Photopolymer, flexible holographic optical film and preparation method thereof

Abstract

The invention discloses a photopolymer, a flexible holographic optical film and a preparation method of the photopolymer. The photopolymer comprises the following raw material components in parts by weight: 100 parts of flexible acrylate resin; 0.01 to 0.1 part of a curing agent; 20 to 70 parts of a functional monomer; 2-5 parts of a photoinitiator; 0.05 to 5 parts of a photosensitive dye; and 10-60 parts of a first solvent. The flexible holographic optical film prepared by the invention has the following characteristics: (1) good bending performance: the holographic optical film can bear 100 thousand times of bending by using the bendable base material and the specially designed photopolymer functional layer, and can still keep a complete structure under the condition that the radius of curvature is as low as 10mm, so that the flexibility of the holographic optical film is improved; the holographic pattern does not have the phenomena of deformation, fracture or color fading and the like; and (2) high durability: the holographic optical film has good bending resistance and environmental resistance through the improved photopolymer and the preparation process.

Description

Technical Field

[0001] The present invention relates to the field of holographic optical film materials, and particularly to a photopolymer, a flexible holographic optical film and a preparation method thereof. Background Art

[0002] Abroad, the research on the production process of holographic optical films started earlier and achieved a series of important results. Countries such as the United States, Japan, and Germany are in the leading position in the basic research and application development of holographic optical films. Some scientific research institutions and enterprises in the United States have invested a large amount of resources in the research of laser holography technology, developed high-resolution and high-stability holographic optical film production technology, which can achieve high-precision holographic image recording and reproduction, and is widely used in the fields of information storage and high-end display. Japanese enterprises have unique advantages in the material research and development and production process optimization of holographic optical films, developed a variety of new holographic photosensitive materials and advanced production processes, improved the performance and production efficiency of holographic optical films, and their products have a high market share in the global market.

[0003] Traditional holographic optical films have been widely used in many fields. However, the production of traditional holographic optical films mainly relies on direct imprinting or indirect transfer printing methods, and they are usually relatively rigid, with limitations in application scenarios that require bending, curling, etc. For example, in some wearable devices, flexible electronic displays, and optical devices with special requirements for space utilization, traditional holographic optical films cannot meet the flexible design requirements of products. With the development of technology, the demand for optical films that can adapt to complex shapes, can be bent, and still maintain good holographic optical performance is increasing. Although there are some technologies for developing flexible optical films in the market currently, there are still many problems to be solved in ensuring the stability of holographic patterns, the consistency of optical performance after bending, and the durability of materials. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a photopolymer, a flexible holographic optical film and a preparation method thereof in view of the above-mentioned deficiencies in the prior art. The flexible holographic optical film provided by the present invention can withstand 100,000 bends without affecting its optical performance and structural integrity while having good holographic optical effects, expanding the application range of holographic optical films.

[0005] To achieve the above object, the technical solution adopted by the present invention is: In the first aspect of the present invention, a photopolymer is provided, which is characterized by including the following raw material components by weight:

[0006]

[0007] The functional monomer is a mixture of a polyfunctional monomer and a monofunctional monomer.

[0008] Preferably, the polyfunctional monomer is selected from at least one of ethoxylated bisphenol fluorene diacrylate, bisphenol A-dimethacrylate, pentaerythritol tetraacrylate, and ethoxylated trimethylolpropane triacrylate.

[0009] Preferably, the monofunctional monomer in the functional monomer is a mixture of a monofunctional high refractive index monomer and a monofunctional flexible monomer.

[0010] Preferably, the monofunctional high refractive index monomer is selected from at least one of N-vinylcarbazole, acryloylmorpholine, m-phenoxybenzyl acrylate, o-phenylphenoxyethyl acrylate, biphenylmethanol acrylate, 6-acryloxymethyldinaphthothiophene, 5-acryloxyethyldinaphthothiophene, and 6-vinyldinaphthothiophene.

[0011] Preferably, the monofunctional flexible monomer is selected from at least one of methoxy (meth)acrylate and ethoxy (meth)acrylate monomers.

[0012] Preferably, the mass ratio of the monofunctional high refractive index monomer: the monofunctional flexible monomer: the polyfunctional monomer is 1:(0.2 - 0.8):(0.1 - 0.5).

[0013] Preferably, the flexible acrylate resin is a bendable acrylic optical resin with a glass transition temperature < -40°C, a storage modulus at 25°C of 0.01 - 0.1 Mpa, a creep recovery ratio > 96%, and a recovery time for 80% ratio < 30 seconds.

[0014] Preferably, the flexible acrylate resin is obtained by polymerizing the following raw materials by weight: 70 - 95 parts of a soft monomer, 5 - 25 parts of a crosslinking monomer, 0.3 - 1.2 parts of an initiator, and 50 - 120 parts of a second solvent;

[0015] wherein, the soft monomer is an acrylate monomer with a glass transition temperature below -50°C, and the crosslinking monomer is an acrylic monomer containing hydroxyl, amino, or carboxyl groups.

