WO2009142396A2

WO2009142396A2 - Luminance-enhanced film

Info

Publication number: WO2009142396A2
Application number: PCT/KR2009/001942
Authority: WO
Inventors: Yeon Soo Kim; Do Hyun Kim; In Young Yang; Jin Soo Kim; Deog Jae Jo
Original assignee: Woongjin Chemical Co., Ltd.
Priority date: 2008-05-19
Filing date: 2009-04-15
Publication date: 2009-11-26
Also published as: KR20090120074A; TW200949300A; WO2009142396A3

Abstract

The present invention relates to a luminance-enhanced film, and more particularly, to a luminance-enhanced film in which islands-in-the-sea yarns with birefringence are included in a base material, thus significantly lowering production costs and also rapidly improving luminance. The luminance-enhanced film of the present invention includes a birefringent islands-in-the-sea yarn within a base material. Accordingly, unlike a conventional stack type luminance-enhanced film, a luminance enhancement effect is excellent while not forming a number of layers. Further, since several hundreds of layers are not formed in one film, fabrication is very convenient and production costs can be saved greatly.

Description

[Rectified under Rule 91 11.06.2009] LUMINANCE-ENHANCED FILM

The present invention relates to a luminance-enhanced film, and more particularly, to a luminance-enhanced film in which island-in-the-sea yarns with birefringence are included in a base material, thus significantly lowering production costs and also rapidly improving luminance.

In information display technology, a cathode ray tube (CRT) of display devices occupied a dominant position over the last half century. However, various methods of display technologies are required in line with a rapidly advanced information era. Of them, it is expected that a flat display will be positioned as a technology surpassing the CRT in the near future. Not only small-sized test devices, but also portable computers have been commercialized, and the existing CRT method has been replaced with a flat display device even up to various monitors and TV.

In the flat display technology, a liquid crystal display (LCD), a projection display and a plasma display panel (PDP), which have already secured their markets in the TV field, have become the main current. It is also expected that a field emission display (FED), an electro-luminescent display (ELD), etc. will occupy the fields according to the respective characteristics in line with the improvements of pertinent technologies. The use range of a LC display has currently been expanded to notebooks, personal computer monitors, liquid crystal TV, vehicles, aircrafts and so on. The LC display occupies about 80% of the flat panel market and has showed signs of prosperity worldwide since the second half of the year 1998 along with the rapid demand for the LCD.

A conventional LC display has liquid crystal and an electrode matrix disposed between a pair of light-absorbent optical films. In this LC display, the liquid crystal portion is moved by an electric field, which is generated by applying voltage to two electrodes, and has an optical state changed accordingly. This process displays information by polarizing 'pixel', having information loaded thereon, in a specific direction. To this end, the LC display includes a front optical film and a rear optical film for inducing such polarization.

It cannot be said that a liquid crystal display device of this LC display has a high use efficiency of light emitted from a backlight. This is because 50% or more of the light emitted from the backlight is absorbed by a rear-side optical film. Thus, in order to increase the use efficiency of the backlight light in this liquid crystal display device, a luminance-enhanced film is disposed between an optical cavity and a liquid crystal assembly.

FIG. 1 is a schematic view illustrating the principle of a conventional luminance-enhanced film.

More specifically, P-polarized light of light orienting from an optical cavity to a liquid crystal assembly is transferred to the liquid crystal assembly through a luminance-enhanced film. S-polarized light of the light is reflected from the luminance-enhanced film to the optical cavity, reflected from a diffusion reflection surface of the optical cavity in a state where the polarization direction of the light becomes random, and then transferred to the luminance-enhanced film again. Consequently, the S-polarized light is converted into P-polarized light that can pass through a polarizer of the liquid crystal assembly and then transferred to the liquid crystal assembly through the luminance-enhanced film.

Selective reflection of the S-polarized light with respect to the incident light on the luminance-enhanced film and a transmission action of the P-polarized light are performed by a difference in the refractive index between respective optical layers, setting of an optical thickness of each optical layer according to an extension process of stacked optical layers and a change in the refractive index of the optical layer, in the state in which an optical layer on a flat sheet having an anisotropic refractive index and an optical layer on a flat sheet having an isotropic refractive index are alternately stacked in plural numbers.

That is, the light incident on the luminance-enhanced film experiences the reflection of the S-polarized light and the transmission action of the P-polarized light while passing through each of the optical layers, and consequently only the P-polarized light of the incident polarized light is transferred to the liquid crystal assembly. Meanwhile, the reflected S-polarized light is reflected from the diffusion reflection surface of the optical cavity in the state in which its polarization state becomes random as described above and then transferred to the luminance-enhanced film. Accordingly, loss of light generated from a light source and waste of power could be reduced.

However, this conventional luminance-enhanced film is fabricated by alternately stacking the isotropic optical layer and the anisotropic optical layer on the flat sheets with different refractive indices and performing an extension process on the stacked layer so that the stacked layer has an optical thickness between the respective optical layers and a refractive index, which can be optimized for selective reflection and transmission of incident polarized light. Accordingly, there was a problem in that the fabrication process of the luminance-enhanced film was complicated.

In particular, since each optical layer of the luminance-enhanced film has the flat sheet structure, P-polarized light and S-polarized light have to be separated from each other in response to a wide range of an incident angle of the incident polarized light. Accordingly, there was a problem in that the stack number of the optical layers was increased excessively and production costs were increased by geometric progression. Further, there was a problem in that optical performance might be lowered because of optical loss due to a structure in which the stack number of the optical layers was excessively many.

Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and an object of the present invention is to provide a luminance-enhanced film with easy production, very low production costs and a further improved luminance effect by replacing a conventional stack type luminance-enhanced film.

Another object of the present invention is to provide a luminance-enhanced film with an excellent visibility and optical effect.

To achieve the above objects, a luminance-enhanced film may include an island-in-the-sea yarn having birefringence within a base material.

The base material preferably has optical isotropy and a refractive index of 1.4 to 2.0. More preferably, the base material may use any one or more of polyethylene naphthalate (PEN), copolyethylene naphthalate (co-PEN), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate (PC) alloy, polystyrene (PS), heat-resistant polystyrene (PS), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), poly vinyl chloride (PVC), styrene acrylonitrile mixture (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea (UF), melanin (MF), non-saturated polyester (UP), silicon (SI), elastomers and cycloolefin polymer.

The island-in-the-sea yarn may be preferably disposed in plural numbers in one direction within the base material. More preferably, the island-in-the-sea yarn may be disposed vertically to a light source within the base material. Further, the island-in-the-sea yarns may be dispersed and disposed within the base material or may be brought in contact with each other within the base material and disposed. Further, the island-in-the-sea yarns may form one or more layers within the base material.

