JP2006339033A - Direct type backlight unit - Google Patents

Abstract

[Configuration] In a direct type backlight unit having a light diffusion plate made of polycarbonate resin on the upper surface of a light source and a light reflection plate on the back surface of the light source,
(1) The diffusivity D50 of the polycarbonate resin light diffusion plate is 30 ° or more, (2) the reflectance of the light reflection plate is 90% or more, and (3) the polycarbonate resin light diffusion plate. The luminance unevenness of the light emitting surface is 3% or less,
This is a direct type backlight unit.
The direct-type backlight unit of the present invention can reduce not only the lamp image on the light emitting surface but also local luminance unevenness due to minute foreign matter, and therefore a liquid crystal television having a high quality image. And can be suitably used for a direct backlight unit of a liquid crystal monitor.
[Selection] Figure 1

Description

  The present invention is a direct type back provided with a light reflecting plate on the back surface of a light source (a cold cathode tube or a light emitting diode (LED), hereinafter abbreviated as a lamp) and a light diffusion plate made of polycarbonate resin on the top surface of the lamp. Regarding the light unit. More specifically, the present invention provides a direct type backlight unit with extremely little luminance unevenness.

  Polycarbonate resins are widely used in the fields of electricity, electronics, OA, automobiles and the like because of their optical transparency, and in each field, resins satisfying the required performance are selected and used properly. In particular, in the use of light diffusion plates used in direct-type backlight units for LCD TVs and LCD monitors, the use of a transparent thermoplastic resin allows the lamp to be seen through because it transmits light. There is a demand for a material imparted with a light diffusibility without recognizing the shape of the lamp behind the lamp and without impairing the luminance of the lamp as much as possible.

  For the purpose of imparting light diffusibility to the polycarbonate resin, the conventional technology employs a method in which a polymer phase or inorganic particle having a different refractive index is blended as a dispersed phase into a thermoplastic resin that forms a continuous phase. Yes. Further, it has been proposed to provide a light diffusing plate with little luminance unevenness by blending a light diffusing agent with a polycarbonate resin and limiting minute foreign substances to a specific range.

JP-A-8-188709 JP-A-9-281309

  However, in recent years, liquid crystal televisions and liquid crystal monitors tend to be larger, and in particular, the direct backlight unit method is becoming mainstream, so the lamp image on the light emitting surface of the light diffusing plate and local brightness due to minute foreign matter There was a problem that unevenness was likely to occur.

  As a result of intensive studies in view of such problems, the inventors have mounted a specific polycarbonate resin light diffusing plate on the light emitting surface of the top surface of the cold cathode tube and a specific light reflecting plate on the back surface of the lamp in combination. As a result, it has been found that not only the lamp image on the light emitting surface can be reduced, but also local luminance unevenness due to minute foreign matter can be improved, and the present invention has been completed.

That is, the present invention provides a direct-type backlight unit having a polycarbonate resin light diffusing plate on the upper surface of a light source and a light reflecting plate on the back surface of the light source.
(1) The diffusivity D50 of the polycarbonate resin light diffusion plate is 30 ° or more, (2) the reflectance of the light reflection plate is 90% or more, and (3) the polycarbonate resin light diffusion plate. The luminance unevenness of the light emitting surface is 3% or less,
A direct-type backlight unit is provided.

  The direct type backlight unit of the present invention can reduce not only the lamp image on the light emitting surface but also local luminance unevenness due to minute foreign matter, and therefore, a liquid crystal television or liquid crystal monitor having a high quality image. It can be suitably used for a direct type backlight unit.

The polycarbonate resin used in the present invention is a polymer obtained by a phosgene method in which various dihydroxydiaryl compounds and phosgene are reacted, or a transesterification method in which a dihydroxydiaryl compound and a carbonate such as diphenyl carbonate are reacted. A typical example is a polycarbonate resin produced from 2,2-bis (4-hydroxyphenyl) propane (bisphenol A).

