HOLOGRAM MEDIUM

Abstract

The present disclosure relates to a hologram recording medium having one surface with a higher surface energy than a polymer resin layer containing at least one polymer selected from the group consisting of triacetyl cellulose, alicyclic olefin polymer and polyethylene terephthalate, a hologram recording medium wherein the surface energy of any one surface is 50 mN/m or more, and an optical element comprising the hologram medium.

Claims

1. A hologram recording medium having one surface with a higher surface energy than a polymer resin layer of a base substrate containing at least one polymer selected from the group consisting of triacetyl cellulose, alicyclic olefin polymer and polyethylene terephthalate.

2. The hologram recording medium according to claim 1, wherein a surface energy of any one surface of the hologram recording medium is at least 50 mN/m.

3. The hologram recording medium according to claim 1, wherein the one surface of the hologram recording medium has a surface energy of 50 mN/m to 60 mN/m.

4. The hologram recording medium according to claim 1, wherein the hologram medium comprises a polymer substrate including a polymer resin having a silane-based functional group in a main chain or a branched chain of the polymer.

5. The hologram recording medium according to claim 4, wherein a fine pattern is formed on a surface of the polymer substrate that is the other surface of the hologram recording medium.

6. The hologram recording medium according to claim 5, wherein the fine pattern has a shape including two or more fine protrusions in which a maximum value of the height, and a minimum value of the height are alternately repeated based on the cross section of the polymer substrate, and a standard error of the distance in the cross-sectional direction of the polymer substrate between the maximum value of the height of the one fine protrusion and the minimum value of the height of the adjacent fine protrusion is 20 nm less.

7. The hologram recording medium according to claim 6, wherein the distance in the cross-sectional direction of the polymer substrate between the maximum value of the height of the one fine projection and the minimum value of the adjacent fine projection is 0.2 μm to 2 μm.

8. The hologram recording medium according to claim 6, wherein an amplitude which is a difference between the maximum value of the height of the one fine projection and the minimum value of the height of the adjacent fine projection is 5 to 50 nm.

9. The hologram recording medium according to claim 4, wherein the polymer substrate includes a cross-linked product between a polymer matrix including a (meth)acrylate-based (co)polymer having a silane-based functional group in a branched chain, and a silane crosslinking agent; and a photoreactive monomer.

10. The hologram recording medium according to claim 9, wherein the polymer matrix includes 10 parts by weight to 90 parts by weight of the silane crosslinking agent based on 100 parts by weight of the (meth)acrylate-based (co)polymer.

11. The hologram recording medium according to claim 9, wherein the (meth)acrylate-based(co)polymer having a silane-based functional group in a branched chain has an equivalent weight of the silane-based functional group of 300 g/eq. to 2000 g/eq.

12. The hologram recording medium according to claim 9, wherein the silane crosslinking agent includes a linear polyether main chain having a weight average molecular weight of 100 to 2000 and a silane-based functional group bonded to the terminal or branched chain of the main chain.

13. The hologram recording medium according to claim 4, wherein the polymer substrate further includes a fluorine-based compound including 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.

14. An optical element comprising the hologram medium of claim 1.

15. The hologram recording medium according to claim 2, wherein the one surface of the hologram recording medium has a surface energy of 50 mN/m to 60 mN/m.

16. The hologram recording medium according to claim 2, wherein the hologram medium comprises a polymer substrate including a polymer resin having a silane-based functional group in a main chain or a branched chain of the polymer.

17. An optical element comprising the hologram medium of claim 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0131] FIG. 1 is a line profile of the shape of the surface of the hologram medium of Example 1 measured using an atomic force microscope (AFM).

[0132] FIG. 2 is a line profile of the shape of the surface of the hologram medium of Example 2 measured using an atomic force microscope (AFM).

[0133] FIG. 3 is a line profile of the shape of the surface of the hologram medium of Example 3 measured using an atomic force microscope (AFM).

[0134] FIG. 4 is a line profile of the shape of the surface of the hologram medium of Example 4 measured using an atomic force microscope (AFM).

[0135] FIG. 5 is a line profile of the shape of the surface of the hologram medium of Comparative Example 1 measured using an atomic force microscope (AFM).

[0136] FIG. 6 is a line profile of the shape of the surface of the hologram medium of Comparative Example 2 measured using an atomic force microscope (AFM).

