JP2011070145A - Light reflector and surface light source apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light reflector that can fully suppress occurrence of unevenness of luminance even when the light reflector is incorporated in a surface light source apparatus in which the number of cold cathode lamps to be used is reduced. <P>SOLUTION: The light reflector has, as an outermost layer, a gloss adjusting layer 1, which contains a thermoplastic resin and 5 to 60 wt.% of a filler having an average particle diameter of 2 to 20 μm, is at least uniaxially extended, and has a thickness of 2 to 20 μm. 45° glossiness is 10 to 80%, and (45° glossiness)/(85° glossiness) is 2 to 25. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light reflector useful as a light reflecting member used in a reflector, a reflector and various lighting fixtures used in a surface light source device, and a surface light source device using the light reflector. .

  Backlight type liquid crystal displays with built-in light sources are widely used. A typical configuration of a direct type backlight that is most frequently used in a backlight type built-in light source, such as a liquid crystal TV, is as shown in FIG. 2, and includes a light reflector 11, a diffusion plate 12, and a cold cathode lamp. 13 and forms a uniform plane light with a diffusion plate. Such a direct type backlight has a problem that the luminance is high in the vicinity of the cold cathode lamp that is a light source, and the luminance is low at a position that is not so, resulting in luminance unevenness.

In order to solve such problems, it has been proposed to use a white polyester film (for example, see Patent Documents 1 to 3) subjected to surface coating for improving luminance unevenness as a light reflector. However, such a white polyester film has another problem of yellowing while being used for a long time.
On the other hand, a white polyolefin film (see, for example, Patent Documents 4 to 6) has been proposed as a light reflector that has little yellowing even when used for a long time. Although the luminance can be improved by using these light reflectors, these documents do not describe how to deal with luminance unevenness.

JP 2005-148515 A JP 2005-173546 A JP 2006-072347 A JP-A-8-262208 International Publication WO03 / 014778 JP 2006-195453 A

In recent years, backlights, particularly direct type backlights such as liquid crystal TVs, tend to reduce the number of cold cathode lamps in the backlight for energy saving and cost reduction. In this manner, the direct type backlight with a small number of cold cathode lamps used has a longer distance between the cold cathode lamps (light sources) than the conventional direct type backlight. Therefore, the space between the cold cathode lamps becomes darker than before, and the bright lines tend to be conspicuous in the vicinity of the cold cathode lamps. Such relatively large luminance unevenness cannot be sufficiently reduced by the above-described white polyester film and white polyolefin film proposed previously. Therefore, it is necessary to develop a light reflector that has a high luminance unevenness suppressing effect even when the number of cold cathode lamps used in the backlight is reduced.
An object of the present invention is to provide a light reflector that can sufficiently suppress the occurrence of uneven brightness even when incorporated in a surface light source device in which the number of cold cathode lamps used is reduced.

  As a result of intensive studies, the inventors of the present invention have made dramatic progress in luminance unevenness by adjusting the directivity of light incident at an acute angle with respect to the film reflecting surface and decreasing the directivity of light incident at an obtuse angle. It was found that it can be improved. Specifically, by giving a specific surface shape in a stretched film made of a thermoplastic resin, the 45 ° gloss and the gloss ratio described by the following formula (1) are in a specific range, respectively. By giving this, the present invention has been completed.

That is, as a means for solving the problems, the present invention having the following configuration has been provided.
[1] A light reflector including a thermoplastic resin (i) having a thickness of 2 to 20 μm and an at least uniaxially stretched gloss adjusting layer as an outermost layer, the gloss adjusting layer having an average particle diameter 2 to 20 μm of filler (ii) is contained in an amount of 5 to 60% by weight, the gloss adjustment layer surface has a 45 ° gloss of 10 to 80%, and a gloss ratio represented by the following formula (1): 2 to 25 light reflectors.
[2] The light reflector according to [1], wherein an average inclination Δa of the surface of the gloss adjusting layer is 0.02 to 0.2.
[3] The light reflector according to [1] or [2], wherein the gloss adjusting layer is stretched at a temperature higher than the melting point of the thermoplastic resin (i).
[4] The light reflector according to any one of [1] to [3], wherein the thermoplastic resin (i) mainly includes a polyolefin resin having a melting point of less than 160 ° C.
[5] The light reflector according to any one of [1] to [4], wherein the gloss adjusting layer contains 10 to 40% by weight of filler (ii) having an average particle diameter of 2 to 20 μm.
[6] [1] to [5], comprising a laminate including a thermoplastic resin (iii) and a filler (iv) and including at least a uniaxially stretched base material layer and the gloss adjusting layer. ] The light reflector as described in any one of.
[7] The light reflector according to [6], wherein the thermoplastic resin (iii) mainly contains a polyolefin resin having at least one of a melting point and a glass transition point of 160 ° C. or higher.
[8] As the filler (iv) in the base material layer, at least one of an inorganic filler having an average particle diameter of 0.05 to 1.5 μm and an organic filler having an average dispersed particle diameter of 0.05 to 1.8 μm is 5 The light reflector according to [6] or [7], which is contained in an amount of ˜75% by weight.

[9] The light reflector according to any one of [6] to [8], wherein the substrate layer has a reflectance of 90% or more.
[10] The laminate including the gloss adjusting layer and the base material layer is higher than the melting point of the thermoplastic resin (i) after laminating both layers, and the melting point and glass transition of the thermoplastic resin (iii). The light reflector according to any one of [6] to [9], wherein the light reflector is stretched at a temperature lower than at least one of the points.
[11] Any one of [6] to [10], wherein the gloss adjusting layer has a porosity of 0 to 4% and the base material layer has a porosity of 15 to 75%. The light reflector as described in.
[12] The light reflector according to any one of [1] to [11], wherein the density is 0.3 to 1.2 g / cm ³ .
[13] Represented by the following formula (2) before and after irradiating with ultraviolet light having an irradiation intensity of 90 mW / cm ² from a metal halide lamp installed at a position 10 cm away at 83 ° C. and 50% relative humidity. The light reflector according to any one of [1] to [12], wherein the color difference ΔE _H is 0 to 10.
ΔE _H = [(L ₀ −L ₁ ) ² + (a ₀ −a ₁ ) ² + (b ₀ −b ₁ ) ² ] ^0.5 Equation (2)
(In the formula (2), L ₀ , a ₀ , and b ₀ are the lightness indexes in the color space of the L _* a _* b _* color system before irradiation, and L ₁ , a ₁ , and b ₁ are the values after irradiation, respectively. L _* and chromaticness index a _* , b _* )
[14] A surface light source device using the light reflector according to any one of [1] to [13].

  When the light reflector of the present invention is incorporated in a surface light source device, the occurrence of uneven brightness can be sufficiently suppressed. In addition, since the surface light source device of the present invention has small luminance unevenness, generation of bright lines is suppressed.

It is the schematic of the structure of the light reflector of this invention. It is the schematic of the cross section of the structure of a direct type | mold backlight. It is the schematic of the cross section of the structure of a sidelight type backlight. It is a schematic diagram which shows the brightness nonuniformity between the cold cathode lamps of a direct type backlight. It is a schematic diagram showing a method for eliminating luminance unevenness between cold cathode lamps in a direct backlight using the light reflector of the present invention. It is the schematic of the brightness nonuniformity when the direct type | mold backlight using the light reflector of Example 1 of this invention is seen from a diffuser plate direction. It is the schematic of the brightness nonuniformity when the direct type | mold backlight using the light reflection body of the comparative example 1 is seen from the diffusion plate direction. It is an example of measurement of surface roughness.