[0016] Preferably, the soft monomer is one or more of methoxy (meth)acrylate, ethoxy (meth)acrylate monomers, isooctyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, and alkyl acrylate; wherein, the methoxy (meth)acrylate or ethoxy (meth)acrylate monomer must be included, and the proportion of the acrylate monomer containing an ether bond in the soft monomer is not less than 50%;

[0017] The crosslinking monomer is one or more of hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxypropyl acrylate, acrylamide, acrylic acid, and methacrylic acid;

[0018] The initiator is one or more of azobisisobutyronitrile, azobisvaleronitrile, and dimethyl azobisisobutyrate;

[0019] The second solvent is one or more of ethyl acetate, toluene, and methyl ethyl ketone.

[0020] Preferably, the methoxy group-containing (meth)acrylate or ethoxy group-containing (meth)acrylate monomer is selected from one or more of ethoxyethoxyethyl acrylate, 2-methoxyethyl acrylate, triethylene glycol monomethyl ether acrylate, methoxydiethylene glycol methacrylate, methoxypolyethylene glycol 230 methacrylate, methoxypolyethylene glycol 400 methacrylate, and methoxypolyethylene glycol 1000 methacrylate.

[0021] Preferably, the flexible acrylate resin is prepared by the following method:

[0022] S1. Charge the soft monomer, crosslinking monomer, first part of the initiator, and part of the second solvent into a reactor;

[0023] S2. Heat to 60 - 65 °C, stir and purge with nitrogen for 10 - 30 minutes, and maintain the temperature for reaction for 2 - 8 hours;

[0024] S3. Add the second part of the initiator, heat to 70 - 78 °C, and maintain the temperature for reaction for 0.5 - 3 hours;

[0025] S4. Add the remaining third part of the initiator, heat to 75 - 80 °C, and maintain the temperature for reaction for 2 - 4 hours to obtain a reaction solution;

[0026] S5. After the reaction solution is cooled to room temperature, add the remaining second solvent and stir to obtain the flexible acrylate resin.

[0027] Preferably, the curing agent is at least one of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, benzylidene diisocyanate, hydrogenated benzylidene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylbenzylidene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate;

[0028] The photoinitiator is at least one of benzophenone, alkyl benzophenone, 4,4'-bis(dimethylamino)benzophenone, anthrone, halogenated benzophenone, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bisacylphosphine oxide, phenylglycolate, camphorquinone, a-aminoalkylbenzophenone, α,α-dialkoxyacetophenone, a-hydroxyalkylbenzophenone, tetrabutylammonium triphenylhexylborate, tetrabutylammonium tris(3-fluorophenyl)hexylborate, tetrabutylammonium tris(3-chloro-4-methylphenyl)hexylborate, ferrocene-based compound, iodonium salt, sulfonium salt, hexaarylbiimidazole;

[0029] The photosensitive dye is selected from at least one of acridine orange, new methylene blue, triethylammonium thioerythrosinate, eosin, erythrosine, rose bengal, thionine, basic yellow, rhodamine 6G, gallocyanine, ethyl violet, victoria blue R, celestine blue, quinidine red, crystal violet, bright green, basic orange G, darrow red, pyronin Y, basic red 29, pyranium iodide, cyanine, methylene blue, azur A;

[0030] The first solvent is at least one of ethyl acetate, butyl acetate, isopropyl alcohol, and methyl ethyl ketone.

[0031] In the second aspect of the present invention, a flexible holographic optical film is provided, which includes a functional layer and two substrate layers located on both sides of the functional layer, and the functional layer is made by exposing the above-mentioned photopolymer.

[0032] In the third aspect of the present invention, a preparation method of the above-mentioned flexible holographic optical film is provided, including the following steps:

[0033] 1) In a dark room or under a protective lamp inert to the photosensitive dye, at a temperature of 10-30 °C, the first solvent, flexible acrylate resin, curing agent, functional monomer, photoinitiator, and photosensitive dye are mixed evenly to obtain a photopolymer;

[0034] 2) Under the conditions of a dark room or a protective lamp inert to the photosensitive dye, the above-mentioned photopolymer is coated on a substrate, dried, another substrate is covered on the formed photopolymer layer, exposed, and finally irradiated with an LED lamp, a fluorescent lamp, or an ultraviolet lamp until complete fixing and bleaching to obtain the flexible holographic optical film.

[0035] The beneficial effects of the present invention are:

[0036] The present invention provides a photopolymer and a flexible holographic optical film based on the photopolymer. In the photopolymer of the present invention, the soft monomer of the flexible resin and the functional monomer cooperate with each other. By defining the structure of the soft monomer and the types and dosages of the three monomers in the functional monomer, they jointly affect the performance of the flexible holographic film such as bending resistance, formation and stability of the holographic pattern, and durability, and solve the performance problems that the holographic film cannot be bent, curled, or folded;

[0037] The flexible holographic optical film prepared by the present invention has the following characteristics:

[0038] (1) Good bendability: The bendable substrate and the specially designed photopolymer functional layer selected in the present invention enable the holographic optical film to withstand 100,000 bends. Even when the radius of curvature is as low as 10 mm, the structure remains intact, and the holographic pattern does not deform, break, or fade, greatly expanding its application in flexible electronic devices;

[0039] (2) High durability: The improved photopolymer and preparation process endow the holographic optical film with good bending resistance and environmental resistance; in daily use and various complex environments, it can maintain its optical properties and bendability for a long time, extending the service life of the product and reducing the maintenance cost. Detailed implementation manners

[0040] The following further describes the present invention in detail with reference to embodiments, so that those skilled in the art can implement it according to the description in the specification.

