WO2015146959A1

WO2015146959A1 - Reflecting sheet, reflection unit for surface light source device, and surface light source device

Info

Publication number: WO2015146959A1
Application number: PCT/JP2015/058853
Authority: WO
Inventors: 若原隆一; 河田融司; 田中正太郎
Original assignee: 東レ株式会社
Priority date: 2014-03-27
Filing date: 2015-03-24
Publication date: 2015-10-01
Also published as: JPWO2015146959A1; TW201539089A; KR102362100B1; KR20160137574A; JP6540508B2; TWI662333B; CN106133561A; CN106133561B

Abstract

The purpose of the present invention is to minimize emission color irregularities by a surface light source device, caused by reflecting sheets. The present invention provides: a reflecting sheet arranged facing the light source of a surface light source device, wherein the reflecting sheet is characterized by having a reflecting part for reflecting light from the light source, and a transmitting part for transmitting light from the light source, and by having a transmitted yellow index (YI) or 50 or less; and a surface light source device having a light source, a lower side reflecting sheet for reflecting light, and an upper surface reflecting sheet comprising the reflecting sheet, wherein the lower side reflecting sheet is situated on the back surface of the light source, and the upper side reflecting sheet is situated facing the lower side reflecting sheet.

Description

Reflective sheet, reflection unit for surface light source device, and surface light source device

The present invention relates to a reflective sheet and a surface light source device used for a surface light source device used in a display device such as a backlight of a liquid crystal display (LCD backlight), a signboard for illumination, an automobile, and a vehicle.

A surface light source device used for a backlight unit of a liquid crystal display generally has a configuration in which a reflection sheet is provided on the back surface of the light source. And the backlight unit using this surface light source device generally has a configuration in which an optical sheet such as a light diffusion film is disposed at a position facing the reflection sheet of the surface light source device. An LED (light emitting diode) light source is generally used for these surface light source devices. However, since the LED light source is provided with a lens for enhancing the directivity of light, it has been a cause of cost increase.

Recently, surface light source devices using LED light sources as they are have been proposed. In this surface light source device, a reflection sheet (lower reflection sheet) is provided on the back surface of the light source (the side opposite to the direction in which the surface light source device emits light), and faces the light source and the lower reflection sheet. An upper reflection sheet having a reflection part that reflects light emitted from a light source and a transmission part that transmits light is arranged (Patent Documents 1 to 3).

In Patent Documents 1 to 3, a light reflection region (reflection portion) and a light transmission region (transmission portion) are provided as an upper reflection sheet by providing an opening pattern composed of a plurality of transmission holes (openings) for transmitting light to the reflection sheet. ) Is formed.

JP 2008-27886 A JP 2009-4248 A JP 2010-272245 A

In reality, it is difficult for the reflection sheet used in the surface light source device to reduce the light transmittance of the reflection sheet itself to 0% because of the configuration, material cost, and the like. (For example, the light transmittance is about 0.5 to 20%). In the case of a reflection sheet in a conventional surface light source device (a reflection sheet disposed on the back surface of a light source), light transmitted through the reflection sheet is not used, and thus the transmission color of the reflection sheet is not considered.

However, in the surface light source devices as proposed in Patent Documents 1 to 3, the light transmitted through the light transmission region (transmission portion) of the upper reflection sheet becomes the main light of the surface light source device, but the emission color unevenness It was easy to occur.

Therefore, an object of the present invention is to provide a reflection sheet in which unevenness in emission color is suppressed in a reflection sheet disposed opposite to the light source of the surface light source device, a surface light source device using the reflection sheet, and the like.

The present invention has the following configuration.
(1) A reflection sheet disposed opposite to a light source of a surface light source device, the reflection sheet having a reflection part for reflecting light from the light source and a transmission part for transmitting light from the light source, and reflecting Reflective sheet having a transmitted yellowness (YI) of 50 parts or less, particularly preferably 30 or less.

And as a preferable aspect of this invention, the following are disclosed here.
(2) The reflection sheet, wherein the transmission part is a through hole.
(3) Any of the reflection sheets described above, wherein the total light transmittance of the reflection portion is 0.5 to 10%.
(4) The reflection sheet according to any one of the above, wherein the center line average roughness Ra of the reflection part is 100 nm or less.
(5) The reflection sheet is a reflection film in which a layer (A layer) for supporting the B layer is laminated on both surfaces of a layer containing air bubbles (B layer). The reflective sheet according to any one of the above.
(6) The said reflection sheet in which A layer contains particle | grains.

And as a preferable usage method of the reflective sheet of this invention, the following are disclosed here.
(7) A unit for a surface light source device having a lower reflection sheet that reflects light, and an upper surface reflection sheet that is opposite to the lower reflection sheet and that is any of the reflection sheets.
(8) A surface light source device having a light source, a lower reflection sheet that reflects light, and an upper surface reflection sheet that is any one of the reflection sheets, wherein the lower reflection sheet exists on the rear surface of the light source, and lower reflection A surface light source device in which an upper reflective sheet exists opposite to the sheet.

By using the reflection sheet, the reflection unit for a surface light source device, and the surface light source device of the present invention, it is possible to suppress uneven emission color of the surface light source device. According to a preferred aspect of the present invention, a surface light source device with uniform brightness can be provided.

FIG. 1 is a schematic cross-sectional view showing an example of a surface light source device in which the reflection sheet of the present invention is used. FIG. 2 is a schematic plan view showing an example of the reflection sheet of the present invention. FIG. 3 is a schematic cross-sectional view of FIG. FIG. 4 is a schematic plan view showing another embodiment of the reflection sheet of the present invention. It is a cross-sectional schematic diagram of the simple surface light source device used for an Example.

An example of a surface light source device using the reflective sheet of the present invention is shown in FIG. FIG. 1 is a schematic cross-sectional view showing the main part of the surface light source device. This surface light source device is used for a backlight unit of a liquid crystal display, for example.

