JP5785202B2 - 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, according to the study by the present inventors, even with the scratch-preventing layer as in Patent Documents 1 to 3, the hardness of the beads (here, 10% compressive strength (S10 strength)) and the surface containing the beads It has been found that depending on the relationship of the hardness of the projections of the layers, it is sometimes impossible to achieve both securing the gap between the reflector and the light guide plate and preventing the light guide plate from being damaged by the reflector.
Then, an object of this invention is to provide the white reflective film which can fully suppress sticking with a light-guide plate, and can fully suppress the damage | wound of a light-guide plate.

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 particles,
Having protrusions formed of the particles on the surface of the surface layer B 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 ,
10% compressive strength of the particles is 0.1 to 1.0 MPa,
Vickers hardness of the protrusions is 10 to 30, the white reflective film.
2. 2. The white reflective film as described in 1 above, wherein the void volume ratio of the reflective layer A is 15 volume% or more and 70 volume% or less, and the void volume ratio of the surface layer B is 0 volume% or more and less than 15 volume%.
3. 3. The white reflective film as described in 1 or 2 above, which is used as a surface light source reflector provided with a light guide plate.
4). The white reflecting film according to any one of 1 to 3 above, which is used as a reflecting plate for an edge light type backlight unit.

  ADVANTAGE OF THE INVENTION According to this invention, the white reflective film which can fully suppress sticking with a light-guide plate, and can fully suppress the damage | wound of a light-guide plate can be provided.

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 a copolymer is preferable from the viewpoint that crystallization is suppressed when the film is stretched uniaxially or biaxially and stretchability and film-forming property are improved. 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 achieving both heat resistance and film forming properties. 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 made of a thermoplastic resin and contains particles.

(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, and from the viewpoint of easily obtaining suitable Vickers hardness of protrusions.

  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 stretchability is improved. Examples of the copolymer component include the dicarboxylic acid component and the diol component described above. From the viewpoint of achieving both heat resistance and film forming property, and from the viewpoint of easily achieving the Vickers hardness of the protrusion, isophthalic acid, 2 , 6-Naphthalenedicarboxylic acid is preferred. 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 setting the proportion of the copolymer component within this range, the Vickers hardness of the protrusion can be easily achieved. Moreover, it is excellent in film forming property and thermal dimensional stability.

(Particles and protrusions)
In the present invention, the surface layer B containing particles forms at least one outermost layer of the white reflective film, and the particles on the surface opposite to the reflective layer A of the surface layer B forming the outermost layer. Has a protrusion formed by.

  In the present invention, the 10% compressive strength (S10 strength) when compressed at a load of 3 gf determined by the measurement method described later of the particles is 0.1 MPa or more and 10 MPa or less, and at the same time, the measurement method of the protrusion described later. It is necessary that the Vickers hardness when measured with a weight of 500 N determined by the above is 5 or more and 30 or less. The present invention employs relatively soft particles as described above as particles forming surface irregularities to secure a gap and suppress sticking to the light guide plate, and at the same time, the hardness of the protrusions as described above. By making it relatively hard, the effect of suppressing sticking to the light guide plate and the effect of suppressing damage to the light guide plate can be achieved at the same time. This is thought to be due to the following mechanism. That is, firstly, the sticking between the reflection plate and the light guide plate is an operation that presses the light guide plate and the reflection plate, and is related to the stress applied to the protrusion in the direction parallel to the height direction of the protrusion. Therefore, it is considered that the Vickers hardness in the height direction of the protrusion can be suppressed by making it a relatively hard region as in the above numerical range. On the other hand, when the light guide plate is scratched, the operation is such that the light guide plate and the reflecting plate are rubbed together, and is therefore related to the stress applied in the direction perpendicular to the height direction of the protrusion. It is considered that the S10 intensity of the particles forming the protrusions can be suppressed by making the region relatively soft as in the above numerical range, because it can be deformed and distorted in a direction perpendicular to the direction.

  If the S10 strength of the particles is too high, deformation tends to be difficult to occur when stress is applied in a direction perpendicular to the height direction of the protrusion, and the effect of suppressing damage to the light guide plate is poor. It is 0 MPa or less, more preferably 2.0 MPa or less, further preferably 1.0 MPa or less, and particularly preferably 0.8 MPa or less. If the S10 strength of the particles is too high, the Vickers hardness of the protrusions may become too high. On the other hand, since the S10 strength of the particles tends to make it difficult to increase the Vickers hardness of the protrusion if it is too low, it is preferably at least 0.12 MPa, more preferably at least 0.13 MPa, even more preferably at least 0.14 MPa. Especially preferably, it is 0.15 MPa or more.

