JP2010271516A - Luminance-equalizing sheet and surface light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a luminance-equalizing sheet free from the deterioration of luminance, capable of sufficiently equalizing the luminance and prevented from deterioration of the luminance in long term use and a surface light source device possessing the same, having high luminance and sufficiently equalized emitted light. <P>SOLUTION: In the luminance-uniformiazing sheet 1, a white diffusion layer 12 containing at least one kind of an ultraviolet absorbent from among cyanoacrylate base, oxalic acid anilide base, malonic ester base is formed in a pattern adjusted so as to equalize and emit an incident light having nonuniformized luminance distribution, on at least one surface of a translucent substrate 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a brightness leveling sheet that can sufficiently level the brightness without causing a decrease in brightness and that is less deteriorated even when used for a long time, and has a high brightness and a sufficient level of emitted light. The present invention relates to a surface light source device.

Usually, a surface light source device used for a backlight unit or illumination of a liquid crystal display device has a light source such as a cold-cathode tube and a light diffuser provided on the light emitting side of the light source in order to equalize the light from the light source. .
The simplest of these light diffusers is that the diffuser is evenly kneaded or coated on the base material, or fine irregularities are applied to the surface. Light diffuser ”. Among these light diffusers, a thick diffusion sheet that has a certain thickness and rigidity and also functions as a support is used as a “light diffusion plate”, and if necessary, several thin diffusion sheets are laminated. Thus, a technique for achieving a desired degree of homogenization is generally used. However, if the diffusion sheets are simply laminated, the luminance can be uniformed, but not only the number of members is increased, but also the luminance loss is increased. In view of energy saving and reduction of member costs, it is desirable to achieve luminance uniformity with fewer members. Therefore, as one of the means for achieving both increase in the number of members and suppression of luminance loss, a pattern in which the diffusion effect is partially adjusted according to the incident non-uniform luminance distribution is printed on the light diffusion member included in the surface light source device. Attempts have been made. As a light diffusing plate of this system, for example, Patent Document 1 attempts to print a luminance distribution inverted image formed by reversing gradation of data obtained by measuring luminance distribution as a bright line prevention unit. Coordination attempts have been proposed.

JP 2004-117023 A JP 2000-164411 A

However, in the surface light source device using the light diffuser described in Patent Documents 1 and 2, it is difficult to achieve sufficient luminance uniformity without causing a decrease in luminance.
Therefore, the present invention provides a brightness leveling sheet that is a light diffuser that can sufficiently level the brightness without lowering the brightness, and has a high brightness, and the emitted light is sufficiently leveled. An object of the present invention is to provide a surface light source device.

The present invention has the following configuration.
[1] A cyanoacrylate-based, oxalic acid anilide-based, or malonic ester-based pattern is formed on at least one surface of the translucent substrate so that incident light having a non-uniform luminance distribution can be emitted in a uniform manner. A brightness leveling sheet, wherein a white diffusion layer containing at least one ultraviolet absorber is formed.
[2] The brightness leveling sheet according to [1], wherein the white diffusion layer is formed by printing a white ink containing titanium oxide.
[3] A surface light source device comprising at least a light source and the luminance leveling sheet according to either [1] or [2].

  The brightness leveling sheet of the present invention has the ability to efficiently level incident light having a non-uniform brightness distribution because of its excellent diffusivity, and in an environment where it is exposed to strong incident light from a nearby light source. It is an optical member that exhibits a stable luminance uniformity effect without causing problems such as discoloration and powder blowing even when used for a long time. In addition, the surface light source device of the present invention having the high brightness and little color tone unevenness even in a state where the casing is thinned, the number of light sources leading to power saving and the optical sheet to be used in combination are reduced. The emitted light can be obtained stably.

It is an expanded sectional view showing one embodiment of a brightness equalization sheet of the present invention. It is an expanded sectional view showing one embodiment of a brightness equalization sheet of the present invention. It is sectional drawing which shows one Embodiment of the luminance equalization sheet | seat and surface light source device of this invention. It is the figure which looked at the brightness | luminance equalization sheet | seat and surface light source device shown in FIG. 2 from diagonally upward. It is sectional drawing of the brightness | luminance equalization sheet | seat of Example 1 of this invention, and a surface light source device. It is sectional drawing of the brightness | luminance equalization sheet | seat and surface light source device of Example 2, 3, 5, 7, 8, 10-12 of this invention, and Comparative Examples 1-6. It is sectional drawing of the brightness | luminance equalization sheet | seat and surface light source device of Example 4 of this invention. It is sectional drawing of the brightness | luminance equalization sheet | seat and surface light source device of Example 6 of this invention. It is sectional drawing of the brightness | luminance equalization sheet | seat and surface light source device of Example 9 of this invention. It is sectional drawing of the brightness | luminance equalization sheet | seat and surface light source device of Example 13 of this invention.

An embodiment of the luminance leveling sheet of the present invention and a surface light source device including the same will be described.

<Brightness leveling sheet>
A cross-sectional view of a luminance leveling sheet 1 exemplified as this embodiment is shown in FIG. The brightness-homogenizing sheet 1 of the present invention is a translucent base material 11 and a cyanoacrylate-based material formed in a pattern so that incident light having a non-uniform brightness distribution can be leveled and emitted on at least one surface thereof. Of the oxalic acid anilide type and malonic acid ester type, the white diffusion layer 12 contains at least one ultraviolet absorber. However, for convenience of illustration, the size of the white diffusion layer 12 is emphasized.

[White diffusion layer]
The means for forming the white diffusion layer 12 formed on at least one surface of the translucent substrate 11 is not particularly limited, but a printing method capable of freely forming a pattern can be preferably used. Examples of printing methods include known printing methods such as screen printing, lithographic offset printing, flexographic printing, ink jet printing, pad printing, and gravure offset printing, but printing with high definition so that incident light can be emitted with high uniformity. The gradation value may be formed by controlling the gradation value, and the printing gradation value (density) can be adjusted by, for example, ink formulation, density, ink thickness, and dot area ratio. The halftone dot area ratio is the area (unit%) of the halftone dot 12a per unit area. When the print gradation value is controlled by the halftone dot area ratio, the AM screen system for adjusting the gradation by changing the size of the halftone dot, the FM screen system for adjusting the gradation by changing the number of halftone dots, Various screen-type halftone printing, such as hybrid systems (for example, Dainippon Screen Mfg. Co., Ltd .: Fairdot, RandotX, Creo Japan Co., Ltd .: Staccto), which take advantage of the advantages, can be used. Round dots, triangle dots, chain dots, honeycomb dots and the like can be used.
FIG. 2 is a cross-sectional view of a luminance leveling sheet 1 ′ in which a white diffusion layer 12 composed of halftone dots 12a is formed on one side of a translucent substrate by adjusting the printing gradation value by the halftone dot area ratio. However, for the convenience of illustration, the size of the halftone dots 12a is emphasized, and the number of halftone dots 12a is shown to be less than the whole.

