JP2001297615A - Optical sheet and backlight unit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical sheet having a bright line preventing layer that enables to decrease loss of rays and that a visivility from the screen of liquid crystal is low and a backlight unit, capable of improving the luminance and preventing generation of unevenness of luminance by using this optical sheet. SOLUTION: The bright line preventing layer 5 for preventing generation of the bright line by the light-diffusing function is laminated on a bright line generating region of the optical sheet 1. The bright line preventing layer 5 is formed by using printing ink, where a light diffuser 11 is scattered and by using a gradation printing where the dot pattern is varied gradually. The haze value of the bight line preventing layer 5 is set in the range of 10% up to 90% and the diameter of the smallest dot 12 for the gradation printing is made from 10 μm up to 200 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sheet suitable for a light diffusion sheet or a prism sheet incorporated in a backlight unit of a liquid crystal display, and a backlight unit using the same.

[0002]

2. Description of the Related Art In a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back surface to emit light has become widespread, and a backlight unit is provided on a lower surface side of the liquid crystal layer. As shown in FIG. 3, the backlight unit 20 generally includes a rod-shaped lamp 21 as a light source, a rectangular plate-shaped light guide plate 22 arranged so that an end of the lamp 21 extends along the lamp 21,
A light diffusion sheet 23 disposed on the surface side of the light guide plate 22,
A prism sheet 24 disposed on the surface side of the light diffusion sheet 23.

The function of the backlight unit 20 will be described. First, a light beam incident on the light guide plate 22 from the lamp 21 is reflected by reflection dots or a reflection sheet (not shown) on the back surface of the light guide plate 22 and each side surface. The light is emitted from the surface of the light guide plate 22. The light emitted from the light guide plate 22 enters the light diffusion sheet 23, is diffused, and is emitted from the surface of the light diffusion sheet 23. Thereafter, the light beam emitted from the light diffusion sheet 23 enters the prism sheet 24, and is emitted by the prism portion 24a formed on the surface of the prism sheet 24 as a light beam having a distribution showing a peak almost directly above. Thus, the light beam emitted from the lamp 21 is
The light is diffused by the light diffusion sheet 23, is refracted by the prism sheet 24 so as to show a peak almost directly above, and illuminates the entire liquid crystal layer (not shown) further above.

[0004] Although not shown, there is also a backlight unit in which a light diffusion sheet or a prism sheet is further disposed on the surface side of the prism sheet 24 in consideration of the light-collecting characteristics of the prism sheet 24 described above.

By the way, the above-mentioned backlight unit 2
In the case of 0, since the luminance on the lamp 21 side is inevitably too large due to the structure, a bright line (a linear portion having higher luminance) is generated in a band such as an outer edge portion along the lamp 21 and an outer edge portion opposed thereto. For this reason, a bright line preventing layer 25 for reducing the transmission of light rays is laminated on a band where the bright lines appear on the back surface of the light diffusion sheet 23, so that substantially uniform luminance is secured on the entire surface.

[0006]

As described above, the bright line preventing layer 25 laminated on the back surface of the light diffusing sheet 23 is
It is formed by printing such as screen printing using a printing ink of white, black, gray, or the like.
In some cases, gradation printing for blurring the boundary of No. 5 is performed.

[0007] Since the bright line preventing layer 25 formed by printing shields light rays, the loss of light rays emitted from the lamp 21 increases. In addition, in today's liquid crystal panels, the transmittance is improved, and there is a possibility that the boundary of the bright line preventing layer 25 and the gradation pattern may be seen.

The present invention has been made in view of these inconveniences, and can provide an optical sheet having a bright line preventing layer which can reduce light ray loss and has low visibility from a liquid crystal screen, and can improve luminance using the optical sheet. It is another object of the present invention to provide a backlight unit capable of preventing the occurrence of luminance unevenness.

[0009]

The invention made to solve the above-mentioned problem is an optical sheet in which a bright line preventing layer for preventing generation of a bright line by a light diffusion function is laminated in a bright line generating zone. The prevention layer is formed by gradation printing in which the dot pattern is gradually changed, and the minimum dot diameter of the gradation printing is 10
It is characterized in that it is not less than μm and not more than 200 μm. Here, the “optical sheet” means a sheet having various optical functions such as diffusion, condensing, and refraction, and specifically includes a light diffusion sheet, a prism sheet, and the like. Further, the “bright line generation band” means a band in which a bright line is generated when the bright line preventing layer of the present invention is not laminated in the backlight unit. Further, the “light diffusion function” means a function of diffusing a transmitted light beam.