  Below, the structure and effect of the light reflector of this invention are demonstrated in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present invention, “to” means a range including numerical values described before and after that as a minimum value and a maximum value, respectively. Further, in the present specification, “mainly includes” means that it contains 50% by weight or more of the whole, preferably 70% by weight or more, more preferably 90% by weight or more, and 100% by weight. Is most preferred.

[Light reflector]
(1) Features of the structure of the light reflector The light reflector of the present invention comprises a thermoplastic resin (i) and a filler (ii), has a thickness of 2 to 20 μm, and is at least uniaxially stretched. As the outermost layer. The average particle size of the filler contained in the gloss adjusting layer is 2 to 20 μm, and its content is 5 to 60% by weight. And 45 degree glossiness of the glossiness adjustment layer surface of the light reflection body of this invention is 10 to 80%, and the glossiness ratio represented by said Formula (1) is 2-25.
Hereinafter, the present invention will be specifically described with reference to preferred embodiments of the light reflector of the present invention.

(2) Gloss control layer The gloss control layer contains a thermoplastic resin (i) and a filler (ii) having an average particle diameter of 2 to 20 μm. The gloss adjusting layer is a stretched resin film stretched at least uniaxially, and has a function of adjusting the gloss by forming the outermost layer of the light reflector and preventing bright lines. Specifically, the average inclination Δa of the surface of the gloss adjusting layer is adjusted to a range of 0.02 to 0.2 by a protrusion having the filler (ii) as a core, and the protrusion has a 45 ° gloss and 85 ° gloss. Adjust the degree.

<Thermoplastic resin (i)>
The type of the thermoplastic resin (i) used for the gloss adjusting layer is not particularly limited. Examples of the thermoplastic resin (i) that can be used in the gloss adjusting layer include ethylene resins such as high-density polyethylene, medium-density polyethylene, and low-density polyethylene; propylene-based resins, polymethyl-1-pentene, and ethylene-cyclic olefins. Polyolefin resins such as copolymers; Polyamide resins such as nylon-6, nylon-6,6, nylon-6,10, nylon-6,12; polyethylene terephthalate and copolymers thereof, polyethylene naphthalate, aliphatic Examples include thermoplastic polyester resins such as polyester; thermoplastic resins such as polycarbonate, atactic polystyrene, syndiotactic polystyrene, and polyphenylene sulfide. These may be used in combination of two or more.
Among these, it is preferable to use a polyolefin resin from the viewpoint of little yellowing during use, chemical resistance, production cost, and the like, and among these, it is more preferable to use a propylene resin.

Examples of the propylene-based resin include propylene homopolymer, co-polymerization of main component propylene and α-olefin such as ethylene, 1-butene, 1-hexene, 1-heptene, and 4-methyl-1-pentene. Coalescence can be used. The stereoregularity of the propylene-based resin is not particularly limited, and isotactic or syndiotactic and those showing various degrees of stereoregularity can be used. When the propylene resin is a copolymer, it may be a binary system, a ternary system, or a quaternary system, and may be a random copolymer or a block copolymer. Among these, it is preferable to use a polyolefin resin having a melting point (DSC peak temperature) of less than 160 ° C., and specifically, it is particularly preferable to use a multi-component random copolymer mainly containing propylene.
The total amount of the thermoplastic resin (i) in the gloss adjusting layer is in the range of 40 to 95% by weight, preferably 50 to 95% by weight, more preferably 55 to 90% by weight, and still more preferably 60 to It is in the range of 90% by weight.

<Filler (ii)>
In the gloss adjusting layer, filler (ii) is used together with the thermoplastic resin (i). Examples of the filler (ii) used for the gloss adjusting layer include various inorganic fillers and organic fillers.
Examples of the inorganic filler include heavy calcium carbonate, precipitated calcium carbonate, calcined clay, talc, titanium oxide, barium sulfate, aluminum sulfate, silica, zinc oxide, magnesium oxide, diatomaceous earth, and the like. Moreover, the surface treatment goods by the various surface treating agent of the said inorganic filler can also be illustrated. Among them, it is preferable to use heavy calcium carbonate, precipitated calcium carbonate and their surface-treated products, clay, and diatomaceous earth because they are inexpensive and have good pore forming properties during stretching. Further preferred are surface treated products with various surface treatment agents of heavy calcium carbonate and precipitated calcium carbonate.

  Examples of the surface treatment agent include resin acids, fatty acids, organic acids, sulfate ester type anionic surfactants, sulfonic acid type anionic surfactants, petroleum resin acids, salts thereof such as sodium, potassium, and ammonium, or These fatty acid esters, resin acid esters, waxes, paraffins, and the like are preferable, and nonionic surfactants, diene polymers, titanate coupling agents, silane coupling agents, phosphoric acid coupling agents, and the like are also preferable. Examples of the sulfate ester type anionic surfactant include long chain alcohol sulfate ester, polyoxyethylene alkyl ether sulfate ester, sulfated oil and the like, or salts thereof such as sodium and potassium. Examples of the activator include alkylbenzene sulfonic acid, alkyl naphthalene sulfonic acid, paraffin sulfonic acid, α-olefin sulfonic acid, alkyl sulfosuccinic acid and the like, and salts thereof such as sodium and potassium. Examples of the fatty acid include caproic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, hebenic acid, oleic acid, linoleic acid, linolenic acid, eleostearic acid. An acid etc. are mentioned. Examples of the organic acid include maleic acid and sorbic acid. Examples of the diene polymer include polybutadiene and isoprene. Examples of the nonionic surfactant include a polyethylene glycol ester type surfactant. These surface treatment agents can be used alone or in combination of two or more. Examples of the surface treatment method of the inorganic filler using these surface treatment agents include, for example, JP-A-5-43815, JP-A-5-139728, JP-A-7-300568, and JP-A-10-176079. JP-A-11-256144, JP-A-11-349846, JP-A-2001-158863, JP-A-2002-220547, JP-A-2002-363443, etc. can be used.

  As said organic filler, the organic filler (for example, 120-300 degreeC) whose melting | fusing point or glass transition point is higher than melting | fusing point or glass transition point of the said thermoplastic resin is used preferably. For example, polyethylene terephthalate, polybutylene terephthalate, polyamide, polycarbonate, polyethylene naphthalate, polystyrene, melamine resin, cyclic olefin homopolymer, copolymer of cyclic olefin and ethylene, polyethylene sulfide, polyimide, polyethyl ether ketone, polyphenylene sulfide, An acrylic resin etc. can be illustrated. Especially, it is preferable from a viewpoint of forming the processus | protrusion which made a filler the core to use an incompatible organic filler with respect to the polyolefin resin preferably used as the said thermoplastic resin.

  In the gloss adjusting layer, it is preferable to use an inorganic filler or an organic filler capable of satisfying a particle size in a preferable range described later as the filler (ii). Silica, alumina, magnesium oxide, zinc oxide, precipitated carbonic acid More preferably, calcium, acrylic resin or the like is used. It is particularly preferable to use precipitated calcium carbonate or crosslinked acrylic beads from the viewpoint of adjusting gloss.

