JPH0961817A - Prism sheet and back light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lens sheet and a back light which can improve the optical efficiency when they are used for a liquid crystal panel and improve the brightness as a liquid crystal display device. SOLUTION: This back light is composed of a light source 1 and a planer light transmission body 2 having at least one incident plane facing to the light source and an outgoing plane. A prism sheet 6 having lots of prism rows arranged parallel to each other formed on at least one surface of a transparent substrate having a light-controlling function corresponding to a λ/8-7λ/8 phase plate is disposed on the outgoing plane of the light transmission body 2.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a notebook computer,
The present invention relates to a backlight of a liquid crystal display device used for a portable liquid crystal TV or the like and a prism sheet used for the same, and more specifically to a prism sheet and a backlight capable of increasing the brightness of the liquid crystal display device. is there.

[0002]

2. Description of the Related Art In recent years, color liquid crystal display devices have been widely used in various fields as a portable notebook personal computer, a portable liquid crystal TV using a color liquid crystal panel, a video integrated liquid crystal TV, and the like. The liquid crystal display device is basically composed of a backlight and a liquid crystal display element section.
As a backlight, there are a direct type in which a light source is provided directly below a liquid crystal display element and an edge light type in which a light source is provided on a side surface of a light guide body, and the edge light type has been widely used due to downsizing of a liquid crystal display device. . The edge light system is a backlight system in which a light source is arranged on the side surface of a plate-shaped light guide so that the entire surface of the light guide is illuminated.

Since such a color liquid crystal display device is driven by a battery, the power consumption of the liquid crystal display device is an obstacle to extending the battery drive time. Above all, the power consumption of the backlight used in liquid crystal display devices is large, and it is important to keep this power consumption as low as possible in order to extend the battery drive time and increase the practical value of the above products. ing. However, by reducing the power consumption of the backlight,
If the luminous intensity of the backlight is lowered, the liquid crystal display becomes difficult to see, which is not preferable. Therefore, in order to suppress the power consumption without sacrificing the brightness of the backlight, it is desired to improve the optical efficiency of the backlight.

A typical structure of such a backlight is shown in FIG. In the figure, 1 is a light source such as a fluorescent lamp, which is installed so as to face one side surface (incident surface) of the light guide 2.
In order to effectively introduce light from the light source 1 to the light guide body 2, the incident surfaces of the light source 1 and the light guide body 2 are covered with a case or a film 4 coated with a reflective agent on the inside. Also,
Diffusing means 3 is formed on the back surface of the light guide body 2 to emit an incident light beam from the exit surface. The light from the light source 1 is guided by the light guide 2.
To the front surface of the light guide 2 by being diffused by the diffusing means 3. This emitted light has a directivity that is inclined by 40 to 70 degrees with respect to the normal direction, and in order to arrange this directional light and direct it in the direction of 20 to 40 degrees with respect to the normal direction. Alternatively, in order to make the emitted light uniform, a diffusion sheet 5 is placed on the emitting surface of the light guide 2 as shown in FIG. Furthermore, in order to arrange this directional light and direct it in the direction of the approximate normal line,
One or a plurality of prism sheets 6 each having a large number of prism rows formed in parallel on one surface are stacked and placed.

[0005]

However, it has been found that in such a backlight, the polarization of emitted light is almost random, but strictly speaking, a specific polarization component is a partial polarization. That is, as shown in FIG. 2, when the polarization intensity of the outgoing light when the diffusion sheet 5 is placed on the outgoing surface of the light guide 2 is measured, it is determined that the end surface of the light guide 2 where the light source 1 is arranged is The parallel polarization component (horizontal polarization) was about 5% stronger than the vertical polarization component (vertical polarization). Therefore, in the liquid crystal panel arranged on the backlight, only one polarized component of the incident light is used. Therefore, in the backlight as described above, it is better to use the horizontal polarized light for the optical efficiency. .

On the other hand, the prism sheet 6 has a property that a polarized light component perpendicular to the prism array of the prism sheet 6 is easily transmitted and a parallel polarized light component is difficult to be transmitted, and a difference in transmittance between them. Is about a few percent to a dozen percent.
Therefore, the polarization intensity of the backlight changes depending on the direction of the prism rows of the mounted prism sheet 6. Usually, such a prism sheet 6 is mounted on the diffusion sheet 5 such that the end face of the light guide 2 on which the light source 1 is arranged and the lens array are parallel to each other as shown in FIG. In this case, since the outgoing light emitted from the diffusion sheet 5 has a strong horizontal polarization and the prism sheet 6 transmits the vertical polarized light well, the effects of both are canceled out, and the outgoing light emitted from the prism sheet 6 is close to random polarized light. Therefore, it was not possible to sufficiently improve the optical efficiency of the liquid crystal panel.