The optical sheet is for dispersing the light transmitted through the bright line preventing layer, thereby reducing the luminance in the band where the bright line preventing layer is laminated and preventing the generation of the bright line.
As described above, the bright line prevention layer of the optical sheet does not block light rays as in the conventional bright line prevention layer, but disperses transmitted light rays, so that light loss can be reduced, and In addition, it is possible to reduce the visibility of the bright line preventing layer from the liquid crystal screen.

Further, since the bright line preventing layer is formed by gradation printing in which a dot pattern is gradually changed, it is possible to incline the light diffusivity of the bright line preventing layer and blur the boundary of the bright line preventing layer. it can. Therefore, the visibility of the bright line preventing layer from the liquid crystal screen can be further reduced.

Further, since the minimum dot diameter of the gradation printing is set to 10 μm or more and 200 μm or less, the dot pattern can be visually recognized on the liquid crystal display screen and the boundary portion of the bright line preventing layer is dark while ensuring printability. It can be prevented from appearing linearly.

Another invention made in order to solve the above problem is an optical sheet in which a bright line preventing layer for preventing the occurrence of bright lines by a light diffusion function is laminated in a bright line generating zone,
The bright line preventing layer is formed by gradation printing using a printing ink in which a light diffusing agent is dispersed, and the haze value of the bright line preventing layer is 10% or more and 90% or less. Here, the "haze value"
It means the cloud value measured by the measurement method A specified in JIS-K-7105 (Test method for optical properties of plastics).

According to this optical sheet, the light diffusing function can be exhibited by the light diffusing agent dispersed in the printing ink, and the above-mentioned specific action of the bright line preventing layer of the present invention can be exhibited.

The haze value of the bright line preventing layer is 10%.
When the content is at least 90% or less, the above-described bright line preventing action and
The effect of reducing the light loss and the effect of reducing the visibility of the bright line preventing layer can be exhibited in a well-balanced manner.

Therefore, an optical sheet in which a bright line preventing layer for preventing the generation of a bright line by a light diffusing function is laminated in a bright line generating zone, wherein (a) the bright line preventing layer comprises a printing ink in which a light diffusing agent is dispersed. Used, and formed by gradation printing in which the dot pattern is gradually changed,
(B) By setting the haze value of the bright line preventing layer to 10% or more and 90% or less and (c) setting the minimum dot diameter of the gradation printing to 10 μm or more and 200 μm or less, all of the above-mentioned effects can be exerted.

In the optical sheet, a blue pigment may be mixed with the printing ink. By mixing a pigment as in this means, the transmittance of light can be controlled, and as a result, the effect of preventing bright lines can be controlled. Further, by using a blue pigment as the pigment, it is possible to prevent the bright line preventing layer portion from developing yellow.

The optical sheet includes a transparent base layer, a light diffusion layer laminated on the front side of the base layer, and an anti-sticking layer laminated on the back side of the base layer. That is, a light diffusion sheet is preferable, and the bright line prevention layer may be laminated on the back surface side of the sticking prevention layer.
In general, since the surface of the light diffusion layer of the light diffusion sheet has irregularities, laminating the bright line prevention layer on the relatively flat outer surface of the anti-sticking layer has higher adhesiveness and enables beautiful gradation printing. .

Therefore, (a) a lamp, (b) a light guide plate for guiding light emitted from the lamp to the surface side, and (c)
When the optical sheet of the present invention is used as the optical sheet in a backlight unit for a liquid crystal display device, the optical unit being provided on the surface side of the light guide plate and guiding the light rays uniformly in the surface direction, the light loss is reduced. , The occurrence of bright lines can be prevented, and as a result, the luminance can be improved and the luminance unevenness can be prevented.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate. FIG. 1A is a schematic sectional view showing an optical sheet according to an embodiment of the present invention.
(B) is a schematic bottom view of the optical sheet of (a).

