the butanone solvent evaporates during drying.

[0068] In step S400, the raw material 1 is dissolved in the solvent and then stored in the dark at 0-4° C. for later use. The viscosity of the photopolymer solution can be adjusted by adjusting the amount of solvent used.

[0069] In step 500, combining Figure 1 and Figure 2 As shown, when creating a volume holographic master for photopolymers, the grating angle, distribution, and other parameters are first designed based on the specific requirements of the optical lens or holographic image. Object and reference beams are then injected from both sides of the photopolymer, forming alternating light and dark stripes within the photopolymer that are nearly parallel to the coating surface. Because the light enters from both sides, the photopolymer support, or protective film, must be transparent. The light source used is a visible light laser. Due to the large incident angles of the reference and object beams, the reproduced viewing angle is also wide, resulting in a more intense and realistic 3D effect for the holographic image. The resulting 3D image has pure, clear colors.

[0070] Because the volume holographic grating is deeply embedded in the photopolymer coating and does not form grooves on the coating surface, there is no need to wash out the master. Instead, the formed grating only needs to be chemically developed and fixed. The refractive index of the new polymer formed at the grating is different from that of the polymer in the matrix, creating a refractive index difference. This achieves refractive index modulation, which is then used for reading and writing. Refractive index modulation is the basis for storing information.

[0071] Volume holographic gratings can be processed using either wet or dry methods. Wet processing typically involves preparing a suitable developer and fixer solution to expand and strengthen the internal grating. Dry processing, typically involving UV light irradiation and heating, also promotes internal chemical reactions, fixing and strengthening the grating. During the design and production of a master, the positioning marks on the master are replicated one-to-one with the desired volume holographic grating onto a photopolymer. Specifically, the photopolymer solution can be coated onto a roll of protective film to produce a roll of photopolymer intermediates, facilitating continuous processing.

[0072] In step S600, Figure 3 and Figure 4 As shown, the photopolymer solution is a semi-fluid, viscous coating before the light-curing reaction. Therefore, a protective film must be applied immediately after coating, ensuring both top and bottom protective films are present before the product can be rolled up. Furthermore, photopolymer light curing involves a free radical reaction, which is strongly inhibited by oxygen. Therefore, protective films are required for the chemical reaction to occur effectively, as they act as an oxygen barrier.

[0073] Specifically, the unexposed photopolymer solution can be coated onto a transparent substrate, such as a transparent protective film, in a light-proof environment, and dried to form a thin coating with a thickness ranging from a few microns to several hundred microns. Depending on the specific product being produced, cover glass, a transparent resin plate, a transparent resin sheet, or another layer of transparent film is selected to form a sandwich structure. In a preferred production, first, in a darkroom, the unexposed photopolymer solution is coated on the entire surface of the substrate using a doctor blade device. The selected substrates are mainly high-transmittance PET protective film and TAC protective film. When coating the entire roll, it is achieved on a roll-to-roll doctor blade coater. After coating, the surface of the substrate is fully covered with the photopolymer solution, and the thickness of the wet coating is 20-2000 microns. After drying, the surface of the substrate is fully covered with an unexposed photopolymer adhesive layer, and the thickness of the dry coating is 2-500 microns, mainly about 10 microns. After compounding a layer of protective film, it is rolled up or stacked for storage for later use.

[0074] In step 700, as Figure 5 and Figure 6 As shown, when the volume holographic grating and its positioning marks on the master are copied to the photopolymer material, it is necessary to pass the reference light through the copied, unexposed photopolymer so that the reference light is reflected on the master. The object light formed after the reflection interferes with the reference light in the unexposed photopolymer to form a copied volume holographic grating.

[0075] During replication, a visible laser light source that can cooperate with the master is still used. The principle of replication is still the light and dark stripes formed by the interference of light, inducing photochemical reactions at the bright stripes to complete the volume holographic grating deeply buried in the photopolymer and parallel to the coating surface.