Therefore, in the present invention, the prism sheet is provided with a function of controlling the plane of polarization of light passing through the prism sheet, so that the light emitted from the light guide is made uniform and the directivity is controlled. It is an object of the present invention to provide a prism sheet and a backlight capable of improving the optical efficiency when used in a liquid crystal panel and improving the brightness as a liquid crystal display device without impairing the function of.

[0008]

That is, in the transparent sheet of the present invention, a large number of prism rows are parallel to at least one surface of a transparent base material having a light control function equivalent to a λ / 8 to 7λ / 8 phase plate. It is characterized in that it is formed in. Further, the backlight of the present invention is composed of a light source and a plate-shaped light guide body having at least one entrance surface and exit surface facing the light source, and light control equivalent to a λ / 8 to 7λ / 8 phase plate. A prism sheet in which a large number of prism rows are formed in parallel on at least one surface of a transparent base material having a function is installed on the exit surface side of a light guide.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The backlight of the present invention, as shown in FIG. 1, is composed of a light source 1 and a light guide 2, and has at least one surface (incident) in the thickness direction of the light guide 2. Light source 1 on surface)
Are arranged. The light guide 2 has at least one side surface as an incident surface and one surface substantially orthogonal thereto as an emission surface, and is made of a synthetic resin having a high light transmittance. As the synthetic resin forming the light guide body 2, various highly transparent synthetic resins such as methacrylic resin, acrylic resin, polycarbonate resin, and vinyl chloride resin can be used. In particular, methacrylic resin has a high light transmittance,
It also has excellent heat resistance, mechanical properties, and moldability, making it ideal as a light guide material.

Such a methacrylic resin is a resin whose main component is methyl methacrylate, and it is preferable that the amount of methyl methacrylate is 80% by weight or more. Copolymer components other than methyl methacrylate include methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and (meth) acrylic acid. Phenyl, benzyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and other (meth) acrylic acid esters, (meth) acrylic acid, ethylene Glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, allyl (meth) acrylate, neopentyl glycol di (meth)
Polyfunctional (meth) acrylates such as acrylate, aromatic vinyl monomers such as styrene and α-methylstyrene,
Examples thereof include maleimides such as phenylmaleimide and cyclohexylmaleimide, and maleic anhydride. In addition, for the purpose of improving the impact resistance of methacrylic resin, a rubber-like copolymer containing acrylate as a main component and a copolymer containing a copolymer containing methacrylate as a main component grafted are also used. it can.

The light source 1 is installed on the incident surface side of the light guide 2 so as to face the incident surface, and an edge light type backlight is constructed. In order to effectively introduce light from the light source 1 to the light guide body 2, it is preferable that the incident surfaces of the light source 1 and the light guide body 2 are covered with a case or a film 5 coated with a reflective agent inside. A diffusion layer 3 is formed on the back surface of the light guide body 2 so as to form a diffusion surface, by which an incident light beam is emitted from the emission surface.

A transparent film or a transparent film is formed on the exit surface of the light guide 2 through a diffusion sheet 5 having a fine shape for two-dimensionally or three-dimensionally diffusing or converging light rays as needed. A prism sheet 6 in which a large number of prism rows are formed in parallel is placed on at least one surface of a transparent base material made of a sheet, and the homogenization of the light emitted from the light guide 2 and the control of the directivity are performed. Be seen. In the present invention, as the transparent base material forming the prism sheet 6,
It is important to use a phase film or a phase sheet having a light control function equivalent to a λ / 8 to 7λ / 8 phase plate. In the present invention, the light control function corresponding to the λ / 8 to 7λ / 8 phase plate is a function of controlling the plane of polarization of light when passing through the prism sheet.

