JPWO2017018280A1 - White reflective film - Google Patents

Abstract

In a normal state, it is possible to sufficiently suppress sticking to the light guide plate, and even though it is an aqueous coating layer, it suppresses sticking to the light guide plate even in a wet and heat environment, and has a high recovery film forming property. An object is to provide a reflective film. Such a problem is a white reflective film having a coating layer formed from an aqueous coating liquid whose solid content contains a binder resin and particles as main components on the surface of the reflective film, the surface of the coating layer Has protrusions formed of the particles, and the protrusions have a number of protrusions having a height of 5 μm or more of 104 / m 2 to 1010 / m 2, and the binder resin has a glass transition temperature Tg of 100 ° C. to 120 ° C. A thermoplastic polyester resin having a glass transition temperature Tg of less than 100 ° C. based on the weight of the binder resin is contained in an amount of 5% by weight to 50% by weight based on the weight of the binder resin. A white reflective film, which is contained at 95% by mass.

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.

  The backlight unit of a liquid crystal display device (hereinafter sometimes referred to as LCD) includes a direct type with a light source on the back of the liquid crystal display panel and a reflective film on the back, and a back reflection on the back of the liquid crystal display panel. There is an edge light type in which a light guide plate provided with a plate is arranged and a light source is provided on a side surface of the light guide plate. Conventionally, as a backlight unit used in a large LCD, a direct type, mainly a direct type CCFL, is used from the viewpoint of excellent screen brightness and uniformity of brightness in the screen. It is often used for relatively small LCDs such as notebook PCs. However, 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. Type backlight units have come into use. This also has the advantage that the LCD can be made thinner.

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

  As a conventional technique, an organic solvent-based coating liquid is used in a method of applying particles to the surface of a reflective film by coating. On the other hand, the use of an organic solvent is not preferable from an environmental point of view. Therefore, it is desired to apply particles to the surface of a reflective film using an aqueous coating liquid. However, when applying particles to the surface of the reflective film, generally, a binder resin is used to hold the particles. However, when an aqueous coating liquid is used, in the conventional mode, for example, it is overlapped with a light guide plate. When used together, there is a problem that the coating layer melts in a durability test with temperature and humidity, such as during a durability test process of a liquid crystal television, and thereby the light guide plate and the reflective film stick. Moreover, when a crosslinking agent is easily introduced in order to avoid the problem, the film forming property when the reflective film including the coating layer is recovered and formed into a film (hereinafter sometimes referred to as recovered film forming property). Affects.

  Therefore, the present invention can sufficiently suppress sticking to the light guide plate in a normal state, and suppresses sticking to the light guide plate even in a wet heat environment while being an aqueous coating layer, and is also a recovery product. It aims at providing a white reflective film with high film property.

The present invention adopts the following configuration in order to achieve the above-described problems.
1. On the surface of the reflective film, a white reflective film having a coating layer formed from an aqueous coating liquid whose solid content contains a binder resin and particles as main components,
The surface of the coating layer has protrusions formed by the particles, and the protrusions have a number of protrusions having a height of 5 μm or more of 10 ⁴ pieces / m ² or more and 10 ¹⁰ pieces / m ² or less,
The binder resin contains a copolyester resin having a glass transition temperature Tg of 100 ° C. or more and 120 ° C. or less in an amount of 5% by mass to 50% by mass based on the mass of the binder resin, and the glass transition temperature Tg is 100. A white reflective film comprising a thermoplastic resin having a temperature of less than 0 ° C. in an amount of 50% by mass to 95% by mass based on the mass of the binder resin.
2. 2. The white reflective film as described in 1 above, wherein the content of the particles in the coating layer is 5% by mass or more and 50% by mass or less with respect to 100% by mass of the coating layer.
3. 3. The white reflective film as described in 1 or 2 above, wherein the copolymerized polyester resin contains a naphthalene dicarboxylic acid component as a constituent component. The white reflective film according to any one of 1 to 3, wherein the average particle diameter (d) of the particles in the coating layer and the thickness (t) of the coating layer satisfy the following formula (1).

1 ≦ d (μm) / t (μm) ≦ 100 (1)
5. The white reflective film of any one of said 1-4 whose amount of volatile organic solvents of a film is 10 ppm or less.
6). The white reflective film of any one of said 1-5 used as a reflecting plate for surface light sources provided with a light-guide plate.

  According to the present invention, it is possible to sufficiently suppress sticking to the light guide plate in a normal state, and to suppress sticking to the light guide plate even in a wet heat environment while being an aqueous coating layer, and to collect A white reflective film having a high film forming property can be provided.

It is a schematic diagram which shows the structure used for sticking evaluation in this invention.

Drawing reference

DESCRIPTION OF SYMBOLS 1 Chassis 2 White reflection film, light-guide plate, optical sheet laminate 3 Equilateral triangle type base 4 Weight

  The white reflective film of the present invention has a coating layer on the surface of the reflective film. And the surface of this application layer has a processus | protrusion, By this, the gap with a light-guide plate can be ensured.

  Hereafter, each structural component which comprises this invention is demonstrated in detail.

[Reflective film]
The reflective film in the present invention is a film that exhibits a white color by including a white colorant or void forming agent in the film. Therefore, this reflective film consists of a thermoplastic resin composition containing a white colorant or a void forming agent in a thermoplastic resin. As the colorant or void forming agent, for example, inorganic particles, organic particles, and a resin that is incompatible with the thermoplastic resin constituting the film (hereinafter, sometimes referred to as incompatible resin) are used. Can do. In addition, a void formation agent is an agent which can form a void in a film, and the film which was made to exhibit white by this will have a void in a film.

