METHOD FOR MANUFACTURING POLARIZING PLATE

Abstract

Provided is a method for manufacturing a polarizing plate, comprising a step of irradiating an optical laminate with ultraviolet rays having an emission wavelength band of 380 nm to 410 nm. The optical laminate sequentially comprises a first base film, a first adhesive layer, a linear polarizer, a second adhesive layer, a second base film and a reverse dispersion liquid crystal layer. The first adhesive layer and the second adhesive layer each comprise a photosensitizer for initiating a curing reaction in a wavelength band of 350 nm to 410 nm, and the ultraviolet rays are irradiated on the first base film side of the optical laminate.

Claims

1. A method for manufacturing a polarizing plate, comprising a step of irradiating an optical laminate with ultraviolet rays having an emission wavelength band of 380 nm to 410 nm, wherein: the optical laminate sequentially comprises a first base film, a first adhesive layer, a linear polarizer, a second adhesive layer, a second base film and a reverse dispersion liquid crystal layer; the first adhesive layer and the second adhesive layer each comprise a photosensitizer for initiating a curing reaction in a wavelength band of 350 nm to 410 nm; and the ultraviolet rays are irradiated on the first base film side of the optical laminate.

2. The method according to claim 1, wherein one side of the first adhesive layer is in contact with the first base film and the other side of the first adhesive layer is in contact with the linear polarizer.

3. The method according to claim 1, wherein one side of the second adhesive layer is in contact with the second base film and the other side of the second adhesive layer is in contact with the linear polarizer.

4. The method according to claim 1, wherein the photosensitizer absorbs light in a wavelength band of 350 nm to 410 nm.

5. The method according to claim 1, wherein the first adhesive layer and the second adhesive layer each comprise an ultraviolet curable resin, and the photosensitizer is present in a ratio within a range of 1 wt % to 5 wt %.

6. The method according to claim 1, wherein the first adhesive layer and the second adhesive layer are cured by irradiation with the ultraviolet rays.

7. The method according to claim 1, wherein the first base film comprises an ultraviolet absorber.

8. The method according to claim 7, wherein the first base film has transmittance of 65% or more at a wavelength of 400 nm.

9. The method according to claim 7, wherein the first base film has transmittance of less than 10% at a wavelength of 380 nm.

10. The method according to claim 1, wherein the second base film, on which the reverse dispersion liquid crystal layer is formed, has transmittance of less than 40% at a wavelength of 400 nm.

11. The method according to claim 1, wherein the second base film, on which the reverse dispersion liquid crystal layer is formed, has transmittance of less than 3% at a wavelength of 380 nm.

12. The method according to claim 1, wherein the polarizing plate further comprises a +C plate formed on one side of the reverse dispersion liquid crystal layer.

13. The method according to claim 1, wherein the light quantity of the ultraviolet rays irradiated on the optical laminate is in a range of 200 mJ to 400 mJ.

14. The method according to claim 1, further comprising a step of forming a pressure-sensitive adhesive layer on the reverse dispersion liquid crystal layer side after irradiating the optical laminate with ultraviolet rays.

15. The method according to claim 1, wherein the polarizing plate manufactured by the method has an adhesive force of 1N or more as immediately measured after submerging it in water at a temperature of 60° C. for 6 hours and then taking it out.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0069] FIG. 1 is a diagram for explaining a method for manufacturing a polarizing plate of the present application.

[0070] FIG. 2 illustratively shows an organic light emitting display device.

EXAMPLES

[0071] Hereinafter, the present application will be described in detail through examples according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited to the examples given below.

Example 1

[0072] A PVA-based linear polarizer was manufactured by a wet stretching method (using the product name M6000L base material from Nippon Gohsei).

[0073] A first adhesive layer having a thickness of 2 μm in an uncured state was formed on one side of a first base film (UZ TAC, Fuji product) having a thickness of 60 μm. The first base film comprises an ultraviolet absorber and has transmittance of about 77% at a wavelength of 400 nm and transmittance of about 4% at a wavelength of 380 nm. The first adhesive layer comprises a photosensitizer (DETX-S manufacturer: IHT), which initiates a curing reaction in a wavelength band of 350 nm to 410 nm to an epoxy-based UV curable resin, in an amount of 2 wt %.

[0074] Reverse dispersion liquid crystals (LG Chemical) were coated on one side of a second base film (Zero Retardation TAC, Konica product) having a thickness of 40 μm to form a reverse dispersion liquid crystal layer having a planar phase difference value of 142 nm for a wavelength of 550 nm. The second base film on which the reverse dispersion liquid crystal layer has been formed has transmittance of about 27% at a wavelength of 400 nm and transmittance of about 0.7% at a wavelength of 380 nm. A second adhesive layer having a thickness of 2 μm in an uncured state was formed on the opposite side of the second base film on which the reverse dispersion liquid crystal layer was formed. The second adhesive layer comprises a photosensitizer (DETX-S manufacturer: IHT), which initiates a curing reaction in a wavelength band of 350 nm to 410 nm to an epoxy-based UV curable resin, in an amount of 2 wt %.

