JP2020073992A - White reflective film for large-sized display - Google Patents

Abstract

To provide a white reflective film which hardly causes heat deflection while having excellent reflection characteristics.SOLUTION: There is provided a white reflective film for a large-sized display which is formed of a thermoplastic resin composition containing calcium carbonate particles, where the calcium carbonate particles satisfy an average particle size of 0.1-1.2 μm, a 10% volume particle diameter D10, a 50% volume particle diameter D50 and a 90% volume particle diameter D90 integrated from a small particle size side satisfy relationship of (D90-D10)/D50≤1.6, and 10-70 mass% of a reflection layer A is contained with respect to the mass of the thermoplastic resin composition, and reflectivity of the film is 60% or more.SELECTED DRAWING: None

Description

  The present invention relates to a white reflective film for a large-sized display that can be suitably used as a reflector.

The surface light source has a reflection plate on the back surface, and the reflection plate reflects the light from the light source to the front surface to improve the light extraction efficiency and improve the brightness.
For example, in a backlight unit of a liquid crystal display device (LCD), a direct type having a light source and a reflective film on the back surface of a liquid crystal display panel and a light guide plate having a reflective plate on the back surface are arranged on the back surface of the liquid crystal display panel. There is an edge light type in which a light source is provided on the side surface of such a light guide plate. Conventionally, CCFLs were often used as the light source, but in recent years, light emitting diodes (LEDs) have been used to reduce power consumption and thickness, and edge light type LED backlights and direct type LED backlights are mainly used. is there. The edge light type backlight has an advantage that the LCD can be made thinner, while the direct type LED backlight is low in cost because it does not use a light guide plate.
Besides, the surface light source is also used for illumination to brighten indoors and outdoors.

As the reflector, for example, a void-containing film in which voids are formed inside by adding inorganic particles or an incompatible resin to a thermoplastic resin such as polyester and stretching the film is often used (Patent Document 1-5).
However, such a reflector may be deformed and bent due to heat or humidity from the light source or the external environment (hereinafter, such bending may be referred to as “thermal bending”). When the reflector plate is bent, it causes brightness unevenness of the surface light source, and, for example, brightness unevenness of the screen in an LCD.

  Therefore, in order to solve the problem of such heat deflection, Patent Document 6 proposes an idea of making the unevenness in brightness less likely to occur even when the metal surface is formed as a reflecting surface having a metal layer formed on an uneven surface. In addition, the deflection of the reflection plate can be prevented by forming a protrusion on the bottom member of the LCD to support the reflection plate (Patent Document 7) or by forming a slit in the reflection plate to absorb the bending (Patent Document 8). Consideration for improvement is being made. However, all of these processes are costly.

JP 2004-330727 A JP, 2011-11370, A JP, 2011-223369, A JP, 2013-88715, A JP, 2013-88716, A JP 2002-100227 A JP, 2013-229185, A JP, 2014-22060, A

The large-sized display has a recess because the back chassis is provided with a circuit board and the like. The present inventors have found that heat is likely to stay in such depressions, and the problem of heat deflection becomes more prominent due to such heat, and paid attention to this.
In view of the background art described above, it is an object of the present invention to provide a white reflective film that has excellent reflection characteristics and is resistant to thermal deflection even when used in a large display.

The present inventors have noticed that the presence of voids in the void-containing film makes heat deflection more likely to occur. However, simply reducing the voids is not preferable because it tends to reduce the reflection characteristics. Further, it has been noted that, even if the weight of the inorganic particles as the void-forming agent is heavy, thermal deflection easily occurs.
That is, the present invention adopts the following configurations in order to achieve the above object.

1. It is composed of a thermoplastic resin composition containing calcium carbonate particles, and the calcium carbonate particles have an average particle diameter of 0.1 to 1.2 μm, 10% volume particle diameter D10 and 50% volume particle particles integrated from the small particle diameter side. Diameter D50 and 90% volume particle diameter D90 satisfy (D90-D10) /D50≦1.6, and the reflective layer A has a content of 10 to 70 mass% with respect to the mass of the thermoplastic resin composition. However, a white reflective film for large-sized displays having a film reflectance of 60% or more.
2. 2. The white reflective film as described in 1 above, wherein the thermoplastic resin of the thermoplastic resin composition is copolymerized polyethylene terephthalate.
3. 3. The white reflective film as described in 2 above, wherein the copolymerization amount of the copolymerized polyethylene terephthalate is 1 to 20 mol% based on 100 mol% of all the acid components of the copolymerized polyethylene terephthalate.
4. The white reflective film as described in any one of 1 to 3 above, wherein the thickness ratio of the reflective layer A to the thickness of the white reflective film is 100% or more.
5. The white reflective film as described in any one of 1 to 4 above, further having a supporting layer B made of a thermoplastic resin or a thermoplastic resin composition.
6. A surface light source using the white reflective film according to any one of 1 to 5 above.

  On the other hand, Patent Document 1 uses barium sulfate having a small standard deviation of the particle size distribution. Since barium sulfate has a large specific gravity, heat deflection is likely to occur. Further, although Patent Documents 2 to 5 use calcium carbonate particles and disclose a ratio D90 / D10 of 90% volume particle diameter D90 and 10% volume particle diameter D10 thereof, in reality, it is narrow as in the present invention. The area of particle size distribution has not been examined. Furthermore, none of them has recognized the problem of heat deflection, and no studies have been made from such a viewpoint.

  According to the present invention, it is possible to provide a white reflective film which has excellent reflection characteristics and is resistant to thermal deflection even when used in a large-sized display.

The white reflective film of the present invention has a reflective layer A made of a thermoplastic resin containing calcium carbonate particles of a specific embodiment.
Hereinafter, each constituent component of the present invention will be described in detail.

