JP2001305313A - Reflection film for surface light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection film for a surface light source and more particularly, a reflection film for a surface light source to be used for a back light mechanism of a liquid crystal display device which uses a liquid crystal element. SOLUTION: The reflection film for a surface light source shows 100% average reflectance in the wavelength region from 760 to 950 nm and the gloss G(60) at 60 deg. incident angle and 60 deg. acceptance angle, gloss G(50) at 60 deg. incident angle and 50 deg. acceptance angle, and gloss G(70) at 60 deg. incident angle and 70 deg. acceptance angle satisfy G(60)>=40%, G(50)>=10%, G(70)>=10% and G(70)/G(60)>=0.2 and G(50)/ G(60)>=0.2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection film for a surface light source, and more particularly to a reflection film for a surface light source used for a backlight mechanism of a liquid crystal display device using a liquid crystal element.

[0002]

2. Description of the Related Art In recent years, as a display device such as a notebook type computer or a word processor, a liquid crystal display device using a liquid crystal element having a backlight mechanism which can be made thinner and has an easy-to-view image has been used. For such a backlight mechanism, an edge light method in which a linear light source such as a fluorescent tube is provided at one end of a light-transmitting light guide plate is often used. In the case of such an edge light system, a surface light source is often configured such that one surface of a light guide plate is partially covered with a light diffusing substance, and the entire surface is further covered with a reflective material. .

The above-mentioned reflector is required to have a high reflectance in a visible light wavelength region and a reflection directivity as small as possible in order to reduce a luminance variation in a surface light source. on the other hand,
In a liquid crystal display device using a liquid crystal element, the basic performance such as the response speed of the liquid crystal changes depending on the temperature environment, and the response speed decreases particularly at lower temperatures. There has been a demand for a reflective material having a high heat ray reflectivity so as to guide the thermal energy generated from the electronic component to the liquid crystal element.

The above-mentioned reflector is disclosed in Japanese Patent Application Laid-Open No.
-286019, an aluminum plate as described in Japanese Utility Model Application Laid-Open No. 4-22755, a metal reflection plate as described in JP-A-8-114798, and a film provided with a silver thin film as described in JP-A-8-114798. 3-25609
No. 0 and JP-B-8-16175, etc. However,
A metal plate such as a conventional aluminum plate or a film provided with a silver thin film on the film surface can obtain sufficiently high reflectivity in the visible light wavelength region and heat ray reflectivity, but has large reflection directivity and large surface light source. There is a problem that the luminance variation becomes large. In order to solve this problem, Japanese Patent Application Laid-Open
As described in JP-A-114798, there is a method in which silver is laminated on the surface of a substrate sheet having a certain degree of unevenness to reduce the variation in luminance by this scattering property, but also has a sufficiently small reflection directivity. However, when the metal surface is directly exposed to the air, the metal surface is discolored due to oxidation or reaction with a sulfurous acid gas or the like, and the reflection performance tends to be reduced.

[0005] From such a point, a white polyester film, which is relatively small in reflection directivity by measurement, has been often used as a reflection material of an edge light type backlight mechanism. Some white polyester films cause light scattering reflection by roughening the surface, and others have a structure that causes light scattering reflection inside the film. Specific examples include those in which a light-scattering white paint is applied to a base sheet, and those in which fine voids are formed by adding a filler to a resin, forming the sheet, and then stretching the sheet. In the former, since the light reflection depends on the applied thickness of the white light scattering paint, the reflective performance is limited by the applied thickness, and in long-term use, the reflectance may be reduced due to the falling off of the paint. As an example of the latter, Japanese Patent Application Laid-Open No. 7-2871
A light reflection sheet made of a porous resin sheet disclosed in Japanese Patent Publication No. 10-107 is known, and this light reflection sheet causes light scattering reflection due to a gap generated between a filler and a resin. The light reflecting layer could be formed with a sufficient thickness, and the reflectance in the visible light region was at a practically usable level, but the heat ray reflectance was not satisfactory.

[0006]

SUMMARY OF THE INVENTION The present invention provides a light source and a liquid crystal display which can maintain a practically sufficient reflection performance in the visible light region, can reduce the luminance variation in the surface light source, and have a high heat ray reflectance. The object of the present invention is to provide a reflective film for a surface light source that efficiently reflects heat energy emitted from electronic components arranged around the element to a liquid crystal element side and can reduce a decrease in the basic performance of a liquid crystal display even when used at a low temperature. I do.

[0007]

