JP2008251350A - Direct backlight unit - Google Patents

Abstract

A direct backlight device capable of improving the luminance uniformity of a light emitting surface is provided.
The light incident surface is a flat surface having a center line average roughness Ra of less than 3 μm, and a region A immediately above the linear light source on the light emitting surface is substantially parallel to the longitudinal direction of the linear light source. A plurality of concave or convex linear prisms are formed side by side, and the linear prism has a cross section of a first prism portion 43 that is a part of a curve having only one of a peak or a valley, and a cross section The second prism portion 44 is a line formed in the position of a peak or valley, concave or convex, and does not overlap the curve indicating the first prism portion, and satisfies a predetermined condition.
[Selection] Figure 2

Description

  The present invention relates to a direct-type backlight device, and more particularly to a direct-type backlight device that can increase the luminance uniformity of a light emitting surface.

Conventionally, a liquid crystal display device includes a plurality of linear light sources (for example, a cold cathode tube (CCFL), a hot cathode tube (HCFL), etc.), a reflector that reflects light from these linear light sources, A direct-type backlight device is used that includes a light diffusing plate that allows direct light from a light source and reflected light from a reflecting plate to enter from a light incident surface and diffuses the incident light from the light emitting surface to be emitted. . In such a direct-type backlight device, the light emitting surface, which is the light emitting surface, has a higher brightness in the portion directly above the linear light source, that is, the portion in which the outline of the linear light source is projected on the light incident surface than the other portions. There was a problem that it was easy to become. For this reason, development of a technique for increasing the luminance uniformity of the light emitting surface is required. Therefore, Patent Document 1 discloses a configuration in which a plurality of lenticular concavo-convex structures extending along the longitudinal direction of a linear light source are provided on a light incident surface of a light diffusion plate in a direct type backlight device.
JP 2000-182418 A

  However, in the region directly above the linear light source, the angle of inclination of the top portion of the lenticular uneven structure is gentler than in other locations, so that the emitted light from the linear light source is large at this top portion. Since it radiates | emits without being refracted, there existed a problem that the brightness | luminance of the front direction in the said part became high too much. For this reason, there has been a problem that the luminance uniformity of the light emitting surface becomes insufficient.

  An object of the present invention is to provide a direct type backlight device capable of increasing the luminance uniformity of a light emitting surface.

According to the present invention, the following direct type backlight device is provided.
(1) A plurality of linear light sources arranged substantially in parallel, a reflecting plate for reflecting light from these linear light sources, direct light from the linear light source and reflected light from the reflecting plate as a light incident surface And a light diffusing plate that diffuses and emits the incident light from the light exit surface, and the light entrance surface has a center line average roughness Ra of less than 3 μm. The region A, which is a flat surface and directly above the linear light source on the light exit surface, extends substantially parallel to the longitudinal direction of the linear light source and is concave or convex in the thickness direction of the light diffusion plate. A plurality of linear prisms arranged side by side, and the linear prism has a cross-sectional shape in the short direction that is a part of a curve having only one of a peak or a valley. And the cross-sectional shape in the short direction is the position of the peak or valley. And a second prism part that is concave or convex in the thickness direction of the light diffusing plate and is a line that does not overlap a curve indicating the first prism part, and the first prism part A line formed by the second prism portion is a line X, and the line X is a line X1 in which an angle between a tangent at an arbitrary position of the line X and the light incident surface exceeds 20 degrees, and the line X A line segment obtained by projecting the line X1 on the light incident surface along the short direction of the linear prism as a line X2 in which an angle formed by a tangent at an arbitrary position and the light incident surface is 20 degrees or less Is a direct-type backlight device satisfying the relationship of LX2 / (LX1 + LX2) ≦ 0.35, where LX1 is LX1, and the length of the line segment projected on the light incident surface is LX2.

  Here, examples of the curve indicating the first prism portion include an arc shape, an elliptical arc shape, a parabolic arc shape, and the like. The area A immediately above the linear light source is a range in which the inner diameter portion of the linear light source is projected onto the light incident surface. In the present specification, the “curve having only one peak or valley” refers to a curve consisting of only one mountain or a curve consisting of only one valley.

(2) The direct-type backlight device, wherein the second prism unit includes one or more second prisms extending along a longitudinal direction of the linear prism.

(3) The direct type backlight device, wherein the second prism has a polygonal cross section in the short direction of the linear light source. Here, examples of the curve indicating the second prism include an arc shape, an elliptical arc shape, a parabolic arc shape, and the like. Here, the second prism is preferably convex.

(4) A plurality of linear light sources arranged substantially in parallel, a reflecting plate that reflects light from these linear light sources, direct light from the linear light source and reflected light from the reflecting plate as a light incident surface And a light diffusing plate that diffuses and emits the incident light from the light exit surface, and the light entrance surface has a center line average roughness Ra of less than 3 μm. In the region immediately above the linear light source on the light emitting surface, the surface extends substantially parallel to the longitudinal direction of the linear light source, and the cross-sectional shape in the short direction is either a mountain or a valley. A plurality of curved linear prisms having only one of them are formed side by side, and the curve forming the linear prism has an angle formed by a tangent at each position of the curve and the light incident surface of 10 degrees or less. A region C and a tangent at each position of the curve A region D having an angle with the light incident surface of more than 10 degrees, and a center line average roughness Ra (C) along the direction of the curve in the region C is 0.1 μm or more, A direct type backlight device that is larger than the center line average roughness Ra (D) along the direction of the curve in the region D. Here, examples of the curve indicating the linear prism include an arc shape, an elliptical arc shape, a parabolic arc shape, and the like.

(5) The light diffusing plate is composed of a resin composition containing a transparent resin, and the resin composition has a total light transmittance of 60% to 98% and a haze of 20% to 100%. The direct-type backlight device.