  For the gloss adjusting layer, one kind selected from inorganic fillers or organic fillers may be used alone, or two or more kinds selected may be used in combination. When using combining 2 or more types, you may mix and use an organic filler and an inorganic filler.

  The filler (ii) used for the gloss adjusting layer has an average particle diameter and an average dispersed particle diameter of 2 to 20 μm. The particle diameter is preferably 2 to 15 μm, more preferably 3 to 10 μm, further preferably 3 to 8 μm, and particularly preferably 4 to 7 μm. When the filler has a particle size of 2 μm or more, the directivity of light incident at an obtuse angle with respect to the reflecting surface in the regular reflection direction is reduced and can be appropriately diffused, so that occurrence of luminance unevenness can be suppressed. When the average particle size of the filler is 20 μm or less, it is difficult to cause surface defects and the appearance of the resulting gloss adjusting layer and light reflector is good.

  The average particle diameter of the inorganic filler and the average dispersed particle diameter of the organic filler are, for example, the observation of the primary particle diameter by a microtrack method or a scanning electron microscope (in the present invention, the average value of 100 particles is defined as the average particle diameter). ), Conversion from the specific surface area (in the present invention, the specific surface area was measured using a powder specific surface area measuring device SS-100 manufactured by Shimadzu Corporation), and the like.

  The blending amount of the filler (ii) in the gloss adjusting layer is in the range of 5 to 60% by weight as a total amount, preferably 5 to 50% by weight, more preferably 10 to 45% by weight, and still more preferably 10 to 10% by weight. It is in the range of 40% by weight. If the blending amount is 5% by weight or more, it is easy to form a protrusion with a filler as a core in the gloss adjustment layer, and light incident at an obtuse angle with respect to the reflection surface is diffusely reflected by the protrusion to reduce the directivity of reflection. By doing so, the gloss does not become too high, and the occurrence of luminance unevenness tends to be suppressed. When the blending amount is 60% by weight or less, the directivity of light incident at an acute angle with respect to the reflecting surface is increased, and the occurrence of uneven brightness tends to be suppressed. Moreover, it is also preferable in that the surface strength can be easily maintained.

When the gloss adjusting layer is used by selecting two or more fillers in combination, the filler having an average particle size of less than 2 μm is constant as long as the particle size obtained from the above observation and conversion satisfies the characteristics of the present invention. An amount may be included. Examples of the filler having an average particle size of less than 2 μm that may be included in the gloss adjusting layer include titanium oxide having an average particle size of about 0.2 μm. It is preferable to contain titanium oxide from the viewpoint of improving durability due to long-term use of the light reflector.
The filler having an average particle size of less than 2 μm which may be contained in the gloss adjusting layer may be contained in an amount of 0.1 to 10% by weight, more preferably 0.2 to 7% by weight, based on the gloss adjusting layer. Particularly preferably, it may be contained in the range of 0.5 to 4% by weight.

<Additives>
If necessary, the gloss adjusting layer of the present invention may contain additives such as a fluorescent brightening agent, a stabilizer (antioxidant), a light stabilizer, a dispersant, and a lubricant. As the stabilizer, 0.001 to 1% by weight of a sterically hindered phenol type, phosphorus type, amine type or the like, and as the light stabilizer, a sterically hindered amine, benzotriazole type, benzophenone type or the like is 0.001 to 1%. As the dispersant for the inorganic filler, 0.01 to 4% by weight of a silane coupling agent, a higher fatty acid such as oleic acid or stearic acid, metal soap, polyacrylic acid, polymethacrylic acid or a salt thereof, etc. You may mix | blend.

<Method for producing gloss adjusting layer>
The method for producing the gloss adjusting layer of the present invention preferably includes biaxial stretching in which longitudinal stretching and lateral stretching are performed, including a stretching process in at least one direction. When stretching the gloss adjusting layer, it is also preferable to stretch a base material layer and an intermediate layer described later together. In the present specification, longitudinal stretching refers to stretching in the MD (machine direction) direction, and lateral stretching refers to stretching in a direction orthogonal to the MD direction.

  In the stretching step, a general uniaxial stretching method or biaxial stretching method can be used. As a specific example, a single layer or multi-layer T die or I die connected to a screw type extruder is used to extrude the molten resin into a sheet shape, and then uniaxially by longitudinal stretching utilizing the peripheral speed difference of the roll group. Examples of the stretching method include a biaxial stretching method in which transverse stretching using a tenter oven is combined, and a simultaneous biaxial stretching method in which a tenter oven and a linear motor are combined.

  The stretching temperature in the stretching step is preferably higher than the melting point of the thermoplastic resin. By stretching at the same temperature, it becomes easier to form surface irregularities (protrusions) having the following optical characteristics without forming pores and surface openings with fillers as nuclei on the surface of the gloss adjusting layer, The directivity of light incident at an obtuse angle with respect to the reflecting surface can be reduced, and the occurrence of uneven brightness can be suppressed.

<Thickness>
The thickness of the gloss adjusting layer of the light reflector of the present invention is the thickest of the same layer calculated from the observed thickness and magnification by observing 50 different points from the cross-sectional photograph of the light reflector by a scanning electron microscope. The part was made into the thickness of the gloss adjusting layer.
The thickness of the gloss adjusting layer is in the range of 2 to 20 μm, and the thickness is preferably 2 to 15 μm, more preferably 2 to 6 μm. If it is 2 μm or more, a filler having a sufficiently large average particle diameter can be blended in the gloss adjusting layer, and the occurrence of luminance unevenness can be easily suppressed without the filler falling off. If it is 20 μm or less, surface irregularities (protrusions) due to the filler blended in the gloss adjustment layer are likely to be attached, the directivity of light incident at an obtuse angle on the reflecting surface can be reduced, and unevenness in luminance is suppressed. it can.
The thickness of the gloss adjusting layer is preferably 1 to 6 times the average particle size of the filler contained in the gloss adjusting layer, more preferably 1 to 3 times, and 1 to 1.5 times. Is more preferable. If the thickness of the gloss adjusting layer is 6 times or less the average particle diameter of the filler, it is preferable in that a predetermined gloss ratio can be easily obtained. Further, according to the thickness measuring method described above, the thickness of the gloss adjusting layer is equal to or greater than the average particle diameter of the filler, so the lower limit is 1 time.

<Average slope Δa>
The average slope Δa of the surface of the gloss adjusting layer of the light reflector of the present invention is measured with a three-dimensional roughness meter (manufactured by Kosaka Laboratory Ltd .: SPA-11). The value obtained from the measurement data by the following equation (3).
In the above equation, h ₁ , h ₂ , h ₃ ... H _n are the height differences between adjacent concavo-convex parts, and L is the measurement length (FIG. 8).
The average inclination Δa represents the shape characteristics such as the size and frequency of the convex structure on the surface of the gloss adjusting layer of the light reflector. The smaller the numerical value, the less frequent the convex structure, and the larger the frequency, the more frequent the convex structure. It shows that.
In the present invention, the specific surface shape is such that the gloss adjusting layer as the outermost layer contains the thermoplastic resin (i) and the filler (ii) having an average particle diameter of 2 to 20 μm in an amount of 5 to 60% by weight and is at least uniaxially stretched. This is achieved by forming a protrusion having a thickness of 2 to 20 μm, in which the filler (ii) is coated with the thermoplastic resin (i).
The average inclination Δa of the surface of the gloss adjusting layer of the light reflector of the present invention is preferably 0.02 to 0.2. The equivalence is more preferably 0.03 to 0.15, further preferably 0.04 to 0.1, and particularly preferably 0.04 to 0.06. If the same value is in the range of 0.02 to 0.2, the 45 ° glossiness and glossiness ratio defined in the claims can be obtained, and unevenness in brightness is easily improved when incorporated in a surface light source device. .

