KR20040085958A - Method for Producing Emissive Plastic Optical Fiber Using Supercritical or High-Pressure Extrusion - Google Patents

Abstract

PURPOSE: A method for manufacturing an emissive plastic optical fiber by using a supercritical or a high pressure extrusion is provided, which has porous dispersion cores and is applied to a backlight unit. CONSTITUTION: A method for manufacturing an emissive plastic optical fiber by using a supercritical or a high pressure extrusion includes the steps of: forming a porous dispersion unit. The method is characterized in that the porous dispersion unit is obtained by pressing out the mixed fluid, wherein the mixed fluid is obtained by mixing the polymer with a supercritical or a high pressure fluid.

Description

Method for Producing Emissive Plastic Optical Fiber Using Supercritical or High-Pressure Extrusion

The present invention relates to a method of manufacturing a divergent plastic optical fiber using supercritical or high pressure extrusion, and more particularly, to form a porous scattering part by mixing and extruding a supercritical or high pressure fluid during extrusion of a polymer. The present invention relates to a method of manufacturing a divergent plastic optical fiber.

Commonly used backlights for liquid crystal display devices include a side-light system in which a cold cathode fluorescent tube is installed outside the light guide plate, and two or four lamps outside the light guide plate to increase the brightness of the backlight unit. There are multiple lamps in the configuration. The conventional light guide plate for liquid crystal display devices is a component constituting a side light type backlight device, and a side light type illumination device is disclosed in Japanese Patent Laid-Open No. 57-128383. This type of lighting device has a structure in which a cold cathode gas discharge tube, a hot cathode gas discharge tube, a light bulb, or an LED light source is positioned on the light emitting surface side, and can be modified into L, U, and W shapes according to the ability to be applied. Do. The illumination device is configured to inject light emitted from the light source from the side to the light guide plate, change its angle by a light scattering device mounted on the surface of the light reflection surface, and then emit the light from the diffuser plate to the observation part through the polarizing plate. It is.

Since the side light type backlight device contributes to reducing the thickness and weight of the entire liquid crystal display device by having a light source on the side of the light guide plate, it has been recently applied as an illuminator of a liquid crystal display device of a laptop or a notebook or a personal computer. Since these portable devices are driven by a built-in battery, it is required that the sidelight type lighting device consumes less power. In portable devices such as laptops, the backlight uses 60% of the power consumption, so that the light guide plate and the diffusion plate are used to increase the light transmission efficiency. The power consumption can be reduced by improving the transparency of materials such as plates and polarizing plates and improving the uniformity of brightness. In addition, since the light guide plate of the backlight unit occupies 60% of the total thickness of the monitor of the liquid crystal display device of the portable device, it is required to reduce the weight and thickness of the light guide plate.

Meanwhile, in the general light guide plate, as shown in the drawing, a light scattering pattern 4 is formed by dot-print printing white ink on the rear surface facing the light exit surface to increase the emission efficiency. The light scattering pattern forming process by such white ink printing, however, has the following problems.

In the light scattering pattern formation by the white ink, the printability of the white ink is lowered toward the finer pattern, and the uniform light reflection function according to the high brightness is lowered. In addition, the brightness deteriorates over time due to discoloration and the like, and as a result, there is a problem of shortening the life of the lighting apparatus.

In order to improve the above problems, a non-printing light guide plate without a printing process has been developed. First, grooves on the surface of the light guide plate are disclosed in US Pat. No. 6,123,431.

Disclosed is a non-printing light guide plate in which a groove is formed to form a light scattering pattern. In addition, U.S. Patent No. 5,881,201 discloses a non-printing light guide plate having a scattering function due to a difference in refractive index within the light guide plate by dispersing inorganic or organic particles having a different refractive index from the base resin in the light guide plate.

In the case of general plastic optical fibers, most of them are composed of constituents of core and clad, and the value of refractive index is higher than that of clad, so when light is irradiated to core, light is totally reflected by the difference in refractive index at the clad interface, so that the light goes straight. It is a principle. Such plastic optical fibers are classified into lighting and communication according to how far the light goes straight, or the core portion having a higher refractive index than the clad is a step type and the refractive index increases to the core center or the grade type increases the refractive index.

