A holographic photopolymer and its preparation method and application

Abstract

This application relates to the technical field of photopolymers, and specifically discloses a holographic photopolymer, its preparation method and application. A holographic photopolymer disclosed in this application specifically comprises the following components in parts by weight: 70 - 75 parts of a polyurethane matrix, 12 - 16 parts of a writing monomer, 0.8 - 1.2 parts of a photosensitizer, 2.4 - 3.6 parts of a photoinitiator, and 9 - 11 parts of a crosslinking agent; the refractive index of the polyurethane matrix is 1.48 - 1.52, and the glass transition temperature ≤ 0 °C; the refractive index of the writing monomer is 1.52 - 1.60. This application also provides a specific preparation method and application of the above holographic photopolymer. By using the technical solution provided in this application, a holographic photopolymer with high diffraction efficiency, high refractive index modulation degree, small volume shrinkage rate, small haze, and high transparency can be obtained.

Description

Technical Field

[0001] The present application relates to the technical field of photopolymers, and specifically relates to a holographic photopolymer and its preparation method and application. Background Art

[0002] In the field of AR optical waveguides, there are two types of holographic gratings: surface relief gratings and volume holographic gratings. Bayer, the market leader in volume holographic gratings, has disclosed a photopolymer formulation comprising a chemically crosslinked matrix polymer, a writing monomer, and a photoinitiator system. This photopolymer formulation can be used to produce holographic media and thereby produce bright and easily visible holograms with a high refractive index difference and a low thickness.

[0003] In the research field of photoresists, some researchers have used a fluorinated acrylate system as a photosensitive material and a fluorinated polyurethane acrylate system as a substrate material to prepare a photopolymer holographic material. This material has achieved the possibility of mass production by adopting a second-order reaction method and has reached a refractive index modulation of about 0.02. However, this refractive index modulation cannot meet the requirements of the near-eye display optical waveguide solution, and the use of fluorides will pose a great potential hazard to the environment.

[0004] In addition, currently, the performance requirements for photopolymers are increasingly tending towards excellent comprehensive performance, such as being able to simultaneously ensure a high diffraction efficiency, a high refractive index modulation, a small volume shrinkage rate, a small haze, and a high transparency of the polymer. Therefore, there is an urgent need to provide a new holographic photopolymer material. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides a holographic photopolymer and its preparation method and application.

[0006] In the first aspect, the present application provides a holographic photopolymer, specifically comprising the following components in parts by weight:

[0007] 70 - 75 parts of a polyurethane matrix, 12 - 16 parts of a writing monomer, 0.8 - 1.2 parts of a photosensitizer, 2.4 - 3.6 parts of a photoinitiator, and 9 - 11 parts of a crosslinking agent;

[0008] The refractive index of the polyurethane matrix is 1.48 - 1.52, and the glass transition temperature ≤ 0°C;

[0009] The refractive index of the writing monomer is 1.52 - 1.60.

[0010] By adopting the above technical solution, the present application uses polyurethane, a writing monomer, a photosensitizer, a photoinitiator, and a crosslinking agent as raw material components and reasonably controls the amounts of each raw material component, and then prepares a holographic photopolymer, which can obtain a diffraction efficiency ≥ 90.9%, a refractive index modulation degree ≥ 0.031, a volume shrinkage rate ≤ 1.45%, a haze ≤ 1.82%, and a transparency ≥ 90.1%. That is, by using the technical solution provided by the present application, a holographic photopolymer with excellent comprehensive performance can be obtained.

[0011] Preferably, the polyurethane matrix is prepared by reacting a polyol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, an aliphatic polyether isocyanate, and dimethyltin bis(neodecanoate) in a weight ratio of 100:20 - 40:15 - 25:1 - 3.

[0012] Further, the weight-average molecular weight of the polyol is 800 - 40000.

[0013] Further, the aliphatic polyether isocyanate is selected from one or more of isocyanatoethyl methacrylate and 1,1-bis(acryloxymethyl)ethyl isocyanate.