  The reflectance at a wavelength of 550 nm of the reflective film is preferably 95% or more, more preferably 96% or more, and particularly preferably 97% or more. The reflective film may be a single layer film or a laminated film. From the viewpoint of obtaining high reflectivity and mechanical strength, a laminated film composed of a layer containing a relatively large amount of voids and a layer containing a relatively small amount of voids or no voids is preferable. Here, a layer containing a relatively large amount of voids is referred to as a reflective layer, and a layer containing relatively few voids or no voids is referred to as a support layer. Moreover, as a thermoplastic resin which comprises a film, polyester, polyolefin, a polystyrene, and an acryl can be mentioned, for example, Polyester is preferable from a viewpoint of obtaining the white film excellent in a mechanical characteristic and thermal stability.

(polyester)
When using polyester as a thermoplastic resin of a reflective film, it is preferable to use polyester which consists of a dicarboxylic acid component and a diol component as polyester. Examples of the dicarboxylic acid component include a terephthalic acid component, an isophthalic acid component, a 2,6-naphthalenedicarboxylic acid component, a 4,4′-diphenyldicarboxylic acid component, an adipic acid component, and a sebacic acid component. Examples of the diol component include an ethylene glycol component, a 1,4-butanediol component, a 1,4-cyclohexanedimethanol component, and a 1,6-hexanediol component.

  Among these polyesters, aromatic polyesters are preferable, and polyethylene terephthalate is particularly preferable. The polyethylene terephthalate may be a homopolymer, but is preferably a copolymer. In particular, when a laminated reflective film composed of a layer containing a relatively large amount of voids and a layer containing a relatively small amount of voids or no voids is used as the reflective film, a layer containing a relatively large amount of voids The polyester used for is preferably a copolymer. In this case, the ratio of the copolymerization component is, for example, 3 mol% or more, preferably 4 mol% or more, more preferably 5 mol% or more, based on 100 mol% of all dicarboxylic acid components, and for example, 20 mol%. Hereinafter, it is preferably at most 15 mol%, more preferably at most 13 mol%. By setting the proportion of the copolymer component within this range, excellent film forming properties can be obtained even for a layer containing a relatively large amount of voids. Moreover, the reflective film excellent in thermal dimensional stability can be obtained.

(Coloring agent, void forming agent)
When inorganic particles are used as the colorant or void forming agent, the inorganic particles are preferably white inorganic particles. Examples of the white inorganic particles include barium sulfate particles, titanium dioxide particles, silicon dioxide particles, and calcium carbonate particles. The average particle diameter of the inorganic particles is, for example, 0.2 μm or more, preferably 0.3 μm or more, more preferably 0.4 μm or more, and for example, 3.0 μm or less, preferably 2.5 μm or less, more preferably 2 0.0 μm or less. The content is preferably 25% by mass or more, more preferably 30% by mass or more, more preferably 55% by mass or less, and further preferably 50% by mass or less, based on the mass of the reflective film. By using such inorganic particles, it becomes easy to achieve a preferable reflectance. Moreover, it can disperse | distribute moderately in a film, the aggregation of particle | grains does not occur easily, and a film without a coarse protrusion can be obtained. At the same time, the surface of the film does not become too rough, and the glossiness can be controlled within an appropriate range. 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 organic particles are used as the colorant or void forming agent, resin particles that are incompatible with polyester are used as the organic particles. As the organic particles, silicone resin particles, polystyrene resin particles, and polytetrafluoroethylene particles are preferable. The average particle size of the organic particles is, for example, 0.2 μm or more, preferably 0.3 μm or more, more preferably 0.4 μm or more, and for example, 10 μm or less, preferably 8.0 μm or less, more preferably 6.0 μm. It is as follows. The content is preferably 25% by mass or more, more preferably 30% by mass or more, more preferably 55% by mass or less, and further preferably 50% by mass or less, based on the mass of the reflective film. By using such organic particles, it becomes easy to achieve a preferable reflectance. Moreover, it can disperse | distribute moderately in a film, the aggregation of particle | grains does not occur easily, and a film without a coarse protrusion can be obtained. At the same time, the surface of the film does not become too rough, and the glossiness can be controlled within an appropriate range. The organic particles may have any particle shape, for example, a plate shape or a spherical shape.

  When an incompatible resin is used as the colorant or void forming agent, the incompatible resin is preferably a polyolefin such as polyethylene, polypropylene, or polymethylpentene, cycloolefin, or polystyrene. The content is preferably 25% by mass or more, more preferably 30% by mass or more, more preferably 55% by mass or less, and further preferably 50% by mass or less, based on the mass of the reflective film. By using such an incompatible resin, it becomes easy to achieve a preferable reflectance.

[Coating layer]
The coating layer in the present invention is formed from a water-based coating liquid whose solid content contains a binder resin and particles as main constituent components. Here, the “main constituent component” is 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, based on the mass of the solid content of the coating liquid. In the solid content, the content of the particles is not particularly limited as long as the aspect of the number of protrusions described below is satisfied, but is preferably 5% by mass or more based on the mass of the solid content of the coating liquid, and more preferably 10% by mass or more, more preferably 20% by mass or more, particularly preferably 25% by mass or more, preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less, Especially preferably, it is 35 mass% or less. Thereby, it becomes easy to set it as the aspect of the preferable coating layer mentioned later further. In addition, about content of binder resin, what is necessary is just to make it the binder resin contain the said particle | grain and the arbitrary component mentioned later in solid content of a coating liquid. As a result, the coating layer in this invention is an aspect which contains binder resin and particle | grains as a main structural component.

  In the present invention, the coating layer is provided on the surface of the reflective film, but it may be provided on at least one surface on the light guide plate side, and may be provided on both surfaces of the reflective film.