<Glossiness>
The 45 ° glossiness of the light reflector of the present invention is determined according to the method described in Method 4 of JIS-Z8741 using a digital variable glossiness meter (manufactured by Suga Test Instruments Co., Ltd .: UGV-5DP). It is a value obtained by measuring the specular gloss at °. The 45 ° glossiness is for observing the reflection of light incident at an acute angle with respect to the reflecting surface, and the 45 ° glossiness of the light reflector of the present invention is 10 to 80%. The equivalent value is preferably 15 to 70%, more preferably 20 to 50%, and further preferably 21 to 45%. If the value is 10% or more, the directivity of light incident at an acute angle with respect to the reflecting surface is sufficiently high, and the occurrence of uneven brightness can be suppressed. Further, if the 45 ° glossiness is 80% or less, the effect of diffuse reflection is also given, and it is possible to suppress the occurrence of uneven brightness (due to specular reflection) due to the deflection of the light reflector.

  When a conventional light reflector is incorporated in a surface light source device as shown in FIG. 2, the direct light from the light source (for example, the cold cathode lamp 13) is gradually attenuated according to the distance from the light source. , A dark portion 15 is generated at a location away from the light source (FIG. 4). Therefore, the bright line 14 is generated in the vicinity of the light source, and luminance unevenness occurs. On the other hand, the light reflector according to the present invention diffuses incident light having an obtuse angle to a certain extent out of obliquely incident light, and can regularly reflect incident light having an acute angle to some extent. Therefore, when the light reflector of the present invention is incorporated in a surface light source device as shown in FIG. 2, the reflected light reflected by the light reflector 11 of the present invention from the light source (for example, the cold cathode lamp 13) is shown in FIG. The reflected light 16 to 18 of 30 to 50 degrees is controlled so that the directivity in the regular reflection direction is increased, and reflected light at other angles (for example, reflected light 19 of 60 degrees and reflected light 20 of 70 degrees). ) Is irregularly reflected, so that directivity in the regular reflection direction is controlled to be low. As a result, the reflected light to the diffusing plate dark part 15 generated by the direct light from the cold cathode lamp 13 shown in FIG. 4 can be condensed, and conversely, the reflected light can be prevented from collecting to the diffusing plate bright line part 14. That is, luminance unevenness due to direct light can be eliminated. Such a principle of the present invention is different from the conventional method of increasing the directivity of reflected light with respect to all incident angles and increasing the luminance of the entire light diffusion plate to make the luminance unevenness inconspicuous.

  The 85 ° glossiness of the light reflector of the present invention is a value obtained by measuring the specular glossiness at an incident angle of 85 ° using a handy 85 ° gloss meter (manufactured by DR LANGGE: LMG063). The 85 ° glossiness is for observing the reflection of light incident at an obtuse angle with respect to the reflecting surface, and the 85 ° glossiness of the light reflector of the present invention is preferably 1 to 40%. The equivalence is more preferably 1 to 30%, further preferably 1 to 15%, still more preferably 1 to 10%, and particularly preferably 1 to 6%. The lower the value, the better. However, if it is 1% or more, the measurement accuracy is reliable. If the value is 40% or less, the directivity of light incident at an obtuse angle with respect to the reflecting surface is sufficiently low, and it is easy to suppress the occurrence of luminance unevenness.

<Gloss ratio>
The light reflector of the present invention has a gloss ratio in the range of 2 to 25 calculated by the formula (1) from the 45 ° glossiness and 85 ° glossiness measured above. The equivalence is preferably in the range of 4-20, more preferably in the range of 5.5-18. If the gloss ratio is 2 or more, the directivity of light incident at an obtuse angle with respect to the reflecting surface does not become too high, and the occurrence of uneven brightness can be suppressed. When the gloss ratio is 25 or less, in the direct type backlight, the portion directly above the cold cathode lamp becomes sufficiently bright, and the occurrence of luminance unevenness can be suppressed. The gloss ratio can be controlled by adjusting the thickness of the gloss adjusting layer, the average particle size of the filler, the filler content, and the like. For example, the thickness of the gloss adjusting layer can be increased while using a filler having a certain average particle diameter (for example, 4 μm or more) or using a filler having a relatively small average particle diameter (for example, 3 μm or less) in an amount of 60% by weight or less. The glossiness ratio can be adjusted within the range of the present invention by adjusting it to the same level as the filler average particle size.

(3) Base Material Layer The light reflector of the present invention is preferably composed of a laminate formed by laminating the gloss adjusting layer as an outermost layer on at least one surface (light reflection surface) of the base material layer.
The base material layer in the light reflector of the present invention is a layer having a large number of minute voids inside, and the incident light is effectively reflected to the incident surface side by the holes to achieve a high reflectance of the light reflector. In addition, when the gloss adjusting layer is stretch-molded, it has a role of assisting stable and uniform stretching as a support.

Therefore, the base material layer is also preferably a stretched resin film including a thermoplastic resin and a filler and stretched at least uniaxially, like the gloss adjusting layer. However, unlike the gloss adjustment layer, the base material layer preferably has a large number of fine pores having a uniform shape inside, so that the filler in the base material layer has an average particle size of 0.05. It is preferable that at least one of the inorganic filler of ˜1.5 μm and the organic filler having an average dispersed particle size of 0.05 to 1.8 μm is included in an amount of 5 to 75% by weight.
Further, in the laminate, in order to form pores selectively in the base material layer without forming almost pores in the gloss adjusting layer, after the lamination of both layers, the thermoplastic resin (i It is efficient to obtain a light reflector by stretching at a temperature higher than the melting point of the thermoplastic resin (iii) of the base material layer and lower than at least one of the melting point and the glass transition point. For that purpose, it is preferable to use the thermoplastic resin used for the gloss adjusting layer and the thermoplastic resin used for the base material layer which have different melting points or glass transition points.

<Thermoplastic resin (iii)>
The kind of thermoplastic resin (iii) used for the base material layer is not particularly limited. As the thermoplastic resin (iii) that can be used for the base material layer, the same ones as exemplified in the above-mentioned thermoplastic resin (i) can be used. Among these, it is preferable to use a polyolefin resin from the viewpoint of little yellowing during use, chemical resistance, production cost, and the like, and among these, it is more preferable to use a propylene resin.
Examples of the propylene-based resin include propylene homopolymer, co-polymerization of main component propylene and α-olefin such as ethylene, 1-butene, 1-hexene, 1-heptene, and 4-methyl-1-pentene. Coalescence can be used. The stereoregularity of the propylene-based resin is not particularly limited, and isotactic or syndiotactic and those showing various degrees of stereoregularity can be used. When the propylene resin is a copolymer copolymer, it may be a binary system, a ternary system, or a quaternary system, and may be a random copolymer or a block copolymer. Among these, it is preferable to use a polyolefin resin having at least one of a melting point (DSC peak temperature) and a glass transition point of 160 ° C. or more, and specifically, it is particularly preferable to use a propylene homopolymer.