[Reflective layer A]
The reflective layer A in the present invention is a layer made of a thermoplastic resin composition containing calcium carbonate particles, the calcium carbonate particles functioning as a void forming agent, containing voids in the layer, and exhibiting a white color. .. The reflective layer A has a reflective function due to such voids. The reflectance of the reflective layer A at a wavelength of 550 nm is preferably 80% or more, more preferably 90% or more, and particularly preferably 95% or more. This facilitates the reflectance of the white reflective film to fall within a preferred range.

The reflective layer A has voids in the layer as described above, and the ratio of the volume of such voids to the volume of the reflective layer A (void volume ratio) is 15% by volume or more and 70% by volume or less. Preferably. With such a range, the effect of improving the reflectance can be enhanced, and the above-described reflectance can be easily obtained. Further, the effect of improving the stretch film-forming property can be enhanced. If the void volume ratio is too low, it tends to be difficult to obtain a preferable reflectance. 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 stretch film-forming property tends to be low. From such a viewpoint, the void volume ratio in the reflective layer A is more preferably 65% by volume or less, and particularly preferably 60% by volume or less.
The void volume ratio can be achieved by adjusting the size and amount of calcium carbonate particles in the reflective layer A.

(Thermoplastic resin)
Examples of the thermoplastic resin forming the reflective layer A include thermoplastic resins made of polyester, polyolefin, polystyrene, and acrylic. Among them, polyester is preferable from the viewpoint of obtaining a white reflective film having excellent mechanical properties and thermal stability.
As the polyester, it is preferable to use a polyester composed of a dicarboxylic acid component and a diol component. 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. Although the polyester (polyethylene terephthalate) may be a homopolymer, it may be a copolymerized polyester (polyester (polyethylene terephthalate)) from the viewpoint that crystallization is suppressed when the film is uniaxially or biaxially stretched and the effect of improving the stretch film-forming property is enhanced. Copolymerized polyethylene terephthalate) is preferred. Examples of the copolymerization component include the above-mentioned dicarboxylic acid component and diol component, but isophthalic acid component and 2,6-naphthalenedicarboxylic acid component are preferable from the viewpoint of high heat resistance and high effect of improving stretch film-forming property. preferable. The content 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 10 mol% based on 100 mol% of all dicarboxylic acid components of the polyester. It is 11 mol%. When the proportion of the copolymerization component is within this range, the effect of improving the stretch film-forming property is excellent. Also, it has excellent thermal dimensional stability. Furthermore, the effect of suppressing heat deflection can be further improved.

The melting point of the thermoplastic resin is preferably 200 to 280 ° C. This makes it easier to suppress heat deflection. If it is too low, the effect of suppressing heat deflection tends to be low, and if it is too high, it tends to be difficult to handle. From this viewpoint, the temperature is more preferably 205 ° C. or higher, further preferably 210 ° C. or higher, more preferably 275 ° C. or lower, further preferably 265 ° C. or lower.
The thermoplastic resin forming the reflective layer A in the present invention may be a mixture of polyester, which is a preferable thermoplastic resin, and another thermoplastic resin different from the polyester.

(Calcium carbonate particles)
In the present invention, the reflective layer A contains calcium carbonate particles having a specific aspect as a void forming agent.
The calcium carbonate particles in the present invention have an average particle size of 0.1 to 1.2 μm and (D90-D10) / D50 of 1.6 or less. Here, D10, D50 and D90 are the 10% volume particle diameter, the 50% volume particle diameter and the 90% volume particle diameter, respectively, which are integrated from the small particle diameter side of the calcium carbonate particles. By adopting the calcium carbonate particles of such an aspect, it is possible to suppress heat deflection while having a high reflectance. That is, when there are coarse voids, heat deflection easily occurs, but by using calcium carbonate particles having a small average particle size and a sharp particle size distribution, a film having many relatively small voids (microvoids) inside In this mode, heat deflection due to coarse voids is suppressed. If the particle size distribution is broad, coarse particles will be present, and as a result, coarse voids are likely to be formed. At the same time, it is possible to suppress the reduction of the amount of the interface between the void and the thermoplastic resin and obtain a high reflectance. Furthermore, since the calcium carbonate particles have a relatively small specific gravity, the mass difference (density difference) between the particles and the thermoplastic resin is small, so that a local density difference is less likely to occur in the portions other than the voids. This also suppresses heat deflection.

  If the average particle size of the calcium carbonate particles is too large, coarse voids tend to be easily formed, and heat deflection cannot be suppressed. Therefore, the average particle diameter is preferably 1.1 μm or less, more preferably 1.0 μm or less, still more preferably 0.95 μm or less, and particularly preferably 0.9 μm or less. On the other hand, if they are too small, the particles agglomerate to form coarse voids, and it is very difficult to obtain such calcium carbonate particles. From this point of view, the average particle size is preferably 0.3 μm or more, more preferably 0.5 μm or more, and further preferably 0.6 μm or more.

Further, in another aspect, the average particle size of the calcium carbonate particles is difficult to suppress the heat deflection when too large, while it is easy to form a coarse void due to aggregation even if it is too small, it becomes difficult to suppress the heat deflection In some cases, there is a point of balance between suppression of heat deflection and improvement of reflectance, and a point of cost. From such a viewpoint, the average particle size of the calcium carbonate particles is preferably 1.2 μm or less, more preferably 1.18 μm or less, further preferably 1.15 μm or less, and preferably 0.6 μm or more, It is more preferably 0.8 μm or more, still more preferably 1.01 μm or more, particularly preferably 1.02 μm or more, and most preferably 1.05 μm or more.
From the above-mentioned viewpoint, the smaller (D90-D10) / D50 is preferably smaller, more preferably 1.5 or less, and further preferably 1.4 or less. The lower limit is theoretically 0.