  Examples of the dihydroxydiaryl compound include bisphenol 4-, bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) butane, 2, 2-bis (4-hydroxyphenyl) octane, bis (4-hydroxyphenyl) phenylmethane, 2,2-bis (4-hydroxyphenyl-3-methylphenyl) propane, 1,1-bis (4-hydroxy-3) -Tert-butylphenyl) propane, 2,2-bis (4-hydroxy-3-bromophenyl) propane, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis ( Bis (hydroxyaryl) alkanes such as 4-hydroxy-3,5-dichlorophenyl) propane, 1,1- (4-hydroxyphenyl) cyclopentane, bis (hydroxyaryl) cycloalkanes such as 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxy-3 Dihydroxy diaryl ethers such as 3,3'-dimethyldiphenyl ether, dihydroxy diaryl sulfides such as 4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxydiphenyl sulfoxide, 4,4'-dihydroxy-3,3 ' -Dihydroxy diaryl sulfoxides such as dimethyldiphenyl sulfoxide, dihydroxy diary such as 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfone Sulfone, and the like. These are used individually or in mixture of 2 or more types. In addition to these, piperazine, dipiperidyl hydroquinone, resorcin, 4,4'-dihydroxydiphenyl, and the like may be mixed and used.

  Furthermore, the above dihydroxyaryl compound and a trivalent or higher phenol compound as shown below may be used in combination. Trihydric or higher phenols include phloroglucin, 4,6-dimethyl-2,4,6-tri- (4-hydroxyphenyl) -heptene, 2,4,6-dimethyl-2,4,6-tri- (4 -Hydroxyphenyl) -heptane, 1,3,5-tri- (4-hydroxyphenyl) -benzol, 1,1,1-tri- (4-hydroxyphenyl) -ethane and 2,2-bis- [4 4- (4,4'-dihydroxydiphenyl) -cyclohexyl] -propane and the like.

  The viscosity average molecular weight of the polycarbonate resin is usually 10,000 to 100,000, preferably 15,000 to 35,000, and more preferably 17,000 to 28,000. In producing such a polycarbonate resin, a molecular weight regulator, a catalyst and the like can be used as necessary.

  The light diffusing agent used in the present invention is not particularly limited in terms of chemical composition such as polymer and inorganic, but when the light diffusing agent is added and dispersed by a known method such as melt mixing with an extruder. In addition, it is necessary that they are not compatible with the matrix phase made of polycarbonate resin or are present as particles that are hardly compatible.

Specific examples of the light diffusing agent include calcium carbonate, silica, silicone, zinc sulfide, zinc oxide, titanium oxide, titanium phosphate, magnesium titanate, magnesium titanate, mica, glass filler, barium sulfate, clay, talc, and silicone. Rubber-like elastic materials, inorganic diffusing agents such as polymethylsilsesoxane, acrylics, styrenes, polyesters, polyolefins, urethanes, nylons, methacrylate-styrenes, fluorines, norbornenes, etc. Examples include diffusing agents.

  In the present invention, a light diffusing agent having an average particle diameter of 1 to 10 μm can be suitably used. If the thickness is less than 1 μm, only light is transmitted, and it may be difficult to obtain a light diffusion effect. On the other hand, if it exceeds 10 μm, a sufficient light diffusion effect cannot be obtained and visibility may be inferior. The particle size distribution is not particularly limited, but is about 0.1 to 100 μm, preferably 0.1 to 25 μm. Further, two or more kinds of light diffusing agents having different average particle sizes, particle size distributions, and types may be used in combination, and the particle size distribution is not uniform, and those having two or more particle size distributions are used alone or It can also be used in combination.

  Although there is no restriction | limiting in particular as a compounding quantity of a light-diffusion agent, The range of 0.3-6 weight part per 100 weight part of polycarbonate resin is preferable. If the blending amount is less than 0.3 parts by weight, it may be difficult to obtain a sufficient light diffusion effect. On the other hand, if it exceeds 6 parts by weight, the light transmittance may be impaired. More preferably, it is in the range of 0.5 to 5 parts by weight.

  Furthermore, in order to make the color tone of the light diffusion plate made of polycarbonate resin used in the present invention vivid, a fluorescent brightening agent may be added up to 0.1 part by weight per 100 parts by weight of the polycarbonate resin. If the amount added exceeds 0.1 parts by weight, the thermal stability may deteriorate. More preferably, it is up to 0.03 parts by weight. Polycarbonate resin has the property of absorbing some of the blue light and has a slight yellowish tinge, so if you add a blue or purple fluorescent compound (fluorescent whitening agent) that corresponds to this yellow complementary color, the fluorescence becomes yellowish. It is possible to obtain a vivid color tone by canceling. A fluorescent whitening agent absorbs energy in the ultraviolet region and emits a wavelength range from blue to violet in the visible region. By using this in combination, the light diffusing performance is maintained and a more vivid color tone is achieved. Obtainable.