[0041] It should be understood that the terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0042] Unless otherwise specified, the test methods used in the following examples are all conventional methods. The materials, reagents, etc. used in the following examples can all be obtained from commercial sources unless otherwise specified. For those not specified in the following examples, they are carried out under conventional conditions or the conditions recommended by the manufacturer. For those reagents or instruments without indicating the manufacturer, they are all conventional products that can be purchased commercially.

[0043] The present invention provides a photopolymer, which comprises the following raw material components by weight:

[0044]

[0045] The functional monomer is a mixture of a polyfunctional monomer and a monofunctional monomer.

[0046] While ensuring high-resolution recording of holographic patterns, the photopolymer has good flexibility and bend resistance; its molecular structure is specially designed, and when subjected to external force bending, the molecular chains can slide and adjust relative to each other and can quickly recover, thus avoiding material rupture, dislocation, or damage to the holographic pattern caused by bending.

[0047] The photopolymer must contain components with different refractive indices. Under light illumination, the photoinitiator generates free radicals to initiate the polymerization of functional monomers. By applying the principle of optical interference, polymerization can occur at the bright fringes, and the monomers at the dark fringes migrate to the bright fringes with lower monomer concentration, forming a suitable grating film with alternating light and dark patterns. In the photopolymer, the refractive index of the flexible acrylate resin is controlled at 1.47 or below, and the refractive index of the functional monomer is controlled above 1.5, preferably above 1.6.

[0048] The bendable design of the photopolymer consists of two parts:

[0049] 1. The glass transition temperature, modulus, and creep of the flexible acrylate resin;

[0050] 2. The elongation at break of the material constituting the holographic pattern.

[0051] Both work synergistically and influence each other. They should possess the following properties simultaneously to ensure that the holographic pattern does not have defects or damage after bending. The flexible acrylate resin part should have a room temperature storage modulus of 0.01 - 0.1 Mpa and a glass transition temperature below -40°C to ensure its sufficient deformation ability, reduce the extrusion and tensile stress on the holographic pattern during bending, and avoid permanent deformation and damage to the holographic pattern. The creep recovery rate of the flexible acrylate resin should reach over 96%, and the recovery time for 80% deformation should be less than 30 seconds to ensure that there are no obvious indentations or protrusions after repeated bending, which would affect the display of the holographic pattern. At the same time, the elongation at break of the holographic pattern material should be controlled above 5% to avoid cracks and misalignments caused by the stress during repeated bending of the holographic film.

[0052] In a preferred embodiment, the flexible acrylate resin is a bendable acrylic optical resin with a glass transition temperature < -40°C, a storage modulus at 25°C of 0.01 - 0.1 Mpa, a creep recovery ratio > 96%, and a recovery time for 80% ratio < 30 seconds.

[0053] In a preferred embodiment, the flexible acrylate resin is obtained by polymerizing the following raw materials by weight: 70 - 95 parts of soft monomer, 5 - 25 parts of crosslinking monomer, 0.3 - 1.2 parts of initiator, and 50 - 120 parts of second solvent.

[0054] In a preferred embodiment, the soft monomer is an acrylate monomer with a glass transition temperature below -50°C, and the crosslinking monomer is an acrylic monomer containing hydroxyl, amino, or carboxyl groups. The flexible acrylate resin of the present invention is mainly composed of long - side - chain acrylate monomers, with a small amount of long - chain isocyanate curing agent as the crosslinking agent. It can retain various weather - resistant adhesion advantages of polyacrylate adhesives while absorbing the interlayer stress during bending and curling, enabling the normal bending and curling of the holographic optical film 100,000 times.

[0055] In a preferred embodiment, the soft monomer is selected from one or more of methoxy (meth) acrylates, ethoxy (meth) acrylate monomers, isooctyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, and alkyl acrylates. Among them, methoxy (meth) acrylate or ethoxy (meth) acrylate monomers must be included, and the proportion of acrylate monomers containing ether bonds in the soft monomer is not less than 50%. The ether bonds in the side chains of methoxy and ethoxy acrylic monomers have good electron transfer ability, which is beneficial to the molecular migration of functional monomers in the components, thus beneficial to the formation of holographic patterns. Moreover, the ether bond structure of C-O-C has relatively high polarity and can produce physical cross-linking with other ether bonds or polar functional groups such as hydroxyl groups and carboxyl groups, improving the recovery ratio and recovery speed of flexible acrylate resins.

[0056] In a preferred embodiment, the methoxy (meth) acrylate or ethoxy (meth) acrylate monomer is selected from one or more of ethoxyethoxyethyl acrylate, 2-methoxyethyl acrylate, triethylene glycol monomethyl ether acrylate, methoxydiethylene glycol methacrylate, methoxypolyethylene glycol 230 methacrylate, methoxypolyethylene glycol 400 methacrylate, and methoxypolyethylene glycol 1000 methacrylate.

[0057] In a preferred embodiment, the crosslinking monomer is one or more of hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxypropyl acrylate, acrylamide, acrylic acid, and methacrylic acid.