(particle)
The particles in the coating layer may be organic particles, inorganic particles, or organic-inorganic composite particles.

  Examples of the organic particles include polyester resin particles, acrylic-modified polyester resin particles, nylon resin particles, polypropylene resin particles, polystyrene resin particles, silicone resin particles, acrylic resin particles, styrene-acrylic resin particles, polyurethane resin particles, and divinylbenzene-acrylic. Examples thereof include polymer resin particles such as resin particles, polyimide resin particles, and melamine resin particles. Among these, polyester resin particles, acrylic-modified polyester resin particles, silicone resin particles, acrylic resin particles, and nylon resin particles are particularly preferable from the viewpoint that it is easy to form protrusions having an appropriate hardness for securing a gap. Among these, polyester resin particles are particularly preferable particles in the present invention from the viewpoint that the recovered film-forming property can be further enhanced. From such a viewpoint, polyethylene terephthalate particles are particularly preferable as the polyester resin particles.

As inorganic particles, (1) silicon dioxide (including hydrates, silica sand, quartz, etc.); (2) alumina in various crystal forms; (3) silicate containing 30% by mass or more of SiO ₂ component ( For example, amorphous or crystalline clay mineral, aluminosilicate (including calcined product and hydrate), warm asbestos, zircon, fly ash, etc.); (4) oxides of Mg, Zn, Zr and Ti; (5 ) Ca and Ba sulfates; (6) Li, Ba and Ca phosphates (including monohydrogen and dihydrogen salts); (7) Li, Na and K benzoates; (8) Ca, Ba, Zn and Mn terephthalates; (9) Mg, Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, Co and Ni titanates; (10) Ba and Pb chromates; (11) Carbon (for example, carbon black, graph (12) glass (for example, glass powder, glass particles, etc.); (13) carbonates of Ca and Mg; (14) fluorite; (15) spinel oxide. Among these, silica particles are preferable, and aggregated silica particles are particularly preferable from the viewpoint that it is easy to form protrusions having an appropriate hardness for securing a gap.

  As the particles in the present invention, organic-inorganic composite particles such as inorganic particles coated with an organic substance and organic particles coated with an inorganic substance can also be used. Specifically, the organic-inorganic composite particles include, for example, an organic-inorganic hybrid in which a polymer having an organometallic compound group such as a silylalkyl group at the side chain or terminal and an inorganic compound component such as silica are complexed by a covalent bond. Particles made of materials, particles whose surface is bonded with inorganic polymer particles such as crosslinked polystyrene on the surface of inorganic particles, or particles where inorganic particles such as alumina are fixedly coated on the surface of organic polymer particles, etc. Is mentioned.

  The average particle diameter of the particles in the coating layer is not particularly limited as long as the aspect of the number of protrusions described later is satisfied. In particular, it is preferable that the distance between the light guide plate and the film is 2 μm or more and 100 μm or less from the viewpoint that the distance between the light guide plate and the film is kept constant and the sticking of these becomes easy. If the average particle size is too small, the white reflective film tends to be partially adhered to the light guide plate. From such a viewpoint, the average particle diameter is more preferably 5 μm or more, further preferably 10 μm or more, particularly preferably 15 μm or more, and most preferably 20 μm. On the other hand, when it is too large, the particles tend to drop off, and when the dropping occurs, the backlight unit tends to stick. From such a viewpoint, the average particle diameter is more preferably 90 μm or less, further preferably 80 μm or less, particularly preferably 70 μm or less, and most preferably 60 μm or less.

  In the present invention, the 10% compressive strength of the particles is preferably 0.1 MPa or more and 15 MPa or less. Thereby, the effect which suppresses the damage to a light-guide plate can be improved more. If the compressive strength is too low, the particles are excessively deformed with respect to the stress, so that the effect of improving the gap with the light guide plate tends to be low. On the other hand, if the compressive strength is too high, the effect of improving the suppression of scratches on the light guide plate tends to decrease. From this viewpoint, the 10% compressive strength is preferably 0.2 MPa or more, more preferably 0.3 MPa or more, further preferably 3 MPa or more, particularly preferably 8 MPa or more, and preferably 14 MPa or less, more preferably 13 MPa. Hereinafter, it is more preferably 12 MPa or less.

  The 10% compressive strength of the particles can be achieved by adjusting the degree of polymerization, the degree of crosslinking and the degree of crystallization of the particles. For example, in the same type of particles, if the degree of polymerization, the degree of crosslinking and the degree of crystallization are increased, the 10% compressive strength tends to increase. From the above viewpoint, the particles in the present invention are preferably organic particles.

(Binder resin)
The binder resin used for forming the coating layer contains 5% by mass or more and 50% by mass or less of a copolyester resin having a glass transition temperature of 100 ° C. or more and 120 ° C. or less based on the mass of the binder resin. Such a copolyester resin does not substantially contain a crosslinkable reactive group. Here, “substantially not containing” preferably means 1 mol% or less with respect to 100 mol% of the polyester component. By setting it as such an aspect, while being able to suppress sticking with a light-guide plate also in a humid heat environment, it is excellent in collection | recovery film forming property. In addition, the tolerance with respect to sticking with the light-guide plate in a humid heat environment may be called moisture heat blocking resistance. If the content is too small, sticking in such a humid heat environment cannot be suppressed. From this viewpoint, it is preferably 10% by mass or more, more preferably 15% by mass or more, further preferably 20% by mass or more, and particularly preferably 23% by mass or more. On the other hand, when there is too much content, collection | recovery film forming properties will fall. In addition, the coating layer tends to be too hard, and the strength of the coating layer itself tends to decrease. Therefore, from this viewpoint, it is preferably 45% by mass or less, more preferably 40% by mass or less, further preferably 35% by mass or less, and particularly preferably 30% by mass or less.