The present invention has the following arrangement. (1) The average reflectance in the wavelength range of light of 760 to 950 nm is 100% or more, and the glossiness at an incident angle of 60 degrees and the light receiving angle of 60 degrees is G (60), the incident angle is 60 degrees, and the light receiving angle is 5
Gloss of 0 degree is G (50), incident angle is 60 degrees, light receiving angle is 70
G (60) ≧ 40, where G (70) is the gloss level
%, G (50) ≧ 10%, G70 ≧ 10%, and further G (70) / G (60) ≧ 0.2, G (50) / G
(60) The reflective film for a surface light source, wherein ≧ 0.2. (2) From the direction of light incidence, at least the polyester film layer (A layer), adhesive layer (B layer), antioxidant layer (C layer), metallic silver layer (D layer), and thermoplastic resin layer (E layer)
Wherein the polyester film layer (A layer) is formed of a white polyester film containing cavities. (3) The reflective film for a surface light source according to (2), wherein the polyester film layer (A layer) contains substantially no inorganic particles. (4) The polyester film layer (A layer) mainly comprises
It is characterized by comprising a white polyester film containing fine voids composed of a polyester resin (a) and a thermoplastic resin (b) incompatible with the polyester resin (a) (2). )) Or (3), the reflective film for a surface light source. (5) The thermoplastic resin (b) is incompatible with the polyester resin (a), and is made of two kinds of thermoplastic resins having different surface tensions, that is, different surface energies. The reflective film for a surface light source according to (1). (6) The reflective film for a surface light source according to any one of (2) to (5), wherein the thermoplastic resin layer (E layer) is mainly composed of a polyethylene terephthalate resin.

In the present invention, the thickness of the "film" is not particularly limited, and includes a so-called "sheet".

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The reflective film for a surface light source of the present invention has an average reflectance of 100% or more in a light wavelength region of 760 to 950 nm, an incident angle of 60 degrees and a light receiving angle of 6 degrees.
Gloss of 0 degree is G (60), incident angle is 60 degrees, light receiving angle is 50
G (50), G (70) is the glossiness at an incident angle of 60 °, and the light receiving angle is 70 °, G (60) ≧ 40%,
G (50) ≧ 10%, G70 ≧ 10%, and G
(70) / G (60) ≧ 0.2, G (50) / G (6
0) must be ≧ 0.2. The setting of the average reflectance and glossiness within the above ranges can be achieved, for example, by the following configurations.

In the reflection film for a surface light source of the present invention, at least a polyester film layer (A layer), an adhesive layer (B layer), an antioxidant layer (C layer), and a metallic silver layer ( D) and a thermoplastic resin layer (E layer) are preferably laminated, and the polyester film layer (A layer) is made of a white polyester film containing a cavity having a reflection function for a surface light source. Is preferred.

By having a white polyester film containing cavities and a metallic silver layer, it is possible to achieve both improvement in the reflection characteristics and heat ray reflectance in the visible light region and reduction in luminance variation in the surface light source, and prevention of oxidation. The presence of the layer prevents oxidation of the metallic silver layer.

[0012] The polyester film layer (layer A) comprises:
It is a film made of a polyester resin, and is preferably a white polyester film containing voids as described above. When the polyester film layer (A layer) contains a cavity, the reflection characteristics in the visible light region and the heat ray region are improved. The polyester-based resin forming the polyester film layer (layer A) is not particularly limited, but when a white polyester film containing fine voids is used,
For example, the polyester resin is composed of a base polyester resin (a) and a thermoplastic resin (b) incompatible with the polyester resin (a). There is a method of developing a cavity.

The polyester constituting the polyester resin (a) includes terephthalic acid, isophthalic acid,
A polyester obtained by polycondensing an aromatic dicarboxylic acid such as naphthalenedicarboxylic acid or an ester thereof with a glycol such as ethylene glycol, diethylene glycol, 1,4-butanediol, or neopentyl glycol is exemplified. Representative examples of such polyesters include polyethylene terephthalate, polyethylene butylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and the like. These polyesters may be a homopolymer, or may be a copolymer obtained by copolymerizing a third component other than the above-mentioned polyester components, but in any case, in the present invention, The ratio of ethylene terephthalate units, butylene terephthalate units, or ethylene-2,6-naphthalate units is
The polyester is preferably at least 70 mol%, more preferably at least 80 mol%, particularly preferably at least 90 mol%, based on all constituent units.

The polyester may be prepared by directly reacting an aromatic dicarboxylic acid and a glycol, or by subjecting an alkyl ester of the aromatic dicarboxylic acid to a transesterification reaction with a glycol followed by polycondensation, or by subjecting the aromatic dicarboxylic acid to a glycol reaction. It can also be produced by a method of polycondensing a diglycol ester.

The thermoplastic resin (b) which is incompatible with the polyester resin (a) is incompatible with the base polyester resin (a), and the polyester resin (a) The material is not particularly limited as long as it is uniformly mixed in a dispersed state and causes peeling at the interface with the polyester-based resin (a) due to stretching of the film or the like so as to develop cavities. Preferably, polystyrene-based resins, polyolefin-based resins, polyacryl-based resins, polycarbonate-based resins, polysulfone-based resins, cellulose-based resins and the like are exemplified. These can be used alone or, if necessary,
More than one species can be used in combination. Among them, the use of polystyrene resins and polyolefin resins such as polymethylpentene and polypropylene is particularly preferred.

The amount of the thermoplastic resin (b) to be mixed with the polyester resin (a) is appropriately determined according to the amount of voids required in the obtained polyester film layer (A layer), physical properties, production conditions such as stretching, and the like. The thermoplastic resin (b) is preferably used in an amount of 3% by weight or more and less than 40% by weight, more preferably 5% by weight, based on the total amount of the resin composition comprising the polyester resin (a) and the thermoplastic resin (b). % And not more than 30% by weight. When the blending amount of the thermoplastic resin (b) is less than 3% by weight, the amount of cavities generated is small, and the heat reflectance of the reflective film for a surface light source of the present invention is hardly improved. In addition, the stretchability at the time of manufacturing is remarkably reduced, and the heat resistance, strength, or stiffness tends to be reduced.

