PHOTOPOLYMER COMPOSITION FOR HOLOGRAM FORMATION, HOLOGRAM RECORDING MEDIUM AND OPTICAL ELEMENTS

Abstract

The present invention relates to a photopolymer composition for hologram formation, comprising: a polymer matrix comprising a siloxane-based polymer and a (meth)acrylate polymer containing one or more reactive functional groups in the side chains, a holographic recording method, and an optical element.

Claims

1. A photopolymer composition for hologram formation, comprising: a polymer matrix comprising a siloxane-based polymer and a (meth)acrylate polymer containing one or more reactive functional groups in the side chains; a photoreactive monomer; and a photoinitiator.

2. The photopolymer composition for hologram formation according to claim 1, wherein: the polymer matrix comprises a cross-linked copolymer between the siloxane-based polymer and the (meth)acrylate polymer containing one or more reactive functional groups in the side chains.

3. The photopolymer composition for hologram formation according to claim 1, wherein: the siloxane-based polymer and the (meth)acrylate polymer containing one or more reactive functional groups in the side chains are cross-linked in the presence of a platinum catalyst.

4. The photopolymer composition for hologram formation according to claim 1, wherein: the reactive functional group has a structure containing one or more functional groups selected from the group consisting of a vinyl group, a hydroxy group, and an epoxy group.

5. The photopolymer composition for hologram formation according to claim 1, wherein: the reactive functional group comprises a functional group represented by the following Chemical Formula 2: ##STR00015## wherein, in the Chemical Formula 2, L.sub.1 is one of an oxyalkylene group having 1 to 10 carbon atoms, an oxyalkenylene group having 2 to 20 carbon atoms, and an oxyalkynylene group having 2 to 20 carbon atoms.

6. The photopolymer composition for hologram formation according to claim 1, wherein: the reactive functional group comprises a functional group represented by the following Chemical Formula 2-1: ##STR00016## wherein, in the Chemical Formula 2-1, L.sub.2 to L.sub.3 are each independently one of an alkylene group having 1 to 10 carbon atoms, an alkenylene group having 2 to 10 carbon atoms, and an alkynylene group having 2 to 10 carbon atoms, L.sub.4 is one of a direct bond, an alkylene group having 1 to 10 carbon atoms, an alkenylene group having 2 to 10 carbon atoms, and an alkynylene group having 2 to 10 carbon atoms, m is an integer from 1 to 10, and n is an integer from 0 to 10.

7. The photopolymer composition for hologram formation according to claim 1, wherein: the (meth)acrylate polymer containing one or more reactive functional groups in the side chains comprises a repeating unit represented by the following Chemical Formula 3 or a repeating unit represented by the following Chemical Formula 4: ##STR00017## wherein, in the Chemical Formula 3, R.sub.3 is hydrogen or an alkyl group having 1 to 10 carbon atoms, and R.sub.4 is a reactive functional group containing one or more vinyl groups, ##STR00018## wherein, in the Chemical Formula 4, R.sub.5 is hydrogen or an alkyl group having 1 to 10 carbon atoms, and R.sub.6 is a reactive functional group containing one or more vinyl groups.

8. The photopolymer composition for hologram formation according to claim 1, wherein: the siloxane-based polymer has a number average molecular weight of 200 g/mol or more and 800 g/mol or less.

9. The photopolymer composition for hologram formation according to claim 1, wherein: the (meth)acrylate polymer containing one or more reactive functional groups in the side chains has a weight average molecular weight of 200,000 g/mol or more and 900,000 g/mol or less.

10. The photopolymer composition for hologram formation according to claim 1, wherein: the (meth)acrylate polymer containing one or more reactive functional groups in the side chains has a reactive functional group equivalent of 500 g/equivalent or more and 3000 g/equivalent or less.

11. The photopolymer composition for hologram formation according to claim 1, further comprising a plasticizer containing at least one compound selected from the group consisting of a phosphorus-based compound and a fluorine-based compound.

12. The photopolymer composition for hologram formation according to claim 11, wherein: the fluorine-based compound comprises a low refractive index fluorine compound containing at least one functional group selected from the group consisting of an ether group, an ester group, and an amide group, and two or more difluoromethylene groups; and has a refractive index of less than 1.45.

13. The photopolymer composition for hologram formation according to claim 1, wherein: the photoreactive monomer has a refractive index of at least 1.50.