A difference in a refractive index between the base material and the island-in-the-sea yarn with respect to two axial directions may be preferably 0.03 or less. More preferably, a difference in a refractive index between the base material and the island-in-the-sea yarn with respect to the remaining one axial direction may be 0.05 or more. More preferably, the remaining one axial direction is a length direction of the island-in-the-sea yarn.

A sea portion of the island-in-the-sea yarn may be preferably isotropic, and an island portion of the island-in-the-sea yarn may be preferably anisotropic.

A difference in a refractive index between the sea portion and the island portion of the island-in-the-sea yarn with respect to two axial directions may be preferably 0.03 or less, and a difference in a refractive index between the sea portion and the island portion of the island-in-the-sea yarn with respect to the remaining one axial direction may be preferably 0.05 or more. In this case, the remaining one axial direction may be a length direction of the island-in-the-sea yarn.

The sea portion may preferably have a refractive index of 1.4 to 2.0.

The island portion of the island-in-the-sea yarn may be disposed in plural numbers. More preferably, an area ratio of the sea portion and the island portion on the basis of a traverse section of the island-in-the-sea yarn may be 2 : 8 to 8 : 2.

A sea portion of the island-in-the-sea yarn may preferably include any one or more of polyethylene naphthalate (PEN), copolyethylene naphthalate (co-PEN), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate (PC) alloy, polystyrene (PS), heat-resistant polystyrene (PS), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), poly vinyl chloride (PVC), styrene acrylonitrile mixture (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea (UF), melanin (MF), non-saturated polyester (UP), silicon (SI), elastomers and cyclo olefin polymer.

The island portion of the island-in-the-sea yarn may preferably include any one or more of polyethylene naphthalate (PEN), co-PEN, PET, co-PET, polybutylene terephthalate (PBT), and polypropylene (PP).

Meanwhile, the plurality of island portions may preferably have the same traverse cross section or different traverse cross sections. More preferably, the island-in-the-sea yarn may be extended in a length direction.

The luminance-enhanced film may further include a structured surface layer. More preferably, the structured surface layer is formed on a surface from which light may be output. More specifically, the structured surface layer may have a prism shape, a lenticular shape or a convex lens shape. In this case, the shapes may be arranged regularly or irregularly.

The birefringent island-in-the-sea yarn may be disposed or not disposed in the structured surface layer. Further, a rear surface of the luminance-enhanced film may have underwent Matt treatment.

The island-in-the-sea yarn may preferably have a thickness of 0.3 to 20 denier. The island-in-the-sea yarn is 500 to 4,000,000 numbers/㎤ within the luminance-enhanced film.

The cross section of the island-in-the-sea yarn may be circular, oval or various non-circular shapes. A refractive index of the sea portion may be identical to that of the base material.

The island-in-the-sea yarn may be weaved in wefts and ends. More preferably, any one of the wefts and the ends may be the island-in-the-sea yarn, and the other of the wefts and the ends may be an isotropic fiber.

The wefts and ends may be formed by 1 to 200 strands of the island-in-the-sea yarns.

Meanwhile, the present invention may provide a backlight unit including the above luminance-enhanced film. Further, the backlight unit may be included in a liquid crystal display device. In this case, the liquid crystal display device may include a phase difference film and/or an absorbent type polarization film.

A luminance-enhanced film according to another aspect of the present invention includes a base material whose refractive index of a x-axis direction may be nX1, a refractive index of a y-axis direction may be nY1 and refractive index of a z-axis direction may be nZ1, and a birefringent island-in-the-sea yarn disposed within the base material. When refractive indices of the birefringent island-in-the-sea yarn may be nX2, nY2 and nZ2, at least one of the x, y and z-axis refractive indices of the base material may be identical to that of x, y and z-axis refractive indices of the birefringent island-in-the-sea yarn. In this case, more preferably, nX2 > nY2 = nZ1, and the base material is isotropic.

Further, when a refractive index of the x-axis direction, which may be a length direction of an island portion of the island-in-the-sea yarn, may be nX3, a refractive index of the y-axis direction may be nY3 and a refractive index of the z-axis direction may be nZ3, and a refractive index of the x-axis direction of a sea portion of the island-in-the-sea yarn may be nX4, a refractive index of the y-axis direction of the sea portion of the island-in-the-sea yarn may be nY4 and a refractive index of the z-axis direction of a sea portion of the island-in-the-sea yarn may be nZ4, an absolute value of a difference in the refractive index between the nX3 and the nX4 or between the nY3 and the nY4 may be 0.15 or more. An absolute value of a difference in the refractive index between the nZ3 and the nZ4 is less than 0.03.

The terminologies used in the specification are described in short.

What a polymer has birefringence means, not otherwise described, that, in the case in which light is irradiated on polymers having different refractive indices according to directions, the light incident on the polymers are refracted as two lights with different directions.

The terminology 'isotropy' means that when light passes through an object, it has a constant refractive index irrespective of its direction.

The terminology 'anisotropy' means that the optical properties of an object differ according to the direction of light. An anisotropic object has birefringence and corresponds to isotropy.

The terminology 'optical modulation' means that irradiated light is reflected, refracted, scattered, or the intensity, cycle of wave motion or property of light is changed.

The present invention is a luminance-enhanced film, a layer is formed to include birefringent island-in-the-sea yarns within a base material unlike a conventional stacked luminance-enhanced film. Accordingly, the luminance-enhanced film of the present invention can have an excellent luminance-enhancing effect while not forming a number of layers. Furthermore, since several hundreds of layers are not stacked in one film, fabrication is very convenient and a cost-saving effect in production cost is excellent.

Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic view illustrating the principle of a conventional luminance-enhanced film;

FIG. 2 is a schematic view of a cutaway cross-sectional view of a luminance-enhanced film in accordance with an embodiment of the present invention;

FIGS. 3 to 11 are cross-sectional views of a birefringent island-in-the-sea yarn in accordance with an embodiment of the present invention;

FIG. 12 is a sectional view showing the path of light incident on the birefringent island-in-the-sea yarn of the present invention;

FIGS. 13 to 18 are sectional views of a structured surface of the luminance-enhanced film of the present invention; and

FIGS. 19 and 20 show the arrangements of the birefringent optical modulated fiber in accordance with an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

A conventional luminance-enhanced film is fabricated by alternately stacking an isotropic optical layer and an anisotropic optical layer on flat sheets with different refractive indices and performing an extension process on the stacked layer so that it has an optical thickness between the respective optical layers and a refractive index, which can be optimized for selective reflection and transmission of incident polarized light. Accordingly, there was a problem in that a fabrication process of the luminance-enhanced film was complicated.