  The reflective layer A is made of a thermoplastic resin composition containing calcium carbonate particles, and the content of calcium carbonate particles in the thermoplastic resin composition is 10 to 10 based on the mass of the thermoplastic resin composition. It is 70% by mass. This facilitates the preferable void volume ratio described above, and thus allows a high reflectance. Further, heat deflection is suppressed. Further, the effect of improving the stretch film-forming property can be enhanced. If the content is too small, the reflectance becomes low. On the other hand, if the content is too large, the number of voids becomes too large and the heat deflection cannot be suppressed. From these viewpoints, the content is preferably 15% by mass or more, more preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 50% by mass or less.

  In order to satisfy the above aspect, it is particularly preferable in the present invention to employ particles made of synthetic calcium carbonate (synthetic calcium carbonate particles) as the calcium carbonate particles. As the calcium carbonate particles, there are particles made of natural calcium carbonate (natural calcium carbonate particles) and synthetic calcium carbonate particles, and natural calcium carbonate particles are usually used. However, with natural calcium carbonate particles, it tends to be difficult to satisfy the above aspect, and it tends to be difficult to achieve the object of the present invention.

As a method of incorporating the calcium carbonate particles into the polyester resin, various conventionally known methods can be used. The following methods are mentioned as typical methods. (A) A method of adding the polyester resin at the stage of esterification during synthesis or after the completion of the transesterification reaction.
(A) A method of adding to the obtained polyester resin and melt-kneading.
(C) In the method of (a) or (a) above, a master pellet is prepared by adding a large amount of calcium carbonate particles to a polyester resin, and this is kneaded with a polyester resin as a diluting polymer to give a predetermined amount of carbon dioxide to the polyester resin. A method of incorporating calcium particles.
(D) A method of directly using the master pellet of (c) above.

(surface treatment)
The calcium carbonate particles in the present invention are preferably surface-treated with a surface-treating agent. This makes it possible to deactivate the Ca activity on the surface of the calcium carbonate particles and further suppress the generation of gas marks. Examples of such a surface treatment agent include phosphorus compounds such as phosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof, fatty acids such as stearic acid, and silane coupling agents. In the present invention, surface treatment with a phosphorus compound is particularly preferable, and specific examples of the phosphorus compound include phosphoric acid, phosphorous acid, trimethyl ester of phosphoric acid, tributyl ester of phosphoric acid, triphenyl ester of phosphoric acid and phosphoric acid. Preference is given to mono- or dimethyl ester, trimethyl phosphite, methylphosphonic acid, methylsulfonic acid diethyl ester, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester and the like. Of these, phosphoric acid, phosphorous acid and their ester-forming derivatives are preferred. In the present invention, the surface treatment with trimethyl phosphate is most preferable. These phosphorus compounds can be used alone or in combination of two or more kinds.

  The surface treatment method of the calcium carbonate particles is not particularly limited, and a conventionally known method can be adopted. For example, when the surface treatment is performed with a phosphorus compound, it is preferable to employ a method of physically mixing the phosphorus compound and the calcium carbonate particles (physical mixing method). The physical mixing method is not particularly limited, for example, using various pulverizers such as a roll rolling mill, a high-speed rotary pulverizer, a ball mill, and a jet mill, while pulverizing calcium carbonate with a phosphorus compound. Examples of the method include a method of surface treatment, or a method of performing surface treatment using a container rotary type mixer in which the container itself rotates, having a rotary blade in a fixed container, or a container fixed type mixer for blowing an air flow. it can. Specifically, a mixer such as Nauta mixer, ribbon mixer, Henschel mixer is preferable.

  The treatment conditions at that time are not particularly limited, and the treatment temperature is preferably 30 ° C. or higher, and more preferably 50 from the viewpoints of dispersibility of the calcium carbonate particles in the polyester, generation of foreign matters when the polyester stays at high temperature, and foaming. C. or higher, particularly 90.degree. C. or higher is preferable. The treatment time is preferably 5 hours or less, more preferably 3 hours or less, and particularly preferably 2 hours or less. Further, the phosphorus compound may be mixed at the same time as the calcium carbonate particles, or the phosphorus compound may be added after the calcium carbonate particles have been charged in advance. At that time, the phosphorus compound may be dropped or sprayed, and may be dissolved or dispersed in water, alcohol or the like.

  Further, in the present invention, a surface treatment agent for calcium carbonate particles may be added to and blended with polyester, and then calcium carbonate particles may be added thereto to perform surface treatment of calcium carbonate. For example, the surface treating agent can be added at any stage until the production of polyester, that is, the completion of the polymerization reaction, or at the stage after the completion of the polymerization reaction and before the melt-kneading.

  The amount of the surface treatment agent added in the surface treatment step may be such that the Ca activity on the surface of the calcium carbonate particles is sufficiently deactivated, but for example, the amount of phosphorus element is 0. The amount is 1 mass% or more. On the other hand, if too much is added, a large amount of the phosphorus compound remains in the film, which is not preferable from the viewpoint of the environment, and it is possible to prevent the calcium carbonate particles from aggregating in the extruder or the like. 5 mass% or less is preferable, 2 mass% or less is more preferable, 1 mass% or less is further preferable, and 0.5 mass% or less is particularly preferable.

(Other ingredients)
The reflective layer A (thermoplastic resin composition constituting the reflective layer A) may be any other component such as an ultraviolet absorber, an antioxidant, an antistatic agent, a fluorescent brightening agent, within a range that does not impair the object of the present invention. A wax can be included. Further, as long as the object of the present invention is not impaired, a void forming agent such as particles or resins (polyolefin etc.) different from the above-mentioned calcium carbonate particles can be contained.

[Supporting layer B]
The white reflective film of the present invention can further have a supporting layer B made of a thermoplastic resin or a thermoplastic resin composition (a thermoplastic resin to which particles or the like are added), in addition to the above-mentioned reflective layer A. The support layer B can improve the stretch film-forming property and can further suppress the heat deflection. Preferably, by providing a support layer B having less voids than the reflective layer A or having a composition with high heat resistance as much as possible on at least one surface of the reflective layer A, local deformation due to heat can be further suppressed, and thermal deflection Can be further suppressed.
Hereinafter, the support layer B in the present invention will be described in detail.