[0014] Through experimental analysis, it can be known that the preparation method of the polyurethane matrix has a great influence on the performance of the holographic photopolymer. In the present application, by screening the raw material substances and the amounts of each raw material substance used in the preparation method of the polyurethane matrix, and then using the polyurethane matrix prepared by this method as a raw material to prepare a holographic photopolymer, the comprehensive performance of the holographic photopolymer is further improved.

[0015] Preferably, the writing monomer is selected from one or more of bisphenol A diglycidyl ether dimethacrylate, bisphenol A glycerol dimethacrylate, and dipentaerythritol hexaacrylate.

[0016] In the technical solution provided by the present application, the writing monomer bisphenol A ether acrylate has a high compatibility with the polyol-based polyurethane matrix, which is conducive to realizing a high-transparency film of the holographic photopolymer.

[0017] Through experimental analysis, it can be known that compared with using an equal amount of bisphenol A glycerol dimethacrylate or dipentaerythritol hexaacrylate as the writing monomer, by using bisphenol A diglycidyl ether dimethacrylate as the writing monomer in the present application, the refractive index modulation degree of the holographic photopolymer is further improved.

[0018] Preferably, the holographic photopolymer further includes 0.06 - 0.24 parts of an antioxidant inhibitor and 0.18 - 0.42 parts of a reactive diluent.

[0019] Through experimental analysis, it can be known that in this application, by controlling the dosage of the antioxidant inhibitor to be 0.06 - 0.24 parts and the dosage of the reactive diluent to be 0.18 - 0.42 parts, the comprehensive performance of the holographic photopolymer such as diffraction efficiency, refractive index modulation, haze, and transparency is further improved.

[0020] Preferably, the antioxidant inhibitor is selected from one or more of hindered phenol antioxidants, phosphite antioxidants, and thioester (ether) antioxidants.

[0021] Preferably, the reactive diluent is selected from one or more of N-ethylpyrrolidone, N-methylpyrrolidone, n-butyl acetate, and DMF.

[0022] Furthermore, the reactive diluent is composed of a mixture of N-ethylpyrrolidone and n-butyl acetate with a weight ratio of 9:3 - 7.

[0023] In some specific embodiments, in the reactive diluent, the weight ratio of N-ethylpyrrolidone to n-butyl acetate can be 9:3 - 4, 9:3 - 5, 9:3 - 6, 9:4 - 5, 9:4 - 6, 9:4 - 7, 9:5 - 6, 9:5 - 7, 9:6 - 7.

[0024] In a specific embodiment, in the reactive diluent, the weight ratio of N-ethylpyrrolidone to n-butyl acetate can also be 9:3, 9:4, 9:5, 9:6, 9:7.

[0025] Through experimental analysis, it can be known that compared with using N-ethylpyrrolidone alone as the reactive diluent, or using a mixture of N-methylpyrrolidone and n-butyl acetate with a weight ratio of 9:5 as the reactive diluent, or using a mixture of N-ethylpyrrolidone and n-butyl acetate with a weight ratio of 9:1 as the reactive diluent, by selecting N-ethylpyrrolidone and n-butyl acetate with the above weight ratio as the reactive diluent in this application, the comprehensive performance of the holographic photopolymer can be further improved.

[0026] Preferably, the crosslinking agent is selected from one or more of N-vinylpyrrolidone and triethanolamine.

[0027] Preferably, the photosensitizer is rose bengal and the photoinitiator is camphorquinone.

[0028] In a second aspect, this application also provides a preparation method of the above-mentioned holographic photopolymer, which specifically includes the following steps: adding the writing monomer, photosensitizer, photoinitiator, and crosslinking agent into the polyurethane matrix system, stirring overnight at 80 - 90 °C, coating on a TAC film and a glass substrate, and removing bubbles for 50 - 70 min to obtain the product.

[0029] In a third aspect, the present application also provides the use of the above holographic photopolymer in the preparation of optical elements or images or for image display or projection.

[0030] In summary, the technical solution of the present application has the following effects:

[0031] The present application uses polyurethane, a writing monomer, a photosensitizer, a photoinitiator, and a crosslinking agent as raw material components and reasonably controls the amounts of each raw material component, and then prepares a holographic photopolymer, and a diffraction efficiency of ≥90.9%, a refractive index modulation of ≥0.031, a volume shrinkage rate of ≤1.45%, a haze of ≤1.82%, and a transparency of ≥90.1% can be obtained. That is, a holographic photopolymer with excellent comprehensive performance can be obtained by using the technical solution provided by the present application.