[0137] FIG. 7 is a line profile of the shape of the surface of the hologram medium of Comparative Example 3 measured using an atomic force microscope (AFM).

[0138] Hereinafter, the present disclosure 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 disclosure thereto.

PREPARATION EXAMPLE

Preparation Example 1: Preparation Method of a (meth)acrylate-based (co)polymer in which a silane-based Functional Group is Located in a Branch Chain

[0139] 154 g of butyl acrylate and 46 g of KBM-503 (3-methacryloxypropyltrimethoxysilane) were added to a 2 L jacket reactor and diluted with 800 g of ethyl acetate. The reaction temperature was set at about 60 to 70° C., and stirring was carried out for about 30 minutes to 1 hour. 0.0:2 g of n-dodecyl mercaptan was further added, and stirring was further carried out for about 30 minutes. Subsequently, 0.06 g of AIBN as a polymerization initiator was added and the polymerization was carried out at the reaction temperature for 4 hours or more and maintained until the residual acrylate content became less than 1%, thereby preparing a (meth)acrylate-based (co)polymer in which a silane-based functional group was located in a branch chain (weight average molecular weight of about 500,000 to 600,000, —Si(OR).sub.3 equivalent weight of 1019 g/eq.).

Preparation Example 2: Preparation Method of a (meth)acrylate-based (co)polymer in which a silane-based Functional Group is Located in a Branch Chain

[0140] 180 g of butyl acrylate and 120 g of KBM-503 (3-methacryloxypropyltrimethoxysilane) were added to a 2 L jacket reactor and diluted with 700 g of ethyl acetate. The reaction temperature was set at 60 to 70° C., and stirring was carried out for about 30 minutes to 1 hour. 0.03 g of n-dodecyl mercaptan was further added, and stirring was further carried out for about 30 minutes. Subsequently, 0.09 g of AIBN as a polymerization initiator was added and the polymerization was carried out at the reaction temperature for 4 hours or more and maintained until the residual acrylate content became less than 1%, thereby preparing a (meth)acrylate-based (co)polymer in which a silane-based functional group was located in a branch chain (weight average molecular weight of about 500,000 to 600,000, —Si(OR).sub.3 equivalent weight=586 g/eq.).

Preparation Example 3: Preparation Method of a (meth)acrylate-based (co)polymer in which a silane-based Functional Group is Located in a Branch Chain

[0141] 255 g of butyl acrylate and 45 g of KBM-503 (3-methacryloxypropyltrimethoxysilane) were added to a 2L jacket reactor and diluted with 700 g of ethyl acetate. The reaction temperature was set at 60 to 70° C., and stirring was carried out for about 30 minutes to 1 hour. 0.03 g of n-dodecyl mercaptan was further added, and stirring was further carried out for about 30 minutes. Subsequently, 0.09 g of AIBN as a polymerization initiator was added and the polymerization was carried out at the reaction temperature for 4 hours or more and maintained until the residual acrylate content became less than 1%, thereby preparing a (meth)acrylate-based (co)polymer in which a silane-based functional group was located in a branch chain (weight average molecular weight of about 500,000 to 600,000, —Si(OR).sub.3 equivalent weight of 1562 g/eq.).

Preparation Example 4: Preparation Method of Silane Crosslinking Agent

[0142] In a 1000 ml flask, 19.79 g of KBE-9007 (3-isocyanatopropyltriethoxysilane), 12.80 g of PEG-400 and 0.57 g of DBTDL were added and diluted with 300 g of tetrahydrofuran. The mixture was stirred at room temperature until it was confirmed by TLC that all the reactants were consumed, and then the reaction solvent was completely removed under reduced pressure.

[0143] 28 g of a liquid product having a purity 95% or more was separated in a yield of 91% through column chromatography under a developing solution condition of dichloromethane:methyl alcohol=30:1, thereby obtaining the above-mentioned silane crosslinking agent.

Preparation Example 5: Preparation Method of Non-Reactive Low Refractive Index Material

[0144] In a 1000 ml flask, 20.51 g of 2,2′-((oxybis(1,1,2,2-tetrafluoroethane-2,1-diyl))bis(oxy))bis(2,2-difluoroethan-1-ol) was added and then dissolved in 500 g of tetrahydrofuran. 4.40 g of sodium hydride (60% dispersion in mineral oil) was carefully added over 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 .sup.1H NMR that all the reactants were consumed, the reaction solvent was completely removed under reduced pressure. The organic layer was collected by extracting with 300 g of dichloromethane three times, and filtered with magnesium sulfate, and then the pressure was reduced to remove all the dichloromethane to obtain 29 g of a liquid product having a purity of 95% or more in a yield of 98%.