(Thermoplastic resin)
As the thermoplastic resin forming the support layer B in the present invention, the same thermoplastic resin as the above-mentioned thermoplastic resin forming the reflective layer A can be used. Among them, polyester is preferable from the viewpoint of obtaining a white reflective film having excellent mechanical properties and thermal stability.
As the polyester, the same polyester as the polyester in the reflective layer A 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 having excellent mechanical properties and thermal stability. The polyester (polyethylene terephthalate) may be a homopolymer, but it is a copolymerized polyester (copolymer) because the crystallization is suppressed when the film is stretched uniaxially or biaxially and the effect of improving the stretch film-forming property is enhanced. Polymerized polyethylene terephthalate) is preferred. Examples of the copolymerization component include the dicarboxylic acid component and the diol component described above in the section of the reflective layer A, but from the viewpoints of high heat resistance and a high effect of improving the stretch film-forming property, an isophthalic acid component, 2, A 6-naphthalenedicarboxylic acid component is preferred. The content ratio of the copolymerization component is, for example, 1 to 20 mol%, preferably 2 to 18 mol%, more preferably 3 to 17 mol%, particularly preferably 12 to 12 mol% based on 100 mol% of all dicarboxylic acid components of the polyester. It is 16 mol%. When the proportion of the copolymerization component is within this range, the effect of improving the stretch film-forming property is excellent. Also, it has excellent thermal dimensional stability. Furthermore, the effect of suppressing heat deflection can be further improved.

The melting point of the thermoplastic resin is preferably 190 to 280 ° C. This makes it easier to suppress heat deflection. If it is too low, the effect of suppressing heat deflection tends to be low, and if it is too high, it tends to be difficult to handle. From this viewpoint, the temperature is more preferably 195 ° C. or higher, further preferably 200 ° C. or higher, more preferably 275 ° C. or lower, still more preferably 270 ° C. or lower.
The thermoplastic resin constituting the support layer B in the present invention may be a mixture of polyester, which is a preferred thermoplastic resin, and another thermoplastic resin different from the polyester.

(Other ingredients)
The support layer B may be composed of a thermoplastic resin composition containing the above-mentioned thermoplastic resin and optional components within a range not impairing the object of the present invention. Examples of such optional components include ultraviolet absorbers, antioxidants, antistatic agents, optical brighteners and waxes.

  In addition, the support layer B may contain the void-forming agent mentioned in the reflective layer A as an optional component as long as the object of the present invention is not impaired, and such a mode improves the reflectance. Can be higher. On the other hand, if the content of the void-forming agent in the support layer B is reduced or the void-forming agent is not contained, the effect of improving the stretch film-forming property can be enhanced. From these viewpoints, the void volume ratio in the support layer B (ratio of the volume of voids in the support layer B to the volume of the support layer B) is preferably 0% by volume or more and less than 15% by volume, and more preferably 5%. It is preferably not more than 3% by volume, particularly preferably not more than 3% by volume. In particular, in the present invention, since the reflection characteristic and the effect of improving the stretch film-forming property can be enhanced at the same time, the preferable void volume ratio in the reflective layer A and the preferable void volume ratio in the support layer B are simultaneously adopted. Is particularly preferable.

[Layer structure]
In the present invention, the thickness of the white reflective film (the thickness of the reflective layer A when the reflective layer A is the only layer) is preferably 155 to 350 μm. Thereby, the effect of improving the reflectance can be enhanced. Further, the effect of improving the heat deflection can be enhanced. If it is too thin, the effect of improving the reflectance is low, and the effect of suppressing the heat deflection is low, while if it is too thick, it is inefficient. From this point of view, it is more preferably 160 μm or more, still more preferably 170 μm or more, particularly preferably 180 μm or more, more preferably 340 μm or less, still more preferably 330 μm or less, and particularly preferably 320 μm or less.

  The reflective layer A preferably has a thickness ratio (ratio of total thickness in the case of having a plurality) of the white reflective film as 100%, preferably 50% or more, more preferably 50 to 95%. It is more preferably 60 to 90%, and particularly preferably 70 to 90%. When the support layer B is provided, the thickness ratio (the ratio of the total thickness when a plurality of support layers are provided) is preferably 5 to 50%, more preferably 10 to 40%, and further preferably 10 to 30%. This makes it possible to improve the balance of each characteristic such as the reflection characteristic and the stretch film-forming property. Further, it is possible to enhance the effect of improving the heat deflection suppression while improving the balance between them.

  The thickness of the support layer B in the present invention (the total thickness when a plurality of films are contained in the film) is preferably 2 to 80 μm. Thereby, the effect of improving the stretch film-forming property can be enhanced, and the effect of suppressing heat deflection can be enhanced. Further, heat shrinkage can be reduced. If the support layer B is too thin, the effect of improving the stretch film-forming property tends to be low. Further, the effect of suppressing heat deflection tends to be low. On the other hand, if it is too thick, the above effect does not change so much and it is inefficient. From these viewpoints, the thickness (total thickness) of the support layer B is more preferably 5 μm or more, further preferably 10 μm or more, more preferably 70 μm or less, and further preferably 65 μm or less.

  Further, when the support layer B is provided on the reflection surface side of the reflection layer A, the thickness of the support layer B affects the reflectance. That is, when the thickness of the support layer B on the reflective surface side of the reflective layer A is too thick, the effect of improving the reflectance tends to be low. On the other hand, if it is too thin, the effect of suppressing the loss of calcium carbonate particles in the reflective layer A and the effect of suppressing damage to the device and other members by the calcium carbonate in the reflective layer A tend to be low. From these viewpoints, the thickness of the support layer B (thickness of one layer) is preferably 1 to 40 μm, more preferably 2.5 μm or more, still more preferably 5 μm or more, and further preferably 35 μm or less, It is preferably 32.5 μm or less.

