JP2011069990A - Reflection sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection sheet that further facilitates sharpness and visualization of a liquid crystal screen by improving luminance of a backlight for liquid crystal. <P>SOLUTION: The reflection sheet includes: a surface layer which contains at least a polypropylene resin (D); and an inner layer which contains a polypropylene resin (A), at least one resin (B) incompatible with the polypropylene resin (A), and a thermoplastic elastomer (C) as a compatibilizer and which has a pore inside. The reflection sheet is composed of at least two layers, the surface layer and the inner layer, and also contains 0.3-20 wt.% of the thermoplastic elastomer (C) based on 100 pts.wt. of the inner layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a reflective sheet of a resin composition having holes therein, and particularly to a reflective sheet suitable for a reflective material used for a backlight of a liquid crystal display device.

  The reflection sheet is used as a reflection plate for obtaining a uniform surface light source by reflecting the light of a point or line light source such as an LED or a cold cathode tube in a surface shape in a liquid crystal display device. In particular, it is used as a reflector for a direct type backlight of a large liquid crystal display device such as a liquid crystal television.

  A reflection sheet used for such a surface light source for a liquid crystal screen is required to have a high light reflection performance as well as a thin film. Conventionally, as the reflection sheet, a sheet including a fine cavity inside, or a sheet provided with a metal reflection layer such as silver on the surface of the sheet is used. In particular, a film containing fine bubbles inside is widely used because it has a certain effect in improving brightness and uniforming screen brightness.

  In a large liquid crystal display device such as a large liquid crystal television, a plurality of cold cathode tubes, which are linear light sources, are arranged in parallel and used in order to brighten the display screen. In this case, since a striped lamp image derived from a cold cathode tube is likely to be generated, the reflection image is also reduced by using a reflection sheet that diffuses and reflects light.

  As a reflection sheet that diffuses and reflects light, a sheet including a fine cavity inside is generally used. For example, a sheet obtained by adding an inorganic powder to a polyester resin or a polypropylene resin is stretched to start the inorganic powder. A reflective sheet in which fine cavities are formed (for example, see Patent Document 1), a reflective sheet in which a sheet made of polyester resin is impregnated with nitrogen gas or carbon dioxide gas and foamed (for example, see Patent Document 2), etc. There is.

  However, when the above-described conventional reflection sheet is used as the reflection sheet that is a surface light source reflection member, the light reflection property is inferior, so that part of the light from the light source is transmitted to the opposite surface. As a result, there is a problem that the brightness of the liquid crystal screen is insufficient, and there is a problem that it does not contribute to a reduction in power consumption. Therefore, a further high reflectivity of the reflection sheet is required.

  Here, in a film in which bubbles are contained in the film, light incident on the film is reflected at the interface between the resin layer (solid phase) and the bubble layer (gas phase) inside the film. Therefore, in order to further improve the light reflection performance and reduce the thickness while maintaining high light reflection performance, the pore nucleating agent is more finely dispersed and the stacking density of bubbles in the film thickness direction, that is, the gas thickness direction Although it is necessary to increase the solid interface number density, the fine dispersion of the above-mentioned pore nucleating agent has recently reached a peak. Even if fine dispersion is achieved and the generation of bubbles is successful, the bubbles are connected to each other in the stretching step, and the problem is that the number of gas-solid interfaces does not contribute to an efficient increase.

  In addition, inorganic particles such as barium sulfate and calcium carbonate may be used as the pore nucleating agent, but the specific gravity of the reflective sheet cannot be reduced. As the particle size is reduced, aggregation is more likely to occur and does not contribute to an efficient increase in the number of gas-solid interfaces. When the surface of the particles is treated with various treatment agents to suppress aggregation, the surface treatment agent is not completely colorless and transparent, so that light absorption caused by the surface treatment agent occurs, and as a result, the light reflection performance of the reflection sheet decreases. It is a problem to do.

Japanese Patent Publication No. 6-89160 Japanese Patent No. 2925745

  This invention is made | formed in view of this point, and it aims at providing the reflective sheet which can improve the brightness | luminance of the backlight for liquid crystals and can make a liquid crystal screen clearer and easy to see.

  The reflective sheet of the present invention comprises a surface layer portion containing at least a polypropylene resin (D), a polypropylene resin (A), at least one resin (B) that is incompatible with the polypropylene resin (A), and a compatibilizing agent. An inner layer part containing a thermoplastic elastomer (C) as an agent and having pores therein, and at least two layers of the surface layer part and the inner layer part, and with respect to 100 parts by weight of the inner layer part It contains 0.3 to 20% by weight of the thermoplastic elastomer (C).

  In the reflective sheet of the present invention, the proportion of the polypropylene resin (A) in the inner layer portion is 30% by weight to 80% by weight, and the proportion of the resin (B) that is incompatible with the polypropylene resin (A). It is preferably 20% by weight to 70% by weight.

  In the reflective sheet of the present invention, the thermoplastic elastomer (C) of the inner layer portion is styrene-ethylene-butylene-styrene, styrene-butadiene-butylene-styrene, styrene-ethylene-propylene-styrene, styrene-butadiene-styrene, And a copolymer containing at least one block structure selected from the group consisting of styrene-isoprene-styrene in the molecular chain, or a modified product of the copolymer.

  In the reflection sheet of the present invention, the thickness of the entire sheet is preferably 70 μm to 1000 μm.

In the reflecting sheet of the present invention, it is preferable density of the entire sheet is ^{0.1g / cm 3 ~0.75g / cm 3} .

  In the reflective sheet of this invention, it is preferable that polycarbonate resin is included as said resin (B) incompatible with said polypropylene resin (A).

  In the reflective sheet of the present invention, the average total reflectance when light having a wavelength of 550 nm is incident is preferably 90% or more.

In the reflecting sheet of the present invention preferably contains an ultraviolet absorber of 0.01g ^{/ m 2} ~5g ^/ m 2 on the surface layer portion.

  In the reflection sheet of this invention, it is preferable that the total reflectance of the said surface layer part is 50% or less.

  In the reflective sheet of the present invention, the inner layer portion and the surface layer portion are preferably produced by coextrusion film formation.

  In the reflecting sheet of the present invention, the reflected light intensity in the 0 degree direction when light is incident at an incident angle of 60 degrees with respect to the vertical direction of the reflecting sheet has anisotropy depending on the incident direction, and the 0 degree direction The ratio L1 / L2 of the reflected light intensity L1 in the incident direction A1 having the highest reflected light intensity to the incident direction A2 and the reflected light intensity L2 in the incident direction A2 orthogonal to the incident direction is preferably 1.2 or more. .

  The backlight unit of the present invention is characterized by comprising the above-described reflection sheet.

