JP6352613B2 - White reflective film - Google Patents

Description

  The present invention relates to a white reflective film. In particular, it is related with the white reflective film used for a liquid crystal display device.

  A backlight unit of a liquid crystal display device (LCD) includes a direct type having a light source on the back of the liquid crystal display panel and a reflective film on the back, and a light guide plate having a reflector on the back of the liquid crystal display panel. There is an edge light type provided with 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 (mainly a direct type CCFL) is mainly used from the viewpoint of excellent screen brightness and uniformity of brightness within the screen, and an edge is used. The light type was often used for relatively small LCDs such as notebook PCs. However, due to the recent development of light sources and light guide plates, the brightness and uniformity of brightness within the screen have been improved even for edge-light type backlight units. As a result, edge-light type backlight units have been used not only for relatively small size but also for large LCDs. This is because there is a merit that the LCD can be thinned.

  In the edge light type backlight unit, the light guide plate and the reflective film are in direct contact with each other. Therefore, in such a structure, when the light guide plate and the reflective film are attached, there is a problem in that the luminance of the attached portion becomes abnormal and in-plane variation in luminance occurs. Therefore, it is necessary to have a gap between the light guide plate and the reflective film and keep this gap constant. For example, by having beads on the surface of the reflective film, the gap between the light guide plate and the reflective film can be kept constant, and sticking of these can be prevented.

  However, at this time, when the light guide plate made of a relatively soft material comes into contact with the reflective film, there is a problem that the light guide plate is damaged by the reflective film or the beads on the surface. As a countermeasure, for example, as in Patent Documents 1 to 3, there is a report of forming a scratch-preventing layer containing elastomeric beads on the surface of a reflective film by coating.

JP 2003-92018 A Special table 2008-512719 gazette JP 2009-244509 A

  However, when soft beads are used as in Patent Documents 1 to 3, damage to the light guide plate is suppressed, but securing a gap that has recently been required may not be achieved. More specifically, the present inventors, for example, in the case of a light guide plate in which it is difficult to secure a gap, such as a light guide plate (laser engraving light guide plate) in which a dot portion is formed by laser engraving that is often used in recent years, It was noted that sticking may not be suppressed in the technical aspect. To deal with the problem of securing the gap, it is conceivable to use beads having high hardness such as inorganic particles such as spherical silica and organic particles such as acrylic particles having a crosslinked structure. It cannot be suppressed. In addition, when such a bead having a high hardness and having a size that can sufficiently secure a gap is used, depending on the bead, the film-forming property of the reflective film is lowered, and the reflective film is manufactured. It has been found that cutting tends to occur in the film.

  Therefore, the present invention has an object to provide a white reflective film that highly suppresses sticking to a light guide plate, can sufficiently suppress scratches on the light guide plate, and is excellent in film formability. And

The present invention adopts the following configuration in order to achieve the above-described problems.
1. A white reflective film having a reflective layer A and a surface layer B made of a thermoplastic resin and containing aggregated particles,
The surface layer B is an oriented layer,
The surface layer B has a projection formed by the aggregated particles on the surface opposite to the reflective layer A;
The number of protrusions having a height of 5 μm or more on the surface is 10 ⁴ to 10 ¹⁰ / m ² ,
The content of the aggregated particles in the surface layer B is 30% by volume or less based on the volume of the surface layer B,
The compression rate when the aggregated particles in the surface layer B are compressed with a weight of 0.3 gf is less than 40%.
White reflective film.
2. 2. The white reflective film as described in 1 above, wherein the amount of volatile organic solvent is 10 ppm or less.
3. 3. The white reflective film as described in 1 or 2 above, wherein the void volume ratio of the reflective layer A is 15% by volume or more and 70% by volume or less.
4). The white reflecting film according to any one of 1 to 3 above, which is used as a surface light source reflecting plate including a light guide plate.

According to the present invention, it is possible to provide a white reflective film that highly suppresses sticking to a light guide plate and can sufficiently suppress scratches on the light guide plate and is excellent in film forming properties. it can.
Since the white reflective film of the present invention has a good sticking suppression effect, for example, a light guide plate having a dot portion by laser engraving, for example, a light guide plate that is difficult to secure a gap is sufficiently attached. Can be suppressed.

