PREPARING METHOD OF BALL-SHAPED BEAD WITH HIGH

REFRACTION RATE

Technical Field

[1] The present invention relates to a method for the preparation of high refractive spherical beads and more particularly, it concerns a method of preparing high refractive spherical beads with excellent dispersion, light properties, UV stability, humidity resistance, thermal dimension stability, and weather resistance, which can effectively prevent bending or yellowing resulting from UV irradiation, heat emission of lamps, heat generated from large-scale LCDs, etc. due to its superior heat resistance and can be usefully applied to large-scale LCDs larger than 40 inches. Background Art

[2] Unlike CRT (cathoderay tube) or PDP (plasma display panel), LCD (liquid crystal display) cannot have luminescence for itself and thus, it requires BLU (black light unit) in order to realize back lightening. Currently, the BLU system used in 19 inch or smaller computers and monitors is an edge light type and its structure comprises a light guiding panel (LGP) where reflection patterns are printed in the center, a cold cathode fluorescent lamps located at the edges, a reflection sheet, diffusion sheet, and prism sheets as shown in Fig. 1.

[3] Further, the BLU system of medium or large-scale LCDs larger than 20 inches employs a direct type where several to tens of cold cathode fluorescent lamps (CCFL) are arranged on a line at the back side of a diffusion sheet as shown in Fig. 2, and the direct type BLU system improves uniformity and increases luminance when compared with the prior edge light type.

[4] Meanwhile, the direct type BLU system uses a extrusion diffusion plate of flat plate type wherein light diffusion agents (usually, spherical beads) which diffuse light and main resins of the diffusion plate are dispersed in the diffusion plate, and there are used anti-oxidants, fluorescent whitening agents, lubricants, etc. as other additives.

[5] As the resins of the prior 40-inch medium-, small-scale LCD backlight diffusion plates, acryl resins that have excellent light transmittance have been used and as light diffusion agents, low-refractive light diffusion agents such as silicon, polymethyl methacrylate (PMMA), etc. have been mostly used.

[6] However, large-scale backlight diffusion plates larger than 40 inches could not use the acryl resins which have poor heat resistance because calorific value increases as LCD size gets larger. Accordingly, PET, PETG, PC, and co-PET resins were used instead. Therefore, there is an increasing demand on high refractive spherical beads

suitable for the above-mentioned resins, and researches thereon are in need. Disclosure of Invention Technical Problem

[7] To solve the problems of the prior art as described in the above, it is an object of the present invention to provide a method of preparing high refractive spherical beads with excellent dispersion, light properties, UV stability, humidity resistance, thermal dimension stability, and weather resistance, which can effectively prevent bending or yellowing resulting from UV irradiation, heat emission of lamps, heat generated from large-scale LCDs, etc. due to their superior heat resistance and can be usefully applied to large-scale LCDs larger than 40 inches.

[8] It is another object of the invention to provide an LCD backlight diffusion plate and

LCD backlight unit which can be usefully applied to large-scale LCDs larger than 40 inches by preventing the heat generated from the large-scale LCDs due to its superior heat resistance, and an LCD to which they are applied. Technical Solution

[9] To achieve the aforementioned objects, the present invention provides a method of preparing high refractive spherical beads comprising:

[10] a) preparing an inorganic composite material by adding an inorganic base compound having the refraction index of at least 1.5 to the inside of an inorganic material having porous or hollow air void and reacting them;

[11] b) coating the inorganic composite material prepared in step a) with a coating agent; and

[12] c) drying the inorganic composite material coated in step b).

[13] Also, the invention provides an LCD backlight diffusion plate comprising a resin and the high refractive spherical beads prepared in the above method.

[14] Also, the invention provides an LCD backlight unit characterized in that the LCD backlight diffusion plate is applied thereto.

[15] Also, the invention provides an LCD characterized in that the LCD backlight unit is applied thereto. Advantageous Effects

[16] The high refractive spherical beads in accordance with the invention have excellent dispersion, light properties, UV stability, humidity resistance, thermal dimension stability, and weather resistance and in particular, they have superior heat resistance so that they can effectively prevent bending or yellowing resulting from UV irradiation, heat emission of lamps, heat generated from large-scale LCDs, etc. and they can be usefully applied to large-scale LCDs larger than 40 inches. Brief Description of the Drawings

[17] Fig. 1 shows an edge light type used in 19 inch or smaller computers and monitors in the prior art.

[18] Fig. 2 shows a direct BLU system of medium-, large-scale LCDs not smaller than

20 inches.

[19] Fig. 3 is a photo showing the upper side of a diffusion plate prepared in one embodiment of the present invention and a prior diffusion plate. Mode for the Invention

[20] The present invention is further described in detail.