14. A hologram recording medium produced from the photopolymer composition for hologram formation according to claim 1.

15. An optical element comprising the hologram recording medium according to claim 14.

16. The photopolymer composition for hologram formation according to claim 2, wherein: the siloxane-based polymer and the (meth)acrylate polymer containing one or more reactive functional groups in the side chains are cross-linked in the presence of a platinum catalyst.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0145] FIG. 1 schematically shows the setup of a recording device for hologram recording. Specifically, FIG. 1 schematically shows the process in which a laser having a specific wavelength (e.g., 660 nm) is irradiated from a light source 10, and the irradiated laser is irradiated to a glass 80 and a PP (photopolymer film) 90 located on one surface of the glass 80, while passing through paths associated with mirrors 20 and 21, a half wave plate (HWP) 30, a spatial filter 40, a collimation lens 50, an iris 60, a Polarized Beam Splitter (PBS) 70, a mirror 22, a half wave plate (HWP) 31 and a mirror 23.

[0146] Hereinafter, the present invention will be described in more detail by way of the following examples. However, these examples are given for illustrative purposes only and are not intended to limit the scope of the present invention thereto.

PREPARATION EXAMPLE

Preparation Example 1: Method for Preparing (Meth)Acrylate Polymer

[0147] 212 g of butyl acrylate, 198 g of ethyl acrylate, and 40 g of methyl 2-allyloxymethyl acrylate (Nippon Shokubai Co., Ltd.) were placed in a 2L jacketed reactor, and the mixture was diluted with 1040 g of ethyl acetate. The reaction temperature was set to about 60~70° C., and stirring was performed for about 30 minutes to 1 hour. 0.32 g of n-dodecyl mercaptan was further added, and stirring was further performed for about 30 minutes. After that, 0.36 g of AIBN as a polymerization initiator was added, and polymerization was performed at the reaction temperature for 6 hours or more and maintained until the residual acrylate content was less than 1%. Thereby, a (meth)acrylate polymer containing vinyl groups in the side chains (weight average molecular weight of about 500,000 g/mol, vinyl group equivalent of 1735 g/equivalent) was prepared.

Preparation Example 2: Method for Preparing (Meth)Acrylate Polymer

[0148] 220 g of butyl acrylate, 185 g of ethyl acrylate, and 45 g of 2-(2-vinyloxy ethoxy)ethyl acrylate (Nippon Shokubai Co., Ltd.) were placed in a 2L jacketed reactor, and the mixture was diluted with 1000 g of ethyl acetate. The reaction temperature was set to about 60~70° C., and stirring was performed for about 30 minutes to 1 hour. 0.52 g of n-dodecyl mercaptan was further added, and stirring was performed for about 30 minutes more. After that, 0.30 g of AIBN as a polymerization initiator was added, and polymerization was performed at the reaction temperature for 6 hours or more and maintained until the residual acrylate content was less than 1%. Thereby, a (meth)acrylate polymer containing vinyl groups in the side chains (weight average molecular weight of about 300,000 g/mol, vinyl group equivalent of 1862 g/equivalent) was prepared.

Preparation Example 3: Method for Preparing a Non-Reactive Low Refractive Index Fluorine Compound

[0149] 20.51 g of 2,2′-((oxybis(1,1,2,2-tetrafluoroethan-2,1-diyl))bis(oxy))bis(2,2-difluoroethan-1-ol) was placed in a 1000 ml flask, and then dissolved in 500 g of tetrahydrofuran, and 4.40 g of sodium hydride (60 % dispersion in mineral oil) was carefully added several times while stirring at 0° C. After stirring at 0° C. for 20 minutes, 12.50 ml of 2-methoxyethoxymethyl chloride was slowly dropped. When it was confirmed by 1H NMR that all of the reactants were consumed, all of the reaction solvent was removed under reduced pressure. After extraction with 300 g of dichloromethane three times, the organic layers were collected, filtered with magnesium sulfate, and then reduced under reduced pressure to completely remove dichloromethane. Thereby, 29 g of a liquid product having a purity of 95% or more was obtained in a yield of 98%. The weight average molecular weight of the prepared non-reactive low refractive index fluorine compound was 586 g/mol, and the refractive index measured with an Abbe refractometer was 1.361.

Comparative Preparation Example 1: Method for Preparing (Meth) Acrylate Polymer

[0150] 99 g of butyl acrylate and 351 g of ethyl acrylate were placed in a 2L jacketed reactor, and diluted with 1000 g of ethyl acetate. The reaction temperature was set to about 60-70° C., and stirring was performed for about 30 minutes to 1 hour. 0.32 g of n-dodecyl mercaptan was further added, and stirring was performed for about 30 minutes. After that, 0.18 g of AIBN as a polymerization initiator was added, and polymerization was performed at the reaction temperature for 6 hours, and was maintained until the residual acrylate content was less than 1%. Thereby, a (meth)acrylate polymer (weight average molecular weight of about 500,000 g/mol, vinyl equivalent of 0 g/equivalent) was prepared.

