DIFFRACTION LIGHT GUIDE PLATE AND MANUFACTURING METHOD THEREOF

Abstract

A diffraction light guide plate having excellent thickness uniformity and flatness, and having low haze, and excellent mechanical properties such as pencil hardness and strength at the same time, and a method for manufacturing the diffraction light guide plate.

Claims

1. A diffraction light guide plate comprising an optical layer in which a diffraction grating pattern is formed on one surface thereof, wherein the diffraction grating pattern is formed in an integrated structure without an interface on the one surface of the optical layer, and wherein a difference in refractive index between the diffraction grating pattern and the one surface of the optical layer is 0.01 or less.

2. The diffraction light guide plate of claim 1, wherein the diffraction grating pattern and the one surface of the optical layer have a refractive index of 1.65 or more, respectively.

3. The diffraction light guide plate of claim 1, wherein the optical layer on which the diffraction grating pattern is formed is a continuous phase of a polymer containing an episulfide compound and a thiol compound.

4. The diffraction light guide plate of claim 3, wherein the episulfide compound is one or more selected from the group consisting of bis(2,3-epithiopropyl)sulfide, bis(2,3-epithiopropyl)disulfide, bis(2,3-epithiopropyl)trisulfide, bis(2,3-epithiopropylthio)methane, 1,2-bis(2,3-epithiopropylthio)ethane, 1,3-bis(2,3-epithiopropylthio)propane, 1,2-bis(2,3-epithiopropylthio)propane, 1,4-bis(2,3-epithiopropylthio)butane, and bis(2,3-epithiopropylthioethyl)sulfide.

5. The diffraction light guide plate of claim 3, wherein the thiol compound is one or more selected from the group consisting of m-xylylenedithiol, p-xylylenedithiol, o-xylylenedithiol, 2,2′-thiodiethanethiol, pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), and 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane.

6. The diffraction light guide plate of claim 3, wherein the continuous phase of the polymer further includes an isocyanate compound.

7. The diffraction light guide plate of claim 1, wherein a thickness of the diffraction light guide plate is 0.1 to 10 mm.

8. The diffraction light guide plate of claim 1, wherein the diffraction grating pattern includes one or more pattern units, and a pitch between the pattern units is 0.1 to 1 μm, and a height of the pattern units is 0.1 to 1 μm.

9. The diffraction light guide plate of claim 1, wherein a warpage of the diffraction light guide plate is 100 μm or less, a haze of the diffraction light guide plate is 4.0% or less, a pencil hardness of the diffraction light guide plate is HB or more, and a thickness deviation of the diffraction light guide plate is 3.0% or less.

10. The diffraction light guide plate of claim 1, wherein the diffraction light guide plate is for a diffraction light guide lens of a wearable device.

11. A method for manufacturing a diffraction light guide plate comprising: a preparing a mold apparatus including a flat-plate lower substrate, a flat-plate upper substrate, a buffer spacer positioned between the flat-plate lower substrate and the flat-plate upper substrate, and a template which has a diffraction grating pattern engraved thereon and is included in the flat-plate lower substrate or the flat-plate upper substrate, wherein a molding space is partitioned by the buffer spacer; a buffering a curable composition in the molding space; and a compressing the curable composition under a load of the flat-plate upper substrate and curing the curable composition, wherein the step of compressing the curable composition under a load of the flat-plate upper substrate and curing the curable composition is carried out so as to satisfy the following Equation 1.
{(Load of flat-plate upper substrate+Curing shrinkage force of curable composition)×0.95}≤Compressive stress of buffer spacer≤{(load of flat-plate upper substrate+curing shrinkage force of curable composition)×1.05}.  Equation 1

12. The method for manufacturing the diffraction light guide plate of claim 11, wherein a flexural elastic modulus of the flat-plate lower substrate and the flat-plate upper substrate is 3 GPa or more, respectively.

13. The method for manufacturing the diffraction light guide plate of claim 11, wherein the template on which the diffraction grating pattern is engraved has a flexural elastic modulus of 1 to 20 GPa.

14. The method for manufacturing the diffraction light guide plate of claim 11, wherein the flat-plate lower substrate and the flat-plate upper substrate has a surface flatness of 5 μm or less, respectively.

15. The method for manufacturing the diffraction light guide plate of claim 11, wherein the buffer spacer has a compressive elastic modulus of 0.1 to 10 MPa.

16. The method for manufacturing the diffraction light guide plate of claim 11, herein the buffer spacer has a laminated structure comprising an inelastic layer and an elastic layer, a laminated structure comprising an elastic layer provided between inelastic layers, or a laminated structure comprising an inelastic layer provided between elastic layers.

17. The method for manufacturing the diffraction light guide plate of claim 11, wherein the curable composition has a curing shrinkage rate of 15% or less.