In particular, since each optical layer of the luminance-enhanced film has a flat sheet structure, P-polarized light and S-polarized light have to be separated from each other in response to a wide range of an incident angle of the incident polarized light. Accordingly, there was a problem in that the stack number of the optical layers was increased excessively and production costs were increased by geometric progression. Further, there was a problem in that optical performance might be lowered due to optical loss because of a structure in which the stack number of the optical layers was excessively many.

In view of the problems, in the present invention, birefringent island-in-the-sea yarns are disposed within a base material such that light incident from a light source is reflected, scattered and refracted at a birefringent interface, i.e., a boundary interface between isotropic base materials of the birefringent island-in-the-sea yarns and therefore optically modulated. Accordingly, luminance can be improved rapidly.

More specifically, light emitted from an external light source can be largely divided into S-polarized light and P-polarized light. In the case in which only a specific polarized light is needed, the P-polarized light passes through a luminance-enhanced film without being influenced by the birefringent interface. However, the S-polarized light is modulated in a wavelength of a refraction, scattering and reflection-random form, that is, S-polarized light or P-polarized light at the birefringent interface. If the modulated light is reflected and irradiated on the luminance-enhanced film again, the P-polarized light passes through the luminance-enhanced film, and the S-polarized light is scattered or reflected again. Through repetition of this process, a desired P-polarized light can be obtained.

Accordingly, if polymer having a birefringent interface is disposed in plural numbers within a base material at a boundary interface between the polymer and the base material, luminance can be improved rapidly even without forming the conventional luminance-enhanced film to have a stack type.

Further, the present inventors had found that, if the polymer having the birefringent interface is used for a general birefringent fiber, there are advantages in that production costs are low and production is convenient since the stack type is not formed, but the general birefringent fiber could not be applied to the industry fields instead of the above-described stack type luminance-enhanced film since it has an insignificant luminance-enhanced effect.

In order to overcome the above problems, a birefringent island-in-the-sea yarn was used as the polymer having the birefringent interface. More particularly, it could be found that, if the birefringent island-in-the-sea yarn was used, optical modulation efficiency and a luminance-enhanced effect were improved significantly as compared with a case where typical fibers were used. In particular, island portions of portions constituting the island-in-the-sea yarn have birefringence and a sea portion partitioning the island portions has isotropy. In this case, not only a boundary interface between the island-in-the-sea yarn and the base material, but also boundary interfaces between a number of the island portions and the sea portions constituting the inside of the island-in-the-sea yarn have a birefringent interface. Accordingly, an optical modulation effect is increased significantly as compared with a typical birefringent fiber in which a birefringent interface is formed only at the boundary interface between the base material and the birefringent fiber. Consequently, the birefringent island-in-the-sea yarn of the present invention can replace the stack type luminance-enhanced film and find its applications to actual industry fields.

Accordingly, when the birefringent island-in-the-sea yarn is used, luminance-enhanced efficiency is excellent as compared with a case where a typical birefringent fiber is used. Furthermore, the birefringent island-in-the-sea yarn includes the island portions and the sea portions with different optical properties and the birefringent interface can be formed within the island-in-the-sea yarn. Therefore, luminance-enhanced efficiency can be improved significantly as compared with a case where the birefringent interface is not formed within the island-in-the-sea yarn.

Furthermore, in the case in which a conjugate fiber is formed by twisting several pieces or several tens of pieces of island-in-the-sea yarns, for example, 10 island-in-the-sea yarns are twisted to form one conjugate fiber, 100 birefringent interfaces exist in the conjugate fiber, and 100 or more optical modulations can be generated. Further, in the case in which several pieces of threaded island-in-the-sea yarns are fabricated, for example, when 10 pieces of island-in-the-sea yarns are fabricated, 100 birefringent interfaces exist in a conjugate fiber, and 100 or more optical modulations can be generated. This island-in-the-sea yarn of the present invention can be fabricated using a co-extrusion method, etc., but not limited thereto.

Consequently, it can be said that, in order to fabricate micro fibers, a typical island-in-the-sea yarn employs island portions, which are left after eluting a sea portion, as the micro fibers irrespective of birefringence. However, in the present invention, the sea portion of the island-in-the-sea yarn is not eluted, but an island-in-the-sea yarn having a sea portion and island portions of optical properties is used as it is. In the present invention, it is assumed that island portions have anisotropy and a sea portion has isotropy. However, the objects of the present invention would be accomplished even when the island portions have isotropy and the sea portion has anisotropy.

The present invention is described in detail with reference to the accompanying drawings.

FIG. 2 is a schematic view of a cutaway cross-sectional view of a luminance-enhanced film in accordance with an embodiment of the present invention. More specifically, a luminance-enhanced film has island-in-the-sea yarns 210, having birefringence, freely arranged within a base material 200 with isotropy. Materials of the base material 200 that can be used at this time include thermoplastic and thermosetting polymers through which an optical wavelength of a target range can pass. The base material 200 that is preferably appropriate may be amorphous or merocrystalline and may comprise a single polymer, a copolymer or a blend thereof. More specifically, poly(carbonate) (PC); syndiotactic and isotacticpoly(styrene) (PS); alkyl styrene; alkyl such as poly(methyl methacrylate) (PMMA) and PMMA copolymer, aromatic and aliphatic pendent (meth)acrylate; ethoxide and propoxide (meth)acrylate; multi-functional (meth)acrylate; acrylated epoxy; epoxy; and other ethylene unsaturated substance; ring-shaped olefin and ring-shaped olefin copolymer; acrylonitrile butadiene styrene (ABS); styrene acrylonitrile copolymer (SAN); epoxy; poly(vinyl cyclohexene); PMMA/poly(vinyl fluoride) blend; poly(phenylene oxide) alloy; styrene block copolymer; polyimide; polysulfone; poly(vinyl chloride); poly(dimethylsiloxane) (PDMS); polyurethane; unsaturated polyester; polyethylene; poly(propylene) (PP); poly(alkane terephthalate), for example, poly(ethylene terephthalate) (PET); poly(alkane naphthalate), for example, poly(etylene naphthalate) (PEN); polyamide; ionomer; vinyl acetate/polyethylene copolymer; cellulose acetate; cellulose acetate butyrate; fluoro polymer; poly(styrene)-poly(ethylene) copolymer; PET and PEN copolymer such as polyolefin PET and PEN; and poly(carbonate)/aliphatic PET blend may be used. More preferably, polyetylene naphthalate (PEN), copolyetylene naphthalate (co-PEN), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate (PC) alloy, polystyrene (PS), heat-resistant polystyrene (PS), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), polyvinyl chloride (PVC), styrene acrylonitrile mixture (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea.melanin (UF.MF), non-saturated polyester (UP), silicon (SI), elastomers, cyclo olefin polymer (COP, ZEON Co. (Japan), JSR Co. (Japan)), either alone or in combination thereof, may be used. Furthermore, the base material may also contain additives, such as an antioxidant, a light stabilizer, a heat stabilizer, a lubricant, a dispersing agent, a UV absorber, white pigment, and a fluorescent whitening agent, unless they do not damage the above physical properties.