(Copolymerized polyester resin)
The binder resin in the coating layer of the present invention contains a copolyester resin having a glass transition temperature (Tg) of 100 ° C. or higher and 120 ° C. or lower. By adopting a copolymer polyester resin having a high glass transition temperature as described above, it is possible to achieve the effect of suppressing sticking to the light guide plate in a humid heat environment while being excellent in the recovery film forming property. If Tg is too low, such sticking suppression effect is not achieved. On the other hand, if it is too high, the recovered film-forming property is inferior, and the strength of the coating layer tends to decrease. From such a viewpoint, Tg is preferably 105 ° C. or higher, and preferably 115 ° C. or lower.

  The above-mentioned copolyester resin is a polyester resin obtained by polycondensation of a polyvalent carboxylic acid component and a polyol component, and that the polyvalent carboxylic acid component contains a naphthalenedicarboxylic acid component is the Tg aspect described above. Is preferable because it is easy to satisfy the above. Preferred examples of the naphthalenedicarboxylic acid component include 2,6-naphthalenedicarboxylic acid component, 2,7-naphthalenedicarboxylic acid component, and the like, and 2,6-naphthalenedicarboxylic acid component is preferable. The content is preferably 60 mol% or more, more preferably 61 mol% or more, still more preferably 65 mol% or more, particularly preferably 70 mol% or more with respect to 100 mol% of the acid component of the copolyester resin. And preferably 100 mol% or less, more preferably 95 mol% or less, still more preferably 88 mol% or less, and particularly preferably 85 mol% or less. When the content of the naphthalenedicarboxylic acid component is too small, Tg tends to be low, and when Tg is too low, it is the same as the case where the Tg is not sufficient. On the other hand, if the content is too large, Tg tends to be high, and if Tg is too high, it is the same as the case where Tg is too high.

  As a preferable polyol component for adjusting the Tg of the copolyester resin to the above range, a bis (4- (hydroxyethoxy) phenyl) fluorene component can be exemplified. For example, such a component is contained as a copolymerization component in an amount of 10 mol% or more, preferably 15 mol% or more, and 30 mol% or less, preferably 25 mol% or less with respect to 100 mol% of the acid component of the copolymerized polyester resin. An aspect can also be mentioned as a preferable aspect.

  Examples of the other polyvalent carboxylic acid component of the copolyester resin in the coating layer include a terephthalic acid component, an isophthalic acid component, a 5-Na sulfoisophthalic acid component, and the polyol component includes an ethylene glycol component. , Diethylene glycol component, 1,4-butanediol component, 1,6-hexanediol component, 1,3-cyclohexanediol component, bisphenol component, and the like. Among them, the 5-Na sulfoisophthalic acid component is preferable in order to make it easy to obtain an aqueous coating liquid. For example, an embodiment containing about 1 mol% or more and 10 mol% or less with respect to 100 mol% of the acid component is preferable. Can be mentioned.

  Moreover, as a copolymer polyester resin in the coating layer of the present invention, as long as the above Tg aspect is satisfied, an acrylic modified resin as described in, for example, JP-A-2009-219545 or the like is used as long as the object of the present invention is not impaired. Polyester resin may be used. In this case, it is preferable from the viewpoint of the recovery film-forming property that the acrylic-modified polyester resin does not substantially contain a crosslinkable reactive group. Here, “substantially free of crosslinkable reactive groups” means that the crosslinkable reactive groups are preferably 1 mol% or less with respect to 100 mol% of the polyester component.

(Thermoplastic resin)
The binder resin of the coating layer is a thermoplastic resin having a glass transition temperature of less than 100 ° C. of 50% by mass or more and 95% by mass or less based on the mass of the binder resin in addition to the above-mentioned copolymer polyester resin having a high glass transition temperature. Contains resin. The glass transition temperature is preferably 90 ° C. or lower, more preferably 80 ° C. or lower, further preferably 70 ° C. or lower, preferably 20 ° C. or higher, more preferably 40 ° C. or higher, and further preferably 60 ° C. or higher. . By containing such a thermoplastic resin in such a content range, the adhesiveness of the coating layer to the reflective film and the recoverability of the film having the coating layer are excellent while maintaining moisture and heat blocking resistance. If the content of the thermoplastic resin is too small, the adhesion of the coating layer to the reflective film tends to deteriorate, and when the film having the coating layer is recovered and used as a recovered material, the resulting film turns yellow. Tend to. On the other hand, when the content of the thermoplastic resin is too large, the content of the copolymer polyester resin having the above high glass transition temperature is decreased, and the effect of suppressing sticking in a moist heat environment tends to be reduced. From this viewpoint, the content of the thermoplastic resin is preferably 55% by mass or more, more preferably 60% by mass or more, further preferably 65% by mass or more, and particularly preferably 70% by mass or more with respect to the binder resin. Further, it is more preferably 90% by mass or less, further preferably 85% by mass or less, further preferably 80% by mass or less, and particularly preferably 77% by mass or less.

  Examples of such thermoplastic resins that can be added to the binder resin include polyester resins, acrylic resins, and urethane resins. Among these, a polyester resin is particularly preferable from the viewpoint of good adhesion between the coating layer and the reflective film and from the viewpoint of recovery film forming properties.

(Other ingredients)
The coating layer 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 surfactants, ultraviolet absorbers, antistatic agents, fluorescent brighteners, waxes, particles different from the above particles, and the like.