Since printing control is relatively easy, when printing halftone dots 12a on a preferably used AM screen, the number of lines of halftone dots 12a is 60 to 250 lines per inch (2.54 cm). And preferred. If the number of lines of the halftone dots 12a is 60 lines or more per inch, the luminance can be more uniform, and if it is 250 lines or less, printing control is relatively easy.
Further, as described above, a white diffusion layer may be printed in advance on a separate substrate for printing, and may be integrated with the translucent substrate by bonding or transfer means. In this case, for example, flexographic printing or gravure printing is suitable. ing. In the case of direct printing, screen printing, gravure offset printing, inkjet printing, and the like are suitable from the viewpoint of the thickness and rigidity of the translucent substrate, and lithographic offset printing is excellent in terms of productivity.

The brightness-homogenizing sheet of the present invention is a cyanoacrylate-based, oxalic acid anilide-based, or malonic ester-based pattern in which incident light having a non-uniform brightness distribution can be leveled and emitted on at least one surface of the translucent substrate. Among them, a white diffusion layer containing at least one ultraviolet absorber is formed.
Even in the above-mentioned “Attempting to print a luminance distribution inverted image formed by reversing gradation of data obtained by measuring luminance distribution as a bright line prevention unit” proposed in Patent Document 1, if black ink is used, a certain level of luminance is obtained. Although a uniform effect was obtained, the loss of luminance was larger than before the homogenization, and it was very inappropriate in terms of effective use of the light quantity from the light source. This is presumably because the light incident on the black print portion has been absorbed. To obtain the most efficient leveling of incident light with non-uniform luminance distribution in a surface light source device, the necessary amount of light after the leveling should be biased in the high-luminance part. Instead, the light is transmitted as it is, and the excess is diffused and reflected so that it can be redistributed, and white is optimal as the light diffusion layer. If the diffusion layer is formed of mirror ink with emphasis on reflection, incident light can be reflected but is not suitable for transmission. In addition, when black or gray ink is used, a part of incident light is absorbed as described above, which is not suitable because luminance is reduced and heat is generated.

On the other hand, when white ink that is suitable from the viewpoint of luminance loss suppression is used, the color tone bias of transmitted light is easily noticeable, and thus control is important. For simple color tone adjustment, it is possible to add the above-mentioned various coloring materials and fluorescent brightening agents, or to optimize the white pigment as proposed in Patent Document 2, but the light source As a luminance leveling sheet that is exposed to high-energy ultraviolet rays in the vicinity, it is necessary to take measures to suppress it in consideration of discoloration due to ultraviolet rays. In the present invention, the requirement is obtained by blending an ultraviolet absorber into the white diffusion layer. To satisfy. Bonding of C—C, C—H, O—H, C—O, etc. in the white diffusion layer may occur due to UV irradiation, but UV absorbers absorb UV light absorbed by, for example, aromatic compounds. By converting to minute heat energy, it has the effect of suppressing bond breakage that leads to damage or discoloration of components containing organic bonds as described above. In particular, titanium oxide, which is a material suitable as a component of the white diffusion layer of the present invention, generates oxygen radicals that promote oxidative degradation of the resin component contained in the white diffusion layer by the action of high energy rays such as ultraviolet rays. It is easy to cause pulverization and loss of gloss of the diffusion layer called “chalking phenomenon” (choking). The powdered omission of the diffusion layer may lead to the malfunction of the surface light source device and the deterioration of the optical performance. In addition, ultraviolet rays irradiated to the white diffusion layer include components that are prevented from entering by light diffusion components such as titanium oxide, but part of the scattered light bypasses and reaches the inside, so the white diffusion layer It is necessary to take countermeasures to the inside.

As a kind of the ultraviolet absorber to be blended, there is little concern that an inappropriate side reaction such as yellowing or formation of a yellow precipitate may occur even when combined with titanium oxide which is suitable as a material for the white diffusion layer of the present invention. At least one ultraviolet absorber is selected from the acrylate, malonic ester, and oxalate anilide types. These ultraviolet absorbers have a maximum absorption wavelength of around 300 nm, and are preferable in that there is no initial coloration because there is little absorption on the relatively long wavelength side (near 340 nm) in the ultraviolet region.
As a specific example, as a cyanoacrylate ultraviolet absorber, 2′-ethylhexyl-2-cyano-3,3-diphenyl acrylate (trade names Uvinul 3035, Uvinul 3039: manufactured by BASF), ethyl-2-cyano-3,3 -Diphenyl acrylate (molecular weight 277.3, trade name SEESORB501: manufactured by Cypro Kasei Co., Ltd.), 2'-ethylhexyl-2-cyano-3,3-diphenyl acrylate (molecular weight 361.5, trade name SESORRB 501: manufactured by Cypro Chemical Co., Ltd.), etc. Examples of the malonic ester-based ultraviolet absorber include dimethyl (4-methoxybenzylidene) malonate (molecular weight 250.3, trade name Hostabin PR-25: manufactured by Clariant), [2,2 ′ -(1,4-phenylene) bis (ethene)]- , 1,1 ', 1'-tetracarboxylic acid tetraethyl (molecular weight 418.4, trade name Hostabin B-CAP: manufactured by Clariant) and the like, N- (2-ethoxyphenyl) is an oxalic acid anilide-based ultraviolet absorber. -N '-(2-ethylphenyl) oxamide (molecular weight 312.4, trade name TINUVIN 312: manufactured by Ciba, Sanduboa VSU, manufactured by Clariant) 1- (2-ethoxy-5-tert-butylanilino) -2 -(2-Ethyl-4-tert-butylanilino) -1,2-ethanedione (molecular weight 424.6, trade name TINUVIN315: manufactured by Ciba) is an example.
In addition to the ultraviolet absorbers exemplified above, any of cyanoacrylates, malonic esters, and oxalic anilides may be derivatives thereof, polymer types having good bleedout resistance, or emulsions. A type of UV absorber may be used.

