JP6336308B2 - White reflective film for direct surface light source - Google Patents

Description

  The present invention relates to a white reflective film suitably used as a reflector for a direct type surface light source. In particular, the present invention relates to a white reflective film suitably used as a reflector for a direct surface light source of a liquid crystal display device.

  A backlight unit of a liquid crystal display device (LCD) includes a direct type having a light source and a reflective film on the back surface of the liquid crystal display panel, and a light guide plate having a reflective plate on the back surface of the liquid crystal display panel. There is an edge light type having a light source on the side surface of the light guide plate. Conventionally, as a backlight unit used for a large LCD, a direct type CCFL backlight unit using a CCFL as a light source has been mainly used from the viewpoint of excellent screen brightness and uniformity of brightness in the screen. The edge light type is often used for relatively small LCDs such as notebook PCs. However, due to the development of light sources and light guide plates in recent years, the brightness of the edge light type and the brightness within the screen have been improved. Uniformity is improved, and an edge light type backlight unit has been used not only for a relatively small size but also for a large LCD. This has the advantage that the LCD can be made thinner. As such an edge light type backlight unit, an edge light type LED backlight unit using a light emitting diode (LED) as a light source is often used.

  In recent years, direct-type backlight units using LEDs as light sources (direct-type LED backlight units) have come to be used for reasons such as reduction of power consumption and cost reduction by omitting a light guide plate ( Patent Documents 1 and 2). Such a direct type LED backlight unit generally has an aspect in which the LED light source is arranged on substantially the same plane as the reflector.

  In the direct type LED backlight unit, in order to suppress power consumption and manufacturing cost, it is desirable to arrange the LED as wide as possible and reduce the number of LEDs to be used. However, when the distance between the LEDs becomes too large, there is a problem in that luminance spots such as portions corresponding to the LEDs in the display device are likely to be dark.

Therefore, in order to suppress the luminance unevenness, a plurality of lens sheets and diffusion sheets are used by being laminated (for example, Patent Documents 3 and 4), or a structure that allows a wide distance from the LED light source to the diffusion board is used. Although the method is adopted, the former has a problem that the loss of light tends to increase and the luminance is lowered, and the latter has a problem that the backlight unit becomes thick and is poor in design as a display device. There is.
In addition, as a technique for suppressing luminance unevenness in a direct type backlight unit using a CCFL light source, a reflection film having an uneven surface has been proposed (Patent Documents 5 and 6).

JP 2012-204336 A JP 2010-210891 A JP 2012-242664 A JP 2012-94266 A JP 2010-266801 A JP 2006-318724 A

  On the other hand, in the direct type LED backlight unit, as described above, the LED light source is on the reflective film on the almost same plane as the reflective film. Therefore, the conventional direct type CCFL backlight unit is relatively different from the light source and the reflective film. The target position is different. Specifically, in the direct type LED backlight unit, the distance between the light source and the reflective film is reduced. For this reason, the present inventors have found that the brightness unevenness suppression in the direct type LED backlight unit may be insufficient with the brightness unevenness suppression technology proposed in the conventional direct type CCFL backlight unit. did.

Furthermore, the problem relating to such luminance spots has been studied by improving a lens cap used in combination with a light source (LED light source).
For example, a reflection type (also referred to as a wide-angle diffusion type) lens cap allows light emitted from a light source (LED light source) toward the front side of the LCD, and a small amount of sub-light is extracted as it is toward the front side of the LCD. The main light is reflected to the back side when passing through the lens cap, led to the reflective film provided on the back side rather than the light source, and then reflected again to the front direction to extract the light in the front direction, thereby extracting the light source The brightness difference between the place where there is and where there is no is reduced, and the brightness unevenness is suppressed.

  In addition, the upward diffusion lens cap is used when a part of the light emitted from the light source toward the front of the LCD is extracted as it is toward the front of the LCD and the remaining part of the light hits the lens cap. The light is reflected back into the lens cap, and is reflected again in the front direction while diffusing light with a diffuse reflector having a prism shape etc. provided on the bottom surface of the lens cap. Thus, the diffusion component of the reflected light is increased to suppress the luminance unevenness.

  However, for example, when a reflective lens cap is used, the light reflected to the back side when passing through the lens cap enters the reflective film at a shallow angle (large incident angle), and as described above, the reflective film The situation of incident light on the screen is significantly different from the case where CCFL is used as a light source, so that the luminance unevenness suppression technology in the conventional CCFL light source may be insufficient and the luminance unevenness suppression effect may be inferior. The present inventors found and focused on this.

  In view of the above background art, the present invention provides a white reflective film capable of suppressing luminance unevenness when used as a direct type surface light source having a light source provided with a lens cap (particularly, a reflective lens cap) as a light source. For the purpose.

  The present inventors have used a light source having a lens cap (particularly, a reflective lens cap) as a light source, and in a direct type surface light source in which the distance between the light source and the reflective film is short, light is emitted at a shallow angle with respect to the reflective film. Therefore, the conventional reflective film was found to have a low diffusibility of the reflected light when the incident angle is shallow, and therefore, it was found that luminance spots were generated. That is, for example, when a conventional CCFL light source is used, the light source is provided at a relatively far position above the reflective film, and the incident angle of light with respect to the reflective film is deep (the incident angle is small, for example, about 10 ° at most). In the case of the conventional reflective film, the reflected light has an appropriate diffusibility and tends to suppress luminance unevenness. On the other hand, for example, a recent direct type LED backlight unit (described above) Including a lens cap such as this) is mainly about 50 to 85 ° with respect to the reflection film, and when the incident angle is shallow (incident angle is large), The reflection film has a low diffusibility of reflected light and is specularly reflected, and a mechanism is considered in which such reflected light selectively irradiates a part, resulting in luminance spots.

  Then, the present inventors have provided a surface layer containing particles on the surface of the reflective layer, and by setting the surface shape of the surface layer to a specific aspect, luminance spots when using the lens cap as described above are used. Has been found to be suppressed, and the present invention has been achieved.

That is, the present invention employs the following configuration in order to achieve the above-described problems.
1. A reflective film having a reflective layer A and a surface layer B containing particles mainly composed of a resin, wherein the reflective layer A contains voids, and the void volume ratio is 15 volume% or more and 70 volume% or less. A projection is formed by the particles on the surface of the surface layer B opposite to the reflective layer A, and a two-dimensional reflected light analysis is performed using a bidirectional reflectance distribution function (BRDF) measuring device. When the incident light angle is 60 °, the integrated value (S60) of the reflected light intensity in all directions when the reflected light intensity at the reflection angle −60 ° is 1, and when the incident angle is 75 °. The integrated value (S75) of the reflected light intensity in all directions when the reflected light intensity at the reflection angle of −75 ° is 1, and the reflected light intensity at the reflection angle of −30 ° when the incident angle is 30 ° is 1. The integrated value of reflected light intensity in all directions (S30) And comprising a white reflective film for a direct type surface light source having a light source with a lens cap.
S75 / S30 = 0.25 or more to 0.50 or less (1)
2. 2. The white reflective film for direct surface light source according to 1 above, wherein the lens cap is a reflective lens cap .
3 . The white reflective film for a direct type surface light source according to 1 or 2 above, wherein the direct type surface light source is an LED light source, and the LED light source is disposed on the white reflective film.
4 . A direct type surface light source using the white reflective film described in any one of 1 to 3 above.