[0032] Compared with most volume grating holographic films for AR / VR in the prior art, which can only achieve good reflection efficiency (50%) at a large thickness (hundreds of microns) and have a low Δn (<0.01), the holographic photopolymer film provided by the present application has a high refractive index modulation Δn (>0.03), and can produce a thinner film without sacrificing the wider viewing field of AR glass.

[0033] Compared with the use of expensive nitrogen purging in the prior art, the present application uses a hindered phenol antioxidant, a phosphite antioxidant, and a thioester (ether) antioxidant as antioxidant inhibitors, which greatly reduces the production cost.

[0034] The present application further improves the comprehensive performance of the holographic photopolymer by further optimizing the preparation method of the polyurethane matrix, the types of writing monomers, and the types of reaction diluents. Detailed Embodiments

[0035] The raw material substances used in the embodiments of the present application specifically include the following substances: 2-ethyl-2-hydroxymethyl-1,3-propanediol with a CAS number of 77-99-6, dimethyltin bis(neodecanoate) with a CAS number of 68928-76-7, bisphenol A diglycidyl ether dimethacrylate with a CAS number of 71281-65-7, bisphenol A glycerol dimethacrylate with a CAS number of 4687-94-9, dipentaerythritol hexaacrylate (DPHA) with a CAS number of 29570-58-9, and pentaerythritol diisodecyl diphosphite with a CAS number of 26544-27-4.

[0036] The present application will be further described in detail below in conjunction with examples, comparative examples, and performance detection tests. These examples should not be construed as limiting the scope claimed by the present application.

[0037] Examples

[0038] Examples 1-6

[0039] Examples 1-6 respectively provide a holographic photopolymer.

[0040] The differences between the above examples are as follows: the dosages of the raw material components in the holographic photopolymer are different, as shown in Table 1 specifically.

[0041] The preparation method of the holographic photopolymer in Examples 1-6 is specifically as follows:

[0042] The preparation method of the polyurethane matrix is: weigh 100 g of polyethylene glycol (weight average molecular weight of 800), 30 g of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 20 g of isocyanate (Covestro XP2890), and 2 g of dimethyltin bis(neodecanoate), and stir and react at room temperature for 90 min to obtain;

[0043] According to the dosages of the respective raw materials shown in Table 1, add the writing monomer bisphenol A diglycidyl ether diacrylate, photosensitizer rose bengal, photoinitiator camphorquinone, crosslinking agent N-vinylpyrrolidone, antioxidant inhibitor pentaerythritol diphosphite diisodecyl ester, and reactive diluent (composed of N-ethylpyrrolidone and n-butyl acetate mixed in a weight ratio of 9:5) to the corresponding weight of the polyurethane matrix system, and stir overnight at 85°C; coat on a TAC film and a glass substrate, remove bubbles for 1 h, and obtain a 6-micron-thick holographic photopolymer film.

[0044] Table 1 Dosages of the respective raw material components in Examples 1-6 and Comparative Examples 1-2

[0045]

[0046] Examples 7-8

[0047] Examples 7-8 respectively provide a holographic photopolymer.

[0048] The differences between the above examples and Example 3 are as follows: the types of the writing monomers are different, as shown specifically below.

[0049] In Example 7: the writing monomer is an equal amount of bisphenol A glycerol dimethacrylate.

[0050] In Example 8: the writing monomer is an equal amount of dipentaerythritol hexaacrylate.

[0051] The remaining raw material components, the dosages of the respective raw materials, and the preparation method of the holographic photopolymer in the above examples are the same as those in Example 3.

[0052] Examples 9-13

[0053] Examples 9-13 respectively provide a holographic photopolymer.

[0054] The differences between the above embodiments and Embodiment 3 are as follows: the types of reactive diluents are different, which are specifically shown as follows.

[0055] In Embodiment 9: the reactive diluent is N-ethylpyrrolidone.