  In addition, various known additives, polymers, and the like can be added as necessary depending on the performance required in addition to light diffusivity. For example, in order to suppress discoloration of resin molded products when exposed to light for a long period of time, UV absorption of hindered amine light stabilizers, benzotriazole, benzophenone, triazine, malonate, and oxalate anilide You may add an agent and these together.

When flame retardancy is required, various known flame retardants, for example, brominated flame retardants such as tetrabromobisphenol A oligomer, monophosphates such as triphenyl phosphate and tricresyl phosphate, bisphenol A diphosphate, In order to further enhance the flame retardancy, various phosphoric flame retardants such as resorcin diphosphate, tetraxylenyl resorcin diphosphate, condensed phosphoric acid esters such as ammonium polyphosphate and red phosphorus, various silicone flame retardants, Examples thereof include metal salts of aromatic sulfonic acid and metal salts of perfluoroalkanesulfonic acid, preferably potassium salt of 4-methyl-N- (4-methylphenyl) sulfonyl-benzenesulfonamide, diphenylsulfone-3- Potassium sulfonate, diphe Rusuruhon -3-3'- potassium disulfonate, sodium para-toluene sulfonic acid, and organic metal salts such as potassium perfluorobutane sulfonate and the like may also be added. Among these flame retardants, phosphorus-based flame retardants can be suitably used because they can improve not only flame retardancy but also fluidity.

Furthermore, known additives other than those described above, such as phenol-based or phosphorus-based heat stabilizer [2,6-di-t-butyl-4-methylphenol, 2- (1-methylcyclohexyl) -4,6-dimethylphenol 4,4'-thiobis- (6-t-butyl-3-methylphenol), 2,2-methylenebis- (4-ethyl-6-t-methylphenol), n-octadecyl-3- (3,5 -Di-t-butyl-4-hydroxyphenyl) propionate, tris (2,4-di-t-butylphenyl) phosphite, 4,4'-biphenylenediphosphinic acid tetrakis- (2,4-di-t-butyl) Phenyl) etc.], lubricants [paraffin wax, n-butyl stearate, synthetic beeswax, natural beeswax, glycerin monoester, montanic acid wax, polyethylene wax , Pentaerythritol tetrastearate, etc.], colorant [eg, titanium oxide, carbon black, dye], filler [calcium carbonate, clay, silica, glass fiber, glass sphere, glass flake, carbon fiber, talc, mica, various types Whiskers, etc.], fluidity improvers, spreading agents [epoxidized soybean oil, liquid paraffin, etc.], and other thermoplastic resins and various impact resistance improvers (polybutadiene, polyacrylates, ethylene / propylene rubbers) For example, rubber reinforced resin obtained by graft polymerization of a compound such as methacrylic ester, styrene, acrylonitrile, etc.) may be added to the rubber such as

  In order to improve the effect of the present invention, that is, the lamp image on the light-emitting surface of the light diffusing plate and the local luminance unevenness around the foreign matter, a polycarbonate resin light diffusing plate having a specific diffusivity on the top surface of the lamp and the back surface of the lamp It is a requirement that a light reflecting plate having a specific reflectivity is used in the part and mounted in a direct type backlight unit.

  The polycarbonate resin light diffusing plate of the present invention is required to have a diffusivity D50 of 30 ° or more. If the diffusivity D50 is less than 30 °, it is not preferable because sufficient diffusivity cannot be obtained even if the reflectance of the light reflector installed on the back of the lamp is increased, and the lamp image becomes stronger, resulting in uneven brightness. Absent. More preferably, the diffusivity D50 is 40 ° or more, and further preferably 45 ° or more. On the other hand, since the upper limit of the diffusivity D50 is saturated at 60 °, even if the blending amount of the light diffusing agent is increased, it is difficult for the diffusivity D50 to exceed 60 ° only by losing light transmittance. It is.

  The diffusivity D50 is an angle with respect to the straight light when the transmittance of the straight light passing through the sample (position of 0 °) is 100, and the transmittance is 50%, manufactured by Murakami Color Research Laboratory. It is measured by a goniophotometer GP-1.

  The polycarbonate resin light diffusion plate of the present invention can be suitably used with a thickness of 0.3 to 3.0 mm. If it is less than 0.3 mm, the rigidity is not sufficient, and if it is thicker than 3.0 mm, it is not practical in terms of product weight. Preferably, it is 1.0-3.0 mm, More preferably, it is 1.5-2.5 mm.