[0058] In a preferred embodiment, the initiator is one or more of azobisisobutyronitrile, azodipentanenitrile, and dimethyl azodicarboxylate.

[0059] In a preferred embodiment, the second solvent is one or more of ethyl acetate, toluene, and methyl ethyl ketone.

[0060] In a preferred embodiment, the flexible acrylate resin is prepared by the following method:

[0061] S1. Charge the soft monomer, crosslinking monomer, first-stage initiator, and part or all of the solvent into a reactor;

[0062] S2. Heat to the first reaction temperature, stir and purge with nitrogen for 10 - 30 minutes, and maintain the first reaction temperature for 2 - 8 hours;

[0063] S3. Add the second-stage initiator, heat to the second reaction temperature, and maintain the second reaction temperature for 0.5 - 3 hours, where the second reaction temperature is higher than the first reaction temperature;

[0064] S4. Add the remaining third-stage initiator, heat to the third reaction temperature, and maintain the reaction temperature for 2 - 4 hours to obtain a reaction solution, where the third reaction temperature is higher than the second reaction temperature;

[0065] S5. After the reaction solution is cooled to room temperature, add the remaining second solvent and stir to dilute to obtain a flexible acrylate resin.

[0066] In a more preferred embodiment, the flexible acrylate resin is prepared by the following method:

[0067] S1. Put soft monomers, crosslinking monomers, the first part of the initiator, and part of the second solvent into a reactor;

[0068] S2. Heat to 60 - 65 °C, stir and pass nitrogen for 10 - 30 minutes, and maintain the temperature for reaction for 2 - 8 hours;

[0069] S3. Add the second part of the initiator, heat to 70 - 78 °C, and maintain the temperature for reaction for 0.5 - 3 hours;

[0070] S4. Add the remaining third part of the initiator, heat to 75 - 80 °C, and maintain the temperature for reaction for 2 - 4 hours to obtain a reaction solution;

[0071] S5. After the reaction solution is cooled to room temperature, add the remaining second solvent and stir to obtain a flexible acrylate resin.

[0072] In a preferred embodiment, the polyfunctional monomer is selected from at least one of ethoxylated bisphenol fluorene diacrylate, bisphenol A - dimethacrylate, pentaerythritol tetraacrylate, and ethoxylated trimethylolpropane triacrylate. The polyfunctional monomer acts as a crosslinking agent to enhance cohesion and shape the grating;

[0073] The monofunctional monomer is a mixture of a monofunctional high-refractive-index monomer and a monofunctional flexible monomer. The monofunctional high-refractive-index monomer includes acrylate and vinyl monomers, which are mainly responsible for providing the refractive index; the monofunctional flexible monomer provides flexibility to achieve the effect of controlling the elongation at break. Secondly, the structures of methoxy and ethoxy are the same as those of the soft monomers in the flexible acrylate resin, achieving the effect of increasing compatibility.

[0074] In a preferred embodiment, the monofunctional high refractive index monomer is preferably a heterocyclic monomer, a fused ring or an aromatic ring monomer, which has a conjugated structure, heteroatom characteristics or molecular planarity, and at the same time has a high refractive index; it contains a strong intramolecular electron transfer function, which can improve the diffraction efficiency and exposure sensitivity of the functional layer. Monomers with a refractive index > 1.5 are preferred. For example, in a preferred embodiment, the monofunctional high refractive index monomer is selected from at least one of N-vinylcarbazole, acryloylmorpholine, m-phenoxybenzyl acrylate, o-phenylphenoxyethyl acrylate, biphenylmethanol acrylate, 6-acryloxymethyldinaphthothiophene, 5-acryloxyethyldinaphthothiophene, 6-vinyldinaphthothiophene. The monofunctional high refractive index monomer is more preferably a biphenyl monomer or a dinaphthothiophene monomer with a refractive index > 1.6.

[0075] In a preferred embodiment, the monofunctional flexible monomer is selected from methoxy group (meth)acrylate or ethoxy group (meth)acrylate monomers.

[0076] More preferably, the monofunctional flexible monomer is selected from one or more of ethoxyethoxyethyl acrylate, 2-methoxyethyl acrylate, triethylene glycol monomethyl ether acrylate, methoxydiethylene glycol methacrylate, methoxypolyethylene glycol 230 methacrylate, methoxypolyethylene glycol 400 methacrylate, methoxypolyethylene glycol 1000 methacrylate.

[0077] In a preferred embodiment, the mass ratio of the monofunctional high refractive index monomer: the monofunctional flexible monomer: the polyfunctional monomer is 1:(0.2 - 0.8):(0.1 - 0.5). If the ratio of the polyfunctional monomer is too high, the haze will increase due to insufficient compatibility, the peel adhesion and adhesion properties will decrease, and the heat resistance and reliability of the holographic pattern material in humid heat will also deteriorate accordingly. If the ratio of the monofunctional high refractive index monomer is too high, there will be a problem of reduced recording efficiency. If the ratio of the monofunctional flexible monomer is too high, the overall refractive index will decrease and the grating effect will deteriorate. In order to ensure that the holographic pattern does not break, misalign, or deform after 100,000 bends and maintains the original display effect, its elongation at break needs to meet the range of 5% - 15%. Further, the network structure needs to be maintained at a certain density. Therefore, the amounts of the polyfunctional monomer, the monofunctional high refractive index monomer, and the monofunctional flexible monomer need to be matched in corresponding proportions.