Furthermore, other types of ultraviolet absorbers may be used in combination as long as they do not interfere with the advantages of at least one ultraviolet absorber among the cyanoacrylate-based, malonic ester-based, and oxalic acid anilide-based.
Specific examples thereof include 2-hydroxy-4-methoxybenzophenone (molecular weight 228.2, trade name SEESORB101: manufactured by Cypro Kasei Co., Ltd.), 2-hydroxy-4-octyloxybenzophenone (molecular weight 326.4, trade name SEESORB102: Sipro Kasei Co., Ltd., trade name CHIMASSORB 81 (FL): Ciba), 4-dodecyloxy-2-hydroxybenzophenone (molecular weight 382.5, trade name SEESORB 103: Sipro Kasei Co., Ltd.), 2-hydroxy-4- ( Phenylmethoxy) benzophenone (molecular weight 304.3, trade name SEESORB105: manufactured by Cypro Kasei Co., Ltd.), bis (2,4-dihydroxyphenyl) ketone (molecular weight 246.2, trade name SEESORB 106: manufactured by Cypro Kasei Co., Ltd., trade name Uvinul 3050: BAS Benzophenone-based ultraviolet absorbers such as 2,2'-dihydroxy-4,4'-dimethoxybenzophenone (molecular weight 274.3, trade name SEESORB107: manufactured by Cypro Kasei Co., Ltd., trade name Uvinul 3049: manufactured by BASF), 2- (2-Hydroxy-5-methylphenyl) benzotriazole (molecular weight 225.3, trade name: TINUVIN P (FL)), 2- (2-hydroxy-3-tert-butyl-5-methylphenyl) -5 -Chlorobenzotriazole (molecular weight 315.2, trade name: TINUVIN 326: manufactured by Ciba, ADK STAB LA-36RG: manufactured by Asahi Denka), 2- (2H-benzotriazol-2-yl) -4,6-bis ( 1-methyl-1-phenylethyl) phenol (molecular weight 447.6, trade name: TINUVIN 234: Ciba) ) 2- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol (molecular weight 323.4, trade name: TINUVIN329 (FL)), 2,2'- Methylenebis [6- (2H-benzotriazol-2-yl) -4- (1,1,3,3-tetramethylbutyl) phenol] (molecular weight 658.9, trade name: TINUVIN 360: manufactured by Ciba), 4, 6-bis (1,1-dimethylpropyl) -2- (2H-benzotriazol-2-yl) phenol (molecular weight 351.5, trade name SEESORB 704: manufactured by Cypro Kasei Co., Ltd., trade name: TINUVIN 328: manufactured by Ciba) 3 -Tert-Butyl-4-hydroxy-5- (2H-benzotriazol-2-yl) benzenepropionate methyl (molecular weight 353.4, trade name: T INUVIN 1130: manufactured by Ciba) 2- (2H-benzotriazol-2-yl) -4- (1-methylpropyl) -6-tert-butylphenol (molecular weight 323.4, trade name: TINUVIN 343: manufactured by Ciba) 2- [2H-benzotriazol-2-yl] -6-dodecyl-4-methylphenol (molecular weight 393.6, trade name: TINUVIN571: manufactured by Ciba) 2- [3- (2H-benzotriazol-2-yl) -2 -Hydroxy-5-methylbenzyl] -4,5,6,7-tetrahydro-2H-isoindole-1,3-dione (molecular weight 388.4, trade name Sumisorb 250, manufactured by Sumitomo Chemical Co., Ltd.), 3- [5 -(2H-benzotriazol-2-yl) -4-hydroxy-3-tert-butylphenyl] octyl propanoate (molecular weight 4 1.6, trade name TINUVIN 384: manufactured by Ciba) and the like, 2- [4,6-bis (2,4-dimethylphenyl) -1,3,5-triazin-2-yl] -5- (Octyloxy) phenol (molecular weight 509, trade name: CYASORB UV-1164, manufactured by Sun Chemical Co., Ltd.), 2- [4,6-bis (2,4-dimethylphenyl) -1,3,5-triazine -2-yl] -5- [3- (dodecyloxy) -2-hydroxypropoxy] phenol (molecular weight 639.9, trade name: TINUVIN 400: manufactured by Ciba) 2- (4,6-diphenyl-1,3,5) -Triazine-2-yl) -5-((hexyl) oxy) -phenol (molecular weight 425.5, trade name: TINUVIN 1577: manufactured by Ciba), etc. Line absorbers, benzoate ultraviolet absorbers such as 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate (molecular weight, trade name: TINUVIN 120), 2-hydroxybenzoic acid Examples include, but are not limited to, salicylic acid-based ultraviolet absorbers such as acid 4- (tert-butyl) phenyl (molecular weight 270.3, trade name SESORB202: manufactured by Cypro Kasei Co., Ltd.), and the like.

The molecular weight of these UV absorbers is not particularly limited, but if it is less than 220, the UV absorber blended in the white diffusion layer tends to bleed out, and the intended UV absorbing effect may not be obtained due to localization. Therefore, it is preferable to select one having a molecular weight of 220 or more.
Moreover, although it does not have ultraviolet absorbing ability itself, it is more preferable to use a hindered amine light stabilizer in combination with the ultraviolet absorber because it has the effect of capturing the generated radicals and suppressing the adverse effects of ultraviolet irradiation.

The addition amount of the ultraviolet absorber is not particularly limited because it varies depending on the formation conditions of the white diffusion layer and the type of the ultraviolet absorber to be used, but is 1 to 20% by mass of the white diffusion layer, more preferably 5 to 15 mass. % Is good. When the addition amount is less than 1% by mass, the effect cannot be sufficiently exerted, and when it exceeds 20% by mass, the light diffusion performance and the scratching properties, which are the original formation purpose, are hindered.

The means for whitening the light diffusing layer is not particularly limited. For example, bubbles having a particle size adjusted to increase the light diffusibility may be formed in the layer. Can be easily whitened. Examples of the white pigment include, but are not limited to, titanium oxide, silicon oxide, zinc oxide, calcium carbonate, talc, clay, basic lead carbonate, strontium titanate, and barium sulfate. Of these, titanium oxide, zinc oxide, and barium sulfate are preferable. In particular, titanium oxide is most preferable because of its high concealability, high refractive index, high light diffusibility, and excellent chemical stability and physical stability. The titanium oxide may be either an anatase type crystal or a rutile type crystal, but the rutile type is preferable from the viewpoint of thermal stability and chemical stability. The average primary particle size of titanium oxide is suitably 220 to 270 nm. Here, the average primary particle diameter is a value obtained by image analysis of an image taken with a scanning electron microscope. If the average primary particle diameter of titanium oxide is 220 nm or more, sufficient light shielding properties can be secured, so that the luminance can be more uniform, and if it is 270 nm or less, uneven color can be prevented. Titanium oxide itself exhibits a slightly yellowish white color, but those having a relatively small average primary particle size (around 220 nm) are preferably used because they are somewhat bluish.

In addition, a color pigment other than the white pigment may be added for adjusting the color tone of the emitted light as long as the white color tone of the diffusion layer is not impaired. This color-adjusting pigment includes disazo yellow (Pigment Yellow 12, 14), brilliant carmine 6B (Pigment Red 57-1), and phthalocyanine blue (Pigment Blue 15-3, 15-4) commonly used for process colors. In addition to carbon black (Pigment Black 7), various colored pigments can be used. Other inorganic pigments include cobalt blue as an oxide, bitumen as a ferrocyanide, molybdenum red as a chromic compound, and silica. Ultraviolet salt as acid salt, manganese violet as phosphate, naphthol green B as nitroso pigment, peacock blue lake as acid dye lake, methyl violet lake as basic dye lake, phthalocyanine as phthalocyanine pigment Green, quinacridone pigment quinacridone bio red, dioqui Examples thereof include dioxazine bio red which is a sun pigment. Among these, titanium oxide that is preferably used as a white pigment is slightly yellowish, and therefore, a blue or violet pigment is preferably used as a color adjusting color pigment.

Although it varies depending on the type of the white pigment and the pattern of the diffusion layer, the content of the white pigment is preferably 20 to 70% by mass in the state of the white diffusion layer. If it is 20% by mass or less, it is difficult to impart sufficient light diffusibility, and if it is 70% by mass or more, it is difficult to maintain scratch resistance after printing. Among them, when a higher level of diffusibility is required, a relatively high content of 40 to 70% by mass is more preferable, and considering the scratch resistance of the diffusion layer forming portion, 45 to 55% by mass is most preferable. . In addition, when a coloring pigment other than the above-mentioned white pigment is added, the addition amount of the coloring pigment is preferably 1% by mass or less with respect to the white pigment, and other than the coloring pigment as long as the white color tone is not greatly impaired. Light diffusing particles may be mixed.