  According to the present invention, the second prism portion having a shape different from the first prism portion is formed at the peak or valley portion of the first prism portion having a curved cross section, and each position of the line X constituting the linear prism is formed. By setting the range of the region where the angle between the tangent line and the light incident surface is 20 degrees or less as a predetermined range, the luminance directly above the linear light source can be reduced and the luminance uniformity of the light emitting surface can be increased. There is an effect that can be done. In addition, according to the present invention, a plurality of curved linear prisms are formed on the light exit surface, and the center line average of the region C in which the angle formed between the tangent at each position of the curve and the light incident surface is a predetermined angle or less. By making the roughness Ra a rough surface, there is an effect that the luminance of the light emitting surface can be increased by reducing the luminance of the portion directly above the linear light source.

<First Embodiment>
(Direct type backlight device)
A direct type backlight device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view schematically showing a direct type backlight device 1 according to the present embodiment. As shown in FIG. 1, the direct type backlight device 1 includes a plurality of linear light sources 10, a reflecting plate 20 that reflects light from the linear light source 10, direct light from the linear light source 10, and a reflecting plate 20. The light diffusing plate 30 which enters the light reflected from the light incident surface 30A and diffuses the incident light from the light emitting surface 30B and emits the light is provided.

(Linear light source)
The linear light source 10 is a straight-tube cold cathode tube from the viewpoint of luminance uniformity. The linear light source 10 is not limited to a cold cathode tube, and for example, a hot cathode tube or a combination of a point light source such as a light emitting diode (LED) and a linear light guide may be used. it can. In this embodiment, a straight light source is used as the linear light source. However, a substantially U-shaped tube in which two substantially parallel tubes are connected by one semicircular tube, Examples include a substantially N-shaped tube in which three tubes are connected by two semicircular tubes, and a substantially W-shaped tube in which four substantially parallel tubes are connected by three semicircular tubes. You can also.

  In the present invention, a combination of a point light source and a light guide is also considered as a single linear light source, and among those connected by a semicircular tube, a substantially U-shaped tube has two linear shapes. Assume that the light source is a substantially N-shaped tube with three linear light sources, and the substantially W-shaped tube is four.

  The number of linear light sources used is not particularly limited. For example, when the direct backlight device of the present invention is used in a 32-inch liquid crystal display device, the number of linear light sources is, for example, 16, 14, 12, 8, 4, 2 Or even odd numbers.

  In the present embodiment, the plurality of linear light sources 10 are arranged substantially parallel to each other. Here, “substantially parallel” means that the angle formed is within a range of ± 5 degrees from a truly parallel state. In the present embodiment, the plurality of linear light sources are arranged substantially in parallel, but may be configured not to be arranged substantially in parallel.

  The average distance between the central axes of any adjacent linear light sources 10 is constant at a (mm). However, the average distance between the central axes of the adjacent linear light sources is not constant as in the present embodiment, but may be random, and has regularity that increases or decreases toward a specific location. It is good also as the structure which made it. Here, the specific location refers to, for example, a central location including a line connecting one long side of a rectangular light diffusing plate or the central locations of opposing short sides.

  The average distance a (mm) between the central axes of the adjacent linear light sources 10 can be 15 mm to 150 mm, preferably 20 mm to 100 mm, and more preferably 20 mm to 65 mm. By setting the average distance a within the above range, the power consumption of the direct type backlight device can be reduced, the assembly of the device is easy, and the luminance unevenness of the light emitting surface can be suppressed.

  The diameter of the linear light source 10 can be 1.5 mm to 20 mm, and preferably 2 mm to 16 mm. By setting it in such a range, the direct type backlight device can be thinned, and damage to the linear light source can be reduced. In the present embodiment, the plurality of linear light sources 10 are of the same type having the same diameter. However, a plurality of types of linear light sources having different diameters can be used.

  The average distance b (mm) between the central axis of the linear light source 10 and the light incident surface 30A of the light diffusing plate 30 may be designed in consideration of the thickness and luminance uniformity of the direct type backlight device. -30 mm, and preferably 3 mm to 25 mm. By setting the average distance b in the above range, luminance unevenness can be reduced, and a reduction in the luminous efficiency of the lamp can be prevented, and the backlight device can be made thinner. In the present embodiment, the plurality of linear light sources 10 are arranged such that the average distance b (mm) from the light incident surface 30A is substantially constant for all the linear light sources. However, a plurality of linear light sources may be arranged so that some linear light sources are closer to the light incident surface 30A than other linear light sources.

  Here, the relationship (1) of 1.7 ≦ a / b ≦ 7.0 may be satisfied between the average distance a (mm) and the average distance b (mm). The relationship (2) of .8 ≦ a / b ≦ 6.0 may be satisfied. By satisfying such a relationship, the number of linear light sources used can be reduced and the power consumption of the device can be suppressed.

(a reflector)
For the reflecting plate 20, a resin colored in white or silver, a metal, or the like can be used. Among these, a resin can be preferably used for the reflecting plate 20 from the viewpoint of weight reduction. The color of the reflector 20 is preferably white from the viewpoint of improving the luminance uniformity. Moreover, what mixed white and silver can also be used from a viewpoint which balances a brightness | luminance and brightness | luminance uniformity highly.

(Light diffusion plate)
As a material constituting the light diffusion plate 30, glass and resin can be used. As the resin, a transparent resin, a resin composition of two or more resins that are difficult to mix, a resin composition in which a light diffusing agent is dispersed in the transparent resin, and the like can be used. Among these, the material constituting the light diffusing plate 30 is preferably a resin because it is lightweight and easy to mold, and a transparent resin is preferable from the viewpoint of easily improving luminance. From the viewpoint of easy adjustment of haze, a resin composition in which a light diffusing agent is dispersed in a transparent resin is preferable.