The island-in-the-sea yarn 210 may employ materials, preferably having optical birefringence and excellent optical transmission. Preferably, the island-in-the-sea yarn 210 may have the same material as that of the base material, but employ materials whose optical property is birefringent. Meanwhile, a method of converting isotropic materials into birefringent materials has been typically known. For example, if isotropic materials are drawn under an adequate temperature condition, the isotropic materials have their polymer molecules oriented and, therefore, have birefringence.

More preferably, any one or more of polyetylene naphthalate (PEN), copolyetylene naphthalate (co-PEN), polyethylene terephthalate (PET), copolyethylene terephthalate (co-PET), polycarbonate (PC), polycarbonate (PC) alloy, polystyrene (PS), heat-resistant polystyrene (PS), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), polyvinyl chloride (PVC), styrene acrylonitrile mixture (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea.melanin (UF.MF), non-saturated polyester (UP), silicon (SI), elastomers and cyclo olefin polymer may be selected and used as a sea component and an island component. In this case, one of the sea portion and the island portion may have isotropy and the other of the sea portion and the island portion may have anisotropy. More preferably, the island portion may have anisotropy and the sea portion may have isotropy. For example, the sea portion of the island-in-the-sea yarn may use isotropic co-PEN and the island portion thereof may use birefringent PEN. Both the sea portion and the island portion of the island-in-the-sea yarn may use resin with different optical properties.

Meanwhile, in an island-in-the-sea yarn having an optically isotropic base material and birefringence, the degree of substantial match or mismatch of the refractive index according to X, Y and Z axes on the space has an effect on the degree of scattering of a ray of light, which is polarized according to the corresponding axes. In general, scattering power is changed in proportion to the square of mismatch in the refractive index. Accordingly, if the degree of mismatch in the refractive index according to a specific axis increases, a ray of light polarized according to the corresponding axis is scattered more strongly. However, when mismatch according to a specific axis is small, a ray of light polarized according to the corresponding axis is scattered to a less degree. In the case in which the refractive index of a base material is substantially identical to that of an island-in-the-sea yarn according to a specific axis, incident light that is polarized by an electric field parallel to this axis is not scattered irrespective of the size, shape and density of a portion of the island-in-the-sea yarn, but may pass through the island-in-the-sea yarn. Furthermore, in the case in which the refractive index of a base material is substantially identical to that of an island-in-the-sea yarn according to a specific axis, a ray of light is not substantially scattered, but pass through an object. Accordingly, in the present invention, it is preferred that a difference in the refractive index between the base material and the island-in-the-sea yarn with respect to two axial directions be 0.03 or less and a difference in the refractive index between the base material and the island-in-the-sea yarn with respect to the remaining one axial direction is 0.05 or more. In this case, P waves pass through a birefringent interface of the base material and the island-in-the-sea yarn. However, S waves experience optical modulation, are reflected, scattered or refracted, and then transformed in the form of S waves or P waves. Of them, the P waves pass through the luminance-enhanced film again and experience optical modulation.

More specifically, the island portion of the birefringent island-in-the-sea yarn may preferably have anisotropy and the sea portion thereof may preferably have isotropy. Assuming that the refractive index of the anisotropy island portion in a x-axis direction is nX3, the refractive index of the anisotropy island portion in a y-axis direction is nY3 and the refractive index of the anisotropy island portion in a z-axis direction of is nZ3, and the refractive index of the isotropic sea portion in the x-axis direction is nX4, the refractive index of the isotropic sea portion in the y-axis direction is nY4 and the refractive index of the isotropic sea portion in the z-axis direction is nZ4, it is preferred that an absolute value of a difference in the refractive index between nX3 and nX4 be 0.05 or more, more preferably, 0.15 or more. In this case, an absolute value of a difference in the refractive index between nY3 and nY4 and/or nZ3 and nZ4 may be less than 0.03.

More preferably, in the case in which the island-in-the-sea yarn is drawn in the x-axis direction, an absolute value of a difference in the refractive index between nX3 and nX4 may be 0.05 or more, and an absolute value of a difference in the refractive index between nY3 and nY4 and nZ3 and nZ4 may be less than 0.03. In this case, it is advantageous to increase optical modulation efficiency. In this case, it may result in nX3 > nY3 = nZ3.

The island portion may preferably comprise a fiber outer cover surrounding a fiber core, the luminance-enhanced film may preferably comprise a plurality of optical modulation fibers with different traverse sections, and one or more of a filler and the island portion may comprise birefringent polymer substance (for example, birefringent cholesteric). Furthermore, one or more of the optical modulation fiber and the island portion may be preferably drawn in a length direction.

In relation to the shape of the birefringent island-in-the-sea yarn of the present invention, the cross section of the island-in-the-sea yarn may have any shape according to its object and may have various forms of non-circular cross sections, such as a circle, an oval shape and a polygon. In a similar way, the cross section of the island portion of the island-in-the-sea yarn may have a non-circular cross section, such as a circle, an oval shape and a polygon, irrespective of the type of its shape.

FIGS. 3 to 11 are cross-sectional views of the birefringent island-in-the-sea yarn in accordance with an embodiment of the present invention. As can be seen from FIGS. 3 to 11, in the present invention, the shape, size, number and arrangement of the island portions may be controlled efficiently according to its optical modulation purpose. FIG. 3 is a cross-sectional view of a typical island-in-the-sea yarn 300 in which approximately circular island portions 320a are partitioned by a sea portion 310a. FIG. 4 is a cross-sectional view of an island-in-the-sea yarn in which the area of the sea portion 310b is larger than that of the island portions 320b. FIG. 5 is a cross-sectional view of an island-in-the-sea yarn in which the shape of the island-in-the-sea yarn is oval. In FIG. 6, the island portion 320d has an oval shape and the island portions are arranged in zigzags. Further, the traverse section of the island-in-the-sea yarn has a rectangular structure, but may have a polygonal structure or a non-circular section.

