Photopolymer composition

Abstract

The present disclosure relates to a hologram recording medium having a main relaxation temperature (Tr) of 0° C. or less, wherein the Tr is a point where a rate of change of phase angle with respect to temperature is the largest in a range of −80° C. to 30° C. in dynamic mechanical analysis. The present disclosure also relates to an optical element including the same and a holographic recording method using the hologram recording medium.

Claims

1. A hologram recording medium having a main relaxation temperature (Tr) of 0° C. or less, wherein the Tr is a point where a rate of change of phase angle with respect to temperature is the largest in a range of −80° C. to 30° C. in dynamic mechanical analysis, wherein the dynamic mechanical analysis is performed under conditions of a strain of 0.1%, a frequency of 1 Hz, and a heating rate of 5° C/min, and the phase angle is an angular value of tan delta calculated as G″(loss modulus)/G′(storage modulus), wherein the hologram recording medium comprises a polymer matrix or a precursor thereof; and a photoreactive monomer, and wherein the polymer matrix or the precursor thereof comprises a (meth)acrylate-based (co)polymer having a silane-based functional group in a branched chain, and a silane cross-linking agent.

2. The hologram recording medium of claim 1, wherein the hologram recording medium further comprises a photoinitiator.

3. The hologram recording medium of claim 1, wherein the hologram recording medium further comprises at least one selected from the group consisting of a phosphate-based compound and a low refractive fluorine-based compound.

4. The hologram recording medium of claim 3, wherein the low refractive fluorine-based compound comprises at least one functional group selected from the group consisting of an ether group, an ester group and an amide group; and at least two difluoromethylene groups.

5. The hologram recording medium of claim 3, wherein the low refractive fluorine-based compound has a refractive index of less than 1.45.

6. The hologram recording medium of claim 1, wherein the polymer matrix has a refractive index of 1.45 to 1.70.

7. The hologram recording medium of claim 1, wherein the silane cross-linking agent comprises a linear polyether main chain having a weight average molecular weight of 100 to 2000 and a silane-based functional group bound to the main chain as a terminal group or a branched chain.

8. The hologram recording medium of claim 1, wherein the photoreactive monomer comprises a polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or more, or a monofunctional (meth)acrylate monomer having a refractive index of 1.5 or more.

9. An optical element comprising the hologram recording medium of claim 1.

10. A holographic recording method comprising selectively polymerizing photoreactive monomers contained in the photopolymer composition of claim 1 by electromagnetic radiation.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Hereinafter, the present invention will be explained in detail with reference to the following examples. However, these examples are only to illustrate the invention, and the scope of the invention is not limited thereto.

PREPARATION EXAMPLES

Preparation Example 1: Synthesis of Polyol

(2) 34.5 g of methyl acrylate, 57.5 g of butyl acrylate and 8 g of 4-hydroxybutyl acrylate were placed in a 2 L jacket reactor and diluted with 150 g of ethyl acetate. Stirring was continued for about 1 hour while maintaining the temperature of the jacket reactor at 60 to 70° C. Then, 0.035 g of n-dodecyl mercaptan was further added to the reactor, followed by further stirring for about 30 minutes. Thereafter, 0.04 g of AIBN (2,2′-azo-bisisobutyronitrile) as a polymerization initiator was added thereto, and polymerization was continued for about 4 hours at a temperature of about 70° C. until the residual acrylate-based monomer content became 1 wt % to synthesize a polyol. The obtained polyol had a weight average molecular weight using polystyrene calibration measured by GPC of about 700,000 and OH equivalent weight measured by a KOH titration method of 1802 g/OH mol.

Preparation Example 2: Preparation of Non-Reactive Low Refractive Material 2

(3) 20.51 g of 2,2′-((oxybis(1,1,2,2-tetrafluoroethane-2,1-diyl))bis(oxy))bis(2,2-difluoroethan-1-ol was placed in a 1000 ml flask, dissolved in 500 g of tetrahydrofuran, and 4.40 g of sodium hydride (60% dispersion in mineral oil) was gently 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 all of the reactants were confirmed to be consumed by .sup.1H NMR, the reaction solvent was completely removed under reduced pressure. The organic layer was collected by extracting three times with 300 g of dichloromethane. Thereafter, it was filtered with magnesium sulfate, and all dichloromethane was removed under reduced pressure to obtain 29 g of a liquid product having a purity of 95% or more at a yield of 98%.