  ADVANTAGE OF THE INVENTION According to this invention, the brightness | luminance of the backlight for liquid crystals can be improved and the reflective sheet which can make a liquid crystal screen clearer and easy to see can be provided.

It is a block diagram of the backlight unit for brightness evaluation. It is a figure which shows the reflected light intensity distribution (TD direction and MD direction incidence) of Example 1. FIG. 2 is a SEM photograph of a cross section in the TD direction of the central portion of the inner layer portion of Example 1. FIG. 6 is a SEM photograph of a cross section in the TD direction of the central portion of the inner layer portion of Comparative Example 1. 6 is a SEM photograph of a cross section in the TD direction of the central portion of the inner layer portion of Comparative Example 2.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, there are cases where the terminology is used in such a way that the thickness is 200 μm or less is called a film and the thickness is more than 200 μm as a sheet, but in the present specification, both the film and the sheet are both sheets. That's it. In the present specification, in the description of the backlight, the screen side is described as the upper side, and the screen back side is described as the lower side.

(Composition constituting the inner layer of the reflection sheet)
The reflective sheet according to the present embodiment is composed of at least two layers of a surface layer portion and an inner layer portion, and the inner layer portion is at least one kind of incompatible with the polypropylene resin (A) and the polypropylene resin (A). The resin (B) is included, and the inner layer portion includes the thermoplastic elastomer (C).

  The polypropylene resin (A) is a polypropylene resin made of a homopolymer of propylene or a copolymer of monomers such as ethylene that can be copolymerized with propylene. The polypropylene resin (A) is preferably a polypropylene resin having a melt flow rate of 0.1 g / min to 10 g / min measured at a temperature of 230 ° C. and a load of 21.2 N by the method of JIS K7210. The melt flow rate is preferably 0.1 g / min or more from the viewpoint of discoloration due to the load of the extruder and heat of the resin composition when the polypropylene resin is melt-molded, from the viewpoint of the viscosity and moldability of the resin. It is preferable that it is 10 g / min or less.

  As the resin (B) that is incompatible with the polypropylene resin (A) (hereinafter also simply referred to as “resin (B)”), a resin having a higher elastic modulus at a temperature at which the polypropylene resin can be stretched than the polypropylene resin is used. More preferable examples include polycycloolefin resins such as polycarbonate resin, polymethylpentene resin, and polynorbornene resin, polyester resin, and polyamide resin. Of these resins, at least one kind of resin is preferably used by being melt mixed with a polypropylene resin, and most preferably a polycarbonate resin.

  The polycarbonate resin which is a preferable example of resin (B) used for this Embodiment can be used individually or in combination from aromatic polycarbonate, linear polycarbonate, and branched polycarbonate. The polycarbonate resin is preferably a polycarbonate resin having a melt flow rate measured by the method of JIS K7210 at a temperature of 300 ° C. and a load of 11.8 N of 0.1 g / 10 min to 50 g / 10 min. From the viewpoint of making the mixing with the polypropylene resin uniform, the melt flow rate of the polycarbonate resin is preferably 0.1 g / 10 min or more, and from the viewpoint of easily forming pores during stretching, the melt flow rate is 50 g / 10 min or less. Is preferred.

  The reflective sheet according to the present embodiment contains the thermoplastic elastomer (C) in the inner layer portion. The thermoplastic elastomer (C) serves as a compatibilizer for the polypropylene resin (A) and the resin (B). Here, the compatibilizing agent in the present invention is an effect of reducing the interfacial energy between the polypropylene resin (A) and the resin (B) and finely dispersing the resin (B) in the polypropylene resin (A) which is a matrix resin. As long as it expresses. In this Embodiment, the interface energy of polypropylene resin (A) and resin (B) falls by adding the thermoplastic elastomer (C) as a compatibilizing agent. As a result, since coarsening due to aggregation of the resin (B) is inhibited, the resin (B) is finely dispersed well in the polypropylene resin (A), and the reflection performance of the reflection sheet can be improved.

  In the present embodiment, the thermoplastic elastomer (C) which is a compatibilizing agent is preferably a block copolymer including a hard segment and a soft segment. For example, styrene-ethylene-butylene-styrene, styrene- Copolymers containing in the molecular chain at least one block structure selected from the group consisting of butadiene-butylene-styrene, styrene-ethylene-propylene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene, or the like The modified body is mentioned. The modified body referred to here is a product obtained by treatment such as hydrogenation of an unsaturated bond of butadiene or further reaction with a compound containing a carboxylic acid group or an amino group. Of these block copolymers, it is preferable to use at least one thermoplastic elastomer by melt mixing.

  Above all, styrene-ethylene is used from the viewpoint of reducing the interfacial energy between the polypropylene resin (A) and the resin (B) and finely dispersing the resin (B) in the polypropylene resin (A) as the matrix resin and heat resistance. -Butylene-styrene or a styrene-butadiene-butylene-styrene copolymer or a modified product thereof is preferable, and a modified product of styrene-ethylene-butylene-styrene copolymer is particularly preferable. As an example of a modified styrene-ethylene-butylene-styrene copolymer, M1913 manufactured by Asahi Kasei Chemicals, Inc., an example of a modified styrene-butadiene-butylene-styrene copolymer is P1500 manufactured by Asahi Kasei Chemicals. It is done.

  In this Embodiment, it is preferable that 30 to 80 weight% of the whole resin composition is a polypropylene resin (A). Furthermore, from the viewpoints of tension during stretching of the resin and stretchability, the proportion of the polypropylene resin (A) in the entire resin composition is more preferably 40% by weight or more. On the other hand, in order to obtain a reflective sheet having a high average total reflectance of 90% or more by stretching a sheet obtained by extruding the resin composition to form holes in the sheet, a polypropylene resin (A ) Is preferably 80% by weight or less, more preferably 70% by weight or less. The average total reflectivity here refers to an average value in both directions when the total reflectivity when light having a wavelength of 550 nm is incident from each of the MD direction and the TD direction of the sheet is measured.

  The resin (B) is preferably 70% by weight or less of the entire resin composition from the viewpoint of reducing the stretching tension. From the viewpoint of increasing the number of holes and the hole volume of the sheet to obtain a high average total reflectance of 90% or more, the resin (B) is preferably 20% by weight or more, particularly preferably 30% by weight or more of the entire resin composition. 60% by weight or less.

  The thermoplastic elastomer (C) is finely dispersed in the resin (B) in the polypropylene resin (A) and has a pore density that is 0.3% by weight or more of the entire resin composition. From the viewpoint, it is 20% by weight or less. Preferably they are 0.5 weight% or more and less than 10 weight%.