Usually, a resin component which becomes a binder or a vehicle component is added to the white diffusion layer as another constituent component. The type of the resin component is not particularly limited, and may be appropriately selected depending on the means for forming the white diffusion layer and other components. For example, a resin containing an ultraviolet absorbing group may be used. In addition, when forming a white diffusion layer by printing, it is necessary to adjust the ink viscosity and tack appropriately from the viewpoint of printability, and the type, molecular weight, and blending of vehicle components are selected so as to obtain optimum values.

Alternatively, a pattern may be formed using an ultraviolet curable ink suitable for high-definition printing. In that case, as a component of the ultraviolet curable ink, in addition to the above-mentioned white pigment, in addition to a vehicle component (photosensitive resin, oligomer, monomer), a photopolymerization initiator, various auxiliary agents, Examples thereof include antioxidants, polymerization inhibitors, and waxes. The ultraviolet curable ink basically does not require a volatile solvent component because drying is completed by ultraviolet irradiation, but may be contained in a small amount as long as it does not impair the printability.

As the vehicle component having the function of fixing the white pigment component contained in the ultraviolet curable white ink, a photosensitive resin, oligomer, monomer, or the like that can be polymerized by ultraviolet irradiation in combination with a photopolymerization initiator is used. For example, as a resin component, an acrylic resin, a styrene resin, an alkyd resin, a urethane resin, an amide resin or the like or a modified or copolymerized resin thereof, and as a monomer or oligomer, a polyester (meth) acrylate, a urethane (meth) acrylate, An epoxy (meth) acrylate etc. are mentioned. Specifically, as the radical polymerization system, monofunctional ethyl carbitol (meth) acrylate, phenol ethylene oxide modified (meth) acrylate, nonylphenol ethylene oxide modified (meth) acrylate, ethoxydiethylene glycol acrylate, acryloylmorpholine, isobornyl (meta) ) Acrylate, N-vinyl pyrrolidone, bifunctional hexanediol di (meth) acrylate, hexanediol ethylene oxide modified diacrylate, neopentyl glycol polyethylene oxide modified di (meth) acrylate, tetraethylene glycol di (meth) acrylate, tri Propylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, bisphenol A ethylene oxide Iodine-modified di (meth) acrylate, polyethylene glycol di (meth) acrylate, tri- or more-functional trimethylolpropane tri (meth) acrylate, trimethylolpropane ethylene oxide-modified tri (meth) acrylate, glycerin propoxytri (meth) acrylate, di Examples of cationic polymerization systems such as pentaerythritol hexaacrylate and ditrimethylolpropane tetraacrylate include, but are not limited to, epoxy compounds such as glycidyl ether compounds and alicyclic epoxy compounds, oxetane compounds, and vinyl ether compounds. .

The photopolymerization initiator contained in the ultraviolet curable white ink is not particularly limited, but varieties having different absorption wavelengths may be used in order to suppress the deactivation of the ultraviolet absorbent, which is an essential component of the present invention. Among them, an acyl phosphine oxide photopolymerization initiator having a small yellowness of the printed layer after ultraviolet irradiation due to the photobleach effect can be preferably exemplified. Specific examples of the acylphosphine oxide photopolymerization initiator include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (trade name: Lucirin TPO manufactured by BASF, DAROCUR TPO manufactured by Ciba) and 2,4,6. -Trimethylbenzoyl-ethoxyphenyl-phosphine oxide (trade name: Lucirin TPOL manufactured by BASF), bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (trade name: IRGACURE819 manufactured by Ciba), bis (2,6-dimethoxybenzoyl) -2,4,4-trimethyl-pentylphosphine oxide (trade name: CGI403 manufactured by Ciba, etc.) can be exemplified, but is not limited thereto. These photopolymerization initiators have absorption at the site that is cleaved by UV irradiation, so they lose their absorption and become white after the formation of phosphinol radicals, which are the starting point for curing the vehicle components, and are effective in suppressing yellowing. In addition, since the inside of the ink layer can be sufficiently cured, it is effective for suppressing peeling of the ink layer.

Moreover, you may provide a translucent upper layer in the form laminated | stacked on a white diffusion layer. As long as it does not interfere with the light diffusion performance of the white diffusion layer formed by white ink printing, an ultraviolet absorber or light diffusing fine particles may be added to the translucent upper layer. Improvements can also be expected. Specific methods for forming the upper layer include overprinting, ultraviolet curable varnish printing on the entire surface, providing a coating layer containing light diffusing particles, and laminating a translucent resin. Can be exemplified.

[Translucent substrate]
The sheet used as the translucent substrate is not particularly limited as long as it transmits light and can form the white diffusion layer of the present invention. For example, a glass substrate, a transparent resin sheet or a plate can be used. Examples of the transparent resin to be configured include polymethyl methacrylate, polycarbonate, polyolefin, cycloolefin polymer, polyethylene terephthalate, polyethylene naphthalate, polypropylene, polystyrene, and a copolymer of methyl methacrylate and styrene. Among them, from the balance of moderate elasticity, heat resistance, light resistance, etc., a biaxially stretched film of polyethylene terephthalate is used as a thin sheet with a thickness of 250 μm or less, and a cycloolefin polymer or polystyrene-polyethylene is used as a thick plate beyond that. A plate-like sheet such as a methyl methacrylate copolymer can be suitably used.
However, in order to achieve both suppression of the increase in the number of members leading to cost increase, weight increase and luminance loss and luminance equalization, it is desirable that the translucent substrate alone has a certain luminance uniformity effect of the incident light. As a means, a light diffusing fine particle exemplified below or a foamable material described in, for example, JP-A-2005-54176 or the like is internally added to a translucent substrate, or a coating layer containing these materials is used. When using a light diffusing plate as a translucent base material, which is provided on the surface or applied with a technique such as providing irregularities such as prisms having light diffusibility on the surface by precision shaping technology, alone or in combination good.

Examples of the light diffusing fine particles include organic particles, inorganic particles, organic or inorganic hollow particles, expanded particles, porous particles, and the like. Especially, since the light diffusibility of a light diffusing plate improves more, it is more preferable when the refractive index difference of transparent resin used as a base and light diffusible microparticles | fine-particles is large.

As light diffusing fine particles, among inorganic particles, inorganic glass beads, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, titanium oxide, calcium carbonate, talc, clay, etc., or a mixture thereof It can be illustrated. As organic particles, a high refractive index episulfide resin (refractive index: 1.70), thiourethane resin (1.67), polyvinylidene chloride (1.6 to 1.63), amorphous polyester (1. 62), polystyrene (1.59), polycarbonate (1.59), polyvinyl chloride (1.54), urea resin (1.54), urethane resin (1.53 to 1.67), olefin-maleimide alternating Copolymer (1.53), polyacrylonitrile (1.52), polymethacrylonitrile (1.52), poly (cyclohexane) (1.51), polypropylene (1.50), polymethacrylate (1.51) ), Polyvinyl alcohol (1.49 to 1.53), alicyclic olefin resin (norbornene), polymethyl methacrylate (1.49), polyacetal ( .48), poly (1,3-cyclohexadiene) (1.45), and vinyl acetate. A copolymer of these resins may also be used as a mixture.
The shape of the light diffusing fine particles is not particularly limited. For example, a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a daruma particle (for example, a particle obtained by joining crosslinked polystyrene particles and crosslinked methacrylate particles), a plate Shape, scale shape, fiber shape, hollow shape and the like.
Among these, hollow particles having a high light diffusion effect have a low refractive index of 1.0 in the air layer in the particles, and can easily obtain a difference in refractive index from the surroundings, thereby efficiently refracting light and obtaining a high light diffusion effect. It is done. Specifically, cross-linked polymethyl methacrylate (refractive index 1.49, for example, Sekisui Chemical Co., Ltd. MBX series), cross-linked polystyrene (refractive index 1.59, for example, Sekisui Chemical Co., Ltd. SBX series), commercially available uncrosslinked acrylic hollow particles Examples thereof include hollow particles of styrene and methyl methacrylate copolymer, and foamed particles such as acrylonitrile resin (for example, Sekisui Chemical Co., Ltd. EHM series) may be heated and foamed to be hollow.