Example: Preparation of Photopolymer Composition and Hologram Medium

[0145] 1. Preparation of Photopolymer Composition

[0146] As shown in Table 1 or Table 2 below, the silane polymers obtained in Preparation Examples 1 to 3, photoreactive monomer (high refractive index acrylate, refractive index 1.600, HR 6022 [Miwon]), the non-reactive low refractive index material of Preparation Example 5, tributyl phosphate ([TBP], molecular weight 266.31, refractive index 1.424, manufactured by Sigma-Aldrich), Safranin O (dye, manufactured by Sigma-Aldrich), Ebecryl P-415 (SK entis), Borate V (Spectra Group), Irgacure 250 (BASF), silicone-based reactive additive (Tego Rad 2500) and methyl isobutyl ketone (MIBK) were mixed in a state cutting off the light, and stirred with a paste mixer for about 10 minutes to obtain a transparent coating solution.

[0147] The silane crosslinking agent obtained in Preparation Example 4 was added to the coating solution, and further stirred for about 10 minutes. Subsequently, 0.02 g of DBTDL as a catalyst was added to the coating solution, stirred for about 1 minute, and then coated in a thickness of 6 μm onto a TAC substrate with a thickness of 80 μm using a Meyer bar and dried at 40° C. for 1 hour.

[0148] 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.

[0149] 2. Preparation of Hologram Medium

[0150] (1) The above-prepared photopolymer-coated surfaces were laminated on a slide glass, and fixed so that a laser first passed through the glass surface at the time of recording.

[0151] (2) Measurement of Diffraction Efficiency (η)

[0152] A holographic recording was done via interference of two interference lights (reference light and object light), and the transmission-type recording was done so that the two beams were incident on the same side of the sample. The diffraction efficiencies are 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 is generated vertically to the film because the incident angles of the two beams are the same on the normal basis.

[0153] 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 general formula 1.

[00001]$\begin{array}{cc}\eta =\frac{P_D}{P_D+P_T}& \left[\mathrm{General}\mathrm{Formula}1\right]\end{array}$

[0154] in the general formula 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.

[0155] (3) Measurement of Refractive Index Modulation Value (n)

[0156] The lossless dielectric grating of the transmission-type hologram can calculate the refractive index modulation value (Δn) from the following general formula 2.

[00002]$\begin{array}{cc}\eta \left(\mathrm{DE}\right)={\sin }^2\left(\sqrt{v^2}\right)={\sin }^2\left(\frac{\pi \Delta \mathrm{nd}}{\lambda \cos \theta }\right)& \left[\mathrm{General}\mathrm{Formula}2\right]\end{array}$

[0157] in the general formula 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.

[0158] (4) Measurement of the Loss Amount of Laser (I.sub.loss)

[0159] The loss amount of laser (I.sub.loss) can be calculated from the following general formula 3.

I.sub.loss=1−{(P.sub.D+P.sub.T)/I.sub.0}  [General Formula 3]

[0160] in the general formula 3, P.sub.D is an output amount (mW/cm.sup.2) of the diffracted beam of the sample after recording, PT is an output amount (mW/cm.sup.2) of the transmitted beam of the recorded sample, and I.sub.0 is an intensity of the recording light.

[0161] (5) Surface Observation of the Hologram Medium

[0162] The shape and size of the linear pattern formed on one surface of the hologram medium obtained in Examples were measured using an atomic force microscope (XE7) manufactured by Park Systems. Then, the distance between the adjacent minimum and maximum values was measured through a line profile from the confirmed surface shape.

[0163] At this time, in the measurement result, the minimum value means a point where the y-axis value decreases and then increases, the maximum value means a point at which the y-axis value increases and then decreases, and “adjacent” means the most adjacent maximum value (or minimum value) with a height difference of 5 nm or more from the minimum value (or maximum value).

[0164] As for the standard error of the adjacent minimum and maximum values, the distance between the adjacent minimum and maximum values having a height difference of 5 nm or more was measured from the line profile of the surface profile measured by atomic force microscopy, and the standard error was calculated according to the following general formula 1.