When prescribing the resin composition, the conversion between weight% and volume% can be calculated from the density of the basic characteristics of each resin. Density of example polypropylene ^{resins, 0.89g / cm 3 ~0.91g / cm} 3, the density of the polycarbonate resin is 1.2 g / cm ^3, the density of the thermoplastic elastomer 0.90g ^/ cm 3 ~0.96g ^/ cm ³ is, and can be easily converted from these values as necessary.

  In the reflection sheet according to the present embodiment, an ultraviolet absorber and other inorganic powder may be added to the resin composition as necessary.

In addition, the kind and content of the content contained in the resin composition can be easily identified by the following method. First, a sample in which the surface layer portion of the reflective sheet is peeled off to make only the inner layer portion is frozen and ground, and subjected to Soxhlet extraction with methylene chloride to extract a composition other than the polypropylene resin. The extraction residue is analyzed by infrared absorption spectrum or the like, and it is confirmed that no components other than the polypropylene resin (A) remain, and the weight of the polypropylene resin (A) can be determined from the weight of the residue. For the extract, reprecipitation with a solvent such as methanol or methyl ethyl ketone, and analyzing each component with ¹ H-NMR and ¹³ C-NMR to quantify the resin (B) and the thermoplastic elastomer (C). I can do it.

(Composition constituting the surface layer portion of the reflective sheet)
The reflective sheet according to the present embodiment includes at least two layers, a surface layer portion and an inner layer portion, and the surface layer portion includes at least a polypropylene resin (D).

  The polypropylene resin (D) may be the same as the polypropylene resin (A) in the inner layer portion, or different types of polypropylene resins may be used. As a kind of preferable thing in a polypropylene resin (D), the same thing as a polypropylene resin (A) is mentioned.

  In the reflective sheet according to the present embodiment, the total reflectance of the surface layer portion is preferably 50% or less. By setting the total reflectance of the surface layer portion to 50% or less, it is possible to bring out the lamp image reduction performance of the reflection sheet without canceling the incident direction anisotropy of the reflected light intensity derived from the inner layer portion. The total reflectance of the surface layer portion is more preferably 45% or less. The total reflectance of the surface layer portion can be easily measured by peeling the surface layer portion and measuring it even with an integrated sheet such as a coextruded sheet.

  The reflective sheet according to the present embodiment preferably contains a UV absorber in the surface layer portion. As the ultraviolet absorber, inorganic powders such as titanium oxide and zinc oxide are preferable because they are less likely to bleed out. An organic ultraviolet absorber is also preferable from the viewpoint of ensuring the transparency of the surface layer portion. As the organic ultraviolet absorber, ultraviolet absorbers such as benzotriazole, benzophenone, triazine, benzoate, hindered phenol, and hindered amine can be used. Of these, benzotriazole-based ultraviolet absorbers can be suitably used because of their ultraviolet resistance and compatibility with resins. Examples of the organic ultraviolet absorber include T234 and T1577 manufactured by Ciba Specialty Chemicals. The concentration of the ultraviolet absorber in the surface layer portion is determined by the balance between bleed-out property and transparency, but is preferably 0.1% by weight or more and 10% by weight or less. Especially preferably, it is 0.15 weight% or more and 8 weight% or less.

  Moreover, when using inorganic powders, such as a titanium oxide and a zinc oxide, as an ultraviolet absorber, surface modification may be carried out as needed to the inorganic powder. In particular, zinc oxide and titanium oxide are generally surface-modified with alumina, silica, etc., so these may be used, and a surface modifier such as stearic acid or zinc stearate is added separately. May be. The average particle size of the inorganic powder used as the ultraviolet absorber is preferably 1 nm or more and 1000 nm or less. If the average particle diameter is 1 nm or more, coarsening due to aggregation of inorganic particles hardly occurs, and if it is 1000 nm or less, sufficient surface layer portion transparency can be ensured. More preferably, they are 5 nm or more and 500 nm or less, Especially preferably, they are 5 nm or more and 400 nm or less.

As for content of the ultraviolet absorber used for this Embodiment, it is preferable that 0.01 g / m < ² > or more and 5 g / m < ² > or less are contained in a surface layer part. If the content of the ultraviolet absorber is 0.01 g / m ² or more, good ultraviolet absorption performance is exhibited, and if it is 5 g / m ² or less, there is little fear of bleed out and sufficient surface layer transparency is obtained. Can be secured. A more preferred range is 0.05 g / ^{m 2} or more, 4g / ^{m 2} or less, particularly preferred is 0.1 g / ^{m 2} or more and 4g / ^{m 2} or less.

In addition to the inorganic powder having the ultraviolet ray absorbing action, the reflective sheet surface layer may contain an inorganic powder as required. As the inorganic powder, those having low light scattering properties and keeping the reflectance of the surface layer portion as low as 50% or less are preferable, and examples thereof include barium sulfate and calcium carbonate. These inorganic powders may be used alone or in combination of two or more. At this time, when adding the inorganic powder, it is preferable to add the inorganic powder to the surface layer portion at 0.01 g / m ² or more and 5 g / m ² or less from the viewpoint of ensuring transparency.

(Reflective sheet structure)
The reflection sheet according to the present embodiment is composed of at least two layers of a surface layer portion and an inner layer portion, and may have, for example, a three-layer structure of surface layer portion / inner layer portion / surface layer portion, and a layer such as a light-resistant layer on the surface layer portion surface. You may have. Moreover, when comprised from two layers, a surface layer part and an inner layer part, let the layer used on the light source side of a reflection sheet be a surface layer part, and let the layer used on the opposite side to a light source be an inner layer part. Furthermore, when it is composed of three or more layers, the surface layer portion and the inner layer portion may be included in the three or more layers. For example, when a light-resistant layer is provided on the outermost layer, the outermost layer portion (light-resistant layer) The structure may be / surface layer part / inner layer part.

  The inner layer portion of the reflection sheet according to the present embodiment has a structure having holes therein, and the reflection performance is exhibited by this hole structure. The thickness of the inner layer portion is preferably 60 μm or more and 900 μm or less. If the thickness of the inner layer portion is 60 μm or more, it is possible to develop good reflection performance, and if it is 900 μm or less, good lightness can be ensured. Further, it is more preferably 70 μm or more and 700 μm or less, and particularly preferably 80 μm or more and 600 μm or less.

  In the reflection sheet according to the present embodiment, the thickness of the surface layer portion is preferably 2 μm or more and 90 μm or less. If the thickness of the surface layer portion is 2 μm or more, good moldability is obtained, and if it is 90 μm or less, good lightness can be ensured. Further, it is more preferably 2 μm or more and 70 μm or less, and particularly preferably 3 μm or more and 50 μm or less.