[21] The terms used in the invention are to be appreciated in accordance with the context of the specification. The term air void in the specification refers to a condition where void space inside in a porous or hollow form is continuously kept without being filled with other impurities.

[22] The high refractive spherical beads of the present invention are characterized in that they are prepared by preparing an inorganic composite material by adding an inorganic base compound having the refraction index of at least 1.5 to the inside of an inorganic material having porous or hollow air void and reacting them, then coating the inorganic composite material with a coating agent, and drying it.

[23] The following will describe the method for the preparation of the high refractive spherical beads of the invention in detail.

[24] a) Preparation of Inorganic Composite Material

[25] This step is to prepare an inorganic composite material by adding an inorganic base compound having the refraction index of at least 1.5 to the inside of an inorganic material having porous or hollow air void and reacting them.

[26] The refraction index of the inorganic material having the porous or hollow air void used in the step can be adjusted by controlling the introduction rate of air void, and it is preferable to use inorganic materials into which air void in a porous or hollow form is introduced in an amount of 5 to 95 % by volume. If the air void is less than 5 % by volume, the refraction index is very slightly lowered and thus it is of no use. If it exceeds 95 % by volume, morphology stability remarkably decreases and it is thus difficult to keep the spherical shape of beads. Meanwhile, the maximum range of the introduction rate of the porous or hollow air void varies by the hardness of the inorganic materials to be used, and materials having high hardness such as silica enable the preparation of composite materials having the high introduction rate of the porous or hollow air void while not harming morphology stability.

[27] It is preferred that the inorganic materials having porous or hollow air void have a pore size of 10 to 100 nm and a particle size of 1.0 to 30 um. If the particle size is less than 1.0 um, it is difficult to obtain satisfactory improvement of front luminance and if

the particle size exceeds 30 urn, it is difficult to achieve sufficient light diffusion effects without impairing the front luminance.

[28] Examples of the commonly -used inorganic materials include silica, alumina, glass,

CaCO , talc, mica, BaSO , ZnO, CeO , TiO , iron oxide, etc. and their refraction index

3 4 2 2 can be lower than their original refraction index by the introduction of porous or hollow air void into the inorganic materials.

[29] For the introduction of the porous or hollow air void, any conventional methods can be utilized and for example, foaming method, sintering method, stretching method, extraction method, track etching method, solvent phase separation method, phase transformation method, optimum method, etc. can be suitably chosen and used according to the type of each inorganic material.

[30] The inorganic base compound having the refractive index of at least 1.5 used in this step is added to the inside of the inorganic material having porous or hollow air void and then reacted to prepare an inorganic composite material. Preferably, the amount of the base compound in the reaction is 18 to 25 % by weight of the inorganic composite material and the inorganic material having air void is comprised in an amount of 75 to 82 % by weight for the improvement of refraction index. A reaction solvent used in the reaction is preferably selected from the group consisting of water, ethanol, isopropyl and mixture thereof and most preferably, ethanol is used.

[31] The base compound is not limited to a special one as long as its refraction index is not less than 1.5 and preferably, the base compounds of TiO , ZnO, CaCO , ZrO ,

2 3 2

MgO, or Fe O are used, and more preferably, the base compounds of TiO , TiCl , TiCl , Ti[OC H ] , Ti[OCH CH(C H )(CH ) CH ] , Ti[OCH(CH ) ] , Ti(OCH CH CH ) , or

3 2 5 4 2 2 5 2 3 3 4 3 2 4 2 2 3 4

Ti[O(CH 2) 3CH 3] 4 are used.

[32] Preferably, the inorganic composite material prepared by the reaction of the base compound has a spherical shape and refraction index of at least 1.65, preferably 1.7. In the case that the shape is not sphere, luminance decrease is too severe to be used as an LCD backlight diffusion plate.

[33] b) Coating

[34] This step is to coat the inorganic composite material prepared in step a) with a coating agent and it endows the inorganic composite material with stability when mixed with resins.

[35] The coating agent used in the step is an amino silane, epoxy silane, alkyl silane, fatty acid or silicon oil, etc. Preferably, the amino silane is aminoethylaminopropy- ltrimethoxysilane, 3-aminopropyltriethoxysilane, aminoethylaminopropyltri- ethoxysilane, aminoethylaminopropyltrimethoxysilane, buthanol- preaminoethylaminopropyltrimethoxysilane, methoxy- preaminoethylaminopropyltrimethoxysilane or N-

2-(benzylamino)-ethyl-3-aminopropyltriethoxysilane, the epoxy silane is 3-glycidoxypropyltrimethoxysilane, the alkyl silane is triethoxysilane or trimethoxysilane, the fatty acid is oleic acid or stearic acid, and the silicon oil is methicon, dimethicon, or dimethiconol copolyol.

