JP2010156930A - Light diffusion plate for white led light source and optical product having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion plate which excels in color reproducibility of a white LED light source, and prevents original color tone of the white LED from being largely changed even if variation is found in color temperature of the white LEDs. <P>SOLUTION: The light diffusion plate for the white LED light source is composed of base material containing: at least one kind of dispersing agent selected from acrylic-based crosslinked beads, melamine-based resin beads, styrene-based crosslinked beads, silicone-based resin beads, aluminum hydroxide, calcium carbonate, barium sulfate, and titanium oxide; an optical whitening agent; and blue-based dyeing pigment, wherein total light transmittance is 50% or more and 70% or less, and a difference of light transmittance in wavelength 460 nm and wavelength 580 nm is 4% or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light diffusion plate for an LED light source.

  As the light diffusing plate used for signboards, signs, lighting covers, and the like, a light diffusing plate in which a material having a refractive index different from that of a base material such as a transparent resin is dispersed is used. For example, Patent Document 1 discloses a light diffusing plate having excellent weather resistance and light diffusibility, and a method for manufacturing the same. Further, Patent Document 2 discloses a light diffusing plate that can be used as a cover material for a white fluorescent lamp of any color tone without causing a great change in the color tone of the fluorescent light.

JP 2002-228807 A JP-A-9-306217

  Most of the light sources used in conventional signs and signs are mainly fluorescent lamps called daylight color, daylight white color, and bulb color. As long as the same type of light source is used, the difference in color temperature is a concern. I never did.

  However, when an LED is used as a light source, a white LED is a semiconductor product manufactured through complicated and delicate manufacturing processes. Therefore, at present, it is unavoidable that the light quantity and the wavelength are varied. For this reason, the different light colors and brightness are classified (grouped) so as to be the same for each production lot or for each LED element and module. Since one white LED is smaller than a fluorescent lamp, for example, when creating a signboard of 1200 × 800 (mm), about 150 to 400 white LEDs are used. When white LEDs having relatively close chromaticity coordinates are grouped and used, those having different chromaticities are mixed in each group. When white LEDs having different chromaticities and a light diffusing plate are combined and viewed from the diffusing plate side in a state where the LED is lit, a difference in color tone (color unevenness) due to the LED occurs. One method of eliminating the color unevenness is to increase the distance between the white LED light source and the light diffusion plate, but it is desired to make the signboard and sign as thin as possible. Moreover, since white LED has little light quantity compared with a fluorescent lamp, it is desired to transmit more light to a light diffusing plate.

  Although the light diffusing plate described in Patent Document 1 has good weather resistance, it does not describe color unevenness suppression when an LED light source is used. The light diffusing plate described in Patent Document 2 is effective when a fluorescent lamp is used as a light source, but does not solve the color unevenness for a white LED light source.

  The present invention provides at least one diffusing agent selected from acrylic crosslinked beads, melamine resin beads, styrene crosslinked beads, silicone resin beads, aluminum hydroxide, calcium carbonate, barium sulfate, and titanium oxide. A white LED having a total light transmittance of 50% or more and 70% or less and a difference in light transmittance between wavelengths of 460 nm and 580 nm of 4% or less. It is the light diffusing plate for light sources.

  Moreover, this invention is an optical product which has a white LED light source and the said light diffusing plate, and the minimum distance from the said light source to the said light diffusing plate is 10 mm or more and 150 mm or less.

  The light diffusing plate of the present invention has excellent light diffusibility, can eliminate the see-through of the LED light source, and reduce color unevenness. Further, the optical product of the present invention has excellent optical characteristics because it has the light diffusing plate.

The following are mentioned as a white LED light source in this invention.
(1) A yellow LED shines with a blue LED (2) A near-ultraviolet or violet LED shines red, green and blue phosphors (3) A combination of red, green and blue LEDs What makes the yellow fluorescent substance shine by said (1) blue LED is suitable as a white LED light source in this invention.

  The light diffusing plate of the present invention is a white LED diffusing plate, among acrylic crosslinked beads, melamine resin beads, styrene crosslinked beads, silicon resin beads, aluminum hydroxide, calcium carbonate, barium sulfate, and titanium oxide. The base material contains at least one diffusing agent selected from the group consisting of a fluorescent brightener and a blue dye / pigment. The material serving as the base material is preferably a transparent resin from the viewpoint of ease of production of the light diffusion plate obtained in the present invention. Examples of the transparent resin include acrylic resin, polystyrene resin, polycarbonate resin, vinyl chloride resin, and polyester resin. Among these, acrylic resins having good transparency and weather resistance are preferable. The light diffusing plate of the present invention is required to have a total light transmittance of 50% to 70% and a difference in light transmittance at wavelengths of 460 nm and 580 nm to 4% or less.