[0056] In Embodiment 10: the reactive diluent is composed of N-methylpyrrolidone and n-butyl acetate mixed in a weight ratio of 9:5.

[0057] In Embodiment 11: the reactive diluent is composed of N-ethylpyrrolidone and n-butyl acetate mixed in a weight ratio of 9:1.

[0058] In Embodiment 12: the reactive diluent is composed of N-ethylpyrrolidone and n-butyl acetate mixed in a weight ratio of 9:3.

[0059] In Embodiment 13: the reactive diluent is composed of N-ethylpyrrolidone and n-butyl acetate mixed in a weight ratio of 9:7.

[0060] The remaining raw material components, the dosages of each raw material, and the preparation method of the holographic photopolymer in the above embodiments are the same as those in Embodiment 3.

[0061] Embodiment 14

[0062] Embodiment 14 provides a holographic photopolymer.

[0063] The differences between this embodiment and Embodiment 3 are as follows: the preparation method of the polyurethane matrix is different, which is specifically shown as follows.

[0064] The preparation method of the polyurethane matrix is as follows: weigh 100 g of polyethylene glycol (Mn is 2000 - 8000), 30 g of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 20 g of isocyanate (Wanhua HT-100), and 2 g of dimethyltin bis(neodecanoate), and stir and react at room temperature for 90 min to obtain.

[0065] The remaining raw material components, the dosages of each raw material, and the preparation method of the holographic photopolymer in this embodiment are the same as those in Embodiment 3.

[0066] Embodiment 15

[0067] Embodiment 15 provides a holographic photopolymer.

[0068] The differences between this embodiment and Embodiment 3 are as follows: the preparation method of the polyurethane matrix is different, which is specifically shown as follows.

[0069] The preparation method of the polyurethane matrix is as follows: Weigh 100 g of polyethylene glycol (weight average molecular weight of 800), 15 g of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 30 g of isocyanate (Covestro XP2890), and 4 g of dimethyltin bis(neodecanoate), and stir and react at room temperature for 90 min to obtain it.

[0070] The remaining raw material components, the dosage of each raw material, and the preparation method of the holographic photopolymer in this example are the same as those in Example 3.

[0071] Comparative Example

[0072] Comparative Examples 1-2

[0073] Comparative Examples 1-2 respectively provide a holographic photopolymer.

[0074] The difference between the above comparative examples and Example 3 lies in that: the dosages of the raw material components in the holographic photopolymer are different, as shown in Table 1 specifically.

[0075] The remaining raw material components, the dosage of each raw material, and the preparation method of the holographic photopolymer in the above comparative examples are the same as those in Example 3.

[0076] Performance Detection Test

[0077] (1) Diffraction efficiency: When exposing, use red light with a wavelength of 633 nm that is not sensitive to the material as the detection light to measure its diffraction efficiency.

[0078] (2) Refractive index modulation Δn: Use the Kogelnik coupled-wave theory to determine the refractive index modulation of the material through the measured diffraction efficiency.

[0079] (3) Volume shrinkage rate: The percentage of the volume reduction value of the monomer during the polymerization process in the initial volume value. The volume shrinkage rate can be obtained by measuring the density change of the material before and after the polymerization reaction: VS = (ρt - ρ0) / ρt.

[0080] (4) Haze: Haze is the percentage of the transmitted light intensity (scattered light intensity) that deviates from the incident light by more than 2.5° in the total transmitted light intensity. The greater the haze, the lower the film gloss and transparency, and it is measured using a haze meter.

[0081] (5) Transparency: Transmittance is the ratio of the light flux passing through the test sample for light transmission to the light flux incident on the test sample, expressed as a percentage, and it is measured using a haze meter.

[0082] Detection results: As shown in Table 2.