  The inner layer portion and the surface layer portion in the reflection sheet according to the present embodiment preferably have the above thickness, and therefore, the thickness of the entire reflection sheet is preferably 70 μm or more and 1000 μm or less. If the thickness of the entire reflection sheet is 70 μm or more, good reflection performance can be exhibited, and if it is 1000 μm or less, good light weight can be ensured. Further, it is more preferably 80 μm or more and 800 μm, and particularly preferably 90 μm or more and 700 μm or less.

The basis weight of the entire reflection sheet according to the present embodiment is preferably 30 g / m ² or more and 500 g / m ² or less. If the basis weight of the entire reflection sheet is 30 g / m ² or more, good reflection performance can be expressed, and if it is 500 g / m ² or less, good light weight can be ensured. Further, it is more preferably 40 g / m ² or more and 400 g / m ² or less, and particularly preferably 50 g / m ² or more and 300 g / m ² or less.

In the reflective sheet according to the present embodiment, the total density including the surface layer portion and the inner layer portion is preferably 0.1 g / cm ³ or more and 0.75 g / cm ³ or less. If the overall density is 0.1 g / cm ³ or more, sufficient strength as a reflective sheet can be maintained. Moreover, if it is 0.75 g / cm < ³ > or less, while forming the structure which has many micropores, while obtaining a high reflectance, favorable lightweight property can be ensured. More preferably 0.2 g / cm ³ or more and 0.5 g / cm ³ or less, particularly preferably 0.2 g / cm ³ or more and 0.45 g / cm ³ or less.

  The reflective sheet according to the present embodiment is configured to include two or more layers of a surface layer portion and an inner layer portion. As a method for producing a reflection sheet of two or more layers, for example, a surface layer part and an inner layer part are separately formed by film formation and laminated, a production method in which the inner layer part is produced and then the surface layer part is formed by coating, a surface layer part, A method of forming the inner layer part integrally by co-extrusion and then stretching and opening is exemplified. Particularly preferably, the surface layer part and inner layer part are integrally formed by co-extrusion and then stretching and opening are performed. This is a manufacturing method.

(Performance of reflective sheet)
In the present embodiment, the reflective sheet preferably has an average total reflectance of 90% or more when light having a wavelength of 550 nm is incident. This is because if the average total reflectance is 90% or more, sufficient luminance can be obtained when mounted on a liquid crystal backlight. More preferably, it is 95% or more.

  In the present embodiment, the reflective sheet preferably has a regular reflectance of 5% or more. By making the regular reflectance of the surface 5% or more, the brightness directly above the cold cathode fluorescent lamp can be reduced more effectively. Particularly preferably, the regular reflectance is 5.5% or more. The specular reflectance is generally measured by measuring the total light reflectance and diffuse reflectance with a spectrocolorimeter (Konica Minolta, CM-2600d, etc.) and subtracting the diffuse reflectance from the total light reflectance. Can be sought.

  In the present embodiment, the reflective sheet preferably has a total reflectance of the surface layer portion of 50% or less. By setting the total reflectance of the surface layer portion to 50% or less, the performance of the reflection sheet can be achieved without canceling the reflectance anisotropy of the inner layer portion. More preferably, it is 45% or less. The total reflectance of the surface layer portion can be easily measured by peeling the surface layer portion and measuring it even with an integrated sheet such as a coextruded sheet.

  In the present embodiment, the reflection sheet has anisotropy in the reflected light intensity in the vertical direction when light is incident at an incident angle of 60 degrees with respect to the vertical direction of the reflection sheet. Anisotropy is evaluated by measuring reflected light intensity. The method will be described below.

  The reflected light intensity is measured using a measuring device generally called a goniophotometer. The variable angle photometer (manufactured by Nippon Denshoku Industries Co., Ltd., GC5000L) has a stage on which a sample is placed and a halogen lamp as a point light source, and a light receiving part. It is possible to measure the reflection angle distribution of the reflected light. In the present invention, it is possible to measure the reflected light intensity by entering a point light source from a direction of 60 degrees with respect to the reflecting sheet surface and obtaining the brightness in the direction of 0 degrees, that is, the apex angle direction. A value obtained by dividing the obtained reflected light intensity in the 0 degree direction by the reflected light intensity in the 0 degree direction obtained by measuring the standard white plate is defined as the reflected light relative intensity in the 0 degree direction. Further, the measurement is performed by rotating the reflection sheet in increments of 5 degrees, the direction in which the reflected light relative intensity in the 0 degree direction is the highest is the A1 direction, the reflected light relative intensity at that time is the reflected light intensity L1, and The orthogonal direction was taken as the A2 direction, and the reflected light relative intensity at that time was taken as the reflected light intensity L2. Here, the standard white plate refers to a standard plate (STANDARD PLATE) attached to a goniophotometer (manufactured by Nippon Denshoku Industries Co., Ltd., GC5000L).

  The ratio of the reflected light intensity of the reflecting sheet according to the present embodiment is preferably the ratio of the reflected light intensity L1 and the reflected light intensity L2, and L1 / L2 is 1.2 or more. By appropriately using a reflective sheet having such reflected light intensity anisotropy, the lamp image of a thin direct type backlight can be reduced. More preferably, L1 / L2 is 1.3 or more, and L1 / L2 is particularly preferably 1.4 or more.

  The reflecting sheet according to the present embodiment is preferably installed in the backlight unit so that the A1 direction and the longitudinal direction of the cold cathode tube are orthogonal to each other. By installing in this way, the brightness directly above the cold cathode tube can be reduced, and the lamp image can be reduced.

The reflective sheet according to the present embodiment preferably has an average luminance of 6100 cd / m ² or more when incorporated in a backlight. The evaluation of luminance is measured using a two-dimensional color luminance meter. If it is 6100 cd / m ² or more, by using it as a surface light source, the liquid crystal screen can be illuminated brightly and the image can be made clearer. Preferably it is 6120 cd / m ² or more, particularly preferably 6140 cd / m ² or more.

  As an example of a method for producing such a reflection sheet, a mixture of polypropylene resin (A) and the polypropylene resin (A) and incompatible resin (B) is extruded from a die while applying a high share, A production method of stretching a material oriented in the MD direction can be given. In this case, in the vicinity of the surface layer of the inner layer portion, the resin (B) is oriented in a rod shape in the extrusion direction (MD) of the reflection sheet. As an example of a method for producing such a reflection sheet, a method for producing a two-layer / three-layer reflection sheet of surface layer portion / inner layer portion / surface layer portion by coextrusion will be specifically described below.