  The transparent resin is a resin having a total light transmittance of 70% or more measured with a 2 mm-thick plate smooth on both sides based on JIS K7361-1, for example, polyethylene, propylene-ethylene copolymer, polypropylene , Polystyrene, a copolymer of an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester having a lower alkyl group, polyethylene terephthalate, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, and Examples thereof include a resin having an alicyclic structure. In addition, (meth) acrylic acid is acrylic acid and methacrylic acid.

  Among these, as a transparent resin, a copolymer of polycarbonate, polystyrene, an aromatic vinyl monomer containing 10% or more of an aromatic vinyl monomer, and a (meth) acrylic acid alkyl ester having a lower alkyl group Further, a resin having a water absorption of 0.25% or less, such as a resin having an alicyclic structure, is preferable in that a large light diffusion plate with little warpage can be obtained because deformation due to moisture absorption is small.

  Furthermore, a resin having an alicyclic structure is more preferable because it has good fluidity and can efficiently produce a large light diffusion plate. Further, a resin composition in which a light diffusing agent is mixed with a resin having an alicyclic structure has both high permeability and high diffusibility necessary for a light diffusing plate, and can improve chromaticity. Can be used.

  The resin having an alicyclic structure is a resin having an alicyclic structure in the main chain and / or side chain. From the viewpoint of mechanical strength, heat resistance, etc., a resin containing an alicyclic structure in the main chain is particularly preferred. Examples of the alicyclic structure include a saturated cyclic hydrocarbon (cycloalkane) structure and an unsaturated cyclic hydrocarbon (cycloalkene, cycloalkyne) structure. From the viewpoint of mechanical strength, heat resistance and the like, the alicyclic structure is preferably a cycloalkane structure or a cycloalkene structure, and more preferably a cycloalkane structure. The number of carbon atoms constituting the alicyclic structure is usually 4 to 30, preferably 5 to 20, and more preferably 5 to 15. In this case, it is preferable that the mechanical strength, heat resistance, and moldability of the light diffusion plate can be highly balanced.

  The proportion of the repeating unit having an alicyclic structure in the resin having an alicyclic structure may be appropriately selected according to the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90%. % By weight or more. When the ratio of the repeating unit having an alicyclic structure is too small, the heat resistance is lowered, which is not preferable. In addition, repeating units other than the repeating unit which has an alicyclic structure in resin which has an alicyclic structure are suitably selected according to the intended purpose.

  Specific examples of the resin having an alicyclic structure include (1) a ring-opening polymer of a norbornene monomer, a ring-opening copolymer of a norbornene monomer and another monomer, and hydrogenated products thereof. Norbornene polymers such as addition polymers of norbornene monomers and addition copolymers of norbornene monomers and other monomers; (2) monocyclic olefin polymers and hydrogenated products thereof; 3) Cyclic conjugated diene polymer and hydrogenated product thereof; (4) Polymer of vinyl alicyclic hydrocarbon monomer and copolymer weight of vinyl alicyclic hydrocarbon monomer and other monomer And hydrogenated products thereof, aromatic hydrogenated products of vinyl aromatic monomer polymers, and aromatic ring hydrogenated products of vinyl aromatic monomers and other monomers Vinyl alicyclic hydrocarbon polymers such as;

  Among these, from the viewpoints of heat resistance, mechanical strength, and the like, norbornene polymers and vinyl alicyclic hydrocarbon polymers are preferred, norbornene monomer ring-opening polymer hydrogenated products, norbornene monomers and other Hydrogenated ring-opening copolymer with monomer, aromatic ring hydrogenated polymer of vinyl aromatic monomer, and aromatic of copolymer of vinyl aromatic monomer and other monomers More preferred are ring hydrogenates.

  The light diffusing agent is a particle having a property of diffusing light, and examples thereof include an inorganic filler and an organic filler. Examples of the inorganic filler include silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, and a mixture thereof. Examples of the organic filler include acrylic resin, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, and benzoguanamine resin. As an organic filler, polystyrene resin, polysiloxane resin, and fine particles composed of a crosslinked product thereof are preferable in terms of high dispersibility, high heat resistance, and no coloration (yellowing) during molding. Fine particles made of a cross-linked product of polysiloxane resin are more preferable in terms of excellent properties.

  Examples of the shape of the light diffusing agent include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scale shape, and a fiber shape. Among these, the light diffusing direction can be exemplified. Spherical shape is preferable in that it can be squarely. The light diffusing agent is preferably used in a state of being uniformly dispersed in the transparent resin.

  In the case where the light diffusing agent is dispersed in the transparent resin, the content ratio of the light diffusing agent can be appropriately selected according to the thickness of the light diffusing plate, the interval between the linear light sources, and the like. The total light transmittance of the resin composition is preferably adjusted to 60% to 98%, more preferably 65% to 95%. Furthermore, the content ratio of the light diffusing agent is preferably adjusted so that the haze is 20% or more and 100% or less, more preferably 25% or more and 100% or less. By setting the total light transmittance and haze within the above-mentioned preferable ranges, the luminance and the luminance uniformity can be further improved.

  The total light transmittance is a value measured according to JIS K7361-1 with a 2 mm thick plate smooth on both sides. The haze is a value measured with a 2 mm-thick plate smooth on both sides according to JIS K7136.

  The thickness of the light diffusing plate 30 is preferably 0.4 mm to 5 mm, and more preferably 0.8 mm to 4 mm. By making the thickness of the light diffusing plate 30 within the above preferable range, it is possible to suppress the bending due to its own weight and to facilitate the molding.