  In addition, the coating layer in the present invention is preferably an embodiment having substantially no cross-linking structure by a cross-linking agent from the viewpoint of recovery film forming properties and coloring during film recovery. The content of the cross-linking agent in the binder resin The amount is preferably less than 1% by mass based on the mass of the resin, more preferably less than 0.5% by mass, and still more preferably less than 0.1% by mass.

[Aspect of coating layer]
In the present invention, the coating layer as described above is provided on at least one surface of the reflective film. And the surface of this application layer has the protrusion formed with the said particle | grain. Such protrusions need to have protrusions with an appropriate height at an appropriate frequency from the viewpoint of securing a gap between the light guide plate and the film.

Therefore, in the present invention, it is usually necessary that the number of projections having a height of 5 μm or more is 10 ⁴ / m ² or more and 10 ¹⁰ / m ² or less on the surface of the coating layer. Thereby, the gap between the light guide plate and the film can be sufficiently secured, and the effect of suppressing sticking in a normal state can be secured. If the projection frequency is too low, the sticking suppression effect is poor. On the other hand, if the protrusion frequency is too high, the probability of particle dropout tends to improve and the reflectance tends to decrease. The number of protrusions is more preferably 10 ⁶ / m ² or more.

(Thickness of coating layer)
The thickness of the coating layer may be adjusted so that the number of protrusions defined by the present invention is in consideration of the amount of particles used and the particle size. For example, if the coating layer is too thick, the particles tend to be buried, and the number of protrusions tends to decrease.

  From such a viewpoint, it is preferable that the relationship between the thickness (t) of the coating layer and the average particle diameter (d) of the particles satisfies the following formula (1).

1 ≦ d (μm) / t (μm) ≦ 100 (1)
By setting it as such an aspect, it becomes easy to satisfy the number of protrusions prescribed | regulated by this invention. From this viewpoint, in the above formula, the left side is preferably 5 or more, and more preferably 10 or more. The right side is preferably 80 or less, more preferably 70 or less, and particularly preferably 30 or less.

  The specific range of the thickness of the coating layer is preferably 0.3 μm or more, more preferably 0.5 μm or more, further preferably 1 μm or more, particularly preferably 2 μm or more, and preferably 30 μm or less, more preferably It is 25 μm or less, more preferably 10 μm or less, and particularly preferably 6 μm or less.

[Method for producing white reflective film]
Hereinafter, an example of the method for producing the white reflective film of the present invention will be described. In this example, an embodiment of a laminated reflective film having a reflective layer and a support layer is employed as the reflective film.

  First, a polyester composition for forming a reflective layer and a polyester composition for forming a support layer are prepared, sufficiently dried, and then charged into separate extruders and melt-extruded. The polyester composition is preferably filtered using a nonwoven fabric type filter having an average opening of 10 μm or more and 100 μm or less made of a stainless steel fine wire having a wire diameter of 15 μm or less. The average opening is preferably 20 μm or more, and preferably 50 μm or less. By performing this filtration, it is possible to suppress agglomeration of particles that are usually agglomerated and become coarse agglomerated particles, and to obtain a laminated film with few coarse foreign matters.

  The filtered polyester composition is extruded in a multilayer state from a die by a simultaneous multilayer extrusion method using a feed block in a molten state to produce a laminated unstretched sheet.

  The laminated unstretched sheet extruded from the die is cooled and solidified by a casting drum to form a laminated unstretched film. This laminated unstretched film is heated by roll heating, infrared heating or the like, and stretched in the longitudinal direction to obtain a laminated longitudinally stretched film. This stretching is preferably performed by utilizing the difference in peripheral speed between two or more rolls. The stretching is preferably performed at a temperature equal to or higher than the glass transition temperature (Tg) of the polyester. More preferably, it is performed at a temperature equal to or higher than Tg of the polyester of the reflective layer. The draw ratio of the machine direction, that is, the machine axis direction, is preferably 2.2 to 4.0 times, more preferably 2.3 to 3.9 times. If it is less than 2.2 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.0 times, breakage tends to occur during film formation, which is not preferable.

  Subsequently, the laminated film after the longitudinal stretching is sequentially subjected to lateral stretching, heat setting, and thermal relaxation to form a laminated biaxially oriented film. These processes are performed while the film is running. The transverse stretching process starts from a temperature higher than Tg. The temperature increase in the transverse stretching process may be continuous or stepwise (also referred to as sequential), but the temperature is generally increased 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 stretching ratio in the transverse direction, that is, the direction perpendicular to the longitudinal direction, is preferably 2.5 to 4.5 times, more preferably 2.8 to, although it depends on the required characteristics of this application. 3.9 times. If it is less than 2.5 times, the thickness unevenness of the film is deteriorated and a good film cannot be obtained, and if it exceeds 4.5 times, breakage tends to occur during film formation.

  The film after transverse stretching is heat-treated at a temperature of (Tm-100 ° C.) to (Tm-20 ° C.) with a constant width or a width reduction of 10% or less, with the melting point of the polyester being Tm, with both ends held. It is preferable to reduce the heat shrinkage rate. The melting point is preferably the melting point of the polyester of the reflective layer. When the heat treatment temperature is higher than (Tm−20 ° C.), the flatness of the film is deteriorated and the thickness unevenness is increased, which is not preferable. If it is lower than (Tm-100) ° C., the heat shrinkage rate may increase, which is not preferable. 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 slowing down to 2.0% (hereinafter, this value may be 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.

  As a coating liquid for forming a coating layer on the surface of the reflective film thus prepared, a binder resin, particles, surfactants described later as optional components and other components were dispersed or dissolved in water. The coating liquid is applied in a predetermined amount using a coating apparatus, and dried in an oven set at a temperature of 70 to 120 ° C., preferably stepwise to form a coating layer, whereby the white reflective film of the present invention is formed. Can be obtained.

