Photopolymer composition

Abstract

The present disclosure relates to a photopolymer composition including: a polymer matrix or a precursor thereof; a photoreactive monomer including a polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or less and a viscosity at 25° C. of 100 cps or less, and a monofunctional (meth)acrylate monomer having a refractive index of 1.5 or more; and a photoinitiator, wherein a content of the monofunctional (meth)acrylate monomer having a refractive index of 1.5 or more in the photoreactive monomer is 60 wt % or more. The present disclosure also relates to a hologram recording medium produced from the photopolymer composition, an optical element including the hologram recording medium, and a holographic recording method using the photopolymer composition.

Claims

1. A photopolymer composition, comprising: a polymer matrix or a precursor thereof; a photoreactive monomer mixture comprising a polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or less and a viscosity at 25° C. of 100 cps or less, and a monofunctional (meth)acrylate monomer having a refractive index of 1.5 or more; and a photoinitiator, wherein the content of the monofunctional (meth)acrylate monomer in the photoreactive monomer mixture is 70 wt % to 90 wt %, wherein the polymer matrix is a reaction product of a compound having at least one isocyanate group and a polyol, and wherein the polyol has a hydroxyl equivalent weight of 300 g/mol to 10,000 g/mol, and a weight average molecular weight of 100,000 to 1,500,000 g/mol.

2. The photopolymer composition of claim 1, wherein the monofunctional (meth)acrylate monomer has a viscosity at 25° C. of 300 cps or less.

3. The photopolymer composition of claim 1, wherein the polyfunctional (meth)acrylate monomer comprises an ether bond, and the monofunctional (meth)acrylate monomer comprises an ether bond and a fluorene functional group.

4. The photopolymer composition of claim 1, wherein each of the polyfunctional (meth)acrylate monomer and the monofunctional (meth)acrylate monomer has a weight average molecular weight of 50 to 1000 g/mol.

5. The photopolymer composition of claim 1, wherein a refractive index of the polymer matrix or the precursor thereof is higher than the refractive index of the polyfunctional (meth)acrylate monomer and lower than the refractive index of the monofunctional (meth)acrylate monomer.

6. The photopolymer composition of claim 1, comprising: 20 wt % to 80 wt % of the polymer matrix or the precursor thereof; 10 wt % to 70 wt % of the photoreactive monomer mixture; and 0.1 wt % to 15 wt % of the photoinitiator.

7. A hologram recording medium produced from the photopolymer composition of claim 1.

8. An optical element comprising the hologram recording medium of claim 7.

9. A holographic recording method comprising selectively polymerizing the photoreactive monomer mixture contained in the photopolymer composition of claim 1 using electromagnetic radiation.

10. The photopolymer composition of claim 1, further comprising a catalyst.

11. The photopolymer composition of claim 10, wherein the catalyst is one or more selected from tin octanoate, zinc octanoate, dibutyltin dilaurate, dimethylbis[(1-oxoneodecyl)oxy]stannane, dimethyltin dicarboxylate, zirconium bis(ethylhexanoate), zirconium acetylacetonate, 1,4-diazabicyclo[2.2.2]octane, diazabicyclononane, diazabicyclo undecane, 1,1,3,3-tetramethylguanidine and 1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido(1,2-a)pyrimidine.

12. The polymer composition of claim 1, wherein the photoinitiator is a monomolecular (type I) initiator or a bimolecular (type II) initiator.

13. The polymer composition of claim 12, wherein the monomolecular (type I) initiator is an aromatic ketone compounds in combination with a tertiary amine.

14. The polymer composition of claim 13, wherein the aromatic ketone compound is one or more selected from benzophenone, alkylbenzophenone, 4,4′-bis(dimethylamino)benzophenone (Michler's ketone), anthrone and halogenated benzophenone, and a mixture thereof.

15. The polymer composition of claim 12, wherein the bimolecular (type II) initiator is one or more selected from benzoin and derivatives thereof, benzyl ketal, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylophosphine oxide, phenylglyoxyl ester, camphorquinone, α-aminoalkylphenone, α.α-dialkylacetophenone, 1-[4-(phenylthio)phenyl]octane-1,2-dione 2-(O-benzoyloxime), and α-hydroxyalkylphenone.

16. The polymer composition of claim 1, wherein the photoinitiator is a mixture of ammonium aryl borate and one or more dyes.

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 Example: 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.

Examples and Comparative Examples: Preparation of Photopolymer Composition

(3) 39.44 g of the polyol of the preparation example, 31.33 g of the monomer shown in Tables 1 to 2, 0.06 g of safranin O (dye, manufactured by Sigma-Aldrich), 2.01 g of N-methyl diethanolamine (manufactured by Sigma-Aldrich), 4.19 g of [4-methylphenyl-(4-(2-methylpropyl)phenyl)]iodonium hexafluorophosphate (Irgacure 250), and 0.42 g of BYK-310 (dispersant) were mixed with light blocked, and stirred with a paste mixer for about 2 minutes to obtain a transparent coating solution.