In FIG. 1, in the surface light source device 11, a light source 1, a lower reflective sheet 2 that reflects light, an upper reflective sheet 3 that reflects light, and a side reflective sheet 4 that reflects light are arranged in a casing 5. Yes. The lower reflective sheet 2 is disposed on the back surface of the light source 1, and the upper reflective sheet 3 is disposed at a position facing the light source 1. The lower reflective sheet 2 and the upper reflective sheet 3 are arranged in parallel so that almost the entire surface is equally spaced. The lower reflective sheet 2 may be integrally formed with the side reflective sheet 4, or separate reflective sheets may be arranged respectively. A point light source such as an LED (light emitting diode) is preferably used as the light source.

Here, the reflective sheet of the present invention is used as the upper reflective sheet 3. In the following description, the term upper reflective sheet may be used as the reflective sheet of the present invention.

The upper reflection sheet 3 has a reflection part 6 that reflects light emitted from the light source and a transmission part 7 that transmits light emitted from the light source 1. The transmission part 7 can be comprised by several opening part, for example, as shown in FIG.2 and FIG.4. The opening is preferably a through hole obtained by a penetrating operation. In FIG. 2 and FIG. 4, the area other than the transmission part 7 is a reflection part.

Most or all of the light emitted from the light source 1 (excluding light transmitted through the reflecting portion 6) is a reflective sheet (the lower reflective sheet 2, the upper reflective sheet 3, and the side surface) disposed in the surface light source device 11. The light is reflected by the reflective sheet 4) or transmitted through the transmission part 7 of the upper reflective sheet 3 and emitted upward while repeating reflection between the lower reflective sheet and the upper reflective sheet.

A part of the light emitted from the light source 1 may be directly transmitted through the transmission part 7 of the upper reflection sheet 3.

The light emitted from the light source 1 and reflected by the reflecting portion 6 of the upper reflecting sheet 3 is reflected by the lower reflecting sheet 2 and the side reflecting sheet 4 or while being repeatedly reflected between these reflecting sheets. The light passes through the transmission part 7 of the sheet 3 and exits upward. On the other hand, a part of the light hitting the reflection part 6 of the upper reflection sheet 3 passes through the reflection part 6 and is emitted upward. That is, the light that passes through the transmissive part 7 of the upper reflective sheet 3 becomes the main light emitted from the surface light source device, but the light that passes through the reflective part 6 also constitutes a part thereof.

In such a surface light source device, it has been found that when the yellowness (YI: yellow index) of the transmitted light of the upper reflection sheet 3 disposed to face the light source is increased, uneven emission color is caused. Then, it discovered that the said subject was solved by making low the transmission yellow degree (YI) in the reflection part of an upper side reflection sheet, and came to this invention.

The transmission yellowness (YI) in the reflection part of the upper reflection sheet of the present invention is preferably 50 or less, more preferably 40 or less, still more preferably 35 or less, and particularly preferably 30 or less. The smaller the transmitted yellowness (YI) at the reflecting portion, the better, but the practical lower limit is about 1.

Since the transmission yellowness (YI) of the reflection sheet of the present invention varies depending on the material, composition, thickness and the like constituting the reflection portion, the transmission yellowness (YI) can be controlled by adjusting these. Details will be described later.

The reflection part of the reflection sheet of the present invention has some light transmission. Specifically, the total light transmittance of the reflecting portion in the reflecting sheet is generally about 0.5 to 20%, but the total light transmittance of the reflecting sheet of the present invention is preferably 0.5 to 10%. When applied to the above-described surface light source device, if the total light transmittance becomes too high, the effect of suppressing unevenness in emission color may be reduced. Accordingly, the total light transmittance in the reflecting portion of the reflecting sheet of the present invention is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. On the other hand, the lower limit of the total light transmittance in the reflecting portion is preferably 0.5% or more, but 1.2% or more is more preferable from the viewpoint of giving an appropriate gradation to the amount of light transmitted through the reflecting sheet and the transmitted color. 0.5% or more is more preferable, 2.0% or more is particularly preferable, and 3.0% or more is most preferable. By applying an appropriate gradation, emission color unevenness can be reduced.

The average reflectance at a wavelength of 400 to 700 nm in the reflecting portion of the reflecting sheet of the present invention is preferably 90% or more, more preferably 95% or more, and particularly preferably 100% or more. The upper limit of the average reflectance is about 150%. When the average reflectance at the reflecting portion of the reflecting sheet is less than 90%, the luminance of the backlight unit may be insufficient.

Here, the reflectance is a relative reflectance with respect to the standard white plate. A part number 210-0740 manufactured by Hitachi Keiki Service Co., Ltd. can be used for the standard white plate.

In a preferred embodiment of the reflection sheet of the present invention, a through-hole is provided in a part of a reflection member whose entire surface is a reflection portion to form an opening, which is used as a transmission portion. In other words, a preferred embodiment of the reflective sheet of the present invention is a reflective portion other than the transmissive portion.

The reflective sheet of the present invention has a reflective part and a transmissive part, and the material and composition of the reflective sheet are not particularly limited as long as the transmission yellowness (YI) of the reflective part is not more than a specific value.

Moreover, as a preferable aspect of the reflection sheet of the present invention, as described above, an opening is provided in a reflection member whose entire surface is a reflection portion, and the opening is used as a transmission portion. A reflective film is preferably used as such a reflective member.

Hereinafter, the reflective film preferably used as the reflective sheet of the present invention will be described in detail.

As the reflective film, a layer for supporting the B layer (hereinafter referred to as A layer) is laminated on at least one surface of a layer containing bubbles (hereinafter referred to as B layer). Is mentioned. In this embodiment, the A layer may be laminated only on one side of the B layer, or two A layers (hereinafter referred to as A1 layer and A2 layer, respectively) may be laminated on both sides of the B layer. Good. That is, a two-layer configuration of A layer / B layer and a three-layer configuration of A1 layer / B layer / A2 layer can be mentioned. Among these, a three-layer configuration of A1 layer / B layer / A2 layer is preferable from the viewpoint of ensuring good workability (formation of a transmission part) and obtaining high rigidity. Here, the A1 layer and the A2 layer may have the same composition and the same thickness, or may be different.