  The coating layer may be formed by so-called off-line coating, in which a coating liquid for forming the coating layer is applied to the manufactured film, or by so-called in-line coating applied to the film being manufactured. Good. In the case of applying to a film during production, the coating liquid is preferably applied to a uniaxially oriented film stretched in one direction, and stretched in the other direction as it is and fixed by heat. As a coating method, a roll coating method, a gravure coating method, a roll brush method, a spray method, an air knife coating method, an impregnation method, a curtain coating method, or the like can be used alone or in combination. Here, a gravure coating method is preferred in order to transfer the particles from the coater evenly to the film. Further, the solvent may be an aqueous coating solution and is preferably composed only of water. However, a solvent in which a small amount of an organic solvent soluble in water is mixed with water as long as the object of the present invention is not impaired is used. be able to. As solid content concentration of a coating liquid, 10 mass% or more and 50 mass% or less are preferable. When the coating solution concentration exceeds 50% by mass, it tends to be difficult to suppress the aggregation of particles in the coating solution. On the other hand, when the coating solution concentration is less than 10% by mass, the coating layer tends to become thin and the particles fall off. It tends to be difficult to suppress.

  A small amount of a surfactant can be added to the coating liquid for forming the coating layer for the purpose of improving the wettability with respect to the reflective film. Preferred surfactants include, for example, nonionic surfactants such as polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, sorbitan fatty acid ester, fluoroalkyl carboxylate, perfluoroalkylbenzene sulfonate, and perfluoroalkyl. Fluorosurfactants such as quaternary ammonium salts and perfluoroalkyl polyoxyethylene ethanol can be mentioned. The addition amount of the surfactant is preferably 1% by mass or more and 20% by mass or less in the solid content of the coating liquid. If it is 1% by mass or less, the wettability with respect to the film tends to deteriorate. When it is 20% by mass or more, it tends to be difficult to achieve other coating liquid performance.

[Characteristics of reflective film]
(Reflectance)
The reflectance measured from the coating layer side of the white reflective film of the present invention is preferably 95% or more, more preferably 96% or more, and still more preferably 97% or more. When the reflectance is 95% or more, high luminance can be obtained when used in a liquid crystal display device or illumination. Such reflectivity tends to increase as the void content of the reflective film increases, increasing the content of the void forming agent, increasing the thickness of the reflective layer in the reflective film, etc. This can be achieved by adopting a preferred embodiment.

(Amount of volatile organic solvent)
In the white reflective film of the present invention, the coating layer is aqueous, and the amount of volatile organic solvent measured by the method described later is preferably 10 ppm or less. Thereby, for example, in an edge light liquid crystal display, the merit of improving the durability of the light guide plate in direct contact with the reflective film can be exemplified. 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 adopt the above-described method without adopting the solution coating method using a large amount of the organic solvent in forming the coating layer. When the amount of the volatile organic solvent is large, the effect of improving the recovery film forming property tends to be low.

  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. In addition, what is necessary is just to implement a measurement in the surface used as the light-guide plate side. In this invention, it carried out on the surface of the side which has a coating layer.

(2) Average particle size of void-forming agent and inorganic particles The particle size distribution of the particles is obtained by a particle size distribution meter (LA-950 manufactured by Horiba, Ltd.), and the particle size d50 is 50% from the smaller side on the volume distribution basis. Was the average particle size.

(3) Average particle diameter of particles in coating layer (d)
Using an S-4700 field emission scanning electron microscope manufactured by Hitachi, Ltd., 100 particles were arbitrarily measured at a magnification of 1000 times to obtain an average particle diameter. In addition, in the case of other than spherical shape, it was determined by (major axis + minor axis) / 2. Here, the minor axis is the maximum diameter orthogonal to the major axis.

(4) Coating layer thickness A cross section in the thickness direction of the film sample was observed and photographed at a magnification of 3000 times using a Hitachi scanning electron microscope Schottky emission electron beam system S-4300SE / N, and particles were present from the photograph. The thickness of the coating layer was measured at a place where the coating was not performed, and 10 points were arbitrarily measured to obtain an average value thereof.

(5) Projection frequency on the film surface (number of protrusions)
The projection profile on the film surface was measured with a three-dimensional roughness measuring device SE-3CKT (manufactured by Kosaka Laboratory Ltd.) with a cutoff of 0.25 mm, a measurement length of 1 mm, a scanning pitch of 2 μm, and a scanning number of 100. The projection profile was recorded at a height magnification of 1000 times and a scanning direction magnification of 200 times. Since the obtained projection profile and the profile are projection profiles with the horizontal axis representing the projection height and the vertical axis representing the number of projections, the number of projections with a height of 5 μm or more (pieces / m ² ) was obtained and used as the projection frequency. . For the analysis, a three-dimensional roughness analyzer SPA-11 (manufactured by Kosaka Laboratory Ltd.) was used.

(6) Adhesion spot evaluation (adhesion evaluation)
Take out the chassis from the LED LCD TV (LG42LE5310AKR) manufactured by LG, place it on a horizontal desk so that the inside of the TV is facing upward, and place a white reflective film of the same size as the chassis on it, with the coating layer facing upward Further, a light guide plate and three optical sheets originally provided in the television, and three such optical sheets were two diffusion films and one prism. Next, an equilateral triangle base (reference numeral 3 in FIG. 1) having three columnar legs having a diameter of 5 mm as shown in FIG. An additional 20 kg weight (symbol 4 in FIG. 1) is placed on top, and the region surrounded by the three legs is visually observed. If there is no abnormally bright part, “no adhesion spots”, that is, evaluation ○ It was. If there is an abnormally bright part, place the DBEF sheet originally provided on the television on the three optical sheets and observe it in the same manner. ”, Ie, evaluation ×, and when there is no abnormally bright portion,“ there is almost no adhesion spot ”, that is, evaluation Δ. In addition, the area surrounded by the three legs was a substantially equilateral triangle having a side length of 10 cm.