  When the reflective layer A is represented by A and the supporting layer B is represented by B, the laminated structure of the white reflective film has a two-layer structure of B / A, a three-layer structure of A / B / A and B / A / B, and B. / A / B / A and B / A / B '/ A having a four-layer structure (wherein B'represents a supporting layer B'having the same structure as the supporting layer B), and similarly A and B There may be mentioned a multi-layered structure having 5 or more layers. Particularly preferred is a two-layer structure of B / A, and a three-layer structure of A / B / A and B / A / B. Most preferably, it has a three-layer structure of B / A / B, and is excellent in stretch film-forming property. Further, if the thicknesses of the support layers B on the front and back sides are close, problems such as curling are unlikely to occur.

  In the present invention, in addition to the reflective layer A and the support layer B, other layers may be included as long as the object of the present invention is not impaired. For example, it may have a layer (preferably a coating layer) for imparting functions such as antistatic property, conductivity and ultraviolet durability. In addition, a bead layer containing beads for imparting diffusivity to the reflected light or securing a gap with the light guide plate may be provided on at least one outermost surface on the reflecting surface side.

[Film manufacturing method]
Hereinafter, an example of the method for producing the white reflective film of the present invention will be described.
In producing the white reflective film of the present invention, the reflective layer A is preferably formed by a melt extrusion method. Further, when the white reflective film has a laminated structure of the reflective layer A and the supporting layer B, it is preferable that the reflective layer A and the supporting layer B are laminated by a coextrusion method to be manufactured. This can enhance the effect of improving the stretch film-forming property. The reflective layer A and the support layer B are preferably laminated directly by a coextrusion method. By laminating by the co-extrusion method in this way, the interfacial adhesion between the reflective layer A and the support layer B can be enhanced, and the support layer B can be formed again by laminating the films or forming the film. Since it is not necessary to go through the process for cutting, it can be mass-produced easily at low cost.

  Hereinafter, a production method in which polyester is adopted as a thermoplastic resin constituting the reflective layer A and a thermoplastic resin constituting the support layer B and a coextrusion method is adopted as a laminating method will be described. The present invention is not limited to the above, and other embodiments can be similarly manufactured with reference to the following. In that case, when the extrusion step is not included, the following “melt extrusion temperature” may be read as “melt temperature”, for example. The melting point of the polyester used is Tm (unit: ° C) and the glass transition temperature is Tg (unit: ° C).

First, as a thermoplastic resin composition (polyester composition) for forming the reflective layer A, a mixture of polyester, calcium carbonate particles, and other optional components is prepared. Moreover, as the thermoplastic resin composition (polyester composition) for forming the support layer B, a mixture of polyester and other optional components is prepared. Here, for the support layer B, a thermoplastic resin (polyester) may be used without adding other optional components. These polyester compositions are used after drying to sufficiently remove water.
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 producing the film, particularly the polyester composition used for the reflective layer A, is filtered using a non-woven fabric type filter made of stainless steel fine wire having a wire diameter of 15 μm or less and having an average opening of 10 to 100 μm. Preferably. By carrying out this filtration, it is possible to suppress the aggregation of particles that are usually agglomerated and tend to become coarse agglomerated particles, and to obtain a film with few coarse foreign matters. Then, by suppressing the agglomerated particles, it becomes easier to form microvoids, and the heat deflection is further suppressed. The average mesh size of the nonwoven fabric is preferably 20 to 50 μm, more preferably 15 to 40 μm. 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 by 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 machine direction of the film-forming machine (hereinafter, sometimes referred to as the machine direction or the machine direction or MD) to obtain a machine-stretched film. .. This stretching is preferably performed by utilizing the peripheral speed difference between two or more rolls. The film after the longitudinal stretching is subsequently guided to a tenter, 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), and biaxially stretched. The film.

  The stretching temperature is preferably Tg of the polyester (preferably the polyester forming the reflective layer A) or more and Tg + 30 ° C. or less, which is excellent in stretch film-forming property and voids are easily formed. The stretching ratio is preferably 2.5 to 4.3 times, and more preferably 2.7 to 4.2 times in both the machine direction and the transverse direction. If the stretching ratio is too low, unevenness in the thickness of the film tends to deteriorate, and voids tend to be difficult to form. 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, transverse stretching) is made higher than the stretching temperature of the first stage by about 10 to 50 ° C. Things are preferred. This is because the Tg as a uniaxial film is increased due to the orientation in the first stretching.

It is also preferable to preheat the film before each stretching. For example, the pre-heat treatment for transverse stretching may be started at a temperature higher than Tg + 5 ° C. of polyester (preferably the polyester forming the reflective layer A) and gradually raised. The temperature rise in the transverse stretching process may be continuous or stepwise (sequential), but is usually done 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 of a predetermined temperature in each zone.
The biaxially stretched film is subsequently subjected to heat-setting and heat-relaxation treatments in order to obtain a biaxially oriented film, but 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 melting point of Tm (Tm−10 ° C.) to (Tm−100 ° C.) of polyester (preferably the polyester forming the reflective layer A) while holding both ends with clips, and a constant width or It is preferable to perform heat treatment for 0.01 to 100 seconds under a width reduction of 10% or less and heat-set to reduce the heat shrinkage rate. If 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 heat shrinkage tends to increase. Further, this can further improve the effect of suppressing heat deflection.

  Further, in order to adjust the heat shrinkage amount, both ends of the gripped film can be cut off, the take-up speed in the longitudinal direction of the film can be adjusted, and the film can be relaxed in the longitudinal direction. As a means for loosening, the speed of the roll group on the tenter exit side is adjusted. As a rate of relaxation, the speed of the roll group is decreased with respect to the film line speed of the tenter, preferably 0.1 to 2.5%, more preferably 0.2 to 2.3%, and particularly preferably 0.3. The film is relaxed by reducing the speed by ˜2.0% (this value is referred to as “relaxation rate”), and the thermal shrinkage in the machine direction is adjusted by controlling the relaxation rate. Further, this can further improve the effect of suppressing heat deflection. In the transverse direction of the film, the width can be reduced in the process of cutting off both ends to obtain a desired heat shrinkage rate.