  When the total light transmittance is less than 50%, the amount of transmitted light is insufficient and the entire light transmittance becomes dark. In order to ensure brightness, it is necessary to increase the number of white LEDs, and there is a problem that power consumption increases. When the total light transmittance exceeds 70%, the diffused light is reduced, so that the white LED light source can be easily seen (hereinafter, the white LED light source can be seen through, that is, the shape of the LED element or module can be confirmed. Is not preferred). One method for preventing see-through is to increase the distance between the LED light source and the diffusion plate, but in that case, it is difficult to reduce the thickness. In order to set the total light transmittance within the above range, the type and amount of a diffusing agent described later can be set by appropriately adjusting the thickness of the light diffusing plate.

  In general, the light transmittance of the light diffusing plate increases as the wavelength increases. In order to reproduce the color of the white LED light source, the difference in light transmittance between wavelengths 460 nm and 580 nm needs to be 4% or less. If the difference in light transmittance is 4% or less, the color of the white LED is visually reproduced as it is even if the light of the white LED passes through the diffusion plate. When the difference in light transmittance exceeds 4% and the light transmittance at 580 nm is high, the color becomes yellowish. In order to set the difference in light transmittance between wavelengths of 460 nm and 580 nm to 4% or less, it is set by appropriately adjusting the type, addition amount, particle size, and addition amount of the blue dye / pigment described later. it can.

  The diffusing agent dispersed in the base material is selected from acrylic crosslinked beads, melamine resin beads, styrene crosslinked beads, silicon resin beads, aluminum hydroxide, calcium carbonate, barium sulfate, and titanium oxide that absorb less light. At least one kind is preferred. The addition amount of these diffusing agents is preferably 0.3 parts by mass or more per 100 parts by mass of the resin base material from the viewpoint of imparting diffusibility, and from the viewpoint of maintaining the total light transmittance, the resin base material 100 The amount is preferably 2 parts by mass or less per part by mass. The particle size of the diffusing agent is preferably 0.1 μm or more and 50 μm or less in terms of weight average.

  When the light diffusing plate is used for various purposes, the whiteness when the light is turned off is also important. Therefore, it is necessary to add a fluorescent whitening agent in order to ensure the whiteness of the reflected light of the light diffusing plate. The fluorescent whitening agent is a specific wavelength conversion material that absorbs ultraviolet light having a wavelength of about 380 nm, which has a low human eye sensitivity (specific visual sensitivity), and converts it into blue having a wavelength of about 440 nm having a higher specific visual sensitivity than 380 nm. When the transmittance near the wavelength of 440 nm increases, it looks whiter than the product without the fluorescent brightener. The fluorescent brightening agent is not particularly limited as long as it is used for a transparent resin, and examples thereof include benzoxazoyl derivatives, coumarin derivatives, styrene biphenyl derivatives, and pyrazolone derivatives. The addition amount of the optical brightener is preferably 0.00001 parts by mass or more and 0.001 parts by mass or less per 100 parts by mass of the resin base material.

  Furthermore, in order to reduce the color unevenness (particularly yellowishness) of the white LED, it is necessary to add a blue dye / pigment which is a specific wavelength absorbing material. A blue dye / pigment that absorbs a specific wavelength has a role of making the yellow LED inconspicuous due to the complementary color effect when the emission color of the white LED is shifted to the yellow side. The blue dye / pigment is not particularly limited as long as it is a dye / pigment that can be used for coloring a transparent resin, and examples thereof include ultramarine blue, Prussian blue, cobalt blue, phthalocyanine blue, cerulean blue, and cobalt chrome blue. The added amount of the blue dye / pigment is preferably 0.0001 parts by mass or more and 0.01 parts by mass or less per 100 parts by mass of the resin base material.

  In order to further enhance the diffusing performance of the light diffusing plate of the present invention, mat processing or embossing processing for forming irregularities on one or both surfaces of the diffusing plate can be performed. Moreover, in order to improve a weather resistance, an ultraviolet absorber can be contained or light stabilizers, such as a hindered amine, can be contained. Further, an antioxidant, an antistatic agent, an antibacterial agent, a rubber component, and the like can be contained. The thickness of the light diffusion plate is preferably 1.0 mm or more from the viewpoint of mechanical strength, and preferably 10.0 mm or less from the viewpoint of reducing the weight of the product.