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

  Evaluation was made when the amount of the volatile organic solvent was 10 ppm or less.

(8) Evaluation of resistance to moisture and heat blocking (Evaluation for sticking to a light guide plate in a humid heat environment)
Condition 1: The front and back of the sample film are overlapped and pressurized to 0.6 kg / cm ² and left in a well-known high-temperature and high-humidity tank set at a temperature of 60 ° C. and a relative humidity of 90% RH for 8 hours. If the taken-out film was not adhered or only slightly adhered and could be easily peeled off, and the coating layer remained without melting, it was evaluated as “Good”. When the film was not attached or only slightly attached and could be easily peeled off, and a slight melting was observed in the coating layer, the evaluation was Δ. If the film was stuck and delamination occurred during peeling or the coating layer was greatly melted, it was evaluated as x.

Condition 2: The light guide plate is taken out from the backlight of the 32-inch Sony Bravia LED edge type television KDL-32EX700, cut to 5 cm × 10 cm, and overlapped so that the patterning surface of the light guide plate and the coating surface of the sample film are in contact with each other. Pressurize to 0.08 kg / cm ² and leave it in a high-temperature and high-humidity tank set at a temperature of 60 ° C. and a relative humidity of 90% RH for 12 hours. If the taken-out film and the light guide plate are not attached or only slightly attached, they can be easily peeled off, and the coating layer remains without melting. When the film and the light guide plate were not attached or only slightly attached, they could be easily peeled off, and when the coating layer was slightly melted, the evaluation was Δ. When the film and the light guide plate were adhered and delamination occurred during peeling or the coating layer was melted greatly, the evaluation was x.

  If both of the above conditions 1 and 2 are evaluated ○, the moisture and heat blocking resistance satisfies practical performance very well, and if either of the conditions 1 and 2 is evaluated x, the moisture and heat blocking resistance is practical. It can be evaluated that performance is not satisfied. If there is no evaluation x, it can be evaluated as practical in terms of moisture and heat blocking resistance.

(9) Recovery 1
20 g of sample film is weighed, cut into small pieces, put into a flask, and stirred and melted at 300 ° C. for 15 minutes in a vacuum state. Then, the flask is filled with nitrogen, and further stirred at 300 ° C. for 15 minutes in a nitrogen atmosphere. Melt. The molten polymer is taken out, sandwiched between metal plates and pressed to create a plate. The color of the resulting plate is visually observed. If the yellow color is low and recyclable, it is rated as “Good”. If it is yellow and difficult to recycle, it is rated as “Good”. If it was a serious level, it was set as evaluation x.

(10) Recovery 2
The film-forming stability when the recovered film described in the Examples was formed by a continuous film-forming method using a tenter was observed and evaluated according to the following criteria.
A: The film can be stably formed for 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.

[Examples 1-6, 10, 11, Comparative Examples 1-4]
(Copolymerized polyester)
132 parts by mass of dimethyl terephthalate and 18 parts by mass of dimethyl isophthalate, that is, the isophthalic acid component is 12 mol% with respect to the acid component of the polyester, 96 parts by mass of ethylene glycol, 3.0 parts by mass of diethylene glycol, 0.05 parts of manganese acetate A mass part and 0.012 parts by mass of lithium acetate were charged into a rectifying column and a flask equipped with a distillation condenser, and heated to 150 to 235 ° C. with stirring to distill methanol to conduct a transesterification reaction. 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. Subsequently, while stirring, the pressure in the reactor was gradually reduced to 0.5 mmHg and the temperature was raised to 290 ° C. to carry out a polycondensation reaction. The amount of the diethylene glycol component relative to the acid component of the obtained copolyester was 2.5% by mass, the amount of germanium element was 50 ppm, and the amount of lithium element was 5 ppm. The strand was extruded and cut to obtain pellets.

(Particle 1)
The pellets of the copolyester obtained above are dried and crystallized by heating at 170 ° C. for 3 hours in an oven, and then pulverized while cooling with liquid nitrogen using Matsubo Co., Ltd. atomizer mill TAP-1. To obtain polyester particles having an average particle diameter of 60 μm. Furthermore, particles 1 having an average particle diameter of 50 μm were obtained by air classification of the polyester particles.

(Film production)
A layer for forming a reflective layer (referred to as layer A) by preparing a masterbatch containing 48% by mass of barium sulfate having an average particle diameter of 1.0 μm as inorganic particles in the copolymerized polyester obtained above. Used as A polymer.

  Further, using the masterbatch containing 48% by mass of barium sulfate described above and the copolyester before adding barium sulfate, the support layer (layer B and layer B) was diluted to 5% by mass of barium sulfate. Used as the layer B polymer to form.

  Feed two extruders, each heated to 275 ° C., and layer A polymer, which has a barium sulfate concentration of 48% by weight, and layer B polymer, which has a barium sulfate concentration of 5% by weight, Three-layer feed block so that layer A and layer B have a layered structure of layer B / layer A / layer B, and the thickness ratio is layer B / layer A / layer B = 10/80/10 They were merged using an apparatus, and formed into a sheet form from a die while maintaining the laminated state. Further, the sheet is cooled and solidified with a cooling drum having a surface temperature of 25 ° C., and the obtained unstretched film is heated at 83 ° C. to be referred to as a film forming machine axial direction (hereinafter referred to as a longitudinal direction or a longitudinal direction or MD). ) Was stretched 2.8 times and cooled with a roll group at 25 ° C.