[0078] The curing agent is an isocyanate crosslinking agent. In a preferred embodiment, the curing agent is at least one of toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate.

[0079] When the photoinitiator is irradiated with light of a specific wavelength with a certain amount of energy, it absorbs photons and jumps to the excited state, generating free radicals to initiate the polymerization of functional monomers. By using the principle of optical interference, polymerization can occur at the bright fringes, and the monomers at the dark fringes migrate to the bright fringes with a lower monomer concentration, forming a suitable grating film with alternating light and dark fringes.

[0080] A photoinitiator is an initiator that can be activated by actinic radiation and initiate the polymerization of corresponding polymerizable groups. In a preferred embodiment, the photoinitiator is at least one of benzophenone, alkyl benzophenone, 4,4'-bis(dimethylamino)benzophenone, anthrone, halogenated benzophenone, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bisacylphosphine oxide, phenylglycolate, camphorquinone, a-aminoalkyl phenyl ketone, α,α-dialkoxyacetophenone, a-hydroxyalkyl phenyl ketone, tetrabutylammonium triphenylhexyl borate, tetrabutylammonium tris(3-fluorophenyl)hexyl borate, tetrabutylammonium tris(3-chloro-4-methylphenyl)hexyl borate, ferrocene-based compounds, iodonium salts, sulfonium salts, and hexaarylbiimidazole.

[0081] The photosensitive dye can be excited by the light irradiated on the photopolymer composition and can also act as an initiator to initiate the polymerization of monomers and crosslinking monomers. The photopolymer can contain 0.05 wt% to 5 wt% of the photosensitive dye. In a preferred embodiment, the photosensitive dye is selected from at least one of acridine orange, new methylene blue, triethylammonium thioerythrosinate, eosin, erythrosine, rose bengal, thionine, basic yellow, rhodamine 6G, gallocyanine, ethyl violet, victoria blue R, celestine blue, quinidine red, crystal violet, bright green, basic orange G (Astrazon Orange G), darrow red, pyronin Y, basic red 29, pyrilium iodide, cyanine, methylene blue, and azurin A.

[0082] In a preferred embodiment, the first solvent is at least one of ethyl acetate, butyl acetate, isopropyl alcohol, and methyl ethyl ketone.

[0083] In a second aspect of the present invention, there is provided a flexible holographic optical film, including a functional layer and two substrate layers located on both sides of the functional layer, and the functional layer is made by exposing the above-mentioned photopolymer.

[0084] The substrate can be materials such as PET, PC, COP, PI, TAC, PMMA, PEN, PAI, etc. To ensure bendability, it is preferred that the substrate thickness < 100 μm, and more preferably the substrate thickness < 75 μm. During the bending process, it can maintain a stable structure, has a high light transmittance, and will not cause obvious interference to the display of the holographic pattern. At the same time, it has a high glass transition temperature, which can ensure that the substrate can still maintain good flexibility and dimensional stability at different ambient temperatures.

[0085] In the third aspect of the present invention, a method for preparing the flexible holographic optical film as above is provided, including the following steps:

[0086] 1) In a dark room or under a protective lamp inert to the photosensitive dye, at a temperature of 10 - 30 °C, mix the first solvent, flexible acrylate resin, curing agent, functional monomer, photoinitiator, and photosensitive dye evenly to obtain a photopolymer.

[0087] 2) Under the conditions of a dark room or a protective lamp inert to the photosensitive dye, coat the above photopolymer on the substrate, dry it, cover another substrate on the formed photopolymer layer, expose it, and finally irradiate it with an LED lamp, fluorescent lamp, or ultraviolet lamp until it is completely fixed and bleached to obtain the flexible holographic optical film.

[0088] The above is the general concept of the present invention. The following provides detailed examples and comparative examples on this basis to further illustrate the present invention.

[0089] The preparation method of the flexible acrylate resin involved in the following examples and comparative examples is as follows:

[0090] Example A1

[0091] Put 45 parts by weight of isooctyl acrylate, 50 parts by weight of ethoxyethoxyethyl acrylate, 5 parts by weight of hydroxybutyl acrylate, and 120 parts by weight of ethyl acetate into the reactor; pass nitrogen and stir for 30 min to remove the air in the reactor, heat to 63 °C, add 0.1 part by weight of azobisisobutyronitrile, and react for 6 hours; add 0.2 part by weight of azobisisobutyronitrile, raise the temperature to 75 °C and react for 1.5 hours; add 0.2 part by weight of azobisisobutyronitrile, raise the temperature to 78 °C and react for 3 hours; after the reaction solution reaches room temperature, add 20 parts by weight of ethyl acetate for dilution, and stir evenly to obtain an adhesive mixture, that is, the flexible acrylate resin.

