JP2008122991A - Light transmissive film, method for producing light transmissive film, and liquid crystal display device - Google Patents

Abstract

Provided is a light transmission film having not only a light collecting function but also a certain polarization separation function.
In the light transmission film (prism sheet 13) of the present invention, the refractive index nx in the prism extending direction and the refractive index ny in the prism array direction are different from each other. By providing a refractive index difference between the prism extending direction and the prism array direction orthogonal to the prism extending direction, the polarization component Lx that vibrates in the prism extending direction and the prism array direction with respect to the light incident on the light transmission film. Different polarization characteristics can be given to the polarization component Ly that oscillates. For example, by making the refractive index in the prism extending direction larger than the refractive index in the prism arranging direction (nx> ny), the prism extends more than the polarization component Ly that vibrates in the prism arranging direction among the light incident on the light transmission film. The amount of the polarized light component Lx that vibrates in the direction becomes return light. As a result, not only the light condensing function but also a constant polarization separating function can be obtained.
[Selection] Figure 3

Description

  The present invention relates to a light transmissive film in which a three-dimensional structure is continuously arranged on one surface, a method for manufacturing the light transmissive film, and a liquid crystal display device.

  A liquid crystal display (LCD) is lower in power consumption, smaller and thinner than a cathode ray tube (CRT), and is now available in mobile phones, digital cameras, and PDAs (Personal Digital Displays). Various sizes are widely used, from small devices such as Assistants) to large-sized LCD TVs.

  Liquid crystal display devices are classified into transmission type, reflection type, and the like. In particular, the transmission type liquid crystal display device includes a liquid crystal display panel in which a liquid crystal layer is sandwiched between a pair of transparent substrates, and a light incident side and a light emission side of the liquid crystal display panel. In addition to the arranged first and second polarizers, a backlight unit is provided as an illumination light source. The backlight unit includes an edge light type using a light guide plate in addition to a direct type in which a light source is arranged directly under a liquid crystal display panel.

  On the other hand, a configuration is known in which a light-transmitting film called a brightness enhancement film is disposed between a backlight unit and a liquid crystal display panel for the purpose of distributing light source light in the front direction (for example, the following). Patent Document 1). The brightness enhancement film is composed of a prism sheet in which prisms having a substantially triangular cross section on one surface are periodically arranged at a fine pitch, and has the effect of concentrating light by raising the light of the backlight in the front direction. is doing.

Japanese Patent No. 3158555

  However, since the refractive index of the conventional prism sheet is isotropic and the light emitted from the prism sheet is usually non-polarized light, about half of the light emitted from the prism sheet is light of the liquid crystal display panel. It will be absorbed by the 1st polarizer arrange | positioned at the incident side. As a result, there is a problem that the illumination light from the backlight cannot be used effectively, and the luminance cannot be improved.

  On the other hand, by inserting a reflective polarizer that transmits one linearly polarized component and reflects the other linearly polarized component between the prism sheet and the liquid crystal display panel, the light utilization efficiency of the backlight is increased and the luminance is increased. It is known to improve the above.

  However, the use of this type of reflective polarizer increases the manufacturing cost of the liquid crystal display device and increases the number of components, which hinders the downsizing and thinning of the device. Further, even if a reflective polarizer is used, it is not always functionally sufficient, for example, a part of the polarization component in the absorption axis direction of the first polarizer leaks out.

  This invention is made | formed in view of the above-mentioned problem, and makes it a subject to provide the manufacturing method and liquid crystal display device of a light transmissive film which has a condensing function and a fixed polarization separation function.

  In solving the above problems, the light-transmitting film of the present invention has a three-dimensional structure continuously arranged on one surface, and the refractive index in the extending direction of the three-dimensional structure and the refractive index in the arranging direction of the three-dimensional structure. Are different from each other.

  A polarization component and a three-dimensional structure that vibrate in the three-dimensional structure extending direction with respect to light incident on the light transmission film by providing a difference in refractive index between the three-dimensional structure extending direction and an arrangement direction perpendicular thereto. The linearly polarized light components that vibrate in the arrangement direction can have different transmission characteristics. The difference in the transmission characteristics of the polarization components increases as the difference in refractive index between the extending direction of the three-dimensional structure and the arrangement direction increases.

The extending direction of the three-dimensional structure is not limited to one direction, and the extending direction of the three-dimensional structure may be different from each other and two-dimensionally arranged in a plurality of directions. The three-dimensional structure in the present invention includes structures such as prisms or lenticular lenses. The prism has a triangular cross section with an apex angle of 90 ° (degrees), for example.

  In the above-described configuration, for example, by making the refractive index in the prism extending direction larger than the refractive index in the prism arrangement direction, out of the light incident on the light transmission film, the prism is more polarized than the polarization component that vibrates in the prism arrangement direction. The amount of polarized light that oscillates in the extending direction of the return light becomes larger. As a result, a certain polarization separation function can be obtained.

  The light-transmitting film of the present invention having refractive index anisotropy between the extending direction of the three-dimensional structure and the arrangement direction is a step of forming a resin film having a three-dimensional structure on one surface, and the three-dimensional structure of the resin film. The film can be manufactured through a process of extending in the extending direction and making a difference in refractive index between the extending direction of the three-dimensional structure and the arrangement direction.