  When using the light diffusing plate, the minimum distance from the white LED light source to the light diffusing plate is preferably 10 mm or more, and more preferably 30 mm or more from the viewpoint of suppressing color unevenness and see-through. Moreover, from a viewpoint of thickness reduction of a product, it is preferable that it is 150 mm or less, and it is more preferable that it is 100 mm or less.

  As a method for producing the light diffusing plate of the present invention, a known method can be applied, and examples thereof include a batch-type cast plate method, a continuous cast plate method, and an extrusion plate method.

  As a batch type cast plate method, a mixture of a diffusing agent, a fluorescent whitening agent, and a polymerizable raw material added with a blue dye / pigment is poured into a mold, the mixture is polymerized and cured, and a plate polymer is obtained. A method for producing a light diffusing plate which is peeled off from a mold is mentioned. Here, the polymerizable raw material is a raw material that is polymerized and becomes a base resin of the light diffusion plate.

  In the case of producing a light diffusing plate using an acrylic resin as a base resin, the polymerizable raw material injected into the mold preferably contains 70% by mass or more of methyl methacrylate (hereinafter referred to as “MMA” as appropriate). Other polymerizable raw materials may be vinyl monomers copolymerizable with MMA, and examples thereof include acrylic esters such as methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, and butyl acrylate. The polymerizable material may be a syrup-like polymerizable material containing a polymer such as MMA and a monomer such as MMA.

  In order to polymerize the polymerizable raw material, 2,2′-azobisisobutyronitrile, 2,2 ′-(2,4-dimethylisovaleronitrile), 2,2′-azobis (4 -Methoxy 2,4-dimethylvaleronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile) and other azo polymerization initiators, lauroyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxydicarbonate, dicyclohexane It is preferable to contain a peroxide polymerization initiator such as peroxydicarbonate.

  Examples of the polymerization conditions for the polymerizable raw material in the batch cast plate method include the following conditions. It is preferable that the polymerization reaction is initially performed using water as a heating medium in a temperature range of 20 ° C to 90 ° C, preferably 35 ° C to 85 ° C. The polymerization time is preferably within 4 hours. After the above-mentioned polymerization, it is then preferable to perform post-polymerization in an air bath in the range of 100 ° C to 140 ° C, preferably 120 ° C to 135 ° C. The polymerization time is preferably within 4 hours. As the continuous cast plate method, a pair of endless belts that run facing each other with a predetermined interval are disposed on opposite surfaces of the endless belt that runs following the running of the endless belt. A mixture of a diffusing agent, a fluorescent whitening agent and a polymerizable raw material added with a blue dye / pigment is injected into the space formed by the gasket, and the mixture is polymerized and cured to endless the plate polymer. The method of peeling and taking out from a belt is mentioned.

  As an extrusion plate making method, a pellet made of a bead-like or pellet-like resin, a diffusing agent, a fluorescent brightener, and a blue dye / pigment is melt-extruded by a single-screw or twin-screw extruder, and the molten resin is a plurality of mirror rolls And a method of producing a resin plate by sandwiching and cooling with a mat-processed roll.

  Examples of a method for further forming the light diffusion plate of the present invention obtained by the above method include vacuum forming, pressure forming, free blow forming, hot press forming, bending forming and the like.

  Examples of the use of the light diffusion plate for an LED light source of the present invention include a signboard, a sign, a liquid crystal backlight diffusion plate, a projection screen plate, and a lighting cover using a white LED light source. Examples of the optical product having the light diffusion plate of the present invention include signboards, notebook computers, projectors, and lighting equipment.

The light diffusing plate of the present invention was manufactured as in Example 1, Example 2, Example 3, and Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 5. The optical properties of the light diffusion plate were evaluated by the following method.
(1) Total light transmittance It measured based on JISK 7105 B method.
Measuring equipment: RH100 manufactured by Murakami Color Research Laboratory
(2) Difference in light transmittance at wavelengths of 460 nm and 580 nm The light transmittance at wavelengths of 460 nm and 580 nm was measured with a spectrophotometer, and these differences were obtained.
Measuring instrument: U-4100 (integrated sphere with a diameter of 60 mmφ) manufactured by Hitachi High-Technologies Corporation
(3) Brightness, See-Through, Color Unevenness Using the following evaluation apparatus, the brightness, see-through, and color unevenness of the light diffusion plate were evaluated.