Preparation Example 3: Preparation of (Meth)Acrylate-Based (Co)Polymer Having a Silane-Based Functional Group in a Branched Chain

(4) 69.3 g of butyl acrylate and 20.7 g of KBM-503 (3-methacryloxypropyltrimethoxysilane) were placed in a 2 L jacket reactor and diluted with 700 g of ethyl acetate. The reaction temperature was set at about 70° C. and stirring was continued for about 1 hour. 0.02 g of n-dodecyl mercaptan was further added thereto, and stirring was further continued for about 30 minutes. Thereafter, 0.06 g of AIBN as a polymerization initiator was added thereto, and polymerization was continued for 4 hours or more at the reaction temperature until the residual acrylate content became less than 1% to obtain a (meth)acrylate-based (co)polymer having a silane-based functional group in a branched chain (the weight average molecular weight was about 900,000, and the equivalent weight of Si—(OR).sub.3 was 1019 g/ea).

Preparation Example 4: Preparation of Silane Cross-Linking Agent

(5) 19.79 g of KBE-9007 (3-isocyanatopropyltriethoxysilane), 12.80 g of PEG-400 and 0.57 g of DBTDL were placed in a 1000 ml flask, and diluted with 300 g of tetrahydrofuran. After stirring at room temperature until all of the reactants were confirmed to be consumed by TLC, the reaction solvent was completely removed under reduced pressure.

(6) 28 g of a liquid product having a purity of 95% or more was separated at a yield of 91% through column chromatography under a developing solution (dichloromethane:methyl alcohol=30:1) to obtain the above-mentioned silane cross-linking agent.

Examples and Comparative Example: Preparation of Photopolymer Composition

Examples 1 to 2 and Comparative Example 1

(7) The polyol of Preparation Example 1, the photoreactive monomer (high refractive acrylate, refractive index of 1.600, HR6022, manufactured by Miwon), safranin O (dye, manufactured by Sigma-Aldrich), the non-reactive low refractive material of Preparation Example 2, tributyl phosphate (TBP, molecular weight of 266.31, refractive index of 1.424, manufactured by Sigma-Aldrich), Ebecryl P-115 (manufactured by SK entis), Borate V (manufactured by Spectra group), Irgacure 250 (manufactured by BASF) and methyl isobutyl ketone (MIBK) were mixed with light blocked, and stirred with a paste mixer for about 10 minutes to obtain a transparent coating solution.

(8) MFA-75X (hexamethylene diisocyanate, diluted to 75 wt % in xylene, manufactured by Asahi Kasei) was added to the coating solution and further stirred for 5 to 10 minutes. DBTDL (dibutyltin dilaurate) as a catalyst was added thereto and stirred for about 1 minute. It was coated on a TAC substrate (80 μm) using a meyer bar to a thickness of 7 μm, and then cured at 40° C. for 1 hour.

Examples 3 and 4

(9) As shown in Table 1 below, the (meth)acrylate-based (co)polymer having a silane-based functional group in a branched chain obtained in Preparation Example 3, the photoreactive monomer (high refractive acrylate, refractive index of 1.600, HR6022, manufactured by Miwon), the non-reactive low refractive material of Preparation Example 2, tributyl phosphate (TBP, molecular weight of 266.31, refractive index of 1.424, manufactured by Sigma-Aldrich), safranin 0 (dye, manufactured by Sigma-Aldrich), Ebecryl P-115 (manufactured by SK entis), Borate V (manufactured by Spectra group), Irgacure 250 (manufactured by BASF), and methyl isobutyl ketone (MIBK) were mixed with light blocked, and stirred with a paste mixer for about 10 minutes to obtain a transparent coating solution.

(10) The above-described silane cross-linking agent of Preparation Example 4 was added to the coating solution, and further stirred for 5 to 10 minutes. Thereafter, DBTDL as a catalyst was added to the coating solution, and stirred for about 1 minute. Then, the coating solution was coated on a TAC substrate (80 μm) using a meyer bar to a thickness of 7 μm, and dried at 40° C. for 1 hour.

Experimental Examples: Holographic Recording

(11) (1) The photopolymer(hologram recording medium)-coated surfaces prepared in each of Examples and Comparative Example were laminated on a slide glass, and fixed so that a laser first passed through the glass surface at the time of recording.