It is a schematic diagram which shows the structure used for the adhesion spot evaluation in this invention. It is a schematic diagram which shows the method of the damage evaluation of the light-guide plate in this invention, and the drop-off evaluation of particle | grains.

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 property can be made high. 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 property 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 is preferably a copolymer because the crystallization is suppressed when the film is stretched uniaxially or biaxially and the effect of improving stretchability and film-forming property 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 the film forming property. 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 property. 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, polystyrene, 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]
The surface layer B in the present invention is a layer made of a thermoplastic resin, containing particles, and oriented. Here, the “oriented layer” is not a layer formed by applying a coating solution to a film that has been stretched, but is subjected to, for example, a coextrusion method as described in the preferred production method described below, and then stretched. Indicates that the layer is formed.
In relation to the method for forming such a surface layer B, the surface layer B is preferably an oriented polyester film layer, and more preferably an oriented polyethylene terephthalate film layer. A biaxially oriented polyester film layer is more preferred, and a biaxially oriented polyethylene terephthalate film layer is particularly preferred. Thereby, it is excellent in film forming property.

(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.
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 a copolymer is preferred from the viewpoint that crystallization is suppressed when the film is stretched uniaxially or biaxially and the effect of improving stretchability and film-forming property 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 the film forming property. 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 property. Moreover, it is excellent in thermal dimensional stability.

(Aggregated particles)
In the present invention, the agglomerated particles contained in the surface layer B are agglomerated particles having a compression ratio of less than 40% when compressed with a weight of 0.3 gf determined by a measurement method described later. In the present invention, by adopting the above aggregated particles as the particles for forming the surface irregularities for securing the gap and suppressing the sticking to the light guide plate, the light guide plate is preferably secured while ensuring the gap. Scratch is suppressed, and the film-forming property of the film is excellent. This is thought to be due to the following mechanism.

That is, first, since the particles are agglomerated particles, the particles can be appropriately deformed following the deformation of the film in the film forming process, particularly in the stretching process, whereby the particles follow the deformation of the film. This is considered to be because the film breakage caused by the failure is suppressed. In particular, in the present invention, the surface of the surface layer B has a specific projection form in order to secure a gap, and in order to obtain such a projection form, aggregate particles having a relatively large particle size are preferably employed. However, when the film contains particles having a relatively large particle size as described above, the film breakage starting from such particles usually tends to occur. This is what suppresses this.
And since the compression rate of this aggregated particle is less than 40%, the processus | protrusion formed with the aggregated particle will have moderate intensity | strength (hardness), and is excellent in the effect of ensuring a gap.

If the compression rate is too high, it tends to be difficult to form protrusions on the surface of the surface layer B, and tends to be in close contact with the light guide plate. From this viewpoint, the compression ratio when the particles are compressed with a weight of 0.3 gf is preferably 35% or less, and more preferably 30% or less. On the other hand, if the compression rate is too low, the formed protrusions may become too hard, and the effect of suppressing damage to the light guide plate tends to be low. Further, the effect of improving the film forming property tends to be low. From this viewpoint, the compression rate is preferably 5% or more, more preferably 10% or more, and further preferably 15% or more.
Since the laser engraving light guide plate does not have a dot portion formed by printing, it has a relatively high resistance to scraping.

  In the present invention, the agglomerated particles are employed as the particles of the surface layer B as described above, but this makes it easier to achieve the compression ratio while making it easier to form suitable protrusions having suitable hardness. Can be. When trying to achieve the above compression ratio with particles that are not agglomerated particles, that is, generally adopting hard inorganic particles or hard resin particles, the resulting protrusions tend to be too hard, suppressing damage to the light guide plate Tend to be less effective. Moreover, since such particles are difficult to follow the deformation of the film during stretching, the film forming property tends to be low.