The light reflecting plate of the present invention is a polycarbonate resin light diffusing plate (light emitting device) that emits light that has not entered the polycarbonate resin light diffusing plate out of the light emitted from the lamp or light reflected by the surface of the polycarbonate resin light diffusing plate. Surface) side. The higher the light reflection performance of the light reflection plate, the less the luminance unevenness is made. If the reflectance is 90% or more, the object of the present invention can be achieved, but 95% or more is preferable. More preferably, it is 98% or more. On the other hand, if it is less than 90%, even if the diffusion degree D50 of the polycarbonate resin light diffusing plate installed on the upper surface of the lamp is increased, the lamp image becomes strong and uneven brightness occurs.

  The reflectance is represented by Y among tristimulus values X, Y, and Z in a 10 ° field of view in ZIS Z8701 by standard light C in JIS Z8120, and UV, visible and infrared spectroscopy manufactured by JASCO Corporation. Measured with a photometer V-570.

  Although there is no restriction | limiting in particular about the kind of the said light reflection board, Thickness 0.2-1.5mm which mixed white pigments, such as a titanium oxide, in polyethylene terephthalate (PET), polypropylene (PP), polycarbonate (PC), etc. A film or a metal plate coated with white is preferably used.

The luminance unevenness in the polycarbonate resin light diffusion plate of the present invention is the light emission surface of the polycarbonate resin light diffusion plate on the top surface of the lamp.
(1) The difference between the luminance immediately above the lamp and the luminance between the lamps is obtained by the following equation 1 and the method shown in FIG.
Formula 1:
Brightness unevenness A (%)
= (Difference in brightness between and directly above the lamp on the light emitting surface / Brightness directly above the lamp on the light emitting surface)
× 100
(2) The difference in luminance between the foreign substance on the polycarbonate resin light diffusion plate and the adjacent position without the foreign substance is obtained by the method shown in the following formula 2.
Brightness unevenness B (%)
= (Difference between the brightness on the foreign object and the brightness at the adjacent position without the foreign substance at the adjacent position) / Brightness at the adjacent position without the foreign object) × 100

  In the present invention, both the luminance unevenness A and B are required to be 3% or less. More preferably, it is 2% or less. On the other hand, if the luminance unevenness exceeds 3%, the lamp image becomes strong or local luminance unevenness occurs, which makes it difficult to obtain a high-quality image.

In order to make the luminance unevenness 3% or less, a polycarbonate resin light diffusing plate having a diffusion degree D50 of 30 ° or more is provided on the upper surface of the lamp, and a light reflecting plate having a reflectance of 90% or more is provided on the rear surface of the lamp. Is realized.

The luminance is measured with a luminance meter BM-7 manufactured by Topcon Corporation under the conditions that the distance from the light emitting surface to the luminance meter objective lens is 35 cm and the viewing angle of the luminance meter is 0.1 °.

  In order to make the diffusivity D50 of the diffusion plate made of polycarbonate resin in the present invention 30 ° or more, it is necessary to add the diffusing agent to the polycarbonate resin. As the average particle diameter of the diffusing agent, those having a particle diameter of 1 to 10 μm can be suitably used. If it is less than 1 μm, it may be difficult to obtain a diffusivity D50 of 30 ° or more simply by transmitting light. On the other hand, if it exceeds 10 μm, the desired diffusion degree D50 cannot be obtained and the visibility may be inferior. The particle size distribution is not particularly limited, but is about 0.1 to 100 μm, preferably 0.1 to 25 μm. Further, two or more kinds of light diffusing agents having different average particle sizes, particle size distributions, and types may be used in combination, and the particle size distribution is not uniform, and those having two or more particle size distributions are used alone or It can also be used in combination.

  Moreover, there is no restriction | limiting in particular as a compounding quantity of a light-diffusion agent, However, The range of 0.3-6 weight part per 100 weight part of polycarbonate resin is preferable. If the blending amount is less than 0.3 parts by weight, it may be difficult to obtain a diffusivity D50 of 30 ° or more. On the other hand, if it exceeds 6 parts by weight, a diffusivity D50 of 30 ° or more can be easily obtained, but the light transmittance may be impaired. More preferably, it is in the range of 0.5 to 5 parts by weight.

  Furthermore, in order to make the reflectance of the light reflector in the present invention 90% or more, a white pigment such as titanium oxide is mixed in polyethylene terephthalate (PET), polypropylene (PP), polycarbonate (PC), or the like. This is achieved by applying a white coating on a resin or metal film. As a density | concentration of the white pigment mix | blended in the said resin, 3-30 weight part is preferable per 100 weight part of these resin. If it is less than 3 parts by weight, sufficient reflectance may not be obtained. On the other hand, if the amount exceeds 30 parts by weight, the reflectance will no longer increase.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples, unless the summary is exceeded. Unless otherwise specified, “%” and “part” in the examples are based on weight standards.

