JP6235299B2 - 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 in an LCD, a direct type (mainly direct type CCFL) has been mainly used from the viewpoint of excellent brightness of the screen and uniformity of brightness within the screen. In recent years, with the development of light sources and light guide plates, the brightness and uniformity of brightness within the screen have been improved even in edge-light type backlight units, and there is a merit that the LCD can be made thinner, so it is relatively small. Edge light type has been used in more backlight units up to large LCDs.

  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

  In the formation of the scratch-preventing layer by coating as in Patent Documents 1 to 3, the cost increases due to the necessity of providing a coating process. Therefore, it is conceivable to add particles into the reflective film to form surface protrusions and maintain a gap between the light guide plate and the reflective film. However, according to the study by the present inventors, in the formation of projections on the film surface by such a method, a light guide plate that has been required in recent years only by paying attention only to the overall number and height of projections as in the past. It was found that there are cases where the sticking suppression and the light guide plate scratching suppression are insufficient. Further, if the amount of particles added to the reflective film is increased, the sticking suppression effect is enhanced, but on the other hand, depending on the type of particles, the film-forming stretchability tends to deteriorate during film production. Therefore, in reality, there is a limit to the amount of particles added, and it is difficult and difficult to obtain a sufficient sticking suppression effect by increasing the amount of particles.

  Therefore, the present invention provides a white reflective film that can sufficiently suppress sticking to a light guide plate, and also can sufficiently suppress scratches on the light guide plate, and is excellent in film-forming stretchability of the film. Objective.

The present invention adopts the following configuration in order to achieve the above-described problems.
1. A laminated film having a reflective layer A and a surface layer B made of a thermoplastic resin and containing particles composed of particles, the particles being inorganic particles,
The surface layer B is an oriented layer, and the surface layer B forms at least one outermost layer of the laminated film, and the particle group is formed on the surface of the surface layer B forming the outermost layer opposite to the reflective layer A. Having protrusions formed by
Regarding the particle group in the surface layer B, the total volume of particles having a particle size of less than 7.0 μm is 10.0% by volume or less with respect to the volume of the surface layer B, and the total number of particles having a particle size of 7.0 μm or more and less than 11.0 μm. volume from 3.0 to 20.0% by volume relative to the volume of the surface layer B, the total volume of the particles to less than the particle diameter 11.0 .mu.m 15.0 .mu.m is the volume of the surface layer B 3.0 to 20. A white reflective film in which the total volume of particles having a volume of 0% by volume and a particle size of 15.0 μm or more is 10.0% by volume or less with respect to the volume of the surface layer B.
2. 2. The white reflective film as described in 1 above, wherein the particles are aggregated particles.
3. On the surface of the surface layer B forming the outermost layer opposite to the reflective layer A, the number of protrusions having a height of 5 μm or more and less than 15 μm is 50 to 500 / mm ² , and the number of protrusions having a height of 15 μm or more is 10 / ^3. The white reflective film as described in 1 or 2 above, which is ² mm or less.
4). The white reflective film according to any one of 1 to 3 above, wherein the volatile organic solvent amount is 10 ppm or less.
5. The white reflective film according to any one of 1 to 4 above, wherein the reflective layer A has voids, and the void volume ratio thereof is 15% by volume or more and 70% by volume or less.
6). The white reflective film of any one of said 1-5 used as a surface light source reflective plate provided with a light-guide plate.

  According to the present invention, there is provided a white reflective film that can sufficiently suppress sticking to a light guide plate, and can sufficiently suppress damage to the light guide plate, and is excellent in film forming stretchability of the film. be able to.

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 stretchability can be heightened. When the void volume ratio is too low, a preferable reflectance tends to be difficult to obtain. From such a viewpoint, the void volume ratio in the reflective layer A is more preferably 30% by volume or more, and particularly preferably 40% by volume or more. On the other hand, if it is too high, the effect of improving the film-forming stretchability tends to be low. From such a viewpoint, the void volume ratio in the reflective layer A is more preferably 65% by volume or less, and particularly preferably 60% by volume or less.
The void volume ratio can be achieved by adjusting the type, size, and amount of the void forming agent in the reflective layer A.

(Thermoplastic resin)
Examples of the thermoplastic resin constituting the reflective layer A include thermoplastic resins made of polyester, polyolefin, polystyrene, and acrylic. Among these, polyester is preferable from the viewpoint of obtaining a white reflective film excellent in mechanical properties and thermal stability.
As such a polyester, it is preferable to use a polyester comprising a dicarboxylic acid component and a diol component. Examples of the dicarboxylic acid component include components derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, adipic acid, sebacic acid, and the like. Examples of the diol component include components derived from ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like. Among these polyesters, aromatic polyesters are preferable, and polyethylene terephthalate is particularly preferable. Polyethylene terephthalate may be a homopolymer, but 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 stretchability. Moreover, it is excellent in thermal dimensional stability.