As a light diffusing plate of the type that contains the light diffusing fine particles and diffuses incident light, a light diffusing plate whose total light transmittance measured in accordance with JIS-K7361 is in the range of 40 to 70% is used. preferable. When the total light transmittance of the light diffusing plate is 70% or more, it is difficult to expect a sufficient light diffusion effect, and when it is 40% or less, the luminance loss in the surface light source device increases.

As a means for imparting light diffusibility to a translucent substrate, it is also effective to impart a fine uneven shape having light diffusibility to the surface of a light diffusing plate or other optical sheet. The shape of the irregularities may be appropriately adjusted depending on the configuration of the surface light source device and the combination with the light source, and is not particularly limited, but is not limited to a sharp prismatic shape of a sawtooth, a rounded tip, a bowl shape, etc. Examples thereof include a sheet having a prism array having a cross-sectional shape and a sheet in which microlenses are arranged.

When a luminance leveling sheet is used as a member of a surface light source device, the translucent substrate also has a small color tone deviation so as not to cause a color tone deviation of emitted light or a color tone unevenness with the white diffusion layer forming part. preferable. As an example, the transmission b * value defined by JIS-Z8729 is preferably in the range of −1 to 8. In order to set the color tone within a preferable range, additives such as various dyes, coloring pigments, and fluorescent brightening agents may be used. In addition, other resin additives such as selective wavelength blocking agents such as ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, lubricants, flame retardants, etc., can be used alone or in combination. May be blended. As the ultraviolet absorber (hereinafter sometimes abbreviated as UVA), for example, various compounds exemplified as a constituent component of the white diffusion layer may be used. Although not particularly limited, if the molecular weight is less than 220, resin molding Care must be taken because the amount of volatilization of UVA becomes too large when exposed to high temperatures. In particular, it is more preferable to add the same kind of UVA to the translucent base material and the white diffusion layer because the characteristics with respect to light become the same.
In addition to the light diffusion plate described above, an optical member such as a simple transparent film or resin plate, or a light diffusion sheet or a brightness enhancement sheet may be used as the translucent substrate.

The thickness of these translucent substrates is difficult to handle at 30 μm or less, which may cause problems in printing, and is unsuitable because of poor dimensional stability. When the thickness is 4 mm or more, from the viewpoint of cost and member weight Since it is disadvantageous, 30 micrometers-4 mm are preferable. Moreover, if it is 1 mm or less, since it becomes easy to print directly by the planographic offset printing method with high productivity, it is preferable.

  In addition, for reasons such as the material, thickness, and rigidity of the translucent substrate, the white diffusion layer is not directly formed on the translucent substrate, for example, the white diffusion layer is printed on another substrate for printing, It may be bonded or transferred using means such as heat, pressure, adhesion, etc., and integrated with the translucent substrate in a subsequent step. When such an integrated method is used, the thickness of the sheet serving as the separate substrate for printing may be thin as long as it does not interfere with the printing and transfer processes, taking into consideration productivity and ease of handling. And you may use for a printing or an integration process with winding up. As for the separate substrate for transfer to be peeled and removed, an opaque substrate such as a transfer foil may be used as long as transferability is good.

<Surface light source device>
An embodiment of the surface light source device of the present invention will be described.
FIG. 3 shows a cross-sectional view of the surface light source device 100 exemplified as the present embodiment, and FIG. The surface light source device 100 includes a plurality of light sources 2 (in FIGS. 3 and 4) including a housing 3 having a rectangular opening, a reflector 4 provided on the bottom surface inside the housing 3, and cold cathode tubes accommodated in the housing 3. 8 light sources 2 are arranged in parallel) and luminance uniformity using a light diffusing plate containing light diffusing particles sequentially stacked on the light emitting side of the light source 2 so as to close the opening of the housing 3 And a diffusion sheet 5 provided with a coating layer containing light diffusing fine particles. 3 and 4, for convenience of illustration, the pattern of the white diffusion layer 12 of the luminance leveling sheet is simplified, and the thickness of the member is appropriately emphasized. Further, in FIG. 4, in order to clarify the member configuration, the members stacked to close the opening of the housing 3 are illustrated in a shifted state.

[light source]
As the light source, a linear light source such as a cold cathode fluorescent tube (CCFL), a hot cathode fluorescent tube (HCFL), an external electrode cathode tube (EEFL), or a point light source such as a light emitting diode (LED) can be adopted. In particular, it is not limited to these. The linear light source may be a straight tube or a bent tube such as a U-shaped tube.
When using a plurality of light sources, their installation positions are not limited and may vary slightly, but from the viewpoint of reducing the thickness of the unit, the light diffusion that installs in the form of closing the opening of the housing The distance from the plate is preferably uniform. The average distance between the light source installation position and the light diffusing plate is preferably 6 mm or less when the surface light source device is intended to be thinned.

[Light diffusion plate]
It is desirable to install a light diffusion plate having a certain degree of strength in the opening of the housing of the surface light source device, which also serves as a light source protection function. This light diffusing plate also serves as a support that keeps the distance between the various sheet-like optical members used in the surface light source device and the light source constant. Therefore, although depending on the material, the thickness is preferably 1 mm or more. In consideration of weight, cost, and thickness of the entire surface light source device, 4 mm or less is preferable. From the viewpoint of providing an efficient brightness uniformity effect and suppressing the number of members, it is preferable to use this light diffusing plate as the translucent substrate used in the brightness uniformity sheet of the present invention. Etc.) are as described above as the material of the translucent substrate.

[a reflector]
In the surface light source device, it is desirable to use a reflector or sheet at the periphery in order to efficiently emit light from the light source. As a material, a white plastic sheet (white polyethylene terephthalate sheet, white polypropylene sheet, etc.) is used. The thing stuck on base materials, such as resin, a metal, a metal vapor deposition board, can be illustrated. These may be integrated with the bottom surface inside the housing, and various processes such as uneven processing and prism bonding may be performed in order to efficiently use the light from the light source.