18. The method for manufacturing the diffraction light guide plate of claim 11, wherein the curable composition contains an episulfide compound and a thiol compound.

19. The method for manufacturing the diffraction light guide plate of claim 18, wherein the episulfide compound is one or more selected from the group consisting of bis(2,3-epithiopropyl)sulfide, bis(2,3-epithiopropyl)disulfide, bis(2,3-epithiopropyl)trisulfide, bis(2,3-epithiopropylthio)methane, 1,2-bis(2,3-epithiopropylthio)ethane, 1,3-bis(2,3-epithiopropylthio)propane, 1,2-bis(2,3-epithiopropylthio)propane, 1,4-bis(2,3-epithiopropylthio)butane, and bis(2,3-epithiopropylthioethyl)sulfide.

20. The method for manufacturing the diffraction light guide plate of claim 18, wherein the thiol compound is one or more selected from the group consisting of m-xylylenedithiol, p-xylylenedithiol, o-xylylenedithiol, 2,2′-thiodiethanethiol, pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), and 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane.

21. The method for manufacturing the diffraction light guide plate of claim 18, wherein the curable composition further includes an isocyanate compound.

Description

DESCRIPTION OF DRAWINGS

[0108] FIG. 1 is a schematic illustration showing a cross section view of an optical layer included in a diffraction light guide plate according to an exemplary embodiment of the present disclosure.

[0109] FIG. 2 is a schematic illustration showing a cross section view of a mold apparatus in a step of curing a curable composition of the method of manufacturing a diffractive light guide plate according to another exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

[0110] Hereinafter, the present disclosure will be described in more detail by way of the following examples. However, these examples are provided for illustrative purposes only and are not intended to limit the scope of the present disclosure.

Preparation Example: Preparation of Curable Composition

[0111] A curable composition containing 88.5 parts by weight pf bis(2,3-epithiopropyl)disulfide, 6.5 parts by weight of 2,2′-thiodiethanethiol, 5.0 parts by weight of isophorone diisocyanate and 0.07 parts by weight of tetrabutylphosphonium bromide was prepared.

[0112] The curing shrinkage force of the prepared curable composition was 2.00×10.sup.−4 N/mm.sup.2 as a result of measuring by the above-mentioned method of measuring the curing shrinkage force.

Example 1

[0113] As a lower substrate, a glass substrate having a flexural elastic modulus of 70 GPa, a surface flatness of 0.5 μm, a thickness of 30 mm, and a diameter of 200 mm was prepared, and a template (flexural elastic modulus: 3 GPa) in which a diffraction grating pattern was engraved was attached to the lower substrate. At this time, it was attached so that the circular center of the lower substrate and the circular center of the template are in contact, and the template was polyethylene terephthalate (PET) having a diameter of 150 mm and a thickness of 200 μm, and the engraved diffraction grating pattern had a pitch of 405 nm and a depth of 500 nm.

[0114] Thereafter, a buffer spacer made of silicon having a compressive elastic modulus of 1.0 MPa, a height of 1,007 μm, and a cross-sectional area of 10×10 mm.sup.2 was provided at 120° intervals to contact the circumference of the lower substrate, thus forming a molding space, and then the curable composition prepared according to the Preparation Example was buffered in the molding space using a glass substrate having a flexural elastic modulus of 70 GPa, a load of 8.2 N, a diameter of 200 mm, and a surface flatness of 0.5 μm as an upper substrate.

[0115] Further, the curable composition was placed in a convection oven (Jeio Tech), allowed to stand at room temperature for 2 hours, and then the temperature rising rate was set to 1° C./min, and then heat-cured for 2 hours at 45° C., for 2 hours at 60° C., for 2 hours at 75° C., and at 90° C. for 4 hours to prepare a diffraction light guide plate having a thickness of 0.8 mm.

Example 2

[0116] The diffraction light guide plate was manufactured in the same manner as in Example 1, except that the template in which the diffraction grating pattern was engraved was attached to the upper substrate rather than the lower substrate.

Example 3

[0117] The diffraction light guide plate was manufactured in the same manner as in Example 1, except that the height of the spacer is 427 μm and the template in which the diffraction grating pattern was engraved was attached to the upper substrate rather than the lower substrate.

Comparative Example 1

[0118] A glass substrate having a flexural elastic modulus of 70 GPa, a surface flatness of 0.5 μm, a thickness of 30 mm, and a diameter of 200 mm was used as the lower substrate, and a buffer spacer made of silicon having a compressive elastic modulus of 1.0 MPa, a height of 805 μm, and a cross-sectional area of 10×10 mm.sup.2 was provided at 120° intervals so as to be contact with the circumference of the lower substrate, thus forming a molding space. Then, the curable composition prepared according to the Preparation Example was injected into the molding space, and then the curable composition using a glass substrate having a flexural elastic modulus of 70 GPa, a load of 8.2 N, a diameter of 200 mm, and a surface flatness of 0.5 μm was used as an upper substrate, so that the curable composition was buffered in the molding space.