SE=σ/√{square root over (n)}  [General Formula 1]

[0165] in the general formula 1, SE is a standard error, σ is a standard deviation, and n is a number.

[0166] FIGS. 1 to 4 are line profiles of the shapes of the surfaces of the hologram media of Examples 1 to 4 measured using an atomic force microscope.

[0167] (6) Measurement of Surface Energy

[0168] In the hologram medium obtained in Examples, the surface energy of one surface making contact with the substrate was measured by the following method.

[0169] For the sample, the substrate was cleanly peeled from the coating film laminated on the glass surface, and then the surface energy of one surface making contact with the substrate was measured with a contact angle measuring device. The contact angle of di-water (Gebhardt) and di-iodomethane (Owens) was measured as 10 points using a DSA100 contact angle measuring equipment form Kruss. After calculating the average value, the surface energy was measured by converting the average contact angle into surface energy. In the measurement of the surface energy, the contact angle was converted to the surface energy by using Dropshape Analysis software and applying the following General Formula 2 of OWRK (Owen, Wendt, Rable, Kaelble) method.

γ.sub.L(1+cos θ)=2√{square root over (γ.sub.S.sup.Dγ.sub.L.sup.D)}+2√{square root over (γ.sub.S.sup.Pγ.sub.L.sup.P)}  [General Formula 2]

TABLE-US-00001 TABLE 1 Measurement results of Experimental Examples of the photopolymer compositions (unit: g) of Examples and the hologram recording medium prepared therefrom Category Example 1 Example 2 Example 3 Example 4 (Meth) Preparation 23.1 23.1 acrylate- Example 1 based Preparation 19.3 copolymer Example 2 Preparation 25.4 Example 3 Linear silane Preparation 8.4 8.4 12.3 6.1 crosslinking Example 4 agent Photoreactive HR6022 31.5 31.5 31.5 31.5 monomer Dye safranin O 0.1 0.1 0.1 0.1 Amine Ebecryl P-115 1.7 1.7 1.7 1.7 Borate salt Borate V 0.3 0.3 0.3 0.3 Onium salt Irgacure 250 0.1 0.1 0.1 0.1 Non-reactive Tributyl 0 17.2 17.2 17.2 plasticizer phosphate (TBP) Non-reactive Preparation 34.4 17.2 17.2 17.2 low refractive Example 5 material(P3) Catalyst DBTDL(dibutyltin 0.02 0.02 0.02 0.02 dilaurate) Additive Tego Rad 2500 0.3 0.3 0.3 0.3 Solvent MIBK 300 300 300 300 Coating thickness (unit: μm) 6 6 6 6 I.sub.loss(%) 25 19 21 20 Surface energy 52 mN/m 53 mN/m 51 mN/m 55 mN/m Standard error (SE) 5.72 nm 2.26 nm 6.72 nm 4.30 nm Diffraction efficiency (η) 67% 69% 80% 46% Δn 0.025 0.027 0.030 0.022 * Non-reactive plasticizer: Tributyl phosphate (molecular weight of 2.66.31, refractive index of 1.424, purchased from Sigma-Aldrich)

Comparative Example: Preparation of Hologram Media

[0170] (1) Synthesis of Polyol

[0171] 34.5 g of methyl acrylate, 57.5 g of butyl acrylate, and 8 g of 4-hydroxy butyl acrylate were added to a 2 L jacket reactor, and diluted with 150 g of ethyl acetate. Stirring was performed 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, and further stirring was performed for about 30 minutes. Then, 0.04 g of a polymerization initiator AIBN (2,2′-azo-bisisobutyronitrile) was added thereto, and polymerized at a temperature of about 70° C. for about 4 hours, and maintained until the content of the residual acrylate monomer became 1% by weight, and thereby the polyol was synthesized. At this time, the obtained polyol had a weight average molecular weight of about 700,000 in terms of polystyrene measured by GPC method, and the OH equivalent measured using KOH titration was 1802 g/OH mol.