  Such a thermoplastic resin is preferably used in the base layer at 25 to 95% by weight, more preferably 30 to 90% by weight, and further preferably 40 to 85% by weight. If the content of the thermoplastic resin in the base material layer is 25% by weight or more, there is a tendency that scratches are not easily generated on the surface during stretch molding of the laminated film to be described later. Tends to be obtained.

  When the main resin constituting the base material layer is a propylene-based resin, a resin having a lower melting point than that of a propylene-based resin such as polyethylene or ethylene vinyl acetate is used for the entire base material layer in order to improve stretchability. You may mix | blend 3 to 25 weight%.

<Filler (iv)>
A filler is used for the base material layer together with the thermoplastic resin (iii). As the filler (iv) used for the base material layer, the same fillers as those exemplified above for the filler (ii) can be used. Among these, it is preferable to use precipitated calcium carbonate. When using an organic filler, an organic filler having a melting point or a glass transition point higher than that of the polyolefin resin preferably used as the thermoplastic resin (iii) and incompatible with the polyolefin resin is used. This is desirable from the viewpoint of preferably forming pores in the base material layer.

  In the base material layer, the average particle diameter of the inorganic filler added to the base material layer is preferably in the range of 0.05 to 1.5 μm for the adjustment of the pore size generated by stretch molding described in detail later. More preferably, it is the range of 0.1-1 micrometer, The average dispersed particle diameter of the said organic filler becomes like this. Preferably it is the range of 0.05-1.8 micrometer, More preferably, it is the range of 0.1-1.5 micrometer. These may be used alone or in combination. If an inorganic filler having an average particle size of 1.5 μm or less or an organic filler having an average dispersed particle size of 1.8 μm or less is used, it becomes easy to form fine pores, and the surface light source device using the light reflector of the present invention The brightness tends to increase. Moreover, if a filler having an average particle diameter or an average dispersed particle diameter of 0.05 μm or more is used, holes are easily obtained, and the luminance of the surface light source device using the light reflector of the present invention tends to be high.

  The filler added to the base material layer is preferably used at a concentration of 5 to 75% by weight in the base material layer in order to adjust the amount of pores generated by stretch molding of the laminate described in detail later. More preferably, it is used at a concentration of 10 to 70% by weight, and more preferably 15 to 60% by weight. If the content of the filler in the base material layer is 5% by weight or more, a sufficient number of pores tends to be obtained, and if it is 75% by weight or less, the surface tends to be hardly scratched.

<Thickness>
The thickness of the base material layer of the light reflector of the present invention was calculated by the same method as that for the gloss adjusting layer. The thickness of the base material layer is preferably 30 to 1000 μm, more preferably 40 to 400 μm, and further preferably 50 to 300 μm. The base material layer may have a single layer structure or a multilayer structure.

(4) Intermediate layer The light reflector of the present invention may be provided with an intermediate layer in addition to the gloss adjusting layer for adjusting the glossiness according to the incident angle of the incident light and the base material layer for ensuring the reflectance. . For example, the intermediate layer is provided for the purpose of imparting other performances such as strength, rigidity, and dimensional stability of the light reflector.

  For the intermediate layer, the same thermoplastic resin as that used for the base material layer can be used. The intermediate layer may contain a filler, and the amount of the filler contained in the intermediate layer is 0 to 60% by weight, preferably 0 to 40% by weight, more preferably 0 to 20% by weight, particularly Preferably it is the range of 0-10 weight%. The said filler can also use the thing similar to what is used for a base material layer.

  The thickness of the intermediate layer is preferably 1 μm or more, more preferably 2 to 30 μm, and further preferably 3 to 20 μm. By setting the thickness to 1 μm or more, the surface strength of the light reflector is improved, and the processability is improved.

(5) Layer Configuration of Light Reflector The light reflector of the present invention preferably includes the gloss adjusting layer and the base material layer.
Moreover, you may have the structure where another layer was laminated | stacked. Specifically, it may have a structure in which a gloss adjusting layer is laminated on both surfaces of the base material layer. Moreover, you may have an intermediate | middle layer between the surface side opposite to the surface which contact | connects the glossiness adjustment layer of a base material layer, or between a base material layer and a glossiness adjustment layer.
That is, as a preferable layer configuration of the light reflector of the present invention,
Gloss adjustment layer / base material layer (see FIG. 1 (a))
Gloss control layer / base material layer / gloss control layer Gloss control layer / base material layer / intermediate layer Gloss control layer / intermediate layer / base material layer (see FIG. 1B)
Gloss control layer / intermediate layer / base material layer / gloss control layer A light reflector having a structure such as gloss control layer / intermediate layer / base material layer / intermediate layer / gloss control layer can be exemplified. In addition, when the left side is installed in a surface light source device, the lamination | stacking aspect in this specification represents the layer of the side used as a light reflection surface, and the right side represents the layer of the side which does not become a reflection surface. That is, if the light reflector has a configuration of gloss adjusting layer / base material layer / intermediate layer, it represents that the gloss adjusting layer becomes a reflecting surface.

(6) Manufacturing method of light reflector The light reflector of this invention can contain the said base material layer. Each layer can be obtained by melt-kneading the composition for an individual layer using an extruder, extruding the melt into a sheet form from the extruder, cooling the melt on a cooling roll, and solidifying. Moreover, as a manufacturing method of the light reflection body as these laminated bodies, the method of co-extruding a molten raw material using a multilayer T die and I die, and extending | stretching and manufacturing the obtained laminated body is mentioned. In addition, when the base material layer is biaxially stretched, it may be biaxially stretched after lamination, but after the uniaxial stretching of the base material layer is completed, the molten raw material for the gloss adjusting layer is extruded and pasted, A method of manufacturing this laminate by further uniaxially stretching is also included. The gloss adjusting layer is formed by stretching so that the filler having the preferable particle diameter is exposed on the surface of the light reflector, and the surface unevenness for satisfying the characteristics of the light reflector of the present invention on the surface of the light reflector ( Or protrusions). By forming protrusions on the light reflector by stretching in this way, productivity will be improved compared to when glass beads are directly applied to the reflective surface, and surface irregularities can be formed evenly on the substrate surface. ,preferable.

  The method for forming the intermediate layer is the same as the method for forming the gloss adjusting layer. Further, in addition to the method for forming the gloss adjusting layer, after the base material layer is stretch-molded, the raw material resin for the intermediate layer is extruded directly or through an easy-adhesion layer and bonded to the base material layer. The method of forming etc. is also mentioned.

In order to adjust the size of the pores generated in the laminate, the area stretch ratio of the base material layer is preferably in the range of 1.3 to 80 times, more preferably in the range of 7 to 70 times, and particularly preferably 22. Double to 65 times, most preferably 25 to 60 times. If the area stretch ratio is in the range of 1.3 to 80 times, fine pores are easily obtained, and a decrease in reflectance is easily suppressed. In addition, in this specification, area stretch ratio is a magnification represented by longitudinal stretch ratio x lateral stretch ratio.
Moreover, the preferable area stretch ratio of a glossiness adjustment layer is the same as the preferable area stretch ratio of the said base material layer. If the area stretch ratio is in the range of 1.3 to 80 times, protrusions due to the filler are easily formed.