[0076] Because the laser light source needs to penetrate the photosensitive material and land on the master during replication, both the upper and lower supports of the photopolymer must be highly transparent. This dictates that the photopolymer support cannot be made of a material coated with a release agent. This is because the opaque component of the release agent will generate significant noise, resulting in blurred and scattered holographic images after replication, resulting in very poor quality and even indiscernible.

[0077] In step S800, Figure 6 As shown, after the volume holographic grating in the photopolymer is exposed and replicated with the master, it needs to undergo post-processing such as UV irradiation fixation, heating strengthening, and UV irradiation termination reaction to make the volume holographic grating stable.

[0078] Combine Figure 8 As shown, the protective film of the photopolymer film can be in the form of a roll. A cold transfer adhesive or a composite hot melt adhesive is applied to the substrate (sheet or continuous substrate, etc.) to positionally transfer the photopolymer material with the volume holographic grating in the photopolymer film. Since the photopolymer with the volume holographic grating has protective films on both the top and bottom, one of the protective films is peeled off first when in use. Cold transfer adhesive or a composite hot melt adhesive is printed and applied to the substrate to be transferred. Simultaneously, the positioning mark copied along with the volume holographic grating is read, and the brittle photopolymer material is cut by blunt cutting using the concave and convex template edge of the device to obtain a photopolymer material with neat edge shapes. After the photopolymer material is transferred to the substrate, the cold transfer adhesive is cured by UV light irradiation, or the hot melt adhesive is cured by cooling, so that the photopolymer material is firmly transferred to the substrate. Simultaneously, the other protective film is peeled off, and the transfer of the photopolymer to the substrate is completed, and the photopolymer is free of upper and lower protective films. That is, the photopolymer on such a substrate is obtained by transfer and has no protective film, so it has a small thickness and a small sense of concave and convex, and the holographic image is clear and three-dimensional.

[0079] An embodiment of the present invention provides a photopolymer for use in the above-mentioned method for preparing a photopolymer film. The photopolymer comprises, by weight, 50-80% matrix and 20-50% complexing group. The matrix can be 50%, 55%, 60%, 65%, 70%, 75%, or 80%, and the complexing group can be 20%, 25%, 30%, 35%, 40%, 45%, or 50%. Preferably, the matrix is ​​60-75% and the complexing group is 25-40%. More preferably, the matrix is ​​66.9% and the complexing group is 33.1%.

[0080] The compound base includes 70-90% high refractive index monomer, 0.1-10% visible light capture agent, and 9-20% photoinitiator.

[0081] Specifically, by mass percentage, the high refractive index monomer may account for 70%, 72%, 75%, 78%, 80%, 83%, 85%, 87%, or 90% of the complex base. The visible light capture agent may account for 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, or 10% of the complex base. The photoinitiator may account for 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of the complex base.

[0082] Wherein, by mass percentage, the matrix includes 40-85% methyl methacrylate, 0-50% low Tg acrylic monomer, 0-20% cross-linked acrylic monomer, 5-20% rigid side group monomer, 4-20% fluorine-containing or silicon-containing acrylic monomer, and 0.5-5% free radical thermal initiator. Specifically, by mass percentage, the proportion of methyl methacrylate in the matrix can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%; the proportion of low Tg acrylic monomer in the matrix can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%; the proportion of cross-linked acrylic monomer in the matrix can be 0%, 5%, 10%. , 15%, 20%; the proportion of rigid side group monomers in the matrix can be 5%, 8%, 10%, 12%, 15%, 17%, 20%; the proportion of fluorine-containing or silicon-containing acrylic monomers in the matrix can be 4%, 8%, 10%, 12%, 15%, 17%, 20%; the proportion of free radical thermal initiators in the matrix can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0083] Generally speaking, during the preparation process, the non-film-forming matrix comprises 30-70% matrix and 30-70% solvent 1. After the non-film-forming matrix is ​​used to prepare a photopolymer solution, solvent 1 and solvent 2 are still present, meaning the photopolymer solution comprises 15-25% solvent 2, with the remainder being the non-film-forming matrix and the compounding base. The non-film-forming matrix comprises solvent 1 and matrix, and the specific components of the matrix and compounding base are as described above and will not be further described here. After the photopolymer solution is dried, solvent 1 and solvent 2 evaporate, resulting in a thin film of photopolymer. At this point, the photopolymer comprises 50-80% matrix and 20-50% compounding base.