  According to the present invention, when used for a direct type surface light source having a light source provided with a lens cap (particularly, a reflective lens cap) as a light source, even if the distance between the reflective film and the light source is short, luminance spots are eliminated. A white reflective film that can be suppressed can be provided.

It is a schematic diagram showing an example of arrangement | positioning with a light source and a reflecting plate. It is a schematic diagram showing an example of arrangement | positioning with a light source and a reflecting plate.

The white reflective film of the present invention has a reflective layer A and a surface layer B.
Hereafter, each structural component which comprises this invention is demonstrated in detail.

[Reflection layer A]
The reflective layer A in the present invention is a layer that is composed of a thermoplastic resin and a void forming agent and contains a void forming agent so as to exhibit a white color. The void forming agent will be described in detail later. For example, inorganic particles and a resin that is incompatible with the thermoplastic resin that constitutes the reflective layer A (hereinafter may be referred to as an incompatible resin). Can be used. The reflectance of the reflective layer A at a wavelength of 550 nm is preferably 95% or higher, more preferably 96% or higher, and particularly preferably 97% or higher. Thereby, it becomes easy to make the reflectance of a white reflective film into a preferable range.

The reflection layer A has voids in the layer as described above, and the proportion of the void volume to the volume of the reflection layer A (void volume ratio) is 15% by volume or more and 70% by volume or less. Preferably there is. By setting it as such a range, the improvement effect of a reflectance can be made high and it becomes easy to obtain the above reflectances. Moreover, the improvement effect of film forming stretchability can be heightened. When the void volume ratio is too low, a preferable reflectance tends to be difficult to obtain. From such a viewpoint, the void volume ratio in the reflective layer A is more preferably 30% by volume or more, and particularly preferably 40% by volume or more. On the other hand, if it is too high, the effect of improving the film-forming stretchability tends to be low. From such a viewpoint, the void volume ratio in the reflective layer A is more preferably 65% by volume or less, and particularly preferably 60% by volume or less.
The void volume ratio can be achieved by adjusting the type, size, and amount of the void forming agent in the reflective layer A.

(Thermoplastic resin)
Examples of the thermoplastic resin constituting the reflective layer A include thermoplastic resins made of polyester, polyolefin, polystyrene, and acrylic. Among these, polyester is preferable from the viewpoint of obtaining a white reflective film excellent in mechanical properties and thermal stability.
As such a polyester, it is preferable to use a polyester comprising a dicarboxylic acid component and a diol component. Examples of the dicarboxylic acid component include components derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, adipic acid, sebacic acid, and the like. Examples of the diol component include components derived from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like. Among these polyesters, aromatic polyesters are preferable, and polyethylene terephthalate is particularly preferable. Polyethylene terephthalate may be a homopolymer, but a copolymer is preferred from the viewpoint that crystallization is suppressed when the film is stretched uniaxially or biaxially and the effect of improving film-forming stretchability is enhanced. Examples of the copolymer component include the dicarboxylic acid component and the diol component described above, and isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferable from the viewpoint of high heat resistance and a high effect of improving film-forming stretchability. The proportion of the copolymerization component is, for example, 1 to 20 mol%, preferably 2 to 18 mol%, more preferably 3 to 15 mol%, particularly preferably 7 to 11 based on 100 mol% of the total dicarboxylic acid component of the polyester. Mol%. By making the ratio of a copolymerization component into this range, it is excellent in the improvement effect of film forming stretchability. Moreover, it is excellent in thermal dimensional stability.

(Void forming agent)
In the reflective layer A, when inorganic particles are used as the void forming agent, the inorganic particles are preferably white inorganic particles. Examples of the white inorganic particles include barium sulfate, titanium dioxide, silicon dioxide, and calcium carbonate particles. These inorganic particles should just select an average particle diameter and content so that a white reflective film may have an appropriate reflectance, and these are not specifically limited. Preferably, the reflectance of the reflective layer A or the white reflective film may be within a preferable range in the present invention. Moreover, what is necessary is just to make it the void volume ratio in the reflection layer A become the preferable range in this invention. Taking these into consideration, the average particle size of the inorganic particles is, for example, 0.2 to 3.0 μm, preferably 0.3 to 2.5 μm, and more preferably 0.4 to 2.0 μm. The content thereof is preferably 20 to 60% by mass, more preferably 25 to 55% by mass, and most preferably 31 to 53% by mass based on the mass of the reflective layer A. Further, by adopting the particle mode as described above, it is possible to appropriately disperse in the polyester, it is difficult for the particles to aggregate, and a film without coarse protrusions can be obtained. Breaking during stretching starting from is also suppressed. The inorganic particles may have any particle shape, for example, a plate shape or a spherical shape. The inorganic particles may be subjected to a surface treatment for improving dispersibility.

  When an incompatible resin is used as the void forming agent, the incompatible resin is not particularly limited as long as it is incompatible with the thermoplastic resin constituting the layer. For example, when the thermoplastic resin is polyester, polyolefin such as polyethylene or polypropylene, cycloolefin, polystyrene, polymethylpentene, or the like is preferable. These may be in the form of particles. Moreover, the content should just select an average particle diameter and content so that a white reflective film may have a suitable reflectance similarly to the case of an inorganic particle, These are not specifically limited. Preferably, the reflectance of the reflective layer A or the white reflective film may be within a preferable range in the present invention. Moreover, what is necessary is just to make it the void volume ratio in the reflection layer A become the preferable range in this invention. Considering these facts, the content is preferably 10 to 50% by mass, more preferably 12 to 40% by mass, and most preferably 13 to 35% by mass based on the mass of the reflective layer A.

(Other ingredients)
As long as the purpose of the present invention is not hindered, the reflective layer A is made of other components such as UV absorbers, antioxidants, antistatic agents, fluorescent brighteners, waxes, particles and resins different from the void forming agents. Can be contained.

[Surface layer B]
Hereinafter, the surface layer B in the present invention will be described in detail.
The surface layer B in the present invention is a layer containing a resin as a main constituent and particles. Projections are formed by the particles on the surface of the surface layer B (surface opposite to the reflective layer A). And the aspect (integral value, a ratio, etc.) of the reflected light intensity in a specific angle has become a specific aspect by this protrusion. Here, the “main constituent component” means that the surface layer B contains an essential component other than the resin and an optional component, and the remaining amount. For example, it is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more with respect to the mass of the surface layer B.

  In the present invention, a two-dimensional reflected light analysis is performed on the surface of the surface layer B using a bidirectional reflectance distribution function (BRDF) measuring device, and the reflection angle is −60 ° when the incident angle is 60 °. The integrated value (S60) of the reflected light intensity in all directions when the reflected light intensity is 1 is 50 or more. By setting it as such an aspect, suitable diffusibility can be provided to the reflected light of the light which injected at a shallow angle, and, thereby, a brightness spot can be suppressed. Note that the incident angle and the reflection angle are represented by 0 ° in the film perpendicular direction, plus the incident angle direction side, and minus the reflection angle direction side. That is, the reflection angle of the specular reflection light with respect to the incident light having an incident angle of 60 ° is expressed as −60 °.