  In the present invention, the aggregated particles in the surface layer B can satisfy the aspect of protrusions on the surface of the surface layer B defined by the present invention, and are not particularly limited as long as the above aspect of compressibility is satisfied. It may be an inorganic aggregated particle or an organic-inorganic composite aggregated particle. Preferred examples of the organic aggregated particles include polyester aggregated particles, acrylic aggregated particles, polyurethane aggregated particles, and polyethylene aggregated particles from the viewpoint of easily obtaining a suitable compressibility and the above-described viewpoints of heat resistance and surface protrusion formation. Among them, the polyester aggregated particles are preferable because they have good compatibility with the main raw material polyester and have little influence on the film forming property. Moreover, as an inorganic aggregated particle, a silica aggregated particle, an alumina aggregated particle, and ceramic aggregated particle are mentioned preferably from a viewpoint that a suitable compressibility is easy to be obtained. Of these, silica agglomerated particles are preferred because a particularly suitable compressibility is easily obtained.

In the present invention, the particles of the surface layer B are preferably inorganic agglomerated particles from the viewpoint of easily obtaining a suitable compressibility and excellent heat resistance and easy surface protrusion formation, that is, silica agglomerated particles are particularly preferred. preferable.
The aggregated particles in the surface layer B preferably have a secondary particle size (ds) of 5 μm or more and 100 μm or less. As a result, the aspect of the protrusion on the surface layer B surface defined by the present invention can be easily satisfied, the distance between the light guide plate and the film can be kept constant, and the sticking of these can be further suppressed, and the film can be formed. The effect of improving the property is increased. When the secondary particle size is too small, the white reflective film tends to be partially adhered to the light guide plate. From such a viewpoint, the secondary particle size is more preferably 6 μm or more, further preferably 8 μm or more, and particularly preferably 10 μm or more. On the other hand, if it is too large, the effect of improving the film forming property tends to be low. In addition, the particles tend to drop off, and if the drop occurs, it becomes a white spot defect in the backlight unit. From such a viewpoint, the secondary particle size is preferably 90 μm or less, more preferably 80 μm or less, further preferably 70 μm or less, particularly preferably 60 μm or less, and most preferably 50 μm or less.
In addition, when the particle | grains in this invention are not aggregated particles, it is preferable that the average particle diameter d of this particle | grain is the same range as the said secondary particle diameter ds.

  Further, the primary particle size (dp) of the aggregated particles is preferably 0.01 μm or more, and preferably 5 μm or less. By satisfying this and the above-mentioned secondary particle size range at the same time, it is easy to obtain a suitable surface protrusion mode, and it is easy to achieve a suitable particle compression ratio, and the effect of improving the film forming property can be further enhanced. When the primary particle size is too small, it tends to be difficult to obtain a sufficiently large secondary particle size, and it is difficult to obtain a suitable surface protrusion mode. From this viewpoint, the primary particle diameter is more preferably 0.02 μm or more, further preferably 0.03 μm or more, and particularly preferably 0.05 μm or more. On the other hand, if it is too large, a suitable surface protrusion mode tends to be difficult to obtain, and a suitable compression rate tends to be difficult to obtain, and the effect of improving the film forming property tends to be low. From this viewpoint, it is more preferably 4 μm or less, further preferably 3 μm or less, particularly preferably 2 μm or less, and most preferably 1 μm or less.

  The content of the aggregated particles in the surface layer B is 30% by volume or less based on the volume of the surface layer B. By setting it as this range, it is excellent in film forming property. Moreover, it is preferable that it is 1 volume% or more and 30 volume% or less, and it becomes easy to set it as the aspect of the surface layer B surface suitable in this invention. If the amount is too small, surface irregularities tend to be reduced, and it tends to be difficult to keep the distance from the light guide plate constant. Therefore, it is more preferably 2% by volume or more, particularly preferably 3% by volume or more. On the other hand, if the amount is too large, the strength of the surface layer B tends to be inferior, the effect of improving the film forming property tends to be low, and the mechanical strength of the obtained film tends to be low. Therefore, it is more preferably 25% by volume or less, further preferably 20% by volume or less, and particularly preferably 15% by volume or less. The volume fraction of particles can be determined from the mass fraction and density of the thermoplastic resin constituting the surface layer B and the mass fraction and density of the particles.

(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 and resins that are different from the aggregated particles.
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 property 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 properties can be enhanced at the same time, the preferable void volume ratio in the reflective layer A and the preferable void volume ratio in the surface layer B described above are simultaneously adopted. Is particularly preferred.