In the prism sheet 6 of the present invention, the transparent substrate used is a film made of a transparent resin such as polyester resin, acrylic resin, polycarbonate resin, vinyl chloride resin, polymethacrylimide resin or the like. Sheets are used. In the present invention, in order to impart a light control function equivalent to λ / 8 to 7λ / 8 phase plate to the transparent substrate, for example, in a film forming or sheet forming process, a λ / 8 to 7λ / 8 phase plate is used. It is necessary to appropriately adjust the birefringence index, the thickness, etc. so that the equivalent light control function is exhibited. This is λ / 8 on the transparent substrate.
By imparting a light control function equivalent to that of a ~ 7λ / 8 phase plate, the prism sheet 6 can be imparted with a function of controlling the polarization plane of light passing therethrough.
As a result, the optical efficiency when used in a liquid crystal panel can be improved, and the brightness as a liquid crystal display device can be improved. If it deviates from this range, the effects of the present invention as described above cannot be obtained, and preferably λ / 4 to
It has a light control function equivalent to that of the 5λ / 8 phase plate, and more preferably has a light control function substantially equivalent to that of the λ / 2 phase plate.

As the prism sheet 6 of the present invention, a large number of prism rows 9 are formed in parallel on at least one surface of the transparent substrate 8 as described above, as shown in FIG. In the prism sheet 6 of the present invention, the prism row 9 may be formed on the surface of the transparent substrate 8 by using an active energy ray-curable resin that can be cured by an active energy ray such as ultraviolet rays or electron beams, or a transparent substrate. The prism rows 9 may be formed on the surface of the material 8 by a method such as heat pressing. The thickness of the prism sheet 6 of the present invention is 0.1
.About.3 mm, the pitch of the prism rows 9 is 30 .mu.m-0.
It is preferably about 5 mm. When manufacturing a transparent sheet using an active energy ray-curable resin, first, an active energy ray-curable resin liquid is injected into a lens mold having a predetermined prism pattern, and the transparent base material 8 is superposed. Next, active energy rays such as ultraviolet rays and electron rays are irradiated through the transparent base material 8 to polymerize and cure the active energy ray-curable resin liquid, and the prism sheet 6 is obtained by separating from the mold.

As the active energy ray-curable resin forming the prism array 9 of the prism sheet 6, bis (methacryloylthiophenyl) sulfoid, 2,4-dibromophenyl (meth) acrylate, 2,3,5-tribromo. Phenyl (meth) acrylate, 2,2-bis (4-
(Meth) acryloyloxyphenyl) propane, 2,
2-bis (4- (meth) acryloyloxyethoxyphenyl) propane, 2,2-bis (4- (meth) acryloyloxydiethoxyphenyl) propane, 2,2-
Bis (4- (meth) acryloylpentaethoxyphenyl) propane, 2,2-bis (4- (meth) acryloyloxyethoxy-3,5-dibromophenyl) propane, 2,2-bis (4- (meth) acryloyl Oxydiethoxy-3,5-dibromophenyl) propane, 2,
2-bis (4- (meth) acryloyloxypentaethoxy-3,5-dibromophenyl) propane, 2,2-
Bis (4- (meth) acryloyloxyethoxy-3,
5-dimethylphenyl) propane, 2,2-bis (4-
(Meth) acryloyloxyethoxy-3-phenylphenyl) propane, bis (4- (meth) acryloyloxyphenyl) sulfone, bis (4- (meth) acryloyloxyethoxyphenyl) sulfone, bis (4
-(Meth) acryloyloxypentaethoxyphenyl) sulfone, bis (4- (meth) acryloyloxyethoxy-3-phenylphenyl) sulfone, bis (4- (meth) acryloyloxyethoxy-3,5-
Dimethylphenyl) sulfone, bis (4- (meth) acryloyloxyphenyl) sulfide, bis (4-
(Meth) acryloyloxyethoxyphenyl) sulfide, bis (4- (meth) acryloyloxypentaethoxyphenyl) sulfide, bis (4- (meth) acryloyloxyethoxy-3-phenylphenyl) sulfide, bis (4- (meth)) Examples thereof include polyfunctional (meth) acrylic compounds such as acryloyloxyethoxy-3,5-dimethylphenyl) sulfide, di ((meth) acryloyloxyethoxy) phosphate, and tri ((meth) acryloyloxyethoxy) phosphate. These may be used alone or in combination of two or more.

In order to adjust the refractive index of the active energy ray-curable resin together with these polyfunctional (meth) acrylic compounds, styrene, vinyltoluene, chlorostyrene, dichlorostyrene, bromostyrene, dibromostyrene, divinylbenzene. , 1-vinylnaphthalene, 2
Vinyl compounds such as vinylnaphthalene and N-vinylpyrrolidone, phenyl (meth) acrylate, benzyl (meth) acrylate, biphenyl (meth) acrylate,
(Meth) acrylic acid esters such as, allyl compounds such as diallyl phthalate, dimethallyl phthalate and diallyl biphenylate, barium, lead, antimony, titanium,
It is also possible to use a metal salt of a metal such as tin or zinc and (meth) acrylic acid. These may be used alone or in combination of two or more.