The stretching temperature when the laminate including the gloss adjusting layer and the base material layer is stretched after laminating both layers is higher than the melting point of the thermoplastic resin (i) and the thermoplastic resin (iii). The temperature is preferably lower than at least one of the melting point and the glass transition point. By setting it as the said conditions, the processus | protrusion which used the filler as the nucleus in the glossiness adjustment layer is formed, and the space | gap which used the filler as the nucleus is formed in the base material layer.
The stretching temperature is a temperature range from 5 ° C. to 35 ° C. higher than the melting point of the thermoplastic resin (i) used, and 2 to 60 ° C. lower than the melting point of the thermoplastic resin (iii) used. The temperature is preferably 2 to 60 ° C. higher.
Specifically, when the thermoplastic resin (i) used is a polypropylene random copolymer (melting point 130 to 145 ° C.) and the thermoplastic resin (iii) is a propylene homopolymer (melting point 155 to 167 ° C.), it is 125. ~ 165 ° C is preferred. When the thermoplastic resin is melt-extruded, it is preferably cooled and solidified, and then reheated to the stretching temperature and stretched. The stretching speed in the stretching step is preferably 20 to 350 m / min.

  The obtained stretched resin film can be subjected to heat treatment (annealing treatment) as necessary to promote crystallization, reduce the thermal shrinkage rate of the laminated film, and the like. Moreover, the ear | edge part of the laminated body obtained as needed can be slit, and it can be set as a light reflector.

(7) Properties of light reflector <porosity>
In the light reflector of the present invention including the gloss adjusting layer and the base material layer, each layer has a different porosity, and the porosity in the gloss adjusting layer is 0 to 4%, and The porosity of the base material layer is preferably 15 to 75%, the porosity of the gloss adjusting layer is 0 to 2%, and the porosity of the base material layer is 30 to 60%. Is more preferable.
The porosity in each layer of the light reflector of the present invention is cut while cooling so as not to crush the holes of the light reflector, creating a cross section in the thickness direction (observation surface), and affixing to the observation sample stage, Gold is vapor-deposited on the observation surface, and an arbitrary magnification (500 times to 3000 times) easy to observe using a scanning electron microscope (device name “scanning electron microscope: SM-200”, manufactured by TOPCON Co., Ltd.) The vacancies in each layer were observed. Further, the observed region is captured as image data, and the image is processed with an image analysis device (device name “small general-purpose image analysis device: Luzex AP”, manufactured by Nireco Corporation) to obtain the area ratio of the pores. It was set as the porosity.

<Density>
In the light reflector of the present invention, the density is preferably 0.3 to 1.2 g / cm ³ , in order to adjust the amount per unit volume of holes generated in the light reflector, and 0.4 to 1.0 g. / Cm ³ is more preferable. If the density is 0.3 g / cm ³ or more, the number of pores in the base material is not too large, the base material strength is sufficient, and folding and wrinkling are less likely to occur during construction. A density of 1.2 g / cm ³ or less is preferable because the number of pores in the substrate is sufficient and the reflectance is increased. The base material referred to here may include a gloss adjusting layer and an intermediate layer in addition to the base material layer described above.

<Color difference △ E _H >
The light reflector of the present invention has the above formula (2) before and after irradiating with ultraviolet light having an irradiation intensity of 90 mW / cm ² from a metal halide lamp installed at a position 10 cm away under an environmental condition of 83 ° C. and 50% relative humidity. color difference represented by) △ E _H 0-10, more preferably 0-5, even more preferably 0-3, particularly preferably 0-1. When ΔE _H is 10 or less, discoloration of the reflector does not occur during long-time use, and it is possible to suppress luminance reduction and luminance unevenness.
This feature can be achieved mainly by using a polyolefin-based resin for the thermoplastic resin constituting the light reflector, and by adding a fluorescent brightener and a light stabilizer as additives.

<Reflectance>
The reflectance of the wavelength measured at a wavelength of 550 nm on the surface of the gloss adjusting layer of the light reflector of the present invention is preferably 90% or more. The reflectance is more preferably 95% or more, and particularly preferably 97% or more. When the reflectance is 90% or more, the luminance due to the reflected light with respect to the specific incident light controlled by the present invention when incorporated in the surface light source device is increased, and the luminance unevenness is easily improved.
This feature can be achieved when the base material layer includes a large number of pores inside and has the above-described porosity.

(8) Utilization of light reflector The light reflector of the present invention is used in a liquid crystal display device with a built-in light source or a low power consumption display device intended to reflect room light without using a built-in light source. It is possible to use. It can also be used widely for the back of indoor and outdoor lighting and light sources for electric signboards.

[Surface light source device]
The surface light source device of the present invention uses the light reflector of the present invention. The surface light source device of the present invention can be preferably used as a surface light source device such as a side light system or a direct light system. Especially, it is extremely useful for a direct light type surface light source device. Examples of the surface light source device of the present invention include a liquid crystal display device such as a liquid crystal television.
The direct light type liquid crystal display device (liquid crystal television or the like) of the present invention has a configuration as shown in FIG. 2, for example, and efficiently makes light incident on the light reflector from all directions to the light reflector. Can be reflected at right angles. For this reason, it is possible to give a natural feeling to a person viewing the liquid crystal display device with high luminance and no luminance unevenness.

  Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples and Test Examples. The materials, amounts used, ratios, operations, and the like shown below can be changed in a timely manner without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[Materials used]
First, Table 1 shows materials used in the present examples and comparative examples. In Table 1, the filler (a), the filler (f), and the filler (h) are observed at a magnification of 3000 using a scanning electron microscope, and the average particle size (major axis) of 100 filler particles. Was the average particle size or average dispersed particle size. For filler (b) and filler (e), the particle size distribution was measured using a Microtrac HRA manufactured by Nikkiso Co., Ltd. as a particle size analyzer, and the particle size at a weight of 50% with respect to the total filler weight. Was the average particle size. In addition, as the filler (c), the filler (d), the filler (g), and the TiO ₂ , fillers each having an average particle diameter adjusted were used.

[Manufacture of light reflectors]
<Examples 1, 2 and 8>
The composition for base layer (A) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 was melt-kneaded at 250 ° C. using an extruder. Then, the base material layer (A) was obtained by extruding to a sheet form and cooling to about 60 degreeC with a cooling roll. This base material layer (A) was reheated to 145 ° C. and then stretched in the longitudinal direction at the magnifications described in Table 2 by utilizing the peripheral speed differences of a large number of roll groups.
A gloss adjusting layer composition (B) prepared by mixing the materials shown in Table 1 with the formulation shown in Table 2 is melt-kneaded, and melt-extruded on one side of the obtained base layer (A) to obtain a gloss adjusting layer ( B) was laminated so as to be B / A. The laminate was then reheated to 160 ° C. and stretched in the transverse direction at a magnification described in Table 2 with a tenter. Then, after annealing at 160 ° C., it was cooled to 60 ° C., the ears were slit, and a two-layer laminated film having the thickness described in Table 2 was obtained. The laminated films were used as the light reflectors of Examples 1, 2, and 8, respectively.