(Aspect of surface layer B)
In the present invention, the surface layer B made of the thermoplastic resin as described above and containing the aggregated particles as described above forms at least one outermost layer of the white reflective film. The surface layer B that forms the outermost layer has a projection formed by the above-described aggregated particles on the surface opposite to the reflective layer A (hereinafter sometimes referred to as the outermost layer surface). Such protrusions need to have protrusions with an appropriate height at an appropriate frequency on the outermost layer surface from the viewpoint of securing a gap between the light guide plate and the film.

Therefore, in the present invention, it is usually necessary that the number of protrusions with a height of 5 μm or more is 10 ⁴ to 10 ¹⁰ / m ² on the outermost layer surface. Thereby, the gap between the light guide plate and the film can be sufficiently secured, and the sticking suppression effect is excellent. If the projection frequency is too low, the sticking suppression effect is poor. On the other hand, if the protrusion frequency is too high, the probability of particle dropout tends to improve and the reflectance tends to decrease.
In the present invention, it is preferable that the ten-point average roughness (Rz) on the outermost layer surface and the secondary particle size ds of the aggregated particles constituting the surface layer B satisfy the following formula.
0.1 × ds (μm) ≦ Rz (μm) ≦ 0.7 × ds (μm)

  By satisfying the above formula, the agglomerated particles are more appropriately buried in the surface layer B on the outermost layer surface, and more appropriately project, and it becomes easier to have surface irregularities having an appropriate height. Thus, the effect of improving the gap can be increased. In the above formula, when the value of Rz is smaller than the value on the left side, it represents a mode in which the aggregated particles are buried too much in the surface layer B, and thus the effect of improving the gap tends to be reduced. From this point of view, it is more preferable that 0.2 × ds (μm) ≦ Rz (μm), and more preferably 0.3 × ds (μm) ≦ Rz (μm). On the other hand, when the value of Rz is larger than the value on the right side, it represents an aspect in which the aggregated particles protrude too much from the surface layer B, and the suppression effect of the aggregated particle falling off at the time of contact with the light guide plate tends to be low. From such a viewpoint, it is more preferable that Rz (μm) ≦ 0.6 × ds (μm), and still more preferably Rz (μm) ≦ 0.5 × ds (μm).

  In order to obtain the above aspect, the thickness of the surface layer B may be adjusted in consideration of the average particle diameter of the aggregated particles to be used. For example, in aggregated particles having a certain average particle diameter, the value of Rz tends to increase when the thickness of the surface layer B is reduced, while the value of Rz tends to decrease when the thickness of the surface layer B is increased. Adjustments can be made in consideration of such trends.

[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.

  Further, 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 guide plate side) is preferably 10 to 70 μm. Accordingly, in addition to the preferred aggregated particle mode, the relationship between the secondary particle size ds of the aggregated particle and the ten-point average roughness Rz can be easily set to the preferred mode as described above, and a gap with the light guide plate can be secured. It becomes easy to do. Moreover, it becomes easy to make the aspect of Rz and protrusion frequency into the preferable aspect mentioned above. Moreover, the improvement effect of a reflectance and the improvement effect of film forming property can be made high. If it is too thin, it is difficult to achieve a preferable Rz, and the effect of suppressing particle dropout tends to be reduced. In addition, the effect of improving the film forming property tends to be low. On the other hand, if it is too thick, the effect of improving the reflectance tends to be low, and preferable Rz and protrusion frequency tend to be difficult to obtain. From this viewpoint, it is more preferably 20 μm or more, and further preferably 60 μm or less.