In the present invention, the photoradical generating catalyst used in the active energy ray-curable resin is, for example, 2-hydroxy-2-methyl-1-phenylpropan-1-one, hydroxycyclohexylphenylketone or methylphenyl. Glyoxylate, 2,4,6-trimethylbenzoylphosphine oxide, benzyl dimethyl ketal and the like can be mentioned. The prism sheet 6 of the present invention is configured by using a transparent base material 8 having a light control function similar to that of a λ / 8 to 7λ / 8 phase plate, and the optical axis of the transparent base material 8 is referred to as a prism array 9. It is preferable to form an angle of 35 to 55 °. In particular, the greatest effect can be obtained when this angle is 45 °.

As shown in FIG. 1, when the prism sheet 6 of the present invention is used by placing it so that the prism array 9 is parallel to the end face of the light guide 2 in which the light source 1 is arranged, The outgoing light emitted from the body 2 becomes the outgoing light whose directivity is converted by the diffusion sheet 5. The emitted light emitted from the diffusion sheet 5 is a light beam having a strong vertical polarization. The outgoing light is transmitted through the prism sheet 6 to become outgoing light whose directivity is converted to a substantially normal direction. At this time, by transmitting through the transparent base material 8 that constitutes the prism sheet 6, the polarization plane of the emitted light emitted from the diffusion sheet 5 is rotated to become strongly vertically polarized light, and further the vertically polarized light of the prism array 9 is transmitted. The emitted light emitted from the prism sheet 6 has a stronger vertical polarization due to the characteristic that it can be easily made. Therefore, the emitted light has vertical polarization of about 10 to 20% stronger than horizontal polarization, and by using this vertical polarization in the liquid crystal panel, the brightness of the liquid crystal display device is increased by several% to 10%. It is possible to raise it by several percent.

Further, as shown in FIG. 3, the first prism sheet 6 (the prism sheet of the present invention) is replaced with the prism array 9
Is placed so as to be parallel to the end surface of the light guide body 2 on which the light source 1 is arranged, and the second prism sheet 7 (prism sheet of the present invention) is mounted thereon and the prism row 9 is the first prism sheet. When the prism 6 of 6 is used so as to be orthogonal to the prism row 9, the emitted light emitted from the first prism sheet 6 is light with strong vertical polarization as described above. When this emitted light passes through the transparent base material 8 that constitutes the second prism sheet 7, the plane of polarization of the emitted light emitted from the first prism 6 is rotated to become strongly horizontally polarized light. The output light emitted from the second prism sheet 7 becomes stronger in horizontal polarization due to the characteristic that the horizontal polarization of the prism array 9 of the second prism sheet 7 is easily transmitted. Therefore, the emitted light has horizontal polarization stronger than that of vertical polarization, and by using this horizontal polarization in the liquid crystal panel, the brightness of the liquid crystal display device is increased by several to ten and several percents as compared with the conventional one. It becomes possible.

Further, as shown in FIG. 5, the first prism sheet 6 is placed so that the prism array 9 is perpendicular to the end face of the light guide 2 on which the light source 1 is arranged, and the first prism sheet 6 is placed thereon. Second
When the prism sheet 7 is used so that the prism row 9 is orthogonal to the prism row 9 of the first prism sheet 6, only the second prism sheet 7 is used for λ / 8 to 7
It is preferable to use the prism sheet of the present invention configured by using the transparent substrate 8 having the same light control function as the λ / 8 phase plate. In this case, the outgoing light emitted from the diffusion sheet 5 has a strong horizontal polarization. Due to the characteristic that the outgoing light transmits the horizontal polarization of the first prism sheet 6 well, the outgoing light with a stronger horizontal polarization is obtained. Are emitted from the first prism sheet 6. This emitted light passes through the transparent base material 8 that constitutes the second prism sheet 7, so that its polarization plane is rotated to become light of strong vertical polarization, and the prism array 9 of the second prism sheet 7 The emitted light emitted from the second prism sheet 7 becomes stronger in the vertically polarized light due to the characteristic that the vertically polarized light is easily transmitted. Therefore, the emitted light has vertical polarization stronger than horizontal polarization, and by using this horizontal polarization in the liquid crystal panel, the brightness of the liquid crystal display device is increased by several to ten and several percents as compared with the conventional one. It becomes possible.

