JP6110220B2 - 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

  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 protrusions on the film surface by such a method, it is possible to suppress sticking to a light guide plate that has been required in recent years only by focusing only on the number of protrusions as in the past. It has been found that there are cases where the suppression of scratches on the light guide plate is 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 white reflective film having a reflective layer A and a surface layer B made of a thermoplastic resin and containing 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 surface layer B forming the outermost layer is formed on the surface opposite to the reflective layer A by the particles. Having projections formed,
On the surface, the number of protrusions having a height of 5 μm to less than 7 μm is 20 to 200 / mm ² , the number of protrusions having a height of 7 μm to less than 10 μm is 20 to 200 / mm ² , and the number of protrusions having a height of 10 μm to less than 15 μm. A white reflective film having a number of protrusions of 10 to 100 pieces / mm ² and a height of 15 μm or more of 10 pieces / mm ² or less.
2. 2. The white reflective film as described in 1 above, wherein the particles are aggregated particles.
3. 3. The white reflective film as described in 1 or 2 above, wherein the average particle diameter of the particles is 7.0 μm or more and less than 15.0 μm.
4). The white reflective film of said 1-3 whose 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 contains a void, 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 a copolymer is preferred from the viewpoint that crystallization is suppressed when the film is stretched uniaxially or biaxially and the effect of improving film-forming stretchability is enhanced. Examples of the copolymer component include the dicarboxylic acid component and the diol component described above, and isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferable from the viewpoint of high heat resistance and a high effect of improving film-forming stretchability. The proportion of the copolymerization component is, for example, 1 to 20 mol%, preferably 2 to 18 mol%, more preferably 3 to 15 mol%, particularly preferably 7 to 11 based on 100 mol% of the total dicarboxylic acid component of the polyester. Mol%. By making the ratio of a copolymerization component into this range, it is excellent in the improvement effect of film forming stretchability. Moreover, it is excellent in thermal dimensional stability.

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

  When an incompatible resin is used as the void forming agent, the incompatible resin is not particularly limited as long as it is incompatible with the thermoplastic resin constituting the layer. For example, when the thermoplastic resin is polyester, polyolefin, 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 particles and having projections formed on the surface by the particles. 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.

(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.

(Aspect of surface layer B)
In the present invention, the surface layer B made of the thermoplastic resin as described above and containing particles forms at least one outermost layer of the white reflective film. The surface layer B that forms the outermost layer has protrusions formed of the 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.

In the present invention, on the surface, the number of protrusions having a height of 5 μm or more and less than 7 μm is 20 to 200 / mm ² , the number of protrusions having a height of 7 μm or more and less than 10 μm is 20 to 200 / mm ² , and the height is 10 μm or more to 15 μm. The number of projections less than 10 to 100 / mm ² and the number of projections having a height of 15 μm or more are required to be 10 / mm ² or less. Thereby, the gap between the light guide plate and the film can be sufficiently secured, and the effect of suppressing sticking and the effect of suppressing light guide plate scraping are excellent.

  Usually, the amount of gap required between the light guide plate and the reflective film is 7 to 15 μm. From this, the number of protrusions having a height of 7 μm or more and less than 15 μm is the most important in the above-mentioned protrusion height classification. is there. On the other hand, if a large amount of particles having a relatively large diameter is applied or added, the effect on the optical properties increases, such as a decrease in the reflectance of the obtained film. There is a need. In addition, when adding large-diameter particles to the film layer, breakage failure tends to occur during film formation stretching, and the productivity is significantly deteriorated. Therefore, the addition amount is appropriate in terms of productivity in addition to quality. Need to control.

From this viewpoint, the number of protrusions having a height of 10 μm or more and less than 15 μm required in the present invention is 10 to 100 / mm ² , more preferably 15 to 95 / mm ² , and still more preferably 20 to 90. / Mm ² is satisfied. If the number of protrusions of 10 μm or more and less than 15 μm is larger than this range, the reflectance and brightness of the obtained film may be reduced, or the film-forming stretchability during production may be extremely reduced, resulting in a product of good quality. Have difficulty. On the other hand, if the number of protrusions is smaller than this, a sufficient gap cannot be secured between the light guide plate and the reflection plate, optical defects such as adhesion spots occur, or the light guide plate is easily scraped because the contact points are extremely small. Defects occur.

The protrusions having a height of 7 μm or more and less than 10 μm are formed so as to complement the protrusions of 10 μm or more and less than 15 μm, and the number of protrusions required in the present invention is 20 to 200 / mm ² , more preferably. Is an aspect satisfying 25 to 190 / mm ² , more preferably 30 to 180 / mm ² . If the number of protrusions is larger than this range, there will be a problem because the effect on the optical characteristics becomes large, such as a large decrease in reflectance of the obtained film. On the other hand, if the number of protrusions is smaller than this, a sufficient gap between the light guide plate and the reflection plate cannot be secured. In addition, when pressure is applied to the light guide plate or the reflection plate, deflection occurs, which causes a problem of adhesion spots and poor shaving.

