Resin composition for optical material and optical film comprising the same

Abstract

The resin composition for an optical material according to the present invention has features that it can implement a low retardation value during the preparation of an optical film, by using a polycarbonate composition satisfying a specific condition as a retardation-adjusting agent while using polymethyl methacrylate not containing a monomer having a cyclic structure at the main chain of the polymer.

Claims

1. A resin composition for optical material, comprising 1) 90% to 99% by weight of polymethyl methacrylate; and 2) 1% to 10% by weight of polycarbonate, wherein the polymethyl methacrylate includes methyl acrylate, and wherein the polymethyl methacrylate does not include a monomer having a cyclic structure, the polymethyl methacrylate has a glass transition temperature of 100 C. or more and less than 120 C. the polycarbonate has a glass transition temperature of 125 C. or more and less than 135 C., and the glass transition temperature difference between the polymethyl methacrylate and the polycarbonate is less than 20 C.

2. The resin composition for optical material according to claim 1, wherein the polymethyl methacrylate has a glass transition temperature of 110 C. or more and 117 C. or less.

3. The resin composition for optical material according to claim 1, wherein the polymethyl methacrylate has a weight average molecular weight of 100,000 to 160,000.

4. An optical film comprising the resin composition for optical material according to claim 1.

5. The optical film according to claim 4, wherein the optical film is prepared by biaxially stretching the film produced from the resin composition for optical material by 1.5 times to 2.5 times in the machine direction (MD) and by 1.5 times to 3.0 times in the transverse direction (TD).

6. The optical film according to claim 5, wherein the ratio of the MI) stretching magnification factor and the TD stretching magnification factor (TD stretch ratio/MD stretch ratio) is 1.05 or more and 1.70 or less.

7. The optical film according to claim 5, wherein the stretching is carried out at a temperature of 10 C. to 30 C. higher than the glass transition temperature of the polymethyl methacrylate.

8. The optical film according to claim 4, wherein the temperature of thermal shrinkage (TTS) in the MD direction and the TI'S in the TD direction of the optical film are respectively 100 C. to 120 C.

9. The optical film according to claim 4, wherein the optical film has an impact energy value of the following Mathematical Equation 1 of 400 kN.Math.m/m.sup.3 or more:
Impact energy=(gravitational accelerationweight of falling-ballheight of falling-ball)/(thickness of optical filmarea of optical film)[Mathematical Equation 1] wherein the weight of falling ball is 16.4 grams, the thickness of optical film is from 10 m to 100 m, and the area of optical film is about 20 mm by about 200 mm.

10. The optical film according to claim 4, wherein the optical film exhibits a retardation of Mathematical Equations 2 and 3:
0 nmRin10 nm (Rin=(nxny)d)[Mathematical Equation 2]
10 nmRth10 nm (Rth=((nx+ny)/2nz)d)[Mathematical Equation 3] in Mathematical Equations 2 and 3, nx, ny, and nz represent refractive indices in a x-axis direction, a y-axis direction and a z-axis direction, respectively, and d means a thickness (nm) of the optical film.

11. A polarizing plate comprising the optical film according to claim 4.

12. An optical film comprising a resin composition for optical material, wherein the resin composition comprises: 1) 90% to 99% by weight of polymethyl methacrylate; and 2) 1% to 10% by weight of polycarbonate, wherein the polymethyl methacrylate includes methyl acrylate, and wherein the polymethyl methacrylate does not include a monomer having a cyclic, the polymethyl methacrylate has a glass transition temperature of 100 C. or more and less than 120 C., the polycarbonate has a glass transition temperature of 125 C. or more and less than 135 C., and the glass transition temperature difference between the polymethyl methacrylate and the polycarbonate is less than 20 C., wherein the optical film comprises the resin composition, and wherein the optical film exhibits a retardation of Mathematical Equations 2 and 3:
0 nmRin10 nm (Rin=(nxny)d)[Mathematical Equation 2]
10 nmRth10 nm (Rth=((nx+ny)/2nz)d)[Mathematical Equation 3] in Mathematical Equations 2 and 3, nx, ny, and nz represent refractive indices in an x-axis direction, a y-axis direction and a z-axis direction, respectively, and d means a thickness (nm) of the optical film.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The FIGURE schematically shows an example in which a protective film according to the present invention is used.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) Hereinafter, preferred examples of the present invention will be described in order to facilitate understanding of the present invention. However, the examples below are provided only for a better understanding of the present invention, and the present invention is not limited thereby.