As illustrated in FIGS. 7 and 8, the island portions may be located at the center of the island-in-the-sea yarn or the sea portion may be located at the center of the island-in-the-sea yarn.

In some embodiments, the island portions may not have the same size. For example, as illustrated in FIGS. 9 and 10, the island-in-the-sea yarn may comprise

island portions

320g, 321g having a different size of traverse sections. In this specific embodiment aspect, any one (320g) of the island portions may have a relatively larger traverse section than that of the other (321g) of the island portions. The island portions may correspond to two or more groups of different sizes and may have substantially different sizes. Furthermore, as shown in FIG. 11, a birefringent and/or isotropic sheath 330i may be added to an island portion 320i.

Preferably, a plurality of the island portions may be disposed within the island-in-the-sea yarn, and the area ratio of the sea portion and the island portions may be preferably 2 : 8 to 8 : 2. The island-in-the-sea yarn may preferably have a thickness of 0.3 to 20 denier, and 500 to 4,000,000 (numbers/㎤) island-in-the-sea yarns may be preferably disposed within the based material. Furthermore, the refractive index of the sea portion may be identical to that of the base material of the luminance-enhanced film.

*Meanwhile, light that transmits the birefringent island-in-the-sea yarn within the base material can be optically modulated at the birefringent interface as described above. More specifically, FIG. 12 is a cross-sectional view of the path of light that transmits the birefringent island-in-the-sea yarn of the present invention. In this case, a P wave (solid line) transmits the birefringent island-in-the-sea yarn 400 without being influenced by birefringent interfaces, i.e., a boundary surface between the base material and the birefringent island-in-the-sea yarn and boundary surfaces between the island portions 420a and the sea portions 410a within the birefringent island-in-the-sea yarn, but S waves (dotted line) are optically modulated under the influence of birefringent interfaces, i.e., a boundary surface between the base material and the birefringent island-in-the-sea yarn and/or the boundary surfaces between the island portions and the sea portion within the birefringent island-in-the-sea yarn.

As a result, a large part of the S waves return back to a light source through optical modulations, such as reflection, scattering or refraction. The returned S waves become S waves or P waves again after being reflected and then pass through the luminance-enhanced film. Accordingly, if the birefringent island-in-the-sea yarn is used as described above, luminance-enhanced efficiency is excellent as compared with a case where typical birefringent fibers are used. The birefringent island-in-the-sea yarn includes the island portions and the sea portion with different optical properties and, therefore, the birefringent interfaces can be formed within the island-in-the-sea yarn. Accordingly, luminance-enhanced efficiency can be increased significantly as compared with a case where the birefringent interfaces are not formed within the island-in-the-sea yarn.

Meanwhile, a plurality of the island-in-the-sea yarn may be drawn in one direction and disposed within the base material. More preferably, the island-in-the-sea yarns 210 may be disposed within the base material vertically to the light source. In this case, optical modulation efficiency can be maximized. On the other hand, the island-in-the-sea yarns 210 arranged in a row may be dispersed from each other and disposed, if appropriate, and the birefringent island-in-the-sea yarns 210 may be brought in contact with each other or may be separated from each other. In the case in which the island-in-the-sea yarns 210 are brought in contact with each other, they may form a layer in a close form and be arranged.

Furthermore, for example, if three or more kinds of island-in-the-sea yarns whose traverse sections with different diameters are circular are arranged, a triangle, which is obtained by interconnecting the centers of three circles being adjacent to each other in the cross sections perpendicular to their long axial directions, becomes a scalene. Further, in the cross sections being perpendicular to the long axial directions of the island-in-the-sea yarns (circular cylindrical body), the circular cylindrical bodies are arranged such that the circle in a first layer and the circle in a second layer are brought in contact with each other. However, with respect to each island-in-the-sea yarn, a condition 「each island-in-the-sea yarn is brought in contact with two or more different island-in-the-sea yarns, which are brought in contact with each other on the side of the circular cylinder, on the sides of their circular cylinders」 has only to be fulfilled. In this range, for example, a construction in which the circle in the first layer and the circle in the second layer are brought in contact with each other, the circle in the second layer and the circle in the third layer are spaced apart from each other with a support medium intervened therebetween, and the circle in the third layer and the circle in the fourth layer are brought in contact with each other is also possible.

It is preferred that the lengths of at least two sides of a triangle, which connects the centers of three circles being directly brought in contact with each other in the cross sections perpendicular to the long axial direction of the island-in-the-sea yarn, be approximately identical. In particular, it is preferred that the lengths of three sides of the triangle be approximately identical. Further, in relation to a stack state of island-in-the-sea yarns in a thickness direction of the luminance-enhanced film, it is preferred that a plurality of layers be stacked in such a way as to be sequentially brought in contact with each other. Furthermore, it is more preferred that island-in-the-sea yarns having a circular cylindrical body with almost the same diameter be closely filled.

Accordingly, in this more preferred form, the diameters of circles of the plurality of island-in-the-sea yarns in the cross section perpendicular to its long axial direction have almost the same circular cylindrical body, and island-in-the-sea yarns located more inwardly than the outermost surface layer in the cross section are brought in contact with birefringent bodies, that is, six different circular cylindrical bodies on the side of the circular cylinder.

Meanwhile, it is preferably advantageous that the birefringent island-in-the-sea yarn have the volume of 1% to 90% with respect to the luminance-enhanced film of 1㎤. If the volume of the island-in-the-sea yarn is 1% or less, a luminance-enhanced effect is insignificant. If the volume of the island-in-the-sea yarn is 90% or more, problems may arise because the amount of scattering increases due to the birefringent interface and therefore optical loss is generated.

Furthermore, 500 to 1010 birefringent island-in-the-sea yarns may be disposed within the luminance-enhanced film of 1 ㎤. The diameter of the cross section of an island portion within the birefringent island-in-the-sea yarn may also have a significant effect on optical modulation. If the diameter of the cross section of each island portion within the birefringent island-in-the-sea yarn is smaller than an optical wavelength, refraction, scattering and reflection effects are decreased and, therefore, optical modulation is rarely generated. If the diameter of the cross section of the island portion is too large, light experiences regular reflection from a surface of the birefringent island-in-the-sea yarn and diffusion in other directions is very insignificant. The diameter of the cross section of an aligned island portion may change according to a purported use of an optical object. For example, the diameter of a fiber may be greatly dependent on the wavelength of electromagnetic ray, which is important in a specific usage, and fibers with different diameters are required in order to reflect, scatter or transmit a visible ray, ultraviolet rays, infrared rays and microwaves.