The reflection sheet obtained by forming the transmission part on these reflection films is arranged so that the surface of the A layer faces the light source. In other words, in the case of the two-layer configuration of A layer / B layer, the surface of the A layer is disposed opposite to the light source to be a reflecting portion, and in the case of the three-layer configuration of A1 layer / B layer / A2 layer, The surface is arranged to face the light source and becomes a reflection portion.

As described above, in the three-layer configuration, the A1 layer and the A2 layer may be configured with exactly the same composition or may be configured with different compositions, but from the viewpoint of the productivity of the reflective film, the A1 layer And the A2 layer preferably have the same composition. In the following description, the A1 layer and the A2 layer may be collectively referred to as “A layer”, and the expression “A layer” includes the A layer in the case of the two-layer configuration and the A1 in the case of the three-layer configuration. Layers and A2 layers are included. In the following description, the amount of various materials contained in the A layer indicates the amount per one of the A layer and the A2 layer in the case of the A layer in the case of the two-layer configuration and the three-layer configuration.

It is preferable that the A layer has a function of supporting the B layer, and further has a function of adjusting the center line average roughness Ra of the reflecting portion to 100 nm or less as described later. From the viewpoint of imparting these functions to the A layer, the A layer is preferably a layer containing a resin as a main component. Here, the layer A is “a layer containing a resin as a main component” means that the resin contains 50% by mass or more of resin with respect to 100% by mass of the total solid content of the A layer. Furthermore, the A layer preferably contains 60% by mass or more of resin, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. The upper limit is about 99% by mass.

As the resin constituting the A layer, a polyester resin is preferable. As such a polyester resin, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) is preferable. In addition, various known additives such as an antioxidant and an antistatic agent may be added to the polyester resin. The content of the polyester resin constituting the A layer is preferably 50% by mass or more, more preferably 60% by mass or more, particularly preferably 70% by mass or more based on the total amount of the resin constituting the A layer. The upper limit is about 99% by mass.

The layer A preferably contains particles. By including particles in the A layer, an appropriate slip property can be imparted to the reflective film. By providing slip properties to the reflective film, handling properties and workability for creating through holes are improved.

Examples of the particles contained in the A layer include organic particles and inorganic particles. Examples of the organic particles include polyester resins, polyamide resins such as benzoguanamine, polyurethane resins, acrylic resins, methacrylic resins, polyamide resins, polyethylene resins, polypropylene resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyacetic acids. Examples thereof include particles made of a resin such as a vinyl resin, a fluorine-based resin, and a silicone resin, and particles made of two or more copolymers of the above resins and a mixture thereof.

Inorganic particles include calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, silica, alumina, mica, titanium mica, talc, clay, kaolin, fluoride. And lithium fluoride and calcium fluoride.

Among the above particles, inorganic particles are preferable, and among the inorganic particles, calcium carbonate, titanium oxide, barium sulfate, and silica are preferably used.

The average particle diameter of the particles is suitably in the range of 0.05 to 10 μm, preferably in the range of 0.1 to 5 μm, and more preferably in the range of 0.2 to 3 μm.

The content of particles in the A layer is preferably 0.005% by mass or more, and more preferably 0.01% by mass or more with respect to the total solid content of the A layer. The upper limit content is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less, based on the total solid content of the A layer. When the content of the particles is less than 0.005% by mass, good sliding properties may not be obtained. On the other hand, when the content of the particles exceeds 20% by mass, the film forming property may be deteriorated.

As described above, the reflection sheet obtained by forming the transmission part on the reflection film is arranged so that the surface of the A layer faces the light source. That is, in the case of a two-layer configuration, the surface of the A layer is a reflection portion, and in the case of a three-layer configuration, the A1 layer or the A2 layer is a reflection portion.

The reflective part of the reflective sheet of the present invention preferably has a higher smoothness. By increasing the smoothness of the reflecting portion, the irregular reflection of the light reflected by the reflecting portion of the reflecting sheet is suppressed, so that a decrease in the amount of light in a region far from the light source is suppressed. As a result, the brightness of the portion directly above the light source and the peripheral portion is uniform.

The smoothness of the reflective part can be expressed by the centerline average roughness Ra. The center line average roughness Ra of the reflecting portion in the reflecting sheet of the present invention is preferably 100 nm or less, more preferably 50 nm or less, and particularly preferably 30 nm or less.

On the other hand, as described above, from the viewpoint of imparting appropriate slipperiness to the reflective sheet and the reflective film as a material thereof, it is preferable to have a certain degree of unevenness, and the center line average roughness Ra of the reflective portion is 5 nm or more is preferable and 10 nm or more is more preferable.

In order to ensure such smoothness, it is preferable to control the average particle diameter and the content of the particles to be contained in the A layer serving as the reflective portion. That is, it is preferable that the average particle diameter (D) of the particles contained in the A layer serving as the reflective portion is sufficiently smaller than the film thickness (T) of the A layer. The ratio (D / T) of the average particle diameter (D) of the particles to the film thickness (T) of the A layer is preferably 0.7 or less, more preferably 0.5 or less, and particularly preferably 0.3 or less.

On the other hand, from the viewpoint of imparting appropriate slipperiness to the reflective sheet and the reflective film, it is preferable to have a certain degree of unevenness. The ratio (D / T) between the thickness (T) of (D) and the A layer is preferably 0.01 or more, more preferably 0.03 or more, and particularly preferably 0.05 or more.

Specifically, the average particle diameter (D) of the particles to be contained in the A layer serving as the reflective portion is preferably 3 μm or less, more preferably 2 μm or less, particularly 1 μm, from the viewpoint of ensuring the smoothness and slipperiness described above. The following is preferred. Moreover, 0.1 micrometer or more is preferable, 0.2 micrometer or more is more preferable, and 0.3 micrometer or more is especially preferable. Further, the content of the particles to be contained in the A layer serving as the reflective portion is preferably in the range of 0.005 to 10% by mass, and in the range of 0.01 to 5% by mass with respect to 100% by mass of the solid content of the A layer. Is more preferable, and the range of 0.02 to 3% by mass is particularly preferable.