The protrusions having a height of 5 μm or more and less than 7 μm are formed so as to complement the protrusions having a height of 7 μm or more but less than 15 μm, and the particles forming these protrusions have less influence on the film-forming stretchability and optical properties. The number of protrusions required in the present invention is 20 to 200 pieces / mm ² , more preferably 25 to 190 pieces / mm ² , and further preferably 30 to 180 pieces / mm ² . If the number of protrusions is larger than this range, the effect on the optical properties becomes problematic, such as a decrease in reflectance of the obtained film. On the other hand, if the number of protrusions is smaller than this, a gap is likely to occur when pressure is applied to the light guide plate or the reflection plate, resulting in problems such as poor adhesion spots.

Further, the number of protrusions having a height of 15 μm or more needs to be 10 pieces / mm ² or less. Such height protrusions are most likely to affect the shaving failure between the light guide plate and the reflective film, and must be controlled to a sufficiently small number. Moreover, there exists a tendency for film forming stretchability to fall.

  In the present invention, the light guide plate is in contact with each protrusion as uniformly as possible by having the protrusions with the specific height as described above on the surface of the outermost layer, and the pressure on the light guide plate by each protrusion is controlled. Dispersion suppresses the light guide plate from being damaged while having an appropriate gap with the light guide plate. If it is not in the above range, for example, the light guide plate comes into contact with only the high protrusions, and the pressure is concentrated on that portion, which makes it easy to scrape.

(particle)
In order to obtain the protrusion frequency as described above, the particle size distribution of the particles to be used may be controlled, or the average particle diameter and the addition amount of the particles may be adjusted. The stretching temperature also affects the protrusion frequency. For example, by increasing the longitudinal stretching temperature, it becomes easy to obtain the aspect of the protrusion frequency defined by the present invention.

  The average particle size of particles that can be preferably used in the present invention is 7.0 μm or more and less than 40.0 μm. Thereby, in the preferable thickness of the surface layer B mentioned later, it becomes easy to set it as the aspect of the protrusion height of the outermost layer surface mentioned above. 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.

  Moreover, as for the preferable particle size distribution of particle | grains, the standard deviation of a particle size is 0.1-5.0 micrometers. Thereby, it becomes easy to achieve the aspect of the protrusion on the outermost layer surface defined by the present invention. From this viewpoint, the standard deviation of the particle diameter is more preferably 0.3 to 4.5 μm, further preferably 0.5 to 4.0 μm, particularly preferably 0.5 to 3.5 μm, and most preferably 0.5. ˜3.0 μm. In order to obtain such a particle size distribution, a method of selecting particles having a wider particle size distribution by air classification may be employed.

In the present invention, the particles contained in the surface layer B may be organic particles, inorganic particles, or organic-inorganic composite particles regardless of the type, but in order to form the surface protrusions described above. In addition, it is necessary to control the particle size distribution of the particles in advance and to use a particle whose shape and shape are generally stable during film forming. In addition, those that do not easily melt or generate gas even when heat-processed are preferable, and inorganic particles such as silica, titanium oxide, barium sulfate, and calcium carbonate are preferable from such a viewpoint.
On the other hand, relatively soft agglomerated particles are preferable in order to further suppress the failure of rupture at the time of film formation stretching, and further to suppress the influence on the failure of rupture and optical properties when producing a film using a self-collecting raw material. .

(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.
Thereby, it becomes easy to make a protrusion frequency into a preferable aspect, and it becomes easy to ensure a gap with a 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, the fall of film forming stretchability is seen. 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), excellent in film-forming stretchability, and voids are preferably formed. The stretching ratio is preferably 2.5 to 4.3 times, more preferably 2.7 to 4.2 times in both the vertical direction and the horizontal direction. If the draw ratio is too low, uneven thickness of the film tends to be worsened, and voids tend not to be formed. On the other hand, if it is too high, breakage tends to occur during film formation. In the case of sequential biaxial stretching in which longitudinal stretching is performed and then lateral stretching is performed, the second stage (in this case, lateral stretching) is made about 10 to 50 ° C. higher than the first stage stretching temperature. Things are preferable. This is due to the fact that the Tg as a uniaxial film is increased due to the orientation in the first stage of stretching.