In the present invention, it is preferable that the secondary particle diameter ds of the aggregated particles in the surface layer B and the thickness (t) of the surface layer B satisfy the following formula.
0.05 ≦ ds (μm) / t (μm) ≦ 20
By satisfying the above formula, it becomes easy to have surface irregularities having an appropriate height on the surface of the outermost layer, thereby enhancing the effect of securing the gap. In the above formula, when the value of ds / t is smaller than the value on the left side, the aggregated particles tend to be buried in the surface layer B, and the effect of improving the gap tends to be reduced. From this viewpoint, preferably 0.07 ≦ ds (μm) / t (μm), more preferably 0.09 ≦ ds (μm) / t (μm), and further preferably 0.3 ≦ ds (μm) / t. (Μm), particularly preferably 0.4 ≦ ds (μm) / t (μm). On the other hand, when the value of d / t is larger than the value on the right side, the aggregated particles tend to protrude from the surface layer B, and the effect of improving the drop-off suppression at the time of contact with the light guide plate tends to be low. From this point of view, ds (μm) / t (μm) ≦ 19 is preferable, ds (μm) / t (μm) ≦ 18 is more preferable, ds (μm) / t (μm) ≦ 10 is particularly preferable. Is a mode satisfying ds (μm) / t (μm) ≦ 2.

  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 property. Further, problems such as curling are unlikely to occur.

  The reflection layer A and the surface layer B have a thickness ratio of the reflection layer A of 50 to 90% and a thickness ratio of the surface layer B of 10 to 50% when the thickness of the entire white reflection film is 100%. Furthermore, the aspect which is 5 to 25% is preferable, and the balance of each characteristic, such as a reflection characteristic and film forming property, can be improved. 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 formability 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.
When the white reflective film of the present invention is produced, the surface layer B is formed on the reflective layer A obtained by a melt extrusion method or the like by a melt resin coating method (including a melt extrusion resin coating method), a co-extrusion method, a lamination method, or the like. It is preferable from the viewpoint of film forming property 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 properties, and voids are easily 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.

  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 reflective film]
(Reflectance, 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, and further preferably 97.5% or more. 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.

The luminance measured from the surface layer B side is determined by a measuring method described below is preferably 5400cd / ^{m 2} or more, more preferably 5450cd / ^{m 2} or more, 5500cd / ^{m 2} or more is particularly preferable.
The reflectance and brightness are values on the surface on the side of the light guide plate when used with the light guide plate in the white reflective film.

(Amount of volatile organic solvent)
In the white reflective film of the present invention, the amount of volatile organic solvent measured by the method described later is preferably 10 ppm or less. Thereby, it can be shown that the surface layer B is not formed by a coating method using an organic solvent. Further, when a self-recovered raw material is obtained and a film is formed using the self-recovered raw material, a gas mark is less likely to be generated, and the film forming property is improved. From this viewpoint, it is more preferably 5 ppm or less, further preferably 3 ppm or less, and ideally 0 ppm. In the present invention, in order to reduce the amount of the volatile organic solvent, it is preferable to employ the above-described method in forming the surface layer B without adopting the solution coating method using the organic solvent. In addition, the amount of volatile organic solvent tends to increase due to the use of organic particles.

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 on the light guide plate side.

(2) Average particle diameter of particles (d)
The particle size distribution of the particles was obtained with a particle size distribution meter (LA-950, manufactured by Horiba, Ltd.), and the particle size at d50 was defined as the average particle size.

(3) Primary particle size (dp) of aggregated particles
When the particles were aggregated particles, the following primary particle size (dp) measurement method was employed.
For a film containing aggregated particles, the resin component is dissolved using a solvent, and the particles (secondary particles) recovered from the resin component are observed at a magnification of 10,000 using a S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd. Then, the state of aggregation of the primary particles on the surface of the secondary particles was observed, the particle size of 100 primary particles was arbitrarily measured, and the primary particle size (dp) was determined from the average value.
In the above method, when the resin component is dissolved with the solvent, the aggregated particles are also dissolved (for example, in the case of organic particles), the aggregated particles before blending are used, and the S-4700 field emission scan manufactured by Hitachi, Ltd. is used. Using an electron microscope, observe at a magnification of 10,000 times, observe the agglomeration state of primary particles on the surface of the secondary particles, measure the particle size of 100 primary particles arbitrarily, and determine the primary particle size from the average value ( dp) was determined.
The case of 1 μm or more and less than 3 μm was designated as “<3”, and the case of less than 1 μm was designated as “<1”.

