JP3991044B2 - Backlight and liquid crystal display device using the same - Google Patents

Description

  The present invention relates to a liquid crystal display device used for a notebook personal computer, a portable liquid crystal TV, and the like. More specifically, the present invention relates to a liquid crystal display device having a narrow distribution angle of emitted light and excellent emission in the normal direction of the emission surface of peak light The present invention relates to a backlight having directivity, and a liquid crystal display device having excellent directivity, a wide viewing angle, good contrast, and no inversion of luminance of intermediate colors.

  In recent years, color liquid crystal display devices have been widely used in various fields as portable notebook personal computers, portable liquid crystal TVs using color liquid crystal panels, or video integrated liquid crystal TVs. In addition, with the increase in the amount of information processing, diversification of needs, compatibility with multimedia, and the like, liquid crystal display devices have been increased in screen size and definition.

  The liquid crystal display device basically includes a backlight unit and a liquid crystal display element unit. As the backlight unit, there are a direct light method in which a light source is provided directly under a liquid crystal display element and an edge light method in which a light source is provided on a side surface of a light guide body. Yes. This edge light system is a backlight of a system in which a light source is disposed on a side surface portion of a plate-shaped light guide to emit light on the entire surface of the light guide.

  The liquid crystal display element section is roughly classified into a thin film transistor type tin film transistor type (TFT) and a spar twisted nematic type (STN) according to the driving method. The TFT type liquid crystal display element is encapsulated by twisting the liquid crystal by 90 ° between a TFT substrate in which a thin film transistor is formed and serving as an electrical switch, and a color filter substrate in which a color filter is provided and plays a role of color development. Have a structure. In addition, polarizing plates are placed on the front and back of the substrate. When light polarized by the polarizing plate enters the liquid crystal layer, it rotates 90 ° along the liquid crystal molecules, and the axis of the polarizing plate on the exit side rotates 90 °. As a result, light is transmitted and emitted. On the other hand, when the switch of the TFT substrate is turned on, the liquid crystal molecules rise, and the light incident on the liquid crystal layer cannot be rotated and cannot be transmitted through the output-side polarizing plate. Thus, image information corresponding to the state of the switch on the TFT substrate is displayed. Such a TFT-type liquid crystal display element is capable of high-speed switching and is said to be suitable for displaying halftone colors corresponding to full color.

  However, in such a liquid crystal display device, the image quality changes greatly depending on the viewing angle.For example, the contrast and brightness change depending on the viewing angle, or the light intensity of the halftone color is reversed and the color tone changes. For example, a normal image cannot be obtained. This is because, in a TFT-type liquid crystal display element, halftone color display is in a state where liquid crystal molecules do not stand up completely, and light viewed in the direction in which the liquid crystal molecules are tilted passes through the liquid crystal molecules at an angle close to vertical. This is because there is a high probability that the light rotates, and the amount of light transmitted through the polarizing plate increases, resulting in a whitish display. Further, when viewed from a direction in which the liquid crystal molecules are not tilted, the light passing through the liquid crystal layer is less affected by the liquid crystal molecules, and the light does not rotate, resulting in a dark display. Such a problem has become a larger problem due to demands for observation by a plurality of persons due to an increase in the screen size of the liquid crystal display device and expansion of applications.

  Therefore, the present invention does not use a component such as a prism sheet, and the distribution angle of the emitted light is narrow, and the normal of the emission surface of the peak light (the light having the highest luminous intensity in the luminous intensity distribution of the emitted light). Provides a directivity backlight that emits light in the direction and has the best directivity that can maximize the luminous intensity in the front, wide viewing angle, good contrast, and less luminance reversal in intermediate colors An object is to provide a liquid crystal display device.

That is, the backlight of the present invention is arranged such that the light source, the light guide having at least one entrance surface and the exit surface facing the light source, and the prism surface on the light guide are on the exit surface side. A plurality of lens rows having an angle of 45 ° to 90 ° with respect to the incident surface are formed in parallel on the back surface of the light guide, and the average inclination angle of the lens rows is 30 ° or more. It is characterized by being. In addition, a liquid crystal display device of the present invention includes the above-described backlight and a liquid crystal display element disposed on the backlight.

  As shown in FIG. 1, the backlight of the present invention includes a light source 4, a light guide 2 and a prism sheet 5. The light guide 2 has at least one side surface as an incident surface, and one surface substantially orthogonal to the incident surface as an output surface 4, and at least one of the output surface 4 or the back surface opposite to the output surface 4, for example, as shown in FIG. A large number of lens rows 3 having a cross-sectional shape are formed in parallel.