  According to the BRDF measuring apparatus, it is possible to evaluate and measure the diffusibility of reflected light with respect to incident light with various incident angles. For example, when the surface of the surface layer B is irradiated with light at an incident angle of 60 ° as described above, the angle to each direction on a plane that includes the incident angle direction and is orthogonal to the plane direction of the reflective film at that time Another reflected light intensity can be measured. At this time, with respect to the intensity of the specular reflection component in the −60 ° direction, the greater the diffusibility, the greater the reflected light intensity at other angles, while the smaller the diffusivity, the reflected light intensity at other angles. , So that the size of the diffusivity can be seen. Therefore, as described above, when the incident angle is 60 °, the total (integral value) of the reflected light intensity in all directions (−90 ° to + 90 °) when the reflected light intensity in the −60 ° direction is 1. By obtaining the diffusivity, the diffusivity can be evaluated so that the diffusivity is high when the value is large.

  From the above viewpoint, S60 is preferably 52 or more, more preferably 54 or more, and further preferably 55 or more. When S60 is small, the light incident at a shallow angle is insufficient in diffusibility of the reflected light, and the light from the light source (LED light source) is reflected in a state close to regular reflection, thereby causing luminance spots. It will occur. In order to suppress such luminance unevenness, S60 is preferably large, but if it is too large, it tends to be a surface aspect that also improves the diffusibility of reflected light at a deep angle. 100, preferably 90, more preferably 80, and even more preferably 73.

Further, in the present invention, the integrated value (S75) of the reflected light intensity in all directions when the reflected light intensity at the reflection angle of −75 ° is set to 1 at the incident angle of 75 ° and the incident angle of 30 °. The integrated value (S30) of the reflected light intensity in all directions when the reflected light intensity at a reflection angle of −30 ° is 1 satisfies the following expression.
S75 / S30 = 0.25 or more and 0.50 or less ... Formula (1)

  By satisfying the above formula, the diffusibility of the reflected light of the light incident on the white film at a shallow angle from the light source (mainly at an incident angle of about 50 to 85 °) becomes appropriate, and luminance spots can be suppressed. If the ratio S75 / S30 is too large or too small, the diffusibility of the reflected light becomes inappropriate and luminance spots are generated. That is, if it is too small, the diffusibility of the reflected light of the light incident at a shallow angle tends to be too low, and on the other hand, if too large, the diffusibility of the reflected light of the light incident at a shallow angle is too high. It tends to be difficult for light to reach the periphery of the display, and tends to cause brightness spots in the periphery. From this viewpoint, the ratio of S75 / S30 is preferably 0.27 or more, more preferably 0.29 or more, still more preferably 0.30 or more, and preferably 0.48 or less, more preferably 0.45 or less, more preferably 0.43 or less, particularly preferably 0.41 or less, and most preferably 0.33 or less.

  In order to change the surface shape of the surface layer B to the above-described aspect, it is possible to adopt a particle aspect as described below or adopt a manufacturing method. The surface layer B may be formed by a method of laminating by a coextrusion method or a laminating method, or a method of laminating by coating. Furthermore, the surface which satisfy | fills the said aspect can also be formed by performing surface treatments, such as a plasma treatment suitable for the surface.

(resin)
The resin constituting the surface layer B in the present invention is preferably a thermoplastic resin.
As the thermoplastic resin constituting the surface layer B, the same thermoplastic resin as the thermoplastic resin constituting the reflective layer A described above can be used. Among these, polyester is preferable from the viewpoint of obtaining a white reflective film excellent in mechanical properties and thermal stability. Moreover, when forming the surface layer B by the apply | coating method, an acrylic resin can also be preferably used as this thermoplastic resin.

  As this polyester, the same polyester as the polyester in the reflective layer A described above can be used. Among these polyesters, aromatic polyesters are preferable, and polyethylene terephthalate is particularly preferable from the viewpoint of obtaining a white reflective film excellent in mechanical properties and thermal stability. Polyethylene terephthalate may be a homopolymer, but is preferably a copolymer from the viewpoint that crystallization is suppressed when the film is stretched uniaxially or biaxially and the effect of improving film-forming stretchability is enhanced. Examples of the copolymer component include the dicarboxylic acid component and the diol component described above, and isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferable from the viewpoint of high heat resistance and a high effect of improving film-forming stretchability. . The proportion of the copolymerization component is, for example, 1 to 20 mol%, preferably 2 to 18 mol%, more preferably 3 to 17 mol%, and particularly preferably 12 to 16 mol%, based on 100 mol% of the total dicarboxylic acid component of the polyester. Mol%. By making the ratio of a copolymerization component into this range, it is excellent in the improvement effect of film forming stretchability. Moreover, it is excellent in thermal dimensional stability.

  Moreover, the surface layer B in this invention may have a crosslinked structure using a crosslinking agent with said thermoplastic resin. In that case, using a thermoplastic resin having a functional group capable of reacting with the reactive group of the crosslinking agent, a crosslinked structure of the crosslinking agent and the thermoplastic resin may be formed, or the reactive group of the crosslinking agent and An embodiment having a thermoplastic resin matrix and a crosslinked structure matrix in which a crosslinking agent is crosslinked may be used by using a thermoplastic resin having no functional group capable of reacting. When it has a crosslinked structure, the strength of the surface layer B tends to be improved. On the other hand, since it will be inferior to the recoverability of a film when there are too many crosslinked structures, it is preferable not to increase too many crosslinked structures from this viewpoint.

  The surface layer B can be formed by applying a coating solution during or after the production of the film. For example, the surface layer B may be formed simultaneously with the reflective layer A by employing a coextrusion method or the like. As described above, in order for the surface layer B to have a crosslinked structure, it is preferably formed by applying a coating liquid. The content of the crosslinking agent is preferably 35% by mass or less, more preferably 30% by mass or less, still more preferably 25% by mass or less, in particular, based on the solid content constituting the coating liquid from the above viewpoint. Preferably it is 20 mass% or less. Further, it is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more, and particularly preferably 5% by mass or more.

  As an example of the case where the surface layer B is formed by applying a coating liquid after the production of the film, particles, a resin (preferably a thermoplastic resin), an optional cross-linking agent and other components are dispersed or dissolved in a solvent. The coating liquid for forming the surface layer B obtained in this manner is applied to the film in a predetermined amount by using a coating apparatus, and is dried in an oven set at a temperature of 70 to 120 ° C., preferably stepwise. An example of forming the layer B can be given. As such a coating apparatus, for example, a die coating apparatus or a gravure roll coating apparatus can be used. As the solvent, methyl ethyl ketone (MEK), ethyl acetate, toluene, or the like can be used. The solid content concentration of the coating liquid is preferably 20 to 50% by mass, which makes it easy to suppress the aggregation of particles and increase the effect of suppressing particle dropout.

(particle)
In the present invention, it is important that the surface layer B surface satisfies the above-described diffusive aspect of reflected light (BRDF diffusibility). If such an aspect is satisfied, the average particle diameter and content of the particles are not particularly limited, but the following aspects can be mentioned as preferable aspects.