(12) (2) Measurement of Main Relaxation Temperature (Tr) Using DMA

(13) The phase angle of the hologram recording medium was measured in a film state before recording by using DMA (dynamic mechanical analysis) in a range of −80° C. to 30° C. under conditions of a strain of 0.1%, a frequency of 1 Hz, and a heating rate of 5° C./min.

(14) The phase angle is an angular value of tan delta calculated as G″(loss modulus)/G′(storage modulus), and the larger the phase angle, the higher the viscous characteristic of the material.

(15) The main relaxation temperature (Tr) was defined as a point where a rate of change of phase angle with respect to temperature is the largest. Tr values of the hologram recording media obtained in Examples and Comparative Example were confirmed.

(16) (3) Measurement of Diffraction Efficiency (η)

(17) A holographic recording was done via interference of two interference lights (reference light and object light), and a transmission-type recording was done so that the two beams were incident on the same side of the sample. The diffraction efficiencies change with 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 is generated perpendicularly to the film because the incident angles of the two beams are equal to a normal line.

(18) The recording (2θ=45°) was done in a transmission-type non-slanted manner using a laser with a wavelength of 532 nm, and the diffraction efficiency (η) was calculated according to the following Equation 1.

(19) $\begin{array}{cc}\eta =\frac{P_D}{P_D+P_T}& \left[\mathrm{Equation}1\right]\end{array}$

(20) In Equation 1, η is a diffraction efficiency, P.sub.D is an output amount (mW/cm.sup.2) of the diffracted beam of a sample after recording, and P.sub.T is an output amount (mW/cm.sup.2) of the transmitted beam of the recorded sample.

(21) (4) Measurement of Refractive Index Modulation Value (η)

(22) The lossless dielectric grating of the transmission-type hologram can calculate the refractive index modulation value (Δn) from the following Equation 2.

(23) $\begin{array}{cc}\eta \left(\mathrm{DE}\right)={\sin }^2\left(\sqrt{v^2}\right)={\sin }^2\left(\frac{\mathrm{\pi \Delta }\mathrm{nd}}{\lambda \cos \theta }\right)& \left[\mathrm{Equation}2\right]\end{array}$

(24) In Equation 2, d is a thickness of the photopolymer layer, Δn is a refractive index modulation value, η(DE) is a diffraction efficiency, and λ is a recording wavelength.

(25) TABLE-US-00001 Example 1 Example 2 Example 3 Example 4 Comp. Ex. 1 Polyol Prep. Ex. 1 26.2 26.2 40.1 Isocyanate MFA-75X 6.4 6.4 9.8 (Meth)acrylate-based Prep. Ex. 3 23.1 23.1 copolymer Linear silane Prep. Ex. 4 8.4 8.4 cross-linking agent Photoreactive HR6022 31.0 31.0 31.5 31.5 47.4 monomer Dye safranin O 0.1 0.1 0.1 0.1 0.1 Amine Ebecryl P-115 1.7 1.7 1.7 1.7 1.7 Borate salt Borate V 0.3 0.3 0.3 0.3 0.3 Onium salt Irgacure 250 0.1 0.1 0.1 0.1 0.1 Non-reactive Tributyl 0 16.9 0 17.2 plasticizer (TBP) phosphate Non-reactive low Prep. Ex. 2 33.8 16.9 34.4 17.2 refractive material (P3) Catalyst DBTDL(dibutyltin 0.02 0.02 0.02 0.02 0.02 dilaurate) Additive Tego Rad 2500 0.3 0.3 0.3 0.3 0.5 Solvent MIBK 400 400 300 300 400 Coating thickness (unit: μm) 7 7 7 7 7 Δn 0.024 0.030 0.027 0.030 0.012 Tr (° C.) −15 −24 −37 −41 13 ** The non-reactive plasticizer: Tributyl phosphate (molecular weight of 266.31, refractive index of 1.424, manufactured by Sigma-Aldrichch)

(26) As shown in Table 1 above, it was confirmed that the hologram recording media of Examples 1 to 4 having a main relaxation temperature (Tr) of 0° C. or less can achieve a refractive index modulation value (Δn) of 0.024 or more, wherein the Tr is a point where a rate of change of phase angle with respect to temperature is the largest in a range of −80° C. to 30° C. in dynamic mechanical analysis.

(27) On the contrary, it was confirmed that the hologram recording medium of Comparative Example 1 in which the Tr is 13° C. had a relatively low diffraction efficiency as compared with Examples.