  The lens array 3 formed on the light guide 2 needs to have a shape characteristic such that the average inclination angle is 30 ° or more. There is no particular limitation, and for example, a lens array such as a prism, a lenticular lens having a semicircular or semi-elliptical cross section, or a wave lens can be formed. By setting the average inclination angle (θa) of the lens array 3 to 30 ° or more, the horizontal distribution of the light emitted from the light guide 2 can be narrowed, and preferably 45 ° or more.

In the present invention, the average tilt angle (θa) that serves as an index of the shape characteristic of the lens array 3 is the average tilt angle (θa) defined by ISO4287 / 1-1987. Specifically, it calculated | required according to ISO4287 / 1-1984. With a stylus type surface roughness meter (Surfcom 570A manufactured by Tokyo Seiki Co., Ltd.) using 010-2528 (1 μmR, 55 ° cone, diamond) as a stylus, the surface roughness of the rough surface was driven at a driving speed of 0.03 mm / Measured in seconds. From the measured average line, the average line is subtracted to correct the inclination, and calculated by the following equations (1) to (2).

  Further, in the present invention, the lens array 3 formed on the light guide 2 needs to be formed with an angle of 45 ° to 90 ° with respect to the incident surface of the light guide 2. This is because the horizontal distribution of the light emitted from the light guide 2 can be narrowed by setting the angle of the lens array to 45 ° or more, that is, 45 ° to 90 °, preferably 60 °. It is in the range of 0 ° to 90 °.

  The pitch of the lens array 3 to be formed can be appropriately selected within a processable range, but is preferably in the range of 10 to 500 μm, and more preferably in the range of 30 to 300 μm. If the light intensity distribution on the light exit surface is uneven due to the shape of the light guide 2 or the like, the light intensity distribution on the light exit surface is changed by changing the pitch of the lens array 3 partially or continuously. Uniformity can be achieved. The lens array 3 formed on the light guide 2 may be formed by processing the back surface of the light guide 2 by a hot press method or the like, or when manufacturing the light guide 2 by extrusion molding, injection molding, or the like. And may be formed simultaneously. Moreover, you may form integrally using a heat | fever or a photocurable resin. In the method in which the lens array 3 is integrally formed on the surface of the light guide 2 using heat or a photo-curing resin or the like, it is possible to manufacture the light guide 2 and the lens array 3 having different refractive indexes. Further, the lens array 3 is formed by an active energy ray curable resin on a transparent substrate such as a polyester film, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, a polymethacrylamide resin, or a transparent film or sheet. The formed lens sheet may be integrated with the light guide 2 by a method such as adhesion or fusion.

  When the lens array 3 is formed using an active energy ray curable resin, an active energy ray curable resin liquid is injected into a mold on which a predetermined lens pattern is formed, and the light guide 2 or the transparent film is overlaid. Next, it can be produced by irradiating active energy rays such as ultraviolet rays and electron beams through the light guide 2, polymerizing and curing the active energy ray-curable resin liquid, and peeling it from the mold. As the active energy ray-curable resin constituting the lens array 3, a polyfunctional (meth) acrylic compound, vinyl compound, (meth) acrylic acid ester, allyl compound, (meth) acrylic acid metal salt, or the like is used. Can do.

  As the light guide 2, various shapes such as a plate shape, a wedge shape, and a ship shape can be used, and the light guide body 2 is made of a synthetic resin having a high light transmittance. In order to effectively introduce light from the light source 4 to the light guide 2, it is preferable that the light incident surfaces of the light source 4 and the light guide 2 are covered with a case or film coated with a reflective agent on the inside. A reflective layer 8 may be formed on the back surface of the light guide 2 by metal vapor deposition or the like to form a reflective surface. As the synthetic resin constituting the light guide 2, various highly transparent synthetic resins such as methacrylic resin, acrylic resin, polycarbonate resin, and vinyl chloride resin are used, and usually extrusion molding, injection molding, etc. It can be manufactured by the molding method. In particular, a methacrylic resin is excellent as a light transmittance, heat resistance, mechanical properties, and molding processability, and is optimal as a light guide material. Such a methacrylic resin is a resin mainly composed of methyl methacrylate, and the methyl methacrylate is preferably 80% by weight or more.

  In the backlight of the present invention, the prism sheet 5 is disposed on the light exit surface of the light guide 2 as described above. The prism sheet 5 has a lens surface in which a large number of prism rows are formed in parallel on one surface of a transparent substrate. The pitch of the prism rows of the prism sheet 5 is preferably about 30 μm to 0.5 mm, and the prism apex angle is appropriately selected depending on the emission angle of the emitted light from the light guide 2, but is in the range of 50 to 120 °. It is preferable that Further, the orientation of the prism sheet 5 is also appropriately selected depending on the emission angle of the emitted light from the light guide 2, and may be placed so that the prism surface is on the emission surface side of the light guide 2. It may be placed in the direction.