B layer preferably contains bubbles inside the layer. The B layer is preferably a film, and a porous unstretched or biaxially stretched polypropylene film or a porous unstretched or stretched polyethylene terephthalate film is preferably used. For example, JP-A-8-262208 (correspondingly, European Patent Application Publication No. 0724181), JP-A-2002-90515 (correspondingly) European Patent Application Publication No. 1302788) and Japanese Patent Application Laid-Open No. 2002-138150 are disclosed in detail and can be used in the present invention.

The B layer is preferably made of a polypropylene resin or a polyester resin, and particularly preferably made of a polyester resin. As the polyester resin constituting the B layer, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) is preferable.

In addition, various additives such as an antioxidant and an antistatic agent may be added to the polyester resin. The content of the polyester resin constituting the B layer is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more with respect to the total solid content of the B layer. The upper limit is about 95% by mass.

Formation of bubbles in the B layer can be achieved, for example, by finely dispersing a resin incompatible with the polyester resin in a polyester film that is a film base material and stretching it uniaxially or biaxially.

The B layer is preferably mixed with the polyester resin constituting the B layer in an incompatible resin (hereinafter sometimes simply referred to as an incompatible resin) and contained in the B layer. By containing the incompatible resin, a cavity is created with the incompatible resin as a core during stretching, and light reflection occurs at the interface between the resin and the cavity. The resin incompatible with the polyester resin may be a homopolymer or a copolymer. Polyolefin resin such as polyethylene, polypropylene, polybutene, polymethylpentene, cyclic polyolefin resin, polystyrene resin, polyacrylate Resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, fluororesins, and the like are preferably used. Two or more of these may be used in combination.

Particularly preferred is a resin that has a large difference in critical surface tension with a polyester resin and is not easily deformed by heat treatment after stretching. Specifically, polyolefin resin is preferable. Examples of the polyolefin resin include polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, cyclic polyolefin resins, and copolymers thereof. Among these, a copolymer of ethylene and bicycloalkene, which is a cyclic olefin copolymer, is particularly preferable.

The preferable content of the incompatible resin to be contained in the B layer is 5% by mass or more and 25% by mass or less with respect to the total solid content of the B layer. In addition, the incompatible resin contained in the B layer is dispersed in a matrix made of a polyester resin with a number average particle diameter of 0.4 μm or more and 3.0 μm or less. It is preferable in obtaining. Furthermore, the number average particle size of the incompatible resin is preferably in the range of 0.5 μm to 1.5 μm.

It is preferable that the layer B further contains particles such as organic particles and inorganic particles. Examples of such particles include the same particles as those that can be contained in the A layer. Among these particles, inorganic particles such as calcium carbonate, barium sulfate, and titanium dioxide that absorb less in the visible light range of wavelength 400 to 700 nm are preferable from the viewpoints of reflection characteristics, concealability, production cost, and the like. In the present invention, barium sulfate and titanium dioxide are most preferable from the viewpoints of film winding property, long-term film-forming stability, and improvement in reflection characteristics. The average particle diameter of the particles is preferably in the range of 0.1 to 3 μm, and the use of such inorganic particles improves the reflectivity and concealability.

The content of the inorganic particles in the B layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more with respect to the total solid content of the B layer, from the viewpoint of ensuring good reflection characteristics and concealment. 1% by mass or more is particularly preferable. On the other hand, when the content of such inorganic particles increases, the transmission yellowness (YI) of the reflective sheet tends to increase. Therefore, the upper limit content of the inorganic particles is preferably 10% by mass or less, and 5% by mass. The following is more preferable, and 3% by mass or less is particularly preferable.

It is preferable that the B layer further contains a copolyester. By containing the copolyester in the B layer, it is possible to stably form a film even when the B layer contains a relatively high concentration of inorganic particles. The copolyester also has a role as a dispersant for the incompatible resin in the B layer.

Examples of such a copolyester include a copolymer of polyethylene terephthalate and isophthalic acid, a copolymer of polyethylene terephthalate and cyclohexanedimethanol, a copolymer of polybutylene terephthalate and polytetramethylene terephthalate, and the like. In this invention, it is preferable to contain at least 2 types chosen from the group which consists of these copolyesters.

In the case where the reflective film has a two-layer structure, the thickness ratio of each layer is such that A layer: B layer = 2: 98 to 20:80 from the viewpoint of reducing the transmission yellowness (YI) while maintaining high reflectance. The range of A layer: B layer = 3: 97 to 10:90 is more preferable.

In addition, the thickness per layer of A layer (in the case of a two-layer configuration means the thickness of the A layer, and in the case of a three-layer configuration means the thickness of each of the A1 layer and the A2 layer) supports the B layer. From the viewpoint of achieving, it is preferably 3 μm or more, more preferably 5 μm or more, and particularly preferably 6 μm or more. The upper limit thickness is preferably 30 μm or less, more preferably 20 μm or less, and particularly preferably 15 μm or less.

The thickness of the B layer is preferably 50 μm or more, more preferably 70 μm or more, and particularly preferably 90 μm or more from the viewpoint of ensuring high reflectance. The upper limit thickness is preferably 440 μm or less, more preferably 350 μm or less, and particularly preferably 300 μm or less.

When the reflective film has a three-layer structure, the thickness ratio of each layer is as follows: A1 layer: B layer: A2 layer = 1 from the viewpoint of adjusting the transmission yellowness (YI) to 50 or less while maintaining high reflectance. : The range of 98: 1 to 15:70:15 is preferable, and the range of A1 layer: B layer: A2 layer = 2: 96: 2 to 10:80:10 is more preferable.

The A layer is preferably a layer that substantially does not contain bubbles from the viewpoint of supporting the B layer. “Contains substantially no bubbles” means a layer state having a porosity of less than 10%. The thickness of the A layer is determined as the thickness from the surface to the depth in the cross-section direction in which bubbles are not substantially contained when the cross section is observed with an electron microscope. And

In the reflective film used for the reflective sheet of the present invention, it is preferable that a bead layer is not provided on the surface to be a reflective portion. This bead layer is formed by a coating layer containing a binder and spherical particles, and has a function of diffusing the light reflected by the reflection film. A reflection sheet provided with a bead layer on a reflection film is widely used as a light guide plate type backlight unit, but is preferably not applied to a surface to be a reflection portion of the reflection sheet of the present invention. On the other hand, the above-mentioned bead layer can be applied to the surface opposite to the reflecting portion of the reflecting sheet of the present invention within a range that does not impair the objects and effects of the present invention or for improving the slipperiness of the reflecting sheet.