[36] The coating agent is preferably coated at the thickness of 1 to 200 nm onto the inorganic composite material and it is preferable to be coated so that it can have water repellency even when water and ethanol are mixed at the ratio of 9:1 by weight and boiled. The coating can be carried out by conventional coating methods.

[37] c) Drv

[38] This step is to dry the inorganic composite material coated with the coating agent in step b).

[39] The dry can be performed by conventional bead drying methods and preferably, vacuum drying is carried out at 80 to 130 ⁰ C and calcination step can be further carried out. The calcination is preferably carried out at the temperature of at least 800 ⁰ C and it is preferred that the moisture amount of the high refractive spherical beads after drying (after calcination, if necessary) is at most 0.5 % by weight.

[40] Preferably, the high refractive spherical beads of the present invention prepared as described above have a refractive index of at least 1.7 and an average particle diameter of 2 to 3 um, and a mega particle within the high refractive spherical beads is preferably at most 10 um. This invention enables the preparation of beads having spherical shape while having a refractive index of not less than 1.65, preferably 1.7, of which the preparation was impossible before.

[41] Further, the invention provides an LCD backlight diffusion plate characterized in that it comprises a resin and the high refractive spherical beads of the invention prepared as above and it can further comprise an additive such as an anti-oxidant, fluorescent whitening agent, lubricant, etc. in addition to the high refractive spherical beads and resin.

[42] The high refractive spherical beads are contained preferably in an amount of 0.1 to

20 % by weight and more preferably in an amount of 2 to 5 % by weight in the LCD backlight diffusion plate. If it deviates from the above ranges, extrusion can be difficult.

[43] For the resin, PET, PETG, PC, or co-PET can be used and it is contained preferably in an amount of 80 to 99.9 % by weight and more preferably, 95 to 98 % by weight in the LCD backlight diffusion plate. If the amount is less than 80 % by weight or exceeds 99.9 % by weight, extrusion can be difficult and luminance is decreased.

[44] In addition, the anti-oxidant, fluorescent whitening agent, lubricant, etc. can be contained in a suitable amount as desired.

[45] Further, the present invention provides an LCD backlight unit characterized in that

the LCD backlight diffusion plate as described is applied thereto and an LCD to which the LCD backlight unit is applied. It has excellent dispersion, light properties, UV stability, humidity resistance, thermal dimension stability, and weather resistance even when applied to large-scale LCDs larger than 40 and it can effectively prevent bending or yellowing resulting from UV irradiation, heat emission of lamps, heat generated from large-scale LCDs, etc. due to its superior heat resistance.

[46] For better understanding of the present invention, preferred examples follow. The following examples are intended to illustrate the invention more fully without limiting the scope of the invention.

[47] EXAMPLES

[48] Example 1

[49] After 30 mL of ethanol and 62.5 mL of TiCl were poured into a 500 mL-beaker in a glove box, they were mixed using a stirrer. 117 g of a porous silica having a pore size of 10 to 100 nm was added to this solution and evenly mixed using a kneading machine. This experiment was carried out in the glove box because the reactivity of TiCl is huge.

[50] Then, 2.2 L of water was poured into a 3 L-round bottom flask equipped with a stirrer, thermometer and nitrogen injector and pH was adjusted to 10 by the addition of ammonia hydroxide. After the powder mixed in the glove box above was added thereto and reacted at the temperature of 100 ⁰ C for 24 hours, the temperature was lowered to 6O ⁰ C.

[51] After 4 g of aminosilane and 20 mL of ethanol were poured into a 100 mL-beaker and stirred using a magnetic bar for 15 min., the reactant of which the temperature was lowered to 60 ⁰ C was added to the above reactant within the flask, which was then warmed up to 100 ⁰ C and reacted for 24 hours. After the completion of the reaction, the reaction product was filtered, washed with 1 L of water two times and vacuum dried at 100 ⁰ C thereby to prepare high refractive spherical beads.

[52] The high refractive spherical beads prepared as above exhibited an average particle diameter of 2 to 3 um and a mega particle size of not more than 10 um. Also, it was verified that the refractive index of the high refractive spherical beads was not less than 1.7.

[53] Example 2

[54] After 117 g of a porous silica having a pore size of 10 to 100 nm and 62.5 g of titanium isopropoxide (TTIP) were poured into a 500 mL-beaker in a glove box, they were evenly mixed using a kneading machine.