  As shown in FIG. 1, a plurality of lenticulars 40 having a convex cross section in the short direction and extending substantially parallel to the longitudinal direction of the linear light source 10 are formed on the light emitting surface 30 </ b> B. Adjacent lenticulars 40 are formed so that their hem portions are connected to each other. The center line average roughness Ra along the direction perpendicular to the longitudinal direction of the lenticular 40 (left and right direction in the figure: short direction) is 3 μm to 1,000 μm. The center line average roughness Ra of the light exit surface 30B can be obtained according to JIS B0601 using an ultradeep shape measuring microscope. The light incident surface 30A is a flat surface having a center line average roughness Ra in an arbitrary direction within the surface of less than 3 μm. The lenticular 40 is a linear prism convex in the thickness direction of the light diffusing plate (vertical direction in FIG. 1).

  As shown in FIG. 1, the light exit surface 30B includes a region A directly above the region directly above the linear light source 10 that is a range obtained by projecting the inner diameter portion of the linear light source 10 onto the light incident surface 30A, and the region directly above this region. It can be divided into areas B other than A.

  2A is a longitudinal sectional view showing the region A immediately above, and FIG. 2B is a longitudinal sectional view showing the region B in an enlarged manner. As shown in FIG. 2, the lenticular 40 includes a first lenticular 41 having a shape corresponding to the region A immediately above, and a second lenticular 42 provided in the region B. In the present embodiment, the first lenticular 41 is provided only in the region A immediately above, but the first lenticular 41 may be provided in the region B.

  The second lenticular 42 has a substantially arc-shaped cross section in the short direction, and is symmetrical with respect to the normal line of the light incident surface 30A. The width dimension P in the short direction of the second lenticular 42 can be, for example, 20 μm to 700 μm, and preferably 30 μm to 300 μm.

  The first lenticular 41 is obtained by changing the shape of the mountain (top portion) of the second lenticular 42 to another shape. The first lenticular 41 has a cross-sectional shape in the short direction, which is formed at a position of a first prism portion 43 that is a part of a curve having one peak 43T and a peak 43T, and is convex upward in the figure. And a second prism portion 44 that is a line having a shape that does not overlap the curve indicating the first prism portion 43.

  The first prism portion 43 has substantially the same shape as the second lenticular 42 except for the mountain 43T. The second prism portion 44 is composed of one second prism having an isosceles triangle shape having an apex angle θ degree. The apex angle θ can be, for example, 40 degrees to 170 degrees, and preferably 45 degrees to 140 degrees. In the present embodiment, the apex angle θ is 100 degrees and the base angle is 40 degrees.

  In the present embodiment, the first prism portion 43 has an arc shape. However, the first prism portion 43 may have an elliptical arc shape, a parabolic arc shape, or the like. In addition, the second prism portion 44 has an isosceles triangle shape in cross section, but may be a triangle having another shape or a polygon such as a pentagon. In the present embodiment, the second prism portion 44 is configured by one isosceles triangle, but may be configured by a plurality of second prisms.

  The line X indicating the outer shape of the first lenticular 41 includes a line X1 in which the angle formed between the tangent at each position of the line X and the light incident surface 30A exceeds 20 degrees, and the tangent and light at each position of the line X. It can be distinguished from a line X2 where the angle formed with the incident surface 30A is 20 degrees or less. The second prism portion 44 is included in the line X1 because its base angle is 40 degrees. In the present embodiment, the first prism portion 43 corresponds to the line X1, and the second prism portion corresponds to the line X2. The following relationships (3) and (4) can be satisfied by appropriately changing the shape, length, and the like of these lines X1 and X2.

  Here, the length of the line segment expressed by projecting the line X1 onto the light incident surface 30A is LX1, and the length of the line segment expressed by projecting the line X2 onto the light incident surface 30A is LX2. In this case, in the present embodiment, the relationship (3) of LX2 / (LX1 + LX2) ≦ 0.35 is satisfied, and the relationship (4) of LX2 / (LX1 + LX2) ≦ 0.25 is preferably satisfied. By satisfying such relationship (3) or (4), in the region A immediately above, the incident light from the linear light source 10 can be emitted in a direction deviating from the normal line of the light incident surface. The luminance at A does not become too high, and the luminance uniformity of the light emitting surface can be increased.

  In the present embodiment, the second prism has a polygonal shape, but the present invention is not limited to this. In short, it may be a shape that satisfies at least the relationship (3). For example, as shown in FIG. 6, the second prism portion may be configured by a plurality of types of arcs having different radii of curvature from the first prism portion. At this time, the second prism portion may be constituted by a plurality of types of arcs or one type. Each type of arc may include a plurality of arcs. Further, although it is an arc, it may be an elliptical arc or a parabolic arc.

  In the present embodiment, the lenticular is convex, but may be concave. In this case, the second prism portion is provided in the concave valley portion. At this time, the second prism portion may be concave or convex.

Next, a method for forming the light exit surface will be described.
The method for forming the linear prism on the surface of the light diffusing plate is not particularly limited. For example, a method of forming the linear prism on the surface of the flat light diffusing plate may be used. A linear prism may be integrally formed simultaneously with the formation of a flat plate portion (in this specification, sometimes referred to as a light diffusing plate base).

  Examples of the method of forming the linear prism on the surface of the flat light diffusion plate include a method of cutting the surface of the flat light diffusion plate, a photocurable resin or a thermosetting resin on the surface of the flat light diffusion plate A method of transferring a desired shape to the coating film with a roll or a die and curing the coating film in that state, and embossing for pressing the surface of the flat light diffusion plate with a roll or a die having a desired shape A processing method etc. can be mentioned.

  Further, as a method of integrally forming the linear prism simultaneously with the formation of the light diffusion plate base, a casting method using a casting mold capable of forming a desired linear prism, or a mold capable of forming a desired linear prism is used. The injection molding method used can be mentioned. Since the injection molding method and the casting method can form the linear prism simultaneously with the formation of the light diffusion plate base as described above, the process is simple. The casting method can be performed in a mold capable of forming a plate, or can be performed continuously while pouring a raw material between two continuous belts and moving the belt. In the injection molding method, in order to increase the shape transfer rate, it is preferable to raise the mold temperature at the time of injecting the resin and rapidly cool the mold during cooling. Moreover, you may apply the injection compression molding method which expands a type | mold when injecting resin and closes a type | mold after that.