When a bead layer is present on the surface to be a reflective part, the center line average roughness Ra is usually 500 nm or more, and the smoothness of the reflective part is deteriorated. As a result, the brightness of the central part and the peripheral part directly above the light source is uneven. It may become.

The thickness of the reflective sheet of the present invention is preferably 100 μm or more, and preferably 150 μm or more from the viewpoint of obtaining high reflectivity and high rigidity. In particular, since the reflection sheet of the present invention has a transmission part and the rigidity of the reflection sheet itself tends to be reduced, the thickness of the reflection sheet is preferably larger from the viewpoint of ensuring high rigidity.

On the other hand, the upper limit of the thickness of the reflective sheet is preferably 500 μm or less, and more preferably 350 μm or less, from the viewpoints of workability for forming the transmission part, handling property, productivity, and cost.

In the reflective sheet of the present invention, the transmission yellowness (YI) of the reflective part is more preferably 50 or less, 40 or less, further preferably 35 or less, and particularly preferably 30 or less. The above-described reflective film tends to increase the transmission yellowness (YI), but is considered to affect the transmission yellowness (YI), the type of particles, the size of particles, the content of particles, the type of resin In addition, by adjusting the content, the thickness ratio of the A layer and the B layer, etc., the transmission yellowness (YI) of the reflective portion can be controlled to be low.

For example, since titanium oxide and barium sulfate used as inorganic particles tend to increase the transmission yellowness (YI), it is preferable to adjust the content thereof. Further, the copolymerized polyester resin also tends to increase the transmission yellowness (YI), although it depends on the type of the copolymer component, and therefore the content thereof is preferably adjusted. In addition, since the B layer is thicker than the A layer and usually contains a large amount of various additives, it is considered that the influence on the transmission yellowness (YI) is larger than that of the A layer. It is preferable to adjust the thickness of the B layer.

The reflection sheet of the present invention has a reflection part and a transmission part. The reflection sheet of the present invention can be obtained, for example, by providing a transmission part (opening) on a reflection member such as a reflection film as described above. This opening (through hole) can be formed by laser processing or punching.

The permeation part is preferably a hole, and examples of the shape include a circle, a triangle, a rectangle, a polygon (for example, 5 to 12 squares), and a ring in which the inside and the outside are partially connected. Among these, an ellipse, a circle, a rectangle, and a polygon are preferable, an ellipse and a circle are more preferable, and a perfect circle is particularly preferable.

In the reflective sheet of the present invention, it is preferable that the transmission part is composed of a plurality of independent openings. In the present specification, the “transmission portion” may indicate an individual opening portion or a transmission region including a plurality of opening portions.

The transmission part in the reflection sheet of the present invention can arrange a plurality of independent openings in a specific pattern. The opening pattern of the transmissive part can be appropriately selected depending on the light amount per light source, the number of light sources arranged, and the like.

Examples of the arrangement pattern of the openings of the transmission part include the patterns shown in FIGS. 3 and 6 of JP 2010-272245 A, but the present invention is not limited to these patterns. These patterns can be arranged for each point light source or for each unit including a plurality of adjacent point light sources as one unit.

Hereinafter, a mode in which the arrangement pattern of the transmission part is provided for each light source such as an LED will be described. As this aspect, the aspect which arrange | positions a transmission part so that the light quantity which permeate | transmits from a transmission part gradually increases as it distances from the area | region located right above the light source of an upper side reflection sheet, for example can be mentioned.

A directional light source such as an LED tends to decrease in light quantity as it moves away from the center position. Therefore, by arranging the transmissive part so that the amount of light transmitted from the transmissive part gradually increases as it moves away from the region located directly above the light source of the upper reflective sheet as described above, the luminance unevenness is suppressed and uniform. A sufficient amount of light can be obtained.

FIG. 2 is a schematic plan view (schematic plan view showing a positional relationship between a light source and an opening pattern) showing an example of the reflection sheet of the present invention, and FIG. 3 is a schematic cross-sectional view of FIG. The upper reflection sheet 3 is provided with a large number of transmission parts 7. As the distance from the region 10 located directly above the light source 1 of the upper reflective sheet 3 increases, the opening area per one transmission portion 7 (circular opening) increases. That is, in the aspect of FIG. 2, the transmissive part is arranged so that the amount of light transmitted from the transmissive part gradually increases as it moves away from the region located directly above the light source of the upper reflective sheet.

FIG. 4 is a schematic plan view showing another aspect (another opening pattern) of the reflection sheet of the present invention. The opening pattern of FIG. 4 is also a pattern that gradually increases the amount of light transmitted from the transmissive portion as it moves away from the region located directly above the light source of the upper reflective sheet, as in FIG. FIG. 4 is a mode in which a large number of transmission parts 7 having substantially the same opening area per one are provided, and the transmission parts 7 are arranged as they move away from the region 10 located directly above the light source 1 of the upper reflection sheet 3. It arrange | positions so that the number may increase.

As shown in FIG. 1, in a surface light source device in which the reflection sheet of the present invention is used as an upper reflection sheet, a lower reflection sheet 2 is disposed on the back surface of a light source 1. The lower reflection sheet 2 and the upper reflection sheet 3 are arranged in parallel via a space (air layer) so that the respective reflection portions face each other. Here, most of the surface of the lower reflective sheet 2 that faces the upper reflective sheet 3 is a reflective portion. However, the place where the light source 1 is installed and the place necessary for connecting the light source 1 do not need to be a reflecting portion.

The reflection sheet of the present invention provides the following reflection unit for a surface light source device and an apparatus for a surface light source in which uneven emission color is suppressed.
A unit for a surface light source device, comprising: a lower reflective sheet that reflects light; and an upper reflective sheet composed of the above-described reflective sheet facing the lower reflective sheet. And a surface light source device having a light source, a lower reflective sheet for reflecting light, and an upper reflective sheet composed of the above-described reflective sheet, wherein the lower reflective sheet is present on the back surface of the light source and faces the lower reflective sheet A surface light source device having an upper reflective sheet.