  Then, the coating liquid shown in Table 1 was apply | coated to the single side | surface of a film with the direct gravure coater so that the coating layer thickness after drying might become the thickness shown in Table 2. The coating liquid is an aqueous coating liquid having a solid content concentration of 30% by mass.

  Subsequently, the both ends of the film are guided to a tenter while being held by clips and are perpendicular to the longitudinal direction in an atmosphere heated to 115 ° C. (hereinafter sometimes referred to as a width direction or a transverse direction or TD). The film was stretched 3.7 times. Thereafter, heat setting was performed at 195 ° C. in a tenter and the mixture was cooled to room temperature to obtain a biaxially stretched film having a thickness of 250 μm. This biaxially stretched film contains fine voids. The evaluation results of the obtained film are shown in Table 2.

  Further, the films of these Examples and Comparative Examples are collected, pulverized, melt-extruded to form chips, and self-collected raw materials are prepared. The self-collected raw materials are formed in the reflective layer A and the mass of the reflective layer A as a reference. A biaxially stretched film having a thickness of 250 μm was produced in the same manner as described above, and the recoverability 2 was evaluated.

[Comparative Example 5]
The same operation as in Example 1 was performed except that the coating layer was not applied. The evaluation results are shown in Table 2.

[Examples 7 to 9]
A direct gravure coating apparatus on a biaxially stretched film obtained in the same manner as in Example 1 except that the coating liquid before uniaxial stretching is not applied and the coating layer is not applied. Then, the coating liquid shown in Table 1 was applied to one side of the film so that the coating layer thickness after drying would be the thickness shown in Table 2, and then dried in an oven at 100 ° C. to obtain a film. . Further, the recoverability 2 was evaluated in the same manner as in Example 1. The coating liquid is an aqueous coating liquid having a solid content concentration of 30% by mass.

[Components of coating layer]
Particle 1: Polyester particles described in the above examples.
SK-RP-25CL: non-porous particles having an average particle diameter of 25 μm, manufactured by Seishin Enterprise Co., Ltd., and made of polyethylene terephthalate. It is provided as a powder.
2003LS: Particles having an average particle diameter of 50 μm, manufactured by Arkema and made of nylon 12.
MBX-40: particles having an average particle size of 40 μm, manufactured by Sekisui Plastics Co., Ltd. and made of PMMA.
BM30X-55: Sekisui Plastics Kogyo Kogyo Co., Ltd., the material is PBMA, particles having an average particle size of 55 μm.
Z-563: a water-soluble polyester having a Tg of 64 ° C. manufactured by Kyoyo Chemical Co., Ltd. It is provided as a solid content concentration of 30% by weight.
Z-690: Water-soluble polyester having a Tg of 110 ° C., manufactured by Kyoyo Chemical Co. Such a water-soluble polyester contains a 2,6-naphthalenedicarboxylic acid component as an acid component, and the content thereof is in the range of 70 to 100 mol% with respect to 100 mol% of the acid component. It is provided as a solid content concentration of 25% by weight.
Z-687: Water-soluble polyester having a Tg of 110 ° C. manufactured by Kyoyo Chemical Co., Ltd. Such a water-soluble polyester contains a 2,6-naphthalenedicarboxylic acid component as an acid component, and the content thereof is in the range of 70 to 100 mol% with respect to 100 mol% of the acid component. It is provided as a solid content concentration of 25% by weight.
Surfactant: Emulgen 420 manufactured by Kao Corporation. This is an ether-based nonionic surfactant.
Z-592: a water-soluble polyester having a Tg of 40 ° C. manufactured by Kyoyo Chemical Co., Ltd. It is provided as a solid content concentration of 25% by weight.

  Even if the white reflective film of the present invention is a water-based coating layer obtained from a water-based coating solution, the coating layer does not melt in a humid heat environment, and can suppress sticking to the light guide plate even in a humid heat environment. it can. Therefore, for example, it can be suitably used as a reflective film for a surface light source including a light guide plate, particularly as a reflective film used in an edge light type backlight unit as used in a liquid crystal display device or the like. Moreover, since it is excellent also in the recovery film forming property and productivity, the industrial applicability is high.

Claims (6)

On the surface of the reflective film, a white reflective film having a coating layer formed from an aqueous coating liquid whose solid content contains a binder resin and particles as main components,
The surface of the coating layer has protrusions formed by the particles, and the protrusions have a number of protrusions having a height of 5 μm or more of 10 ⁴ pieces / m ² or more and 10 ¹⁰ pieces / m ² or less,
The binder resin contains a copolyester resin having a glass transition temperature Tg of 100 ° C. or more and 120 ° C. or less in an amount of 5% by mass to 50% by mass based on the mass of the binder resin, and the glass transition temperature Tg is 100. A white reflective film comprising a thermoplastic resin having a temperature of less than 0 ° C. in an amount of 50% by mass to 95% by mass based on the mass of the binder resin.   The white reflective film according to claim 1, wherein the content of the particles in the coating layer is 5% by mass or more and 50% by mass or less with respect to 100% by mass of the coating layer.   The white reflective film according to claim 1 or 2, wherein the copolymerized polyester resin contains a naphthalenedicarboxylic acid component as a constituent component thereof. The white reflective film of any one of Claims 1-3 with which the average particle diameter (d) of the said particle | grain in a coating layer and the thickness (t) of a coating layer satisfy | fill following formula (1).
1 ≦ d (μm) / t (μm) ≦ 100 (1)   The white reflective film of any one of Claims 1-4 whose amount of volatile organic solvents of a film is 10 ppm or less.   The white reflective film of any one of Claims 1-5 used as a reflecting plate for surface light sources provided with a light-guide plate.

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