  The reason why the extending direction of the resin film is the extending direction of the three-dimensional structure is to reduce the fluctuation of the optical characteristics due to the prism shape change before and after the stretching. In the case where the refractive index in the extending direction is made larger than the refractive index in the arrangement direction of the three-dimensional structure, it is preferable to select a material having a refractive index large in the stretching direction as a constituent material of the light transmission film. Examples of materials whose refractive index increases in the stretching direction include, for example, PET (polyethylene terephthalate), PEN (polyethylene naphthalate), and mixtures thereof, or copolymers such as PET-PEN copolymer, polycarbonate, polyvinyl alcohol, polyester, and polyfluoride. Examples include vinylidene, polypropylene, and polyamide.

  On the other hand, when making the refractive index in the arrangement direction larger than the refractive index in the extending direction of the three-dimensional structure, it is preferable to select a material having a refractive index small in the stretching direction as a constituent material of the light transmission film. Examples of the material having a refractive index that decreases in the stretching direction include methacrylic resin, polystyrene-based resin, styrene-methyl methacrylate copolymer, and mixtures thereof.

  And when using the light transmission film which concerns on this invention as a brightness improvement film in a liquid crystal display device, there exist the following two structures. One is that the light-transmitting film is formed such that the refractive index in the extending direction is larger than the refractive index in the arrangement direction of the three-dimensional structure, and the liquid crystal display of the three-dimensional structure and the pair of polarizers. In this configuration, the angle formed by the light transmission axis direction of the polarizer disposed on the light incident side of the panel is provided in the range of 0 ° to 45 °. The other is that the light transmission film is formed such that the refractive index in the arrangement direction is larger than the refractive index in the extension direction of the three-dimensional structure, and the extension direction of the three-dimensional structure and the pair of polarizers. The angle formed by the light transmission axis direction of the polarizer disposed on the light incident side of the liquid crystal display panel is provided in the range of 0 ° to 45 °.

  With these configurations, the light emitted from the light transmissive film can be efficiently incident on the liquid crystal display panel, so that the backlight can be effectively used and the brightness of the liquid crystal display device can be improved. It becomes like this.

  As described above, according to the light transmissive film of the present invention, since there is anisotropy of the refractive index in the extending direction and the arrangement direction of the three-dimensional structure, not only the light collecting action but also the constant polarization separation An effect can also be obtained. Therefore, the brightness improvement effect of the liquid crystal display device can be enhanced without using an optical element such as a reflective polarizer, and the number of parts and the manufacturing cost can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a liquid crystal display device 10 including a light transmission film according to an embodiment of the present invention. First, the overall configuration of the liquid crystal display device 10 will be briefly described.

  The liquid crystal display device 10 of the present embodiment includes a liquid crystal display panel 11, a first polarizer 12A and a second polarizer 12B that sandwich the liquid crystal display panel 11, a prism sheet 13, a diffuser plate 14, and a backlight unit 15. And.

  The liquid crystal display panel 11 has a structure in which a liquid crystal layer is sandwiched between a pair of transparent substrates. In this embodiment, a liquid crystal material for driving mode having excellent viewing angle characteristics such as VA (vertical alignment) and IPS (in-plane switching) is applied, but besides this, a TN (twisted nematic) type is also available. Applicable.

  The first polarizer 12 </ b> A is a polarizer disposed on the light incident side of the liquid crystal display panel 11, and the second polarizer 12 </ b> B is a polarizer disposed on the light emitting side of the liquid crystal display panel 11. The direction of the light transmission axis a of the first polarizer 12A is determined by the refractive index of the prism arrangement direction of the prism sheet 13 (hereinafter referred to as “prism arrangement direction”) and the prism extension direction (hereinafter “prism extension direction”). It is determined by the magnitude relationship between the refractive index and the refractive index.

  For example, when the refractive index in the prism extending direction is larger than the refractive index in the prism array direction, the direction of the transmission axis a of the light of the first polarizer 12A is changed to a prism as shown in FIG. The greatest effect can be obtained when the direction is the arrangement direction. However, if the orientation of the transmission axis a and the prism arrangement direction cannot be matched due to other reasons such as obtaining an appropriate angular luminance distribution and improving the contrast of the liquid crystal display panel 11, the transmission axis a and the prism arrangement direction You may widen the angle formed by. In this case, in order to improve the front luminance, this angle needs to be from 0 ° to 45 °, and more preferably from 0 ° to about 20 °.

  On the other hand, when the refractive index in the prism array direction is larger than the refractive index in the prism extending direction, the direction of the light transmission axis a of the first polarizer 12A is the direction in the prism extending direction. Sometimes the greatest effect is obtained. However, for other reasons such as obtaining an appropriate angular luminance distribution and improving the contrast of the liquid crystal display panel 11, if the direction of the transmission axis a and the prism extending direction cannot be matched, the transmission axis a and the prism extension The angle formed by the current direction may be widened. In this case, in order to improve the front luminance, this angle needs to be from 0 ° to 45 °, and more preferably from 0 ° to about 20 °.

  The prism sheet 13 corresponds to the light transmission film according to the present invention, and is used as a brightness enhancement film for improving the front brightness of the liquid crystal display device 10. The prism sheet 13 is disposed on the light exit side of the diffuser plate 14 that diffuses and emits illumination light from the backlight unit 15 (hereinafter also referred to as “backlight light”). It has a separating action.

  The backlight unit 15 is configured as a direct type including a plurality of linear light sources 16 and a reflecting plate 17, but is not limited thereto, and may be configured as a side edge type using a light guide plate. The light source 16 is a linear light source such as a cold cathode fluorescent lamp (CCFL). In addition to this, for example, a point light source such as a light emitting diode (LED) is used. Also good.