The luminance-enhanced film may preferably comprise a structured surface layer according to its purpose. FIGS. 13 to 18 are sectional views of structured surfaces of the luminance-enhanced film in accordance with an embodiment of the present invention. In FIG. 13, an incident surface and an outgoing surface of the luminance-enhanced film can be parallel to light emitted from a light source 500a. In this case, as shown in FIG. 14, birefringent island-in-the-sea yarns 521b, which are located (adjacent to) over a light source 500b, can be disposed closely, and birefringent island-in-the-sea yarns 520b, which are far from the light source 500b, can be disposed brokenly.

The structured surface layer may be formed on a surface from which light is output. The structured surface layer may have a prism shape, a lenticular shape or a convex lens shape. More specifically, in FIG. 15, a surface from which light is output on a luminance-enhanced film may have a curved surface 530c having a convex lens shape. The curved surface 530c can focus or defocus light that transmits the surface. Further, as shown in FIG. 16, a prism pattern 530d may be formed in a light outgoing surface. In this case, birefringent island-in-the-sea yarns 520d may not be formed in a structured surface layer 530d as shown in FIG. 16, birefringent island-in-the-sea yarns 520e may be formed both in a base material and a surface layer 530e as shown in FIG. 17, or birefringent island-in-the-sea yarns 520f may be formed only in a structured surface layer 530f as shown in FIG. 18.

Concave-convex portions may be formed in a rear surface of the luminance-enhanced film through Matt treatment and may be given a scratch-resistant property. This may be performed under a condition that an adverse effect does not occur in the effects of the present invention.

Meanwhile, light transmitted from a light source may include natural light and polarized light, and several materials having birefringence may be used as the birefringent island-in-the-sea yarn. However, it is preferred that the birefringent island-in-the-sea yarn be solid from a viewpoint of orientation, stability of a cross section shape, durability, etc.

As shown in FIGS. 19 and 20, the island-in-the-sea yarn may be preferably weaved using

wefts

610a, 600b and

warps

600a, 610b. Any one of the wefts and the warps may be the island-in-the-sea yarns and the other of the wefts and the warps may be isotropic fibers. The wefts or the warps may be preferably formed using 1 to 200 threads of the island-in-the-sea yarns.

The birefringent island-in-the-sea yarn of the present invention may be spinned and extended, and arranged t in one direction into a woven fabric or beam, and then impregnated in a base material and then fixed it thereto. The threading and extending process of the island-in-the-sea yarn or the weaving process of the woven fabric or beam may be performed using a known method, but not specially limited thereto. In impregnating the woven fabric or beam in the base material and fixing it thereto, a method of immersing non-woven fabric in monomer and/or oligomer solution, i.e., a precursor of the base material and then polymerizing the precursor of a support medium using light and/or heat, a method of immersing woven fabric or beam in a polymer solution of a support medium and then removing a solvent, a method of making a support medium in fine powder, impregnating the fine powder in woven fabric or beam and then melting it, or the like may be used.

Further, as another method, the present invention may be implemented using a melt extrusion method. More specifically, in the case in which a cross section perpendicular to the long axial direction of birefringent island-in-the-sea yarns, which are dispersed and arranged in a base material, has a polygon, a profile extrusion method of partitioning an extruder discharge port into a plurality of confinements, extruding resin constituting the birefringent island-in-the-sea yarns in a polygonal form from every other spinneret, and extruding resin constituting the base material from a spinneret between the spinneret s may be adopted. In the case in which a cross section perpendicular to the long axial direction of birefringent island-in-the-sea yarns, which are dispersed and arranged in a support medium, is substantially circular, a profile extrusion method of partitioning an extruder discharge port into a plurality of spinneret s, extruding resin constituting the birefringent island-in-the-sea yarns in a round pole form from the spinnerets being consecutive within the cross section, and extruding resin constituting a base material from a spinneret between the spinnerets may be adopted. In these cases, the extruder and confinements may be designed such that different kinds of melted resins are alternately extruded from the spinnerets of the extruder in a specific form and thus form the above dispersed arrangement structure.

Meanwhile, there can be provided a backlight unit, including the above luminance-enhanced film of the present invention, and a liquid crystal display device including the backlight unit can also be provided. In this case, the liquid crystal display device may comprise a phase difference film and/or an absorbent type polarization film.

As a result, in the case in which a birefringent island-in-the-sea yarn, comprising anisotropic island portions disposed in an isotropic sea portion within a luminance-enhanced film, is used as a birefringent fiber, not only an optical modulation effect between a base material and the birefringent island-in-the-sea yarn, but also an optical modulation effect between the anisotropic island portions and the isotropic sea portion within the birefringent island-in-the-sea yarn are generated. Accordingly, the optical modulation effect of the luminance-enhanced film can be increased significantly. In particular, in the case in which, after the island-in-the-sea yarns are threaded to form a conjugate fiber, they are weaved in the form of ends and wefts and disposed in a luminance-enhanced film, an excellent optical modulation effect, which cannot be compared with a case where a typical birefringent fiber is used, can be obtained.

The present invention will now be described in detail in connection with embodiments and experimental examples. The following embodiments and experimental examples illustrate only the present invention, and the range of the present invention is not limited by the following embodiments and experimental examples.

37 island portions, comprised of anisotropic PEN (nx=1.88, ny=1.57, nz=1.57), were disposed within a filler of isotropic Co-PEN (nx=1.57, ny=1.57, nz=1.57). In this composition, thread was performed using an undrawn yarn 150/24 under a condition in which a spinning temperature was 305℃ and a spinning speed was 1500 M/min, and a drawn yarn 50/24 was obtained through three-time drawings. The island-in-the-sea yarn fabricated at this time included the 37 island portions comprised of the anisotropic PEN (nx=1.88, ny=1.57, nz=1.57) disposed within the filler of the isotropic Co-PEN (nx=1.57, ny=1.57, nz=1.57). After 4,200 strands (since a raw yarn of 24 strands behaves as one group, an actual number of fiber strands is 100,800 strands, i.e., 4,200×24) of the fabricated island-in-the-sea yarn was wound on the beam of 762mm in parallel, the wound beam was placed on a PC alloy sheet having a rear surface on which Met treatment was performed and then stacked using specific tension. Here, the refractive index of the PC alloy sheet was 1.57. Thereafter, mixed UV-hardening coating resin of epoxy acrylate and urethane acrylate, which have the refractive index of 1.54, was coated on the PC alloy sheet in which the fibers were stacked and a point where a mirror face roll was introduced, and experienced primary and secondary UV-hardening processes, thereby fabricating a blending sheet in which the birefringent island-in-the-sea yarns were stacked. The coating resin showed the refractive index of 1.54 before UV coating hardening, but showed the refractive index of 1.57 after hardening. Based on this fact, a luminance-enhanced film having a thickness of 400㎛ was fabricated.