<Example 3>
A base layer composition (A) and a gloss control layer composition (B) prepared by mixing the materials shown in Table 1 with the formulation shown in Table 2 were melt-kneaded at 250 ° C. using separate extruders. did. Thereafter, the base layer composition (A) and the gloss adjusting layer composition (B) are supplied to one co-pressing die, and the surface of the base layer composition (A) in the co-pressing die. After laminating the composition for gloss adjustment layer (B), the sheet was extruded into a sheet and cooled to about 60 ° C. with a cooling roll to obtain a B / A laminate.
The laminate was reheated to 145 ° C., then stretched in the longitudinal direction using the difference in peripheral speed between a number of roll groups, reheated to about 150 ° C., and stretched in the transverse direction with a tenter. The laminate was then reheated to 160 ° C. and stretched in the transverse direction with a tenter. Then, after annealing at 160 ° C., it was cooled to 60 ° C., and the ears were slit to obtain a laminated film having a two-layer structure. This laminated film was used as the light reflector of Example 3.

<Examples 4-6, 9 and Comparative Examples 1, 2, 4-6>
The composition for base layer (A) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 was melt-kneaded at 250 ° C. using an extruder. Then, the base material layer (A) was obtained by extruding the base material layer composition (A) into a sheet shape and cooling to about 60 ° C. with a cooling roll. This base material layer (A) was reheated to 145 ° C. and then stretched in the longitudinal direction at the magnifications described in Table 2 by utilizing the peripheral speed differences of a large number of roll groups.
Both sides of the base material layer (A) obtained by melt-kneading the composition for gloss adjustment layer (B) and the composition for intermediate layer (C) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 The substrate layer (A), the gloss adjusting layer (B), and the intermediate layer (C) were laminated so as to be B / C / A / C. The laminate was then reheated to 160 ° C. and stretched in the transverse direction at a magnification described in Table 2 with a tenter. Then, after annealing at 160 ° C., it was cooled to 60 ° C., and the ears were slit to obtain a laminated film having a four-layer structure having the thickness shown in Table 2. The laminated films were used as light reflectors of Examples 4 to 6, 9 and Comparative Examples 1, 2, 4 to 6, respectively.

<Example 7>
The composition for base layer (A) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 was melt-kneaded at 250 ° C. using an extruder. Then, the base material layer (A) was obtained by extruding to a sheet form and cooling to about 60 degreeC with a cooling roll. This base material layer (A) was reheated to 145 ° C. and then stretched in the longitudinal direction at the magnifications described in Table 2 by utilizing the peripheral speed differences of a large number of roll groups.
Both sides of the base material layer (A) obtained by melt-kneading the composition for gloss adjustment layer (B) and the composition for intermediate layer (C) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 The substrate layer (A), the gloss adjusting layer (B), and the intermediate layer (C) were laminated so as to be B / A / C. The laminate was then reheated to 160 ° C. and stretched in the transverse direction at a magnification described in Table 2 with a tenter. Then, after annealing at 160 ° C., it was cooled to 60 ° C., and the ears were slit to obtain a laminated film having a three-layer structure having the thickness shown in Table 2. This laminated film was used as the light reflector of Example 7.

<Example 10>
The composition for base layer (A) prepared by mixing the materials shown in Table 1 with the formulation shown in Table 2 was melt-kneaded at 260 ° C. using an extruder. Then, the base material layer (A) was obtained by extruding the base material layer composition (A) into a sheet shape and cooling to about 60 ° C. with a cooling roll. This base material layer (A) was reheated to 150 ° C., and then stretched in the longitudinal direction at the magnifications described in Table 2 by utilizing the peripheral speed differences of many roll groups.
Both sides of the base material layer (A) obtained by melt-kneading the composition for gloss adjustment layer (B) and the composition for intermediate layer (C) obtained by mixing the materials shown in Table 1 with the formulation shown in Table 2 The substrate layer (A), the gloss adjusting layer (B), and the intermediate layer (C) were laminated so as to be B / A / C. The laminate was then reheated to 160 ° C. and stretched in the transverse direction at a magnification described in Table 2 with a tenter. Then, after annealing at 160 ° C., it was cooled to 60 ° C., and the ears were slit to obtain a laminated film having a three-layer structure having the thickness shown in Table 2. This laminated film was used as the light reflector of Example 10.

<Comparative Example 3>
According to Example 1 of Unexamined-Japanese-Patent No. 2006-195453, the laminated film of the 4 layer structure of the structure of following Table 2 was obtained. This laminated film was used as the light reflector of Comparative Example 3.

[Measurement and test]
Using the light reflectors of Examples 1 to 10 and Comparative Examples 1 to 6, the following measurements and tests were performed.

<Layer thickness>
The total thickness of the light reflectors of each Example and Comparative Example was measured based on JIS-P-8118. Separately, the light reflectors of the examples and comparative examples were randomly sampled, cut by a cross section using a microtome, and the thickness of the layer was calculated by observing the cut surface at 3000 times using a scanning electron microscope. It was. In the calculation of the thickness of the gloss adjusting layer, the thickest part in the observation visual field was defined as the layer thickness.

<Light reflector density>
The light reflectors of the examples and comparative examples were sampled at a 3 cm square, and the density was measured by the underwater substitution method in a 23 ° C. environment using a high-precision electronic hydrometer (Mirage Trading Co., Ltd .: SD-200L). did.

<Porosity>
Cut while cooling so as not to crush the holes of the light reflectors of each Example and Comparative Example, create a cross section in the thickness direction (observation surface), attach it to the observation sample stage, and deposit gold on the observation surface Using a scanning electron microscope (device name “Scanning Electron Microscope: SM-200”, manufactured by TOPCON Co., Ltd.), the vacancies in each layer were observed at an arbitrary magnification (500 times to 3000 times) that can be easily observed. . Further, the observed region is captured as image data, and the image is processed with an image analysis device (device name “small general-purpose image analysis device: Luzex AP”, manufactured by Nireco Corporation) to obtain the area ratio of the pores. It was set as the porosity.

<Average slope Δa>
The average inclination Δa on the gloss adjusting layer side surface of the light reflectors of the examples and the comparative examples is obtained by measuring the surface roughness of the sample obtained by cutting the light reflector into 3 cm square using a three-dimensional roughness meter (Kosaka Research Co., Ltd.). Manufactured by SPA-11) over a length (L) of 5 mm, and from the height differences h ₁ , h ₂ , h ₃ ... H _n shown in FIG. ).

<Reflectance>
The reflectance on the gloss adjusting layer side surface of the light reflector of each example and comparative example was measured using a spectrophotometer (manufactured by Hitachi, Ltd .: U-3310) equipped with an integrating sphere having a diameter of 150 mm. The reflectance at a wavelength of 550 nm was measured according to the method described in Z8722 Condition d. The measurement result was expressed as a relative reflectance when the reflectance of aluminum oxide was 100%.

<45 ° glossiness>
Using a digital variable glossiness meter (manufactured by Suga Test Instruments Co., Ltd .: UGV-5DP), according to the method described in Method 4 of JIS-Z-8741, the glossiness at an incident angle of 45 ° on the gloss adjusting layer side surface was measured. It was measured. The measured value was defined as the 45 ° glossiness of the light reflectors of the examples and comparative examples.

<85 ° glossiness>
Using a handy 85 ° gloss meter (manufactured by DR LANGGE: LMG063), the gloss at an incident angle of 85 ° on the gloss adjusting layer side surface was measured. The measured value was made into 85 degree glossiness of the light reflector of each Example and a comparative example.