In contrast to this, an emissive plastic rod is reported. It is proposed by Bastiaansen et al. Of Eindhoven University. The bead type polymer copolymer particles are used to increase the efficiency of emitting light to the surface when the light is irradiated with the core due to the low refractive index of the core and slightly high refractive index of the clad. (POF world 2000, Bastiaansen et al, Eindhoven Univ.) There is a US Patent No. 3,718,814, which is a technology applied to billboards using the side-fiber plastic optical fiber manufactured as described above.

Meanwhile, Korean Patent Application No. 2002-77401 by the present inventors proposes a new concept backlight unit for a liquid crystal display device using a divergent plastic optical fiber instead of a light guide plate.

The present invention provides a novel manufacturing method of a divergent plastic optical fiber for forming a porous scattering part by supercritical extrusion for the purpose of applying to a backlight unit for a liquid crystal display device of the new concept.

That is, the present invention is a method of manufacturing a divergent plastic optical fiber comprising a porous scattering portion, the porous scattering portion is formed by a method of extruding by mixing the polymer with a supercritical or high-pressure fluid It relates to a manufacturing method of an optical fiber.

Another aspect of the invention relates to a divergent plastic optical fiber produced by the method.

Another aspect of the invention is a plurality of divergent plastic optical fibers having a constant length and disposed in close proximity to one another; And a light source disposed at one or both ends of the plastic optical fiber, wherein the divergent plastic optical fiber is manufactured by the above method. It is about.

Another aspect of the present invention relates to a liquid crystal display device including the backlight unit.

1A and 1B are views showing an example of the divergent plastic optical fiber according to the present invention;

2 is a diagram showing a phase diagram of carbon dioxide,

3 shows an apparatus for performing supercritical or high pressure extrusion of the invention,

4 is a view showing a principle of emitting light by the divergent plastic optical fiber according to the present invention, and

5 is a view showing the operation principle of the backlight unit for a liquid crystal display device including the divergent plastic optical fiber according to the present invention.

Hereinafter, the present invention will be described in more detail.

In the present invention, the divergent plastic optical fiber includes a porous scattering portion therein, and unlike the conventional optical fiber which transmits light without light loss, it emits light to the surroundings. 1A and 1B are views showing a representative structure of a plastic optical fiber including a porous scattering part. 1A shows a core layer 31, an intermediate layer 32 and a cladding layer

In the optical fiber made of (33), when the porous scattering portion is formed in the core layer 31, high scattering can be exhibited at a short distance. 1B is a case where a porous scattering portion is formed in the intermediate layer 42 in the optical fiber composed of the core layer 41, the intermediate layer 42, and the cladding layer 43. Light transmitted to the core layer may be gradually scattered by the intermediate layer to uniformly scatter at a relatively long distance. In addition, the present invention is not limited to the above structure, and the present invention can be applied to divergent optical fibers having various structures predicted from the prior art. In addition, the present invention is not limited to the above structure, and the present invention can be applied to divergent optical fibers having various structures predicted from the prior art.

The divergent plastic optical fiber is manufactured using an amorphous polymer having good permeability such as polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), Teflon AF, Cytop, and the like.

More preferably, methyl methacrylate, benzyl methacrylate, phenyl methacrylate, 1-methylcyclohexyl methacrylate, cyclohexyl methacrylate, chlorobenzyl methacrylate, 1-phenylethyl methacrylate, 1, 2-diphenylethyl methacrylate, diphenylmethyl methacrylate, perfuryl methacrylate, 1-phenylcyclohexyl methacrylate, pentachlorophenyl methacrylate, pentabromophenyl methacrylate, styrene, TFEMA ( 2,2,2-trifluoroethyl methacrylate), TFPMA (2,2,3,3-trifluoropropylmethacrylate), PFPMA (2,2,3,3,3-pentafluoropropyl Methacrylate), HFIPMA (1,1,1,3,3,3-hexafluoroisopropylmethacrylate), HFBM (2,2,3,4,4,4-hexafluorobutyl methacrylate ), HFBMA (2,2,3,3,4,4,4-heptafluorobutyl methacrylate), PFOM (1H, 1H-perfluoro-n-octyl methacrylate) Be a homopolymer or a copolymer polymerized from Murray Examples, but is not limited thereto that are known to be used in a conventional optical material or the like can be used.