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

  When an incompatible resin is used as the void forming agent, the incompatible resin is not particularly limited as long as it is incompatible with the thermoplastic resin constituting the layer. For example, when the thermoplastic resin is polyester, polyolefin, 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 an oriented layer made of a thermoplastic resin containing particle groups and having protrusions formed on the surface by the particle groups. Here, the “oriented layer” is not a layer formed by applying a coating liquid during or after production of the film, but by performing, for example, a co-extrusion method as described in the preferred production method described below, and then stretching. It is a layer formed by being done.
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 stretchability.

  In the present invention, the surface layer B made of the thermoplastic resin as described above and containing the particle group forms at least one outermost layer of the white reflective film. The surface layer B forming the outermost layer has a protrusion formed by the particle group on the surface opposite to the reflective layer A (hereinafter sometimes referred to as the outermost layer surface).

(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 is preferably a copolymer from the viewpoint that crystallization is suppressed when the film is stretched uniaxially or biaxially and the effect of improving film-forming stretchability is enhanced. Examples of the copolymer component include the dicarboxylic acid component and the diol component described above, and isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferable from the viewpoint of high heat resistance and a high effect of improving film-forming stretchability. . The proportion of the copolymerization component is, for example, 1 to 20 mol%, preferably 2 to 18 mol%, more preferably 3 to 17 mol%, and particularly preferably 12 to 16 mol%, based on 100 mol% of the total dicarboxylic acid component of the polyester. Mol%. By making the ratio of a copolymerization component into this range, it is excellent in the improvement effect of film forming stretchability. Moreover, it is excellent in thermal dimensional stability.

(Particle group)
In the present invention, in order to obtain the effect of suppressing damage to the light guide plate, the effect of suppressing adhesion with the light guide plate, and the effect of improving the film-forming stretchability, the surface layer B has particles 1 to 1 each having a particle size range described later. At the same time that the particle group consisting of 4 is contained, the particle group needs to be in an embodiment containing a specific amount of particles having a specific particle size. That is, such particles are
The total volume of particles (particle 1) having a particle size of less than 7.0 μm is 10.0% by volume or less with respect to the volume of the surface layer B,
The total volume of particles (particle 2) having a particle size of 7.0 μm or more and less than 11.0 μm is 3.0 to 20.0% by volume with respect to the volume of the surface layer B,
Particles having a total particle size of 11.0 μm or more and less than 15.0 μm (particle 3) are 3.0 to 20.0% by volume with respect to the volume of the surface layer B, and particles having a particle size of 15.0 μm or more (particles) The total volume of 4) is required to be 10.0% by volume or less with respect to the volume of the surface layer B.

  Usually, the amount of gap required between the light guide plate and the reflective film is 7 to 15 μm, and in order to ensure such a gap amount, the particle size is 11.0 μm or more among the above-mentioned particle size classifications. Most important are particles less than 15.0 μm. From this viewpoint, the total volume of particles having a particle diameter of 11.0 μm or more and less than 15.0 μm required in the present invention is 3.0 to 20.0% by volume with respect to the volume of the surface layer B, and more preferably. Is 4.0 to 20.0% by volume, more preferably 5.0 to 18.0% by volume, and particularly preferably 5.0 to 13.0% by volume. When the amount of particles having a particle diameter of 11.0 μm or more and less than 15.0 μm is larger than this range, the reflectance of the obtained film is lowered or the film-forming stretchability at the time of production is extremely lowered, resulting in a product of good quality. It becomes difficult to obtain. Also, if it is less than this range, the effect of suppressing sticking to the light guide plate tends to be inferior, so that a sufficient gap between the light guide plate and the reflective plate cannot be secured, or the light guide plate and the reflective plate It is difficult to obtain a product of good quality because of poor cutting (light guide plate scraping and / or reflecting plate scraping).

  When particles having a larger diameter than this are contained in a large amount, the influence on the optical properties tends to increase, such as a decrease in the reflectance of the obtained film. Furthermore, failure to break easily occurs during film forming stretching, and the productivity is remarkably deteriorated. Therefore, it is necessary to control the content of large-diameter particles to be sufficiently small in terms of both quality and production. From this viewpoint, the total volume of particles having a particle size of 15.0 μm or more required in the present invention needs to be 10.0% by volume or less with respect to the volume of the surface layer B, and more preferably 8%. Volume% or less, More preferably, it is 7 volume% or less.