In addition, the various compounding components used are as follows.
Polycarbonate resin:
Caliber 200-3 manufactured by Sumitomo Dow
(Viscosity average molecular weight: 28000, hereinafter abbreviated as PC)
Light diffusing agent:
Rohm and Haas Paraloid EXL-5136 (hereinafter abbreviated as LD-1)
MSP-S020 manufactured by Nikko Rica (hereinafter abbreviated as LD-2)
Optical brightener:
HOSTALUX KSN (hereinafter abbreviated as FD) manufactured by Clariant Japan

A method for measuring various evaluation items in the present invention will be described.
(Evaluation of luminance unevenness A: Evaluation of lamp image)
Using a 21-inch direct backlight unit, the luminance between the lamp on the light emitting surface and between the lamps on the light emitting surface of the polycarbonate resin light diffusion plate on the upper surface of the cold cathode tube was measured with a luminance meter BM-7 manufactured by Topcon Corporation. The measurement was performed under the conditions of a distance of 35 cm and a viewing angle of 0.1 °, and the luminance unevenness A was determined by the following formula 1. A case where the luminance unevenness A was 3% or less was indicated by (◯), and a case where the luminance unevenness A exceeded 3% was indicated by (×).
Formula 1:
Brightness unevenness A (%)
= (Difference in brightness between and directly above the lamp on the light emitting surface / Brightness directly above the lamp on the light emitting surface)
× 100

(Evaluation of luminance unevenness B: Evaluation of local luminance unevenness)
Using the 21-inch backlight unit shown in FIG. 1, the brightness on the foreign material on the polycarbonate resin light diffusion plate on the upper surface of the cold cathode tube and on the adjacent position where there is no foreign material was measured using a luminance meter BM-7 manufactured by Topcon The measurement was performed under the conditions of a measurement distance of 35 cm and a viewing angle of 0.1 °, and the luminance unevenness B was determined by the following formula 2. A case where the luminance unevenness B was 3% or less was evaluated as (◯), and a case where the luminance unevenness B exceeded 3% was evaluated as (×).
Formula-2:
Brightness unevenness B (%)
= (Difference between the brightness on the foreign object and the brightness at the adjacent position where there is no foreign object / brightness at the adjacent position where there is no foreign object) × 100

(Comprehensive judgment)
In the evaluation of the luminance unevenness A and the luminance unevenness B, those satisfying both were determined to be acceptable (◯) and those not satisfied were determined to be unacceptable (x).

Example 1
PC and LD-1 were dry-mixed by a super floater manufactured by Kawata according to the blending ratio shown in Table 1. Next, the mixture was melt-kneaded at a temperature of 250 to 290 ° C. by a twin screw extruder KTX-37 (shaft diameter = 37 mmφ, L / D = 30) manufactured by Kobe Steel. The obtained pellets were extruded by a sheet extruder under a temperature condition of 250 to 290 ° C., a 2 mm-thick polycarbonate resin light diffusion plate was formed, cut into the size of the backlight unit, and brightness unevenness A and B Evaluation was performed. At this time, the luminance unevenness was evaluated using a direct type backlight unit in which a white reflector made of polycarbonate resin having a reflectance of 97% was incorporated in the back surface of the cold cathode tube. The evaluation of luminance unevenness A was 0.5%, and the evaluation of luminance unevenness B was 2.2%. In any evaluation, the luminance unevenness was 3% or less (◯), which was good. In addition, the diameter of the foreign material in the evaluation of the luminance unevenness B was 410 μm. Further, the diffusion degree D50 of the light diffusion plate made of polycarbonate resin was 55 °.

(Example 2)
A polycarbonate resin light diffusing plate was obtained in the same manner as in Example 1 except that the amount of the light diffusing agent was changed to 4 parts. Next, luminance unevenness was evaluated. The evaluation of luminance unevenness A was 0.4%, and the evaluation of luminance unevenness B was 1.2%. In any evaluation, the luminance unevenness was 3% or less (◯), which was good. The diameter of the foreign material at this time was 350 μm. Further, the diffusion degree D50 of the polycarbonate resin light diffusion plate was 60 °.