  Next, the details of the prism sheet 13 as the light transmission film according to the present invention will be described.

  FIG. 2 schematically shows the overall configuration of the prism sheet 13. The prism sheet 13 is formed of a translucent resin material, and a prism structure surface in which columnar prisms having a uniform triangular section are continuously arranged in one direction (Y direction) on one surface thereof. 13a. Each prism constituting the prism structure surface 13a corresponds to the “three-dimensional structure” according to the present invention, and is formed with the same apex angle and pitch. In this embodiment, the prism apex angle is 90 °, and the arrangement pitch is For example, 50 μm. The other surface of the prism sheet 13 is a flat surface 13b. The prism sheet 13 is arranged with the prism structure surface 13a facing the light emission side (the liquid crystal display panel 11 side).

  The prism sheet 13 has different refractive indexes in the prism extending direction (X direction) and the prism array direction (Y direction). Thus, by providing in-plane anisotropy to the refractive index of the prism sheet 13, the transmission characteristics of light incident on the prism sheet 13 can be changed according to the polarization state. FIG. 3 shows a path of light incident on the prism sheet 13, and particularly shows a case where the refractive index nx in the prism extending direction is larger than the refractive index ny in the prism array direction (nx> ny). Here, Lx represents a polarization component that vibrates in the prism extending direction (X direction) of the backlight light L, and Ly represents a polarization component that vibrates in the prism arrangement direction (Y direction) of the backlight light L. Show.

  Referring to FIG. 3, the backlight light that is incident on the flat surface 13 b of the prism sheet 13 at an incident angle θ <b> 1 from an oblique direction is split in the prism extension direction (X direction) and the arrangement direction (Y direction). Since the refractive index of the sheet 13 is different (nx> ny), the X-direction polarization component Lx and the Y-direction polarization component Ly of the backlight light are refracted at different refraction angles rx, ry (rx <ry), and are different. The light is emitted from the prism slope at the emission angles φx and φy. At this time, the emission angle φy of the Y-direction polarization component Ly is smaller than the emission angle φx of the X-direction polarization component Lx (φx> φy).

  In the above example, both the polarization components Lx and Ly are emitted from the light exit surface (prism structure surface 13a) of the prism sheet 13. However, since the prism extending direction (X direction) and the prism arrangement direction (Y direction) have different refractive indexes, the polarization component that vibrates in these directions is an interface such as the prism sheet flat surface 13b and the prism slope. Therefore, the light is reflected with different reflectances. Therefore, in the present embodiment, the refractive index nx in the prism extending direction is larger than the refractive index ny in the prism array direction, so that the polarization component Lx that vibrates in the prism extending direction becomes Ly. Compared with the amount of reflection. As a result, the amount of backlight light transmitted through the prism sheet 13 is greater in Ly than in Lx.

  Further, since the emission angles of the polarization components Lx and Ly emitted from the prism inclined surface have a relationship of φx> φy, if the incident angle of the backlight light incident on the prism sheet 13 satisfies a certain condition, the polarization component Lx is It is possible to realize a complete polarization separation state in which total reflection is repeated on the slope of the prism to become return light and only the polarization component Ly is transmitted through the prism sheet 13. FIG. 3 shows how this example is established under the condition of the incident angle θ2. A specific example of θ2 is about 11 to 25 degrees under the conditions of nx = 1.9, ny = 1.6, and the apex angle of the prism is 90 degrees.

  On the other hand, when the incident angle of the backlight light with respect to the prism sheet 13 becomes too small, the backlight light is not different from the case where the backlight light is incident on the flat surface 13b of the prism sheet 13 perpendicularly. In this case, as shown in FIG. 3, the backlight light L becomes return light that repeats total reflection on the prism slope of the prism structure surface 13a and returns to the backlight side regardless of the polarization state.

  As described above, by providing the prism sheet 13 with in-plane refractive index anisotropy, in addition to the condensing function of the backlight light, a certain polarization separation function can be obtained. In each of the above examples, the light reflected by the prism sheet 13 is reflected on the reflecting plate 17 (FIG. 1) of the backlight unit 15 and the surface of the diffusing plate 14, is made non-polarized, and enters the prism sheet 13 again. As a result, the light utilization efficiency is increased and it is possible to contribute to the improvement of the front luminance.

  Next, an example of a method for manufacturing the prism sheet 13 configured as described above will be described.

  The prism sheet 13 of the present embodiment includes a step of forming a resin film having a prism structure surface 13a formed on one surface, and the resin film is stretched in the prism extending direction so that the prism extending direction and the prism are And a step of making a difference in refractive index depending on the arrangement direction.

  The molding method of the resin film is not particularly limited, and for example, a hot press method, a melt extrusion method, or the like is applicable. Alternatively, a flat resin sheet may be used as a base, and a prism layer may be formed thereon. In addition, the method which can produce a resin film continuously by a roll system is preferable.

  The produced resin film is provided with refractive index anisotropy by being stretched in the prism extending direction. The prism sheet 13 of the present embodiment is configured such that the refractive index nx in the prism extending direction is larger than the refractive index ny in the prism array direction. Therefore, as shown in FIG. 4A, after producing the resin film 23 using a resin material having a refractive index large in the stretching direction, the resin film 23 is stretched in the prism extending direction (X direction). The objective prism sheet 13 is obtained. The stretch ratio can be appropriately set according to the required in-plane refractive index difference, the type of resin film material, and the like.