Second Embodiment
Next, a direct type backlight device according to a second embodiment of the present invention will be described.
This embodiment is different from the first embodiment in that a rough surface is provided instead of the second prism portion. Therefore, this difference will be mainly described. In addition, the same code | symbol is attached | subjected to the component similar or equivalent to 1st Embodiment, and the description is abbreviate | omitted or simplified.

  FIG. 3 is a vertical cross-sectional view for explaining the shape of the region A directly above the portion directly above the linear light source on the light exit surface of the light diffusing plate used in the direct backlight device according to this embodiment. As shown in FIG. 3, an arc-shaped linear prism 60 that extends substantially parallel to the longitudinal direction of the linear light source 10 and whose cross-sectional shape in the short direction has one peak or valley is located in the region A immediately above. A plurality are formed side by side.

  A curve indicating the linear prism 60 is formed by a region C in which an angle formed between the tangent at each position of the curve and the light incident surface 30A is 10 degrees or less, and a tangent at each position of the curve and the light incident surface 30A. It can be divided into a region D in which the angle exceeds 10 degrees. At this time, the centerline average roughness Ra (C) along the direction of the curve in the region C is 0.1 μm or more, and the centerline average roughness Ra (D) along the direction of the curve in the region D ) Is larger than. By satisfying such a relationship, since the incident light from the linear light source 10 can be emitted in a direction deviating from the normal line of the light incident surface in the region B directly above, the luminance in the region B directly above increases. However, the luminance uniformity of the light emitting surface can be increased.

  Further, in the direct type backlight device, in order to further improve the luminance and the luminance uniformity, for example, an optical member such as a diffusion sheet or a prism sheet can be disposed downstream of the light exit surface. Further, for the purpose of further improving the luminance of the light emitting surface, for example, a reflective polarizer shown below can be arranged at the rear stage of the light emitting surface.

  As the reflective polarizer, a reflective polarizer that utilizes the difference in reflectance of the polarization component depending on the Brewster angle (for example, the one described in JP-T-6-508449); selective reflection characteristics by cholesteric liquid crystal are used. Reflective polarizer; specifically, a laminate of a film made of cholesteric liquid crystal and a quarter-wave plate (for example, one described in JP-A-3-45906); a fine metal linear pattern is applied Reflective polarizers (for example, those described in JP-A-2-308106); at least two kinds of polymer films are laminated, and the reflective polarization using the anisotropy of the reflectance due to the refractive index anisotropy Child (for example, those described in Japanese Patent Publication No. 9-506837); having a sea-island structure formed of at least two kinds of polymers in a polymer film, and anisotropy of reflectance due to refractive index anisotropy Profit Reflective polarizer used (for example, those described in US Pat. No. 5,825,543); particles are dispersed in a polymer film, and anisotropy of reflectance due to refractive index anisotropy is utilized Reflective polarizer (for example, the one described in JP-A-11-509014); reflection utilizing anisotropy of reflectance based on scattering ability difference depending on size, in which inorganic particles are dispersed in a polymer film Type polarizers (for example, those described in JP-A-9-297204) can be used.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. The present invention is not limited to these examples. Parts and% are based on weight unless otherwise specified.

<Production Example 1: Light Pellet Pellets P1>
99.7 parts of a resin having an alicyclic structure as a transparent resin (Nippon Zeon Co., Ltd., ZEONOR 1060R, water absorption 0.01%) and a cross-linked product of a polysiloxane polymer having an average particle diameter of 2 μm as a light diffusing agent Were mixed with 0.3 part of fine particles, extruded with a twin-screw extruder, extruded into a strand, and cut with a pelletizer to produce a light diffusion plate pellet P1. From this light diffusion plate pellet P1, a 100 mm × 50 mm test plate with a smooth thickness of 2 mm on both sides was molded using an injection molding machine (clamping force 1000 kN). The total light transmittance and haze of this test plate were measured using an integrating sphere color difference turbidimeter according to JIS K7361-1 and JIS K7136. The total light transmittance was 85%, and the haze was 99%.

<Production Example 2: Stamper S1>
Nickel-phosphorous electroless plating with a thickness of 100 μm was applied to the entire surface of stainless steel SUS430 having dimensions of 340 mm × 250 mm and a thickness of 2 mm. The nickel-phosphorous electroless plating layer is cut with a bit having a semicircular cross-section having a radius of 0.100 mm to form a recess corresponding to the first prism portion, and then cut with a bit having a triangular cross-section having an apex angle of 100 °. By forming a concave portion corresponding to the prism portion, a stamper S1 having a shape inverted from the shape shown in FIG. 4 (φ1 = 50 °, φ2 = 10 °, pitch W1 = 0.173 mm) was obtained.

<Production Example 3: Stamper S2>
In the same manner as in Production Example 2, except that a crevice corresponding to a second prism composed of two convex portions was formed by cutting twice per one repeating unit with a cutting tool having a triangular cross section with an apex angle of 90 °, A stamper S2 having the shape shown in FIG. 5 (φ3 = 50 °, φ4 = 14 °, pitch W2 0.180 mm) was obtained.

<Production Example 4: Stamper S3>
Cutting with a semicircular cross-section cutting tool having a radius of 0.180 mm to form a recess corresponding to the first prism portion, and then cutting with a semicircular cross-section cutting tool having a radius of 0.052 mm three times for each repeating unit 3 The shape shown in FIG. 6 (φ4A is 50 °, φ5 is 60 °, φ6 is 30 °, and φ7 is the same as in Production Example 2 except that a concave portion corresponding to the second prism portion made of two convex portions is formed. A stamper S3 having an inverted shape of 40 ° and a pitch W3 of 0.338 mm was obtained.