[0092] Comparative Example B1

[0093] Charge 75 parts by weight of isooctyl acrylate, 20 parts by weight of ethoxyethoxyethyl acrylate, 5 parts by weight of hydroxybutyl acrylate, and 120 parts by weight of ethyl acetate into the reactor; pass nitrogen and stir for 30 min to remove the air in the reactor, heat to 63 °C, add 0.1 part by weight of azobisisobutyronitrile, and react for 6 hours; add 0.2 part by weight of azobisisobutyronitrile, raise the temperature to 75 °C and react for 1.5 hours; add 0.2 part by weight of azobisisobutyronitrile, raise the temperature to 78 °C and react for 3 hours; after the reaction solution reaches room temperature, add 20 parts by weight of ethyl acetate for dilution, stir evenly to obtain an adhesive mixture, namely a flexible acrylate resin.

[0094] Comparative Example B2

[0095] Charge 65 parts by weight of isooctyl acrylate, 15 parts by weight of methyl acrylate, 20 parts by weight of hydroxyethyl acrylate, 80 parts by weight of ethyl acetate, and 20 parts by weight of butanone into the reactor in terms of mass percentage, pass nitrogen and stir to remove the air in the reactor, add 0.1 part by weight of azobisisobutyronitrile at 66 °C, and react for 3 hours; add 0.2 part by weight of azobisisobutyronitrile, react at 75 °C for 1.5 hours; add 0.2 part by weight of azobisisobutyronitrile, react at 78 °C for 3 hours; after the reaction solution reaches room temperature, add the diluent ethyl acetate thereto, stir evenly to obtain an adhesive mixture.

[0096] Add 0.03 part by weight of aliphatic isocyanate HDI trimer to every 100 parts by weight of the flexible acrylate resin prepared above, mix evenly and coat it on a 50-μm thick heavy release film, dry at 100 °C for 3 min, the adhesive thickness is 25 μm, and bond a 50-μm light release film to obtain a test sample;

[0097] Place the test sample statically in an environment of 23 ± 1 °C and a humidity of 50 ± 5% for 24 h, use glass to test properties such as peel strength and light transmittance, and use 50PET transfer test for the bonding strength. The test results are shown in Table 1 below.

[0098] Table 1

[0099]

[0100] Example 1

[0101] A flexible holographic optical film, comprising a functional layer and two substrate layers located on both sides of the functional layer, which is prepared by the following method:

[0102] S1. Prepare a photopolymer. By weight, mix 100 parts of flexible acrylate resin A1, 0.03 parts of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 6 parts of ethoxyethoxyethyl acrylate, 3 parts of ethoxylated bisphenol fluorene diacrylate, 1 part of acridine orange, 2 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate evenly at 25°C in a darkroom or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0103] S2. Prepare a flexible holographic optical film: Under the conditions of a darkroom or a protective lamp inert to photosensitive dyes, coat the above-mentioned photopolymer on a substrate, dry it at 90°C for 5 minutes, cover another substrate on the formed photopolymer layer with a thickness of 10 μm, expose it, and finally irradiate it with an LED lamp, a fluorescent lamp, or an ultraviolet lamp until it is completely fixed and bleached to obtain the flexible holographic optical film. Among them, both substrates are 50-μm-thick PET films.

[0104] Example 2

[0105] A flexible holographic optical film, comprising a functional layer and two substrate layers located on both sides of the functional layer, is prepared by the following method:

[0106] S1. Prepare a photopolymer. By weight, mix 100 parts of flexible acrylate resin A1, 0.03 parts of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 24 parts of ethoxyethoxyethyl acrylate, 15 parts of ethoxylated bisphenol fluorene diacrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate evenly at 25°C in a darkroom or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0107] S2. Prepare a flexible holographic optical film, the same as in Example 1.

[0108] Example 3

[0109] A flexible holographic optical film, comprising a functional layer and two substrate layers located on both sides of the functional layer, is prepared by the following method:

[0110] S1. Prepare a photopolymer. By weight, mix 100 parts of flexible acrylate resin A1, 0.03 parts of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 15 parts of ethoxyethoxyethyl acrylate, 5 parts of ethoxylated trimethylolpropane triacrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate evenly at 25°C in a darkroom or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0111] S2. Prepare the flexible holographic optical film, the same as in Example 1.

[0112] Comparative Example 1

[0113] A flexible holographic optical film includes a functional layer and two substrate layers located on both sides of the functional layer, and is prepared by the following method:

[0114] S1. Prepare the photopolymer. By weight, mix 100 parts of flexible acrylate resin A1, 0.03 part of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 5 parts of ethoxylated trimethylolpropane triacrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate evenly at 25 °C in a dark room or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0115] S2. Prepare the flexible holographic optical film, the same as in Example 1.

[0116] Comparative Example 2

[0117] A flexible holographic optical film includes a functional layer and two substrate layers located on both sides of the functional layer, and is prepared by the following method:

[0118] S1. Prepare the photopolymer. By weight, mix 100 parts of flexible acrylate resin A1, 0.03 part of aliphatic isocyanate HDI trimer, 15 parts of ethoxyethoxyethyl acrylate, 5 parts of ethoxylated trimethylolpropane triacrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate evenly at 25 °C in a dark room or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0119] S2. Prepare the flexible holographic optical film, the same as in Example 1.

[0120] Comparative Example 3

[0121] A flexible holographic optical film includes a functional layer and two substrate layers located on both sides of the functional layer, and is prepared by the following method:

[0122] S1. Prepare the photopolymer. By weight, mix 100 parts of flexible acrylate resin A1, 0.03 part of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 15 parts of ethoxyethoxyethyl acrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate evenly at 25 °C in a dark room or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0123] S2. Prepare the flexible holographic optical film, the same as in Example 1.