  Examples of the resin material whose refractive index increases in the stretching direction include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), a mixture thereof, or a copolymer such as PET-PEN copolymer, polycarbonate, polyvinyl alcohol, polyester, and polyfluoride. Examples include vinylidene, polypropylene, and polyamide.

  Here, the reason that the extending direction is the prism extending direction is to prevent the target optical characteristics from changing due to the change in the prism shape before and after the extending. FIG. 4B shows changes in the outer shape of the prism structure surface before and after stretching, where the solid line indicates before stretching and the alternate long and short dash line indicates after stretching. By setting the stretching direction to the prism extending direction (X direction), the prism cross-sectional shape after stretching is substantially similar to the prism cross-sectional shape before stretching, so that fluctuations in optical characteristics are suppressed and necessary. It becomes possible to control the prism shape with high accuracy.

  On the other hand, as shown in FIGS. 5A and 5B, when the resin film 23 is stretched in the prism arrangement direction (Y direction) to have the refractive index anisotropy, the change in the outer shape of the prism becomes remarkable. The prism apex angle and prism arrangement pitch are enlarged, and it becomes difficult to control the required optical characteristics with high accuracy. In FIG. 5B, a two-dot chain line indicates before stretching, and a solid line indicates after stretching.

  When the refractive index in the prism array direction is configured to be larger than the refractive index in the prism extending direction, a resin material having a small refractive index in the extending direction may be used to extend in the prism extending direction. Good. Examples of resin materials whose refractive index is small in the stretching direction include methacrylic resins such as polymethyl methacrylate, polystyrene resins, styrene-acrylonitrile copolymers (AS resins), styrene-methyl methacrylate copolymers, and mixtures thereof. Can be mentioned.

  Next, the operation of the liquid crystal display device 10 of the present embodiment will be described with reference to FIG. FIG. 6 is a schematic side view of the liquid crystal display device 10 for explaining the polarization state of light transmitted through the prism sheet 13, the first polarizer 12A, the liquid crystal display panel 11, and the second polarizer 12B.

  As described above, the transmission axis a of the first polarizer 12A is determined by the magnitude relationship between the refractive index in the prism array direction of the prism sheet 13 and the refractive index in the prism extending direction. FIG. 6 shows a case where the refractive index in the prism extending direction is larger than the refractive index in the prism array direction, and the transmission axis a of the first polarizer 12A is in the prism array direction (Y direction). ) Is preferable. In FIG. 6, Lx indicates a polarization component that vibrates in the prism extending direction (X direction) of the backlight light L, and Ly vibrates in the prism arrangement direction (Y direction) of the backlight light L. The polarization component is shown.

  Non-polarized light (backlight light L) irradiated from a backlight unit 15 (not shown) and transmitted through the diffusion plate 14 enters the flat surface 13 b of the prism sheet 13. The backlight light L is condensed in the front direction on the prism sheet 13 and emitted from the prism structure surface 13a, and then enters the first polarizer 12A. The first polarizer 12A absorbs Lx of the incident backlight L and transmits Ly. The Ly that has passed through the first polarizer 12A is subjected to polarization control in the pixel unit in the liquid crystal display panel 11 and is incident on the second polarizer 12B, and only the polarized light having the transmission axis of the second polarizer 12B is transmitted therethrough. An image is formed on.

  Now, the incident angle θ of the backlight light L incident on the prism sheet 13 is not uniform and has a certain range of angular distribution. Since the prism sheet 13 of the present embodiment is formed such that the refractive index nx in the prism extending direction is larger than the refractive index ny in the prism arrangement direction, the backlight light L transmitted through the prism sheet 13 is shown in FIG. As described with reference to FIG. 5, Ly is larger than Lx, and the quantitative ratio is determined by the difference between the refractive index of the prism sheet 13 in the prism arrangement direction and the refractive index in the prism extending direction, and the prism sheet 13. It depends on the distribution of the incident angle θ of the incident backlight L.

  On the other hand, a part of the backlight light L reflected by the prism sheet 13 is reflected by the surface of the diffusion plate 14 or the reflection plate 17 of the backlight unit 15 and enters the prism sheet 13 again. By repeating such a recycling action, the backlight light L can be effectively used.

  As described above, according to the present embodiment, since the prism sheet 13 has not only the light condensing function but also a certain polarization separation function, the prism extending direction of the backlight light L emitted from the prism sheet 13. The amount of emitted light of the polarized component Lx can be made smaller than the amount of emitted light of the polarized component Ly in the prism array direction, and the amount of absorption of the backlight light L in the first polarizer 12A can be reduced, so that the backlight light L can be effectively used. It becomes like this. Thereby, the extraction efficiency of the backlight light L is increased, and the front luminance can be improved.

  In addition, since an expensive optical element such as a reflective polarizer is not necessarily required, it is possible to further reduce the thickness of the liquid crystal display device by reducing the number of parts and to reduce the manufacturing cost.

  The polarization separation effect of the backlight light L by the prism sheet 13 becomes more prominent as the difference between the refractive index nx in the prism extending direction and the refractive index ny in the prism array direction increases. FIG. 7 shows a simulation result of the luminance improvement rate when the refractive index ny in the prism arrangement direction is larger than the refractive index nx in the prism extending direction, where nx = 1.60 and ny = nx + Δn. Yes. This indicates how much the luminance is improved when the birefringence Δn is set to 0 as a reference. The prism apex angle was 90 °.

  As apparent from FIG. 7, the luminance improvement rate increases as Δn increases. Since the angular luminance distribution is determined by nx, this value can be appropriately determined by product design or the like. On the other hand, it is preferable that ny is larger than nx, and the luminance improvement rate can be increased.