<Production Example 5: Stamper S4>
Cutting with a semi-elliptical cross-section bit having a major axis of 0.400 mm and a minor axis of 0.100 mm to form a recess corresponding to the first prism portion, and then cutting with a trigonal cross-section bit having an apex angle of 100 °, the second prism portion 7 was obtained in the same manner as in Production Example 2 except that the concave portions corresponding to were formed, and the stamper S4 having an inverted shape shown in FIG. 7 (triangular bottom surface width WX1 was 0.020 mm, pitch W4 was 0.162 mm) was obtained. .

<Production Example 6: Stamper S5>
A nickel-phosphorous electroless plating layer similar to that of Production Example 2 is cut with a cutting tool having a cross-sectional shape of a parabolic arc of y = 25 × ² when considered in mm units to form a recess corresponding to the first prism portion. Then, a concave part corresponding to the second prism part is formed by cutting with a cutting tool having a triangular cross section with an apex angle of 100 °, and further electroformed to a thickness of 0.2 mm with nickel sulfamate to obtain the shape shown in FIG. A stamper S5 having a shape in which WX2 is 0.020 mm and pitch W5 is 0.090 mm) is obtained.

<Production Example 7: Stamper S6>
Nickel-phosphorus electroless plating similar to Production Example 2 is performed by using FIB to roughen the circumference of the bit of a semicircular cross-section tool having a radius of 0.100 mm (the range in which WX3 in FIG. 9 is 0.035 mm) to Ra = 0.25 μm. The layer was cut with the above-mentioned cutting tool to obtain a stamper S6 having a shape reversed as shown in FIG. 9 (φ8 = 50 °, φ9 = 10 °, pitch W6 = 0.173 mm).

<Production Example 8: Stamper S7>
The same nickel-phosphorous electroless plating layer as in Production Example 2 was cut with a semicircular cross-section tool with a radius of 0.100 mm, and the shape shown in FIG. 10 (φ10 = 60 °, pitch W7 = 0.173 mm) was reversed. A stamper S7 having a shape was obtained.

<Example 1>
A reflective sheet (manufactured by Tsujiden Co., Ltd., RF188) is attached to the inner surface of a milky white plastic case having an inner width of 320 mm, a depth of 230 mm, and a depth of 20 mm to form a reflector, and the diameter is 3.5 mm away from the bottom of the reflector. Seven cold cathode tubes having a length of 3 mm and a length of 270 mm were arranged so that the distance a between the centers of the cold cathode tubes was 30 mm, the vicinity of the electrodes was fixed with a silicone sealant, and an inverter was attached. In the backlight of this design, the distance b between the cold cathode tube center and the light incident surface of the light diffusion plate (surface on the cold cathode tube side) was 15 mm.

  Next, a mold to which the stamper S1 obtained in Production Example 2 was attached was prepared, and using this and the light diffusion plate pellet P1 obtained in Production Example 1, an injection molding machine (clamping force 4,410 kN) Was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. Thus, a light having a thickness of 2 mm and a thickness of 320 mm × 230 mm is provided on one surface, which has a concavo-convex structure in which a plurality of substantially semi-cylindrical lenticulars are arranged in parallel so as to extend in the longitudinal direction, and the other surface is a flat surface. A diffusion plate D1 was obtained.

  FIG. 4 is a diagram showing the light diffusing plate D1. As shown in FIG. 4, a second prism having a triangular cross section is formed at a portion of the first prism portion (lenticular) having a circular cross section.

  When the center line average roughness Ra was measured on the flat surface opposite to the surface on which the lenticular was formed using an ultra-deep microscope, Ra was 0.6 μm. LX2 / (LX1 + LX2) was 0.194, which satisfied the condition of 0.35 or less.

  Such a light diffusing plate D1 was disposed on the plastic case so that the surface on which the lenticulars were formed was the light emitting surface opposite to the cold cathode tube. Furthermore, a diffusion sheet (188GM3 manufactured by Kimoto Co., Ltd.) is installed thereon, and a prism sheet (manufactured by Sumitomo 3M Co., Ltd., BEF3) is disposed thereon, and the longitudinal direction of the prism row of the prism sheet is parallel to the cold cathode tube, It was installed on the side far from the light diffusion plate. On top of that, a diffusion sheet (PBS072 manufactured by Ewasha) was installed.

Next, a tube current of 5.5 mA was applied to the produced direct type backlight to light the cold cathode tube, and the two-dimensional color distribution measuring device was used to make 100 at equal intervals in the short direction on the center line of the light diffusion plate. The brightness in the front direction of the points was measured, and the brightness average value La and brightness unevenness Lu were obtained according to the following formulas 1 and 2. In this example, the average luminance was 6887 cd / m ² and the luminance unevenness was 0.5%.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance unevenness Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average brightness maximum value directly above a plurality of cold cathode fluorescent lamps installed L2: Average brightness minimum value sandwiched between brightness maximum values Note that brightness unevenness is an indicator of brightness uniformity and brightness When the unevenness is bad, the value increases.

<Example 2>

  A light diffusing plate D2 was obtained in the same manner as in Example 1 except that the stamper S2 obtained in Production Example 3 was used.

  FIG. 5 is a view showing the light diffusion plate D2. As shown in FIG. 5, two second prisms having a triangular cross section are formed at the top of a first prism portion (lenticular) having a circular cross section.

When the center line average roughness Ra was measured on the flat surface opposite to the surface on which the lenticular was formed using an ultra-deep microscope, Ra was 0.6 μm. LX2 / (LX1 + LX2) was 0.111, which satisfied the condition of 0.35 or less. A direct type backlight device was obtained in the same manner as in Example 1 except that this light diffusion plate D2 was used. In this example, the average luminance value was 6868 cd / m ² , and the luminance unevenness was 0.3%.