[0124] Comparative Example 4

[0125] A flexible holographic optical film, comprising a functional layer and two substrate layers on both sides of the functional layer, is prepared by the following method:

[0126] S1. Prepare a photopolymer. By weight, 100 parts of flexible acrylate resin A1, 0.03 parts of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 15 parts of ethoxyethoxyethyl acrylate, 40 parts of ethoxylated trimethylolpropane triacrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate are mixed evenly at 25°C in a darkroom or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0127] S2. Prepare the flexible holographic optical film, the same as in Example 1.

[0128] Comparative Example 5

[0129] A flexible holographic optical film, comprising a functional layer and two substrate layers on both sides of the functional layer, is prepared by the following method:

[0130] S1. Prepare a photopolymer. By weight, 100 parts of flexible acrylate resin B1, 0.03 parts of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 15 parts of ethoxyethoxyethyl acrylate, 5 parts of ethoxylated trimethylolpropane triacrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate are mixed evenly at 25°C in a darkroom or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0131] S2. Prepare the flexible holographic optical film, the same as in Example 1.

[0132] Comparative Example 6

[0133] A flexible holographic optical film, comprising a functional layer and two substrate layers on both sides of the functional layer, is prepared by the following method:

[0134] S1. Prepare a photopolymer. By weight, 100 parts of flexible acrylate resin B2, 0.03 parts of aliphatic isocyanate HDI trimer, 30 parts of 6-acryloxymethyldinaphthothiophene, 15 parts of ethoxyethoxyethyl acrylate, 5 parts of ethoxylated trimethylolpropane triacrylate, 1 part of acridine orange, 3 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 20 parts of ethyl acetate are mixed evenly at 25°C in a darkroom or under a protective lamp inert to photosensitive dyes to obtain the photopolymer.

[0135] S2. Prepare the flexible holographic optical film in the same way as in Example 1.

[0136] Performance test:

[0137] Perform the following performance tests on the flexible holographic optical films prepared in each example and each comparative example:

[0138] (1) Interlayer force test:

[0139] Under the measurement environment of 23°C and 50% RH, cut the film into a size of 25 mm in width and 100 mm in length, and use it as a test piece. Bond and pull one side with 50PET, and stick the other side on a steel plate. Place it in this environment for 30 minutes, then use a universal tensile and compression testing machine to stretch the PET, and measure the peel strength (adhesive force) [N / 25mm] under the conditions of a pulling speed of 300 mm / minute and a peeling angle of 180 degrees.

[0140] (2) Storage modulus and glass transition temperature: The flexible resin is stacked in multiple layers to a thickness of about 1 mm for measurement. Use ARES manufactured by TA Instruments to measure the dynamic viscoelasticity at a frequency of 1HZ. Read the storage modulus G' at 25°C and the glass transition temperature from the measurement results.

[0141] (3) Creep recovery rate and 80% recovery speed: The flexible resin is stacked in multiple layers to a thickness of about 1 mm for measurement. Use ARES manufactured by TA Instruments, apply a stress load of 10 kPa at a temperature of 25°C for 600 s, remove the stress and recover for 600 s, and read the maximum strain on the load curve, the minimum strain on the recovery curve, and the time corresponding to the strain value of 20% of the maximum strain in the recovery curve.

[0142] (4) Transmittance and haze: Attach the flexible resin to the ink surface of the CG glass, and use a haze meter to measure the transmittance and haze of the above test piece. Subtract the total light transmittance and haze of the CG glass from the measured values to obtain the total light transmittance and haze values of the material.

[0143] (5) Holding force: Attach the flexible resin to a 0.05MM transparent PET film, cut it into a sample with a width of 25.4 mm and a length of 160 m, prepare the sample according to the method of GB / T4851-2014, hang it in a 70°C holding force box, and record the displacement and falling situation.

[0144] (6) Refractive index: Use an Abbe refractometer (manufactured by ATAGO, model "DR-M4") to measure the refractive index of the flexible resin under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C.

[0145] (7) Elongation at break: The functional monomer is combined with a photoinitiator (the type and dosage of the functional monomer are the same as those of the functional monomer and photoinitiator in the examples or comparative examples), coated on 50-μm PET (Toray U483) with a thickness of 4 μm, and cured by an LED lamp under nitrogen protection (the solid content energy is 700 mj) to obtain a functional monomer polymer coating. A 4-μm functional monomer polymer coating (excluding flexible acrylic resin) is coated on 50-μm PET (Toray U483), cured under LED lamp conditions (the solid content energy is 700 mj), laser cut into a size of 10 mm × 100 mm, with a distance of 50 mm between the upper and lower jigs and a stretching speed of 5 mm / min, and the elongation at break when the coating cracks is recorded.

[0146] (8) The holographic performance (diffraction efficiency, spectral bandwidth, etc.) is tested according to the industry standard ISO 17901-1:2015.

[0147] The test results are shown in Table 2 below:

[0148] Table 2

[0149]

[0150]

[0151] According to the test results in Table 2:

[0152] For the flexible holographic optical films prepared in Examples 1-3, when the radius of curvature is 10 mm and they are bent 100,000 times, the holographic patterns are still clear and the optical properties do not decrease significantly.