[Other optical members]
In addition to the above, the surface light source device of the present embodiment may use an optical member such as a diffusion sheet or a brightness enhancement sheet using a light condensing effect for further equalization and brightness improvement.
The diffusion sheet is a sheet that can diffuse incident light and has uniform light diffusivity in the surface direction, and is effective in eliminating luminance unevenness together with the light diffusion plate. For example, it can be prepared by applying a paint containing the above-mentioned various light diffusing fine particles on a light transmissive substrate or printing a light diffusing ink. Examples of commercially available products include lenticular films (trade name: Estina ED) manufactured by Sekisui Chemical Film Co., Ltd., diffusion films (trade name: light-up) manufactured by Kimoto Co., Ltd., and the like.
As a brightness enhancement sheet, which is a transparent resin sheet that efficiently uses emitted light by utilizing the light condensing effect, a prism sheet composed of a serrated linear serrated cross section on the surface of the sheet, and a cylindrical cylindrical lens Lenticular sheets arranged in parallel, microlens sheets (fly-eye lens sheets) in which single lenses are arranged vertically and horizontally, and the like. Commercially available brightness enhancement films (trade name: BEFII) manufactured by Sumitomo 3M Limited. , BEFIII, RBEF, DBEF), lenticular film (trade name: Estina EL) manufactured by Sekisui Chemical Film Co., Ltd., microlens array pattern sheet (trade name: UTE sheet) manufactured by Mirai Nanotech (Korea) . The thickness of these optical sheets other than the light diffusing plate serving as a support is preferably 50 μm to 1 mm, and more preferably 100 μm to 500 μm. When the thickness is 50 μm or less, the sheet is easy to bend, and when sheets of 1 mm or more are laminated, there is a risk of increasing the weight and cost.
Similarly to the light diffusing plate, these optical sheets may be used as the translucent base material of the luminance leveling sheet of the present invention, and a white diffusion layer may be printed on one side or both sides.

[About pattern of white diffusion layer]
In the surface light source device 100 of FIGS. 3 and 4, the light incident on the luminance leveling sheet 1 using the light diffusing plate as a base material has a large amount of light in a portion almost directly above the light source 2, and the light amount decreases as the distance from the light source 2 increases. And having a non-uniform luminance distribution.
Therefore, in the luminance leveling sheet 1 of the present embodiment, the white ink printing pattern is adjusted so that the light diffusibility is high in the portion where the amount of incident light is large. For example, the print gradation value becomes a maximum value at a portion immediately above each of the eight light sources 2, and the print gradation value becomes a minimum value at a portion substantially immediately above an intermediate point of the plurality of light sources 2. Adjust as follows. As a result, the light incident on the luminance leveling sheet 1 is leveled, and outgoing light with a uniform luminance distribution is obtained. Due to the effect of the brightness leveling sheet 1, a sufficient brightness leveling effect can be obtained even if the diffusion sheet 5 exemplified in the surface light source device 100 is omitted. The level can be maintained.

Note that the configuration of the surface light source device is not limited to the above-described embodiment, and various optical sheets such as the above-described brightness enhancement sheet and diffusion sheet may be additionally used according to the required quality. Of course, the number and order of stacking can be selected as appropriate, and a plurality of the same materials may be used. For example, the light diffusing plate or the diffusing sheet may be a foam in which bubbles are uniformly formed in the surface direction. In addition, the light diffusing plate has light diffusibility by forming irregularities on one surface or both surfaces, or white diffusing layers 12 are provided on both surfaces of the translucent substrate 11 used in the luminance leveling sheet 1. It may be done. The white diffusion layer forming surface may face the light source side or the outgoing surface side in the surface light source device.

  Since the printing pattern of the brightness leveling sheet also varies greatly depending on the combination of the light source used and other optical members, it is necessary to design the pattern according to the conditions. For example, when the surface light source device 100 uses a transparent prism plate having a prism shape with a precisely defined angle for refracting incident light instead of a light diffusing plate containing light diffusing particles, the above-described example Unlike the above, there are cases where the amount of light is greater at the midpoint between the plurality of light sources 2 than in the portion directly above each light source 2. As means for dealing with these situations, Japanese Patent Application No. 2008-283605, Japanese Patent Application No. 2008-283604, Japanese Patent Application No. 2008-223909, Japanese Patent Application No. 2008-223908, Japanese Patent Application No. 2008-230996, and Japanese Patent Application No. 2008-273708. The print pattern may be adjusted according to the method described in Japanese Patent Application No. 2008-273710.

[Surface light source device]
Sectional drawing of the surface light source devices 101-106 prepared for the Example and the comparative example is shown in FIGS. All the surface light source devices include a housing 3 having a rectangular opening, a reflector 4 provided on the inner bottom surface, and light sources accommodated in the housing 3 (eight cold cathode tubes arranged in parallel: diameter). 4 mm) and various planar optical members that are appropriately stacked on the light emitting side of the light source 2 so as to close the opening of the housing 3 (the distance between the nearest planar optical member and the upper end of the light source is 3 mm). . The light diffusing plate is made of transparent resin (styrene-methyl methacrylate copolymer) as a raw material, and if necessary, a suitable amount of silica particles are uniformly dispersed as light diffusing fine particles to adjust the transmittance or to collect light. Surface shaping was applied to impart

<Example 1>
A light diffusing plate A adjusted to have a total light transmittance of 51% with a thickness of 1.5 mm was used as a translucent base material, and designed to have a pattern in which incident light having a non-uniform luminance distribution could be emitted uniformly. Using a 150 mesh gravure plate, 45% by mass of titanium oxide as a solid content, (4-methoxybenzylidene) dimethyl malonate (molecular weight 250, trade name: hostabin PR-25, Clariant, which is a malonic ester UV absorber After the gravure offset printing of the white ink containing 3% by mass as a solid content, it was dried with hot air at 60 ° C. to obtain a luminance leveling sheet A having a patterned white diffusion layer on one side of the light diffusion plate A It was.
The printing pattern was a printing pattern in which the luminance distribution unevenness of the surface light source device in the state before the light diffusing plate A was arranged was measured and the gradation was adjusted so that it could be homogenized. In this case, the print gradation value becomes a maximum value at the same interval as the light source so that the print gradation value becomes higher as the amount of light increases.
The obtained luminance leveling sheet A was installed in the opening of the housing 3 so that the white diffusion layer forming surface was on the light source side, and the surface light source device A having the configuration 101 was obtained.

(Brightness distribution unevenness measurement method)
The luminance distribution unevenness of the surface light source device before the planar optical member is arranged is a luminance meter (product name “UA-1000” manufactured by Topcon Technohouse Co., Ltd.) installed at a position 1000 mm above the device. Was measured as a tristimulus value Y (luminance) [cd / m ² ] at intervals of 0.6 mm from end to end in a direction transverse to the light source arranged in parallel.

<Example 2>
White ink, 40% by mass of titanium oxide as a solid content, 5% by mass of calcium carbonate as a solid content, ethyl-2-cyano-3,3-diphenyl acrylate (molecular weight 277, trade name: SEESORB501) which is a cyanoacrylate-based ultraviolet absorber , Produced by Cyclo Kasei Co., Ltd.) was changed to a white ink containing 4% by mass, and a luminance equalizing sheet B was formed in the same manner as in Example 1.
The resulting brightness leveling sheet B is placed in the opening of the housing 3 so that the white diffusion layer forming surface is on the light source side, and the brightness enhancement sheet (Korea) is a microlens array pattern sheet made by Mirai Nanotech (Korea) (Product name: UTE sheet) was overlapped with the flat surface facing the light source side to obtain a surface light source device B having the constitution 102.