(4) Secondary particle size (ds) of aggregated particles
When the particles were agglomerated particles, the following secondary particle size (ds) measurement method was employed.
For a film containing aggregated particles, the resin component is dissolved using a solvent, and the particles (secondary particles) recovered from the resin component are observed at a magnification of 1000 times using a Hitachi S-4700 field emission scanning electron microscope. Then, the particle size was measured arbitrarily for 100 particles, and the secondary particle size (ds) was determined from the average value. In addition, in the case of other than spherical shape, it was determined by (major axis + minor axis) / 2. Here, the minor axis indicates the maximum diameter in the direction perpendicular to the major axis.
In the above method, when the resin component is dissolved with the solvent, the aggregated particles are also dissolved (for example, in the case of organic particles), the aggregated particles before blending are used, and the S-4700 field emission scan manufactured by Hitachi, Ltd. is used. Using an electron microscope, observation was performed at a magnification of 1000 times, the particle size of 100 particles was arbitrarily measured, and the secondary particle size (ds) was obtained from the average value. In addition, in the case of other than spherical shape, it was determined by (major axis + minor axis) / 2. Here, the minor axis indicates the maximum diameter in the direction perpendicular to the major axis.

(5) Particle compression rate (%)
Using a compression tester MCTM-200 manufactured by Shimadzu Corporation, a compression test was performed for each particle at a load of 0.3 gf and a load speed of 0.0725 gf / sec, and the 10-point measurement average value was defined as the compression rate.

(6) Amount of volatile organic solvent At room temperature (23 ° C.), 1 g of a film sample was put in a 10 L fluororesin bag, and the inside was purged with pure nitrogen and sealed. Next, immediately from the nitrogen in the bag, 0.2 L and 1.0 L of nitrogen were collected in two analytical TENAX-TA collection tubes at a flow rate of 0.2 L / min. The mass of the organic solvent component contained in the collected nitrogen was quantified by HPLC, GCMS. The obtained value is converted into the amount in 10 L of nitrogen, and the mass of the organic solvent volatilized in 10 L of nitrogen is obtained from 1 g of the film sample, and the amount of volatile organic solvent (unit: ppm, based on the mass of the film sample) did. The aldehydes were quantified by HPLC by eluting the aldehyde derivatized product from the collection tube with acetonitrile. Moreover, when the value was different between HPLC and GCMS, the value of the more detected one was adopted.

(7) 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.

(8) 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 the 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 the 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 ).

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

(10) Ten-point average roughness (Rz) and projection frequency The projection profile on the film surface of the surface layer B is cut off by a three-dimensional roughness measuring device SE-3CKT (manufactured by Kosaka Laboratory Ltd.) at 0.25 mm. The projection profile was recorded at a measurement length of 1 mm, a scanning pitch of 2 μm, a scanning number of 100, and a height magnification of 1000 times and a scanning direction magnification of 200 times. In the obtained protrusion profile, 5 points from the highest peak (Hp) and 5 points from the lower valley (Hv) were taken, and the 10-point average roughness (Rz, unit: nm) was determined by the following formula. . For the analysis, a three-dimensional roughness analyzer SPA-11 (manufactured by Kosaka Laboratory Ltd.) was used.
Further, from the obtained projection profile (horizontal axis: projection height, vertical axis: projection profile of the number of projections), the number of projections (pieces / mm ² ) having a height of 5 μm or more was obtained and used as the projection frequency.

(11) Luminance The reflective film is taken out from the LED liquid crystal television (LG42LE5310AKR) manufactured by LG, and installed in various reflective films (surface layer B side on the screen side (surface in contact with the light guide plate). Using a meter (Model MC-940, manufactured by Otsuka Electronics Co., Ltd.), the luminance was measured at a measurement distance of 500 mm from the front of the center of the backlight.