Further, the thermoplastic resin (b) is a thermoplastic resin (b) which is incompatible with the polyester resin (a).
1) and a thermoplastic resin which is incompatible with both the polyester resin (a) and the thermoplastic resin (b1) and has a higher surface tension (surface energy) than the thermoplastic resin (b1). It is preferred to be composed of resin (b2).

By forming the thermoplastic resin (b) from the above two kinds of thermoplastic resin (b1) and the thermoplastic resin (b2), the thermoplastic resin (b1) mainly exerts a cavity generating effect. To become a “cavity developing agent”,
The thermoplastic resin (b2) is incompatible with the thermoplastic resin (b1) and has a higher surface tension than the thermoplastic resin (b1). As a result, a “dispersing action” of effectively dispersing the thermoplastic resin (b1) in the polyester-based resin (a) is achieved, thereby providing a “dispersing resin” having an action of uniformly forming fine cavities. .

The combination of the thermoplastic resin (b1) and the thermoplastic resin (b2) is incompatible with the polyester resin (a), and the thermoplastic resin (b2) is more soluble than the thermoplastic resin (b1). The surface tension (surface energy) is not particularly limited as long as it is large, and examples thereof include the following. When a polyolefin-based resin such as polymethylpentene-based resin, polypropylene-based resin, cyclic olefin polymer, or silicone-based resin is used as the thermoplastic resin (b1), the thermoplastic resin (b2) is
It is preferable to use a polystyrene-based resin, a polycarbonate-based resin, a polyacryl-based resin, a polyphenylene ether-based resin, a polyolefin-based resin modified with a maleimide, a carboxylic acid, or the like, a polystyrene-based resin, or the like. Alternatively, when a polystyrene resin is used as the thermoplastic resin (b1), a polycarbonate resin, a polyacrylic resin, a polyphenylene ether resin, a polyolefin modified with maleimide, carboxylic acid, or the like is used as the thermoplastic resin (b2). It is preferable to use a system resin. Further, the thermoplastic resin (b1) and the thermoplastic resin (b2)
Can be used alone or in combination of two or more resins, if necessary.

The thermoplastic resin (b1) and the thermoplastic resin (b
The blending amount of 2) is not particularly limited as long as a desired void-forming action is obtained with respect to the polyester resin (a), but preferably, the thermoplastic resin (b1) is mixed with 100 parts by weight of the thermoplastic resin (b1). b2) It is preferred that the amount be 0.01 to 20 parts by weight. Thermoplastic resin (b1) 100
The lower limit of the amount of the thermoplastic resin (b2) relative to parts by weight is more preferably 0.02 parts by weight, particularly preferably 0.1 part by weight. The upper limit is more preferably 15 parts by weight, particularly preferably 10 parts by weight.

If the amount of the thermoplastic resin (b2) is less than 0.01 part by weight per 100 parts by weight of the thermoplastic resin (b1), the effect of finely dispersing the thermoplastic resin (b1) as a “dispersible resin” is not obtained. On the other hand, if it exceeds 20 parts by weight, the thermoplastic resin (b2) becomes
It is difficult to obtain a cavity having a desired size, for example, by covering most of 1) and forming a cavity having a length shorter than the thickness. By setting the mixing ratio of the thermoplastic resin (b1) and the thermoplastic resin (b2) within the above range, the thermoplastic resin (b2) having a large surface tension partially replaces the thermoplastic resin (b1) having a small surface tension. The coating or the whole is thinly coated, and the influence on the adhesiveness of the thermoplastic resin (b1) to the polyester resin (a) is negligible. Therefore, the fine dispersion effect of the thermoplastic resin (b2) is effectively exhibited, and the thermoplastic resin (b1) can be finely dispersed in the polyester-based resin (a). Can be obtained in large numbers. In the polyester resin (a), the thermoplastic resin (b2)
There is no particular limitation on the state in which the resin is coated with the thermoplastic resin (b1). For example, a state in which a coated part and an uncoated part are present regularly, such as a mesh, a state in which the coated part is randomly distributed, and a state in which the whole is thinly coated. A state, or a state in which a plurality of the above states coexist, may be mentioned.

When the thermoplastic resin (b) is composed of the above two kinds of thermoplastic resins (b1) and (b2), polyester of the thermoplastic resin (b1) and the thermoplastic resin (b2) The compounding amount in the system resin (a) is
The properties required for the reflective film for a surface light source of the present invention, in particular, the amount of voids formed in the polyester film layer (A layer) and the stretching conditions at the time of manufacturing the polyester film layer (A layer) may be appropriately set. The polyester resin (a), the thermoplastic resin (b1), and the thermoplastic resin (b2) mainly constituting the (A layer)
The sum of the amounts of the thermoplastic resin (b1) and the thermoplastic resin (b2) is preferably 3 to 30% by weight,
More preferably, the content is in the range of 5 to 25% by weight. Thermoplastic resin (b1) and thermoplastic resin (b
If the sum of the amounts of 2) is less than 3% by weight, the amount of cavities generated in the stretching step during the production of the polyester film layer (A layer) is reduced, and the reflectance and light scattering in the visible light region are reduced. On the other hand, if it exceeds 30% by weight, the stretchability during the production of the polyester film layer (A layer) is remarkably reduced, and the strength or stiffness may be reduced.