[0119] Further, the curable composition was placed in a convection oven (Jeio Tech), allowed to stand at room temperature for 2 hours, and then the temperature rising rate was set to 1° C./min, and then heat-cured at 45° C. for 2 hours, at 60° C. for 2 hours, at 75° C. for 2 hours, and at 90° C. for 4 hours to prepare a plastic substrate.

[0120] The imprint resin composition (refractive index 1.70) containing 8.3 parts by weight of zirconia particles having a particle diameter of 20 nm, 8.3 parts by weight of dipentaerythritol hexaacrylate (DPHA), 83 parts by weight of butyl carbitol acetate and 0.4 parts by weight of ethyl (2,4,6-trimethylbinzoyl)phenylphosphinate was coated onto the plastic substrate and dried to form an imprint resin layer having a thickness of 1 μm. Then, a template (diameter 150 mm, thickness 200 μm, polyethylene terephthalate) in which a diffraction grating pattern having a pitch of 405 nm and a depth of 1 μm was engraved was pressed on the imprint resin layer applied at a temperature of 40° C. and a pressure of 20 bar to form a diffraction grating, which was then cured by irradiating with UV (360 nm light source) of 1000 mJ/cm2 to prepare a diffraction light guide plate having a thickness of 0.8 mm, and cut into a rectangular shape of 6×5 cm.

[0121] Evaluation

[0122] Measurement of Thickness Deviation

[0123] The thickness deviation of the diffraction light guide plates of Examples and Comparative Examples was calculated using the following General Formula 1, and the results are shown in Table 1 below.

Thickness deviation (%)=(Maximum deviation/Average thickness)×100  General Formula 1

[0124] Specifically, the thickness of the diffraction light guide plate was measured as follows. The maximum thickness or the minimum thickness was measured by a contact measuring method using Mitsutoyo Digimatic Thickness Gauge 547-401 under an atmosphere of 25° C. and 50 RH %. Also, the average value of the thickness measured at an interval of 22.5 degrees with a radius of 10 mm from an arbitrary point of the test piece as the origin was measured as the average thickness.

[0125] Measurement of Warpage

[0126] A test piece of a rectangular region of a major axis 600 mm and a minor axis 400 mm for the diffraction light guide plates of Examples and Comparative Examples was prepared, and warpage was calculated using the following General Formula 2, and the results are shown in Table 1 below.

Warpage=Maximum deviation between center surface and reference surface−Minimum deviation between center surface and reference surface  General Formula 2

[0127] The center surface can be derived by using a non-contact measuring method using an OWTM (Optical Wafer Thickness Measurement System) (Fiberpro) under an atmosphere of 25° C. and 50 RH %, and measuring the thickness of the diffraction light guide plate and the distance between the reference optical body installed under the diffraction light guide plate and the diffraction light guide plate. Meanwhile, the reference surface may be calculated using a least squares fit with respect to the center surface.

[0128] Measurement of Haze

[0129] Haze of the diffraction light guide plates of Examples and Comparative Examples was measured according to ASTM D-1003, and the results are shown in Table 1 below.

[0130] Measurement of Pencil Hardness

[0131] A pencil was set on the surface of the diffractive light guide plates of Examples and Comparative Examples at an angle of 45° under a load of 0.5 kg, and the surface was scratched for each pencil hardness. Whether the test piece was scratched or not was determined with the naked eye, and the maximum pencil hardness that did not cause scratches was measured and shown in Table 1 below.

TABLE-US-00001 TABLE 1 Comparative Example 1 Example 2 Example 3 Example 1 Thickness 2.1 2.2 2.2 2.1 deviation (%) Warpage (μm) 28 24 24 65 Haze (%) 1.4 1.55 1.58 4.2 Pencil hardness 2H 2H 2H 6B

[0132] According to Table 1 above, it was confirmed that the diffraction light guide plate of Examples including the optical layer having the diffraction grating pattern formed on one surface thereof exhibited remarkably excellent pencil hardness as compared with Comparative Example where there was an interface between the plastic substrate and the diffraction grating pattern. In addition, it can be predicted that since the Examples did not contain inorganic particles, the haze was significantly lower and thus the visibility was high as compared with Comparative Example containing inorganic particles. Furthermore, it was confirmed that the warpage of the Examples was significantly lower than that of Comparative Example.

TABLE-US-00002 DESCRIPTION OF REFERENCE NUMBERS 200: diffraction grating pattern 300: optical layer 400: pattern unit 501: flat-plate lower substrate 502: flat-plate upper substrate 503: buffer spacer 504: template having diffraction grating pattern 600: curable composition