<Gloss ratio>
It calculated | required by calculation from the said Formula (1) using the value of the said 45 degree glossiness and 85 degree glossiness calculated | required by measurement.

<Color difference △ E _H >
The light reflectors of the examples and comparative examples were sampled, and color measurement was performed using a spectral densitometer (X-Rite 508) before and after the start of the weathering acceleration test under the following conditions. The lightness index L value, the chromaticness index a value, and the b value were obtained, and the color difference ΔE _H was determined by calculation from the above formula (2).
The weather resistance test was performed using a weather resistance acceleration tester (Daiplau Intes: Metal Weather Co., Ltd.) at a temperature of 83 ° C. and a relative humidity of 50% from a metal halide lamp installed at a position 10 cm away from the metal halide lamp. / Cm ² of ultraviolet light was irradiated for 100 hours.

<Luminance unevenness>
The light reflectors of the examples and comparative examples were mounted on a direct type backlight type surface light source device of the type shown in FIG. In this apparatus, three cold cathode lamps 13 are installed, the distance d between the cold cathode lamps is 30 mm, the distance between the light reflector 11 and the center of the cold cathode lamp 13 is 2 mm, the light reflector 11 and the diffusion plate. The distance to the bottom surface of 12 was 21 mm, and the overall width of the direct type backlight was 100 mm.
Luminance unevenness generated when this direct type backlight was turned on was visually confirmed and evaluated according to the following criteria.
A: Brightness unevenness cannot be confirmed and is good.
○: Brightness unevenness is confirmed, but there is no practical problem.
(Triangle | delta): Brightness nonuniformity is confirmed and it is a problem practically.
X: Brightness unevenness is bad and not practical.

[Measurement and test results]
These test results are shown in Table 3. In Table 2, in the column of filler, the number represents the content (% by weight) of the filler contained in each layer, and the symbol represents the type of filler contained in each layer in Table 1.

As shown in Table 3, it was found that all of the light reflectors of the present invention were good without unevenness in brightness and that the color difference ΔE _H was also small. On the other hand, in Comparative Examples 1 to 6 in which the gloss ratio is less than the range of the present invention, luminance unevenness improvement is insufficient, and in particular, Comparative Example 1 in which the 45 ° glossiness exceeds the upper limit value of the present invention and the 45 ° glossiness is In Comparative Examples 2 and 3 below the lower limit of the present invention, the luminance unevenness was poor and was not at a practical level.

[Measurement of uneven brightness]
The light reflector of Example 1 was mounted on the direct backlight type surface light source device used for the measurement of the luminance unevenness. The luminance unevenness generated when the direct type backlight was turned on was measured in the transverse direction of the three cold cathode lamps using a CCD luminance meter (manufactured by Highland: RISA-COLOR-ONE). The result is shown in FIG.
On the other hand, in place of the light reflector of Example 1, the luminance unevenness generated when the direct backlight adjusted in the same manner except that the light reflector of Comparative Example 1 was used was measured in the same manner. The result is shown in FIG.

  As shown in FIGS. 6 and 7, when the light reflector of the present invention is used, the generation of bright lines is suppressed and the occurrence of luminance unevenness is suppressed even in a surface light source device with a small number of cold cathode lamps used. Was actually measured.

  As described above, the light reflector of the present invention is less likely to cause uneven brightness even when incorporated in a surface light source device with a small number of cold cathode lamps and a large distance between lamps, and less yellowing due to ultraviolet irradiation. I found out that Therefore, the surface light source device using the light reflector of the present invention has little luminance unevenness and can be used for a long time.

1 Gloss adjustment layer (B)
2 Base material layer (A)
3 Intermediate layer (C)
11 Light Reflector 12 Diffusion Plate 13 Cold Cathode Lamp 14 Bright Line Portion Generated on Diffusion Plate 15 Dark Portion Generated on Diffusion Plate 16 30 ° Reflected Light 17 40 ° Reflected Light 18 50 ° Reflected Light 19 60 ° Reflected Light 20 70 ° Reflected Light d Distance between cold-cathode lamps h Difference in height between adjacent irregularities L Measurement length

Claims (14)

A light reflector containing a thermoplastic resin (i) and having a wall thickness of 2 to 20 μm and having at least a uniaxially stretched gloss adjusting layer as an outermost layer, the gloss adjusting layer having an average particle diameter of 2 to 20 μm 5 to 60% by weight of the filler (ii), 45 ° glossiness of the gloss adjusting layer surface is 10 to 80%, and glossiness ratio represented by the following formula (1) is 2 to 25 Is a light reflector.
  The light reflector according to claim 1, wherein an average inclination Δa of the surface of the gloss adjusting layer is 0.02 to 0.2.   The light reflector according to claim 1, wherein the gloss adjusting layer is stretched at a temperature higher than the melting point of the thermoplastic resin (i).   The light reflector according to any one of claims 1 to 3, wherein the thermoplastic resin (i) mainly contains a polyolefin resin having a melting point of less than 160 ° C.   The said glossiness adjustment layer contains 10 to 40 weight% of fillers (ii) with an average particle diameter of 2-20 micrometers, The light reflector as described in any one of Claims 1-4 characterized by the above-mentioned.   The thermoplastic resin (iii) and the filler (iv) are included, and the substrate layer is at least uniaxially stretched, and comprises a laminate including the gloss adjusting layer. The light reflector according to Item.   The light reflector according to claim 6, wherein the thermoplastic resin (iii) mainly includes a polyolefin resin having at least one of a melting point and a glass transition point of 160 ° C. or higher.   As the filler (iv) in the base material layer, at least one of an inorganic filler having an average particle diameter of 0.05 to 1.5 μm and an organic filler having an average dispersed particle diameter of 0.05 to 1.8 μm is 5 to 75 weights. The light reflector according to claim 6, wherein the light reflector is contained.   The light reflector according to any one of claims 6 to 8, wherein the reflectance of the base material layer is 90% or more.   The laminate including the gloss adjusting layer and the base material layer is higher than the melting point of the thermoplastic resin (i) after laminating both layers, and out of the melting point and glass transition point of the thermoplastic resin (iii). The light reflector according to any one of claims 6 to 9, wherein the light reflector is stretched at a temperature lower than at least one.   11. The light reflection according to claim 6, wherein a porosity of the gloss adjusting layer is 0 to 4%, and a porosity of the base material layer is 15 to 75%. body. The light reflector according to claim 1, wherein the density is 0.3 to 1.2 g / cm ³ . A color difference ΔE expressed by the following formula (2) before and after irradiating ultraviolet rays having an irradiation intensity of 90 mW / cm ² from a metal halide lamp installed at a position 10 cm away at an environmental condition of 83 ° C. and 50% relative humidity for 100 hours. _H is 0-10, The light reflector as described in any one of Claims 1-12 characterized by the above-mentioned.
ΔE _H = [(L ₀ −L ₁ ) ² + (a ₀ −a ₁ ) ² + (b ₀ −b ₁ ) ² ] ^0.5 Equation (2)
(In the formula (2), L ₀ , a ₀ , and b ₀ are the lightness indexes in the color space of the L _* a _* b _* color system before irradiation, and L ₁ , a ₁ , and b ₁ are the values after irradiation, respectively. L _* and chromaticness index a _* , b _* )   The surface light source device using the light reflector as described in any one of Claims 1-13.