  The surface layer raw material containing the polypropylene resin (D) and the inner layer raw material containing the polypropylene resin (A), resin (B) and thermoplastic elastomer (C) are melt-mixed in another extruder, and the tip of the extruder Extruded into a sheet form from the laminated die attached to. Here, a gear pump may be used between the extruder and the die in order to stabilize the amount of the resin composition to be extruded. When extruded from the die, the resin (B) in the inner layer portion can be oriented in the MD direction due to the share with the die. By orienting the resin (B), the reflected light intensity in the 0 degree direction of the light incident from the TD direction increases, and the reflected light intensity in the 0 degree direction of the light incident from the MD direction decreases, that is, diffusion. However, the mechanism is not clear.

  The obtained laminated sheet is cooled and solidified with a cooling roller or the like, and then stretched with a stretching machine. In the stretching step, the interface between the polypropylene resin (A) and the resin (B) in the inner layer portion is cleaved to generate holes in the sheet, and at the same time, the thickness of the sheet can be reduced to a desired thickness. Here, in the stretching step, a normal biaxial stretching method can be used. That is, longitudinal / horizontal sequential biaxial stretching, lateral / longitudinal sequential biaxial stretching, simultaneous biaxial stretching, and after these biaxial stretching, re-stretching may be performed in either or both of the longitudinal and lateral directions. Preferably, it is the most versatile longitudinal and transverse sequential biaxial stretching. Stretching includes a longitudinal stretching process in which a sheet is passed between a plurality of rollers with different speeds to stretch the sheet in the MD direction, and a transverse stretching process in which the sheet is stretched in the TD direction using a clip tenter or the like. Or it can carry out in combination. Alternatively, the MD direction and the TD direction can be simultaneously stretched using a simultaneous biaxial stretching machine such as a pantograph stretching machine. The stretching ratio of biaxial stretching is preferably 1.5 times or more in each of the MD direction and the TD direction, and the area stretching ratio is preferably from 3 times to 50 times. Moreover, you may heat-shrink after extending | stretching as needed.

  Next, examples performed for clarifying the effects of the present invention will be described. In addition, this invention is not limited at all by the following examples.

<Evaluation method>
First, the physical property items to be evaluated for the reflective sheet and the evaluation method will be described.

(Thickness)
The thickness of the reflection sheet was measured using a thickness meter (Peacock). Moreover, the thickness of each layer was measured for the reflective sheet produced by coextrusion by cross-sectional observation with a digital microscope (made by Keyence Corporation).

(Total reflectance / average reflectance)
The total reflectance of the reflective sheet was measured at an incident angle of 8 degrees using a spectrophotometer (manufactured by Shimadzu Corporation, UV-3150) and an integrating sphere sample stand (manufactured by Shimadzu Corporation, MPC2200). The relative reflectance of 100% polytetrafluoroethylene standard white plate (Spectralon, manufactured by Labosphere) was measured in the wavelength range of 400 nm to 700 nm, and the MD direction and TD of the reflective sheet were measured for light having a wavelength of 550 nm. The measured value when incident from each direction was taken as the total reflectance, and the average value of both was taken as the average total reflectance.

(Basis weight)
The reflection sheet was cut into 50 mm squares and measured by measuring the weight.

(density)
The reflective sheet was cut into 50 mm squares, and the average value of the weight, the thickness of the central part and the central part of each side at five points was determined, and the density was calculated.

(Scanning electron microscope observation)
The reflection sheet was cut out in the MD direction and TD direction sections with a cryomicrotome, and loaded on the sample stage. After etching with a flat milling apparatus, the observation surface was coated with about 2 nm of Os to obtain a right mirror sample. The cross section of the reflection sheet was enlarged and observed using a scanning electron microscope (SEM) (manufactured by Hitachi, Ltd., S-4700), and a cross-sectional photograph was collected.

(60 degree incidence, 0 degree reflected light intensity measurement)
It measured using the goniophotometer (Nippon Denshoku Industries make, GC5000L). The incident angle of the point light source was set to 60 degrees, the sample (reflective sheet) was placed on the stage, and the reflected light intensity was measured in steps of 1 degree from -85 degrees to +85 degrees for the light receiving part. The values in the range of ± 1 degree of the obtained results were averaged to obtain the reflected light intensity in the 0 degree direction. Moreover, the same measurement was performed using the standard plate (STANDARD PLATE) attached to a variable angle photometer (Nippon Denshoku Industries Co., Ltd. GC5000L) as a standard white plate. Whether the reflected light intensity in the 0 degree direction is 20% to 200% of the standard white plate is determined by measuring the reflected light intensity in the 0 degree direction obtained by measuring the reflective sheet on the standard white plate. It was calculated by dividing by the obtained reflected light intensity in the 0 degree direction. In this measurement, the reflected light intensity of the standard white plate in the 0 degree direction was 89.9 cd / m ² .

(Regular reflectance measurement)
The total light reflectance and diffuse reflectance were measured with a spectrocolorimeter (Konica Minolta, CM-2600d), and the total light reflectance was obtained by subtracting the diffuse reflectance.

(Brightness, lamp image evaluation)
As the backlight unit, the existing reflection sheet of the backlight unit of the liquid crystal TV (manufactured by Sony, BRAVIA (registered trademark) 32 inch S-2500) (cold cathode light source) is removed, and the reflection sheet described in the examples, etc. Was used instead. The brightness evaluation was performed with the initial dimensions of the backlight unit. The distance between each cold cathode tube was 23.4 mm (from the tube center to the tube center), and the distance between the reflective sheet and the cold cathode tube was 6.5 mm. The distance between the lower surface of the diffusion plate and the cold cathode tube (from the tube center) was 15.0 mm (from the tube center). Regarding the lamp image evaluation, the presence or absence of the lamp image was confirmed when only the distance between the cold cathode tubes in the backlight was changed to 42.5 mm. The configuration of the backlight is shown in FIG. As shown in FIG. 1, in this embodiment, two cold cathode tubes 1 are arranged substantially in parallel with a predetermined interval, and a reflection sheet 2 is arranged on the lower surface side of the two cold cathode tubes 1. Then, the optical sheet 4 was arranged on the upper surface side through the diffusion plate 3 to constitute a backlight. As the optical sheet 4, a laminated sheet in the order of a diffusion sheet, a prism sheet, and a reflective polarizing sheet was used from the diffusion plate 3 side.