An optical sheet 1 shown in FIG. 1 is a light diffusion sheet for diffusing a transmitted light, and includes a base layer 2, a light diffusion layer 3 laminated on the surface side of the base layer 2, and a base layer. 2 and a bright line preventing layer 5 laminated on the back side of the anti-sticking layer 4.

The base material layer 2 is formed of a transparent, particularly colorless and transparent synthetic resin because it is necessary to transmit light. Examples of the synthetic resin used for the base layer 2 include:
There is no particular limitation, and examples include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather-resistant vinyl chloride. Although the thickness of the base material layer 2 is not particularly limited, for example, 10 μm or more and 500 μm or less, preferably 75 μm
It is not less than 250 μm. If the thickness of the base material layer 2 is less than the above range, curling may easily occur when the resin composition forming the light diffusion layer 3 is applied. Conversely, if the thickness of the base material layer 2 exceeds the above range, the brightness of the liquid crystal display device may decrease, and the thickness of the backlight unit increases, which is contrary to the demand for thinning the liquid crystal display device. It will also be.

The light diffusion layer 3 comprises a binder 6 and beads 7 dispersed in the binder 6. By dispersing the beads 7 in this manner, the light beam transmitted through the light diffusion layer 3 from the back side to the front side can be uniformly diffused. In addition, by providing a bead 7 whose upper end protrudes from the binder 6 or is embedded in the binder 6, the light beam can be diffused better. The thickness of the light diffusion layer 3 (the binder 6 excluding the beads 7)
Is not particularly limited, but is, for example, about 1 μm or more and 30 μm or less.

The polymer used for the binder 6 includes, for example, acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamideimide, epoxy resin and the like. Further, in addition to the above-mentioned polymer, for example, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersant, and the like may be blended in the binder 6.

The beads 7 have a substantially spherical shape, and examples of the material include acrylic resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide and the like.

The particle size of the beads 7 is 0.1 μm or more and 100
μm or less, preferably 1 μm or more and 50 μm or less. If the particle size of the beads 7 is less than the above range, the light diffusion effect becomes insufficient. Conversely, if the particle size exceeds the above range, the coating of the resin composition forming the light diffusion layer 3 is not performed. This is because the work becomes difficult. The particle diameter of the beads 7 is derived by magnifying a 100 beads 7 arbitrarily extracted with a microscope, measuring the diameter of the particles, and averaging the diameters. When the beads 7 are not spherical, the average of the dimensions of the beads 7 in an arbitrary direction and the dimensions of the beads 7 in a direction orthogonal thereto is used.

The mixing amount of the beads 7 in the light diffusion layer 3 is preferably 0.1 to 500 parts by weight, and more preferably 10 to 3 parts by weight based on 100 parts by weight of the polymer in the binder 6.
Particularly preferred is not more than 00 parts by weight. If the amount is less than the above range, the light diffusion effect becomes insufficient. Conversely, if the amount exceeds the above range, the coating of the resin composition forming the light diffusion layer 3 is performed. This is because the work becomes difficult.

The anti-sticking layer 4 comprises a binder 8
And beads 9 dispersed in the binder 8. The beads 9 projecting from the binder 8 prevent sticking with the light guide plate (see FIG. 3). The binder 8 and the beads 9 of the sticking prevention layer 4 are the same as the binder 6 and the beads 7 of the light diffusion layer 3.

The blending amount of the beads 9 is relatively small, so that the beads 9 are dispersed in the binder 8 apart from each other. On the other hand, the thickness of the sticking prevention layer 4 (meaning the thickness of the binder 8 excluding the beads 9) is not particularly limited, but is, for example, 1 μm or more and 10 μm or more.
m or less. For this reason, the lower end of most of the beads 9 protrudes from the binder 8 to prevent sticking with the light guide plate.

As shown in FIG. 1B, the bright line preventing layer 5 is laminated on a band where bright lines are generated, for example, on the outer edge of the lamp, on the back surface of the anti-sticking layer 4. The bright line preventing layer 5 is obtained by dispersing the light diffusing agent 11 in the printing ink 10.