  In addition, if the Vickers hardness of the protrusion is too low, the effect of suppressing sticking to the light guide plate is inferior, and is preferably 8 or more, more preferably 10 or more, and still more preferably 12 or more. On the other hand, if it is too high, it is difficult to form very hard protrusions with relatively soft particles as described above, and the protrusions are hard even if the particles are relatively soft and easily deformed. This is superior, and the effect of suppressing damage to the light guide plate is poor. From such a viewpoint, the Vickers hardness of the protrusion is preferably 25 or less, more preferably 20 or less, and still more preferably 15 or less.

  In the present invention, the particles in the surface layer B can satisfy the aspect of the protrusion on the surface of the surface layer B defined by the present invention, and are not particularly limited as long as the aspect of the S10 strength is satisfied. Further, it may be an inorganic particle or an organic-inorganic composite particle. The shape of the particles is not particularly limited, and examples thereof include spherical particles, tabular particles, aggregated particles, and hollow particles.

(Aggregated particles)
The particles of the surface layer B in the present invention are preferably aggregated particles. This makes it easier to achieve the S10 strength while making it easier to form a suitable protrusion by having suitable heat resistance. When trying to achieve the S10 strength with particles that are not agglomerated particles, that is, in general, soft resin particles will be employed, and as such, such resin particles often have low heat resistance, and particles in a film manufacturing process such as an extrusion process. However, it tends to be difficult to maintain the shape as particles, and it is difficult to obtain a suitable surface protrusion mode.

  Such aggregated particles may be organic aggregated particles or inorganic aggregated particles. 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 suitable S10 strength 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 a ceramic aggregated particle are mentioned preferably from a viewpoint from which suitable S10 intensity | strength 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, that is, silica agglomerated particles are particularly preferred from the viewpoint of easily obtaining suitable S10 strength, and from the viewpoint of heat resistance and surface protrusion formation.

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. Property is improved. 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, when too large, it exists in the tendency to be inferior to film forming property. 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 95 μm or less, more preferably 90 μm or less, still more preferably 80 μm or less, particularly preferably 30 μm or less, and most preferably 25 μm or less.
In addition, when the particle | grains in this invention are not agglomerated particle | grains, it is preferable that the average particle diameter d of this particle | grain is in the range similar to the said secondary particle diameter ds from a viewpoint similar to the above.

  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, when it is too large, it is difficult to obtain a suitable surface protrusion, and it is difficult to obtain suitable S10 strength, 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 particles in the surface layer B is preferably 1% by volume or more and 50% by volume or less based on the volume of the surface layer B. By setting it as such a range, it becomes easy to set it as the Vickers hardness of the protrusion suitable in this invention, and it becomes easy to set it as the aspect of the surface layer B surface. 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 Vickers hardness of the desired protrusion tends to be difficult to obtain, and the strength of the surface layer B tends to be inferior, and the effect of improving the film forming property tends to be low. Moreover, it exists in the tendency for the mechanical strength of the obtained film to become low. Therefore, it is more preferably 45% by volume or less, further preferably 40% by volume or less, and particularly preferably 30% 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 achieved 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 are simultaneously employed. It 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 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 of the above-described 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 can be secured. 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, the ten-point average roughness (Rz) on the outermost layer surface and the average particle diameter d of the particles constituting the surface layer B (the secondary particle diameter ds when the particles are aggregated particles) are: It is preferable to satisfy the following formula.
0.1 × d (μm) ≦ Rz (μm) ≦ 0.7 × d (μm)

  By satisfying the above formula, the particles are more appropriately buried in the surface layer B at the outermost layer surface, and more appropriately protrude, and it becomes easier to have surface irregularities having an appropriate height, Thereby, the improvement effect of securing the gap can be enhanced. In the above formula, when the value of Rz is smaller than the value on the left side, it represents an aspect in which the particles are buried too much in the surface layer B, and thus the effect of improving the gap tends to be reduced. From such a viewpoint, it is more preferable that 0.2 × d (μm) ≦ Rz (μm), and still more preferably 0.3 × d (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 particles protrude too much from the surface layer B, and the effect of suppressing particle dropout at the time of contact with the light guide plate tends to be low. From this point of view, it is more preferable that Rz (μm) ≦ 0.6 × d (μm) and more preferably Rz (μm) ≦ 0.5 × d (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.

  Further, from the viewpoint of realizing an appropriate protrusion hardness necessary for the present invention, the average particle diameter d of the particles added to the surface layer B (secondary particle diameter ds when the particles are aggregated particles) and the surface layer B Is preferably in a relationship of 1.5d ≦ t ≦ 5.0d (the thickness of the portion of the surface layer B where no particles protrude from the surface). More preferably, 2.0d ≦ t ≦ 4.0d, and most preferably 2.5d ≦ t ≦ 3.5d.