In the present invention, the fluid used for supercritical or high pressure extrusion may be used alone or in combination of a solvent or a non-solvent material in the polymer material.

During supercritical or high pressure extrusion, the polymer is melted or swelled in a supercritical or high pressure fluid and extruded in a state where the glass transition temperature is lowered. The scattering part is formed. In this case, as the polymer forming the porous scattering unit, all of the above-mentioned amorphous transparent polymers may be applied, and the size of pores formed in the porous scattering unit by applying two or more polymer blends having different solubility to a supercritical or high pressure fluid. It is also possible to adjust.

Specific examples of the fluid applied to the supercritical extrusion or the high pressure extrusion include, but are not limited to, CO ₂ , SF ₆ , C ₂ H ₆ , CCl ₃ F, CClF ₃ , CHF ₃ , isopropanol, and the like. More preferably supercritical CO ₂ is used. Supercritical carbon dioxide is environmentally friendly, reusable, and can dissolve or swell most polymers, allowing extrusion at low temperatures. In addition, since supercritical carbon dioxide has good solubility in organic monomers and monomers, removal after dissolution or swelling helps to remove residual monomers or additives remaining during polymer polymerization.

The critical temperature and pressure of carbon dioxide are 31.1 ° C. and 72.0 atm, respectively, as shown in the carbon dioxide phase diagram of FIG. 2. The pressure and temperature conditions of carbon dioxide useful for application in supercritical or high pressure extrusion in the present invention are supercritical carbon dioxide. Depending on the polymer material used, it is preferably at a temperature of 50 ° C. or higher than the glass transition temperature of the polymer used above the pressure that can be used, but is approximately 50 to 500 atm, more preferably 100 to 200 atm, The temperature is adjusted to approximately 30 to 300 ° C, more preferably in the range of 100 to 200 ° C.

When carbon dioxide is used as a supercritical or high pressure fluid, when polymers having different solubility for carbon dioxide, for example, PVDF and PMMA are blended, pores are formed in a region formed by PVDF due to a difference in solubility in supercritical carbon dioxide. Scattering pores of size are preferred in terms of being able to control the scattering degree for a particular wavelength.

The supercritical or high pressure extrusion of the present invention can be specifically performed by the apparatus as shown in FIG. In order to enable supercritical extrusion, the supercritical fluid is injected into the extruder through a high pressure pump (2) in the cylinder (1) as shown in FIG. 3, and the pressure gauge (5) through the valve (3) and the relief valve (4) Adjust the pressure with). The pressure in each part of the more precise extruder is controlled via the transducer 6. The polymerized polymer is introduced in the form of beads or pallets through the feeder 7, and the cooling unit 8 is located at the inlet side, and is melted and extruded through the extruder 9. Since the heater 10 is divided into several parts and controlled separately, the temperature of each part can be adjusted. The extruded part to be extruded has a die adapter 11 and a mixer 12, and this part is also equipped with a heater 13 for fine temperature control. The size of the fiber varies depending on the size or shape of the nozzle 14 through which the porous fiber comes out, and a cooler is mounted.

Meanwhile, in the manufacture of the divergent plastic optical fiber of the present invention, the remaining constituent layers except for the porous scattering part may be manufactured by various methods, and in particular, may be manufactured by simultaneously extruding the porous scattering part by coextrusion or in the case of a clad layer. It can be formed by the method of coating.

The divergent plastic optical fiber manufactured by the present invention can be used as a function of replacing a conventional light guide plate in a backlight unit for a liquid crystal display. The backlight unit has a structure in which light sources are disposed at one or both ends of the optical fiber after arranging the plastic optical fibers for side lighting in a row according to the present invention. The optical fiber supplied with the light from the light source serves to replace the light guide plate by emitting light as shown in FIG. 4. 5 is a conceptual diagram showing the operation principle of a backlight unit using a plastic optical fiber for side lighting having a porous scattering core according to the present invention.