[0084] The photopolymer of the present invention uses a non-film-forming matrix as a base material, wherein the non-film-forming matrix comprises 30-70% of a matrix and 130-70% of a solvent. During the preparation process, the solvent in the non-film-forming matrix evaporates, leaving only the matrix. The matrix includes methyl methacrylate, a low-Tg acrylic monomer, a cross-linked acrylic monomer, a rigid side group monomer, a fluorine-containing or silicon-containing acrylic monomer, and a free radical thermal initiator. Such a photopolymer can meet optical requirements such as high transmittance, low refractive index, and low haze, while also having a high Tg, low adhesion to the protective film, and being non-sticky to the protective film. Removal of the protective film during transfer does not damage the photopolymer. The photopolymer itself is relatively brittle and can be processed by hot stamping, cold transfer, and other methods, as well as by partially transferring by blunt cutting of the concave and convex portions of the die head.

[0085] Specifically, the present invention changes the brittleness of the photopolymer coating formula so that it does not form a film (i.e., it does not form a continuous film layer) and does not stick to the protective film. In terms of process, after it is coated on the protective film and dried, it is covered with the protective film to obtain a roll of unexposed photopolymer, which is suitable for assembly line production. It also reduces the difficulty and space of cold storage of semi-finished products, greatly saving production costs. Then, a volume holographic grating master with a volume holographic grating is made and designed. On a continuous device, a single-beam laser is used to copy the volume holographic grating of the volume holographic grating master to the photopolymer roll material and post-process it. Since a single-beam laser has no strict requirements for vibration, it does not require static table time, and continuous production can be achieved, greatly improving production efficiency. After dry post-treatment and curing (heating and UV curing), the protective film on one side can be peeled off, and the required part of the photopolymer with a volume holographic grating structure can be partially transferred by UV cold transfer, hot stamping, etc. through a die with a concave and convex surface or a flat die, and the other protective film can be peeled off at the same time. This solves the problem of making photopolymer holographic gratings on curved surfaces and eliminates the need for a protective film, thereby improving transmittance.

[0086] The non-film-forming matrix of the present invention is based on the high transparency of acrylic polymers, with methyl methacrylate having a relatively high Tg as the main body. A small amount of other monomers with rigid side groups, such as isobornyl methacrylate, dicyclopentadiene and its derivatives, and adamantyl acrylates, are added to the formula. The rigid monomers with large side groups can reduce the rotational mobility of the molecular chain, causing the molecular chain to freeze. The brittleness of the synthesized non-film-forming matrix is ​​greatly increased, making it easy to break, which is conducive to blunt cutting and separation. During transfer and partial transfer die-cutting, the edges can be cut very neatly by a blunt instrument.

[0087] Because rigid pendant monomers and polymers with cyclic side groups have a relatively high refractive index, the addition of fluorine- or silicon-containing acrylic monomers is necessary to reduce the refractive index of the non-film-forming matrix and further reduce the adhesion between the non-film-forming matrix and the protective film, thereby facilitating peeling. Optical materials require very high light transmittance, and the only commercially available protective films with a certain strength that can support roll-to-roll coating and drying are PET or TAC films without a release agent coating. Protective films with release agents, typically silicone oil and fluoride, have low adhesion and are prone to detachment from the photopolymer, resulting in black spot defects. Furthermore, these release-coated protective films have low transmittance, typically only around 80%. The release coating also contributes to high haze, which can introduce significant noise during optical capture, blurring volume holographic images.