In the present invention, the polyester film layer (layer A) preferably contains substantially no inorganic particles. That is, it is preferable that the reflection of light in the heat ray region and the visible light region appears by the cavities formed in the polyester film layer (A layer). Polyester film layer (A
When the layer contains inorganic particles, the scattering in the polyester film layer (A layer) becomes strong, and the absorption of light energy becomes large. Here, “substantially contains no inorganic particles” means that the content of the main component constituting the inorganic particles in the polyester film layer (layer A) is not more than the detection limit of the fluorescent X-ray analysis method. I do.

In the present invention, if necessary, a fluorescent whitening agent, an antistatic agent, an ultraviolet absorber and the like are appropriately added to the polyester film layer (layer A) as long as the action of the present invention is not impaired. It is possible to include it.

The polyester film layer (layer A) preferably has an apparent density in the range of 0.6 to 1.3 g / cm ³ . If the apparent density is less than 0.6 g / cm ³ , the void content is too high and the polyester film layer (A
Layer) or the polyester film layer (A)
Layer) Cracks and wrinkles are likely to occur on the surface and the commercial value is lowered. Conversely, those having a high density of more than 1.3 g / cm ³ have too low a void content to obtain a desired visible light region and heat ray. It is difficult to obtain the reflection characteristics of the area.

When the polyester film layer (layer A) is a white polyester film containing voids, the voids contained therein are preferably as follows. That is, when a cross section is cut in an arbitrary direction with respect to the polyester film layer (A layer), the average thickness of a cavity appearing in the cross section is T1, the average length of the cavity is L1, and the cross section is perpendicular to the cross section. The average thickness of the cavity when the cross section is cut out is T2,
When the average cavity length is L2, L1 / T1 and L1
The average of 2 / T2 is preferably 7.0 or more, more preferably 10.0 or more, and particularly preferably 1 or more.
It is preferably 3.0 or more. Generating a large number of cavities thinner than the length in this way is advantageous for improving the reflectance in the visible light region. When the average of L1 / T1 and L2 / T2 is less than 7.0, the polyester film layer (A
Wrinkles due to heat are easily generated in the layer).

Further, a polyester film layer (layer A)
When cut in a section of any one direction with respect to, is preferably the number of cavities that appear in the cross section is 30/2500 [mu] m ^2, more preferably 35/2500 [mu] m ² or more, particularly preferably 40/2500 [mu] m ^It is good to be ² or more. When the number of cavities is less than 30, even if the length ratio of the cavities is 7.0 or more as described above, the size of each cavity is large and the polyester film layer (A
Wrinkles are likely to be generated.

By forming the polyester film layer (layer A) as described above, the reflection film for a surface light source of the present invention can easily obtain desired reflection characteristics, particularly, reflection characteristics in a visible light region and a heat ray region. Become.

In the present invention, the polyester film layer (layer A) may be a single layer film or a multilayer structure having two or more layers such as having a surface layer and a center layer. In the case of a multilayer structure, each layer may have the same configuration or different configurations, but at least the outermost layer on the side in the light incident direction when forming the surface light source reflective film of the present invention has a light scattering effect or absorption. It is preferable to use a white polyester film that does not contain many large particles and contains fine cavities, and it is particularly preferable to use a film having each of the above-described configurations.

In the present invention, the method of forming the polyester film layer (layer A) is not particularly limited, but it is usually formed into a film separately from other layers, and a commonly used film forming method can be used. As a film forming method, from the viewpoint of productivity, a polyester film layer (A layer)
After extruding from an extruder, guiding the material to a die to obtain an unstretched sheet, and then stretching the unstretched sheet in the biaxial direction is most preferred.

In the present invention, specific examples of the method for forming the polyester film layer (layer A) will be described below. First, the components constituting the polyester film layer (A layer) are mixed and extruded to form an unstretched sheet. Examples of the method for forming the unstretched sheet include, for example, a method in which a mixture of each component such as a resin chip is melted and kneaded in an extruder and then extruded and solidified, and a method in which these components are kneaded in a kneader in advance. A method of dissolving and extruding with an extruder to solidify, in a polymerization step of a polyester constituting the polyester resin (a), adding a thermoplastic resin (b) incompatible with the polyester resin (a), and stirring and dispersing. And then extruding and solidifying the selected chips. The unstretched sheet thus obtained is usually in a non-oriented or weakly oriented state, and is a thermoplastic resin (b) incompatible with the polyester resin (a).
Will be dispersed in the polyester-based resin (a) in various shapes such as spherical or elliptical spherical shapes or thread shapes.