In the biaxial stretching, besides the longitudinal-transverse sequential biaxial stretching method as described above, a lateral-longitudinal sequential biaxial stretching method may be used. Further, it is possible to form a film by using the 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 machine direction and the transverse direction.
Thus, the white reflective film of the present invention can be obtained.

[Characteristics of white reflective film]
(Reflectance, front brightness)
The reflectance of the white reflective film of the present invention is 60% or more. It is preferably 70% or more, more preferably 80% or more, further preferably 90% or more, particularly preferably 95% or more, and most preferably 97% or more. When the reflectance is within the above range, high brightness can be obtained when used in a liquid crystal display device, lighting, or the like. Such a reflectance is set in a preferable mode such as increasing the void volume ratio of the reflective layer A, the thickness of the reflective layer A is increased, a void forming agent is contained in the support layer B, or the reflective surface is more reflective than the reflective layer A. This can be achieved by reducing the thickness of the support layer B on the side or by making the aspect of each layer a preferable aspect.

Further, the front luminance is determined by a measuring method described below is preferably 2000 cd / ^{m 2} or more, more preferably 3000 cd / ^{m 2} or more, more preferably 4000 cd / ^{m 2} or more, 4400cd / ^{m 2} or more is particularly preferable.
Here, the reflectance and the front luminance are values for the surface used as the reflecting surface of the white reflective film.

(Heat deflection)
An object of the present invention is to suppress heat deflection. Heat deflection refers to a product generated by a backlight unit (light source), an electric circuit for driving a display device such as a liquid crystal display in a product such as a television or a monitor, or heat or humidity from a use environment. This is a phenomenon in which the white reflective film included in the item is bent (distorted). When the white reflective film is thermally bent, it causes unevenness in brightness, which directly leads to deterioration in image quality.

[Use]
The white reflective film of the present invention is for a large display. Here, the large display refers to a liquid crystal display having a size of 30 inches or more, preferably 32 inches or more, more preferably 40 inches or more, and further preferably 42 inches or more. In such a large-sized display, a recess (partition) for incorporating an electric circuit or the like is provided in the back chassis. Therefore, the heat generated due to the above-mentioned causes and the like locally accumulates in the depression, and the heat deflection is more likely to occur. The larger the size of the display, the larger the number of light sources required to secure the brightness, and the more complicated the circuit and the like, the larger the amount of accumulated heat, and the more the heat deflection tends to occur. Therefore, it has been difficult to suppress thermal deflection in such a large-sized display by the conventional technique. On the other hand, the present invention can favorably suppress heat deflection even in such a large display.

Hereinafter, the present invention will be described in detail with reference to examples. Each characteristic value was measured by the following method.
(1) Light reflectance A spectrophotometer (UV-3101PC manufactured by Shimadzu Corporation) was equipped with an integrating sphere, and the reflectance was measured at a wavelength of 550 nm when the BaSO ⁴ white plate was 100%, and this value was used as the reflectance. In addition, the measurement was performed on the surface which is the side (light source side) used as the reflecting surface.

(2) Average particle size of particles Measured using a laser scattering particle size distribution analyzer SALD-7000 manufactured by Shimadzu Corporation. The dispersion in ethylene glycol before measurement is performed by measuring the particle powder so as to correspond to a slurry concentration of 5% by mass, stirring with a mixer (for example, National MXV253 type cooking mixer) for 10 minutes, cooling to room temperature, and then using a flow cell method. It was supplied to the supply device. Then, ultrasonic treatment was performed for 30 seconds in the supply device for defoaming (the strength of the ultrasonic treatment was 60% from the position showing the MAX value with the knob of the ultrasonic treatment device), and then subjected to the measurement. .. The 50% volume particle size (D50) was determined from the particle size distribution measurement results, and this was used as the average particle size. In addition, 10% volume particle diameter (D10) and 90% volume particle diameter (D90) were similarly obtained.

(3) Content of particles The film was incinerated at a temperature of 500 ° C. for 6 hours, the weight before and after that was measured, and the weight of the residual ash was taken as the content of the particles. The particle content of each layer in the laminate was determined by performing the above operation after separating each layer.

(4) Film thickness and layer structure The white reflective film was sliced with a microtome to obtain a cross section, and the cross section was observed with a Hitachi S-4700 type field emission scanning electron microscope at a magnification of 500 times. The thickness of the entire film, the thickness of the reflective layer A, and the thickness of the support layer B were determined. The thickness was measured as an average value by measuring an arbitrary position with n = 7. The thickness (μm) of each layer was determined, and then the thickness ratio of each layer was calculated.

(5) Calculation of void volume ratio The calculated density was obtained from the density and blending ratio of the polymer of the layer for which the void volume ratio is obtained, the added particles, and other components. At the same time, the layer was isolated by peeling it off, the mass and volume were measured, the actual density was calculated from these, and the calculated density and the actual density were calculated by the following formula.
Void volume ratio = 100 × (1- (actual density / calculated density))
The density of isophthalic acid-copolymerized polyethylene terephthalate (after biaxial stretching) was 1.39 g / cm ³ , the density of calcium carbonate particles was 2.7 g / cm ³ , and the density of barium sulfate particles was 4.5 g / cm ³ . did.
Further, only the layer for measuring the void volume ratio was isolated, and the mass per unit volume was obtained to obtain the actual density. The volume was calculated as area × thickness by cutting the sample into an area of 3 cm ² and measuring the thickness at that size with an electric micrometer (K-402B manufactured by Anritsu) at 10 points, and taking the average value as the area. The mass was measured with an electronic balance.
As the specific gravity of other particles (including aggregated particles), the value of bulk specific gravity obtained by the following graduated cylinder method was used. A graduated cylinder having a volume of 1000 ml was filled with absolutely dry particles, the total weight was measured, the weight of the graduated cylinder was subtracted from the total weight to obtain the weight of the particles, and the volume of the graduated cylinder was measured. , The particle weight (g) divided by the volume (cm ³ ).