Thus, by replacing the light guide plate function with a fiber type instead of a plate type, it has excellent brightness uniformity compared to the conventional light guide plate, and above all, it is possible to minimize the thickness of the conventional light guide plate by arbitrarily adjusting the fiber thickness. There is an advantage.

The diameter of the plastic optical fiber for side lighting used at this time is 0.001 micrometer-10 cm, Preferably it is the range of 0.01 micrometer-5 cm.

As the light source above, a white LED or a cold cathode fluorescent lamp is preferably used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are intended to illustrate the present invention and are not intended to limit the present invention.

In the embodiment, the side luminance is measured by using a luminance meter (Tfcon Co., Ltd., BM-7) and measuring the luminance in the longitudinal direction of the optical fiber at the side of the 10 cm divergent plastic optical fiber and integrating it with the judgment standard. It is as shown in the following formula (1).

(One)

Where I ₀ is the intensity of incident light incident on one cross-section of the divergent plastic optical fiber, I (x) is the intensity of light emitted from the side measured by the luminance meter, and R is the distance from the center of the divergent optical fiber to the luminance meter. Where L is the length of the divergent optical fiber.

Example 1:

The carbon dioxide pressure was fixed at 35 MPa, and PMMA (polymethyl methacrylate, molecular weight 107,000) having a melt flow index of 1.24 g / min at 200 ° C was extruded at 120 ° C with a carbon dioxide concentration of 6.0% by weight. The intermediate layer and the clad layer were formed by coextrusion to a structure as shown in FIG. 1A to produce a divergent plastic optical fiber. (D ₁ = 0.1 mm (refractive index, n = 1.49), d ₂ = 0.45 mm (n = 1.47), d ₃ = 0.75 mm (n = 1.46)) The interlayer and the cladding are copolymers of TFPMA (2,2,3,3-trifluoropropylmethacrylate) and MMA (methyl methacrylate). The molecular weight was 120,000. The measured side luminance was 0.75.

Example 2:

The carbon dioxide pressure was fixed at 35 MPa and PMMA (molecular weight 107,000) having a melt index of 1.24 g / min at 200 ° C was extruded at 120 ° C at 6.0% by weight of carbon dioxide. The intermediate layer and the cladding layer were formed by coextrusion to a structure as shown in FIG. 1A to produce a divergent plastic optical fiber. (D ₁ = 0.5 mm (refractive index, n = 1.49), d ₂ = 0.6 mm (n = 1.47), d ₃ = 0.75 mm (n = 1.46)) The intermediate layer and the cladding were prepared by varying the composition by radical polymerization with a copolymer of TFPMA and MMA, and the molecular weight was 120,000. The measured side luminance was 0.81.

Example 3:

The carbon dioxide pressure was fixed at 35 MPa and PMMA (molecular weight 107,000) having a melt flow index of 1.24 g / min at 200 ° C. was extruded at 120 ° C. to 6.0 wt% carbon dioxide concentration. The core layer and the cladding layer were formed by coextrusion to a structure as shown in FIG. 1B to produce a divergent plastic optical fiber. (D ₁ = 0.4 mm (refractive index, n = 1.50), d ₂ = 0.5 mm (n = 1.49) , d ₃ = 0.75 mm (n = 1.46)) The core layer had a molecular weight of 100,000 as a copolymer of BMA (benzyl methacrylate) and MMA, and the clad layer was a copolymer of TFPMA and MMA with a molecular weight of 120,000. The measured side luminance was 0.89.

Example 4:

The divergent plastic optical fibers obtained in Examples 1 to 3 were formed into flat bundles, and a reflecting tape of RF188 of Tsujimoto Electric Machinery Co., Ltd. was attached to the side of the backlight unit other than the light incident end face, and then the diameter of Harison Electric Machinery Co., Ltd. 2.4 After the mm cold cathode lamp was installed, a reflector of GR38W manufactured by Kimoto Co., Ltd. was applied around the lamp and the light guide plate incidence. A light diffusion sheet of PCMSA, a product of TM Chimoto Electric Machinery Co., Ltd., was manufactured on the light exit surface side, and a reflection sheet of RF188 of TM Chimoto Electric Machinery Co., Ltd. was disposed on the opposite side of the light exit plate of the light guide plate to produce a planar light source unit. This unit was used to evaluate luminance uniformity and impact resistance, and the results are shown in Table 1.