[0088] Specifically, the invention uses methyl methacrylate (MMA), a relatively high Tg acrylic monomer, as the backbone. The resulting polymethyl methacrylate (PMMA) after cross-linking and polymerization of methyl methacrylate has high transmittance (approximately 92%) and a relatively high Tg (approximately 105°C), as well as high brittleness and weak impact resistance, making it suitable as a base material for brittle photopolymers. Specifically, the invention uses methyl methacrylate (MMA) as the primary component, adds a small amount of rigid side-group monomers with giant cyclic groups, further increasing the brittleness of the photopolymer, and then adds fluorine- or silicon-containing acrylic monomers to reduce the adhesion between the photopolymer and the protective film, allowing for complete removal of the protective film. The invention involves oily free radical polymerization of acrylic monomers, and the polymerization reaction can be initiated using butanone as a solvent and a free radical thermal initiator.

[0089] Specifically, by mass percentage, the proportion of methyl methacrylate in the matrix can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%; the proportion of low Tg acrylic monomer in the matrix can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%; the proportion of cross-linked acrylic monomer in the matrix can be 0%, 5%, 10% , 15%, 20%; the proportion of rigid side group monomers in the matrix can be 5%, 8%, 10%, 12%, 15%, 17%, 20%; the proportion of fluorine-containing or silicon-containing acrylic monomers in the matrix can be 4%, 8%, 10%, 12%, 15%, 17%, 20%; the proportion of free radical thermal initiators in the matrix can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0090] Specifically, by mass percentage, the matrix comprises 69.4% methyl methacrylate, 6% butyl acrylate, 0% hydroxyethyl methacrylate, 13.6% isobornyl methacrylate, 10% dodecafluoroheptyl methacrylate, 0.7% dibenzoyl peroxide, and 0.3% N,N-dimethyl-p-toluidine. With this composition, the non-film-forming matrix has an elongation at break of only 8.02% and a glass strength of only 0.23N / 25mm. The resulting photopolymer is brittle and easily fractured, making it easier to separate using blunt cutting techniques and preventing adhesion to protective films.

[0091] Low-Tg acrylic monomers are one or more of ethyl acrylate (EA), butyl acrylate (BA), isooctyl acrylate (2-EHA), lauryl acrylate, and dodecyl acrylate. The longer the carbon chain of the low-Tg acrylic monomer, the greater the monomer flexibility, with the flexibility ranking being ethyl acrylate (EA) < butyl acrylate (BA) < isooctyl acrylate (2-EHA) < lauryl acrylate < dodecyl acrylate. The greater the flexibility, the greater the amount added, the lower the brittleness of the non-film-forming matrix, the stronger the adhesion to the protective film, and the lower the glass transition temperature. Therefore, depending on the different protective films, one or more of these monomers can be selected or not selected, allowing the photopolymer to both properly adhere to the protective film, achieving the effect of being covered and protected by the protective film, and also to not stick to the protective film.

[0092] Cross-linking acrylic monomers include hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), other hydroxy acrylic monomers, acrylamide (AAM), hydroxymethyl acrylamide (NMA), diacetone acrylamide (DAAM), ethyl acetoacetate methacrylate (AAEM), glycidyl methacrylate (GMA), and dimethylaminoethyl methacrylate (DMAEMA). These cross-linking acrylic monomers contain functional monomers such as amide, amino, and epoxy groups that provide cross-linking functionality and can be selected based on the requirements of different products. Certain cross-linking groups can improve the hardness and weather resistance (high and low temperature resistance, light, UV rays, oxidation, water, solvents, etc.) of the non-film-forming matrix, reduce brittleness, improve heat resistance, and enhance adhesion to the protective film. These cross-linking acrylic monomers serve as a regulator and can be added or omitted depending on the protective film and the application environment.

[0093] The rigid side group monomers are isobornyl methacrylate (IBOA), dicyclopentadiene and its derivatives, and one or more adamantyl acrylates, wherein dicyclopentadiene is a difunctional monomer. The adamantyl acrylate can specifically be adamantane methyl acrylate. The structural formulas of isobornyl methacrylate (IBOA), dicyclopentadiene, and adamantane methyl acrylate are as follows:

[0094]

[0095] Fluorinated acrylic monomers include one or more of trifluoroethyl acrylate (TFEA), trifluoroethyl methacrylate (TFEMA), hexafluorobutyl acrylate (HFBA), and dodecafluoroheptyl methacrylate (DFMA). Silicone-containing acrylic monomers include one or more of methylvinylchlorosilane, vinyltrichlorosilane, and vinyltriethoxysilane (VTES). These silicone-containing acrylic monomers are organosilicon monomers with a vinyl group. Fluorinated or silicone-containing acrylic monomers reduce the adhesion between the non-film-forming substrate and the protective film, allowing for complete removal of the protective film.