The method of stretching the unstretched film obtained as described above is not particularly limited, but it is preferable to stretch at least one axis. By stretching
Peeling occurs at the interface between the polyester resin (a) and the thermoplastic resin (b), and many cavities are generated. The stretching method is
Roll stretching method (a method of stretching between two or more rolls having different peripheral speeds in the running direction of the film), long gap stretching method, tenter stretching method (a stretching method in which the film is held by clips and spread), tubular Any known method such as a stretching method and an inflation stretching method (a stretching method of expanding by air pressure) can be used, and the film is stretched in a predetermined one direction (main stretching direction). In the case of stretching, any of the methods can use sequential biaxial stretching, simultaneous biaxial stretching, monoaxial stretching, and combinations thereof. When biaxial stretching is performed, simultaneous biaxial stretching in which stretching in the vertical and horizontal directions may be performed simultaneously may be performed. Good to do. In the case of performing sequential biaxial stretching, the stretching order in the longitudinal and transverse directions may be performed first, but in consideration of the mechanical properties of the obtained film, after stretching in the longitudinal direction corresponding to the flow direction of the film first, Next, stretching in the transverse direction is preferred.

The following is an example of a stretching method in the case of performing successive biaxial stretching. In the present invention, the formation of the polyester film layer (layer A) is preferably carried out in two or more different temperature ranges when performing transverse stretching, and the final transverse stretching temperature is preferably in the range of 180 ° C. or more. As described above, in the transverse stretching, by performing the stretching at a temperature higher than the stretching temperature generally used (80 to 140 ° C.), the cavities are sufficiently deformed, and the cavities sufficiently long with respect to the thickness are formed as described above. it can.

Usually, sequential biaxial stretching is described in JP-A-63-16 / 1988.
No. 8441, JP-A-63-193938, JP-A-2-80247, JP-A-2-284929, JP-A-3-114817, JP-A-4-20
As described in, for example, Japanese Patent No. 2540, the unstretched sheet is roll-stretched in the longitudinal direction, then tenter-stretched in the width direction, and then heat-treated at 150 ° C. or higher. In the roll stretching (longitudinal stretching), the stretching temperature is set to 80 to 100 ° C. and the stretching ratio is set to 2.0 to 100% in order to generate a large number of cavities.
5.0 and then tenter stretching (transverse stretching) of 80 to 1
Although the stretching is performed at 40 ° C. and the stretching ratio is 2.8 to 5.0, in the present invention, the sequential biaxial stretching is specifically preferably performed as follows. That is, after the longitudinal stretching of the unstretched film, the first transverse stretching is first performed at 100 to 150 ° C. at a stretching ratio of 2.0 to 3.0 times, and the second transverse stretching is further performed at 18 to 20 times.
The stretching is performed at a stretching ratio of 1.2 to 2.0 times at 0 to 230 ° C. Here, the first horizontal stretching magnification is preferably lower than the longitudinal stretching magnification. In this case, the first stretching is to sufficiently generate cavities in the film, and the second stretching is
This cavity is intended to be a cavity having a small thickness and a well-balanced vertical and horizontal size, and there is almost no increase in the number of cavities due to the second stretching. Note that the total of the first and second horizontal stretching ratios may exceed the vertical stretching ratio. After performing the two-stage transverse stretching as described above, it is preferable to further perform a heat treatment, and the temperature of the heat treatment is preferably 200 ° C. or more, more preferably 220 ° C. or more, and particularly preferably 230 ° C. or more. Good. The heat treatment is
You may perform after 2-5% relaxation processing is performed.

In the present invention, the sequential biaxial stretching is performed under the above-mentioned specific conditions, whereby the cavities in the film are easily deformed, and the thermoplastic resin (b) for generating the cavities is, for example, polymethyl. Even when a resin such as a polyolefin resin such as pentene or polypropylene, or a resin such as a polystyrene resin is used, the cavity is easily deformed without collapsing during tenter stretching.

The thickness of the polyester film layer (layer A) is not particularly limited. However, when the purpose is to reduce the weight and thickness of a liquid crystal display device using the reflective film for a surface light source of the present invention, the polyester film layer (A layer) is used. Layer) preferably has a thickness of 50 μm or more and 250 μm or less, more preferably 10 μm or less.
0 μm or more and 200 μm or less, particularly preferably 150 μm
The thickness is preferably 200 μm or less. When the thickness of the polyester film layer (layer A) is less than 50 μm, it becomes difficult to obtain sufficient reflection characteristics in the visible light region and the heat ray region.

The adhesive layer (B layer) is for joining the polyester film layer (A layer) and the antioxidant layer (C layer), and is used for bonding the polyester film layer (A layer).
Layer) and the antioxidant layer (C layer) are not particularly limited as long as they can be joined with a desired adhesive strength.
It is preferable that the absorption of light energy in the visible light region and the heat ray region is as small as possible, and furthermore, the color fading property is small over time. In particular, the adhesive layer (B layer) is made of visible light (wavelength region 400 to 7).
(00 nm) having a transparency of 95% or more.

The adhesive layer (B layer) can be formed by an adhesive. As the pressure-sensitive adhesive forming the adhesive layer (B layer), various transparent pressure-sensitive adhesives can be used, and specifically, for example, an acrylic resin-based pressure-sensitive adhesive, a silicone resin-based pressure-sensitive adhesive, a vinyl resin-based pressure-sensitive adhesive Agents and the like. These transparent adhesives may be used singly,
Alternatively, two or more kinds can be used in combination. Among these transparent pressure-sensitive adhesives, preferred are acrylic resin-based transparent pressure-sensitive adhesives.

The adhesive layer (B layer) may contain a stabilizer, an ultraviolet absorber and the like as required. Examples of the ultraviolet absorber include a benzophenone-based ultraviolet absorber and a benzotriazole-based ultraviolet absorber. Examples of the light stabilizer include a hindered amine light stabilizer.