Preparation Example 1: Polymethyl Methacrylate

(3) 1,000 g of a monomer mixture of 98 wt % methyl methacrylate and 2 wt % methyl acrylate was added to a 5 liter reactor to which 2,000 g of distilled water, 8.4 g of 5% polyvinyl alcohol solution (POVAL PVA217, Kuraray Co.) and 0.1 g of boric acid as a dispersion assistant were added and dissolved. Here, 2.5 g of n-octyl mercaptane as a chain transfer agent and 1.5 g of 2,2-azobisisobutyronitrile as a polymerization initiator were added and dispersed in water while stirring at 400 rpm to obtain a suspension. The temperature was raised to 80 C. and polymerized for 90 minutes, and then cooled to 30 C. The obtained beads were washed with distilled water, dehydrated, and then dried to prepare a polymethyl methacrylate resin. As a result of the measurement of the glass transition temperature and molecular weight of the produced resin, the glass transition temperature was 116 C. and the weight average molecular weight was 120,000. The glass transition temperature was measured using a differential scanning calorimeter (DSC) manufactured by Mettler Toledo under conditions of temperature raising rate of 10 C./min.

Preparation Example 2: Polycarbonate

(4) A polycarbonate resin having a glass transition temperature of 134 C. (UF 1004 A, LG Chem Ltd., hereinafter referred to as PC-1), a polycarbonate resin having a glass transition temperature of 143 C. (LUPOY 1080 DVD, LG Chem Ltd., hereinafter referred to as PC-2) and a polycarbonate resin having a glass transition temperature of 148 C. (UF 1004C, LG Chem Ltd., hereinafter referred to as PC-3) were used as the polycarbonate.

Example 1

(5) 95 wt % of polymethyl methacrylate prepared in Preparation Example 1 and 5 wt % of PC-1 were mixed, and an antioxidant (Irganox 1010, manufactured by BASF) was formulated in an amount of 0.5 phr, dry-blended, and the mixture was compounded in a twin-screw extruder to prepare a resin composition. The resin composition was melted at 265 C. and extruded in the form of a sheet through a T-die to obtain a sheet of 180 um.

Comparative Example 1

(6) A sheet was obtained in the same manner as in Example 1, except that 85 wt % of polymethyl methacrylate prepared in Preparation Example 1 and 15 wt % of PC-1 were mixed.

Comparative Example 2

(7) A sheet was obtained in the same manner as in Example 1, except that 95 wt % of polymethyl methacrylate prepared in Preparation Example 1 and 5 wt % of PC-2 were mixed.

Comparative Example 3

(8) A sheet was obtained in the same manner as in Example 1, except that 95 wt % of polymethyl methacrylate prepared in Preparation Example 1 and 5 wt % of PC-3 were mixed.

Comparative Example 4

(9) An antioxidant (Irganox 1010, manufactured by BASF) was formulated into the polymethyl methacrylate prepared in Preparation Example 1 in an amount of 0.5 phr, dry-blended and compounded with a twin-screw extruder to prepare a resin composition. The resin composition was melted at 265 C. and extruded in the form of a sheet through a T-die to obtain a sheet of 180 um.

Experimental Example 1

(10) The properties of the sheets obtained in Examples and Comparative Examples were evaluated as follows.

(11) 1) Glass transition temperature difference (Tg): The difference between the glass transition temperature of polycarbonate (PC-1, PC-2 or PC-3) and the glass transition temperature of polymethyl methacrylate was calculated.

(12) 2) Total light transmittance (Tt): Total light transmittance of the sheet was measured using a turbidimeter.

(13) 3) Haze: Measured using Hazemeter HM-150.

(14) The results are shown in Table 1 below.

(15) TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Comparative Ex. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Composition Polymethyl 95 85 95 95 100 of resin methacrylate composition PC-1 5 15 (wt %) PC-2 5 PC-3 5 Glass transition 19 19 32 29 temperature difference( C.) Optical Tt(%) 92 81 74 74 92 properties Haze(%) 0.3 5.2 6.6 6.8 0.2

(16) As shown in Table 1, in Example 1, the glass transition temperature difference was less than 20 C. and the content of polycarbonate was 10 wt % or less. Thereby, the transparent sheet having excellent total light transmittance and haze value was prepared. Meanwhile, in Comparative Example 1, the glass transition temperature difference was less than 20 C., but the content of polycarbonate was 10 wt % or more. Thereby, an opaque sheet having a low total light transmittance and a large haze value was prepared. In Comparative Examples 2 and 3, the content of polycarbonate was 10 wt % or less, but the glass transition temperature difference was 20 C. or more. Thereby, an opaque sheet was prepared. In Comparative Example 4, a transparent sheet having good total light transmittance and haze value was produced without adding a polycarbonate resin.

Experimental Example 2

(17) In Experimental Example 1, the following experiments were carried out using the sheets of Example 1 and Comparative Example 4 in which transparent sheets were produced.