  As mentioned above, although embodiment of this invention was described, of course, this invention is not limited to this, A various deformation | transformation is possible based on the technical idea of this invention.

  For example, in the above embodiment, the in-plane refractive index difference of the prism sheet 13 is configured as nx> ny, but instead of this, nx <ny may be used. In this case, a resin material whose refractive index is small in the stretching direction when stretched in the prism extending direction may be used. In this case, it is preferable that the prism arrangement direction is oriented in a direction orthogonal to the transmission axis of the first polarizer.

  In the above embodiment, an example in which one prism sheet 13 is used has been described. However, two prism sheets 13 may be used in an overlapping manner. In this case, the prism extending direction is arranged so as to be orthogonal between the upper and lower sheets, one prism sheet increases the refractive index in the prism extending direction, and the other prism sheet increases the refractive index in the prism arranging direction. It is desirable. Alternatively, a prism sheet having a refractive index difference is used only for the prism sheet disposed on the upper side, and a general isotropic prism sheet (for example, “BEF” (trademark) manufactured by 3M) is used for the prism sheet disposed on the lower side. It may be used.

  In addition, in the above embodiment, the stretching is used for the expression of the refractive index anisotropy of the prism sheet 13, but the present invention is not limited to this. For example, a liquid crystal material having a refractive index anisotropy. Alternatively, the prism sheet may be formed using a crystal material having a refractive index anisotropy, and the refractive index anisotropy may be exhibited in the prism extending direction and the prism arrangement direction.

  Hereinafter, although each Example of this invention is described, this invention is not limited to these. In each of the following examples, the prism sheet having refractive index anisotropy according to the present invention may be referred to as an “anisotropic prism sheet”.

(Example 1)
[Formation of prism sheet]
As a metal embossing original plate for hot pressing for transferring and forming a prism shape on a resin film, the surface is alternately and parallel with a right-angled isosceles triangle having a vertical cross-sectional shape of 90 degrees, and crests and crests. A trough and a trough were regularly engraved at intervals of 50 μm. The resin film was a thermoplastic resin, and a 200 μm thick A-PET (amorphous PET) sheet (“Novaclear (trademark) SG007” manufactured by Mitsubishi Chemical Corporation, Tg of about 70 ° C.) was used. This resin film was poured into ice water immediately after pressing under hot pressing conditions of 100 kgf / cm ² (9.8 MPa) at 100 ° C. for 10 minutes to obtain a transparent isotropic prism sheet.

[Extension of prism sheet]
The obtained isotropic prism sheet is cut into a rectangular shape of 8 cm in length (prism extending direction) × 5 cm in width, and then the triangular section (prism section) at both ends in the longitudinal direction is chucked with a manual stretching machine and extended Uniaxial stretching was performed at a stretching speed of 1 cm / sec in a warm water of 55 ° C. in the direction so that the center of the sample was 3.5 times to obtain an anisotropic prism sheet.

  When the triangular cross section of the obtained anisotropic prism sheet and the isotropic prism sheet before stretching was measured with a surface roughness meter (Surfcoder ET4001A, manufactured by Kosaka Laboratory Ltd.), both were 45 degrees same as the original plate. It was an isosceles triangle with a base angle. Further, the prism of the sample before stretching had a pitch of about 50 μm, which was the same as that of the original plate, whereas the prism of the sample after stretching had a pitch of about 30 μm.

FIG. 8 shows a schematic cross-sectional shape of the prism sheet before and after stretching. In the figure, the alternate long and short dash line indicates the cross-sectional shape of the sample before stretching, and the solid line indicates the cross-sectional shape of the sample after stretching. It can be seen that the prism is similar before and after stretching.
In addition, the alternate long and two short dashes line has shown the prism shape when the sample cut | judged in length 1.5cm x width 5cm is extended in the vertical direction (prism extension direction). As is apparent from the illustrated example, when a sample having an aspect ratio of less than 1 is stretched in the longitudinal direction, the cross-sectional shape of the sheet is distorted and a similar prism shape cannot be obtained. Therefore, it is preferable to cut out the sample so that the aspect ratio is 1 or more.

[Measurement of birefringence]
Next, the birefringence of the obtained anisotropic prism sheet was measured. For the measurement of birefringence, as shown in FIG. 9, polarized light is vertically incident from the prism surface of the sheet 45, the transmitted light is detected by the measuring device 46, and the prism extension is determined by the difference in the outgoing angle φ of the transmitted light. A difference Δn (= nx−ny) between the refractive index nx in the current direction and the refractive index ny in the prism array direction was calculated. That is, the outgoing angle φ of the transmitted light varies depending on the incident polarization direction, and as shown in FIG. 10, the outgoing angle φx of the polarization component that vibrates parallel to the prism extending direction (hereinafter referred to as “vertical polarization Lx”). The emission angle φy of the polarization component that vibrates parallel to the prism array direction (hereinafter referred to as “horizontal polarization Ly”) is larger. Using this, Δn can be calculated.

  FIG. 11 is a measurement result showing the relationship between the light amount of the vertically polarized light Lx and the horizontally polarized light Ly transmitted through the sheet 45 and the emission angle. The unit (a.u.) on the vertical axis is an “arbitrary unit” (arbitrary unit), which indicates “relative value”. As a result of the measurement, as shown in FIG. 12, the refractive index nx in the prism extending direction of the obtained anisotropic prism sheet 45 is 1.62, the refractive index ny in the prism array direction is 1.55, and Δn is 0.07.