[0096] The free radical thermal initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate, hydrogen peroxide, ammonium persulfate, potassium persulfate, benzoyl peroxide, tert-butyl benzoyl peroxide, and methyl ethyl ketone peroxide. One or more of them can be selected according to needs.

[0097] Specifically, dibenzoyl peroxide (BPO) and N,N-dimethylaniline (DMA) or dimethyl-β-propionate thiazolinone (DMPT) are preferred in the present invention. They can be used for room-temperature polymerization of methyl methacrylate and other monomers. Specifically, the decomposition and polymerization rates of the BPO-DMPT initiation system are faster than those of the BPO-DMA initiation system, and the color stability of the polymer using DMPT is better than that using DMA.

[0098] To prepare the non-film-forming matrix, the matrix components are added to a butanone solvent and heated under reflux for 1-8 hours to obtain a clear, transparent, and viscous non-film-forming matrix solution. This non-film-forming matrix solution can be directly used to prepare the photopolymer. The butanone solvent evaporates during subsequent preparation steps.

[0099] The high refractive index monomer can be one or more of phenyl bisether fluorene, phenol ethoxy acrylate, ethoxybisphenol fluorene diacrylate, vinyl carbazole, and sulfur-containing acrylate monomers. The visible light harvester can be an acridine dye (460 nm), a xanthene dye (565 nm), a thiazine dye (668 nm), and the like, such as methylene blue, erythrosine b, eosin, and azure I.

[0100] The photoinitiator can be a diaryl titanocene such as 6, bis-2,6-difluoro-3-pyrrolphenyl titanocene (GR-FMT, 784), an aryl ferrocenium salt such as η6-isopropylbenzene (II) hexafluorophosphate (i-261), a UV initiator bisimidazole, a borate, etc.

[0101] The above high-refractive index monomer, visible light scavenger, and photoinitiator are added to the non-film-forming matrix solution containing butanone solvent. An appropriate solvent (e.g., 15-25% solvent) such as butanone, ethyl acetate, methanol, or dichloromethane is then added, with the remainder being the non-film-forming matrix and the compounding base. The concentration is adjusted and the solution is stirred in a darkroom at room temperature until completely dissolved to obtain a photopolymer solution. The solution is then stored in the dark at 0-4°C until ready for use. Stirring and storing in the dark prevents external light from initiating polymerization. During use, the photopolymer solution is coated onto a support such as a glass plate or a protective film. After covering the protective film, the solution is exposed to a 532nm green laser. The diffraction efficiency can reach over 85%.

[0102] The present invention also discloses a non-film-forming matrix for the above-mentioned photopolymer, which comprises, by weight, 30-70% matrix and 30-70% solvent 1. Solvent 1 may be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%, and matrix may be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. The matrix comprises:

[0103]

[0104] The proportion of methyl methacrylate in the matrix can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%; the proportion of low Tg acrylic monomer in the matrix can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%; the proportion of cross-linked acrylic monomer in the matrix can be 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%. 0%; the proportion of rigid side group monomers in the matrix can be 5%, 8%, 10%, 12%, 15%, 17%, 20%; the proportion of fluorine-containing or silicon-containing acrylic monomers in the matrix can be 4%, 8%, 10%, 12%, 15%, 17%, 20%; the proportion of free radical thermal initiators in the matrix can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0105] The matrix is ​​the matrix in the above-mentioned photopolymer. Its component composition, specific types of components, and effects are the same as those mentioned above and will not be repeated here.