(18) The sheet of Example 1 was biaxially stretched at a stretching temperature and a stretching magnification as described in the following Table 2 to produce optical films (Examples 2 to 7). Further, the sheet of Comparative Example 4 was biaxially stretched at a stretching temperature and a stretching magnification as described in Table 2 below to prepare an optical film (Comparative Example 5). For comparison, the sheet of Example 1 which was not biaxially stretched was set as Comparative Example 6.

(19) The optical films thus prepared were evaluated for their properties as described below.

(20) 1) TTS (Temperature of Thermal Shrinkage): A sample of optical film was measured at a size of 804.5 mm and measured using a TA TMA (Q400) instrument. Specifically, when the temperature was applied under the conditions of a temperature raising rate of 10 C./min and a load of 0.02 N, the temperature (tangent slope of 0) of the inflection point at which the sample starts shrinking after expansion in the MD and TD directions, respectively.

(21) 2) Retardation: The retardation was measured at a wavelength of 550 nm using a birefringence meter (AxoScan, Axometrics). The in-plane retardation Rin and the thickness direction retardation Rth are calculated as the measured values of a refractive index nx in the x-axis direction, a refractive index ny in the y-axis direction, and a refractive index nz in the z-axis direction.
Rin (nm)=(nxny)d
Rth (nm)=((nx+ny)/2nz)d

(22) wherein, d means the thickness (nm) of the optical film.

(23) 3) Heat shrinkage: A sample for optical film was measured with a size of 20200 mm, and then the length of the sample changed relative to its initial length after being maintained in an oven at 85 C. for 100 hours was measured. The changed length was taken as the value of dimensional change as a percentage value relative to the initial length.

(24) 4) Impact strength (kN.Math.m/m.sup.3): The thickness of the optical film was measured, and the film was placed in a circular frame having a diameter of 76 mm. Then, the film was allowed to fall freely while changing its height using a circular ball (iron beads) weighing 16.4 g, and it was confirmed whether the optical film was broken. The breakage of the optical film was judged by whether the film withstands without being destroyed more than 8 times when it was allowed to fall freely 10 times at the same height. The impact energy value of the optical film was calculated according to the following equation using the maximum height withstanding at least 8 times.
Impact energy=(gravitational accelerationweight of falling-ballheight of falling-ball)/(thickness of polarizing plate protective filmarea of film)

(25) The results are shown in Table 2 below.

(26) TABLE-US-00002 TABLE 2 Stretching Thermal Stretching magnification TTS shrinkage Impact Resin temperature (MD/TD) (MD/TD) Rin/Rth (MD/TD) Energy Unit composition C. times C. nm/nm % kN .Math. m/m.sup.3 Ex. 2 Ex. 1 131 1.8 2.6 105/103 1.8/2.4 0.43/0.53 418 Ex. 3 131 1.7 3.0 108/99 3.2/2.8 0.38/0.91 452 Ex. 4 136 1.8 2.6 108/106 1.5/2.1 0.41/0.50 360 Ex. 5 136 1.7 3.0 109/102 2.2/2.5 0.37/0.72 401 Ex. 6 126 1.8 2.6 99/97 2.6/2.3 0.82/0.96 474 Ex. 7 126 1.7 3.0 101/94 3.4/1.2 0.78/1.18 493 Comparative Comparative 131 1.8 2.6 105/104 2.1/18.2 0.48/0.61 409 Ex. 5 Ex. 4 Comparative Ex. 1 1.2/1.9 0.01/0.00 107 Ex. 6

(27) As shown in Table 2, when the resin composition of Example 1 was used, it was confirmed that it exhibited a low retardation property under any stretching conditions. On the other hand, when the optical film was prepared by using only polymethyl methacrylate as in the resin composition of Comparative Example 4, it was confirmed that the retardation value Rth was high. Moreover, when biaxial stretching was not performed as in Comparative Example 6, it was confirmed that the impact energy was low.

(28) Further, when comparing Example 2 and Example 4, it was confirmed that as the stretching temperature was increased at the same stretching magnification, an optical film exhibiting a high TTS value and less dimensional change could be produced. On the other hand, in the case of Examples 3 and 5 where the MD stretching magnification and the TD stretching magnification were large under the same stretching temperature condition, the TTS value in the TD direction with a large stretching magnification becomes small and the heat shrinkage ratio becomes large, thereby curl or bending could be occurred due to shrinkage during preparation of the polarizing plate. In addition, it was confirmed that, in the case of Example 6 and Example 7, in which the stretching temperature was low at the same stretching magnification, the TTS value also decreased and the heat shrinkage ratio also increased.