The lower reflective sheet preferably has a reflective portion on the entire surface facing the upper reflective sheet. However, there may be an opening for installing or connecting the light source.

It is preferable that the lower reflective sheet has a high reflectance. The reflection unit for a surface light source device and the surface light source device of the present invention include a large amount of light that passes through the transmission part of the upper reflection sheet and emits upward while repeating reflection between the upper reflection sheet and the lower reflection sheet. ing. Therefore, it is desirable to avoid as much as possible the decrease in the light quantity in the process of repeating reflection.

Therefore, the average reflectance at a wavelength of 400 to 700 nm in the reflecting portion of the lower reflective sheet is preferably 90% or more, more preferably 95% or more, and particularly preferably 100% or more. The upper limit average reflectance is about 150%. When the average reflectance at the reflecting portion of the lower reflective sheet is low, the luminance of the backlight unit may be insufficient.

The reflective part of the lower reflective sheet preferably has higher smoothness. By increasing the smoothness of the reflection part of the lower reflection sheet, the irregular reflection of the light reflected by the reflection part of the lower reflection sheet is suppressed, so that a decrease in the amount of light in a region far from the light source is suppressed. As a result, the brightness of the portion directly above the light source and the peripheral portion away from directly above are uniform. That is, the uniformity of brightness is improved.

The smoothness of the reflective part of the lower reflective sheet can be expressed by the centerline average roughness Ra. The center line average roughness Ra of the reflective portion of the lower reflective sheet is preferably 100 nm or less, more preferably 50 nm or less, and particularly preferably 30 nm or less. On the other hand, from the viewpoint of imparting appropriate slipperiness to the lower reflective sheet, it is preferable to have some unevenness, and the center line average roughness Ra of the reflective portion of the lower reflective sheet is preferably 5 nm or more. 10 nm or more is more preferable.

The total light transmittance of the lower reflective sheet is preferably 0.5 to 10% from the viewpoint of securing a high reflectance. The upper limit of the transmittance is preferably 10% or less, more preferably 7% or less, and particularly preferably 5% or less. The lower limit of the transmittance is preferably 0.5% or more, more preferably 1.0% or more, still more preferably 1.2% or more, particularly 1.5% from the viewpoint of the material cost and productivity of the lower reflective sheet. % Or more is preferable.

The lower reflective sheet may be the same as the reflective film that can be used in the above-described reflective sheet of the present invention. However, it is not necessary to provide a transmission part, that is, an opening part. That is, a layer in which a layer (A layer) for supporting the B layer is laminated on at least one surface of a layer containing bubbles (B layer) can be used. In this embodiment, the A layer may be laminated only on one side of the B layer, or may be laminated on both sides of the B layer. That is, a two-layer configuration of A layer / B layer and a three-layer configuration of A1 layer / B layer / A2 layer can be mentioned. Among these, a three-layer configuration of A1 layer / B layer / A2 layer is preferable. Here, the A1 layer and the A2 layer are A layers, and the A1 layer and the A2 layer may have the same composition and thickness, or may have different compositions or thicknesses.

When using the above-described reflective film as the lower reflective sheet, the surface of the A layer is a reflective part. That is, in the reflection film having a two-layer structure, the surface of the A layer is a reflection part, and in the reflection film having a three-layer structure, the surface of the A1 layer or the A2 layer is a reflection part.

It is preferable that the bead layer described above is not laminated on the reflective portion of the lower reflective sheet for the same reason as described above. On the other hand, the above bead layer can be laminated on the surface of the lower reflective sheet opposite to the reflecting portion in order to improve the sliding property of the lower reflective sheet.

[Usage]
The surface light source device using the reflection sheet and the reflection unit of the present invention is suitable for use in a backlight unit such as a liquid crystal display. By arranging an optical sheet (not shown) such as a light diffusion film above the upper reflection sheet 3 of the surface light source device of FIG. 1, a backlight unit can be obtained. Further, the reflection unit for a surface light source device of the present invention can be widely used for lighting devices, electronic signboards, and the like.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. The measurement method, evaluation method, and materials used in this example are shown below.

[Measurement method and evaluation method]
(1) Measurement of transmission yellowness (YI) Transmission yellowness of a reflection part at a C light source (2-degree visual field) from a transmission spectrum obtained by a spectrophotometer (UV-3150 manufactured by Shimadzu Corporation) according to JIS K7373 (2006) (YI) was calculated. The transmitted yellowness (YI) is the same value when measured from any surface of the reflective sheet. Three points were measured at random, and the average value was taken as the transmission yellowness (YI).

(2) Measurement of total light transmittance In accordance with JIS K7105 (1981), the total light transmittance of the reflecting portion was measured using a haze meter (manufactured by Suga Test Instruments: IS-2B). The light incident surface was the surface of the A1 layer. Measurements were made at three locations at random, and the average value was taken as the total light transmittance.

(3) Measurement of average reflectance The average reflectance was measured with a spectrophotometer U-3410 (Hitachi Ltd.) and a φ60 integrating sphere 130-0632 (Hitachi Ltd.) and a 10 ° C. inclined spacer attached. The relative reflectance with respect to the standard white plate was measured in the wavelength range of 400 to 700 nm at intervals of 10 nm, and the average value thereof was calculated. In addition, part number 210-0740 manufactured by Hitachi Sokki Service Co., Ltd. was used as the standard white plate, and three points were randomly measured to calculate an average value, and these average reflectances were adopted. The average reflectance was measured on the A1 layer surface.

(4) Measurement of total thickness of reflection sheet The total thickness of the reflection sheet was measured with a micrometer in accordance with JIS C2151 (2006). In addition, the thickness of each layer is cut in the width direction (TD) without crushing the reflecting sheet in the thickness direction using a microtome to create a section sample, and the section of the obtained section sample is made by Hitachi, Ltd. Using a scanning electron microscope (FE-SEM) model S-2100A, an image was taken at a magnification of 3,000 times, and the thickness of each layer was measured from the image. Measurements were made at three locations at random, and the average value was taken as the layer thickness.