[0106] The present invention also discloses a photopolymer film, which is made by the above-mentioned photopolymer film preparation method and comprises the above-mentioned photopolymer and two layers of protective films, wherein the two layers of protective films respectively cover two sides of the photopolymer.

[0107] When preparing the photopolymer film, a volume holographic grating master with positioning marks is first designed and manufactured. The volume holographic grating master has the required volume holographic image information.

[0108] The unexposed photopolymer solution is applied to a transparent protective film using a roll-to-roll blade coater in a dark environment. After drying, a thin coating with a thickness ranging from a few microns to several hundred microns is formed. Another layer of transparent protective film is then applied to form a sandwich structure. Highly transparent PET or TAC protective films are preferred. However, glass, transparent resin plates, or transparent resin sheets can also be used in place of or in combination with the protective film.

[0109] The present invention uses a PET protective film as an example carrier. A photopolymer solution is applied to the PET protective film and dried, then covered with another layer of PET protective film and rolled into a roll. During exposure and replication, the rolled photopolymer film continuously replicates the volume holographic grating on the volume holographic grating master onto the photopolymer film using a single laser beam. When replicating the photopolymer volume holographic grating, reference light must be transmitted through the unexposed photopolymer during replication, causing it to reflect off the volume holographic grating master. The resulting object light and the reference light interfere with each other in the photopolymer, forming a replicated volume holographic grating within the photopolymer. Replication still utilizes a visible laser light source compatible with the volume holographic grating master, and the replication principle is still to generate light interference to form light and dark fringes, inducing a photochemical reaction at the light fringes, and forming a volume holographic grating deeply embedded in the photopolymer and parallel to the coating surface.

[0110] Because the laser light source needs to penetrate the photopolymer and land on the volume holographic grating master during replication, both the upper and lower carriers of the photopolymer must be highly transparent. This dictates that the photopolymer carrier cannot be made of a material coated with a release agent. In light of the aforementioned, the opaque portion of the release agent can generate significant noise, resulting in blurred and scattered holograms after replication, and very poor holographic image quality, even indiscernible. The photopolymer of the present invention, however, can avoid adhesion to protective films without the use of a release agent, thus avoiding interference from the release agent during replication of the volume holographic grating.

[0111] After the photopolymer is composited with the volume holographic grating master and exposed for replication, it undergoes post-processing, including UV irradiation fixation, heating for strengthening, and UV irradiation for reaction termination. The resulting product, a photopolymer film, consists of a replica of the volume holographic grating hologram, sandwiched between protective films on top and bottom.

[0112] The comparison between the photopolymer film of the present invention and other volume holographic products currently on the market is shown in the following table:

[0113]

[0114] The present invention also discloses a photopolymer substrate, comprising the above-mentioned photopolymer, wherein the photopolymer is solidified on the substrate. When the photopolymer film is used, one layer of the protective film is first peeled off, and a cold stamping adhesive or a composite hot melt adhesive is applied to the sheet-like or continuous substrate. At the same time, the positioning mark on the photopolymer, which is produced by photographing the volume holographic grating, is read. By bluntly cutting the edges of the concave and convex templates, the brittle photopolymer is cut to obtain neatly shaped edges. At this time, after curing the UV cold transfer adhesive by UV light irradiation or curing the hot melt adhesive by cooling, the photopolymer is firmly transferred to the substrate. During the transfer process, another layer of the protective film is simultaneously peeled off, and a photopolymer substrate without upper and lower protective films can be obtained.

[0115] The printing materials can be AR lenses, AR-HUD displays, transparent displays, projected transparent HUD displays, AR smart helmet display masks, security camera AR display lenses, airborne sight displays, individual soldier sights, film lenses and other transparent and display screens, as well as various packaging materials and anti-counterfeiting materials.

[0116] The technical solution of the present invention is described below by using specific examples and comparative examples of non-film-forming substrates.