(4) 7.56 g of MFA-75X (hexafunctional isocyanate, diluted to 75 wt % in xylene, manufactured by Asahi Kasei) was added to the coating solution and further stirred for about 1 minute. DBTDL (0.05 wt % with respect to the synthesized urethane resin) as a catalyst was added thereto and stirred for about 1 minute. It was coated on a PC substrate (125 μm) using a Mayer bar to a thickness of 18 μm, and then cured at 80° C. for 30 minutes. Thereafter, the sample was allowed to stand for 12 hours or more in a dark room under constant temperature and humidity conditions of about 25° C. and 50 RH %.

Experimental Examples: Holographic Recording

(5) (1) The photopolymer-coated surfaces prepared in each of the examples and comparative examples were laminated on a slide glass, and fixed so that a laser first passed through the glass surface at the time of recording.

(6) (2) 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.

(7) 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.

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

(9) 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.

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

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

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

(13) TABLE-US-00001 TABLE 1 Types of mono/polyfunctional acrylate monomer of examples and measurement results of refractive index modulation values (Δn) Examples 1 to 3 Example 1 Example 2 Example 3 Types of mono/polyfunctional acrylate monomer Monofunctional Polyfunctional Polyfunctional Polyfunctional acrylate monomer acrylate monomer acrylate monomer acrylate monomer [M1142 (Miwon)] [M282 (Miwon)] [M284 (Miwon)] [M3130 (Miwon)] Refractive index 1.59 1.475 1.476 1.492 Tg (° C.) 33 14 −13 40 Mw 268 308 408 428 Viscosity (cps, 25° C.) 150 25 40 60 Weight ratio relative 0.2 0.2 0.2 to all monomers Δn 0.0123 0.0123 0.0122

(14) TABLE-US-00002 TABLE 2 Types of mono/polyfunctional acrylate monomer of Comparative Examples and measurement results of refractive index modulation value (Δn) Comp. Exs. 1 Comp. Comp. Comp. Comp. Comp. Comp. Comp. to 7 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Types of mono/polyfunctional acrylate monomer Mono- Poly- Poly- Poly- Poly- Poly- Poly- Poly- functional functional functional functional functional functional functional functional acrylate acrylate acrylate acrylate acrylate acrylate acrylate acrylate monomer monomer monomer monomer monomer monomer monomer monomer [M1142 [M282 [M284 [M3130 [M2100 [M2100 [M244 [M244 (Miwon)] (Miwon)] (Miwon)] (Miwon)] (Miwon)] (Miwon)] (Miwon)] (Miwon)] Refractive 1.59 1.475 1.476 1.492 1.529 1.529 1.557 1.557 index Tg (° C.) 33 14 −13 40 −7 −7 67 67 Mw 268 308 408 428 776 776 468 468 Viscosity 150 25 40 60 660 660 1730 1730 (cps, 25° C.) Weight 0.4 0.4 0.4 0.4 0.2 0.4 0.2 ratio relative to all monomers Δn 0.0118 0.0118 0.0114 0.0115 0.0117 0.0108 0.0109

(15) 1) Measurement of Refractive Index of Monomers

(16) Irgacure 184 (UV initiator, manufactured by Ciba) and F477 (surfactant, manufactured by DIC) were used in an amount of 0.5 wt % and 0.2 wt % relative to the monomer, respectively, to prepare a coating solution. The coating solution was coated on a glass substrate to a thickness of 2 μm and dried at 60° C. for 2 minutes. After curing by irradiating ultraviolet rays at 150 mJ/cm.sup.2, the refractive index was measured at 632.8 nm using SPA-3DR.

(17) 2) Measurement of Glass Transition Temperature (Tg) of Monomers

(18) Irgacure 184 (UV initiator, manufactured by Ciba) was used in an amount of 0.5 wt % relative to the monomer to prepare a coating solution. The coating solution was coated on a glass substrate to a thickness of 10 μm and dried at 60° C. for 2 minutes. After curing by irradiating ultraviolet rays at 150 mJ/cm.sup.2, the film was peeled off and the glass transition temperature of the film was measured using DSC. Specifically, when using DSC, the temperature was increased from −100° C. to 200° C. at a rate of 10° C./min and decreased from 200° C. to −100° C. at a rate of −10° C./minute. This process was repeated twice, and the glass transition temperature was confirmed at the second heating period.

(19) As shown in Tables 1 and 2 above, it was confirmed that the examples using a photoreactive monomer including a polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or less and a viscosity at 25° C. of 100 cps or less, and a monofunctional (meth)acrylate monomer having a refractive index of 1.5 or more, wherein a content of the monofunctional (meth)acrylate monomer is 60 wt % or more, can provide holograms exhibiting a significantly improved refractive index modulation value as compared with the comparative examples even with a thin thickness.