As the pressure-sensitive adhesive for forming the adhesive layer (B layer), for example, Olivine BPS-5160 (manufactured by Toyo Ink Mfg.), Olivine BPS3233 (manufactured by Toyo Ink Mfg.), X-395-270S-1 (Seiden Chemical Co., Ltd.) Commercially available products, such as those manufactured by the company, can also be used.

When the adhesive layer (B layer) is formed of a pressure-sensitive adhesive, for example, the pressure-sensitive adhesive is
A method of applying the composition to the surface of the polyester film layer (A layer) and / or the surface of the antioxidant layer (C layer) is mentioned. Coating methods include, for example, reverse roll coating, gravure coating, kiss coating, roll brushing, spray coating, air knife coating, wire barber coating, pipe doctoring, impregnation / coating, and curtain coating. A known method such as a method can be used, and these methods can be used alone or in combination.

The thickness of the adhesive layer (B layer) is not particularly limited. When the adhesive layer (B layer) is formed by applying an adhesive, the amount of the applied adhesive is 5 to 30 g / m2 when dried. it is preferable to ^two. When the coating amount is less than 5 g / m ² , the adhesive strength decreases, and when it exceeds 30 g / m ² , the absorption of light energy in the visible light region and the heat ray region increases.

In the present invention, the antioxidant layer (C layer)
Are provided for the purpose of preventing discoloration of the metallic silver layer (D layer) and improving the durability. The structure of the antioxidant layer is not particularly limited as long as it can be bonded to the polyester film layer (A layer) by the adhesive layer (B layer) and has a function of preventing oxidation of the metallic silver layer (D layer). Examples of the material for forming the antioxidant layer (C layer) include resins such as acrylic resins, epoxy resins, polyester resins, urethane resins, and alkyd resins, and inorganic substances such as SiO ₂ . When the antioxidant layer (C layer) is formed from a resin, for example, a method such as roll coating, gravure coating, or spray coating can be used.
When the antioxidant layer (C layer) is formed from an inorganic material, for example, a method such as a vapor deposition method can be used. The thickness of the antioxidant layer (C layer) is not particularly limited, but when the antioxidant layer (C layer) is formed of an inorganic material, the thickness is preferably 5 n.
m to 50 nm, and when the antioxidant layer (C layer) is formed of a resin, the thickness is preferably 1 to 10 μm. If the thickness of the antioxidant layer (C layer) is smaller than the above range, a sufficient antioxidant effect cannot be obtained. When the antioxidant layer (C layer) is formed of a resin, the energy of reflected light tends to decrease.

Since the reflection film for a surface light source of the present invention has a metal silver layer (D layer), the reflection characteristics in the visible light region and the heat ray region, particularly, the heat ray reflectivity are improved. The configuration of the metallic silver layer (D layer) is not particularly limited, but the metallic silver layer (D
As a method for forming the layer, for example, a method usually used for forming a metal thin film such as an evaporation method, a sputtering method, and an ion plating method can be used. The thickness of the metallic silver layer (D layer) is not particularly limited, but is preferably in the range of 10 nm to 80 nm. When the thickness of the metallic silver layer (D layer) is less than 10 nm, the reflectance in the visible light region and the heat ray region is reduced, and the thickness is 80 n.
If it exceeds m, the productivity of the reflective film for a surface light source of the present invention will decrease, and the cost will increase.

In the present invention, the thermoplastic resin layer (E
The layer serves as a base material for forming the metallic silver layer (D layer), and also serves as a protective layer for the metallic silver layer (D layer). The configuration of the thermoplastic resin layer (E layer) is not particularly limited. For example, as a material for forming a thermoplastic resin layer (E layer),
The same polyester-based resin (a) as the polyester-based resin (a) used for the polyester film layer (layer A) can be used, but polyethylene terephthalate-based resin is preferable from the viewpoint of dimensional stability.

In the present invention, the pressure-sensitive adhesive layer (B layer)
Each of the antioxidant layer (C layer), the metallic silver layer (D layer), and the thermoplastic resin layer (E layer) has a fluorescent whitening agent, an antistatic agent, An appropriate amount of an ultraviolet absorber or the like can be contained.

In the present invention, the antioxidant layer (C layer), the metallic silver layer (D layer), and the thermoplastic resin layer (E layer) are used in order to efficiently produce a surface light source film. A metal silver layer (D layer) is laminated on one surface of the (E layer) by a vapor deposition method or the like, and the thermoplastic resin layer (E layer) of the metal silver layer (D layer) is laminated.
It is preferable to form an antioxidant layer (C layer) on the surface opposite to the layer) side by a coating method or the like. Further, an antioxidant layer (C layer), a metallic silver layer (D layer), and a thermoplastic resin layer (E
) May be used as a laminate in which a commercially available product such as a silver vapor-deposited film (thickness: 12 μm, 38 μm, or the like) manufactured by Saiichi Kogyo Co., Ltd. may be used.