  The brightness and the lamp image were measured using a two-dimensional color luminance meter (Konica Minolta, CA2000), installed 75 cm away from the light control unit, and the center of the light control unit 22 mm × 178 mm [34 dots (x) × The average luminance value measured in the range of 275 dots (y)] was defined as the luminance. Here, the x direction is parallel to the longitudinal direction of the cold cathode tube, and the y direction is perpendicular to the longitudinal direction of the cold cathode tube. The lamp image is obtained as an average luminance value in the x-axis (22 mm) direction, and as a standard deviation value obtained by dividing the luminance value of each point by the average luminance value of ± 17 dots from each point in the y-axis direction. We asked for a lamp image. That is, the smaller this value is, the lower the lamp image is. Regarding the diffuser plate and optical sheet of the backlight unit, a diffuser plate (hereinafter abbreviated as DP) used in a liquid crystal TV (BRAVIA (registered trademark) 32 inch S-2500, manufactured by Sony Corporation), a diffuser sheet ( Hereinafter, an optical sheet having an arrayed prism arrangement structure (hereinafter abbreviated as a prism sheet) and a reflective polarizing sheet were used.

  Next, the present inventors made various reflective sheets containing the thermoplastic elastomer (C) in Examples 1 to 5 below, and performed backlight mounting evaluation. As a result, when a specific block copolymer is used as the thermoplastic elastomer (C) (Example 1), when a block copolymer different from Example 1 is used (Example 2), Example 1 is used. Both the case where the content of the block copolymer was changed (Example 3, Example 4) and the case where the longitudinal and horizontal stretch ratios were changed relative to Example 4 (Example 5) were good. Brightness was able to be obtained.

  Moreover, when not containing a thermoplastic elastomer with respect to Example 1 as Comparative Examples 1 to 3 (Comparative Example 1), the inventors contain a polymer compound different from the thermoplastic elastomer (C). About the case (comparative example 2, comparative example 3), the backlight mounting test was implemented similarly to Example 1- Example 5. FIG. As a result, it was found that when the reflective sheets of Comparative Examples 1 to 3 were used, the luminance was lower than that of Examples 1 to 5. Hereinafter, the contents investigated by the present inventors will be described in detail.

Example 1
As the inner layer material, 62% by volume (55% by weight) of polypropylene resin (manufactured by Nippon Polypro, EA7A), 35% by volume (42% by weight) of polycarbonate resin (E2000, manufactured by Mitsubishi Engineering Plastics), styrene-ethylene A raw material resin in which 3% by volume (3% by weight) of a butylene-styrene copolymer (M1913, manufactured by Asahi Kasei Chemicals Corporation) was mixed was used. This raw material resin was melted at an operating condition of a cylinder temperature of 230 ° C. and a screw rotation speed of 100 rpm using a co-rotating twin screw extruder with a cylinder diameter of 25 mm and a cylinder to diameter ratio of 48. A multi-manifold die was supplied through a gear pump adjusted to ° C.

  Moreover, as a surface layer raw material, polypropylene resin (manufactured by Nippon Polypro Co., Ltd., EA7A) 93% by weight, as an ultraviolet absorber, zinc oxide (manufactured by Sakai Chemical Co., Finex 50W, average particle size 20 nm) 5% by weight, and benzotriazole 2 wt% of an ultraviolet absorber (manufactured by Ciba Specialty Chemicals, T234) was used. This surface layer raw material is melted under the operating conditions of a cylinder temperature of 210 ° C. and a screw rotation speed of 100 rpm using a single screw extruder having a cylinder diameter of 25 mm and a cylinder to diameter ratio of 48, and is supplied to a multi-manifold die. did. Here, the raw materials were supplied to the multi-manifold die so that the ratio of the surface layer portion / inner layer portion / surface layer portion was 1/10/1, merged, and extruded with a lip width of 400 mm and a clearance of 1.9 mm. . Here, the extrusion was performed so that the extrusion line speed was 1.0 m / min. The extruded molten resin was taken up by a pair of pinch rollers set at 80 ° C., and the resin was cooled and solidified while pulling the molten resin in the MD direction to produce a sheet having a thickness of 1.7 mm. The resulting sheet was stretched 3 times in the MD direction (longitudinal direction) at a temperature of 155 ° C. using a roll longitudinal stretching machine, and then tripled in the TD direction (transverse direction) at a temperature of 155 ° C. using tenter transverse stretching. Stretched to obtain a reflection sheet with two types and three layers coextruded.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 19 μm / 329 μm / 19 μm, 205 g / m ² , and 0.56 g / cm, respectively. ³ and 97.6%. The average total reflectance of the surface layer portion was 23%. The incident direction in which the reflected light intensity in the 0 degree direction was highest was the TD direction of the reflective sheet, and L1 / L2 was 2.61.

  For reference, the reflected light intensity when incident from the TD (L1) direction and the reflected light intensity when incident from the MD (L2) direction are shown in FIG. As shown in FIG. 2, it can be seen that the reflected light intensity of the incident light in the A2 direction is greatly reduced with respect to the reflected light intensity of the incident light in the A1 direction, and the reflected intensity varies greatly depending on the incident direction. In FIG. 2, the incident light is incident from an angle indicated as −60 degrees, and the reflected light intensity around +60 degrees is derived from regular reflection.

  From cross-sectional observation using a scanning electron microscope (SEM), the polycarbonate resin is finely dispersed in the polypropylene resin in the central portion of the inner layer thickness direction D1 of the sheet before stretching obtained by extrusion. It was confirmed. For reference, FIG. 3 shows an SEM photograph (magnification 1000 times) of a cross section perpendicular to the MD direction at the central portion of the inner layer thickness direction D1. As shown in FIG. 3, in the MD vertical cross section of the central portion D1 in the inner layer thickness direction, the polycarbonate resin is almost uniformly dispersed, and a large number of fine dispersed phases extending slightly in the A1 direction are formed. I understand. This polycarbonate resin had an average dispersion diameter of about 1.9 μm in the extending direction of the dispersed phase.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. Under the conditions, the diffusion plate / DS / prism sheet / reflective polarizing sheet was disposed (hereinafter, all sheets were disposed), and the luminance and the lamp image were confirmed. As a result, the luminance was as high as 6134 cd / m ^2. It was as low as 0.00234.

(Example 2)
As raw materials for the inner layer, 62% by volume (55% by weight) of polypropylene resin (manufactured by Nippon Polypro Co., Ltd., EA7A), 35% by volume (42% by weight) of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics, E2000), styrene-butylene -Butylene-styrene copolymer (Asahi Kasei Chemicals Co., Ltd., P1500) mixed with 3% by volume (3% by weight) of raw material resin was extruded in the same manner as in Example 1 and tripled in the MD and TD directions, respectively. Stretched to obtain a two-type, three-layer coextruded reflective sheet.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 19 μm / 290 μm / 18 μm, 200 g / m ² , and 0.61 g / cm ^{3, respectively.} 96.7%. The average total reflectance of the surface layer portion was 22%. The incident direction with the highest reflected light intensity in the 0 degree direction was the TD direction of the reflective sheet, and L1 / L2 was 2.42.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. When all the sheets were arranged under the conditions and the luminance and the lamp image were confirmed, the luminance was as high as 6110 cd / m ² and the lamp image was as low as 0.00186.