  From the above results, it was possible to obtain an anisotropic prism sheet having a different refractive index between the prism extending direction and the arrangement direction by uniaxially stretching after hot pressing the A-PET sheet to give a prism shape. . Further, as shown in FIG. 11, it can be confirmed that the transmittance of the horizontally polarized light Ly is higher than that of the vertically polarized light Lx. This is because the refractive index nx in the prism extending direction is larger than the refractive index ny in the prism array direction, so that the total reflection action on the prism slope of the polarization component Lx parallel to the prism extending direction is high and transmitted compared to Ly. This is because the amount of light decreases.

[Brightness orientation evaluation]
Subsequently, the luminance orientation of the anisotropic prism sheet 45 according to this example was measured. As shown in FIG. 13, the backlight unit is an edge light type having a light source 50, a reflecting plate 51, and a light guide plate 52. On the light guide plate 52, a diffusion plate 53, a brightness enhancement film 54, an anisotropic prism sheet 45, and The polarizer 55 was arranged in order, and the front luminance and illuminance were measured with a luminance / color difference meter (EZ-contrastXL88 (manufactured by ELDIM)).

  For the brightness enhancement film 54, an isotropic prism sheet ("BEF" (trademark) manufactured by 3M) was used, and the prism extending direction was arranged in the horizontal direction of the screen (horizontal direction). The anisotropic prism sheet 45 was arranged with the prism extending direction in the vertical direction of the screen (vertical direction), and the prism extending direction was orthogonal to the brightness enhancement film 54. Two types of polarizers 55, one having a light transmission axis A in the vertical direction and one having a light transmission axis B in the horizontal direction, were prepared, and the luminance orientation of vertical polarization and horizontal polarization was measured using each of them.

(Comparative Example 1)
The front luminance and illuminance were measured in the same manner as in Example 1 except that an unstretched isotropic prism sheet (prism apex angle 90 degrees, 50 μm pitch) was used instead of the anisotropic prism sheet 45.

  The measurement results are shown in FIGS.

  From the results of FIGS. 14 and 20, the vertical polarization of the anisotropic prism sheet of this example is reduced in both front luminance and illuminance as compared with the isotropic prism sheet of Comparative Example 1. On the other hand, the horizontal polarized light is higher than the isotropic prism sheet of Comparative Example 1 in both front luminance and illuminance.

  From the above results, in the anisotropic prism sheet, more vertical polarized light is reflected by the prism surface and recycled to omnidirectional light in the diffuser or reflector, thereby increasing the luminance and illuminance of horizontal polarized light. You can see that it contributes. Therefore, by directing the transmission axis of the polarizer 55 in the direction of horizontal polarization, that is, in the prism arrangement direction of the anisotropic prism sheet 45, the front luminance and illuminance (light extraction efficiency) can be efficiently utilized by using light. Can be improved.

(Example 2)
[Formation of prism sheet]
As a metal embossing original plate for hot pressing for transferring and forming a prism shape on a resin film, the surface is alternately and parallel with a right-angled isosceles triangle having a vertical cross-sectional shape of 90 degrees, and crests and crests. A trough and a trough were regularly engraved at intervals of 50 μm. The resin film was a thermoplastic resin, and an A-PEN (amorphous PEN) sheet (Tg of about 120 ° C.) having a thickness of 200 μm was used. This resin film was poured into ice water immediately after pressing under hot pressing conditions of 150 kg at 10 ° C. and 100 kgf / cm ² (9.8 MPa) to obtain an isotropic prism sheet.

[Extension of prism sheet]
The obtained isotropic prism sheet was cut into a rectangular shape of 8 cm in length (prism extending direction) × 5 cm in width, and then the triangular cross section (prism cross section) at both ends in the longitudinal direction was chucked with a manual stretching machine. Uniaxial stretching was performed at a stretching speed of 1 cm / sec so that the center of the sample was 3.5 times in an environment of 140 ° C. in the present direction, and an anisotropic prism sheet was obtained.

  When the triangular cross section of the obtained anisotropic prism sheet and the isotropic prism sheet before stretching was measured with a surface roughness meter (Surfcoder ET4001A, manufactured by Kosaka Laboratory Ltd.), both were 45 degrees same as the original plate. It was an isosceles triangle with a base angle. Further, the prism of the sample before stretching had a pitch of about 50 μm, which was the same as that of the original plate, whereas the prism of the sample after stretching had a pitch of about 30 μm.

  FIG. 15 shows a schematic cross-sectional shape of the prism sheet before and after stretching. In the figure, the solid line indicates the cross-sectional shape of the sample before stretching, and the broken line indicates the cross-sectional shape of the sample after stretching. It can be seen that the prism is similar before and after stretching.

[Measurement of birefringence]
Next, the birefringence of the obtained anisotropic prism sheet was measured. For the measurement of birefringence, the same measurement as in Example 1 was performed.

  FIG. 16 is a measurement result showing the relationship between the amount of light of the vertically polarized light Lx and the horizontally polarized light Ly transmitted through the anisotropic prism sheet and the emission angle. The unit (a.u.) on the vertical axis is an “arbitrary unit” (arbitrary unit), which indicates “relative value”. As a result of the measurement, as shown in FIG. 17, the refractive index nx in the prism extending direction of the obtained anisotropic prism sheet is 1.79, the refractive index ny in the prism array direction is 1.56, and Δn is 0. .23.

