KR20050027567A - Hologram recording photopolymer manufacturing method using a medium prepared by the sol-gel method as a binder - Google Patents

Abstract

Provided is a photopolymer for hologram recording using medium produced by sol-gel method as a binder which uses silicone oxide as the binder to enable to produce an excellent thin film in manufacturing holography elements. In production process of the photopolymer for hologram recording using medium produced by sol-gel method as the binder, the photopolymer includes the sol-gel binder made by using silicone alkoxy silane represented by formula 1, 2 and 3, in which R is a low-valent alkyl radical such as CH3, CH2CH3, CH2CH(CH3)CH3, CH2CH2CH2CH3, CH(CH3)2 or so on; and X is all kinds of aliphatic molecular unit or aromatic molecular unit.

Description

Hologram recording photopolymer manufacturing method using a medium prepared by the sol-gel method as a binder {omitted}

The purpose of this study is to improve the diffraction grating formation speed and stability of diffraction efficiency by the same interference light intensity as compared with the conventional photopolymer. This increases the refractive index in the bright region by photopolymerization or photocrosslinking of the monomer diffused from the dark region to the bright region by optical interference. In this case, the polymer binder used as the support layer and the newly formed polymer are physically bonded. The mixture is a conventional form. Unlike conventional thermoplastic polymers, monomer diffusion is improved, and the density of newly formed polymers that control refractive index modulation, that is, conversion to new polymers, is improved to further improve high diffraction efficiency and lattice formation rate and improve their stability. There is a purpose.

In the case of the photopolymer for the hologram, the optical interference pattern can be stored as a hologram by the photopolymerization of the low molecular monomers, so that the medium, the light diffuser, the optical wavelength divider, the reflection type and the transmissive color filter of the optical memory system can be used. Many uses have been proposed. The photopolymer compound for holograms, which is widely used, is composed of a photosensitizer, a monomer, an initiator, and a polymer binder. The initiator is activated by light absorption of a specific wavelength of the photosensitizer by irradiation of two interference beams. Polymerization of the monomers mixed in the binder begins to occur. At this time, an active photopolymerization reaction proceeds in a region where constructive interference occurs due to an interference phenomenon between two incident beams, so that the monomer is transferred to a polymer, and in the region where destructive interference occurs, the monomer is not initiated by light absorption and thus an unreacted monomer exists. Done. In order to achieve a concentration equilibrium by reducing the concentration gradient of the monomer, the monomer is diffused from the destructive interference region to the constructive interference region. That is, concentration gradients of the monomer and the polymer are generated according to the interference patterns of the two incident beams, and the polymers of the two regions are diffused and polymerized to change the refractive index between the two regions.

Although the research and application of DuPont's photopolymer, which has been used in holographic device materials, is well known, the development of materials is limited, and the light stability during the post-curing process by lattice formation rate and ultraviolet irradiation is known. There was a drawback in that problems were found. Therefore, there is an urgent need to develop a domestic photopolymer that maintains high diffraction efficiency and stable hologram that can compete with it.

On the other hand, as their application ranges, with the recent rapid development of liquid crystal display technology, the need for a flat panel display with improved large area, high brightness, high efficiency, low power consumption, light uniformity, color reproducibility, viewing angle, etc. As this important part, the importance is greatly raised. Especially for the production of holographic memory media from next generation information storage media, photopolymers have emerged as a very important medium with 3-D displays. Therefore, the development of photopolymer having high lattice speed, high diffraction efficiency and excellent stability can be important not only for academic value but also for next generation industrial application.

Therefore, the present invention is to develop a photopolymer that can implement a hologram by the interference pattern of the two beams and can store information, and improve the photopolymerization of the high-speed lattice formation, high diffraction efficiency and stored hologram. In the present study, the inventors used the sol-gel method for the photopolymer compound and used the silicon oxide containing the organic molecular groups to support the support layer together with the photopolymerization of the monomer in the reinforcing interference region of the two beams. By promoting the transition phenomenon of the monomer, improving the conversion rate to the polymer, and inducing a photopolymerization reaction between the newly formed polymer and the existing silicon oxide binder, it was possible to implement holograms with high diffraction efficiency and environmental stability. .

Photopolymer showing high lattice formation rate and high diffraction efficiency using a silicon oxide medium which can be prepared by hydrolysis condensation of alkoxy silane by the sol-gel method according to the present invention (Formula 1, Formula 2, Formula 3) as a binder To provide. Hereinafter, the binder developed and used in the present study will be referred to as a sol-gel binder.

In the above formula, in the R position, there are small, low-cost alkyl groups such as CH ₃ , CH ₂ CH ₃ , CH ₂ CH (CH ₃ ) CH ₃ , CH ₂ CH ₂ CH ₂ CH ₃ , CH (CH ₃ ) _2, etc. At the X position any aliphatic molecular group or aromatic molecular group can be located.

Hereinafter, the present invention will be described in more detail.