[0153] From the comparison between Comparative Example 1 and the examples, it can be seen that without adding the flexible functional monomer, the elongation at break of the functional layer after curing is too low, which will have a greater impact on the bending performance. From the comparison between Comparative Example 2 and the examples, it can be seen that without adding the monofunctional high-refractive monomer, the diffraction efficiency is too low. From the comparison between Comparative Example 3 and the examples, it can be seen that without adding the polyfunctional monomer, the recording effect is poor. From the comparison between Comparative Example 4 and the examples, it can be seen that if there are too many polyfunctional monomers, the crosslinking is too high, the interlayer force decreases, and the elongation at break is too low, which affects the bending. From the comparison between Comparative Examples 5 and 6 and the examples, it can be seen that the type ratio of the monomers of the flexible resin affects the compatibility, and insufficient recovery will affect the bending.

[0154] Although the embodiments of the present invention have been disclosed as above, they are not limited to only the applications listed in the description and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A photopolymer, characterized in that, Comprising the following raw material components by weight parts: The functional monomer is a mixture of a multi-functional monomer and a mono-functional monomer.

2. The photopolymer according to claim 1, characterized in that, The multi-functional monomer is selected from at least one of ethoxylated bisphenol fluorene diacrylate, bisphenol A-dimethacrylate, pentaerythritol tetraacrylate, and ethoxylated trimethylolpropane triacrylate.

3. The photopolymer according to claim 1, wherein The mono-functional monomer in the functional monomer is a mixture of a mono-functional high refractive index monomer and a mono-functional flexible monomer.

4. The photopolymer according to claim 3, wherein The mono-functional high refractive index monomer is selected from at least one of N-vinylcarbazole, acryloylmorpholine, m-phenoxybenzyl acrylate, o-phenylphenoxyethyl acrylate, biphenylmethanol acrylate, 6-acryloxymethyldinaphthothiophene, 5-acryloxyethyldinaphthothiophene, and 6-vinyldinaphthothiophene.

5. The photopolymer according to claim 3, wherein The mono-functional flexible monomer is selected from at least one of methoxy (meth)acrylate and ethoxy (meth)acrylate monomers.

6. The photopolymer according to claim 3, wherein The mass ratio of the mono-functional high refractive index monomer: mono-functional flexible monomer: multi-functional monomer is 1:(0.2 - 0.8):(0.1 - 0.5).

7. The photopolymer according to claim 1, wherein The flexible acrylate resin is obtained by polymerizing the following raw materials by weight parts: 70 - 95 parts of a soft monomer, 5 - 25 parts of a cross-linking monomer, 0.3 - 1.2 parts of an initiator, and 50 - 120 parts of a second solvent; Wherein, the soft monomer is an acrylate monomer with a glass transition temperature lower than -50 °C, and the cross-linking monomer is an acrylic monomer containing a hydroxyl group, an amino group, or a carboxyl group.

8. The photopolymer according to claim 7, characterized in that, The soft monomer is one or more of methoxy (meth)acrylate, ethoxy (meth)acrylate monomer, isooctyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, butyl acrylate, butyl methacrylate, isooctyl acrylate, and alkyl acrylate; wherein, the methoxy (meth)acrylate or ethoxy (meth)acrylate monomer must be contained, and the proportion of the acrylate monomer containing an ether bond in the soft monomer is not less than 50%; The cross-linking monomer is one or more of hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxypropyl acrylate, acrylamide, acrylic acid, and methacrylic acid; The initiator is one or more of azobisisobutyronitrile, azodipentanenitrile, and dimethyl azodisobutyrate; The second solvent is one or more of ethyl acetate, toluene, and butanone.

9. The photopolymer according to claim 8, characterized in that, The methoxy (meth)acrylate or ethoxy (meth)acrylate monomer is selected from one or more of ethoxyethoxyethyl acrylate, 2-methoxyethyl acrylate, triethylene glycol monomethyl ether acrylate, methoxydiethylene glycol methyl methacrylate, methoxypolyethylene glycol 230 methyl methacrylate, methoxypolyethylene glycol 400 methyl methacrylate, and methoxypolyethylene glycol 1000 methyl methacrylate.

10. A flexible holographic optical film, characterized in that, Comprising a functional layer and two substrate layers located on both sides of the functional layer, and the functional layer is made by exposing the photopolymer as described in any one of claims 1 - 9.

11. A method for preparing a flexible holographic optical film as described in claim 10, characterized in that, Comprising the following steps: 1) In a darkroom or under a protective lamp inert to the photosensitive dye, at a temperature of 10 - 30 °C, mix the first solvent, flexible acrylate resin, curing agent, functional monomer, photoinitiator, and photosensitive dye uniformly to obtain a photopolymer; 2) Under the conditions of a darkroom or a protective lamp inert to the photosensitive dye, coat the above-mentioned photopolymer on a substrate, dry it, cover another substrate on the formed photopolymer layer, expose it, and finally irradiate it with an LED lamp, fluorescent lamp, or ultraviolet lamp until complete fixing and bleaching to obtain the flexible holographic optical film.

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