  On the other hand, it is necessary to sufficiently control the addition amount of small-diameter particles. Particles having a particle diameter of 7.0 μm or more and less than 11.0 μm form protrusions that complement the protrusions of the particles having a particle diameter of 11.0 μm or more and less than 15.0 μm, and the total volume required in the present invention is It is 3.0-20.0 volume% with respect to the volume of the surface layer B, More preferably, it is 4.0-20.0 volume%, More preferably, it is 5.0-20.0 volume%. When the content is larger than this range, there is a problem because the influence on the optical characteristics becomes large, such as a large decrease in reflectance of the obtained film. Moreover, it exists in the tendency to deteriorate film forming stretchability. On the other hand, if the amount is too small, the above-mentioned supplementary protrusions tend to decrease, and the effect of suppressing sticking to the light guide plate tends to be inferior.

Furthermore, it is necessary to sufficiently limit the amount of particles having a small diameter. Since such particles have a very large surface area, when added to the resin in the production stage, the contact area between the resin and the particles tends to increase, which tends to promote deterioration of the resin, thereby reducing the reflectivity, etc. Problems arise. Moreover, it exists in the tendency to reduce film forming stretchability. From this viewpoint, the total volume of particles having a particle diameter of less than 7.0 μm required in the present invention needs to be 10.0% by volume or less with respect to the volume of the surface layer B, and more preferably 8%. Volume% or less, More preferably, it is 7 volume% or less.
Such a particle group can be obtained, for example, by performing classification operation such as wind classification, or by mixing a plurality of particle groups having a specific particle diameter into one particle group.

  In the present invention, by setting the particle group in the surface layer B to the specific mode as described above, the mode of the projection on the outermost layer surface is set to a mode in which the light guide plate contacts the projection as uniformly as possible. By dispersing the pressure on the light plate, the light guide plate is prevented from being damaged while having an appropriate gap with the light guide plate. If the mode of the particle group is not within the above range, for example, the projection is such that the light guide plate comes into contact with only the high projection, and the pressure is concentrated on that portion, which makes it easy to cut.

In the present invention, the particles constituting the particle group contained in the surface layer B may be organic particles, inorganic particles, or organic-inorganic composite particles regardless of their types. In addition, those in which the particle size and shape are generally stable during film forming and those that are difficult to melt or generate gas even when heated are preferred. From such a viewpoint, silica, titanium oxide, barium sulfate, calcium carbonate, etc. Inorganic particles are preferred.
On the other hand, in order to further suppress the breakage failure at the time of film formation stretching, and further suppress the failure to breakage and the optical properties when producing a film using a self-collecting raw material, the particles are relatively soft. Aggregated particles are preferred.

  The average particle size of the particle group in the present invention is preferably 7.0 μm or more and less than 40.0 μm. Thereby, it becomes easy to set it as the aspect of the protrusion height of the outermost layer surface mentioned later in the preferable thickness of the surface layer B mentioned later. If the average particle size is too large, the frequency of high protrusions tends to increase and the frequency of low protrusions tends to decrease. In addition, the reflectance and brightness may be affected. On the other hand, if it is too small, the frequency of high projections decreases and the frequency of low projections tends to increase. From this viewpoint, it is more preferably 8.0 to 20.0 μm, and further preferably 9.0 to 15.0 μm.

(Aspect of surface layer B)
From the viewpoint of securing a gap between the light guide plate and the film, the surface layer B preferably has protrusions with an appropriate height at an appropriate frequency on the outermost layer surface.
In the present invention, the number of protrusions having a height of 5 μm or more and less than 15 μm is preferably 50 to 500 / mm ² on the surface. The number of protrusions having a height of 15 μm or more is preferably 10 / mm ² or less. Thereby, it becomes easier to secure a gap between the light guide plate and the film, and a film further excellent in the sticking suppression effect and the light guide plate scraping suppression effect is obtained.

As described above, usually, the amount of gap required between the light guide plate and the reflective film is 7 to 15 μm, and from this, the number of protrusions having a height of 5 μm or more and less than 15 μm is more important. It is easy to secure a more appropriate gap by appropriately having a proper protrusion. From this viewpoint, in the present invention, the number of protrusions having a height of 5 μm or more and less than 15 μm is preferably 50 pieces / mm ² or more, more preferably 55 pieces / mm ² or more, further preferably 60 pieces / mm ² or more, and further preferably. Is an embodiment that satisfies 65 / mm ² or more, particularly preferably 80 / mm ² or more, and most preferably 100 / mm ² or more. Also, 500 pieces / mm ² or less is preferable, more preferably 475 pieces / mm ² or less, further preferably 450 pieces / mm ² or less, particularly preferably 400 pieces / mm ² or less, and most preferably 350 pieces / mm ² or less. It is the aspect which satisfy | fills. If the number of protrusions of 5 μm or more and less than 15 μm is larger than this range, the effect of improving the reflectance and luminance of the obtained film tends to be lowered. On the other hand, if the number of protrusions is smaller than this, it tends to be difficult to secure a gap between the light guide plate and the reflector, and optical defects such as adhesion spots tend to occur, and the number of contact points decreases. The light guide plate tends to be easily cut.