  The surface layer B in the present invention may be formed by any method as long as it satisfies the above requirements. For example, it can be melted at the same time as the material of the reflective layer, and extruded (smelted coextrusion method) to obtain a sheet formed by extruding from the same or adjacent die. It can also be provided by a method (coating method) in which a coating solution dissolved in an appropriate solvent or water is applied and then dried. Among these, from the viewpoint that the surface layer B can be efficiently formed simultaneously with the formation of the reflective layer A, a melt coextrusion method and formation from a coating solution using water as a solvent are preferable. By analyzing the amount of the organic solvent when the formed film is heated, it can be confirmed that it is not a coating with an organic solvent but a co-extrusion or formation from a coating solution using water as a solvent. In the present invention, from the viewpoint of easily making the protrusions of the surface layer B moderately hard while using particles having low S10 strength, the resin added with the particles is melted simultaneously with the material of the reflective layer, and the same. Most preferred is a method of stretching and crystallizing a sheet formed by extruding from an adjacent die.

  In relation to such a preferable method of forming the 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. This makes it easy to obtain a suitable Vickers hardness of the protrusion.

[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 it has two or more, the thickness of 1 layer which forms the outermost layer which becomes the light-guide plate side) is 10-70 micrometers. Accordingly, in addition to the above preferred particle mode, the relationship between the average particle diameter d of the particles or the secondary particle size ds of the aggregated particles and the ten-point average roughness Rz can be easily set to the preferable mode as described above. It becomes easy to secure a gap with the optical plate. 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.

  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 problems such as curling hardly occur.

  The reflective layer A and the surface layer B have a thickness ratio of the reflective layer A of 50 to 90% and a thickness ratio of the surface layer B of 5 to 50% when the thickness of the entire white reflective 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 to form a laminated structure. This makes it easier to obtain the desired Vickers hardness of the protrusion. 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.
As a method for forming the surface layer B, the surface layer B can also be formed by applying a liquid obtained by dissolving or dispersing a layer forming material in water after drying in the longitudinal direction and then performing lateral stretching after drying. Drying can also serve as preheating for transverse stretching.
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 reflective layer B. Can be achieved.

The luminance measured from the reflective 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.

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 reflective layer B side. In the case of having different reflective layers B on the front and back, the measurement was performed on the surface of the reflective 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 (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 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) 10% compressive strength (S10 strength)
Using a micro hardness tester ENT-1100a manufactured by Elionix, the compressive strength of each particle at a load of 3 gf was measured, and the compressive strength (MPa) at 10% deformation was adopted. The average value of 5 measurements was used.

(6) Vickers hardness of protrusions In the same manner as the measurement of the 10% compressive strength described above, by using a micro hardness tester ENT-1100a manufactured by Elionix, an indenter was pushed onto the protrusions of each surface layer with a weight of 500 N, and the Vickers hardness was determined. Calculated. The average value of 5 measurements was used.

(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) 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.

(9) 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 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 ).

(10) Brightness Take out the reflective film from the LED liquid crystal television (LG42LE5310AKR) manufactured by LG, and install it on 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.

(11) Evaluation of scratches on light guide plate (evaluation of shaving) and dropout evaluation 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, the light guide plate (with a size of at least 400 mm × 200 mm) with the dot surface up is fixed on a horizontal desk, and the evaluation film and the light guide plate are in contact with the reflection film fixed on the iron plate created above. As shown, place the reflective film side face down on the light guide plate, and place a 1 kg weight (reference numeral 10 in FIG. 2) on it, and fix it to the iron plate at a distance of 200 mm (400 mm × 200 mm region). The reciprocating film was moved 15 times at a speed of about 5 to 10 seconds. 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 loupe after 15 reciprocating movements, it is determined that “cannot be scraped” (scraping evaluation ○), and scratches that can be observed after 10 reciprocating movements. 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.

(12) White spot evaluation Using the reflective film and light guide plate used in the evaluation of (11) 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 light source of an LED liquid crystal television (LG42LE5310AKR) 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 ○).

(13) Adhesion spot evaluation (adhesion evaluation)
Take out the chassis from the LED liquid crystal television (LG42LE5310AKR) 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. Further, a light guide plate and three optical sheets (two diffusion films and one prism) originally provided in the television were placed thereon. 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.

(14) Ten-point average roughness (Rz) and protrusion frequency The protrusion profile on the film surface was cut off with a three-dimensional roughness measuring device SE-3CKT (manufactured by Kosaka Laboratory Ltd.) with a cutoff of 0.25 mm and a measurement length of 1 mm. The projection profile was recorded at 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.