[0083] Table 2 Performance Detection Results of the Holographic Photopolymers in Examples 1-15 and Comparative Examples 1-2

[0084]

[0085]

[0086] Combined with Table 2, by comparing the test results of Examples 1-15 and Comparative Examples 1-2, the present application uses polyurethane, writing monomer, photosensitizer, photoinitiator, and crosslinking agent as raw material components and reasonably controls the dosages of each raw material component, and then prepares a holographic photopolymer, which can obtain a diffraction efficiency ≥ 90.9%, a refractive index modulation degree ≥ 0.031, a volume shrinkage rate ≤ 1.45%, a haze ≤ 1.82%, and a transparency ≥ 90.1%. The above test results show that a holographic photopolymer with excellent comprehensive performance can be obtained by using the technical solution provided by the present application.

[0087] In Example 1, no antioxidant inhibitor and reactive diluent were added, and the performance of the prepared holographic photopolymer was poor. By comparing the test results of Examples 2-6 and Comparative Examples 1-2, the dosages of each raw material component have a great influence on the performance of the holographic photopolymer. The present application reasonably controls the dosages of each raw material component, so that the comprehensive performance of the holographic photopolymer is significantly improved. By comparing the test results of Examples 3, 5-6, the present application further improves the comprehensive performance of the diffraction efficiency, refractive index modulation degree, haze, and transparency of the holographic photopolymer by controlling the dosage of the antioxidant inhibitor to be 0.06-0.24 parts and the dosage of the reactive diluent to be 0.18-0.42 parts.

[0088] By comparing the test results of Examples 3, 7-8, compared with Examples 7-8 using the same amount of bisphenol A glycerol dimethacrylate or dipentaerythritol hexaacrylate as the writing monomer, Example 3 uses bisphenol A diglycidyl ether dimethacrylate as the writing monomer, which further improves the refractive index modulation degree of the holographic photopolymer.

[0089] By comparing the test results of Examples 3, 9-13, compared with using N-ethylpyrrolidone alone as the reactive diluent, or using a mixture of N-methylpyrrolidone and n-butyl acetate with a weight ratio of 9:5 as the reactive diluent, or using a mixture of N-ethylpyrrolidone and n-butyl acetate with a weight ratio of 9:1 as the reactive diluent, the present application uses a mixture of N-ethylpyrrolidone and n-butyl acetate with a weight ratio of 9:3-7 as the reactive diluent, which further improves the comprehensive performance of the holographic photopolymer.

[0090] By comparing the detection results of Examples 3 and 14-15, it can be seen that the preparation method of the polyurethane matrix has a great influence on the performance of the holographic photopolymer. In this application, the raw material substances used in the preparation method of the polyurethane matrix and the dosage of each raw material substance are screened, and then the polyurethane matrix prepared by this method is used as the raw material to prepare the holographic photopolymer, further improving the comprehensive performance of the holographic photopolymer.

[0091] Although the present invention has been described in detail with general descriptions and specific embodiments above, on the basis of the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A holographic photopolymer, characterized in that: Specifically include the following components: 72g of polyurethane matrix, 14g of writing monomer, 1g of photosensitizer Bengal rose red, 2.8g of photoinitiator camphorquinone, 10g of crosslinking agent N-vinyl pyrrolidone, 0.12g of antioxidant inhibitor diisobutyl diphosphite pentaerythritol ester, and 0.28g of reactive diluent; The preparation method of the polyurethane matrix is ​​as follows: 100 g of polyethylene glycol with a weight average molecular weight of 800, 30 g of 2-ethyl-2-(hydroxymethyl)-1,3-propylene glycol, 20 g of Covestro XP2890 isocyanate, and 2 g of dimethyltin dineodecanoate are stirred and reacted at room temperature for 90 minutes to prepare the polyurethane matrix; The writing monomer is bisphenol A diglycidyl ether dimethacrylate; The reactive diluent is composed of a mixture of N-ethylpyrrolidone and n-butyl acetate in a weight ratio of 9:

5.