The number of protrusions having a height of 15 μm or more is preferably 10 pieces / mm ² or less. More preferably, it is 8 pieces / mm < ² > or less, More preferably, it is 5 pieces / mm < ² > or less. The protrusion having such a height is liable to affect the shaving failure between the light guide plate and the reflective film, and the effect of suppressing the shaving of the light guide plate can be further enhanced by controlling the number of protrusions to a sufficiently small number.
In addition, the stretching temperature also affects the aspect of the protrusion frequency. For example, by increasing the longitudinal stretching temperature, it becomes easy to achieve the above-described aspect of the protrusion frequency.

(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 different from the above 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 stretchability can be increased. From these viewpoints, the void volume ratio in the surface layer B (ratio of the volume of voids in the surface layer B to the volume of the surface layer B) is preferably 0% by volume or more and less than 15% by volume, more preferably 5%. It is not more than volume%, particularly preferably not more than 3 volume%. In particular, in the present invention, since the effect of improving the reflection characteristics and film-forming stretchability can be enhanced at the same time, the preferred void volume ratio in the reflective layer A and the preferred void volume ratio in the surface layer B are simultaneously employed. It is particularly preferred.

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

  By setting the thickness of the surface layer B to such a mode in addition to the above-described mode of the particle group, it is easy to achieve the above preferable projection frequency, and it becomes easier to secure a gap with the light guide plate. If the surface layer B is too thin, there is a tendency that the particles fall off in the protrusions formed on the surface of the surface layer B. Moreover, it exists in the tendency for the improvement effect of film forming stretchability to become low. On the other hand, if it is too thick, the effect of improving the reflectance tends to be low, and a preferable protrusion frequency tends 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 is excellent in film-forming stretchability. Further, problems such as curling are unlikely to 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 stretchability, 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-forming stretchability of the film is relatively low (preferably 0% by volume or more and less than 15% by volume, more preferably 5% by volume or less, particularly preferably 3% by volume or less. A support layer C can also be provided.

[Film Production Method]
Hereinafter, an example of the method for producing the white reflective film of the present invention will be described.
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 stretchability 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). 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 (reflectance at a wavelength of 550 nm) of the white reflective film of the present invention measured from the surface layer B side is preferably 96% or more, more preferably 97% or more, still more preferably 97.5% or more, particularly preferably. Is 98.0% 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-recovery raw material is obtained and a film is formed using the raw material, a gas mark is hardly generated, and the film-forming stretchability 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) Particle size distribution and average particle size The particle size distribution and average particle size (D50) of the particles were measured with a laser scattering particle size distribution analyzer (SALD-7000 manufactured by Shimadzu Corporation). In addition, the particle size distribution of the particles contained in the film is obtained by peeling the laminated film in advance, dissolving the corresponding part in an organic solvent, and collecting the recovered particles using the same method. D50) was measured.
In addition, using the obtained particle size distribution data of the particle group in the surface layer B, the density of the surface layer B (by the density gradient tube), and the bulk density of the obtained particle group, the ratio of the particle volume of each particle size is calculated. Asked. That is, the volume of the particle group was determined from the mass and bulk density of the particle group contained in the surface layer B having a constant volume. Further, from the particle size distribution data, the volume ratio of particles in each particle size range in the particle group was determined, and this was divided by the volume of the particle group to determine the volume ratio of particles in each particle size range in the surface layer B.

(3) Projection frequency on the film surface (number of protrusions)
Using a laser microscope (Keyence VK-X100), surface unevenness analysis was performed for a surface of 1.0 mm × 1.0 mm on the outermost layer surface of the reflective film, and the height was 5.0 μm or more to less than 15.0 μm from the surface. The number of protrusions of 15.0 μm or more was calculated.

(4) Amount of Volatile Organic Solvent At room temperature (23 ° C.), 1 g of a film sample was placed in a 10 L fluororesin bag, which 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.

(5) Film thickness and layer structure A white reflective film is sliced with a microtome to obtain a cross section, and the 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.

(6) Calculation of void volume ratio Calculated density was calculated 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 ).