  The particles used for the surface layer B preferably have an average particle size of 0.5 μm or more and less than 20.0 μm. By setting it as such an aspect, it will become easy to satisfy the surface aspect mentioned above. If the average particle diameter is too small, it tends to be difficult to form a high protrusion, and the diffusibility of reflected light of light incident from a shallow angle tends to be small (S75 and S60 are small). The aspect of the reflected light intensity specified by the present invention tends to be difficult to achieve. From this viewpoint, the average particle diameter of the particles is more preferably 1.0 μm or more, further preferably 1.5 μm or more, further preferably 2.0 μm or more, and particularly preferably 3.0 μm or more. On the other hand, if the particles to be used are too large, the diffusibility to light incident from above tends to be small (S30 is small), and it is difficult to achieve the range defined by the present invention. Further, the particles tend to drop off from the surface layer B, and when dropped, the effect of improving the diffusibility of reflected light tends to be reduced. From this viewpoint, it is more preferably 18 μm or less, further preferably 17 μm or less, further preferably 10 μm or less, and particularly preferably 5 μm or less.

  Moreover, in order to make the surface aspect of the surface layer B surface more satisfactory, the content of particles in the surface layer B is preferably 3 to 50% by volume based on the volume of the surface layer B. If the content is too small, the surface diffusivity (S30, S60 and S75) tends to be reduced as a whole, and the range defined by the present invention related to this tends to be difficult to achieve. From this viewpoint, the content is more preferably 5% by volume or more, further preferably 7% by volume or more, particularly preferably 10% by volume or more, more preferably 45% by volume or less, and further preferably 40% by volume. Hereinafter, it is more preferably 35% by volume or less, particularly preferably 30% by volume or less.

The particles used for the surface layer B in the present invention may be organic particles, inorganic particles, or organic-inorganic composite particles regardless of the type.
More specifically, a particularly preferred embodiment will be described. Preferred organic particles include, for example, fluorine-containing resin particles such as polytetrafluoroethylene, high heat-resistant nylon particles, and high heat-resistant acrylic particles. Preferred inorganic particles include titanium oxide particles, barium sulfate, calcium carbonate, zinc oxide particles, zirconium oxide particles, aluminum oxide particles, silica particles, and the like. Among these, aggregated particles are preferable, aggregated inorganic particles are preferable, and aggregated silica particles are particularly preferable. By adopting such preferred particles, it becomes easier to achieve the surface aspects (S30, S60, S75) defined by the present invention.

In the present invention, it is preferable to employ aggregated particles as the particles, since light diffusion can be expected even in the aggregated particles, so that the diffusibility of reflected light of light having a shallow incident angle can be further improved. In addition, the use of aggregated particles also has the effect of further suppressing breakage failure at the time of film-forming stretching, and suppressing breakage failure during film production using self-collecting raw materials and influence on optical properties.
In addition, the inorganic particles, the high heat resistant nylon particles, and the high heat resistant acrylic particles have an effect that they are hardly melted or gas generated even if they are heat-processed. Furthermore, it is preferable from the point that the particle size distribution and the shape hardly change when the surface layer B is formed.

(Other ingredients)
The surface layer B may contain components other than the above-described constituent components as long as the object of the present invention is not impaired. Examples of such components include ultraviolet absorbers, antioxidants, antistatic agents, fluorescent brighteners, waxes, particles different from the above particles, resins different from the above resins, and the like.

  Further, the surface layer B may contain the void forming agent mentioned in the reflective layer A within a range not impairing the object of the present invention, and by making such an aspect, the effect of improving the reflectance is enhanced. be able to. On the other hand, if the content of the void forming agent in the surface layer B is reduced or if no void forming agent is contained, the effect of improving the film-forming stretchability can be increased. From these viewpoints, the void volume ratio in the surface layer B (ratio of the volume of voids in the surface layer B to the volume of the surface layer B) is preferably 0% by volume or more and less than 15% by volume, more preferably 5%. It is not more than volume%, particularly preferably not more than 3 volume%. In particular, in the present invention, since the effect of improving the reflection characteristics and film-forming stretchability can be enhanced at the same time, the preferred void volume ratio in the reflective layer A and the preferred void volume ratio in the surface layer B are simultaneously employed. It is particularly preferred.

[Layer structure]
The thickness of the reflective layer A in the present invention is preferably 80 to 300 μm. Thereby, the improvement effect of a reflectance can be made high. If it is too thin, the effect of improving the reflectance is low, while if it is too thick, it is inefficient. From such a viewpoint, it is more preferably 150 to 250 μm.

  Moreover, it is preferable that the thickness of the surface layer B (when there are a plurality of layers, the thickness of one layer forming the outermost layer on the light source side and serving as the reflection surface) is 5 to 70 μm. Thereby, the aspect of the protrusion formed on the surface of the surface layer B is more preferable in combination with the particles of the preferable aspect described above, and thus the diffusibility of the reflected light of the incident light at a shallow angle tends to be improved. In addition, problems due to thermal deflection and shrinkage are less likely to occur during actual use. If the surface layer B is too thin, there is a tendency for particles to drop off in the protrusions formed on the surface of the surface layer B. If the surface layer B is dropped, the effect of improving the diffusibility of reflected light tends to be reduced. Moreover, there exists a tendency for film forming stretchability to fall. On the other hand, if it is too thick, it tends to be difficult to form protrusions, and the diffusibility of reflected light at a shallow angle tends to decrease. In addition, the reflectance tends to be low. From this viewpoint, it is more preferably 10 μm or more, further preferably 15 μm or more, particularly preferably 18 μm or more, more preferably 60 μm or less, still more preferably 50 μm or less, still more preferably 40 μm or less, particularly preferably 30 μm or less. is there.

  In the present invention, preferred examples of the method for forming the surface layer B include a coextrusion method and a lamination method, and a coating method (various coating methods described later). In addition to the viewpoint of obtaining the above-mentioned more preferable protrusion mode, the more preferable thickness range of the surface layer B is the same as described above in the coextrusion method in consideration of the process suitability of each method. In the coating method, the thickness is more preferably 6 μm or more, further preferably 6.5 μm or more, more preferably 10 μm or less, and further preferably 8 μm or less.

  When the reflective layer A is A and the surface layer B is B, the laminated structure of the white reflective film is B / A two-layer configuration, B / A / B three-layer configuration, B / A / B ′ / A four-layer configuration of A (where B ′ represents an inner layer B ′ having the same configuration as the surface layer B), and a multilayer configuration of five or more layers in which B is disposed on at least one of the outermost layers. it can. Particularly preferred are a two-layer structure of B / A and a three-layer structure of B / A / B. Most preferably, it has a three-layer structure of B / A / B, and is excellent in film-forming stretchability. Further, problems such as curling are unlikely to occur.

  When the reflective layer A and the surface layer B are formed by the coextrusion method or the laminate method, particularly when the thickness of the entire white reflective film is 100%, the thickness ratio of the reflective layer A is preferably 50 to 95%, more preferably 60 to 90%, still more preferably 70 to 90%, and the thickness ratio of the surface layer B is preferably 5 to 50%, more preferably 10 to 40%, Preferably it is 10 to 30%. Thereby, the balance of each characteristic, such as a reflection characteristic and film forming stretchability, can be improved. Moreover, when forming by the apply | coating method, the thickness ratio of the reflection layer A becomes like this. Preferably it is 90 to 99%, More preferably, it is 92 to 98%, More preferably, it is 93 to 97%. The ratio is preferably 1 to 10%, more preferably 2 to 8%, still more preferably 3 to 7%. Thereby, the improvement effect of a reflection characteristic can be made high. Here, the thickness ratio of each layer refers to the ratio between the integrated thicknesses when there are a plurality of layers.