(12) Evaluation of scratches on light guide plate (evaluation of shaving property) and evaluation of dropout of particles As shown in FIG. 2, an iron plate (length: 200 mm × width: 200 mm × thickness: 3 mm) at the end of the handle portion (reference numeral 7 in FIG. 2) 2 and a reflective film (reference numeral 9 in FIG. 2) having a width of 250 mm × length of 200 mm with the evaluation surface facing upward are respectively 25 mm from both ends in the width direction. The paste was made so that the portion protruded from the iron plate (so that the central 200 mm × 200 mm portion overlapped the iron plate). At this time, the evaluation surface (surface layer surface) of the reflective film was placed outside. In addition, the 25 mm portion remaining at both ends in the width direction of the reflective film is folded back to the back side of the iron plate, and the end portion of the reflective film (the portion where the blade is inserted with a knife or the like at the time of sampling) has the effect of scraping the light guide plate. Eliminated.
Next, a light guide plate with a dot surface facing upward (at least 400 mm × 200 mm in size, a laser engraving light guide plate provided in an LED liquid crystal television LG47LV5510 manufactured by LG) is fixed on a horizontal desk and created as described above. The reflective film fixed to the iron plate is placed on the light guide plate with the reflective film side facing downward so that the evaluation surface and the light guide plate are in contact with each other, and further a 500 g weight (reference numeral 10 in FIG. 2). ) And moved 15 times at a speed of about 5 to 10 seconds for one reciprocation at a distance of 200 mm (to move the reflective film fixed to the iron plate in a region of 400 mm × 200 mm). Then, on the surface of the light guide plate, the degree of shaving and the presence / absence of particles dropped off from the reflective film were observed using a 20-fold magnifier and evaluated according to the following criteria.
In the entire range of 400 mm × 200 mm rubbed on the light guide plate, if there are no scratches that can be observed with a magnifying glass after 15 reciprocating movements, “scratch is not evaluated” (scraping evaluation ○), and scratches that can be observed after 10 reciprocating movements are observed. Although there were no scratches that could be observed after 15 reciprocating movements, “scratch was difficult” (shave evaluation Δ), and when there were scratches that could be observed after 10 reciprocations, “scraped” (scraping evaluation ×).
Moreover, after 15 reciprocating movements, if there was no white foreign matter that could be observed with a loupe in the entire range of 400 mm × 200 mm rubbed on the light guide plate, it was determined that “particles did not fall off” (dropout evaluation ○). In addition, when there is a white foreign matter that can be observed, the white foreign matter is observed with a microscope to confirm that the white foreign matter is an aggregated particle. Dropout evaluation Δ), and if 6 or more, “particles dropped out” (dropout evaluation ×).
In the evaluation, in order to suppress the influence of the dot size as much as possible, an area having a large dot size was selected as much as possible on the light guide plate, and the evaluation samples were aligned.

(13) White spot evaluation Using the reflective film and light guide plate used in the evaluation of (12) above, a reflective film is placed on a desk so that the surface layer surface faces upward, and the dot surface faces downward. A light guide plate is placed on each of the four sides of the light guide plate, 200 g weights are placed and fixed, and light is incident from the side of the light guide plate using a backlight source of an LED liquid crystal television (LG47LV5510) manufactured by LG. If there are bright spots other than the light guide plate dots that can be visually observed, white spots are generated (evaluation x). On the other hand, if there were no abnormal bright spots that could be observed visually, no white spots were generated (evaluation ○).

(14) Evaluation of adhesion spots (adhesion evaluation)
Take out the chassis from the LED liquid crystal television (LG47LV5510) manufactured by LG and place it on a horizontal desk so that the inside of the television is facing upward. On top of that, a reflective film of almost the same size as the chassis is facing upward. Furthermore, a light guide plate (laser engraving light guide plate in which dots are formed by laser engraving) and three optical sheets (two diffusing films and one prism) originally provided on the television are placed thereon. It was. Next, an equilateral triangular base having three circular feet with a diameter of 5 mm as shown in FIG. 1 is placed in an area including the most severely uneven portion of the chassis within the plane, and a weight of 15 kg is further provided thereon. The area surrounded by these three legs was visually observed, and if there was no abnormally bright part, “no adhesion spots” (adhesion spots evaluation ○) was designated. If there is an abnormally bright part, place the DBEF sheet originally provided on the television on top of the three optical sheets and observe it in the same manner. When there was a spot (evaluation x), and when there was no abnormally bright part, it was set as "there was almost no adhesion spot" (evaluation (triangle | delta)). In addition, the area surrounded by the three legs was a substantially equilateral triangle having a side length of 10 cm.