<Example 3>
A light diffusing plate D3 was obtained in the same manner as in Example 1 except that the stamper S3 obtained in Production Example 4 was used.

  FIG. 6 is a diagram showing the light diffusion plate D3. As shown in FIG. 6, three circular second prisms having a smaller radius of curvature than the first prism portion are formed at the top of the first prism (lenticular) having a circular cross section.

Using an ultradeep microscope, the centerline average roughness Ra was measured on the flat surface opposite to the surface on which the lenticular was formed, and Ra was 0.6 μm. LX2 / (LX1 + LX2) was 0.21 and satisfied the condition of 0.35 or less. A direct type backlight device was obtained in the same manner as in Example 1 except that this light diffusion plate D3 was used. In this example, the average luminance value was 6856 cd / m ² and the luminance unevenness was 0.9%.

<Example 4>
A light diffusing plate D6 was obtained in the same manner as in Example 1 except that the stamper S6 obtained in Production Example 7 was used.

  FIG. 9 is a diagram showing the light diffusion plate D6. As shown in FIG. 9, an area where the center line average roughness Ra is larger than other portions is formed near the apex of the linear prism (lenticular) having a circular cross section.

When the center line average roughness Ra was measured for the flat surface, Ra was 0.6 μm.
On the surface on which the other lenticular is formed, the center line average roughness Ra (C) along the direction of the curve in the region where the angle formed with the light incident surface is 10 degrees or less (region C in FIG. 3) is The center line average roughness Ra (D) along the direction of the curve in the region where the angle exceeds 10 degrees (region D in FIG. 3) was 0.015 μm. For this reason, the condition that the center line average roughness Ra (C) is 0.1 μm or more and is larger than the center line average roughness Ra (D) was satisfied. A direct type backlight device was obtained in the same manner as in Example 1 except that this light diffusion plate D6 was used. In this example, the average luminance was 6895 cd / m ² and the luminance unevenness was 1.0%.

<Comparative Example 1>
A light diffusing plate D7 was obtained in the same manner as in Example 1 except that the stamper S7 obtained in Production Example 8 was used.

  FIG. 10 is a view showing the light diffusion plate D7. As shown in FIG. 10, only a linear prism (lenticular) having a circular cross section is formed.

When the center line average roughness Ra was measured for the flat surface, Ra was 0.6 μm. LX2 / (LX1 + LX2) was 0.394, and the condition of 0.35 or less was not satisfied. In the surface where the other lenticular is formed, the center line average roughness Ra (C) along the direction of the curve in the region where the angle formed with the light incident surface is 10 degrees or less is 0.015 μm, and the angle The center line average roughness Ra (D) along the direction of the curve in the region where the angle exceeds 10 degrees was 0.015 μm. For this reason, the condition that the center line average roughness Ra (C) is 0.1 μm or more and is larger than the center line average roughness Ra (D) was not satisfied.
A direct type backlight device was obtained in the same manner as in Example 1 except that this light diffusion plate D7 was used. In this example, the average luminance value was 6890 cd / m ² and the luminance unevenness was 1.6%.

  From the above, Examples 1 to 3 satisfying the condition of X2 / (LX1 + LX2) ≦ 0.35, the centerline average roughness Ra (C) is 0.1 μm or more, and the centerline average roughness Ra (D In Example 4 that satisfies the condition of greater than (), the luminance uniformity is high, and in Comparative Example 1 that does not satisfy any of these conditions, the luminance uniformity is low.

<Example 5>
First, four cold cathode tubes having a diameter of 3 mm and a length of 270 mm are arranged 3.5 mm away from the bottom of the reflector, and the distance a between the centers of the cold cathode tubes is set to 55 mm. It was fixed with a silicone sealant and an inverter was attached. In the backlight of this design, the distance b between the center of the cold cathode tube and the light incident surface (the surface on the cold cathode tube side) of the light diffusion plate was 20 mm.

  Next, using the stamper S4 obtained in Production Example 5, a light diffusing plate D4 was obtained in the same manner as in Example 1. FIG. 7 is a view showing the light diffusion plate D4. As shown in FIG. 7, a second prism having a triangular cross section is formed at the top of the first prism portion (lenticular) having an elliptical cross section.

  When the center line average roughness Ra was measured on the flat surface opposite to the surface on which the lenticular was formed using an ultra-deep microscope, Ra was 0.6 μm. LX2 / (LX1 + LX2) was 0, which satisfied the condition of 0.35 or less.

Such a light diffusing plate D4 was disposed on the plastic case so that the surface on which the lenticular was formed was the light emitting surface opposite to the cold cathode tube. Furthermore, a diffusion sheet (188GM3 manufactured by Kimoto Co., Ltd.) is installed thereon, and a prism sheet (manufactured by Sumitomo 3M Co., Ltd., BEF3) is disposed thereon, and the longitudinal direction of the prism row of the prism sheet is parallel to the cold cathode tube, It was installed on the side far from the light diffusion plate. On top of that, a reflective polarizer using birefringence (DBEF-D manufactured by Sumitomo 3M Co., Ltd.) was installed to produce a direct type backlight device. In this example, the average luminance value was 2789 cd / m ² , and the luminance unevenness was 0.7%.

<Example 6>
A light diffusing plate D5 was obtained in the same manner as in Example 5 except that the stamper S5 obtained in Production Example 6 was used. FIG. 8 is a view showing the light diffusion plate D5. As shown in FIG. 8, a second prism having a triangular cross section is formed at the top of a first prism portion (lenticular) having a parabolic arc cross section.