  Of the hexahedrons having a length of 300 mm, a width of 420 mm, and a height of 50 mm, five surfaces other than one of the 300 mm length and 420 mm width are made of Acrylite (trade name) # 401 (color white, thickness 3 mm) manufactured by Mitsubishi Rayon ), And the obtained light diffusion plate was placed on the remaining surface of 300 mm length and 420 mm width. A total of 20 white LED light source modules (4 in 60 mm intervals and 5 in 70 mm intervals on the inner surface of the surface (300 mm in length and 420 mm in width) using acrylite manufactured by Mitsubishi Rayon Co., Ltd. (( Konami LED module, Shining Eye L (trade name)) was placed. 18 of the 20 LED light sources are made invisible when viewed directly as color unevenness, and the remaining 2 are colored in a yellowish color when viewed directly compared to the 18 LED light sources. It was arranged to be visually recognized as unevenness.

1) Brightness The brightness of the transmitted light from the light diffusing plate was visually evaluated.
Evaluation: ○ Same brightness with reference to the light diffusing plate obtained in Example 1 × Dark with respect to the light diffusing plate obtained in Example 1 2) Transparent shape of the LED light source through the light diffusing plate The visual confirmation was made to confirm whether or not
Evaluation: ○ The shape of the LED light source cannot be confirmed × The shape of the LED light source can be confirmed 3) Color unevenness The presence or absence of color unevenness of the transmitted light from the light diffusion plate was visually evaluated.
Evaluation: ○ Color unevenness cannot be confirmed.
× Uneven color can be confirmed

[Example 1]
1.6 parts by weight of barium sulfate (trade name MB270, average particle size 1 to 3 μm) manufactured by Sakai Chemical Industry Co., Ltd. with respect to 100 parts by weight of a polymerizable raw material consisting of 30 parts by weight of MMA polymer and 70 parts by weight of MMA And 0.3 parts by mass of silicon resin beads (trade name Tospearl 145, average particle size 4.5 μm) manufactured by Toshiba Silicon Co., Ltd., and a fluorescent whitening agent (trade name Hostalcus KS-N) manufactured by Clariant Japan Co., Ltd. 0.00015 part by mass and 0.001 part by mass of a blue pigment (trade name # 1500, ultramarine blue) manufactured by Daiichi Kasei Co., Ltd. and 0.05 part by mass of azobisisobutyronitrile as a polymerization initiator As a UV absorber, 0.01 part by mass of 2- (5-methyl-2-hydroxyphenyl) -benzotriazole was added and stirred to obtain a mixture. After degassing dissolved oxygen from the mixture, the mixture was poured into a mold formed of two 65 cm × 50 cm × 6 mm thick tempered glass and an endless gasket made of vinyl chloride and heated in 70 ° C. warm water for 2 hours. Polymerized. Subsequently, polymerization was completed in an air bath at 120 ° C. over 2 hours to produce a light diffusion plate having a thickness of 3 mm. The optical value was 60.0% of total light transmittance, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 2.9%.
Although the diffusion plate was visually observed after the LED was turned on, no see-through was confirmed. Further, color unevenness could not be confirmed, which was good.

[Example 2]
Polymerization was completed in the same manner as in Example 1 except that 150 ppm of titanium oxide (TR840, average particle size 0.2 to 0.5 μm) manufactured by Fuji Titanium Industry Co., Ltd. was produced to produce a light diffusion plate having a thickness of 3 mm. did. As a result of evaluation in the same manner as in Example 1, the total light transmittance was 52.0%, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 1.4%. The brightness was equivalent to that in Example 1. Transparent and color unevenness could not be confirmed, and it was good.

[Example 3]
Polymerization was completed in the same manner as in Example 1 except that barium sulfate (trade name MB270, average particle diameter of 1 to 3 μm) manufactured by Sakai Chemical Industry Co., Ltd. was changed to 0.8 part by mass, and a light diffusion plate having a thickness of 3 mm. Manufactured. As a result of evaluation in the same manner as in Example 1, the total light transmittance was 65.0%, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 3.5%. The brightness was equivalent to that in Example 1. Transparent and color unevenness could not be confirmed, and it was good.