(15) Film-forming property The film-forming stability when the film described in the example was 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 2.5 hours or more.
○: A film can be stably formed for 1 hour or more and less than 2.5 hours.
Δ: Cutting occurred once in less than 1 hour.
X: Cutting occurs multiple times in less than 1 hour, and stable film formation is not possible.

[Example 1]
<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 extruder, mixed so that the content of barium sulfate particles is 63% 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>
To the isophthalic acid copolymerized polyethylene terephthalate 2 obtained above, P-78F (aggregated silica) manufactured by Mizusawa Chemical Industry Co., Ltd. was air-classified as aggregated particles A, and particles having an average particle size (secondary particle size) of 15 μm were obtained. The mixture was mixed to 8 mass% and extruded at a melting temperature of 235 ° C. to prepare a particle master chip 2.

(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 2.9 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 setting is performed at 185 ° C. in the tenter, the width is set to 2%, the width is set in the horizontal direction at a temperature of 130 ° C., then both ends of the film are cut off, and the film is thermally relaxed at a longitudinal relaxation rate of 2%. After cooling, a film having a thickness of 250 μm was obtained as shown in Table 1. The evaluation results of the obtained film are shown in Table 2.

[Examples 2-8, Comparative Examples 1-4]
A white reflective film was obtained in the same manner as in Example 1 except that the aspect of the particles used for the surface layer was as shown in Table 1. The evaluation results of the obtained film are shown in Table 2.

[Example 9]
As shown in Table 1, the void forming agent for 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.

The types of particles used are as follows.
Aggregated particles B: BY-001 (aggregated silica) manufactured by Tosoh Silica Co., Ltd. was air-classified to an average particle size (secondary particle size) of 15 μm.
Aggregated particles C: P-510 (aggregated silica) manufactured by Mizusawa Chemical Industry Co., Ltd. was air-classified to an average particle size (secondary particle size) of 15 μm.
Agglomerated particles D: Silicia 470 (agglomerated silica) manufactured by Fuji Silysia Chemical Co., Ltd. was air-classified to an average particle size (secondary particle size) of 15 μm.
Aggregated particles E: L-300 (aggregated silica) manufactured by Tosoh Silica Co., Ltd. was air-classified to an average particle size (secondary particle size) of 15 μm.
Aggregated particles F: BY-001 manufactured by Tosoh Silica Co., Ltd. was air-classified to an average particle size (secondary particle size) of 20 μm.
Aggregated particles G: BY-001 manufactured by Tosoh Silica Co., Ltd. was air-classified to obtain an average particle size (secondary particle size) of 10 μm.
Crosslinked acrylic particles: EXM (true spherical particles) manufactured by Sekisui Plastics Co., Ltd. was air-classified to an average particle size of 15 μm.

ND: not detected (detection limit)

  The white reflective film of the present invention highly suppresses sticking to the light guide plate, can sufficiently suppress scratches on the light guide plate, and is excellent in film-forming properties of the film. As a surface light source reflecting plate, among others, it can be suitably used as a reflecting film used in an edge light type backlight unit such as used in a liquid crystal display device or the like.

4 Chassis 5 Reflective Film, Light Guide Plate, Optical Sheet Laminate 601 Equilateral Triangular Base 602 Weight 7 Handle Part 8 Iron Plate 9 Reflective Film 10 Weight 11 Light Guide Plate 1101 Dot

Claims (4)

A white reflective film having a reflective layer A and a surface layer B made of a thermoplastic resin and containing aggregated particles,
The surface layer B is an oriented layer,
The surface layer B has a projection formed by the aggregated particles on the surface opposite to the reflective layer A;
The number of protrusions having a height of 5 μm or more on the surface is 10 ⁴ to 10 ¹⁰ / m ² ,
The content of the aggregated particles in the surface layer B is 30% by volume or less based on the volume of the surface layer B,
The compression rate when the aggregated particles in the surface layer B are compressed with a weight of 0.3 gf is less than 40%.
White reflective film.   The white reflective film of Claim 1 whose amount of volatile organic solvents is 10 ppm or less.   The white reflective film of Claim 1 or 2 whose void volume ratio of the reflection layer A is 15 volume% or more and 70 volume% or less.   The white reflective film of any one of Claims 1-3 used as a surface light source reflective board provided with a light-guide plate.