The printing ink 10 is not particularly limited as long as it can be used for printing. For example, an evaporation drying ink, an oxidation polymerization ink, a heat curing ink,
Liquid reaction type inks, ultraviolet curable type inks and the like can be used.
Above all, an ultraviolet curable ink suitable for gradation printing is preferable. In order to improve the light transmittance, the printing ink 10 is preferably transparent (colored and transparent), and particularly preferably colorless and transparent.

The light diffusing agent 11 is a particle having a property of diffusing light rays, and is roughly classified into an inorganic filler and an organic filler. As the inorganic filler, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide,
Magnesium silicate or a mixture thereof can be used. As the organic filler, acryl, acrylonitrile, non-yellowing urethane, styrene and the like can be used. Inorganic fillers are preferred from the viewpoint of low swellability due to the printing ink 10, and urethane-based fillers are preferred among organic fillers.

The shape of the light diffusing agent 11 is not particularly limited, and examples thereof include spherical, cubic, needle, rod, spindle, plate, scale, and fiber shapes. Considering the above, beads are preferable. The particle size of the light diffusing agent 11 is preferably 1 μm or more and 50 μm or less, particularly preferably 2 μm or more and 20 μm or less. If the particle size of the light diffusing agent 11 is less than the above range, the light diffusing effect becomes insufficient. Conversely, if it exceeds the above range, it is difficult to apply the resin composition for forming the bright line preventing layer 5. It is because it becomes.

The compounding amount of the light diffusing agent 11 in the bright line preventing layer 5 is preferably 10 parts by weight or more and 80 parts by weight or less based on 100 parts by weight of the polymer component of the printing ink 10.
It is particularly preferable that the amount is from 60 parts by weight to 60 parts by weight. If the amount is less than the above range, the effect of preventing bright lines will be insufficient. Conversely, if the amount exceeds the above range, the coating of the resin composition for forming the bright line preventing layer 5 will be insufficient. This is because the work becomes difficult.

According to the optical sheet 1, the bright line preventing layer 5
In the band in which is present, the diffusivity is improved by the dispersed light diffusing agent 11, and the high diffusivity can reduce the luminance of the band, and as a result, the generation of bright lines can be prevented. Therefore, unlike the conventional bright line prevention layer formed by light-shielding printing, light loss due to the bright line prevention layer can be reduced. In addition, since the bright line preventing layer 5 utilizes the diffusivity to lower the luminance, the visibility of the bright line preventing layer 5 from a liquid crystal screen such as a conventional bright line preventing layer by printing can be reduced.

The bright line preventing layer 5 is formed by gradation printing of a dot pattern in which the dot diameter is gradually reduced inward from one edge. According to such gradation printing, the light diffusivity of the bright line preventing layer 5 is inclined, and the boundary of the bright line preventing layer 5 can be blurred. Therefore, the visibility of the bright line preventing layer 5 from the liquid crystal screen can be further reduced.

The diameter of the smallest dot 12 on the innermost side of the bright line preventing layer 5 is preferably 10 μm or more and 200 μm or less, particularly preferably 50 μm or more and 150 μm or less. If the diameter of the minimum dot 12 is smaller than the above range, gradation printing becomes technically difficult, and conversely,
Beyond the above range, the dots 12 are visible from the liquid crystal screen, and furthermore, the inner edge (boundary portion) of the bright line preventing layer 5.
Is dark and linearly expressed.

The haze value of the bright line preventing layer 5 is preferably from 10% to 90%, particularly preferably from 15% to 50%. When the haze value of the bright line preventing layer 5 is smaller than the above range, the light diffusing property is small and the generation of the bright line cannot be completely prevented.
It is necessary to remarkably increase the compounding amount of No. 1 and, as a result, clogging of the printing composition occurs at the time of gradation printing,
This is because good printing becomes difficult.

By mixing a pigment in the printing ink 10, the transmittance of light can be controlled, and as a result, the effect of preventing bright lines can be controlled. Among them,
Blue pigments are preferred. The bright line preventing layer 5 due to the light diffusion effect tends to look yellow on the backlight, but the yellowish color can be eliminated by containing a blue pigment as described above.

The content of the blue pigment is preferably from 0.05 to 1.0 part based on 100 parts of the printing ink. This is because when the content of the blue pigment is smaller than the above range, the effect of eliminating the appearance of the yellow color is small. On the contrary, when the content exceeds the above range, the blue color is too dark and the dots 12 are seen from the liquid crystal screen. This is because the edge (boundary portion) on the inner side of the bright line preventing layer 5 is dark and linear.