2. A holographic photopolymer, characterized in that: Specifically include the following components: 70g of polyurethane matrix, 12g of writing monomer, 0.8g of photosensitizer Bengal rose red, 2.4g of photoinitiator camphorquinone, 9g of crosslinking agent N-vinyl pyrrolidone, 0.12g of antioxidant inhibitor diisobutyl diphosphite pentaerythritol ester, and 0.28g of reactive diluent; The preparation method of the polyurethane matrix is ​​as follows: 100 g of polyethylene glycol with a weight average molecular weight of 800, 30 g of 2-ethyl-2-(hydroxymethyl)-1,3-propylene glycol, 20 g of Covestro XP2890 isocyanate, and 2 g of dimethyltin dineodecanoate are stirred and reacted at room temperature for 90 minutes to prepare the polyurethane matrix; The writing monomer is bisphenol A diglycidyl ether dimethacrylate; The reactive diluent is composed of a mixture of N-ethylpyrrolidone and n-butyl acetate in a weight ratio of 9:

5.

3. A holographic photopolymer, characterized in that: Specifically include the following components: 75g of polyurethane matrix, 16g of writing monomer, 1.2g of photosensitizer Bengal rose red, 3.6g of photoinitiator camphorquinone, 11g of crosslinking agent N-vinyl pyrrolidone, 0.12g of antioxidant inhibitor pentaerythritol diphosphite diisobutyl ester, and 0.28g of reactive diluent; The preparation method of the polyurethane matrix is ​​as follows: 100 g of polyethylene glycol with a weight average molecular weight of 800, 30 g of 2-ethyl-2-(hydroxymethyl)-1,3-propylene glycol, 20 g of Covestro XP2890 isocyanate, and 2 g of dimethyltin dineodecanoate are stirred and reacted at room temperature for 90 minutes to prepare the polyurethane matrix; The writing monomer is bisphenol A diglycidyl ether dimethacrylate; The reactive diluent is composed of a mixture of N-ethylpyrrolidone and n-butyl acetate in a weight ratio of 9:

5.

4. A holographic photopolymer, characterized in that Specifically include the following components: 70g of polyurethane matrix, 12g of writing monomer, 0.8g of photosensitizer Bengal rose red, 2.4g of photoinitiator camphorquinone, 9g of crosslinking agent N-vinyl pyrrolidone, 0.12g of antioxidant inhibitor diisobutyl diphosphite pentaerythritol ester, and 0.28g of reactive diluent; The preparation method of the polyurethane matrix is ​​as follows: 100 g of polyethylene glycol with a weight average molecular weight of 800, 30 g of 2-ethyl-2-(hydroxymethyl)-1,3-propylene glycol, 20 g of Covestro XP2890 isocyanate, and 2 g of dimethyltin dineodecanoate are stirred and reacted at room temperature for 90 minutes to prepare the polyurethane matrix; The writing monomer is bisphenol A diglycidyl ether dimethacrylate; The reactive diluent is composed of a mixture of N-ethylpyrrolidone and n-butyl acetate in a weight ratio of 9:

3.

5. A holographic photopolymer, characterized in that: Specifically include the following components: 70g of polyurethane matrix, 12g of writing monomer, 0.8g of photosensitizer Bengal rose red, 2.4g of photoinitiator camphorquinone, 9g of crosslinking agent N-vinyl pyrrolidone, 0.12g of antioxidant inhibitor diisobutyl diphosphite pentaerythritol ester, and 0.28g of reactive diluent; The preparation method of the polyurethane matrix is ​​as follows: 100 g of polyethylene glycol with a weight average molecular weight of 800, 30 g of 2-ethyl-2-(hydroxymethyl)-1,3-propylene glycol, 20 g of Covestro XP2890 isocyanate, and 2 g of dimethyltin dineodecanoate are stirred and reacted at room temperature for 90 minutes to prepare the polyurethane matrix; The writing monomer is bisphenol A diglycidyl ether dimethacrylate; The reactive diluent is composed of a mixture of N-ethylpyrrolidone and n-butyl acetate in a weight ratio of 9:

7.

6. The method for preparing a holographic photopolymer according to any one of claims 1 to 5, characterized in that: The specific steps include: Add writing monomer, photosensitizer, photoinitiator, crosslinking agent, antioxidant inhibitor and reactive diluent into the polyurethane matrix system, stir overnight at 80-90° C., apply on TAC film and glass substrate, and remove bubbles for 50-70 minutes.

7. Use of the holographic photopolymer according to any one of claims 1 to 5 in the preparation of optical elements or images or for image display or projection.

Images