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

(7) Front Brightness The reflective film was taken out from the edge light type LED liquid crystal television (LG42LE5310AKR) (42 inches) manufactured by LG, and the various reflective films obtained in the examples were replaced with the reflective surface side being the screen side. The diffusing film and the prism sheet, which were originally installed, were arranged, and the luminance was measured using a luminance meter (Model MC-940 manufactured by Otsuka Electronics) in the state of the backlight unit.

(8) Stretching film-forming property The film-forming stability when the film described in the example was formed by a continuous film-forming method using a tenter was observed and evaluated according to the following criteria.
A: A stable film can be formed for 8 hours or more.
◯: A stable film can be formed for 3 hours or more and less than 8 hours.
Δ: Cutting occurred once in less than 3 hours.
X: Multiple breaks occur in less than 3 hours, and stable film formation cannot be performed.

(9) Heat Deflection Evaluation An edge light type LED liquid crystal television (LG42LE5310AKR) (42 inches) manufactured by LG is disassembled, a reflection film originally provided therein is taken out, and the white reflection film of the example is arranged instead, and the television is set. Was assembled, and in that state, the television was stored in an environment of 50 ° C. × 80% for 72 hours with the white display turned on, and the luminance unevenness before and after that was evaluated.
[Evaluation of brightness spots 1]
Brightness unevenness was visually judged and evaluated according to the following criteria: ○: No brightness unevenness was observed at all △: Brightness unevenness was barely recognized ×: Significant brightness unevenness was observed [Brightness Spot evaluation 2]
The luminance was measured at an average of 10 arbitrary points in the screen with a luminance meter (CA-2000 manufactured by Konica Minolta), and the value of (highest luminance-lowest luminance) / average luminance in the screen was evaluated. When the above-mentioned value is 5% or less, it is possible to determine that there is little unevenness in brightness due to heat deflection and the state is good. It is preferably 4% or less, more preferably 3% or less.

<Production Example 1: Synthesis of isophthalic acid-copolymerized polyethylene terephthalate 1>
Dimethyl terephthalate 136.5 parts by mass, dimethyl isophthalate 13.5 parts by mass (9 mol% based on 100 mol% of all acid components of the obtained polyester), ethylene glycol 98 parts by mass, diethylene glycol 1.0 part by mass. , 0.05 parts by mass of manganese acetate and 0.012 parts by mass of lithium acetate were charged into a flask equipped with a rectification column and a distillation condenser, and heated to 150 to 240 ° C. with stirring to distill methanol to carry out a transesterification reaction. went. After methanol was distilled off, 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. Then, while stirring, the pressure inside 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>
Dimethyl terephthalate 129.0 parts by mass, dimethyl isophthalate 21.0 parts by mass (14 mol% based on 100 mol% of the total acid component of the polyester obtained) except that 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 a part of the isophthalic acid copolymerized polyethylene terephthalate 1 obtained above and synthetic calcium carbonate particles having an average particle size of 0.9 μm and (D90-D10) / D50 of 1.4 as a void forming agent, Kobe Steel With a NEX-T60 tandem extruder manufactured by K.K., they are mixed so that the content of the synthetic calcium carbonate particles becomes 60 mass% with respect to the mass of the obtained master chip, and the mixture is extruded at a resin temperature of 260 ° C to synthesize the synthetic calcium carbonate. Particle-containing particle master chip 1 was prepared. The synthetic calcium carbonate particles are surface-treated with trimethyl phosphate.

<Production Example 4: Preparation of particle master chip 2>
A particle master chip 2 containing synthetic calcium carbonate particles was prepared in the same manner as in Production Example 3 except that the isophthalic acid copolymerized polyethylene terephthalate 2 obtained above was used in place of the isophthalic acid copolymerized polyethylene terephthalate 1.

<Production Example 5: Preparation of particles 1 used for bead layer>
150 parts by mass of dimethyl terephthalate, 98 parts by mass of ethylene glycol, 1.0 part by mass of diethylene glycol, 0.05 part by mass of manganese acetate, and 0.012 parts by mass of lithium acetate were charged into a flask equipped with a rectification column and a distillation condenser. The mixture was heated to 150 to 240 ° C. with stirring to distill off methanol to carry out a transesterification reaction. After methanol was distilled off, 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. Then, while stirring, the pressure inside 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 polyethylene terephthalate 3. The obtained polyethylene terephthalate 3 was extruded from a strand die, cooled and cut into pellets. As a result of adjusting the shape of the strands, the shape of this pellet was a substantially rectangular parallelepiped shape, and the average shape was 4 mm × 3 mm × 2 mm. Then, the obtained pellets are dried and crystallized by heating in an oven at 170 ° C. for 3 hours, and crushed while being cooled with liquid nitrogen using an atomizer mill TAP-1 manufactured by Matsubo Co., Ltd. Polyester particles having a particle diameter of 60 μm were obtained. Further, the polyester particles were subjected to air classification to obtain particles 1 (non-spherical particles) having an average particle diameter of 43 μm.

