JP2018101116A - Reflection sheet and edge-light type backlight using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection sheet capable of contributing to improve the quality and the productivity of an edge-light type backlight by satisfying both of the thermoformability and the heat tolerance while ensuring optical characteristics as well as satisfactory handling performance.SOLUTION: A reflection sheet 1 includes: a porous resin layer 11 containing an olefinic resin as a base resin; and a coating layer 12 which is laminated over both surfaces of the porous resin layer 11. The thickness of the coating layer 12 is 0.5 μm or more and 5 μm or less, and the indentation elastic modulus of the coating layer 12 is 2000 MPa or more and 2800 MPa or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a reflective sheet, an edge light type backlight, and a liquid crystal display module using the same.

  In recent years, the spread of small portable information processing terminals such as smartphones and tablet computers is rapidly progressing. As information display devices in these portable information processing terminals, liquid crystal display devices having features such as light weight, thinness, and low power consumption are widely used.

  In this liquid crystal display device, the backlight used as a surface light source for irradiating illumination light from behind the liquid crystal display panel is roughly classified into an edge light method and a direct type depending on the location of the light source. Of both types, particularly in terms of reduction in thickness and weight, an edge light method in which a surface light source is configured by allowing light to enter from the side of a light guide plate arranged to face the liquid crystal display panel is more advantageous. Therefore, particularly in a small portable information processing terminal, an edge light type backlight is often used as a surface light source (see Patent Document 1).

  In an edge-light type backlight, a light guide plate for converting light from a point light source into planar light is installed. Usually, in addition to this, an opposite side of the light emission surface of the light guide plate (liquid crystal panel) On the back side, which is the opposite side of the arrangement side, a reflection sheet is arranged to reflect the light leaking to this side and improve the luminance of the backlight and the uniformity of the light.

  As the reflection sheet disposed in the edge light type backlight, a white PET film (see Patent Document 2) made of polyethylene terephthalate (PET) having excellent heat resistance and having a multilayer structure including a hollow layer is used. Yes.

  However, the reflective material described in Patent Document 2 made of polyester resin such as PET having excellent heat resistance, on the other hand, does not have good thermoformability like olefin resin, so there is room for improvement in terms of productivity. Was leaving.

  In order to solve this problem, the present inventors examined a configuration in which a foamed sheet made of an olefin resin such as polypropylene (PP) having excellent thermoformability is coated with a PET film having excellent heat resistance. . However, when a foam sheet that is slightly fragile in its internal structure and has a high heat shrinkage ratio during heat processing is excellent in heat resistance, but is laminated with a PET film that has high rigidity, for example, when it is incorporated into a backlight. Even if the film is bent slightly, it may cause damage due to internal peeling of the foam sheet, or damage such as irreversible folds on the film surface. As a result, we have come to recognize a new problem that the risk of reducing backlight quality and productivity will increase.

JP 2013-201031 A JP 2008-309975 A

  The present invention has been made in view of the situation as described above. By maintaining both the optical formability and the thermoformability and heat resistance, and maintaining good handling properties, the edge light type back is provided. An object of the present invention is to provide a reflective sheet that can contribute to the improvement of light quality and productivity.

  The present inventors can solve the above-mentioned problems by using a reflective sheet that covers a coating layer having a specific indentation elastic modulus on both surfaces of an olefin-based porous resin layer excellent in thermoformability. As a result, the present invention has been completed. Specifically, the present invention provides the following.

  (1) A reflective sheet comprising a porous resin layer containing an olefin-based resin as a base resin and coating layers laminated on both surfaces of the porous resin layer, the thickness of the coating layer A reflective sheet having a thickness of 0.5 μm or more and 5 μm or less and an indentation elastic modulus of the coating layer of 2000 MPa or more and 2800 MPa or less.

  The invention of (1) is a reflective sheet having a layer structure in which coating layers having a specific indentation elastic modulus are laminated on both surfaces of an olefin-based porous resin layer excellent in thermoformability. This reduces the risk of film breakage due to, for example, the weakness of the foam layer, the difference in thermophysical properties between layers, and the high rigidity of the coating layer, as described above. It can be set as the reflective sheet which can contribute to the improvement in quality and productivity for lights. In addition, by setting it as the 3 layer structure which formed the coating layer on both surfaces, the curvature of the reflection sheet by the difference in the thermal expansion coefficient of a porous resin layer and a coating layer can be prevented. Moreover, the heat resistance of the reflective sheet is also improved by providing the coating layer to suppress the thermal shrinkage of the porous resin layer.