  In the present invention, in addition to the reflective layer A and the surface layer B, other layers may be provided as long as the object of the present invention is not impaired. For example, you may have the layer for providing functions, such as antistatic property, electroconductivity, and ultraviolet durability. Moreover, the void volume ratio for improving the film-forming stretchability of the film is relatively low (preferably 0% by volume or more and less than 15% by volume, more preferably 5% by volume or less, particularly preferably 3% by volume or less. A support layer C can also be provided.

[Film Production Method]
Hereinafter, an example of the method for producing the white reflective film of the present invention will be described.
In producing the white reflective film of the present invention, the reflective layer A obtained by a melt extrusion method or the like is coated with a melt resin coating method (including a melt extrusion resin coating method), a coating liquid coating method (in-line coating method or off-line coating). It is preferable from the viewpoint of film-forming stretchability that the surface layer B is formed by a coextrusion method, a laminating method, or the like to form a laminated structure. Especially, it is especially preferable that the white reflective film of the present invention is produced by laminating the reflective layer A and the surface layer B by a coextrusion method. Moreover, it is preferable that the reflective layer A and the surface layer B are directly laminated by a coextrusion method. Thus, by laminating by the coextrusion method, the interfacial adhesion between the reflective layer A and the surface layer B can be increased, and the surface layer B is formed again after the films are bonded together or after the film is formed. Therefore, mass production can be easily performed at low cost.

  Hereinafter, a manufacturing method in which polyester is employed as the thermoplastic resin constituting the reflective layer A and the thermoplastic resin constituting the surface layer B and a co-extrusion method is employed as a laminating method will be described. It is not limited to this, and other embodiments can be produced in the same manner with reference to the following. At that time, when the extrusion step is not included, the following “melt extrusion temperature” may be read as, for example, “melt temperature”. Here, the melting point of the polyester used is Tm (unit: ° C), and the glass transition temperature is Tg (unit: ° C).

First, a polyester composition for forming the reflective layer A is prepared by mixing polyester, a void forming agent, and other optional components. Moreover, what mixed polyester, particle | grains, and another arbitrary component as a polyester composition for forming the surface layer B is prepared. These polyester compositions are used after drying to sufficiently remove moisture.
Next, the dried polyester composition is put into separate extruders and melt-extruded. The melt extrusion temperature needs to be Tm or higher, and may be about Tm + 40 ° C.

  At this time, the polyester composition used for the production of the film, particularly the polyester composition used for the reflective layer A, is filtered using a nonwoven fabric type filter having an average opening of 10 to 100 μm made of stainless steel fine wires having a wire diameter of 15 μm or less. It is preferable. By performing this filtration, it is possible to suppress aggregation of particles that normally tend to aggregate into coarse aggregated particles, and to obtain a film with few coarse foreign matters. In addition, the average opening of a nonwoven fabric becomes like this. Preferably it is 20-50 micrometers, More preferably, it is 15-40 micrometers. The filtered polyester composition is extruded in a multilayer state from a die by a simultaneous multilayer extrusion method (coextrusion method) using a feed block in a molten state to produce an unstretched laminated sheet. The unstretched laminated sheet extruded from the die is cooled and solidified with a casting drum to obtain an unstretched laminated film.

  Next, this unstretched laminated film is heated by roll heating, infrared heating or the like, and stretched in the film forming machine axial direction (hereinafter sometimes referred to as the longitudinal direction or the longitudinal direction or MD) to obtain a longitudinally stretched film. . This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The film after the longitudinal stretching is then guided to a tenter and stretched in a direction perpendicular to the longitudinal direction and the thickness direction (hereinafter sometimes referred to as a transverse direction or a width direction or TD) to be biaxially stretched. A film.

  The stretching temperature is preferably a temperature of Tg or more and preferably Tg + 30 ° C. or less of the polyester (preferably the polyester constituting the reflective layer A), excellent in film-forming stretchability, and voids are preferably formed. The stretching ratio is preferably 2.5 to 4.3 times, more preferably 2.7 to 4.2 times in both the vertical direction and the horizontal direction. If the draw ratio is too low, uneven thickness of the film tends to be worsened, and voids tend not to be formed. On the other hand, if it is too high, breakage tends to occur during film formation. In the case of sequential biaxial stretching in which longitudinal stretching is performed and then lateral stretching is performed, the second stage (in this case, lateral stretching) is made about 10 to 50 ° C. higher than the first stage stretching temperature. Things are preferable. This is due to the fact that the Tg as a uniaxial film is increased due to the orientation in the first stage of stretching.

  Moreover, it is preferable to preheat a film before each extending | stretching. For example, the pre-heat treatment for transverse stretching may start from a temperature higher than Tg + 5 ° C. of the polyester (preferably the polyester constituting the reflective layer A) and gradually increase the temperature. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone.

The film after biaxial stretching is subsequently subjected to heat-fixing and heat-relaxing treatments in order to obtain a biaxially oriented film. However, following melt-extrusion to stretching, these treatments can also be performed while the film is running. it can.
The film after biaxial stretching has a constant width or a Tm −20 ° C. to (Tm−100 ° C.) melting point of the polyester (preferably the polyester constituting the reflective layer A) while holding both ends with clips. It is preferable to heat-treat under a width reduction of 10% or less and heat-set to lower the heat shrinkage rate. When the heat treatment temperature is too high, the flatness of the film tends to deteriorate, and the thickness unevenness tends to increase. On the other hand, if it is too low, the thermal shrinkage tends to increase.

  In the heat setting step, it is preferable to adopt the following conditions in order to satisfy the range of S60 and the range of S75 / S30 defined by the present invention. That is, in the present invention, in the heat setting step, the first heat treatment is performed at (Tm-100 ° C) to (Tm-50 ° C), the heat setting is performed at (Tm-50 ° C) to (Tm-20 ° C), The second heat treatment is performed at (Tm-100 ° C) to (Tm-50 ° C), these are continuously performed, and the heat setting temperature is higher by 30 ° C than the first heat treatment temperature and the second heat treatment temperature. Is preferred. Here, Tm is the same as described above. In combination with the preferred particle mode described above, the desired surface morphology can be obtained by rapidly increasing the temperature from the first heat treatment to heat setting and rapidly decreasing the temperature from the heat setting to the second heat treatment. It becomes easy to achieve S60 and S75 / S30 mentioned above. The temperature difference between the heat setting temperature and the first heat treatment temperature is preferably 40 ° C. or more, more preferably 50 ° C. or more, and the first heat treatment temperature is preferably (Tm−100 ° C.) to (Tm−). 60 ° C), more preferably in the range of (Tm-100 ° C) to (Tm-70 ° C). The temperature difference between the heat setting temperature and the second heat treatment temperature is preferably 40 ° or higher, more preferably 50 ° C. or higher, and the second heat treatment temperature is preferably (Tm-100 ° C.) to ( Tm-60 ° C), more preferably in the range of (Tm-100 ° C) to (Tm-70 ° C). The first heat treatment time, the heat setting time, and the second heat treatment time are each preferably preferably 1 to 60 seconds, more preferably 2 to 45 seconds, still more preferably 3 to 30 seconds, and S60 and S75 / S30 described above. Can be achieved more easily.