[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>
The isophthalic acid copolymerized polyethylene terephthalate 2 obtained above was mixed as agglomerated particles A with 8% by mass of Carriert P-10 manufactured by Fuji Silysia Chemical Co., Ltd., and extruded at a melting temperature of 235 ° C. Chip 2 was created.

(Manufacture of white reflective film 1)
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. Each layer was mixed so as to have the structure described in Table 1, and charged into an extruder. The A layer was melt extruded at a temperature of 255 ° C., the B layer was melt extruded at a temperature of 230 ° C., Using a three-layer feed block device, the layers were merged so as to have a layer configuration of layer A / layer B, 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 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 3.8 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 white reflective 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.

[Example 2]
A white reflective film was obtained in the same manner as in Example 1 except that AY-603 manufactured by Tosoh Silica Co., Ltd. was used as the particles of the surface layer B. The evaluation results of the obtained film are shown in Table 2.

[Example 3]
A white reflective film was obtained in the same manner as in Example 1 except that G0105 manufactured by Tosoh Silica Co., Ltd. was used as the particles of the surface layer B, and the lateral draw ratio was set to 4.0 times. The evaluation results of the obtained film are shown in Table 2.

[Comparative Example 1]
A white reflective film was obtained in the same manner as in Example 1 except that cross-linked poly (methyl methacrylate) (PMMA) particles manufactured by Soken Chemical were used as the particles of the surface layer B.

[Comparative Example 2]
(Adjustment of coating liquid)
Water-soluble polyester binder Z565 (solid content 30%) manufactured by Kyodo Chemical Co., Ltd. is 60% by mass as a solid content, and carrier ct P-10 manufactured by Fuji Silysia Chemical Co., Ltd. is 35% by mass as a solid content. The coating liquid for forming the surface layer B was prepared by diluting 420 with 5% by mass as a solid content and diluting with water so that the total solid content concentration of the coating liquid was 30% by mass.

(Manufacture of white reflective film 2)
The above-obtained isophthalic acid copolymerized polyethylene terephthalate 1 and particle master chip 1 were used as the raw material for the reflective layer (A layer), and isophthalic acid copolymerized polyethylene terephthalate 2 was used as the raw material for the support layer (C layer). Are mixed in such a manner as shown in Table 1 and charged into an extruder. The layer A has a melt extrusion temperature of 255 ° C., the layer C has a melt extrusion temperature of 230 ° C., and the layer configuration of layer C / layer A Then, they were merged using a two-layer feed block device 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 C layer / A layer might become 20/80 after biaxial stretching. Further, this sheet was an unstretched film cooled and solidified with a cooling drum having a surface temperature of 25 ° C. The coating liquid having the above-described composition is applied to the A layer side of this unstretched film with a roll coater so that the coating layer thickness after drying is 3 μm, and then passed through a preheating zone at 73 ° C., followed by a preheating zone at 75 ° C. The film was led to a longitudinal stretching zone maintained at 92 ° C., stretched 2.9 times in the longitudinal direction, and cooled by a roll group at 25 ° C. 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 3.8 times in the transverse direction. By this step, the surface layer B can be formed simultaneously. 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%. As shown in Table 1, a white reflective film in which a coating layer B having a thickness of 3 μm was formed on a base material (A layer + C layer) having a thickness of 250 μm was obtained. The evaluation results of the obtained film are shown in Table 2.

[Comparative Example 3]
A white reflective film was obtained in the same manner as in Comparative Example 2 except that the particles added to the coating liquid for forming the surface layer B were changed to AY-603 manufactured by Tosoh Silica Corporation. Table 2 shows the evaluation results of the obtained film.

  Since the white reflective film of the present invention can sufficiently suppress sticking to the light guide plate and can sufficiently suppress scratches on the light guide plate, the surface light source reflector provided with the light guide plate, among others, for example, It can be suitably used as a reflective film used in an edge light type backlight unit 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 particles,
Having protrusions formed of the particles on the surface of the surface layer B 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 .
10% compressive strength of the particles is 0.1 to 1.0 MPa,
Vickers hardness of the protrusions is 10 to 30, the white reflective film.   2. The white reflective film according to claim 1, wherein the void volume ratio of the reflective layer A is 15 volume% or more and 70 volume% or less, and the void volume ratio of the surface layer B is 0 volume% or more and less than 15 volume%.   The white reflective film of Claim 1 or 2 used as a surface light source reflective board provided with a light-guide plate.   The white reflective film of any one of Claims 1-3 used as a reflecting plate for edge light system backlight units.