Monomers mixed in the sol-gel binder for the preparation of photopolymers are vinyl, acrylate, or methacrylate-based monomers containing double bonds that can be initiated by radically active species, such as bisphenol A ethoxy diacrylate or bisphenol A propoxyl. Late glycerol diacrylate or pentaerythritol triacrylate was used, and the tetrabromo pulluolesine compound was used as a dye for visible light photosensitization. Triethanolamine was used as the electron transfer compound. The photopolymer solution prepared by mixing the compounds was prepared as a film having a constant thickness by using a spin coating or casting method or a doctor blade, and used in a diffraction grating formation experiment.

By selecting one of 488 nm, 514 nm, or 532 nm wavelengths in the previously prepared photopolymer film, two lights were coupled at a constant angle to form an interference pattern in the medium. That is, reinforcement interference and destructive interference are repeated on the surface and internal structure in a constant pattern according to the interference of light, and at this time, radicals in the amine initiator are caused by the sensitization action of the photosensitizer with the dye structure in the selective region where reinforcement interference occurs Is generated. The polymerization reaction of monomers mixed by the generated radicals is initiated, and the polymerization reaction is known to proceed in the region where constructive interference of two beams occurs, and the inventors also polymerize the structure by infrared spectroscopy. Change was confirmed. As the polymerization reaction of the monomer proceeds in the selected region, the concentration gradient of the monomer occurs in the destructive interference region and the constructive interference region, and the monomer concentration is reduced from the destructive interference region having a relatively high concentration of the monomer to the constructive interference region having a low concentration. Diffusion proceeds. Therefore, there is a difference in concentration in the constructive interference region and the destructive interference region where the polymerization reaction proceeds, and the refractive index grating is generated by the increase of the newly formed polymer density. From this principle, it is possible to form a periodic refractive index distribution and to control the change of diffraction efficiency from the change of angle and intensity of incident light and light irradiation time.

In this study, we focused on the development of new polymer binder with the highest concentration in formula for preparing photopolymer, and the polymerization of diffusion monomer was designed to show high conversion in sol-gel binder. The sol-gel medium, together with the free volume inside, has a hydroxyl group on the uncondensed silicon atom, which facilitates chain transfer during polymerization of the monomer, thereby inducing high conversion from the monomer even with a low molecular weight polymer. have. As a result, the rate of grating formation for diffraction was greatly improved, and high diffraction efficiency was obtained.

In general, photopolymers used in optical memory media and light diffusion plates require post-curing process by ultraviolet light irradiation to exhaust residual monomer after hologram recording, and photopolymerization of unreacted monomers in the reinforcing interference region. In addition, the non-diffusion monomer present in the destructive interference region also reacts, and in general, the difference in the refractive index of the constructive interference and the destructive interference portion is reduced, the phenomenon that the value of the diffraction efficiency is slightly reduced. The present inventors can make the photopolymer compound lattice formation at a very high speed by using the sol-gel binder prepared by the above formulas (1), (2) or (3). Very little characteristic change was observed.

By using such a sol-gel binder in the photopolymer, there is an advantage of improving linear optical characteristics, improving lattice formation speed, and improving hologram stability and optical diffraction efficiency. The effect of using the sol-gel medium described above as a binder will be apparent from the examples described below.

Example 1

Preparation of Photopolymer Using Silane of Formula 2 Series

Synthesis of trialkoxy silane compound of formula (II) (Formula 4) was synthesized and dissolved 1.5 g of the synthesized silane in 5 ml of tetrahydrofuran, hydrochloric acid (35wt%) and 0.3 g of water were mixed and hydrolyzed for 24 hours. , Partially condensed, and then mixed bisphenol A ethoxylate diacrylate into the above solution in four different concentrations in a viscous solution, followed by 0.05 g (3.4 × 10 ^-5 mol) of triethanolamine, tetrabromoflu 0.002 g (2.9 × 10 ⁻⁶ mol) of oresin was mixed together to prepare a solution, and dissolved oxygen was removed through nitrogen bubbling and stored in a dark room at room temperature for about 48 hours in a nitrogen atmosphere.

The prepared solution was prepared by thin coating or thick film by spin coating or casting, and vacuum dried in a dark room for use as a sample for hologram recording.

By changing the composition ratio of the binder and the monomer used in Example 1, four different photopolymer samples were prepared and their diffraction characteristics could be observed. Table 1 shows the maximum diffraction efficiency of the sol-gel photopolymer samples having different composition ratios of the binder and the monomer and the rate constant reaching their saturation. In Table 1, the rate constant refers to an increase rate of diffraction efficiency with irradiation time by the diffraction grating generated. As expected, in the above monomer composition distribution, as the monomer concentration increases, the diffraction efficiency increases and the lattice formation rate also increases.