<Example 3>
White ink, 50% by mass of titanium oxide as solid content, N- (2-ethoxyphenyl) -N '-(2-ethylphenyl) oxamide (molecular weight 312; trade name: TINUVIN 312) which is an oxalic anilide UV absorber : Manufactured by Ciba) was changed to a white ink containing 3% by mass, and a luminance leveling sheet C was formed in the same manner as in Example 2 to obtain a surface light source device C having configuration 102.

<Example 4>
Except for measuring the luminance distribution unevenness of the surface light source device with the non-printed light diffusing plate A disposed, and printing a pattern in which the gradation is adjusted so that it can be uniformed, the same as in Example 3. Luminance leveling sheet D was formed.
The obtained brightness leveling sheet D is installed in the opening of the housing 3 so that the surface opposite to the white diffusion layer forming surface is on the light source side, and the brightness enhancement sheet used in Example 2 is placed there, and the flat surface is used as the light source. The surface light source device D having the configuration 103 was obtained by stacking toward the side.

<Example 5>
A screen ink of Seiko Advance Co., Ltd. 2500 110 Denshoku White, a white ink prepared by mixing 3% by mass of the malonate UV absorber used in Example 1 as a solid content, is screened by 320 mesh and printed in 80 lines. After the dot printing, the brightness leveling sheet E was formed in the same manner as in Example 3 except that the white diffusion layer was obtained by drying with hot air to obtain the surface light source device E having the configuration 102.

<Example 6>
An unprinted light diffusing plate A is placed on the substrate surface side of a sheet provided with a coating layer containing acrylic beads on a transparent polyethylene terephthalate film (Toyobo Co., Ltd., Cosmo Shine A4300) having a thickness of 250 μm. The brightness distribution unevenness of the surface light source device in the above state was measured, and a pattern in which the gradation was adjusted so that it could be leveled was printed in the same manner as in Example 5 to form the brightness leveling sheet F.
The light diffusing plate A was installed in the opening of the housing 3, and the obtained luminance leveling sheet F was overlapped so that the white diffusion layer forming surface was on the light source side to obtain the surface light source device F having the configuration 104.

<Example 7>
Using a UV curable white ink in which 5% by mass of the oxalic acid anilide UV absorber used in Example 3 is mixed with white UV ink for screen printing (Reicure PF4200 high concentration white, manufactured by Jujo Chemical Co., Ltd.) as a solid content, 320 mesh After carrying out screen printing in the same manner as in Example 5 except that the ink was set by irradiating with ultraviolet rays (ultraviolet ray irradiation amount: 400 mJ / cm ² ) instead of hot air drying, a luminance leveling sheet G was formed and constituted 102 surface light source devices G were obtained.

<Example 8>
White for offset printing with a commercially available water containing an acyl phosphine oxide photopolymerization initiator using a light diffusing plate B adjusted to have a thickness of 1.0 mm and a total light transmittance of 62% as a translucent substrate. UV curable type obtained by mixing 4% by mass of oxalic acid anilide UV absorber used in Example 3 with UV ink (Toyo Ink Mfg. Co., Ltd., FDO New HF1 Aoguchi T White: main component rutile type titanium oxide). After printing halftone dots of AM 100 lines / inch (2.54 cm) square dots by lithographic offset printing using white ink, ink was set by irradiating with ultraviolet rays (ultraviolet ray irradiation amount 400 mJ / cm ² ) instead of hot air drying. Except for this, the luminance equalizing sheet H was formed in the same manner as in Example 2 to obtain the surface light source device H having the configuration 102.

<Example 9>
It is possible to measure the luminance distribution unevenness of a surface light source device in a state where a light diffusion plate A that is not printed is arranged on a transparent polyethylene terephthalate film (Cosmo Shine A4300, manufactured by Toyobo Co., Ltd.) having a thickness of 250 μm, and it can be uniform A pattern with adjusted gradation was printed using the ultraviolet curable white ink a having the following formulation in the same manner as in Example 8 to form a luminance-homogenizing sheet J.
[Composition of UV curable white ink a]
-Miramer PU240 (aliphatic urethane acrylate oligomer) manufactured by Toyo Chemicals: 18 parts by mass-NK ester A-DPH manufactured by Shin-Nakamura Scientific Co., Ltd .: 4 parts by mass-Acrylate monomer ODA-N manufactured by Daicel-Cytec: 25 parts by mass Ishihara Sangyo Co., Ltd. Typek CR-90 (white pigment: rutile titanium oxide with a particle size of 250 nm): 46.5 parts by mass • Ciba MICROLITH BLUE 4G-K (phthalocyanine-based blue coloring pigment): 0.5 parts by mass Ciba IRGACURE 819 (acylphosphine oxide-based photopolymerization initiator phenylbis (2,6-dimethylbenzoyl) phosphine oxide): 3 parts by mass; Clariant's hostabin B-CAP (molecular weight 418, malonic ester UV absorption Agent: α, α'-Bis (Eto Cycarbonyl) -1,4-benzenedipropenoic acid diethyl): 3.0 parts by mass A light diffusing plate A is installed in the opening of the housing 3, and the resulting brightness-homogenizing sheet J has a substrate surface on the light source side. Subsequently, a resin sheet having a prism shape on the surface (trade name: BEFIII, manufactured by Sumitomo 3M Co., Ltd.) is stacked as a brightness enhancement sheet so that the surface without unevenness is directed to the light source side, and the surface light source device J having the configuration 105 is obtained. It was.

<Example 10>
In the same manner as in Example 2, except that ultraviolet curable printing was performed with an ultraviolet curable ink jet printer using a white ink in which 3% by mass of the oxalic anilide ultraviolet absorber used in Example 3 was mixed as a solid content, A leveling sheet K was formed to obtain a surface light source device K having configuration 102.

<Example 11>
AM80 line / inch (2.54 cm) square dot by flexographic printing using white ink for flexographic printing mixed with 5% by mass of oxalic anilide UV absorber used in Example 3 as solid content. After performing the halftone dot printing, a luminance leveling sheet L was formed in the same manner as in Example 2 except that hot air drying was performed, and the surface light source device L having the configuration 102 was obtained.

<Example 12>
A release layer is formed on a 38 μm thick polyethylene terephthalate film using a transparent ink composed of a melamine resin by a gravure printing method, and then a heat-resistant release varnish (46-7) manufactured by Showa Ink Industry Co., Ltd. is gravure printed as the release layer. Next, a luminance equalization pattern using a white ink containing 35% by mass of titanium oxide as a solid content and 5% by mass of an oxalic acid anilide UV absorber used in Example 3 and an acrylic resin as a solid content. The layers were sequentially formed by gravure printing.
Subsequently, a transparent ink adhesive (made by Showa Ink Industries, HS32) made of an acrylic resin was formed as a whole surface adhesive layer by a gravure printing method to obtain a transfer sheet.

The transfer sheet was laminated so that the adhesive layer surface was in contact with the light diffusing plate A, and heated and pressurized through a silicon rubber-coated metal roll heated to a surface temperature of 150 ° C. Thereafter, the polyethylene film of the transfer film is peeled off, and a brightness leveling sheet M that is adjusted so that incident light having a non-uniform brightness distribution is leveled and emitted can be transferred and integrated to form a brightness leveling sheet M. A surface light source device M having configuration 102 was obtained.