  The prism sheet 5 is arranged so that the prism row is at an angle of 20 ° or less with respect to the incident surface of the light guide 2, narrows the vertical distribution of light emitted from the light guide 2, and emits light. The angle is changed in a direction substantially perpendicular to the surface. The light emitted from the light guide 2 is light having a directivity inclined by about 70 to 40 ° with respect to the direction perpendicular to the emission surface, and this is changed in a direction substantially perpendicular to the emission surface. Therefore, it is necessary to enter the liquid crystal display element 6. The degree of the angle change can be designed using Snell's law depending on the prism apex angle and the refractive index of the prism sheet 5. For example, in the prism sheet 5 made of acrylic resin and having a refractive index of about 1.49 to 1.53, the prism apex angle is 55 ° to 65 °, and the prism surface is on the light exit surface side of the light guide 2. The light having an inclination of about 60 ° can be changed in a direction substantially perpendicular to the emission surface.

  In the present invention, the prism sheet 5 is preferably manufactured using a material having a high visible light transmittance and a relatively high refractive index. For example, acrylic resin, polycarbonate resin, vinyl chloride resin, active energy Examples thereof include a linear curable resin. Among these, active energy ray-curable resins are preferable from the viewpoint of scratch resistance, handleability, and productivity of the lens sheet. Moreover, additives, such as an antioxidant, an ultraviolet absorber, a yellowing inhibitor, a bluing agent, a pigment, and a diffusing agent, may be added to the prism sheet 5 as necessary. As a method of manufacturing the prism sheet 5, a normal molding method such as extrusion molding or injection molding can be used. When the prism sheet 5 is manufactured using an active energy ray curable resin, a transparent resin such as a polyester resin, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, a polymethacrylimide resin, or a polyolefin resin is used. A prism portion is formed of an active energy ray-curable resin on a transparent substrate such as a transparent film or sheet. First, an active energy ray-curable resin liquid is injected into a lens mold on which a predetermined prism pattern is formed, and a transparent substrate is overlaid. Next, active energy rays such as ultraviolet rays and electron beams are irradiated through the transparent substrate, the active energy ray-curable resin liquid is polymerized and cured, and peeled from the lens mold to obtain the prism sheet 5.

  As shown in FIG. 1, the liquid crystal display device 1 according to the present invention includes a light source 4 and a backlight unit including a light guide 2 having the above-described configuration and a liquid crystal display element 6. By using the light guide 2 composed of the specific exit surface as described above, the light emitted from the light guide 2 becomes pseudo-parallel light having a small angular distribution when passing through the liquid crystal display element 6, and the liquid crystal Since the influence of the tilt direction of the molecule can be minimized, the liquid crystal display device 1 can be obtained in which there is little change in the color tone due to the contrast depending on the viewing angle and the luminance reversal of the intermediate color. The liquid crystal display element 6 is not particularly limited, and any of an active matrix driving TFT liquid crystal display element and a simple matrix driving STN liquid crystal display element can be used. Further, in the TFT type liquid crystal display element, various active elements such as the element and polysilicon, amorphous silicon, metal insulator metal and the like can be used.

  In addition, as shown in FIG. 1, a microlens sheet or a diffusion sheet 7 in which a large number of fine lenticular lenses and the like are formed in parallel on at least one surface may be placed on the liquid crystal display element 6. By placing the microlens sheet 7 and the diffusion sheet on the liquid crystal display element 6 in this way, the quasi-parallel light transmitted through the liquid crystal display element 6 enters the microlens sheet and the diffusion sheet 7, and the incident light is diffused and emitted. Therefore, the viewing angle of the liquid crystal display device 1 can be widened. In other words, the light guide 2 constituted by a specific light exit surface can minimize the influence of the tilt direction of the liquid crystal molecules with pseudo-parallel light having a small angular distribution when passing through the liquid crystal display element 6. Since the light is diffused by the microlens sheet or the diffusion sheet 7 after passing through 6, the liquid crystal display device 1 with a wide viewing angle can be provided with little change in color tone due to the contrast depending on the viewing angle and the luminance inversion of intermediate colors.