(5) Measurement of centerline average roughness Ra Based on JIS B0601 (1982), the centerline average roughness of the reflecting part was measured using a stylus type surface roughness measuring instrument SE-3400 (manufactured by Kosaka Laboratory Ltd.). Ra was measured. Three places selected at random were measured, and the average value thereof was defined as the centerline average roughness Ra.

<Measurement conditions>
Feeding speed: 0.5mm / s
Evaluation length: 8mm
Cut-off value λc:
When Ra is 20 nm or less, λc = 0.08 mm
When Ra is greater than 20 nm and less than or equal to 100 nm, λc = 0.25 mm
When Ra is greater than 100 nm and less than or equal to 2,000 nm, λc = 0.8 mm
In the measurement under the above measurement conditions, first, measurement is performed with a cutoff value λc = 0.8 mm, and when Ra is larger than 100 nm, Ra is adopted. On the other hand, if Ra is 100 nm or less as a result of the above measurement, the measurement is performed again at λc = 0.25 mm. If Ra is larger than 20 nm, Ra is adopted. On the other hand, if Ra is 20 nm or less as a result of the above re-measurement, the re-measurement is performed at λc = 0.08 mm, and the Ra is adopted.

(6) Measurement of average particle diameter of particles contained in layer A (A1 layer and / or A2 layer) The cross section of the reflection sheet was observed with an electron microscope, and from the cross-sectional photograph, the average of the particles contained in layer A The particle size was calculated. Specifically, the average particle size was calculated by the following measurement.

The reflecting sheet is cut at an arbitrary position, and the cross section is magnified 1,000 to 50,000 times with an SEM (scanning electron microscope (Hitachi scanning electron microscope S-3400N manufactured by Hitachi High-Technologies Corporation)). Observed. The magnification was appropriately adjusted according to the particle size contained in the A layer. From the cross-sectional photograph obtained in this way, 30 particles were randomly selected, each particle size was measured, and the average value of these was taken as the average particle size of the particles.

Here, the particle size of the particle is a square or rectangle that has the smallest area in contact with the particle on the four sides, and the length of one side is adopted for the square, and the length of the long side is adopted for the rectangle. did. By this method, the particle size of each of 30 randomly selected particles was measured, and the number average value was taken as the average particle size of the particles.

In addition, when 30 particles were not observed in one image, another cross-sectional image cut at a different position of the reflection sheet was taken, and the particle size of a total of 30 particles was measured.

The standard of the observation (photographing) magnification according to the particle diameter is as follows.
(A) Magnification 1,000 times Particle size suitable for observation: 5 μm or more and 10 μm or less (b) Magnification 5,000 times Particle size suitable for observation: 1 μm or more and less than 5 μm (c) Magnification 10,000 times Particle size suitable for observation: 500 nm or more and less than 1 μm (d) magnification 20,000 times Particle size suitable for observation: 100 nm or more and less than 500 nm (e) Particle size 50,000 times Particle size suitable for observation : Less than 100 nm.

(7) Sensory evaluation of emission color unevenness in surface light source device Using a simple surface light source device shown in FIG. 5, the light emission color unevenness of light passing through and passing through the reflection sheet (upper reflection sheet) is visually observed, The evaluation was made in four stages (best, good, slightly good, and bad) depending on the degree of unevenness of the emission color. One sample was prepared and the evaluation result was adopted.

<Simple surface light source device>
The simple surface light source device of FIG. 5 has the following configuration. The upper opening surface is a square having a side length (L) of 100 mm and a depth (H) of 20 mm. One LED light source and a lower reflective sheet are disposed at the center of the bottom surface of the casing, and the same reflective sheet as the lower reflective sheet is disposed on the side surface of the casing. An upper reflective sheet is disposed so as to close the upper opening surface.

The reflective film produced in Example 1 was used for the lower reflective sheet and the side reflective sheet. As the upper reflection sheet, each of the reflection sheets prepared in each example was used. In the upper reflection sheet, a circular opening having a diameter of 2 mm is provided in the reflection film in the pattern of FIG. 4 as a transmission part.

The reflective surface of the lower reflective sheet and the side reflective sheet is A layer when the reflective sheet is composed of two layers of A layer and B layer, and A1 when the reflective sheet is composed of three layers of A1, B and A2. It was set as the surface of the layer, and the reflection part of the upper reflective sheet was also set as the surface of the A layer or the A1 layer.

(8) Sensory evaluation of brightness uniformity A simple surface light source device is produced in the same manner as in (7) above, and the brightness of light passing through and passing through the reflective sheet (upper reflective sheet) is the upper aperture surface. It was visually evaluated whether or not the brightness was uniform in the entire area corresponding to (100 mm × 100 mm).
Best: uniform.
Good: Although the brightness of the peripheral part is slightly lower than that of the central part, it is an acceptable level.
Defect: The brightness of the peripheral part is clearly lower than that of the central part.
One sample was prepared and the evaluation result was adopted.

[Example 1]
A reflective film was produced in the following manner, and the reflective sheet of the present invention was produced by providing an opening serving as a transmission part in the reflective film.

This reflective film has a three-layer structure of A1 layer / B layer / A2 layer, and the A1 layer and the A2 layer have the same composition. The thickness of each layer was 8 μm for the A1 layer, 210 μm for the B layer, and 8 μm for the A2 layer.

<Reflection film>
<B layer composition>
Polyethylene terephthalate having a color tone of polyethylene terephthalate after polymerization (measured by JIS K7105 (1981), stimulus value direct reading method) having an L value of 62.8, a b value of 0.5, and a haze of 0.2% is used. 84 parts by mass (hereinafter referred to as addition amount X of polyethylene terephthalate), copolymer of polybutylene terephthalate and polytetramethylene glycol (hereinafter referred to as PTMG) (PBT / PTMG: trade name: Toray Copolymer polyethylene in which 0.5 parts by mass of “Hytrel” (registered trademark) manufactured by DuPont Co., Ltd. and 33 mol% of 1,4-cyclohexanedimethanol (hereinafter referred to as CHDM) is copolymerized with respect to the diol component. 0.5 parts by mass of terephthalate (33 mol% PET / CHDM copolymer), 5 parts by mass of cycloolefin copolymer having a glass transition temperature of 210 ° C. (trade name: “TOPAS” manufactured by Polyplastics Co., Ltd.), master chip containing titanium dioxide (50 mass of titanium dioxide having an average particle size of 0.25 μm) % Polyethylene-containing terephthalate master chip) (hereinafter referred to as addition amount Y) is prepared and mixed, dried at 180 ° C. for 3 hours, and then heated to 270-300 ° C. Feeded to Extruder B.