Further, in order to adjust the heat shrinkage, both ends of the film being held can be cut off, the take-up speed in the film vertical direction can be adjusted, and the film can be relaxed in the vertical direction. As a means for relaxing, the speed of the roll group on the tenter exit side is adjusted. As the rate of relaxation, the speed of the roll group is reduced with respect to the film line speed of the tenter, preferably 0.1 to 2.5%, more preferably 0.2 to 2.3%, particularly preferably 0.3. The film is relaxed by performing a speed reduction of ˜2.0% (this value is referred to as “relaxation rate”), and the longitudinal heat shrinkage rate is adjusted by controlling the relaxation rate. Further, the width of the film in the horizontal direction can be reduced in the process until both ends are cut off, and a desired heat shrinkage rate can be obtained.
In the biaxial stretching, a lateral-longitudinal sequential biaxial stretching method may be used in addition to the longitudinal-lateral sequential biaxial stretching method as described above. Moreover, it can form into a film using a simultaneous biaxial stretching method. In the case of the simultaneous biaxial stretching method, the stretching ratio is, for example, 2.7 to 4.3 times, preferably 2.8 to 4.2 times in both the longitudinal direction and the transverse direction.
Thus, the white reflective film of the present invention can be obtained.

[Characteristics of white reflective film]
(Reflectance, front brightness)
The reflectance measured from the surface layer B side of the white reflective film of the present invention is preferably 96% or more, more preferably 97% or more, still more preferably 97.5% or more, and particularly preferably 98.0% or more. is there. When the reflectance is 96% or more, high luminance can be obtained when used in a liquid crystal display device or illumination. Such a reflectance may be a preferable aspect such as increasing the void volume ratio of the reflective layer A, or a preferable aspect of each layer such as increasing the thickness of the reflective layer A or reducing the thickness of the surface layer B. Can be achieved.
Moreover, although the front luminance measured from the surface layer B side is calculated | required with the measuring method mentioned later, 5400 cd / m < ² > or more is preferable, 5450 cd / m < ² > or more is more preferable, 5500 cd / m < ² > or more is especially preferable.

[Direct type surface light source]
The white reflective film of the present invention is suitably used as a reflector for a direct type surface light source. Here, the direct type surface light source refers to a surface light source having a light source below the light emitting surface and a reflecting plate below the light emitting surface when the light emitting surface is turned up. On the other hand, when the light emitting surface is turned up, a light source plate is provided below the light emitting surface, a light reflector is provided below the light guide plate, and a surface light source having a light source on the side surface of the light guide plate is used as an edge. A light type (or side light type) surface light source will be distinguished.

  The direct type surface light source according to the present invention is an arrangement in which the distance between the light source and the reflector is particularly short. More precisely, the distance is the height of the light emitting surface of the light source (when the light source is an LED light source, the light emitting surface of the LED element) from the same plane as the reflecting plate surface (FIGS. 1 and 2). reference). By adopting the white reflective film of the present invention as a reflector of such a direct type surface light source, the effect of the present invention is exhibited. The distance between the light source and the reflecting plate is, for example, preferably 10 mm or less, more preferably 9 mm or less, and further preferably 8 mm or less. The conventional direct-type CCFL backlight unit adopting CCFL as the light source has a relatively long distance between the light source and the reflecting plate and exceeds 10 mm, so that it is difficult to obtain the effect of employing the white reflective film of the present invention. .

  The white reflective film of the present invention is particularly preferably used as a reflector for a direct type surface light source in which an LED light source is disposed on a reflector. An example of such a surface light source is a direct type LED backlight unit. Such a surface light source is usually in the form of the distance between the preferred light source and the reflector. Therefore, this is an application in which the effects of the present invention are particularly easily achieved. In addition, the description “the LED light source is disposed on the reflection plate” is not limited to the aspect in which the reflection plate and the LED light source are in contact with each other. For example, a module (substrate) may be arranged on the reflector and the LED light source may be arranged (FIG. 1), the module is arranged on the back of the reflector, and a hole is made in the LED light source portion of the reflector. And it is good also as an aspect which the LED light source protrudes from the reflecting plate surface (FIG. 2).

  The white reflective film of the present invention is more effective in suppressing luminance unevenness when used with a light source having a lens cap, a light source having a reflective lens cap, particularly an LED light source having a reflective lens cap. Therefore, it is particularly preferably used for a direct type surface light source using such a light source.

Hereinafter, the present invention will be described in detail by way of examples. Each characteristic value was measured by the following method.
(1) Light reflectance The integrating sphere was attached to a spectrophotometer (Shimadzu Corporation UV-3101PC), the reflectance when the BaSO ₄ white plate was 100% was measured at a wavelength of 550 nm, and this value was defined as the reflectance. The measurement was performed on the surface on the surface layer B side. In the case where the front and back surfaces have different surface layers B, the measurement was performed on the surface of the surface layer B serving as the reflecting surface (light source side).

(2) Average particle size of particles The surface layer B is peeled off and isolated from the sample film, the resin component containing the thermoplastic resin is dissolved using a solvent, and the particles obtained therefrom are converted into a laser scattering particle size distribution analyzer. (SALD-7000 manufactured by Shimadzu Corporation), the particle size distribution (standard deviation of the particle size) of the particles is obtained, and the particle size at d50 (the particle size that becomes 50% distribution from the smaller side on the volume distribution basis) is the average particle The diameter.

(3) Content of particles The surface layer B of a certain volume is peeled and isolated from the sample film, and the resin component containing the thermoplastic resin is dissolved using a solvent, and the mass and bulk density of the particles obtained therefrom are determined. Weighed and determined the content (mass%, volume%). The volume of the surface layer B was determined from the density (by the viscosity gradient tube method) and the mass of the surface layer B.

(4) Film thickness and layer structure A white reflective film is sliced with a microtome to obtain a cross section, and this cross section is observed at a magnification of 500 times using a Hitachi S-4700 field emission scanning electron microscope. The thickness of the whole film, the reflective layer A, and the surface layer B was determined. In addition, the thickness of the whole film and the surface layer B was made into the thickness of the part except the part which particle | grains protruded from the surface layer B surface. After determining the thickness (μm) of each layer, the thickness ratio of each layer was calculated.