The optical sheet 15 shown in FIG. 2 is composed of a base layer, a light diffusion layer, an anti-sticking layer and a bright line preventing layer 5, and the bright line preventing layer 5 is formed by gradation printing of a dot pattern. Figure 1 above
, Except that the dot pattern of the bright line preventing layer 5 is different. The dot pattern of the bright line preventing layer 5 is configured such that the dot diameter is constant and the dot arrangement density (the number per unit area) gradually decreases inward from one edge. The light diffusing property of the bright line preventing layer 5 is inclined so as to gradually decrease inward from the edge.

Incidentally, the optical sheet of the present invention is not limited to the above embodiment, and for example, the bright line preventing layer can be laminated on the back surface of the prism sheet. In addition, since the bright line preventing layer prevents the generation of bright lines due to diffusivity, the visibility from the liquid crystal screen is reduced even if it is not gradation printing. Furthermore, in a direct-type backlight unit, a bright line generation band is formed linearly above a linear lamp. In this case, the bright line is prevented by gradation printing at a position above the lamp where the bright line generation band is formed. Layers may be stacked. The gradation printing includes a method of gradually changing the dot pattern as described above, a method of inclining the basis weight of the resin composition, and a method of inclining the compounding amount of the light diffusing agent 11.

[0043]

As described above, according to the optical sheet of the present invention, the light loss due to the bright line preventing layer can be reduced, and the bright line preventing layer is hardly visible from the liquid crystal screen. Therefore, the backlight unit using the optical sheet of the present invention has improved luminance and can prevent the occurrence of luminance unevenness.

[Brief description of the drawings]

FIG. 1A is a schematic cross-sectional view illustrating an optical sheet according to an embodiment of the present invention, and FIG. 1B is a schematic bottom view of the optical sheet of FIG.

FIG. 2 is a schematic bottom view showing an optical sheet having a form different from that of FIG. 1;

FIG. 3 is a schematic perspective view showing a general backlight unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Base material layer 3 Light diffusion layer 4 Sticking prevention layer 5 Bright line prevention layer 6 Binder 7 Bead 8 Binder 9 Bead 10 Printing ink 11 Light diffusing agent 12 Minimum dot 15 Optical sheet

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // F21Y 103: 00 G02F 1/1335 530

Claims (6)

[Claims] 1. An optical sheet in which a bright line preventing layer for preventing generation of a bright line by a light diffusion function is laminated on a bright line generating zone, wherein the bright line preventing layer is formed by gradation printing in which a dot pattern is gradually changed. An optical sheet characterized in that the minimum dot diameter of the gradation printing is 10 μm or more and 200 μm or less. 2. An optical sheet in which a bright line preventing layer for preventing generation of a bright line by a light diffusing function is laminated on a bright line generating zone, wherein the bright line preventing layer is formed by gradation printing using a printing ink in which a light diffusing agent is dispersed. An optical sheet, wherein the haze value of the bright line preventing layer is 10% or more and 90% or less. 3. An optical sheet in which a bright line preventing layer for preventing the generation of a bright line by a light diffusion function is laminated in a bright line generating zone, wherein the bright line preventing layer uses a printing ink in which a light diffusing agent is dispersed, and And the dot pattern is formed by gradation printing in which the dot pattern is gradually changed, the haze value of the bright line preventing layer is 10% or more and 90% or less, and the minimum dot diameter of the gradation printing is 10 μm or more and 200 μm or less. An optical sheet characterized by the above-mentioned. 4. The optical sheet according to claim 1, wherein a blue pigment is mixed with the printing ink. 5. A transparent substrate layer, a light diffusion layer laminated on the front side of the substrate layer, and a sticking prevention layer laminated on the back side of the substrate layer. The optical sheet according to any one of claims 1 to 4, wherein the bright line preventing layer is laminated on the back surface side of the layer. 6. A lamp, a light guide plate for guiding light rays emitted from the lamp to a front surface side, and a light guide plate disposed on the front surface side of the light guide plate for uniformly guiding light beams in a surface direction. A backlight unit for a liquid crystal display device, comprising: the optical sheet according to claim 1.