<Composition of A layer (A1 layer and A2 layer)>
77 parts by mass of polyethylene terephthalate, 3 parts by mass of a silicon dioxide-containing master chip (polyethylene terephthalate master chip containing 1% by mass of silicon dioxide having an average particle diameter of 0.6 μm), and 18 mol% of isophthalic acid were copolymerized with polyethylene terephthalate. 20 parts by mass (hereinafter referred to as “PET / I”) were dried under reduced pressure at 180 ° C. for 3 hours, and then supplied to an extruder A heated to 280 ° C.

<Manufacture of reflective film>
The composition (polymer) of the above B layer and A layer was laminated through a laminating apparatus so as to be A1 layer / B layer / A2 layer, and formed into a sheet form from a T die. Further, the unstretched film obtained by cooling and solidifying the film with a cooling drum having a surface temperature of 25 ° C. was led to a roll group heated to 85 to 98 ° C., stretched 3.4 times in the longitudinal direction, and cooled with a roll group at 21 ° C. Subsequently, the film stretched in the longitudinal direction was guided to a tenter while being gripped by clips, and was stretched by 3.6 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Thereafter, heat setting at 190 ° C. is performed in a tenter, followed by a relaxation treatment of 6% in the width direction at the same temperature, and then uniformly cooled, cooled to room temperature, and biaxially stretched (reflective film) ) Then, after standing at 25 ° C. for 24 hours, heat treatment was performed in an oven at 150 ° C. for 20 seconds.

<Production of reflection sheet>
In the reflective film produced above, a large number of circular openings (circular through-holes having a diameter of 2 mm) were provided with transmission portions in the pattern shown in FIG. The transmission part was formed by providing a through hole by punching.

[Examples 2 to 4, 6 to 7]
A reflective film was produced in the same manner as in Example 1 except that the B layer composition was changed as follows, and a reflective sheet was produced in the same manner as in Example 1.

<B layer composition>
Reflective films having the transmission yellowness (YI) shown in Table 1 were prepared with the addition amount Y of the titanium dioxide-containing master chip in the B layer composition as shown in Table 1. The B layer composition other than the above is the same as in Example 1.

In addition, the addition amount X of polyethylene terephthalate in the B layer composition was adjusted such that the total amount with the addition amount Y of the titanium dioxide-containing master chip was 94 parts by mass.

[Example 5]
A reflective film was produced in the same manner as in Example 3 except that the A layer composition was changed as follows, and a reflective sheet was produced in the same manner as in Example 3.

<Composition of A layer (A1 layer and A2 layer)>
72 parts by mass of polyethylene terephthalate, 8 parts by mass of a silicon dioxide-containing master chip (polyethylene terephthalate master chip containing 1% by mass of silicon dioxide having an average particle diameter of 1.2 μm), and 18 mol% of isophthalic acid were copolymerized with polyethylene terephthalate. 20 parts by mass (PET / I) was dried under reduced pressure at 180 ° C. for 3 hours, and then supplied to Extruder A heated to 280 ° C.

[Example 8]
A reflective film was produced in the same manner as in Example 6 except that the composition of layer A was changed as follows, and a reflective sheet was produced in the same manner as in Example 6.

<Composition of A layer (A1 layer and A2 layer)>
65 parts by mass of polyethylene terephthalate, 15 parts by mass of a silicon dioxide-containing master chip (polyethylene terephthalate master chip containing 6% by mass of silicon dioxide having an average particle diameter of 3.5 μm), and 18 mol% of isophthalic acid were copolymerized with polyethylene terephthalate. 20 parts by mass (PET / I) was dried under reduced pressure at 180 ° C. for 3 hours, and then supplied to Extruder A heated to 280 ° C.

[Evaluation]
The above-described measurements and evaluations were performed on the reflective sheets prepared in the above examples. The results are shown in Table 1. In each of the examples, the reflective sheet included in the present invention has little uneven emission color. Also, the uniformity of brightness is good.

DESCRIPTION OF SYMBOLS 1 Light source 2 Lower reflection sheet 3 Upper reflection sheet 4 Side reflection sheet 5 Casing 6 Reflection part of upper reflection sheet 7 Transmission part of upper reflection sheet 10 Area | region located just above the light source 1 of the upper reflection sheet 11 Surface light source device

Claims

A reflection sheet disposed opposite to a light source of a surface light source device, the reflection sheet having a reflection part that reflects light from the light source and a transmission part that transmits light from the light source, and is transmitted through the reflection part. A reflective sheet having a yellowness (YI) of 30 or less.
The reflection sheet according to claim 1, wherein the transmission part is a through hole.
The reflecting sheet according to claim 1 or 2, wherein the total light transmittance of the reflecting portion is 0.5 to 10%.
The reflecting sheet according to any one of claims 1 to 3, wherein the center line average roughness Ra of the reflecting portion is 100 nm or less.
The said reflective sheet provides a transmission part in the reflective film by which the layer (A layer) for supporting the said B layer was laminated | stacked on both surfaces of the layer (B layer) which contains a bubble inside. 5. The reflection sheet according to any one of 1 to 4.
The reflective sheet according to claim 5, wherein the A layer contains particles.
A unit for a surface light source device, comprising: a lower reflective sheet that reflects light; and an upper reflective sheet that is opposed to the lower reflective sheet and that is the reflective sheet according to any one of claims 1 to 6.
A surface light source device having a light source, a lower reflective sheet for reflecting light, and an upper reflective sheet as a reflective sheet according to any one of claims 1 to 6, wherein the lower reflective sheet exists on the rear surface of the light source, A surface light source device in which an upper reflective sheet exists opposite to the reflective sheet.