  The microlens sheet or the diffusion sheet 7 placed on the liquid crystal display element 6 is a member having a function of widening the viewing angle by diffusing the light transmitted through the liquid crystal display element 6. The microlens sheet 7 is formed by forming a large number of parallel lenses such as a lenticular lens having a semi-cylindrical shape, a semi-elliptical column shape, or a similar shape on at least one surface, and has a thickness of 0.1. It is preferable that the lens pitch is about 10 to 800 μm. The microlens sheet or the diffusion sheet 7 is preferably manufactured using a material having a high visible light transmittance. For example, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, an active energy ray curable resin, or the like is used. For example, conventional molding methods such as extrusion molding, injection molding, and a method using an active energy ray curable resin can be used. In the present invention, additives such as an antioxidant, an ultraviolet absorber, a yellowing inhibitor, a bluing agent, a pigment, and a diffusing agent can be added to the microlens sheet and the diffusion sheet 7 as necessary. .

  Hereinafter, the present invention will be described specifically by way of examples. In addition, the measurement of each physical property in the following examples was performed as follows.

Measurement of luminous intensity distribution A cold cathode tube of a light guide was connected to a DC power source via an inverter (CXA-M10L manufactured by TDK), and lit by applying DC 12V. The liquid crystal display device was placed on a measuring table and adjusted so as to rotate around a rotation axis parallel to the cold cathode tube axis at the center thereof. Next, a black paper having a 3 mmφ pinhole is fixed on the light guide so that the pinhole is located at the center of the light guide, and measured using a luminance meter (Minolta nt-1 °). The distance was adjusted so as to be 8 to 9 mm. After the aging time of the cold cathode tube was 30 minutes or longer, the angular distribution of the luminous intensity of the emitted light was measured while rotating the rotating shaft at intervals of 5 ° from 80 ° to −80 °.

Average tilt angle (θa)
With a stylus type surface roughness meter (Surfcom 570A manufactured by Tokyo Seiki Co., Ltd.) using 010-2528 (1 μmR, 55 ° cone, diamond) as a stylus, the surface roughness of the rough surface was driven at a driving speed of 0.03 mm / Measured in seconds. From the measured average line, the average line was subtracted to correct the inclination, and the calculation was made according to the equations (1) to (2).

Example 1
A size of 100 mm × 100 mm in which a lenticular lens having a pitch of 100 μm having an inclined surface with an average inclination angle (θa) of 60 ° on one surface is formed in a direction of 90 ° with respect to the long side by injection molding of acrylic resin. A light guide having a thickness of 90 mm and a thickness of 4 mm was produced. Adhering and pasting silver-deposited PET film on two 90mm end faces of the obtained light guide, and then tapering the silver-deposited PET film on the surface opposite to the surface on which the lenticular lens was formed Formed. A cold cathode tube (KC130T4E72, 4 mmφ × 130 mm) manufactured by Matsushita Electric Industrial Co., Ltd. was wound around two 100 mm end faces of an acrylic plate with a silver-deposited PET film, and installed as a light source lamp.

  On the other hand, an acrylic ultraviolet curable resin liquid is injected into a mold having a prism pattern with a prism apex angle of 63 ° and a pitch of 50 μm, and a polyethylene terephthalate film with a thickness of 150 μm is overlapped using a roll, and then polyethylene terephthalate. The acrylic ultraviolet curable resin liquid was polymerized and cured by irradiating ultraviolet rays of 570 mJ through the film, and then peeled from the mold to obtain a prism sheet having a refractive index of 1.59 and an apex angle of 63 °.

  The prism sheet was placed on the light exit surface (surface on which the lenticular lens was formed) of the obtained light guide so that the prism surface was positioned on the light exit surface side of the light guide to constitute a backlight. Using the obtained backlight, the angular distribution of the luminous intensity of the emitted light was measured, and the half width in the horizontal direction and the half width in the vertical direction with respect to the light source were obtained and shown in Table 1. Further, a TFT type liquid crystal display element is placed on the prism sheet, and a microlens sheet in which a lenticular lens having a pitch of 0.22 mm is formed on an acrylic resin plate having a thickness of 5 mm is placed thereon, and the liquid crystal display device Assembled. The obtained liquid crystal display device was used to measure the angular distribution of the luminous intensity of the emitted light, and the half width in the horizontal direction and the half width in the vertical direction with respect to the light source were determined and shown in Table 1. Also, the liquid crystal display device is observed from an angle of 30 ° with respect to the normal direction (from two directions, the horizontal direction and the vertical direction with respect to the light source), and the state of the image (contrast, color tone, brightness) is visually observed The results are shown in Table 1.