When the center line average roughness Ra was measured on the flat surface opposite to the surface on which the lenticular was formed using an ultra-deep microscope, Ra was 0.6 μm. LX2 / (LX1 + LX2) was 0, which satisfied the condition of 0.35 or less. Example 5 was the same as Example 5 except that the light diffusion plate D4 was changed to the light diffusion plate D5. In this example, the luminance average value was 2822 cd / m ² and the luminance unevenness was 1.1%.

<Comparative example 2>
Example 5 was the same as Example 5 except that the light diffusion plate D5 was changed to the light diffusion plate D7. In this example, the average luminance value was 2836 cd / m ² and the luminance unevenness was 2.3%.

  From the above, it was found that in Examples 5 and 6 that satisfy the condition of X2 / (LX1 + LX2) ≦ 0.35, the luminance uniformity is high, and in Comparative Example 2 that does not satisfy this condition, the luminance uniformity is low.

It is a longitudinal cross-sectional view which shows typically the direct type | mold backlight apparatus which concerns on 1st Embodiment of this invention. It is a longitudinal cross-sectional view which expands and shows a light-projection surface. It is a longitudinal cross-sectional view which shows typically the direct type | mold backlight apparatus which concerns on 2nd Embodiment of this invention. It is a longitudinal cross-sectional view which expands and shows the light diffusing plate D1 which concerns on Example 1. FIG. It is a longitudinal cross-sectional view which expands and shows the light diffusing plate D2 which concerns on Example 2. FIG. It is a longitudinal cross-sectional view which expands and shows the light diffusing plate D3 which concerns on Example 3. FIG. It is a longitudinal cross-sectional view which expands and shows the light diffusing plate D4 which concerns on Example 4. FIG. It is a longitudinal cross-sectional view which expands and shows the light diffusing plate D5 which concerns on the comparative example 1. FIG. It is a longitudinal cross-sectional view which expands and shows the light diffusing plate D6 which concerns on Example 5. FIG. It is a longitudinal cross-sectional view which expands and shows the light diffusing plate D7 which concerns on Example 6. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Direct type backlight apparatus 10 Linear light source 20 Reflector 30 Light diffusing plate 30A Light incident surface 30B Light output surface 40 Uneven structure 41 First lenticular 42 Second lenticular 43 First prism part 43T Mountain 44 Second prism part 60 Line Prism

Claims (8)

A plurality of linear light sources arranged substantially in parallel;
A reflector that reflects light from these linear light sources;
A light diffusing plate that emits direct light from the linear light source and reflected light from the reflecting plate from a light incident surface, and diffuses the incident light from the light emitting surface;
A direct-type backlight device comprising:
The light incident surface is a flat surface having a center line average roughness Ra of less than 3 μm,
In the region A immediately above the linear light source on the light emitting surface, the linear light source extends substantially parallel to the longitudinal direction of the linear light source and is concave or convex in the thickness direction of the light diffusion plate. A plurality of prisms are formed side by side,
The linear prism has a first prism portion whose cross-sectional shape in the short direction is a part of a curve having only one of a mountain and a valley;
The cross-sectional shape in the short direction is a line that is formed at the position of the peak or valley and is concave or convex in the thickness direction of the light diffusing plate, and does not overlap the curve indicating the first prism portion. A second prism portion, and
A line composed of the first prism portion and the second prism portion is defined as a line X,
The line X is a line X1 in which an angle between a tangent at an arbitrary position of the line X and the light incident surface exceeds 20 degrees, and an tangent at an arbitrary position of the line X and the light incident surface is formed. As a line X2 with an angle of 20 degrees or less,
LX1 is the length of the line segment projected on the light incident surface along the short direction of the linear prism, and LX2 is the length of the line segment projected on the light incident surface of the line X2. , LX2 / (LX1 + LX2) ≦ 0.35 direct-type backlight device that satisfies the relationship. In the direct type backlight device according to claim 1,
The said 2nd prism part is a direct type | mold backlight apparatus comprised by the 1 or 2 or more 2nd prism extended along the longitudinal direction of the said linear prism. The direct type backlight device according to claim 2,
The second prism is a direct type backlight device in which a cross section in a short direction of the linear light source is polygonal. The direct type backlight device according to claim 2,
The second prism is a direct type backlight device in which a cross section in a short direction of the linear light source is a concave or convex curve in a thickness direction of the light diffusion plate. In the direct type backlight device according to claim 4,
The direct-type backlight device in which the curve has an arc shape, an elliptical arc shape, or a parabolic arc shape. The direct type backlight device according to claim 3 or 4,
The second prism is a direct type backlight device having a convex shape. A plurality of linear light sources arranged substantially in parallel;
A reflector that reflects light from these linear light sources;
A light diffusing plate that makes direct light from the linear light source and reflected light from the reflecting plate incident from a light incident surface, and diffuses and emits the incident light from the light emitting surface;
A direct-type backlight device comprising:
The light incident surface is a flat surface having a center line average roughness Ra of less than 3 μm,
The region directly above the linear light source on the light exit surface extends substantially parallel to the longitudinal direction of the linear light source, and the cross-sectional shape in the lateral direction has only one of a mountain or a valley. A plurality of curved linear prisms are formed side by side,
The curve that forms the linear prism includes a region C in which an angle between the tangent at each position of the curve and the light incident surface is 10 degrees or less, and a tangent at each position of the curve and the light incident surface. A region D where the angle formed is greater than 10 degrees;
The center line average roughness Ra (C) along the direction of the curve in the region C is 0.1 μm or more, and the center line average roughness Ra (D) along the direction of the curve in the region D. Larger direct-type backlight device. In the direct type backlight device according to any one of claims 1 to 7,
The light diffusion plate is composed of a resin composition containing a transparent resin,
This resin composition is a direct type backlight device having a total light transmittance of 60% to 98% and a haze of 20% to 100%.

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