[0172] (2) Preparation of Photopolymer Composition

[0173] The polyol of Preparation Example 1, the photoreactive monomer (high refractive acrylate, refractive index of 1.600, HR6022 [Miwon]), safranin O (dye, manufactured by Sigma Aldrich), the non-reactive low refractive material of Preparation Example 5, (tributyl phosphate [TBP], molecular weight of 266.31, refractive index of 1.424, manufactured by Sigma Aldrich), Ebecryl P-115 (SK entis), Borate V (Spectra group), Irgacure 250 (BASF), and methyl isobutyl ketone (MIBK) were mixed in a state cutting off the light, and stirred with a paste mixer for about 10 minutes to obtain a transparent coating solution.

[0174] MFA-75X (Asahi Kasei, hexa-functional isocyanate, diluted to 75% by weight in xylene) was added to the coating solution, and further stirred for about 5-10 minutes. DBTDL (dibutyltin dilaurate) as a catalyst was added thereto, stirred for about 1 minute, and then coated in a thickness of 7 μm onto a TAC substrate with a thickness of 80 μm using a Meyer bar and dried at 40° C. for 1 hour.

[0175] (3) Preparation of Hologram Medium

[0176] A hologram medium was prepared in the same manner as in the above Examples, and the diffraction efficiency (η), the refractive index modulation value (n) and the laser loss (I.sub.loss) were measured according to the same method and the same conditions as in Examples.

[0177] (4) Surface Observation of Hologram Media.

[0178] The shape and size of the linear pattern formed on one surface of the hologram media obtained in Comparative Examples and the surface of the hologram media were measured and observed in the same manner as in Examples.

[0179] FIGS. 5 to 7 are line profiles of the shapes of the surfaces of the hologram media of Comparative Examples 1 to 4 measured using an atomic force microscope.

TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Category Example 1 Example 2 Example 3 Polyol Preparation 26.2 26.2 26.2 Example 1 Isocyanate MFA-75X 6.4 6.4 6.4 Photoreactive HR6022 31 31 31 monomer Dye safranin O 0.1 0.1 0.1 Amine Ebecryl P-115 1.7 1.7 1.7 Borate salt Borate V 0.3 0.3 0.3 Onium salt Irgacure 250 0.1 0.1 0.1 Non-reactive Tributyl 16.9 33.8 plasticizer(TBP) phosphate Non-reactive low Preparation 16.9 33.8 refractive Example 5 material (P3) Catalyst DBTDL(dibutyltin 0.02 0.02 0.02 dilaurate) Additive Tego Rad 2500 0.5 0.5 0.5 Solvent MIBK 400 400 400 Coating thickness (unit: μm) 7 7 7 Surface energy 40 mN/m 42 mN/m 38 mN/m Standard error (SE) 187.98 nm 232.23 nm 150.50 nm Δn 0.010 0.011 0.013 Diffraction efficiency (η) 19% 22% 28%

[0180] As seen from FIGS. 1 to 4, it was confirmed that in the hologram media of Examples, the standard error of the distance in the cross-sectional direction of the polymer substrate between the maximum value of the height of the one fine protrusion and the minimum value of the height of the adjacent fine protrusion is 20 nm or less. As shown in Tables 1 and 2, and that the hologram media of Examples have a refractive index modulation value (ΔN) of 0.020 or more and a diffraction efficiency of 40% or more.

[0181] Further, as shown in Table 1 above, it was confirmed that the other one surface of the hologram recording medium of Examples had a surface energy of about 51 to 55 N/m, and it was also confirmed that it was easily peeled off from a TAC substrate used in the manufacturing process of the hologram recording medium.

[0182] In contrast, as seen in FIGS. 5 to 7, it was confirmed that in the hologram media of Examples, the standard error of the distance in the cross-sectional direction of the polymer substrate between the maximum value of the height of the one fine protrusion and the minimum value of the height of the adjacent fine protrusion exceeds 20 nm, and in such hologram media, image distortion may occur or additional scattering or interference of diffracted light may occur, and diffraction efficiency may also decrease. Specifically, as shown in Tables 1 and 2, it was confirmed that the photopolymer-coated films provided by the compositions of Comparative Examples have a relatively low diffraction efficiency of 30% or less and a refractive index modulation value (Δn) of 0.015 or less as compared with Examples.

[0183] In addition, as shown in Table 2 above, it was confirmed that the other one surface of the hologram recording medium of Comparative Examples had a surface energy of about 38 to 40 N/m. However, these hologram recording media did not peel off from the TAC substrate used in the manufacturing process, and therefore, there is a limit in actual applications in that the optical design must be proceeded in consideration of the reflection, scattering, and absorption effects by the substrate.