  From the above results, it was possible to obtain anisotropic prism sheets having different refractive indexes in the prism extending direction and the array direction by uniaxially stretching after hot pressing the A-PEN sheet to give a prism shape. . Further, as shown in FIG. 16, it can be confirmed that the transmittance of the horizontally polarized light Ly is higher than that of the vertically polarized light Lx. This is because the refractive index nx in the prism extending direction is larger than the refractive index ny in the prism array direction, so that the total reflection action on the prism slope of the polarization component Lx parallel to the prism extending direction is high and transmitted compared to Ly. This is because the amount of light decreases.

[Brightness orientation evaluation]
Subsequently, the luminance orientation of the anisotropic prism sheet according to this example was measured. As shown in FIG. 13, the backlight unit is an edge light type having a light source 50, a reflection plate 51, and a light guide plate 52, and a diffusion plate 53, a brightness enhancement film 54, and an anisotropic prism sheet 45 are provided on the light guide plate 52. And the polarizer 55 was arrange | positioned in order and front luminance and illumination intensity were measured with the brightness | luminance and color difference meter (EZ-contrastXL88 (made by ELDIM)).

  For the brightness enhancement film 54, an isotropic prism sheet ("BEF" (trademark) manufactured by 3M) was used, and the prism extending direction was arranged in the horizontal direction of the screen (horizontal direction). The anisotropic prism sheet 45 is arranged with the prism extending direction in the vertical direction of the screen (vertical direction), and the prism extending direction is orthogonal to the brightness enhancement film 54. Two types of polarizers 55, one having a light transmission axis A in the vertical direction and one having a light transmission axis B in the horizontal direction, were prepared, and the luminance orientation of vertical polarization and horizontal polarization was measured using each of them.

(Comparative Example 2)
Front luminance and illuminance were measured in the same manner as in Example 2 except that an unstretched isotropic prism sheet (prism apex angle 90 degrees, 50 μm pitch) was used instead of the anisotropic prism sheet 45.

  The measurement results are shown in FIGS.

  From the results of FIGS. 18 and 21, the vertical polarization of the anisotropic prism sheet of this example is reduced in both front luminance and illuminance as compared with the isotropic prism sheet of Comparative Example 2. On the other hand, the horizontal polarized light is higher than the isotropic prism sheet of Comparative Example 2 in both front luminance and illuminance.

From the above results, in the anisotropic prism sheet, more vertical polarized light is reflected by the prism surface and recycled to omnidirectional light in the diffuser or reflector, thereby increasing the luminance and illuminance of horizontal polarized light. You can see that it contributes. Therefore, by directing the transmission axis of the polarizer 55 in the direction of horizontal polarization, that is, in the prism arrangement direction of the anisotropic prism sheet 45, the front luminance and illuminance (light extraction efficiency) can be efficiently utilized by using light. Can be improved.

(Example 3)
When the prism sheet according to the present invention is used in a liquid crystal display device, an angle formed by transmission axes of the prism sheet and a polarizer (a polarizer located on the light incident side of the liquid crystal display panel; the same applies hereinafter) is important. As shown in Example 1 and Example 2, the polarization of the light emitted from the prism sheet is biased, and it is preferable to align the transmission axis of the polarizer in the direction corresponding thereto. However, the present invention is also effective when the transmission axis of the polarizer cannot be matched for reasons such as improvement of contrast as a liquid crystal display device and suppression of moire.

  In this embodiment, in the case where a prism sheet in which the refractive index in the prism extending direction is larger than the refractive index in the prism arrangement direction as in the second embodiment is used in a liquid crystal display device, the prism arrangement direction and the polarizer are used. The front luminance of the liquid crystal display device with respect to the angle formed by the light transmission axis direction was measured.

(Comparative Example 3)
The front luminance was measured in the same manner as in Example 3 except that an unstretched isotropic prism sheet (prism apex angle of 90 degrees, 50 μm pitch) was used instead of the prism sheet of Example 3.

The measurement results are shown in FIG. From the result of FIG. 19, when the angle formed by the prism array direction of the prism sheet and the light transmission axis direction of the polarizer is 0 ° to 45 °, the front luminance can be increased compared to the isotropic prism sheet. It can be seen that the angle is more preferably 0 ° to 20 °.

  In contrast to the case where the refractive index in the prism extending direction is larger than the refractive index in the prism arranging direction as in this embodiment, the refraction in the prism arranging direction is larger than the refractive index in the prism extending direction. When the prism sheet is formed so that the rate is larger, the angle formed by the prism extending direction and the light transmission axis direction of the polarizer is 0 ° to 45 °, compared to the isotropic prism sheet, It can be seen that the front luminance can be increased, and more preferably 0 ° to 20 °.