(5) Calculation of Void Volume Ratio Calculated density was determined from the density and blending ratio of the polymer, additive particles, and other components of the layer for which void volume ratio was determined. At the same time, it was isolated by peeling off the layer, and the mass and volume were measured. The actual density was calculated from these, and the following formula was obtained from the calculated density and actual density.
Void volume fraction = 100 × (1− (actual density / calculated density))
The density of isophthalic acid copolymerized polyethylene terephthalate (after biaxial stretching) was 1.39 g / cm ³ , and the density of barium sulfate was 4.5 g / cm ³ .
Moreover, only the layer which measures a void volume ratio was isolated, the mass per unit volume was calculated | required, and the real density was calculated | required. The volume was calculated as an area × thickness, where the sample was cut into an area of 3 cm ² and the thickness at that size was measured at 10 points with an electric micrometer (K-402B manufactured by Anritsu). The mass was weighed with an electronic balance.
In addition, as the specific gravity of the particles (including aggregated particles), the value of bulk specific gravity obtained by the following graduated cylinder method was used. Fill a 1000 ml measuring cylinder with completely dry particles, measure the total weight, subtract the weight of the measuring cylinder from the total weight to obtain the weight of the particle, and measure the volume of the measuring cylinder. , By dividing the weight (g) of the particles by the volume (cm ³ ).

(6) Melting point, glass transition temperature Using a differential scanning calorimeter (TA Instruments 2100 DSC), the measurement was performed at a heating rate of 20 ° C./min.

(7) Front luminance The reflective film is taken out from the direct LED liquid crystal television (LG50LN5400) manufactured by LG, and instead the various reflective films obtained in the examples are installed so that the surface layer B side is the screen side, Luminance was measured using a luminance meter (Model MC-940, manufactured by Otsuka Electronics Co., Ltd.) in the state of a backlight unit with the originally provided diffusion film and prism sheet. The LED liquid crystal television includes an LED light source including a direct type surface light source and a reflective lens cap as a light source.

(8) Luminance unevenness evaluation Using the same method as in (7) above, luminance unevenness was measured using a direct LED liquid crystal television (LG50LN5400) manufactured by LG and a luminance meter (Model MC-940 manufactured by Otsuka Electronics) . The direct type LED liquid crystal television uses a reflective LED lens cap, and the average distance between the light source (LED light source) and the reflecting plate is 8 mm or less.
The brightness spot is judged visually when there is no brightness spot at the center of the backlight unit (lamp placement spot) and the peripheral part (dark spot around the monitor). When it was possible, ○, and when it was strongly spotted, it was marked as “X”.

(9) BRDF diffusion degree (S30, S60, S75)
Using a BRDF measuring device IS-SA manufactured by Radiant, the reflected light measurement conditions for each of the incident light angle 30 ° (S30), the incident light angle 60 ° (S60), and the incident light angle 75 ° (S75) The angle on the plane orthogonal to the plane was measured at a pitch of 1 °, and the angle in the rotation direction within the film plane was measured at a pitch of 5 °. The light source used was a metal haloid light source.
The incident angle and the reflection angle are represented by 0 ° in the film normal direction, plus the incident angle direction side, and minus the reflection angle direction side. That is, the reflection angle of the specular reflected light with respect to the incident light with an incident angle of 30 ° is expressed as −30 °.
Moreover, according to the said apparatus, in addition to the reflected light on the plane orthogonal to a film surface including an incident light direction, the reflected light in the direction which rotated this plane to the rotation direction in the film surface can also be observed. However, in the present invention, the reflected light on the plane including the incident light direction and orthogonal to the film surface is observed (two-dimensional reflected light analysis).
As an analysis software, “Imaging Sphere ver 1.3” was used.
From the obtained data, the two-dimensional component of the reflected light on the plane that includes the incident light direction and is orthogonal to the film surface is taken out, and for this reflected light component, the reflected light intensity in the regular reflection direction is set to 1 The integrated value of the reflected light of −90 ° to + 90 ° was determined and used as BRDF diffusibility.
In addition, the measurement was performed in one arbitrary direction in the film plane and the direction orthogonal thereto, and the average value was taken. (If the MD and TD of the film are known, they can be MD and TD.)

(10) Film-forming stretchability The film-forming stability when the films described in the Examples were formed by a continuous film-forming method using a tenter was observed and evaluated according to the following criteria.
A: The film can be stably formed for 8 hours or more.
○: The film can be stably formed for 3 hours or more and less than 8 hours.
Δ: Cutting occurred once in less than 3 hours.
X: Cutting occurs multiple times in less than 3 hours, and stable film formation is not possible.

<Production Example 1: Synthesis of isophthalic acid copolymerized polyethylene terephthalate 1>
136.5 parts by mass of dimethyl terephthalate, 13.5 parts by mass of dimethyl isophthalate (9 mol% with respect to 100 mol% of total acid components of the obtained polyester), 98 parts by mass of ethylene glycol, 1.0 part by mass of diethylene glycol , 0.05 parts by mass of manganese acetate and 0.012 parts by mass of lithium acetate were charged into a rectification column and a flask equipped with a distillation condenser, and heated to 150 to 240 ° C. with stirring to distill methanol to conduct a transesterification reaction. went. After methanol was distilled, 0.03 parts by mass of trimethyl phosphate and 0.04 parts by mass of germanium dioxide were added, and the reaction product was transferred to the reactor. Next, while stirring, the pressure in the reactor was gradually reduced to 0.3 mmHg and the temperature was raised to 292 ° C. to carry out a polycondensation reaction to obtain isophthalic acid copolymerized polyethylene terephthalate 1. The melting point of this polymer was 235 ° C.

<Production Example 2: Synthesis of isophthalic acid copolymerized polyethylene terephthalate 2>
Except for changing to 129.0 parts by mass of dimethyl terephthalate and 21.0 parts by mass of dimethyl isophthalate (14 mol% with respect to 100 mol% of the total acid component of the resulting polyester), the same as in Production Example 1 above. Thus, isophthalic acid copolymerized polyethylene terephthalate 2 was obtained. The melting point of this polymer was 215 ° C.

<Production Example 3: Preparation of particle master chip 1>
Using part of the isophthalic acid copolymerized polyethylene terephthalate 1 obtained above and barium sulfate particles having an average particle diameter of 1.0 μm (in the table, indicated as BaSO ₄ ) as a void forming agent, manufactured by Kobe Steel In a NEX-T60 tandem type extruder, mixed so that the content of barium sulfate particles is 60% by mass with respect to the mass of the obtained master chip, extruded at a resin temperature of 260 ° C., and particles containing barium sulfate particles Master chip 1 was created.

<Production Example 4: Preparation of particle master chip 2>
Particle master obtained from the above-obtained isophthalic acid-copolymerized polyethylene terephthalate 2 as particles A with AY-601 (aggregated silica) manufactured by Tosoh Silica Co., Ltd. The mixture was mixed by a twin screw extruder so that the concentration in the chip was 8% by mass, and extruded at a melting temperature of 250 ° C. to prepare a particle master chip 2.