Luminance uniformity is measured by using a luminance meter (Tfcon Co., Ltd., BM-7) and measuring three points of luminance at equal intervals on a divergent plastic optical light guide plate, and luminance uniformity (%) = (minimum / maximum) x 100 It evaluated as the following judgment criteria.

Mechanical strength was evaluated by impact resistance by drop test. At the same position of the prepared 10 light guide plates, a missile scale (10 grams in weight) of 3/4 inch radius was naturally dropped from a height of 50 cm to observe whether cracking or cracking occurred. Table 1 shows the number of light guide plates that were cracked or cracked.

Luminance Uniformity (%) Impact resistance (long ten pieces) Example 1 74 One Example 2 71 0 Example 3 86 0

According to the present invention, a plastic optical fiber for side lighting having a porous scattering core having a new structure can be provided and applied to a backlight unit for a liquid crystal display device.

Claims (14)

In the method for manufacturing a divergent plastic optical fiber comprising a porous scattering portion, The method of manufacturing a divergent plastic optical fiber, characterized in that the porous scattering unit is formed by mixing a polymer with a supercritical or high pressure fluid. The method of claim 1, wherein the divergent plastic optical fiber has a cladding layer, an intermediate layer, and a core layer, and the porous scattering part is formed in the intermediate layer or the core layer. The method of manufacturing a divergent plastic optical fiber according to claim 1, wherein during the extrusion of the porous scattering portion, other constituent layers are formed simultaneously with the porous scattering portion by coextrusion. The method of claim 2, wherein the cladding layer is formed by dip coating. The method of claim 1, wherein the supercritical or high pressure fluid is carbon dioxide, SF ₆ , C ₂ H ₆ , CCl ₃ F, CClF ₃ , CHF ₃ , or isopropanol. The method of claim 2, wherein the clad layer, the intermediate layer, and the core layer are each made of the same or different types of amorphous homopolymer or copolymerized polymers. The method of claim 6, wherein the amorphous polymer is methyl methacrylate, benzyl methacrylate, phenyl methacrylate, 1-methylcyclohexyl methacrylate, cyclohexyl methacrylate, chlorobenzyl methacrylate, 1-phenylethyl Methacrylate, 1,2-diphenylethyl methacrylate, diphenylmethyl methacrylate, perfuryl methacrylate, 1-phenylcyclohexyl methacrylate, pentachlorophenyl methacrylate, pentabromophenyl methacrylate Latex, styrene, TFEMA (2,2,2-trifluoroethylmethacrylate), TFPMA (2,2,3,3-trifluoropropylmethacrylate), PFPMA (2,2,3,3, 3-pentafluoropropylmethacrylate), HFIPMA (1,1,1,3,3,3-hexafluoroisomethacrylate), HFBM (2,2,3,4,4,4-hexafluoro Robutylmethacrylate), HFBMA (2,2,3,3,4,4,4-heptafluorobutylmethacrylate) and PFOM (1H, 1H-perfluoro-n-octylmethacryl) The method of diverging plastic optical fiber, characterized in that the homopolymer or copolymer of monomers selected from the group consisting of a byte). The method of claim 1, wherein at least two polymers having different solubility in supercritical or high-pressure fluids are blended and used for extrusion in forming the porous scattering unit. The method of manufacturing a divergent plastic optical fiber according to claim 8, wherein when the supercritical or high pressure fluid is carbon dioxide, the polymers having different solubility are PVDF and PMMA. A diverging plastic optical fiber manufactured by the method of claim 1. A plurality of divergent plastic optical fibers having a constant length and disposed in close proximity to one another; And A backlight unit for a liquid crystal display device comprising a light source disposed at one or both ends of the plastic optical fiber, A backlight unit for a liquid crystal display device, wherein the divergent plastic optical fiber is manufactured by the method of claim 1. 12. The backlight unit for a liquid crystal display device according to claim 11, wherein the plastic optical fiber has a diameter of 0.001 µm to 10 cm. 12. The backlight unit of claim 11, wherein a white LED or a cold cathode fluorescent lamp is used as the light source. A liquid crystal display device comprising the backlight unit of claim 11.