(Example 3)
As the inner layer material, 62% by volume (55% by weight) of polypropylene resin (manufactured by Nippon Polypro Co., Ltd., EA7A), 37% by volume (44% by weight) of polycarbonate resin (Mitsubishi Engineering Plastics, E2000), styrene-ethylene -Butylene-styrene copolymer (manufactured by Asahi Kasei Chemicals Co., Ltd., M1913) was extruded in the same manner as in Example 1 using a raw material resin mixed with 1% by volume (1% by weight) and tripled in the MD and TD directions, respectively. Stretched to obtain a two-type, three-layer coextruded reflective sheet.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 27 μm / 338 μm / 24 μm, 220 g / m ² , 0.56 g / cm ^{3, respectively.} 96.9%. Moreover, the average total reflectance of the surface layer portion was 20%. The incident direction in which the reflected light intensity in the 0 degree direction was highest was the TD direction of the reflective sheet, and L1 / L2 was 2.62.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. When all the sheets were arranged under the conditions and the luminance and the lamp image were confirmed, the luminance was as high as 6102 cd / m ² and the lamp image was as low as 0.00237.

Example 4
As the inner layer raw material, 62 volume% (55 wt%) of polypropylene resin (manufactured by Nippon Polypro Co., Ltd., EA7A), 33 volume% (40 wt%) of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics Co., Ltd., E2000), styrene-ethylene -Butylene-styrene copolymer (manufactured by Asahi Kasei Chemicals Corporation, M1913) was extruded in the same manner as in Example 1 using a raw material resin mixed with 5% by volume (5% by weight), and tripled in the MD direction and TD direction, respectively. Stretched to obtain a two-type, three-layer coextruded reflective sheet.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 19 μm / 311 μm / 17 μm, 213 g / m ² , and 0.61 g / cm ^{3, respectively.} , 96.4%. The average total reflectance of the surface layer portion was 22%. The incident direction where the reflected light intensity in the 0-degree direction was highest was the TD direction of the reflective sheet, and L1 / L2 was 2.37.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. When all the sheets were arranged under the conditions and the luminance and the lamp image were confirmed, the luminance was as high as 6155 cd / m ² and as low as 0.00233.

(Example 5)
As the inner layer raw material, 62 volume% (55 wt%) of polypropylene resin (manufactured by Nippon Polypro Co., Ltd., EA7A), 33 volume% (40 wt%) of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics Co., Ltd., E2000), styrene-ethylene -Butylene-styrene copolymer (manufactured by Asahi Kasei Chemicals Co., Ltd., M1913) was extruded in the same manner as in Example 1 using a raw material resin mixed with 5% by volume (5% by weight), and tripled in the MD direction and TD direction. Stretched 6 times to obtain a coextruded reflective sheet of two types and three layers.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 14 μm / 184 μm / 13 μm, 117 g / m ² , and 0.55 g / cm ^{3, respectively.} 97.5%. The average total reflectance of the surface layer portion was 21%. The incident direction in which the reflected light intensity in the 0 degree direction was the highest was the TD direction of the reflective sheet, and L1 / L2 was 2.25.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. When all the sheets were arranged under the conditions and the luminance and the lamp image were confirmed, the luminance was as high as 6113 cd / m ² and the lamp image was as low as 0.00231.

(Comparative Example 1)
Raw material resin in which 62% by volume (55% by weight) of polypropylene resin (manufactured by Nippon Polypro Co., Ltd., EA7A) and 38% by volume (45% by weight) of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics, E2000) are mixed as the inner layer raw material Was extruded in the same manner as in Example 1, and stretched 3 times in the MD direction and TD direction, respectively, to obtain a coextruded reflective sheet of two types and three layers.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 22 μm / 339 μm / 21 μm, 205 g / m ² , and 0.54 g / cm ^{3, respectively.} 96.5%. The average total reflectance of the surface layer portion was 21%. The incident direction in which the reflected light intensity in the 0 degree direction was the highest was the TD direction of the reflective sheet, and L1 / L2 was 2.14.

  From cross-sectional observation using a scanning electron microscope (SEM), it was confirmed that the polycarbonate resin was dispersed in the polypropylene resin in the central portion D1 center direction of the inner layer portion thickness direction of the sheet before stretching obtained by extrusion. . For reference, FIG. 4 shows an SEM photograph (magnification 1000 times) of a cross section perpendicular to the MD direction at the center of the inner layer thickness direction D1. As shown in FIG. 4, compared with FIG. 3, the polycarbonate resin forms a non-uniform dispersed phase. Further, it can be seen that each of the dispersed phases extends in the A1 direction and has a larger dispersed diameter and a smaller number than the dispersed phase of FIG. The dispersed diameter of this dispersed phase was about 4.3 μm in the extending direction of the dispersed phase.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. When all the sheets were arranged under the conditions and the luminance and the lamp image were confirmed, the luminance was as low as 6070 cd / m ² and the lamp image was as low as 0.00223. Since no compatibilizer is used in the inner layer portion, the interfacial tension between the polypropylene resin and the polycarbonate resin is high, and as a result of the polycarbonate resin not being finely dispersed in the polypropylene resin, the luminance is considered to be low.

(Comparative Example 2)
As inner layer raw materials, 62 vol% (55 wt%) of polypropylene resin (manufactured by Nippon Polypro Co., Ltd., EA7A), 35 vol% (42 wt%) of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics, E2000), polystyrene resin ( Extruded in the same manner as in Example 1 using a raw material resin mixed with 3% by volume (3% by weight) of HH102 manufactured by PS Japan, and stretched 3 times in the MD direction and TD direction, respectively. An extruded reflective sheet was obtained.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 22 μm / 264 μm / 19 μm, 174 g / m ² , and 0.57 g / cm ^{3, respectively.} 95.6%. The average total reflectance of the surface layer portion was 23%. The incident direction with the highest reflected light intensity in the 0 degree direction was the TD direction of the reflective sheet, and L1 / L2 was 1.51.

  From cross-sectional observation using a scanning electron microscope (SEM), it was confirmed that the polycarbonate resin was dispersed in the polypropylene resin in the central portion D1 center direction of the inner layer portion thickness direction of the sheet before stretching obtained by extrusion. . For reference, FIG. 5 shows a SEM photograph (magnification 1000 times) of a cross section perpendicular to the MD direction of the central portion D1 in the inner layer thickness direction. As shown in FIG. 5, it can be seen that in this example, the polycarbonate resin is further dispersed less than the example shown in FIG. 4, and a plurality of dispersed phases extending in the A1 direction and having a large dispersion diameter are formed. The dispersed diameter of this dispersed phase was about 13.4 μm in the extending direction of the dispersed phase.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. When all the sheets were arranged under the conditions and the luminance and the lamp image were confirmed, the luminance was as low as 5961 cd / m ² and the lamp image was as low as 0.00227. Since an appropriate compatibilizing agent is not used, the polycarbonate resin is not finely dispersed in the polypropylene resin. As a result, the luminance is considered to be low.