In the case of forming a laminate in which an antioxidant layer (C layer), a metallic silver layer (D layer) and a thermoplastic resin layer (E layer) are formed in advance, the laminate and the above-mentioned polyester film ( The method of laminating the layer (A layer) with the pressure-sensitive adhesive layer (B layer) is not particularly limited. The reflective film for a surface light source of the present invention is formed by a polyester film layer (A layer), an adhesive layer (B layer), an antioxidant layer (C layer), a metal silver layer (D layer), and a thermoplastic resin layer (E layer). As a laminating method in the case of forming a multi-layer structure in which is laminated, for example, the following method can be mentioned.

The pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer (layer B) is applied to one surface of the polyester film (layer A) as described above. The coating method is preferably a die coating method. In addition, it is preferable from the point of stable formation of the pressure-sensitive adhesive layer and smoothing of the surface that the pressure is guided between the pair of rolls immediately after the application of the pressure-sensitive adhesive to adjust the amount of the pressure-sensitive adhesive applied. When a solvent is used at the time of applying the adhesive, the solvent is dried and removed immediately after the application to form an adhesive layer (B layer). Thereafter, the surface of the laminate in which the antioxidant layer (C layer), the metallic silver layer (D layer), and the thermoplastic resin layer (E layer) are formed in advance and on the antioxidant layer (C layer) side and the pressure-sensitive adhesive layer (B A reflective film for a surface light source is formed by, for example, a method of laminating the layer and the surface, guiding the sheet between two rolls, and applying heat and pressure. When thermocompression bonding is performed between two rolls as described above, the surface temperature of each roll is in the range of 30 ° C. to 100 ° C., and the thermoplastic resin layer (E layer) side surface of the laminate and the polyester film It is preferable that the temperature condition is such that the temperature difference on the (A layer) side surface is within 50 ° C. When the above temperature difference exceeds 50 ° C., the film is easily curled, and the workability in the cutting and printing processes in the subsequent process and the quality of the film are deteriorated.
In the case of heat-pressing between two rolls as described above, the pressure at the time of pressing varies depending on the temperature of the rolls, but the linear pressure is preferably in the range of 100 to 2000 N / cm. It is preferable from the viewpoint of improving the smoothness of the surface of the light source reflective film.

When the reflective film for a surface light source of the present invention has the above-mentioned multilayer structure, the polyester film (A layer), the pressure-sensitive adhesive layer (B layer), the antioxidant layer (C layer), and the metallic silver layer In addition to the (D layer) and the thermoplastic resin layer (E layer), other layers may be provided as long as the function of the present invention is not impaired.

Hereinafter, the effects of the present invention will be described in more detail with reference to Test Examples and Examples. However, the present invention is not limited to these, and changes may be made within a range not to impair the effects of the present invention. Are all included in the technical scope of the present invention. Test example Test method (1) Average reflectance in the light wavelength region of 760 nm to 950 nm (heat ray region) Example 1 and the light incident surfaces of the reflecting films for surface light sources of Comparative Examples 1 to 3 and the reflecting plate of Comparative Example 4 were spectrally analyzed. Photometer (spectrophotometer U-3500,
Attach an integrating sphere to Hitachi, Ltd.
The reflectance at each wavelength of 1 nm was measured in the range of nm to 950 nm, and the average value was defined as the average reflectance. This average reflectivity represents the thermal warfare reflectivity. In addition, as a standard of the reflectance, an alumina white plate (210-0740 manufactured by Hitachi Instrument Service Co., Ltd.)
Was set to 100%.

(2) Gloss For the reflecting film for the surface light source of Example 1 and Comparative Examples 1 to 3, and the light incident surface of the reflecting plate of Comparative Example 4, a gloss meter (VGS-101DP, Nippon Electric Co., Ltd.) Color Industry Co., Ltd.
The angle of the light incident direction (incident angle) is 60 degrees, and the angle on the light receiving side (light receiving angle) is 50 degrees, 60 degrees, and 70 degrees.
Gloss (G (50), G (60), G (7
0)), and G (70) / G (60) and G (50) / G (60) were calculated.

2. Test Results Table 1 shows the results of the tests (1) and (2).

[0054]

Example 1 [Preparation of polyester film layer (layer A)] The following materials were charged into a twin-screw extruder with the following composition, melted and extruded from a T-die at 290 ° C, and then subjected to static electricity. The unstretched sheet was obtained by tightly contacting with a cooling rotating roll and solidifying. Next, the unstretched sheet was stretched 3.1 times at 80 ° C. in a roll stretching machine, and then transversely stretched 2.6 times at 125 ° C. with a tenter, and further stretched 220 ° C. with a tenter. And stretched 1.4 times. Then 235
By subjecting the film to a relaxation heat treatment of 4% at 4 ° C., a 188 μm-thick polyester resin film having a large number of cavities inside the film was obtained.
Layer). [Constituent material of polyester film layer (A layer)] Polyethylene terephthalate resin (intrinsic viscosity: 0.62) 74% by weight General-purpose polystyrene resin (PS) [T575-57U manufactured by Mitsui Toatsu Chemicals, Inc.] 25% by weight maleimide Modified polystyrene resin (M-PS) [NH1200 manufactured by Mitsui Toatsu Chemicals, Inc.] 1% by weight