EXAMPLES AND COMPARATIVE EXAMPLES

Example 1

[0151] First, 0.019 g of PMHS (Poly(methylhydrosiloxane), trimethylsilyl terminated, Sigma-Aldrich) having a number average molecular weight of about 390 g/mol and 0.32 g of the (meth)acrylate polymer prepared in Preparation Example 1 were mixed. 0.2 g of the fluorine compound of Preparation Example 3, 0.002 g of a photoreactive dye HNu-640 (Spectra), and 0.003 g of a silicone-based additive (Tego Rad 2500), and methyl ethyl ketone (MEK) as a solvent were added thereto, and stirred with a paste mixer in a state cutting off the light for about 10 minutes.

[0152] After that, a Karstedt (Pt-based) catalyst was added for matrix cross-linking, and liquid-phase cross-linking was performed at room temperature for 30 minutes or more.

[0153] 0.34 g of HR 6042 (Miwon Specialty Chemical Co., Ltd., bisphenol fluorene epoxy acrylate, refractive index of 1.60) which is a highly refraction photoreactive monomer to the matrix, and 0.002 g of photoinitiator HR 6042 (Spectra), which is a photoinitiator, were added to a coating solution, and the mixture was further mixed for 5 minutes or more.

[0154] The coating solution was coated onto a TAC substrate having a thickness of 80 .Math.m to a predetermined thickness using a Meyer bar, and dried at 40° C. to 60° C. within 10 minutes. After drying, the coating thickness of the photopolymer was about 15 .Math.m, and the refractive index (n) of the photopolymer was about 1.5.

[0155] Then, the sample was allowed to stand for 24 hours or more in a dark room under constant temperature and humidity conditions of about 25° C. and 50 RH%.

Example 2

[0156] A photopolymer composition and a photopolymer film were produced in the same manner as in Example 1, except that 0.32 g of the (meth)acrylate polymer prepared in Preparation Example 2 was used instead of the (meth)acrylate polymer prepared in Preparation Example 1. The refractive index (n) of the prepared photopolymer was about 1.5.

Comparative Example 1

[0157] A photopolymer composition and a photopolymer film were produced in the same manner as in Example 1, except that a non-crosslinked matrix was formed using only a siloxane polymer (PMHS (poly(methylhydrosiloxane), trimethylsilyl terminated, Sigma-Aldrich) (not using a (meth) acrylate polymer) at the time of forming the matrix. A photopolymer composition and a photopolymer film were produced in the same manner as in Example 1.

Comparative Example 2

[0158] A photopolymer composition and a photopolymer film were produced in the same manner as in Example 1, except that 0.32 g of the (meth)acrylate polymer prepared in Comparative Preparation Example 1 was used instead of the (meth)acrylate polymer prepared in Preparation Example 1. The refractive index (n) of the photopolymer was about 1.5.

EXPERIMENTAL EXAMPLE

[0159] The photopolymer coating surface prepared in each of Examples and Comparative Examples was laminated so as to contact the 0.70 mm thick slide glass, and at the time of recording, the laser was fixed so as to pass through the glass surface first. 660 nm and 532 nm lasers were used for recording, and the ratio of the reference beam and the object beam was 1, and the recording equipment setup was the same as in FIG. 1, and recording was performed in a reflective slanted manner (reference light = 30 °, object light = 40 °).

[0160] The film on which the reflective diffraction grating was recorded using a laser was placed in a UV irradiator (Dymax model 2000 flood) in a state attached to the glass, and irradiated with UV with UVA intensity of 105 mW/S for about 1 minute to remove the color of the dye. A photobleaching process was performed so that the reaction of the monomers could be terminated.

1. Diffraction Efficiency (η)

[0161] As described in relation to Examples and Comparative Examples, the photopolymer coated surface prepared in each of Examples and Comparative Examples was laminated on slide glass, and fixed so that the laser first pass through the glass surface at the time of recording. Lasers of 660 nm and 532 nm were used for recording, and the ratio between reference beam and object beam was 1. The setup of the recording device was as the same as shown in FIG. 1, and recording was performed in a reflective slanted manner (reference light = 30 °, object light = 40 °).