[0075] The first base film was attached to one side of the linear polarizer via the first adhesive layer. The second base film on which the reverse dispersion liquid crystal layer was formed was attached to the side of the linear polarizer to which the first base film was not attached via the second adhesive layer. At this time, they were attached such that the angle formed by the light absorption axis of the linear polarizer and the slow axis of the reverse dispersion liquid crystal layer was 45 degrees.

[0076] Through the above process, an optical laminate comprising the first base film, the first adhesive layer, the linear polarizer, the second adhesive layer, the second base film and the reverse dispersion liquid crystal layer sequentially was provided. A polarizing plate was manufactured by irradiating the first base film side of the optical laminate with ultraviolet rays having a main emission wavelength of 380 nm to 410 nm at a light quantity of 250 mJ by using ultraviolet light emitting equipment (electrodeless type UV curing machine) and curing the first adhesive layer and the second adhesive layer.

Comparative Example 1

[0077] A polarizing plate was manufactured in the same manner as in Example 1, except that the first adhesive layer and the second adhesive layer were cured by the following method. With regard to the first adhesive layer and the second adhesive layer of Comparative Example 1, adhesive layers having a thickness of 100 nm in an uncured state were formed by using a water-based adhesive (product name: Z3, manufacturer: LG Chemical) containing a polyvinyl alcohol resin (there was no photosensitizer in the water-based adhesive), and cured by a thermosetting method (90° C., 2 minutes).

Comparative Example 2

[0078] A polarizing plate was manufactured in the same manner as in Example 1, except that the ultraviolet rays were irradiated to the reverse dispersion liquid crystal layer side instead of the first base film side in Example 1.

Comparative Example 3

[0079] A polarizing plate was manufactured in the same manner as in Example 1, except that the ultraviolet rays were irradiated to the reverse dispersion liquid crystal layer side instead of the first base film side in Example 1, and the light quantity of ultraviolet rays was changed to 900 mJ.

Measurement Example 1. Adhesive Force Measurement

[0080] The manufactured polarizing plate sample was cut to a size of 20 mm×150 mm and the surface to be peeled is placed down and attached to the peeling machine substrate without foaming with a double-sided tape, and then the film opposite to the PVA was peeled off by 90 degrees at a rate of 300 mm/min to measure the adhesive force (unit N/20 mm). The adhesive force measurement equipment was a TA.XT texture analyzer. In Table 1, the initial adhesive force means the adhesive force measured at a temperature of 25° C.

Evaluation Example 1. Water Resistance Evaluation

[0081] The manufactured polarizing plate was submerged at 60° C. in water for 6 hours and then taken out, and the adhesive force was immediately measured to evaluate water resistance.

Evaluation Example 2. Evaluation of Curing Degree

[0082] For the manufactured polarizing plate, the cured adhesive surface was rubbed by hand, and the curing degree was evaluated based on the following criteria.

[0083] ⊚: instant curing (state where adhesive is completely cured and solidified)

[0084] Δ: incomplete curing (state where adhesive is not completely cured and sticky)

[0085] X: uncured (state where adhesive is not cured and flows down into the liquid)

TABLE-US-00001 TABLE 1 Comparative Example Classification Example 1 1 2 3 Curing method UV curing Thermosetting UV curing Adhesive UV adhesive Water-based UV adhesive adhesive UV light quantity 250 mJ — 250 mJ 900 mJ UV irradiation surface Upper base — Lower base material material (UZ) (ZRT surface) Curing degree ⊚ ⊚ X Δ Adhesive force Top (UZ surface) 3.0 2.7 Not measured 0.2 (Initial) Bottom (ZRT surface) 3.8 3.6 due to uncured 0.3 Adhesive force Top (UZ surface) 4.8 0.3 — — (Water resistance) Bottom (ZRT surface) 5.7 0.4 — —

[0086] As a result of the evaluation, in both of the UV adhesion and the water-based adhesion for Example 1 and Comparative Example 1, the initial adhesive force is in the same level as 1N or more, but in the water resistance evaluation, the adhesive force of Comparative Example 1 is reduced to less than 1N, so that it can be seen that it is vulnerable to water resistance.

[0087] With respect to Example 1 and Comparative Example 2, the bottom base material surface (ZRT+liquid crystal) of Comparative Example 2 has been irradiated with UV rays and the adhesive has not been sufficiently cured due to the low transmittance of the bottom base material surface in the wavelength range of 400 nm or less as compared to the top base material surface, and as shown in Comparative Example 3, even if the light quantity of UV rays is increased 3 times or more as compared to Example 1, it can be seen that the adhesive force is reduced due to incomplete curing.

TABLE-US-00002 Explanation of Reference Numerals 101: first base film 102: second base film 201: first adhesive layer 202: second adhesive layer 300: linear polarizer 400: reverse dispersion liquid crystal layer 1000: organic light emitting 2000: polarizing plate display panel