[55] Then, 2.2 L of water was poured into a 3 L-round bottom flask equipped with a stirrer, thermometer and nitrogen injector and pH was adjusted to 10 by the addition of ammonia hydroxide. After the powder mixed in the glove box above was added thereto

and reacted at the temperature of 100 ⁰ C for 24 hours, the temperature was lowered to 6O ⁰ C.

[56] After 4 g of epoxysilane and 20 mL of ethanol were poured into a 100 mL-beaker and stirred using a magnetic bar for 15 min., the reactant of which the temperature was lowered to 60 ⁰ C was added to the above reactant within the flask, which was then warmed up to 100 ⁰ C and reacted for 24 hours. After the completion of the reaction, the reaction product was filtered, washed with 1 L of water two times and vacuum dried at 100 ⁰ C thereby to prepare high refractive spherical beads. It was verified that the refractive index of the high refractive spherical beads prepared above was not less than 1.7.

[57] Example 3

[58] After 117 g of a porous silica having a pore size of 10 to 100 nm and 85 g of titanium butoxide (TBT) were poured into to a 500 mL-beaker in a glove box, they were evenly mixed using a kneading machine.

[59] Then, 2.2 L of water was poured into a 3 L-round bottom flask equipped with a stirrer, thermometer and nitrogen injector and pH was adjusted to 10 by the addition of ammonia hydroxide. The powder mixed in the glove box above was added thereto and reacted at the temperature of 100 ⁰ C for 24 hours. After the completion of the reaction, the reaction product was filtered, washed with 1 L of water two times and vacuum dried at 100 ⁰ C and then, it was placed in an electric furnace where its temperature was raised by 5 ⁰ C per minute to 800 ⁰ C, at which it was placed for 3 hours and then, the temperature was lowered to a room temperature, at which it was filtered with a sieve of 500 meshes thereby to prepare high refractive spherical beads. It was also verified that the high refractive spherical beads prepared above was not less than 1.7.

[60] Example 4

[61] After 117 g of a porous silica having a pore size of 10 to 100 nm and 76 g of titanium ethoxide (TET) were poured into to a 500 mL-beaker in a glove box, they were evenly mixed using a kneading machine.

[62] Then, 2.2 L of water was poured into a 3 L-round bottom flask equipped with a stirrer, thermometer and nitrogen injector and pH was adjusted to 10 by the addition of ammonia hydroxide. The powder mixed in the glove box above was added thereto and reacted at the temperature of 100 ⁰ C for 24 hours. After the completion of the reaction, the reaction product was filtered, washed with 1 L of water two times and vacuum dried at 100 ⁰ C and then, it was placed in an electric furnace where its temperature was raised by 5 ⁰ C per minute to 1,000 ⁰ C, at which it was placed for 2 hours and then, the temperature was lowered to a room temperature, at which it was filtered with a sieve of 500 meshes thereby to prepare high refractive spherical beads. It was also verified that the high refractive spherical beads prepared above was not less than 1.7.

[63] Example 5 [64] 0.2 % by weight of the high refractive spherical beads prepared in Example 1 was added to 99.8 % by weight of PETG and mixed to prepare a backlight diffusion plate, which is shown in Fig. 3.

[65] Example 6 [66] 20 % by weight of the high refractive spherical beads prepared in Example 1 was added to 80 % by weight of PETG and mixed to prepare a backlight diffusion plate.

[67] Example 7 [68] 2 % by weight of the high refractive spherical beads prepared in Example 1 was added to 98 % by weight of PETG and mixed to prepare a backlight diffusion plate.

[69] Example 8 [70] 5 % by weight of the high refractive spherical beads prepared in Example 1 was added to 95 % by weight of PETG and mixed to prepare a backlight diffusion plate.

[71] After each of the backlight diffusion plates prepared in Examples 5 to 8 was injected for 1 min at 270 ⁰ C and extruded for 10 to 15 min at 270 ⁰ C, color change and luminance were measured and the results are shown in Table 1 below. The extrusion processing condition was Twin Ext L/D=32, 45 φ.

[72] Table 1

[73] As a result, the diffusion plates prepared using the high refractive spherical beads prepared in accordance with the invention showed excellent heat resistance with little color change and at the same time, their transmittance was superior. Industrial Applicability

[74] The high refractive spherical beads in accordance with the invention have excellent dispersion, light properties, UV stability, humidity resistance, thermal dimension stability, and weather resistance and in particular, they have superior heat resistance so that they can effectively prevent bending or yellowing resulting from UV irradiation, heat emission of lamps, heat generated from large-scale LCDs, etc. and they can be usefully applied to large-scale LCDs larger than 40 inches.