Comparative Example 1

Preparation of Photopolymer Using Cellulose Acetate Butyrate Polymer as Binder

Cellulose acetate butyrate [acetate: 14%, butyrate: 37%, hydroxyl: 49%] Dissolve 1.0 g of the same polymer in 5 ml of tetrahydrofuran and mix with 1.2 g (0.0023 mol) of bisphenol A ethoxylate diacrylate. Next, 0.04 g (2.7 × 10 ⁻⁴ mol) of triethanolamine and 0.0004 g (5.8 × 10 ⁻⁷ mol) of tetrabromo fluorescein were all mixed together to prepare a mixed solution, the same method as shown in Example 1 Thin films or thick films were prepared and dried in a dark room for use as samples for hologram recording.

Comparing the two photopolymers prepared using the conventional thermoplastic polymer binder and the binder prepared by the sol-gel method shows clear differences in terms of diffraction efficiency and their kinetic behavior.

2 shows the phenomenon of change in diffraction efficiency with visible light irradiation time in the four samples mentioned in Table 1. The highest saturation diffraction efficiency was obtained at the highest monomer concentration (binder: monomer = 61.1: 36.7), and a sharp increase was observed initially compared to other photopolymers. FIG. 3 shows the change behavior of the diffraction efficiency of the photopolymer described in the comparative example using the conventional thermoplastic polymer binder and the dynamic behavior of the diffraction efficiency of the sample of (D) in Example 1 under the same light intensity under the same irradiation light source. Compared to In the figure, (A) shows the increase of the diffraction efficiency when using the sol-gel binder, (B) shows the increase of the diffraction efficiency of the photopolymer of Comparative Example 1. The most obvious difference between the two photopolymers is that the rate of grating formation was very fast with the sol-gel binder. This facilitates the diffusion of the monomers due to the inherent low glass transition temperature of the sol-gel medium and the relatively large free volume, and the migration of hydrogen in the hydroxy group in which the diffused monomers are bonded to the silicon atoms during polymerization and the condensation reaction has not yet occurred. This phenomenon is indicated by the chain transfer chain reaction caused by the high molecular weight, but high conversion to the polymer.

It is uniquely used in the low temperature process of hydrolysis and condensation reaction, not polymerization, in the conventional form in which the sol-gel binder used as the support layer and the newly formed polymer are mixed by physical bonding during the refractive index modulation process by optical interference. By forming a silicon oxide medium and using a conventional thermoplastic polymer binder it can be seen that contributed to achieve a very faster lattice formation rate and high diffraction efficiency.

In conclusion, the key point of the present invention is that by using a silicon oxide medium prepared by the sol-gel method as a binder, the optical diffraction efficiency and the optical diffraction efficiency can be improved as well as the lattice formation rate for the hologram of the photopolymer. .

As apparent from the above description, a photopolymer compound using a silicon oxide medium prepared as a binder by the sol-gel method of the present invention as a binder can be produced as a material for manufacturing a holographic device, and can be manufactured with excellent thin films. It is a new photopolymer compound that shows the effect of easily increasing the diffraction efficiency and the stability of the resulting hologram by light irradiation.

1 shows an example of the trialkoxy silane compound used for preparing the sol-gel photopolymer medium according to the present invention and shows the internal structure of the medium prepared therefrom.

Figure 2 shows the change in the light irradiation time of the respective diffraction efficiency according to the change in the intensity of the two beams forming the interference pattern when manufacturing the hologram of the photopolymer prepared in Example 1.

Figure 3 shows the comparison of the grating formation rate and the diffraction efficiency due to the lattice formation by the irradiation of two light sources in the production of the hologram of the sample (D) and the photopolymer prepared in Comparative Example 1 in Example 1.

Claims (4)

Application as a hologram implementing material using a photopolymer containing a sol-gel binder which can be prepared using a silicon alkoxy silane having the structural forms of the formulas (1), (2) and (3). In the above formula, at the R position, there is a small-size, low-cost alkyl group such as CH ₃ , CH ₂ CH ₃ , CH ₂ CH (CH ₃ ) CH ₃ , CH ₂ CH ₂ CH ₂ CH ₃ , CH (CH ₃ ) _2, etc. At the X position any aliphatic molecular group or aromatic molecular group can be located. An application for preparing a photopolymer binder of a silicon oxide viscous solution, which is dissolved in an organic solvent using the silane used in Claim 1, hydrolyzed using any acid or base, and partially condensed. The compound according to claim 1, wherein any compound having the following structure at the molecular group X position, such as cinnamoyl group, chalcone group, anthracene group, coumarin, etc., may cause cyclic addition reaction by ultraviolet irradiation, Newly formed polymer chains or compounds that can impose geometric constraints on the polymer chain movement of the support. Where A is an electron donor or a substituent. or The compound according to claim 1, wherein a compound having a structure having the following structure in the silane of Compound 2 series and a compound capable of participating in a functional group of a binder can be produced in a polymerization reaction with a monomer diffused using the compound. A photofunctional acrylate and methacrylate side chain polymer compound characterized by a polymerization reaction between a side chain of a polymer binder and a diffusion monomer. R here means H or an aliphatic alkyl group substituent. n is 0-10. or