(Example 3)
A light diffusion plate made of polycarbonate resin was obtained in the same manner as in Example 1 except that the type and blending amount of the light diffusing agent were changed to LD-2 and 0.5 parts, respectively. Next, luminance unevenness was evaluated. The evaluation of luminance unevenness A was 1.6%, and the evaluation of luminance unevenness B was 2.5%. In any evaluation, the luminance unevenness was 3% or less (◯), which was good. The diameter of the foreign material at this time was 390 μm. Further, the diffusion degree D50 of the light diffusion plate made of polycarbonate resin was 50 °.

Example 4
A polycarbonate resin light diffusion plate was obtained in the same manner as in Example 1 except that 0.005 part of the fluorescent brightening agent was blended. Next, luminance unevenness was evaluated. In the evaluation of luminance unevenness A, it was 0.5%, and in the evaluation of luminance unevenness B, it was 2.6%. In any evaluation, the luminance unevenness was 3% or less (◯), which was good. At this time, the diameter of the foreign matter was 490 μm. Further, the diffusion degree D50 of the light diffusion plate made of polycarbonate resin was 55 °.

(Comparative Example 1)
Using the polycarbonate resin light diffusing plate obtained in Example 1, an aluminum plate having a reflectance of 75% was placed on the back surface of the cold cathode tube, and luminance unevenness was evaluated. In the evaluation of the luminance unevenness A, the luminance unevenness was 5.1% and it was rejected (x). Further, in the evaluation of the luminance unevenness B, the luminance unevenness was 3.5%, which was rejected (x).

(Comparative Example 2)
Using the polycarbonate resin light diffusing plate obtained in Example 2, an aluminum plate having a reflectance of 75% was arranged on the back surface of the cold cathode tube in the same manner as in Comparative Example 1, and luminance unevenness was evaluated. In the evaluation of the luminance unevenness A, the luminance unevenness was 4.5%, which was rejected (x). Further, in the evaluation of the luminance unevenness B, the luminance unevenness was 3.3%, which was rejected (x).

(Comparative Example 3)
A light diffusion plate made of polycarbonate resin was obtained in the same manner as in Example 1 except that the type and blending amount of the light diffusing agent were changed to LD-2 and 0.05 parts, respectively. Next, luminance unevenness was evaluated. In the evaluation of the luminance unevenness A, the luminance unevenness was 90.0%, which was rejected (x). Further, in the evaluation of the luminance unevenness B, the luminance unevenness was 4.8%, which was rejected (x). The diameter of the foreign material at this time was 450 μm. Further, the diffusion degree D50 of the light diffusion plate made of polycarbonate resin was 5 °.

(Comparative Example 4)
Using the polycarbonate resin light diffusing plate obtained in Example 3, the brightness unevenness was evaluated using a direct type backlight unit incorporating a polycarbonate resin white reflector having a reflectance of 85% on the back of the cold cathode tube. went. In the evaluation of the luminance unevenness A, the luminance unevenness was 3.9%, which was rejected (x). Also in the evaluation of the luminance unevenness B, the luminance unevenness was 3.2%, which was rejected (x).

  As described above, the combination of the specific polycarbonate resin light diffusing plate and the specific light reflecting plate of the present invention not only reduces luminance unevenness A (lamp image) between the lamp and the lamp, but also foreign objects and their adjacent parts. It has been found that local luminance unevenness B in the region can also be improved.

It is a figure which shows the measuring method of the brightness | luminance between lamps of this invention.

Explanation of symbols

A: Luminance meter B: Cold cathode tube C: Luminance measurement site D: Light diffusion plate made of polycarbonate resin E: Light reflection plate

Claims (5)

In the direct type backlight unit having a light diffusion plate made of polycarbonate resin on the upper surface of the light source and a light reflection plate on the rear surface of the light source,
(1) The diffusivity D50 of the polycarbonate resin light diffusion plate is 30 ° or more, (2) the reflectance of the light reflection plate is 90% or more, and (3) the polycarbonate resin light diffusion plate. The luminance unevenness of the light emitting surface is 3% or less,
This is a direct type backlight unit. 2. The direct type backlight unit according to claim 1, wherein a diffusion degree D50 of the light diffusion plate made of polycarbonate resin is 40 ° or more and a reflectance of the light reflection plate is 95% or more. 2. The direct type backlight unit according to claim 1, wherein the blending amount of the light diffusing agent in the polycarbonate resin light diffusion plate is 0.3 to 6 parts by weight per 100 parts by weight of the polycarbonate resin. The direct type backlight unit according to claim 1, wherein the light source is a cold cathode tube. The direct type backlight unit according to claim 1, wherein the light source is a light emitting diode (LED).

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