<Example 13>
Using the light diffusing plate C having a prism array on one side as a translucent substrate and printing on the opposite side of the shaping surface, the brightness leveling sheet N was obtained in the same manner as in Example 2. Formed.
The light diffusing plate C does not contain light diffusing fine particles, and the surface-shaped prism row has V-shaped grooves formed by connecting protrusions having isosceles triangles in cross-section to each other. The protrusions were shaped to have a pitch of 69 μm and an apex angle of 110 °. The printing pattern was a printing pattern in which the gradation was adjusted so that the luminance distribution unevenness of the surface light source device in a state before the planar optical member was arranged could be equalized.
The resulting brightness leveling sheet N is placed in the opening of the housing 3 so that the white diffusion layer forming surface is on the light source side, and the microlens array pattern sheet used in Example 2 is used as the brightness enhancement sheet. The surfaces were overlapped toward the light source side to obtain a surface light source device N having configuration 106.

<Comparative Example 1>
A luminance leveling sheet P was formed in the same manner as in Example 2 except that the ultraviolet absorber was not blended, and the surface light source device P having the configuration 102 was obtained.

<Comparative example 2>
A luminance leveling sheet Q was formed in the same manner as in Example 5 except that the ultraviolet absorber was not blended, and the surface light source device Q having the configuration 102 was obtained.

<Comparative Example 3>
A luminance leveling sheet R was formed in the same manner as in Example 7 except that the ultraviolet absorber was not blended, and the surface light source device R having the configuration 102 was obtained.

<Comparative example 4>
A luminance leveling sheet S was formed in the same manner as in Example 10 except that the ultraviolet absorber was not blended, and the surface light source device S having the configuration 102 was obtained.

<Comparative Example 5>
A brightness-homogenizing sheet T was formed in the same manner as in Example 5 except that 2,4-dihydroxybenzophenone (molecular weight 214, trade name: SEESORB100, manufactured by Cyclochemical Co., Ltd.) was used as the ultraviolet absorber. The surface light source device T was obtained.

<Comparative Example 6>
Luminance leveling in the same manner as in Example 5 except that screen printing 2500 ink 110 Seishoku Advance manufactured by Seiko Advance Co., Ltd. was used instead of black ink for screen printing (VAR screen ink 911 ink: manufactured by Teikoku Ink Manufacturing Co., Ltd.). The sheet U was formed, and the surface light source device U having the configuration 102 was obtained.

(Evaluation methods)
The luminance leveling sheets and surface light source devices obtained in the examples and comparative examples were evaluated by the following methods.

《Surface light source evaluation》
Luminance leveling sheets obtained in the examples and comparative examples were incorporated into the corresponding surface light source devices, and with the light source turned on, the luminance and leveling status were visually evaluated based on the following indices based on the following four levels. . In addition, a luminance meter (product name “UA-1000” manufactured by Topcon Technohouse Co., Ltd.) is installed at a position 1000 mm above the surface light source device, and the center of the surface light source device is traversed in the vertical direction of the light sources arranged in parallel. Measure tristimulus value Y (luminance) [cd / m ² ], chromaticity x, and chromaticity y at intervals of 0.6 mm from end to end, and check the state of luminance loss and luminance equalization. As a guide.
Further, in order to confirm the state after a long time, the surface light source device was held in a state of being lit for 120 days, and then the state of homogenization was confirmed in the same manner as described above.

(Luminance evaluation)
A: The accumulated luminance before the homogenization is almost maintained.
◯: Although it is slightly lower than that before homogenization, it is an acceptable level. Δ: The accumulated luminance amount is lower than before homogenization.
X: Compared with the case before homogenization, the luminance drop is large and unsuitable within a clearly visible range.
(Equalization evaluation)
(Double-circle): It has fully homogenized.
○: Almost uniform and acceptable level.
Δ: Almost uniform, but somewhat uneven in brightness and color tone.
X: Brightness and color tone unevenness are greatly inappropriate within a clear range.

<Evaluation of brightness leveling sheet>
Take out the brightness leveling sheet from each surface light source device that has been lit for 120 days, and check the degree of deterioration of the white diffused layer forming part with high print gradation values due to long-term use. After printing under conditions, a visual appearance comparison with a sample stored in a dark place and tape pick evaluation were performed, and evaluation was made in three stages based on the following indices.
(Visual appearance evaluation)
A: Almost the same as the comparative sample not used in the surface light source device, and no change.
(Triangle | delta): When it arranges with a comparison sample, deterioration, such as discoloration and a gloss fall, can be discriminate | determined.
X: Discoloration and gloss reduction are clearly confirmed.

(Tape pick evaluation)
A Nichiban cellophane tape having a width of 24 mm was applied to the printing surface of each luminance leveling sheet so that it was attached to about 50 mm, and was attached by rubbing with an eraser. After 2 minutes, it was peeled off instantaneously while holding the edge of the tape and kept at a right angle from the printing surface, and the peeled state of the white diffusion layer was confirmed.
A: Deterioration of the diffusion layer is good and there is no tape adhering material.
(Triangle | delta): There exists some tape deposits which show deterioration of a diffused layer.
X: Unsatisfactory due to many tape deposits indicating deterioration of the diffusion layer.

Table 1 shows the production conditions and transmittance measurement results of each luminance leveling sheet and surface light source device, and Table 2 shows the evaluation results of the surface light source device and the white diffusion layer (luminance leveling sheet).

As shown in Table 2, a surface light source using the luminance leveling sheets of Examples 1 to 13 in which at least one ultraviolet absorber among cyanoacrylate, oxalic acid, and malonic ester is mixed with the white diffusion layer. The apparatus has a sufficiently high brightness and is sufficiently homogenized, and the degree of homogenization does not decrease even after being used in the vicinity of the light source for a long time. As a member of the surface light source device, the brightness leveling sheet used for a long time in the immediate vicinity of the light source was taken out and the state was confirmed, but the chalking phenomenon that causes discoloration and equipment trouble of electrical appliances is not It did not occur.
On the other hand, in the surface light source device using the brightness leveling sheet that did not contain the ultraviolet absorbers of Comparative Examples 1 to 4, the brightness leveling performance was reduced due to the adverse effect of the deterioration of the white diffusion layer after long-term use. Was confirmed. Further, the tape pick evaluation was unsuitable because a chalking phenomenon causing troubles in the surface light source device was also observed. Even when an ultraviolet absorber different from the present invention was blended, a sufficient effect was not obtained as in Comparative Example 5. In addition, when the light diffusion layer was black, luminance equalization was possible but loss of luminance was large and unsuitable (Comparative Example 6).

DESCRIPTION OF SYMBOLS 1 Luminance equalization sheet | seat 11 Translucent base material 12 White diffused layer 12a Halftone dot 2 Light source 3 Housing 4 Reflecting plate 5 Diffusion sheet 6 Brightness improvement sheet 7 Light diffusing plate 100-106 Surface light source device

Claims (3)

  At least one of cyanoacrylate-based, oxalic acid anilide-based, and malonic acid ester-based patterns in a pattern adjusted so that incident light having a non-uniform luminance distribution can be emitted uniformly on at least one surface of the translucent substrate. A brightness leveling sheet, wherein a white diffusion layer containing a seed ultraviolet absorber is formed. The brightness leveling sheet according to claim 1, wherein the white diffusion layer is formed by printing with a white ink containing titanium oxide. A surface light source device comprising at least a light source and the luminance leveling sheet according to claim 1.

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