[0021]

The present invention will be described below in detail with reference to examples. Prism sheet Using a mold in which a lens pattern having a large number of parallel prism rows with a pitch of 50 μm and an apex angle of 90 ° is formed on one surface of a polycarbonate stretched phase film having a light control function equivalent to that of a λ / 2 phase plate, acrylic is used. A prism portion was formed from a system ultraviolet curable resin (refractive index 1.52) to obtain a prism sheet A. Using a mold in which a lens pattern having a large number of prism rows with a pitch of 50 μm and a vertical angle of 90 ° in parallel is formed on one surface of a polyester stretched phase film having a light control function equivalent to that of a λ / 2 phase plate, an acrylic ultraviolet ray is used. A prism portion was formed from a curable resin (refractive index 1.52) to obtain a prism sheet B. Acrylic UV curing using a mold in which a lens pattern having a large number of prism rows with a pitch of 50 μm and an apex angle of 90 ° is formed in parallel on one side of a polymethylmethacrylate stretched film that does not have a light control function as a phase film. Type resin (refractive index 1.
52) to form a lenticular lens to obtain a lens sheet E. The prism sheets A and B were formed such that the optical axis of the transparent substrate and the prism rows were at 45 °.

Examples 1 and 2, Comparative Example 1 Using the prism sheet shown in Table 1, a backlight as shown in FIG. 1 was assembled. The front luminances of the horizontally polarized light and the vertically polarized light at this time were measured, and the results are shown in Table 1 as relative values when the front luminance of Comparative Example 1 was 100.

Example 3, Comparative Example 2 Using the two prism sheets shown in Table 1, a backlight as shown in FIG. 3 was assembled. The front luminances of the horizontally polarized light and the vertically polarized light at this time were measured, and the results are shown in Table 1 as relative values when the front luminance of Comparative Example 1 was 100.

Example 4, Comparative Example 3 Using the two prism sheets shown in Table 1, a backlight as shown in FIG. 5 was assembled. The front luminances of the horizontally polarized light and the vertically polarized light at this time were measured, and the results are shown in Table 1 as relative values when the front luminance of Comparative Example 1 was 100.

[0025]

[Table 1]

[0026]

In the present invention, the prism sheet used for the backlight is formed by using the transparent base material having the light control function equivalent to that of the specific phase plate.
A function to control the plane of polarization of the light that passes through the prism sheet is added, and the optical function when used in a liquid crystal panel is maintained without impairing the original function of the prism sheet to control the directivity of the light emitted from the light guide. The efficiency can be improved and the brightness of the liquid crystal display device can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration example of a backlight of the present invention.

FIG. 2 is a perspective view showing a configuration example of a part of the backlight of the present invention.

FIG. 3 is a perspective view showing a configuration example of a back light of the present invention.

FIG. 4 is a partial perspective view showing a configuration example of a prism sheet of the present invention.

FIG. 5 is a partial perspective view showing a configuration example of a backlight of the present invention.

[Explanation of symbols]

 1 ... Light source 2 ... Light guide 3 ... Diffusion layer 4 ... Covering film 5 ... Diffusion sheet 6 ... Prism sheet (first prism sheet) 7 ... Second Prism sheet 8 ・ ・ ・ Transparent base material 9 ・ ・ ・ Prism row

Claims (4)

[Claims] 1. A prism sheet comprising a large number of prism rows formed in parallel on at least one surface of a transparent substrate having a light control function equivalent to a λ / 8 to 7λ / 8 phase plate. 2. An optical axis of a transparent substrate having a light control function equivalent to a λ / 8 to 7λ / 8 phase plate and a prism array are arranged to form an angle of 35 to 55 °. The prism sheet according to claim 1. 3. A transparent material having a light source and a plate-shaped light guide body having at least one entrance surface and an exit surface facing the light source, and having a light control function equivalent to a λ / 8 to 7λ / 8 phase plate. A backlight characterized in that a prism sheet in which a large number of prism rows are formed in parallel on at least one surface of a base material is installed on the exit surface side of a light guide. 4. A λ / 8 to 7λ constituting a prism sheet.
4. The backlight according to claim 3, wherein the transparent base material having a light control function equivalent to a / 8 phase plate and the prism array form an angle of 35 to 55 [deg.].