It is a disassembled perspective view which shows schematic structure of the liquid crystal display device by embodiment of this invention. It is a whole perspective view showing typically composition of a prism sheet as a light transmission film concerning the present invention. It is principal part sectional drawing for demonstrating one effect | action of the prism sheet which concerns on this invention. It is a schematic diagram for demonstrating the manufacturing method of the prism sheet which concerns on this invention, A shows the extending | stretching direction and B has shown the change of the prism shape before and behind extending | stretching. It is a figure explaining the mode of a change of a prism shape when it is made to extend in the direction different from the case shown in FIG. It is a principal part side view for demonstrating one effect | action of the liquid crystal display device of FIG. It is a figure which shows the relationship between the magnitude | size of the in-plane refractive index difference of the prism sheet concerning this invention, and a brightness improvement rate. It is a figure which shows the result of having measured the cross-sectional shape of the anisotropic prism sheet demonstrated in Example 1 of this invention. It is a figure for demonstrating the birefringence measuring method of an anisotropic prism sheet. It is a figure for demonstrating the difference of the output angle of a perpendicularly polarized light and a horizontally polarized light with respect to an anisotropic prism sheet. It is a figure which shows the light transmission characteristic of the anisotropic prism sheet of Example 1. FIG. FIG. 3 is a diagram for explaining a refractive index in each in-plane direction of the anisotropic prism sheet of Example 1. 6 is a diagram for explaining measurement conditions for evaluating luminance characteristics of the anisotropic prism sheet of Example 1. FIG. It is a figure which shows the evaluation result of the luminance orientation characteristic of the anisotropic prism sheet of Example 1. It is a figure which shows the result of having measured the cross-sectional shape of the anisotropic prism sheet demonstrated in Example 2 of this invention. It is a figure which shows the light transmission characteristic of the anisotropic prism sheet of Example 2. FIG. FIG. 6 is a diagram for explaining a refractive index in each in-plane direction of the anisotropic prism sheet of Example 2. It is a figure which shows the evaluation result of the brightness | luminance orientation characteristic of the anisotropic prism sheet of Example 2. FIG. It is a figure which shows the angle dependence characteristic of the brightness | luminance with respect to the polarizer of the anisotropic prism sheet demonstrated in Example 3 of this invention. It is a figure which shows the measurement result of Example 1 of this invention. It is a figure which shows the measurement result of Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Liquid crystal display device 11 ... Liquid crystal display panel 12A ... 1st polarizer 12B ... 2nd polarizer 13 ... Prism sheet (light transmission film)
DESCRIPTION OF SYMBOLS 14 ... Diffusing plate 15 ... Backlight unit 23 ... Resin film 45 ... Anisotropic prism sheet 55 ... Polarizing plate Lx ... Polarization of the backlight light which vibrates in the prism extension direction Component Ly: Polarization component of backlight light oscillating in the prism arrangement direction nx: Refractive index in the prism extending direction of the prism sheet ny: Refractive index in the prism arrangement direction of the prism sheet

Claims (15)

A light transmitting film in which three-dimensional structures are continuously arranged on one side,
The light transmission film, wherein a refractive index in an extending direction of the three-dimensional structure and a refractive index in an arrangement direction of the three-dimensional structure are different from each other. The light transmissive film according to claim 1,
The light transmission film, wherein the refractive index in the extending direction of the three-dimensional structure is larger than the refractive index in the arrangement direction of the three-dimensional structure. The light transmissive film according to claim 1,
The light transmission film, wherein the refractive index in the arrangement direction of the three-dimensional structure is larger than the refractive index in the extending direction of the three-dimensional structure. The light transmissive film according to claim 1,
The said light transmissive film consists of a resin film extended | stretched in the extending direction of the said three-dimensional structure. The light transmissive film characterized by the above-mentioned. The light transmissive film according to claim 4,
The resin film is made of a material having a refractive index that increases in the stretching direction. The light transmissive film according to claim 4,
The resin film is made of a material whose refractive index is small in the stretching direction. The light transmissive film according to claim 4,
The resin film is made of a copolymer such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), a mixture thereof, or a PET-PEN copolymer. The light transmissive film according to claim 1,
The three-dimensional structure is a prism or a lenticular lens. A method for producing a light transmissive film in which three-dimensional structures are continuously arranged on one side,
Forming a resin film having the three-dimensional structure on one surface;
A step of extending the resin film in the extending direction of the three-dimensional structure, and making a difference in refractive index between the extending direction of the three-dimensional structure and the arrangement direction of the three-dimensional structure. Manufacturing method. It is a manufacturing method of the light transmission film according to claim 9,
As the material of the resin film, a material having a refractive index large in the stretching direction is used. It is a manufacturing method of the light transmission film according to claim 9,
As the material of the resin film, a material having a refractive index that is small in the stretching direction is used. A liquid crystal display panel, a pair of polarizers sandwiching the liquid crystal display panel, a light source that illuminates the liquid crystal display panel, a liquid crystal display panel and the light source, disposed between the liquid crystal display panel and the light source. A liquid crystal display device comprising a light transmissive film arranged continuously,
The liquid crystal display device, wherein the light transmission film has a refractive index in an extending direction of the three-dimensional structure and a refractive index in an arrangement direction of the three-dimensional structure. The liquid crystal display device according to claim 12,
The light transmitting film is formed such that the refractive index in the extending direction of the three-dimensional structure is larger than the refractive index in the arrangement direction of the three-dimensional structure, and
An angle formed by the arrangement direction of the three-dimensional structure and the light transmission axis direction of the polarizer disposed on the light incident side of the liquid crystal display panel among the pair of polarizers is provided in a range of 0 ° to 45 °. A liquid crystal display device characterized by comprising: The liquid crystal display device according to claim 12,
The light transmitting film is formed such that the refractive index in the arrangement direction of the three-dimensional structure is larger than the refractive index in the extending direction of the three-dimensional structure, and
An angle formed between the extending direction of the three-dimensional structure and the light transmission axis direction of the polarizer disposed on the light incident side of the liquid crystal display panel among the pair of polarizers is provided in a range of 0 ° to 45 °. A liquid crystal display device characterized by comprising: The liquid crystal display device according to claim 12,
The light transmission film is made of a copolymer such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), a mixture thereof, or a PET-PEN copolymer.

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