(Comparative Example 3)
As raw materials for the inner layer, 62% by volume (55% by weight) of polypropylene resin (manufactured by Nippon Polypro, EA7A), 35% by volume (42% by weight) of polycarbonate resin (manufactured by Mitsubishi Engineering Plastics, E2000), cycloolefin copolymer Extrusion was performed in the same manner as in Example 1 using a raw material resin in which 3% by volume (3% by weight) of a resin (polyplastics, 5013L-10) was mixed, and each was stretched 3 times in the MD direction and the TD direction. A two-type, three-layer coextruded reflective sheet was obtained.

The thickness (surface layer portion / inner layer portion / surface layer portion), basis weight, density, and total reflectance of the obtained two-type three-layer reflective sheet were 23 μm / 316 μm / 20 μm, 202 g / m ² , and 0.56 g / cm ^{3, respectively.} 96.5%. The average total reflectance of the surface layer portion was 22%. The incident direction with the highest reflected light intensity in the 0 degree direction was the TD direction of the reflective sheet, and L1 / L2 was 2.02.

This reflective sheet was placed on the backlight so that the A1 direction and the longitudinal direction of the cold cathode tubes were orthogonal to each other, the distance between the DP and the cold cathode tubes was 15 mm, and the distance between each cold cathode tube was 42.5 mm. When all the sheets were arranged under the conditions and the brightness and the lamp image were confirmed, each of them was as low as 6066 cd / m ² and the lamp image was as low as 0.00152. Since an appropriate compatibilizing agent is not used, the polycarbonate resin is not finely dispersed in the polypropylene resin. As a result, the luminance is considered to be low.

  As a result, by including the compatibilizing agent described in the examples in the inner layer part, the polycarbonate resin can be remarkably finely dispersed in the polypropylene resin as compared with the conventional case, and as a result, the pores can be efficiently formed. The density can be increased. The obtained results are shown together in Table 1. It can be seen that, by containing an appropriate compatibilizing agent in the inner layer portion, it is possible to increase the brightness while suppressing an increase in the lamp image.

  As shown in Table 1, it can be seen that Examples 1 to 5 containing the thermoplastic elastomer (C) in a predetermined ratio all show high average luminance. Moreover, as shown in Example 1 and Example 2, if it is a block copolymer which has a predetermined structure, even if it adds a different thermoplastic elastomer (C), it turns out that an effect expresses. Moreover, as shown in Example 1, Example 3, and Example 4, it can be seen that the same luminance can be obtained even when the content of the thermoplastic elastomer (C) is changed. Furthermore, as shown in Example 4 and Example 5, it can be seen that the same luminance can be obtained even if the aspect ratio of the draw ratio is changed.

  On the other hand, as shown in Comparative Example 1, it can be seen that when the thermoplastic elastomer (C) is not used, the luminance is lowered as compared with Example 1. Moreover, as shown in Comparative Example 2 and Comparative Example 3, it can be seen that the luminance is not improved when a polymer compound different from the thermoplastic elastomer (C) is added.

  As described above, according to the reflective sheet according to the present invention, by adding the predetermined thermoplastic elastomer (C), it is possible to improve the reflective performance of the reflective sheet without light absorption, The luminance of the liquid crystal backlight can be improved.

  The reflective sheet of the present invention has the characteristics of having both excellent reflective performance and light weight, and can improve the brightness of the backlight for liquid crystal, making the liquid crystal screen clearer and easier to see, It can be suitably used as a backlight unit of a display device.

DESCRIPTION OF SYMBOLS 1 Cold cathode tube 2 Reflection sheet 3 Diffusion plate 4 Optical sheet

Claims (12)

  Surface layer part containing at least polypropylene resin (D), polypropylene resin (A), at least one resin (B) that is incompatible with the polypropylene resin (A), and thermoplastic elastomer as a compatibilizer ( C) and an inner layer portion having pores therein, and at least two layers of the surface layer portion and the inner layer portion, and the thermoplastic elastomer (C) 0. A reflective sheet comprising 3% by weight to 20% by weight.   The proportion of the polypropylene resin (A) in the inner layer portion is 30 wt% to 80 wt%, and the proportion of the resin (B) incompatible with the polypropylene resin (A) is 20 wt% to 70 wt%. The reflection sheet according to claim 1, wherein the reflection sheet is provided.   The inner layer thermoplastic elastomer (C) comprises styrene-ethylene-butylene-styrene, styrene-butadiene-butylene-styrene, styrene-ethylene-propylene-styrene, styrene-butadiene-styrene, and styrene-isoprene-styrene. The reflective sheet according to claim 1, comprising a copolymer containing at least one block structure selected from the group in the molecular chain, or a modified product of the copolymer.   The thickness of the whole sheet | seat is 70 micrometers-1000 micrometers, The reflective sheet in any one of Claims 1-3 characterized by the above-mentioned. Reflecting sheet according to any one of claims 1 to 4, the density of the entire sheet is characterized in that it is a ^{0.1g / cm 3 ~0.75g / cm 3} .   The reflective sheet according to any one of claims 1 to 5, wherein the resin (B) that is incompatible with the polypropylene resin (A) includes a polycarbonate resin.   The reflective sheet according to any one of claims 1 to 6, wherein an average total reflectance when light having a wavelength of 550 nm is incident is 90% or more. Reflecting sheet according to any one of claims 1 to 7, characterized by containing the ultraviolet absorbent according to the 0.01g ^/ m ² ~5g / m 2 on the surface layer portion.   The reflective sheet according to any one of claims 1 to 8, wherein the total reflectance of the surface layer portion is 50% or less.   The reflective sheet according to any one of claims 1 to 9, wherein the inner layer portion and the surface layer portion are produced by coextrusion film formation.   The reflected light intensity in the 0 degree direction when light is incident at an incident angle of 60 degrees with respect to the vertical direction of the reflecting sheet has anisotropy depending on the incident direction, and the reflected light intensity in the 0 degree direction is the highest. The ratio between the reflected light intensity L1 in the incident direction A1 and the reflected light intensity L2 in the incident direction A2 orthogonal to the incident direction, L1 / L2 is 1.2 or more, characterized in that: The reflective sheet according to any one of 10.   A backlight unit comprising the reflective sheet according to any one of claims 1 to 11.