[0162] A holographic recording was performed via the interference of two interference lights (reference light and object light), and the transmission-type recording was performed so that the two beams (reference light and object light) were incident on opposite surfaces of the sample. The diffraction efficiencies were changed according to the incident angle of the two beams, and become non-slanted when the incident angles of the two beams are the same. In the non-slanted recording, the diffraction grating was generated vertically to the film because the incident angles of the two beams were the same on the normal basis. Recording was performed using a laser with a wavelength such as 532 nm and 660 nm in a reflective slanted manner (reference light = 30 °, object light = 40 °), and the diffraction efficiency (η) was calculated using Equation 1 below.

[00004]$\eta ={\text{P}}_{\text{D}}/\left({\text{P}}_{\text{D}}{\text{+P}}_{\text{T}}\right)$

[0163] In Equation 1, η is the diffraction efficiency, P.sub.D is the output amount of the diffracted beam of the sample after recording (mW/cm.sup.2), P.sub.T is the output amount (mW/cm.sup.2) of the transmitted beam of the sample after recording. The diffraction efficiency value calculated by Equation 1 was calculated as a percentage (%).

2. Laser Loss (I.SUB.loss.)

[0164] The laser loss (I.sub.loss) was calculated from Equation 2 below.

[00005]${\text{I}}_{\text{loss}}=1-\left\{\left({\text{P}}_{\text{D}}{\text{+P}}_{\text{T}}\right)/{\text{I}}_{\text{O}}\right\}$

[0165] In Equation 2, P.sub.D is the output amount of the diffracted beam of the sample after recording (mW/cm.sup.2), P.sub.T is the output amount of the transmitted beam of the recorded sample (mW/cm.sup.2), and I.sub.0 is the intensity of the recording light.

3. Peak Shift

[0166] First, a specific wavelength (or wavelength band) A.sub.0 having a maximum reflectance (i.e., a lowest transmission rate) seen by the sample recording the diffraction grating was analyzed in the same manner as in Examples and Comparative Examples (analyzed at room temperature and non-high humidity conditions). UV-Vis spectroscopy was used for the analysis, and the analysis wavelength range was 300 to 1,200 nm.

[0167] After that, the same sample was stored under high temperature/high humidity conditions with a temperature of 60° C. and a humidity of 90 RH% for 72 hours, and the wavelength (or wavelength band) (A.sub.1) having the maximum reflectance (lowest transmittance) was recorded by the same method. The peak shift, which is the degree of shift of the wavelength having the lowest transmittance before and after evaluation, was measured according to Equation 3 below. At this time, it was assumed that deformation of the film (e.g., contraction or expansion) did not affect the surface pitch, but occurred only in the direction perpendicular to the plane of the film.

[00006]$\text{Peak}\text{Shift}=\left(1-{\text{A}}_1/{\text{A}}_{\text{0}}\right)\text{x}100$

[0168] The degree of peak shift being low means that the deformation (contraction or expansion) of the diffraction grating can be suppressed, such as having a peak shift of grade A even when exposed to harsh conditions such as high temperature/high humidity, and as a result, the holographic recording medium can provide good color reproducibility and image clearness property even when exposed to harsh conditions.

4. Refractive Index Modulation Value

[0169] It was calculated using Equation 4 and Bragg’s equation below.

[00007]$\eta ={\tanh }^2\left|\frac{\pi \Delta nd}{\lambda {\left({\cos }^2\theta -\frac{\lambda }{n\Lambda }\cos \Phi \right)}^{1/2}}\right|$

[0170] In Equation 4, η is the reflectance diffraction efficiency (DE), d is the thickness of the photopolymer layer, λ is the recording wavelength, n is the refractive index of the photopolymer, A is the diffraction grating period, Δn means a refractive index modulation value.

[00008]$\cos \left(\theta -\varphi \right)=\frac{\lambda }{2n\Lambda }$

wherein, θ is the angle of incidence, Φ is the slant angle of the grid, n is the refractive index of the photopolymer, and λ means the recording wavelength.

TABLE-US-00001 Example 1 Example 2 Comparative Example 1 Comparative Example 2 Laser efficiency (DE, %) 85 85 5 80 Lase loss (Iloss)(%) 10 10 11 12 Peak shift(%) 1 1 40 30 Refractive index modulation value (Δn) 0.018 0.018 0.003 0.017

[0171] As shown in Table 1, it was confirmed that in the case of the photopolymer compositions of Examples, the diffraction efficiency is excellent, the peak shift and laser loss are low, and thus good color reproducibility and image clearness property can be achieved even when exposed to harsh conditions, and further, high refractive index modulation value can be realized.

[0172] Meanwhile, it was confirmed that in the case of the photopolymer compositions of Comparative Examples, not only the diffraction efficiency is poor and the laser loss is large, but also the peak shift value is large.