[Comparative Example 1]
Polymerization was completed in the same manner as in Example 1 except that the blue pigment (trade name # 1500, ultramarine blue) manufactured by Daiichi Kasei Co., Ltd. was omitted, and a light diffusion plate having a thickness of 3 mm was produced. The optical value was 60.0% of total light transmittance, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 3.0%.
As a result of evaluation in the same manner as in Example 1, slight color unevenness (yellowishness) was confirmed.

[Comparative Example 2]
Polymerization was conducted in the same manner as in Example 1 except that the brightening agent (trade name Hostalcus KS-N) manufactured by Clariant Japan Co., Ltd. and the blue pigment (trade name # 1500, ultramarine blue) manufactured by Daiichi Kasei Co., Ltd. were excluded. As a result, a light diffusion plate having a thickness of 3 mm was produced. As a result of evaluation in the same manner as in Example 1, the total light transmittance was 60.0%, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 3.0%. Slight color unevenness (yellowishness) was confirmed. In addition, the whiteness when turned off decreased.

[Comparative Example 3]
0.8 parts by mass of Sakai Chemical Industry Co., Ltd. barium sulfate (trade name MB270, average particle size 1 to 3 μm) with respect to 100 parts by mass of a polymerizable raw material consisting of 30 parts by mass of MMA polymer and 70 parts by mass of MMA Then, 0.0085 parts by mass of titanium oxide (average particle diameter 0.2 μm) and 1.5 parts by mass of styrene beads (trade name BR-50, average particle diameter 10 μm) manufactured by Mitsubishi Rayon Co., Ltd. were added and polymerized. 0.05 parts by mass of azobisisobutyronitrile as an initiator and 0.01 parts by mass of 2- (5-methyl-2-hydroxyphenyl) -benzotriazole as an ultraviolet absorber are added and stirred to obtain a mixture. It was. The polymerization conditions were the same as in Example 1.
As a result of evaluation in the same manner as in Example 1, the total light transmittance was 58.0%, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 1.8%. Slight color unevenness (yellowishness) was confirmed.

[Comparative Example 4]
0.068 parts by mass of titanium oxide (average particle size 0.2 μm) and styrene-based beads (average particle size 10 μm) per 100 parts by mass of a polymerizable material consisting of 30 parts by mass of MMA polymer and 70 parts by mass of MMA .9 parts by mass, 0.05 parts by mass of azobisisobutyronitrile as a polymerization initiator, and 0.01 parts by mass of 2- (5-methyl-2-hydroxyphenyl) -benzotriazole as an ultraviolet absorber And stirred to obtain a mixture. The polymerization conditions were the same as in Example 1.
As a result of evaluation in the same manner as in Example 1, the total light transmittance was 30.0%, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 1.0%. The brightness was darker than that of Example 1. Further, slight color unevenness (yellowishness) was confirmed.

[Comparative Example 5]
2.8 parts by mass of a crosslinked styrene bead (average particle size 10 μm) is added to 100 parts by mass of a polymerizable raw material composed of 30 parts by mass of MMA polymer and 70 parts by mass of MMA, and azobisisobutyro is used as a polymerization initiator. 0.05 parts by mass of nitrile and 0.01 parts by mass of 2- (5-methyl-2-hydroxyphenyl) -benzotriazole as an ultraviolet absorber were added and stirred to obtain a mixture. The polymerization conditions were the same as in Example 1.
As a result of evaluation in the same manner as in Example 1, the total light transmittance was 75.0%, and the difference in light transmittance at wavelengths of 460 nm and 580 nm was 6.9%. Slight color unevenness (yellowishness) was confirmed. In addition, sheerness was also confirmed.

  The light diffusion plate for an LED light source of the present invention is suitable for various optical members.

Claims (3)

  At least one diffusing agent selected from acrylic crosslinked beads, melamine based resin beads, styrene based crosslinked beads, silicon based resin beads, aluminum hydroxide, calcium carbonate, barium sulfate, and titanium oxide, fluorescent whitening agent, And a light diffusing plate for a white LED light source, comprising a base material containing a blue dye / pigment, having a total light transmittance of 50% or more and 70% or less, and a difference in light transmittance between wavelengths of 460 nm and 580 nm of 4% or less.   The light diffusion plate for a white LED light source according to claim 1, wherein the material to be the base material is an acrylic resin.   An optical product comprising a white LED light source and the light diffusing plate according to claim 1, wherein a minimum distance from the light source to the light diffusing plate is 10 mm or more and 150 mm or less.