A luminance-enhanced film having a thickness of 400㎛ was fabricated in the same manner as the embodiment 1 except that the number of the island portions was 217.

A luminance-enhanced film having a thickness of 400㎛ was fabricated in the same manner as the embodiment 2 except that the island-in-the-sea yarn used in the embodiment 2 experienced four conjugation (50/24×4) to obtain a 200/96 raw yarn and then used.

In order to simplify the process of mixing the fiber used in the embodiment 2 in the sheet, a yarn of 4,200 strands were weaved to have a weft density 50 numbers/inch using a beam, which was obtained by winding the 4,200 strands in such a way as to be arranged 762mm in width in parallel as in the embodiment 1. Fabric underwent plain weaving in order to minimize the weft density. The fabricated woven fabric was stacked on the sheet while being released through a roll over a sheet extrusion die as in the embodiment 1, coated with a coating agent, and hardened to thereby fabricate a luminance-enhanced film having a thickness of 400㎛.

In order to improve optical use efficiency of the luminance-enhanced film, the structured surface layer was formed over the luminance-enhanced film of the embodiment 3. A luminance-enhanced film having a thickness of 400㎛ was fabricated in the same manner as the embodiment 3 except that the structured surface layer was formed using a prism pattern roll during the blending sheet fabrication process.

A luminance-enhanced film having a thickness of 400㎛ was fabricated in the same manner as the embodiment 1 except that an undrawn isotropic fiber 150/24, comprised of co-PEN (nx=ny=nz=1.57), was used instead of a birefringent island-in-the-sea yarn.

A luminance-enhanced film having a thickness of 400㎛ was fabricated in the same manner as the embodiment 1 except that an undrawn yarn having an island-in-the-sea structure (including 24 island portions), comprised of PET (nx=ny=nz=1.57) and co-PEN (nx=ny=nz=1.57), was used.

After PEN resin of IV 0.53 was polymerized instead of the birefringent island-in-the-sea yarn according to the embodiment 1, a raw yarn of an undrawn yarn 150/24 was fabricated. At this time, thread was performed using a spinning temperature of 305℃ and a spinning speed of 1500 M/min. The obtained undrawn yarn was drawn three times in a temperature range of 150℃, thus fabricating a 50/24 drawn yarn. The drawn PEN fiber showed birefringence, and the refractive indices in respective directions were nx=1.88, ny=1.57 and nz=1.57. A luminance-enhanced film having a thickness of 400㎛ was fabricated in the same manner as the embodiment 1 except that the birefringence PEN fiber was included instead of the island-in-the-sea yarn of the embodiment 1.

The following physical properties of the luminance-enhanced films, fabricated according to the embodiments 1 to 5 and the comparison examples 1 to 3, were evaluated, and the results thereof were listed in Table 1.

1. Luminance

In order to measure the luminance of the fabricated luminance-enhanced film, the following tests were performed. After a panel was assembled on a 52" direct lighting type backlight unit equipped with a diffusion plate, two sheets of diffusion sheets, and the luminance-enhanced film, luminance at 9 points was measured using BM-7 tester (TOPCON, Korea) and average values thereof were listed.

2. Transmittance

Transmittance was measured according to an ASTM D2003 method using COH500A analysis equipment (NIPPON DENSHOKU Co., Japan).

3. Degree of polarization

The degree of polarization was measured using RETS-200 analysis equipment (OTSKA Co., Japan).

4. Moisture absorption factor

The luminance-enhanced film was immersed in water of 23℃ for 24 hours according to ASTM D570 and a change in weight% before and after the process was measured.

5. Sheet sprout

The luminance-enhanced film was assembled in a 52-inch backlight unit, left in a thermo-hygrostat under condition of 60℃ and 75% for 96 hours, and dissolved in order to monitor a degree in which sprouts of the luminance-enhanced film were generated by the naked eyes. The monitoring results were marked by ○, △ and ×.

○: Good, △: Normal, ×: Bad

6. UV-resistant property

The luminance-enhanced film was irradiated by the output of a 130 mW-ultraviolet lamp (365 nm) at the height of 10 cm using SMDT51H (SEI MYUNG VACTRON CO., LTD. (Korea)) for 10 minutes. YI (Yellow Index) before and after the process was measured using SD-5000 analysis equipment (NIPPON DENSHOKU Co., (Japan)), and the yellowness index thereof was evaluated.

It could be seen from Table 1 that the luminance-enhanced films of the embodiments 1 to 5, comprising the birefringent island-in-the-sea yarns, had a much excellent optical property than that of the comparison examples 1 and 2 comprising the isotropic fibers. It could be also seen that the luminance-enhanced films of the embodiments 1 to 5, comprising the birefringent island-in-the-sea yarns, had a much better optical property than that of the comparison example 3 comprising the birefringent fiber.

The luminance-enhanced film of the present invention can be widely used for liquid crystal display devices such as mobile phones and LCDs requiring high luminance.

Claims

A luminance-enhanced film comprises an island-in-the-sea yarn having birefringence within a base material.
The luminance-enhanced film of claim 1, wherein the base material has isotropic property.
The luminance-enhanced film of claim 2, wherein the base material comprises any one or more selected from a group of polyethylene naphthalate (PEN), copolyethylene naphthalate (co-PEN), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate (PC) alloy, polystyrene (PS), heat-resistant polystyrene (PS), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), poly vinyl chloride (PVC), styrene acrylonitrile mixture (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea (UF), melanin (MF), non-saturated polyester (UP), silicon (SI), elastomers and cycloolefin polymer.
The luminance-enhanced film of claim 2, wherein a refractive index of the base material ranges from 1.4 to 2.0.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn is disposed in plural numbers in one direction within the base material.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn is disposed vertically to a light source within the base material.
The luminance-enhanced film of claim 5, wherein the island-in-the-sea yarns are randomly disposed within the base material.
The luminance-enhanced film of claim 5, wherein the island-in-the-sea yarns are brought in contact with each other within the base material and disposed.
The luminance-enhanced film of claim 5, wherein the island-in-the-sea yarns form one or more layers within the base material.
The luminance-enhanced film of claim 1, wherein:

a difference in a refractive index between the base material and the island-in-the-sea yarn with respect to two axial directions is 0.03 or less, and a difference in a refractive index between the base material and the island-in-the-sea yarn with respect to the remaining one axial direction is 0.05 or more.
The luminance-enhanced film of claim 10, wherein the remaining one axial direction is a length direction of the island-in-the-sea yarn.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn is 500 to 4,000,000 numbers/㎤ within the luminance-enhanced film.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn has a circular or oval cross section in a length direction.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn has a non-circular cross section in a length direction.
The luminance-enhanced film of claim 1, wherein a sea portion of the island-in-the-sea yarn is isotropic.
The luminance-enhanced film of claim 1, wherein an island portion of the island-in-the-sea yarn is anisotropic.
The luminance-enhanced film of claim 1, wherein:

a difference in a refractive index between a sea portion and an island portion of the island-in-the-sea yarn with respect to two axial directions is 0.03 or less, and

a difference in a refractive index between the sea portion and the island portion of the island-in-the-sea yarn with respect to the remaining one axial direction is 0.05 or more.
The luminance-enhanced film of claim 17, wherein the remaining one axial direction is a length direction of the island-in-the-sea yarn.
The luminance-enhanced film of claim 17, wherein the sea portion has a refractive index of 1.4 to 2.0.
The luminance-enhanced film of claim 1, wherein an island portion of the island-in-the-sea yarn is disposed in plural numbers.
The luminance-enhanced film of claim 1, wherein an area ratio of the sea portion and the island portion on the basis of a traverse section of the island-in-the-sea yarn is 2 : 8 to 8 : 2.
The luminance-enhanced film of claim 1, wherein a sea portion of the island-in-the-sea yarn comprises any one or more selected from a group of polyethylene naphthalate (PEN), copolyethylene naphthalate (co-PEN), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate (PC) alloy, polystyrene (PS), heat-resistant polystyrene (PS), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), poly vinyl chloride (PVC), styrene acrylonitrile mixture (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea (UF), melanin (MF), non-saturated polyester (UP), silicon (SI), elastomers and cyclo olefin polymer.
The luminance-enhanced film of claim 1, wherein the island portion of the island-in-the-sea yarn comprises any one or more selected from a group of polyethylene naphthalate (PEN), copolyethylene naphthalate (co-PEN), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate (PC) alloy, polystyrene (PS), heat-resistant polystyrene (PS), polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide (PI), poly vinyl chloride (PVC), styrene acrylonitrile mixture (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea (UF), melanin (MF), non-saturated polyester (UP), silicon (SI), elastomers and cyclo olefin polymer and is anisotropic.
The luminance-enhanced film of claim 20, wherein the plurality of island portions has the same traverse cross section.
The luminance-enhanced film of claim 20, wherein the plurality of island portions has different traverse cross sections.
The luminance-enhanced film of claim 1, wherein the base material includes a plurality of the island-in-the-sea yarns having different traverse section shapes.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn is extended in a length direction.
The luminance-enhanced film of claim 1, further comprising a structured surface layer.
The luminance-enhanced film of claim 28, wherein the structured surface layer is formed on a surface from which light is output.
The luminance-enhanced film of claim 28, wherein the structured surface layer has a prism shape.
The luminance-enhanced film of claim 30, wherein the structured surface layer has an irregular prism shape.
The luminance-enhanced film of claim 28, wherein the structured surface layer has a lenticular shape.
The luminance-enhanced film of claim 32, wherein the structured surface layer has an irregular lenticular shape.
The luminance-enhanced film of claim 33, wherein the structured surface layer has a convex lens shape.
The luminance-enhanced film of claim 34, wherein the structured surface layer has an irregular convex lens shape.
The luminance-enhanced film of claim 28, wherein the birefringent island-in-the-sea yarn is disposed or not disposed in the structured surface layer.
The luminance-enhanced film of claim 28, wherein a rear surface of the luminance-enhanced film has underwent Matt treatment.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn has a thickness of 0.3 to 20 denier.
The luminance-enhanced film of claim 1, wherein a cross section of an island portion of the island-in-the-sea yarn has a non-circular section.
The luminance-enhanced film of claim 1, wherein a refractive index of a sea portion is identical to that of the base material.
The luminance-enhanced film of claim 1, wherein the island-in-the-sea yarn is weaved in wefts and warps.
The luminance-enhanced film of claim 41, wherein:

any one of the wefts and the ends is the island-in-the-sea yarn, and

the other of the wefts and the warps is an isotropic fiber.
The luminance-enhanced film of claim 41, wherein the wefts and ends are formed by 1 to 200 strands of the island-in-the-sea yarns.
A backlight unit comprising a luminance-enhanced film according to any one of claims 1 to 43.
A liquid crystal display device comprising a backlight unit according to claim 44.
The liquid crystal display device of claim 45, wherein the liquid crystal display device comprises a phase difference film.
The liquid crystal display device of claim 45, wherein the liquid crystal display device comprises an absorbent type polarization film.
A luminance-enhanced film, comprising:

a base material whose refractive index of a x-axis direction is nX1, a refractive index of a y-axis direction is nY1 and refractive index of a z-axis direction is nZ1;

a birefringent island-in-the-sea yarn disposed within the base material,

wherein, when refractive indices of the birefringent island-in-the-sea yarn is nX2, nY2 and nZ2, at least one of the x, y and z-axis refractive indices of the base material is identical to that of x, y and z-axis refractive indices of the birefringent island-in-the-sea yarn.
The luminance-enhanced film of claim 48, wherein the nX2 > nY2 = nZ2.
The luminance-enhanced film of claim 48, wherein the base material is isotropic.
The luminance-enhanced film of claim 48, wherein, when a refractive index of the x-axis direction, which is a length direction of an island portion of the island-in-the-sea yarn, is nX3, a refractive index of the y-axis direction is nY3 and a refractive index of the z-axis direction is nZ3, and a refractive index of the x-axis direction of a sea portion of the island-in-the-sea yarn is nX4, a refractive index of the y-axis direction of the sea portion of the island-in-the-sea yarn is nY4 and a refractive index of the z-axis direction of a sea portion of the island-in-the-sea yarn is nZ4, an absolute value of a difference in the refractive index between the nX3 and the nX4 or between the nY3 and the nY4 is 0.15 or more.
The luminance-enhanced film of claim 51, wherein an absolute value of a difference in the refractive index between the nZ3 and the nZ4 is less than 0.03.