Moreover, it is preferable to preheat a film before each extending | stretching. For example, the pre-heat treatment for transverse stretching may start from a temperature higher than Tg + 5 ° C. of the polyester (preferably the polyester constituting the reflective layer A) and gradually increase the temperature. Although the temperature rise in the transverse stretching process may be continuous or stepwise (sequential), the temperature is usually raised sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone.
The film after biaxial stretching is subsequently subjected to heat-fixing and heat-relaxing treatments in order to obtain a biaxially oriented film. However, following melt-extrusion to stretching, these treatments can also be performed while the film is running. it can.
The film after biaxial stretching has a constant width or a Tm −20 ° C. to (Tm−100 ° C.) melting point of the polyester (preferably the polyester constituting the reflective layer A) while holding both ends with clips. It is preferable to heat-treat under a width reduction of 10% or less and heat-set to lower the heat shrinkage rate. When the heat treatment temperature is too high, the flatness of the film tends to deteriorate, and the thickness unevenness tends to increase. On the other hand, if it is too low, the thermal shrinkage tends to increase.

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

[Characteristics of reflective film]
(Reflectance, brightness)
The reflectance measured from the surface layer B side of the white reflective film of the present invention is preferably 96% or more, more preferably 97% or more, still more preferably 97.5% or more, and particularly preferably 98.0% or more. is there. When the reflectance is 96% or more, high luminance can be obtained when used in a liquid crystal display device or illumination. Such a reflectance may be a preferable aspect such as increasing the void volume ratio of the reflective layer A, or a preferable aspect of each layer such as increasing the thickness of the reflective layer A or reducing the thickness of the 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.

(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 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 size of particles The particle size distribution (standard deviation of particle size) of the particles is obtained with a laser scattering type particle size distribution analyzer (SALD-7000 manufactured by Shimadzu Corporation), and the particle size at d50 is defined as the average particle size. did.

(3) Projection frequency on the film surface (number of protrusions)
Using a laser microscope (Keyence VK-X100), a surface unevenness analysis is performed on the surface of the outermost layer of the reflective film in the range of 1.0 mm × 1.0 mm, and the height is 5.0 μm or more to less than 7.0 μm from the surface. 7.0 μm or more to less than 10.0 μm, the number of protrusions of 10.0 μm or more to less than 15.0 μm, or 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, and 300 g weights are placed and fixed. Using a backlight light source of an LED liquid crystal television (LG42LE5310AKR) manufactured by LG, light is incident from the side of the light guide plate. 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 LCD TV (47 inch size) made by LG and place it on a horizontal desk so that the inside of the TV is facing upward. On top of it, a reflective film of the same size as the chassis, with the surface layer 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 triangle base having three circular feet 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 20 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>
Particles obtained by air classifying AY-601 (aggregated silica) manufactured by Tosoh Silica Co., Ltd. into the isophthalic acid copolymerized polyethylene terephthalate 2 obtained above and having an average particle diameter of 10.9 μm and a standard deviation of 1.0 μm. Were mixed at 8 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 250 μm was obtained as shown in Table 1. The evaluation results of the obtained film are shown in Table 2.

[Examples 2-6, Comparative Examples 1-3]
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 Table 2.

The types of particles used are as follows.
Particle B: AY-601 (aggregated silica) manufactured by Tosoh Silica Co., Ltd. was air-classified to obtain an average particle size of 10.2 μm and a standard deviation of 3.0 μm.
Particle C: BMX-40 (true spherical crosslinked acrylic particle) manufactured by Sekisui Plastics Co., Ltd. is used (average particle size 35.0 μm, standard deviation 0.5 μm)
Particle D: Pyrosphere (spherical silica) manufactured by Fuji Silysia Co., Ltd. was air-classified to obtain an average particle diameter of 14.5 μm and a standard deviation of 3.8 μm.

[Example 7]
As shown in Table 1, the void forming agent of the reflective layer A was changed to a resin incompatible with polyester (cycloolefin, “TOPAS 6017S-04” manufactured by Polyplastics Co., Ltd.). A white reflective film was prepared and evaluated. The evaluation results are shown in Table 2.

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 white reflective film having a reflective layer A and a surface layer B made of a thermoplastic resin and containing 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 surface layer B forming the outermost layer is formed on the surface opposite to the reflective layer A by the particles. Having projections formed,
On the surface, the number of protrusions having a height of 5 μm to less than 7 μm is 20 to 200 / mm ² , the number of protrusions having a height of 7 μm to less than 10 μm is 20 to 200 / mm ² , and the number of protrusions having a height of 10 μm to less than 15 μm. A white reflective film having a number of protrusions of 10 to 100 pieces / mm ² and a height of 15 μm or more of 10 pieces / mm ² or less.   The white reflective film according to claim 1, wherein the particles are aggregated particles.   The white reflective film of Claim 1 or 2 whose average particle diameter of the said particle | grain is 7.0 micrometers or more and less than 15.0 micrometers.   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 reflection layer A contains a void and whose 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.