[Example 1]
(Production of white reflective film)
The isophthalic acid copolymerized polyethylene terephthalate 1 and the particle master chip 1 obtained above were used as the raw materials for the reflective layer (A layer), and the isophthalic acid copolymerized polyethylene terephthalate 2 and the particle master chip 2 were used as the raw materials for the support layer (B layer), respectively. Each layer was mixed so as to have the constitution described in Table 1 and put into an extruder. A layer was melt-extruded at a temperature of 255 ° C. through a nonwoven fabric type filter having an average opening of 30 μm, and B layer was an average grain. Melt and extrude through a non-woven fabric type filter having an opening of 30 μm at a temperature of 230 ° C. using a three-layer feed block device so as to have a layer structure of B layer / A layer / B layer as shown in Table 1, and the laminated state While holding the above, it was formed into a sheet from a die. At this time, the discharge ratio of each extruder was adjusted so that the thickness ratio of B layer / A layer / B layer was 10/80/10 after biaxial stretching. Furthermore, this sheet was cooled and solidified by a cooling drum having a surface temperature of 25 ° C. to obtain an unstretched film. This unstretched film is led through a preheating zone of 73 ° C and then a preheating zone of 75 ° C to a longitudinal stretching zone kept at 92 ° C, stretched 3.0 times in the longitudinal direction, and cooled by a roll group of 25 ° C. did. Subsequently, while holding both ends of the film with clips, the film was led through a preheating zone of 115 ° C. to a transverse stretching zone kept at 130 ° C. and stretched in the transverse direction by 3.6 times. Then, heat treatment at 155 ° C for 10 seconds, heat setting at 200 ° C for 10 seconds, heat treatment at 155 ° C for 10 seconds were continuously performed in a tenter, and then a width-setting ratio of 2% and a width-setting temperature of 130 ° C were applied to the transverse direction. A width was performed, then both ends of the film were cut off, heat-relaxed at a longitudinal relaxation rate of 2.5%, and cooled to room temperature to obtain a film having a thickness of 300 μm. The evaluation results of the obtained film are shown in Table 1.

[Examples 2 to 9 and 11, Comparative Examples 1 to 6]
A white reflective film was obtained in the same manner as in Example 1 except that the aspect of particles and the film configuration were as shown in Table 1. The evaluation results of the obtained film are shown in Table 1. The synthetic calcium carbonate particles used are surface-treated with trimethyl phosphate.
In Example 11, the film layer thickness was 188 μm.

[Comparative Example 7]
A particle master chip was prepared in the same manner as in Production Examples 3 and 4 except that barium sulfate particles having an average particle size of 0.9 μm and a (D90-D10) / D50 of 1.4 were used as the void forming agent, and the film configuration. A white reflective film was obtained in the same manner as in Example 1 except that as shown in Table 1. The evaluation results of the obtained film are shown in Table 1. The barium sulfate was obtained by repeating air classification.

[Example 10]
On one surface of a biaxially stretched film obtained in the same manner as in Example 1, a direct gravure coating apparatus was used to apply a coating solution having the composition shown in Coating Solution 1 for forming the following bead layer to a wet thickness. After coating with a coating amount of 15 g / m ² , it was dried at 100 ° C. in an oven to obtain a white reflective film having a bead layer. The evaluation results of the obtained film are shown in Table 1. In the evaluation, the bead layer side was used as a reflecting surface.

<Coating liquid 1, solid content concentration 30 mass%>
Particles: Particle 1 obtained in Production Example 5 (non-spherical particles) ... 7.5% by mass
-Acrylic resin (thermoplastic resin): Acrydic A-817BA manufactured by DIC (solid content concentration 50 mass%) ... 30 mass%
-Crosslinking agent: Nippon Polyurethane Industry Co., Ltd., Coronate HL (isocyanate-based crosslinking agent, solid content concentration 75% by mass) ... 10% by mass
Diluting solvent: butyl acetate ... 52.5% by mass
The solid content ratio of each component in the coating liquid 1 is as follows.
・ Particles: 25% by mass
-Acrylic resin (thermoplastic resin): 50% by mass
・ Crosslinking agent: 25% by mass

  The white reflective film of the present invention, while having excellent reflection characteristics, suppresses heat deflection generated by heat generated from an electric circuit or a light source or heat or humidity from a use environment even when used for a large-sized display. be able to. As a result, it is possible to suppress the luminance unevenness caused by the bending of the white reflective film, and therefore the industrial applicability is high.

Claims (6)

A method for producing a white reflective film for a large-sized liquid crystal display, comprising a reflective layer A and a support layer B, comprising:
(1) a step of laminating a polyester composition for a reflective layer A containing polyester and calcium carbonate particles and a polyester composition for a support layer B containing polyester by a coextrusion method to obtain an unstretched laminated film,
Here, the calcium carbonate particles have an average particle diameter of 0.1 to 1.2 μm, and 10% volume particle diameter D10, 50% volume particle diameter D50 and 90% volume particle diameter D90, which are integrated from the small particle diameter side. Satisfies (D90-D10) /D50≦1.6,
The content of the calcium carbonate particles is 10 to 70 mass% with respect to the mass of the polyester composition for the reflective layer A,
In the coextrusion method, the polyester composition for the reflective layer A is melt extruded through a non-woven fabric type filter having an average opening of 10 to 100 μm.
(2) biaxially stretching the unstretched laminated film to obtain a white reflective film,
A manufacturing method including.   The manufacturing method according to claim 1, wherein the polyester of the polyester composition for the reflective layer A is copolymerized polyethylene terephthalate.   The production method according to claim 2, wherein the copolymerization amount of the copolymerized polyethylene terephthalate is 1 to 20 mol% based on 100 mol% of all the acid components of the copolymerized polyethylene terephthalate.   The manufacturing method according to any one of claims 1 to 3, wherein the thickness ratio of the reflective layer A to the 100% thickness of the white reflective film is 50% or more.   The laminated structure in the white reflective film is B / A, A / B / A, or B / A / B / A, where A is the reflective layer and B is the supporting layer. 4. The manufacturing method according to any one of 4 above. A method for manufacturing a surface light source for a large liquid crystal display,
A step of obtaining a white reflective film for a large-sized liquid crystal display by the manufacturing method according to claim 1, and a step of combining a light source with the white reflective film,
And a manufacturing method.