(7) 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.

(8) 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.

(9) 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 having a length of 200 mm × width of 200 mm × thickness of 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 described above, the reflective film side is placed on the light guide plate with the surface facing downward, and a 500 g weight (reference numeral 10 in FIG. 2) is placed thereon, and fixed 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.
If there are no scratches that can be observed with a loupe after 30 reciprocating movements in the entire range of 400 mm × 200 mm rubbed on the light guide plate, the scratches can be observed with a magnifying glass (scratch evaluation ○). Although there were no scratches that could be observed after 30 reciprocating movements, the result was “hard to scrape” (scraping evaluation Δ), and when there were scratches that could be observed after 20 reciprocating movements, “scraped” (scraping evaluation ×).
Moreover, after moving back and forth 30 times, if there was no white foreign substance 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 would not fall out” (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.

(10) White spot evaluation Using the reflective film and light guide plate used in the evaluation of (9) above, place the reflective film on the desk so that the surface layer surface faces upward, and the dot surface faces downward on it. 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 ○).

(11) 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 columnar legs with a diameter of 5 mm as shown in FIG. 1 is placed in the area including the most severely uneven portion of the chassis within the plane, and a weight of 12 kg is further placed 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.

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

[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 type extruder, mixed so that the content of barium sulfate particles is 60% by mass with respect to the mass of the obtained master chip, extruded at a resin temperature of 260 ° C., and particles containing barium sulfate particles Master chip 1 was created.

<Production Example 4: Preparation of particle master chip 2>
The isophthalic acid copolymerized polyethylene terephthalate 2 obtained above was air-classified as particles A with carrier ct P-10 (aggregated silica particles) manufactured by Fuji Silysia Co., Ltd., with an average particle diameter of 10.5 μm and a standard deviation of 1.0 μm. The particles thus obtained were mixed so as to be 8% by mass, and extruded at a melting temperature of 250 ° 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 225 μm was obtained as shown in Table 1. The evaluation results of the obtained film are shown in Tables 1 and 2.

[Examples 2 to 5, Comparative Examples 1 to 3]
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 Tables 1 and 2.
The types of particles used are as follows.
Particle B: Carriage P-10 (aggregated silica particles) manufactured by Fuji Silysia Co., Ltd. was air-classified to obtain an average particle size of 10.2 μm and a standard deviation of 2.0 μm.
Particle C: Pyrosphere (spherical silica) manufactured by Fuji Silysia Co., Ltd. was air-classified to have an average particle size of 10.4 μm and a standard deviation of 3.0 μm.

[Example 6]
As shown in Table 1, the void forming agent of the reflective layer A was changed to a resin incompatible with polyester (cycloolefin, “TOPAS 6017S-04” manufactured by Polyplastics Co., Ltd.). A white reflective film was prepared and evaluated. The evaluation results are shown in Tables 1 and 2.

ND: not detected (detection limit)

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

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 (6)

A laminated film having a reflective layer A and a surface layer B made of a thermoplastic resin and containing particles composed of particles, the particles being inorganic particles,
The surface layer B is an oriented layer, and the surface layer B forms at least one outermost layer of the laminated film, and the particle group is formed on the surface of the surface layer B forming the outermost layer opposite to the reflective layer A. Having protrusions formed by
Regarding the particle group in the surface layer B, the total volume of particles having a particle size of less than 7.0 μm is 10.0% by volume or less with respect to the volume of the surface layer B, and the total number of particles having a particle size of 7.0 μm or more and less than 11.0 μm. The volume is 3.0 to 20.0% by volume with respect to the volume of the surface layer B, and the total volume of particles having a particle diameter of 11.0 μm or more and less than 15.0 μm is 3.0 to 20% with respect to the volume of the surface layer B. A white reflective film in which the total volume of particles having a volume of 0% by volume and a particle size of 15.0 μm or more is 10.0% by volume or less with respect to the volume of the surface layer B.   The white reflective film according to claim 1, wherein the particles are aggregated particles. On the surface of the surface layer B forming the outermost layer opposite to the reflective layer A, the number of protrusions having a height of 5 μm or more and less than 15 μm is 50 to 500 / mm ² , and the number of protrusions having a height of 15 μm or more is 10 / The white reflective film of Claim 1 or 2 which is mm < ² > or less.   The white reflective film of any one of Claims 1-3 whose amount of volatile organic solvents is 10 ppm or less.   The white reflective film of any one of Claims 1-4 whose reflective layer A has a void and the void volume ratio is 15 volume% or more and 70 volume% or less.   The white reflective film of any one of Claims 1-5 used as a surface light source reflective board provided with a light-guide plate.