Example 2
A back surface is formed in the same manner as in Example 1 except that a lenticular lens with a pitch of 100 μm having an inclined surface with an average inclination angle (θa) of 60 ° on the surface of the light guide is formed in a direction of 85 ° with respect to the long side. A light and liquid crystal display were assembled. Using the obtained backlight, the angular distribution of the luminous intensity of the emitted light was measured, and from the results, the half width in the horizontal direction and the half width in the vertical direction with respect to the light source were determined and shown in Table 1. In addition, the liquid crystal display device is observed from an angle of 30 ° with respect to the normal direction (from two directions, the horizontal direction and the vertical direction with respect to the light source), and the state of the image (contrast, color tone, brightness) is visually observed. The results are shown in Table 1.

Example 3
A backlight and a liquid crystal display device were assembled in the same manner as in Example 1 except that a rough surface having an average inclination angle (θa) of 5 ° was formed on the surface of the light guide opposite to the surface on which the lenticular lens was formed. Using the obtained backlight, the angular distribution of the luminous intensity of the emitted light was measured, and the half width in the horizontal direction and the half width in the vertical direction with respect to the light source were obtained and shown in Table 1. Also, the liquid crystal display device is observed from an angle of 30 ° with respect to the normal direction (from two directions, the horizontal direction and the vertical direction with respect to the light source), and the state of the image (contrast, color tone, brightness) is visually observed. The results are shown in Table 1.

Comparative Example 1
A backlight and a liquid crystal display device were assembled in the same manner as in Example 1 except that the surface of the light guide was changed to a lenticular lens and a mat surface having an average inclination angle (θa) of 15 ° was formed. Using the obtained backlight, the angular distribution of the luminous intensity of the emitted light was measured, and the half width in the horizontal direction and the half width in the vertical direction with respect to the light source were obtained and shown in Table 1. Also, the liquid crystal display device is observed from an angle of 30 ° with respect to the normal direction (from two directions, the horizontal direction and the vertical direction with respect to the light source), and the state of the image (contrast, color tone, brightness) is visually observed. The results are shown in Table 1.

Comparative Example 2
A back surface is formed in the same manner as in Example 1 except that a lenticular lens with a pitch of 100 μm having an inclined surface with an average inclination angle (θa) of 15 ° on the surface of the light guide is formed in a direction of 90 ° with respect to the long side. A light and liquid crystal display were assembled. Using the obtained backlight, the angular distribution of the luminous intensity of the emitted light was measured, and the half width in the horizontal direction and the half width in the vertical direction with respect to the light source were obtained and shown in Table 1. Also, the liquid crystal display device is observed from an angle of 30 ° with respect to the normal direction (from two directions, the horizontal direction and the vertical direction with respect to the light source), and the state of the image (contrast, color tone, brightness) is visually observed. The results are shown in Table 1.

Comparative Example 3
A back surface is formed in the same manner as in Example 1 except that a lenticular lens having a pitch of 100 μm and having an inclined surface with an average inclination angle (θa) of 60 ° on the surface of the light guide is formed in a direction of 5 ° with respect to the long side. A light and liquid crystal display were assembled. Using the obtained backlight, the angular distribution of the luminous intensity of the emitted light was measured, and the half width in the horizontal direction and the half width in the vertical direction with respect to the light source were obtained and shown in Table 1. Also, the liquid crystal display device is observed from an angle of 30 ° with respect to the normal direction (from two directions, the horizontal direction and the vertical direction with respect to the light source), and the state of the image (contrast, color tone, brightness) is visually observed. The results are shown in Table 1.

It is a perspective view which shows the structural example of the liquid crystal display device of this invention. It is a fragmentary sectional view showing a lenticular lens formed in a light guide of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 2 ... Light guide 3 ... Lens row 4 ... Light source 5 ... Prism sheet 6 ... Liquid crystal display element 7 ... Micro lens sheet, Diffusion sheet

Claims (4)

A light source, a light guide having at least one entrance surface and an exit surface facing the light source, and a prism sheet disposed on the light guide so that the prism surface is on the exit surface side. A backlight having a plurality of lens rows having an angle of 45 ° to 90 ° with respect to the incident surface formed in parallel on the back surface of the light body, and an average inclination angle of the lens rows of 30 ° or more. . 2. The backlight according to claim 1, wherein the lens array formed on at least one of the exit surface and the back surface of the light guide is one of a prism array, a lenticular lens array, and a corrugated lens array. .   3. The backlight according to claim 1, wherein a surface of the light guide opposite to the surface on which the lens array is formed is a rough surface.   A liquid crystal display device comprising: the backlight according to claim 1; and a liquid crystal display element disposed on the backlight.

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