[0117] Examples 1-3

[0118] In Examples 1-3, the components and amounts of the non-film-forming matrix in Table 1 were added to a flask, and the mixture was kept refluxed at 110 degrees Celsius for 3.5 hours. The non-film-forming matrix solution was taken out, air-dried and bonded to a 25 mm test piece, and then its elongation at break and 90-degree peel strength were tested using a tensile tester to identify its brittleness and peelability. The results are shown in Table 1.

[0119] Comparative Example

[0120] Comparative Example: 50 g of commercially available EVA resin (LG Chemical, ES28005) was added to a flask, 50 g of butanone was added, and the mixture was refluxed at 110 degrees Celsius for 3.5 hours. The non-film-forming matrix solution was taken out, air-dried and bonded to a 25 mm test piece, and then its elongation at break and 90-degree peel strength were tested using a tensile testing machine to identify its brittleness and peelability. The results are shown in Table 1.

[0121] Table 1

[0122] Components Example 1 Example 2 Example 3 Comparative Example 1 Methyl methacrylate 34.7g 36.7g 38.5g / Butyl acrylate 3g 3g 3g / Hydroxyethyl methacrylate 0g 3g 3g / Isobornyl methacrylate 6.8g 6.8g 0 / Dodecafluoroheptyl methacrylate 5g 0g 5g / Benzoyl peroxide 0.35g 0.35g 0.35g / N,N-dimethyl-p-toluidine 0.15g 0.15g 0.15g / Butanone 50g 50g 50g / Elongation at break 8.02％ 4.55％ 136％ 800％ Peel strength 0.23N / 25mm 7.3N / 25mm 1.77N / 25mm 10N / 25mm

[0123] Furthermore, 50 g of each of the non-film-forming matrices prepared in Examples 1-3 above were added, respectively, 3 g of phenolic ethoxy acrylate, 7.54 g of vinyl carbazole, 1.8 g of bis-2,6-difluoro-3-pyrrolphenyl titanocene (GR-FMT, 784), 0.028 g of erythrosine b, and 28 g of butanone were added, stirred and dissolved at room temperature, and then coated on a glass plate or a protective film. After covering the protective film, the glass plate was exposed with a 532 nm green laser, and the diffraction efficiency could reach more than 85%.

[0124] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Those skilled in the art may modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein; and all these modifications and replacements should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a photopolymer film, characterized in that: Including steps: By mass percentage, 69.4% of methyl methacrylate, 6% of butyl acrylate, 13.6% of isobornyl methacrylate, 10% of dodecafluoroheptyl methacrylate, 0.7% of dibenzoyl peroxide, and 0.3% of N,N-dimethyl-p-toluidine were weighed in proportion to form a matrix; The matrix is ​​heated under reflux in solvent 1 for 1-8 hours to obtain a non-film-forming matrix; wherein the weight ratio of solvent 1 to matrix is ​​1:1; Weigh 50 g of non-film-forming matrix, 3 g of phenol ethoxy acrylate, 7.54 g of vinyl carbazole, 1.8 g of bis-2,6-difluoro-3-pyrrolylphenyl titanocene, and 0.028 g of erythrosine B according to the proportion to prepare the first raw material; The raw material 1 was stirred and dissolved in 28 g of solvent 2 to obtain a photopolymer solution; Making a volume holographic grating master with positioning marks; coating a photopolymer solution on a protective film and drying the solution to form a photopolymer coating, and covering the photopolymer coating with a protective film to obtain a photopolymer intermediate; replicating the volume holographic grating on the volume holographic grating master to a photopolymer intermediate to obtain a photopolymer film with the volume holographic grating; UV irradiation and heating of photopolymer films.

2. A photopolymer, characterized in that The photopolymer solution according to claim 1 is dried and solvent 1 and solvent 2 are volatilized to obtain the photopolymer solution.

3. A photopolymer film, characterized in that: The photopolymer comprises the photopolymer as claimed in claim 2 and two layers of protective films, wherein the two layers of protective films respectively cover two sides of the photopolymer.

4. A photopolymer substrate, characterized in that: The method comprises a substrate and the photopolymer according to claim 2, wherein the photopolymer is cured on the substrate and has a volume holographic grating.

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