[Lamination of Each Layer] An adhesive (X395-270S-1: manufactured by Seiden Chemical Co., Ltd.) was applied to one surface of the polyester film layer (layer A) by a die coat method.
It was applied so as to be 30 g / m ^{2 by} ET, and dried at 100 ° C. for 1 minute to form an adhesive layer (B layer). Subsequently, 1 μm
An antioxidant layer having a thickness of 50 nm, a metallic silver layer having a thickness of 50 nm,
The surface of the antioxidant layer of a silver film (Ag12, manufactured by Saiichi Kogyo Co., Ltd.) having a μm-thick polyester layer (composed of polyethylene terephthalate: corresponding to the E layer) and the surface of the pressure-sensitive adhesive layer (B layer) are superposed. , Guided between two rolls, and bonded by heating and pressing to obtain a reflection film for a surface light source as an antioxidant layer (C layer), a metallic silver layer (D layer), and a thermoplastic resin layer (E layer). . In addition, when bonding the antioxidant layer surface and the pressure-sensitive adhesive layer (B layer) surface between two rolls,
The surface temperature of each roll was set to 50 ° C., and the pressure during bonding was set to a linear pressure of 1000 N / cm. The polyester film layer (layer A) of the obtained reflection film for a surface light source was used as a light incident surface.

Comparative Example 1 A reflective film for a surface light source was obtained in the same manner as in Example 1 except that the constituent materials and the composition of the polyester film layer (layer A) were changed to the following materials and compositions. A layer) was used as a light incident surface. [Constituent material of polyester film layer (A layer)] Polyethylene terephthalate resin (intrinsic viscosity: 0.62) 71% by weight General-purpose polystyrene resin (PS) [T575-57U manufactured by Mitsui Toatsu Chemicals, Inc.] 25% by weight Maleimide-modified polystyrene resin (M-PS) [NH1200 manufactured by Mitsui Toatsu Chemicals, Inc.] 1% by weight Titanium dioxide [TA-300 manufactured by Fuji Titanium Co., Ltd.] 3% by weight

Comparative Example 2 A 150 μm-thick polyester resin film having a large number of voids inside a film produced by the same method as the polyester film layer (layer A) of Example 1 was used as a reflective film for a surface light source. Is a light incident surface.

Comparative Example 3 A polyester film (manufactured by Toyobo Co., Ltd., No. E5000, thickness 18) was coated on the surface of the antioxidant layer of the same silver film (Ag12, manufactured by Saiichi Kogyo Co., Ltd.) as used in Example 1.
8 μm) was adhered in the same manner as the adhesion between the antioxidant layer surface and the pressure-sensitive adhesive layer (B layer) surface in Example 1 to obtain a reflective film for a surface light source. The surface of the antioxidant layer of the silver film was used as the light incident surface.

Comparative Example 4 An aluminum plate (Ra = 0.161 μm) having a thickness of 0.5 mm was used as a reflector.

[0060]

[Table 1]

[0061]

The reflection film for a surface light source of the present invention has a practically sufficient reflection performance in the visible light region by limiting the average reflectance and the glossiness so as to satisfy the above-mentioned specific relationship. In addition, it is possible to reduce a variation in luminance in the surface light source when the surface light source is formed. Furthermore, since the heat ray reflectance is high, it is possible to efficiently reflect the heat energy emitted from the light source and the electronic components arranged around the liquid crystal element to the liquid crystal element side, and to reduce the deterioration of the basic performance of the liquid crystal display even at low temperatures. It is suitable for a surface light source used for a backlight mechanism of a liquid crystal display device using a liquid crystal element.

Continued on the front page F-term (reference) 2H042 BA01 BA20 2H091 FA16Z FB02 FB08 FC09 GA16 GA17 KA10 LA05 LA18 4F100 AB24C AK01A AK01D AK41A AK42D AL05A AL05D BA04 BA07 BA10A BA10D DC11A DJ10A EC03 ECB3EBH EBH EBH 382 JB16D JL10A JN06 JN21

Claims (6)

[Claims] An average reflectance in a wavelength region of light of 760 to 950 nm is 100% or more, and an incident angle is 60
G (60), incident angle 60
G (50), incident angle 60
When the glossiness at a light receiving angle of 70 degrees is G (70), G
(60) ≧ 40%, G (50) ≧ 10%, G70 ≧ 10
%, G (70) / G (60) ≧ 0.2, G
(50) / G (60) ≧ 0.2, wherein the reflective film is for a surface light source. 2. A polyester film layer (A layer), an adhesive layer (B layer), an antioxidant layer (C layer), a metallic silver layer (D layer), and a thermoplastic resin layer in at least the direction of light incidence. (E layer) and a polyester film layer (A
2. The reflection film for a surface light source according to claim 1, wherein the layer (1) is made of a white polyester film containing cavities. 3. The polyester film layer (layer A) contains substantially no inorganic particles.
The reflective film for a surface light source according to the above. 4. A fine polyester film layer (layer A) mainly composed of a polyester resin (a) and a thermoplastic resin (b) incompatible with the polyester resin (a). The reflective film for a surface light source according to claim 2, wherein the reflective film is made of a white polyester film containing cavities. 5. The thermoplastic resin (b) is incompatible with the polyester resin (a), and is made of two kinds of thermoplastic resins having different surface tensions, that is, different surface energies. The reflective film for a surface light source according to claim 4. 6. The reflection film for a surface light source according to claim 2, wherein the thermoplastic resin layer (E layer) is mainly composed of a polyethylene terephthalate-based resin.