[Example 1]
(Manufacture of white reflective film)
The isophthalic acid copolymerized polyethylene terephthalate 1 and particle master chip 1 obtained above as raw materials for the reflective layer (A layer), and the isophthalic acid copolymerized polyethylene terephthalate 2 and particle master chip 2 as the raw material for the surface layer (B layer), respectively. Used, mixed so that each layer has the structure described in Table 1, and put into an extruder. Layer A is melt extrusion temperature 255 ° C., layer B is melt extrusion temperature 230 ° C. As shown, the layers were combined using a three-layer feed block device so as to have a layer structure of B layer / A layer / B layer, and formed into a sheet shape from a die while maintaining the laminated state. At this time, it adjusted with the discharge amount of each extruder so that the thickness ratio of B layer / A layer / B layer might become 10/80/10 after biaxial stretching. Further, this sheet was an unstretched film cooled and solidified with a cooling drum having a surface temperature of 25 ° C. This unstretched film is led to a longitudinal stretching zone maintained at 92 ° C. through a preheating zone at 73 ° C., followed by a preheating zone at 75 ° C., stretched 3.0 times in the longitudinal direction, and cooled by a roll group at 25 ° C. did. Subsequently, while holding both ends of the film with clips, the film was led to a transverse stretching zone maintained at 130 ° C. through a preheating zone at 115 ° C. and stretched 3.6 times in the transverse direction. Then, heat treatment at 155 ° C. for 10 seconds, heat setting at 200 ° C. for 10 seconds, and heat treatment at 155 ° C. for 10 seconds are carried out continuously in the tenter, and then the width ratio is 2% and the width is 130 ° C. The width of the film was cut, then both ends of the film were cut off, heat-relaxed at a longitudinal relaxation rate of 2.5%, and cooled to room temperature to obtain a film having a thickness of 188 μm as shown in Table 1. The evaluation results of the obtained film are shown in Table 2.

[Examples 2 to 5, Comparative Examples 1 to 4]
A white reflective film was obtained in the same manner as in Example 1 except that the configuration of the film was as shown in Table 1. The evaluation results of the obtained film are shown in Table 2.
The types of particles used are as follows.
Particle B: AY-601 (aggregated silica) manufactured by Tosoh Silica Co., Ltd. was subjected to air classification to an average particle size of 3.0 μm.
Particle C: AY-601 (aggregated silica) manufactured by Tosoh Silica Co., Ltd. was air-classified to an average particle diameter of 10.5 μm.

[Example 6]
The isophthalic acid copolymerized polyethylene terephthalate 1 and the particle master chip 1 obtained above as raw materials for the reflective layer (A layer), and the isophthalic acid copolymerized polyethylene terephthalate 2 and the particle master chip 2 as raw materials for the support layer (C layer), respectively. Used, mixed so that each layer has the structure described in Table 1, and put into an extruder. The A layer was melt extruded at 255 ° C, the C layer was melt extruded at 230 ° C, and Table 1 was used. As shown, the layers were combined using a three-layer feed block device so as to have a layer configuration of C layer / A layer / C layer, and formed into a sheet from a die while maintaining the laminated state. At this time, it adjusted with the discharge amount of each extruder so that the thickness ratio of C layer / A layer / C layer might become 10/80/10 after biaxial stretching. Further, this sheet was an unstretched film cooled and solidified with a cooling drum having a surface temperature of 25 ° C. This unstretched film is led to a longitudinal stretching zone maintained at 92 ° C. through a preheating zone at 73 ° C., followed by a preheating zone at 75 ° C., stretched 3.0 times in the longitudinal direction, and cooled by a roll group at 25 ° C. did. Subsequently, while holding both ends of the film with clips, the film was led to a transverse stretching zone maintained at 130 ° C. through a preheating zone at 115 ° C. and stretched 3.6 times in the transverse direction. Then, heat treatment at 155 ° C. for 10 seconds, heat setting at 200 ° C. for 10 seconds, and heat treatment at 155 ° C. for 10 seconds are carried out continuously in the tenter, and then the width ratio is 2% and the width is 130 ° C. The width of the film was cut, then both ends of the film were cut off, heat-relaxed at a longitudinal relaxation rate of 2.5%, and cooled to room temperature to obtain a film having a thickness of 188 μm as shown in Table 1.
On the support layer (C layer) of the obtained biaxially stretched film, a coating liquid having the composition shown in the following coating liquid 1 for forming a surface layer (B layer) with a direct gravure coating apparatus, After coating so that the thickness was as shown in Table 1 (with a coating thickness of 15 g / m ² wet thickness), it was dried in an oven at 80 ° C. to obtain a film.

<Coating liquid 1, solid content concentration 33% by mass>
Particles: Nylon 66 resin CM3006 pellets (Ny particles E) manufactured by Toray Industries, Inc. 8.3% by mass
Acrylic resin (thermoplastic resin): DIC's ACRICID A-817BA (solid content concentration 50% by mass) ... 30% by mass
・ Crosslinking agent: Coronate HL (isocyanate-based crosslinking agent, solid content concentration: 75% by mass) manufactured by Nippon Polyurethane Industry Co., Ltd .: 10% by mass
Diluting solvent: butyl acetate 51.7% by mass
The evaluation results of the obtained film were as shown in Table 2. In addition, the solid content ratio of each component in the coating liquid 2 is as follows.
・ Particles: 33% by mass
-Acrylic resin (thermoplastic resin): 47% by mass
・ Crosslinking agent: 20% by mass

[Example 7]
In coating solution 1, the type of particles used was changed to MBX-5 (true spherical acrylic particles, average particle size 5 μm, Ac particles F) manufactured by Sekisui Plastics Co., Ltd. A white reflective film was obtained in the same manner as in Example 6 except for passing. The evaluation results of the obtained film are shown in Table 2.
・ Particles: 42% by mass
-Acrylic resin (thermoplastic resin): 38% by mass
・ Crosslinking agent: 20% by mass

[Example 8]
As shown in Table 1, the void forming agent of the reflective layer A was changed to a resin incompatible with polyester (cycloolefin, “TOPAS 6017S-04” manufactured by Polyplastics Co., Ltd.). A white reflective film was prepared and evaluated. The evaluation results are shown in Table 2.

  Since the white reflective film of the present invention is excellent in diffusibility of reflected light, it is preferably used as a reflector for a direct type surface light source, and in particular, a reflector for a direct type surface light source in which the distance between the light source and the reflective plate is short. Can be suitably used, has excellent luminance unevenness suppressing effect, and has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Lens cap 2 LED element 3 Module 4 Reflector plate 5 The same plane as the reflector surface 6 Distance between light source and reflector

Claims (4)

A reflective film having a reflective layer A and a surface layer B containing particles mainly composed of a resin, wherein the reflective layer A contains voids, and the void volume ratio is 15 volume% or more and 70 volume% or less. A projection is formed by the particles on the surface of the surface layer B opposite to the reflective layer A, and a two-dimensional reflected light analysis is performed using a bidirectional reflectance distribution function (BRDF) measuring device. When the incident light angle is 60 °, the integrated value (S60) of the reflected light intensity in all directions when the reflected light intensity at the reflection angle −60 ° is 1, and when the incident angle is 75 °. The integrated value (S75) of the reflected light intensity in all directions when the reflected light intensity at the reflection angle of −75 ° is 1, and the reflected light intensity at the reflection angle of −30 ° when the incident angle is 30 ° is 1. The integrated value of reflected light intensity in all directions (S30) And comprising a white reflective film for a direct type surface light source having a light source with a lens cap.
S75 / S30 = 0.25 or more to 0.50 or less (1)   The white reflective film for a direct type surface light source according to claim 1, wherein the lens cap is a reflective lens cap. The white reflective film for a direct type surface light source according to claim 1 or 2 , wherein the direct type surface light source is an LED light source, and the LED light source is disposed on the white reflective film. The direct type surface light source using the white reflective film of any one of Claims 1-3 .