Here, “the indentation elastic modulus of the resin for the coating layer” in this specification refers to a value obtained by the following measurement method and measurement conditions.
(Measuring method)
Under the following measurement conditions, a resin material that is the same as the resin material that forms the coating layer to be measured has a face angle of 136 ° from the direction perpendicular to the surface of the sample resin film molded under the same molding conditions as the actual product. A Vickers indenter is pushed in, the indentation elastic modulus is calculated from the obtained load-displacement curve, and the average obtained at three places is defined as the indentation elastic modulus of the coating layer.
In addition, the thickness of said sample resin film should just be 10 times or more of the maximum pushing amount at the time of a test. On the other hand, the load may be adjusted so that the maximum pushing amount becomes 1/10 or less of the thickness of the sample resin film. Also, the load speed is the maximum load applied over 10 seconds.
(Measurement condition)
Applied load 0mN ~ 1mN
Load speed 0.1 mN / sec Holding time 5 sec Load unload speed 0.1 mN / sec Indenter Vickers (face angle of the tip of the square pyramid 136 °)
Measurement temperature 25 ℃

  In the measurement of film-like materials, when the film is placed on the measuring table, the film partially floats off the measuring table and cannot be accurately measured. It is preferable to carry out the measurement while fixing it in a state where it does not float.

  As a reference example, a measurement table that can actually be vacuum-adsorbed is prepared, and (indentation elastic modulus) is measured by the above measurement method in a state where a (biaxially stretched) polypropylene film is adsorbed and fixed to the measurement table. The indentation elastic modulus of the biaxially stretched polypropylene film was 1936 MPa.

  (2) The base resin of the porous resin layer is a polypropylene resin, and the base resin of the coating layer is any one of an acrylic resin, a urethane resin, and an acrylic urethane resin, (1) Reflective sheet as described in 1.

  In the invention of (2), each material resin constituting each layer in the invention of (1) is specified as a particularly preferable resin. Thereby, the said effect which the reflection sheet of (1) can show | play can be expressed easily with higher accuracy.

  (3) The thickness of the porous resin layer is 50 μm or more and 95 μm or less, and the thickness of each layer of the coating layer laminated on both surfaces of the porous resin layer is 0.5 μm or more and 5 μm or less. The reflective sheet according to any one of (1) and (2), wherein the total thickness of all layers is 100 μm or less.

  According to the invention of (3), by optimizing the thickness of each layer and all layers of the reflective sheet within the range peculiar to the present invention, the workability when incorporated into the backlight, the reflective performance, and the final product All adaptability to the demand for thinning can be improved in a well-balanced manner.

  (4) Among the coating layers, the coating layer laminated on one surface of the porous resin layer contains a filler, and the coating layer laminated on the other surface of the porous resin layer contains a filler. The reflective sheet according to any one of (1) to (3), which is not contained.

  According to the invention of (4), while maintaining the preferable reflection performance of the light reflecting surface facing the light guide plate, blocking during manufacturing can be avoided, and the productivity of the backlight can be improved.

  (5) The porous resin layer is a stretched resin film containing a filler, and the porosity of the porous resin layer is 25% or more and 80% or less in any one of (1) to (4) The reflective sheet as described.

  According to the invention of (5), by optimizing the porosity and stretching and forming an olefin resin containing a filler, the light reflectance, diffuse reflectance, and regular reflectance are controlled within a preferable range, and reflection is performed. The optical properties of the sheet can be optimized.

  (6) The method for producing a reflective sheet according to (1) to (5), wherein a coating liquid containing a base resin and a solvent for the coating layer is directly applied to both surfaces of the porous resin layer. The manufacturing method of the reflective sheet which forms the said coating layer into a coating film by this.

  According to the invention of (6), a reflective sheet including a coating layer having a thickness of 5 μm or less can be produced with high productivity while enjoying the effects of the inventions of (1) to (5). For example, if a manufacturing method in which a resin film (PET, etc.) having a thickness of about 5 μm is laminated on a porous resin layer by dry lamination as a coating layer, there is a risk of defective products due to damage of the resin film during mass production. It becomes relatively large. In order to avoid this, if the resin film is thickened, it is necessary to reduce the thickness of the porous resin layer under the influence on the optical characteristics (decrease in reflectivity, etc.) and restrictions on the thickness of the product. Similarly, the thickness of the adhesive layer is disadvantageous, and the reduction in the thickness of the porous resin leads to a loss of reflectance. For these reasons, it is more advantageous to form the coating layer by a manufacturing method (coating) in which the coating liquid is directly applied to both surfaces of the porous resin layer.

  (7) An optical module for an edge light type backlight, wherein the reflection sheet according to any one of (1) to (5) is disposed to face a light guide plate.

  According to the invention of (7), the above-mentioned effects of the inventions of (1) to (5) are enjoyed, and an optical module for an edge light type backlight having excellent optical characteristics is manufactured with good productivity. be able to.

  (8) An optical module for an edge-light type backlight, in which a light guide plate is disposed opposite to the reflection sheet according to (5), wherein the reflection sheet has a coating layer that does not contain a filler. An optical module, wherein one surface facing the light guide plate is arranged so that the other surface on which a coating layer containing a filler is formed faces the opposite side to the light guide plate.

  According to the invention of (8), the optical module for the backlight of the edge light system that is excellent in optical characteristics and enjoys the above-mentioned effect of the invention of (5) is extremely good even in the roll-to-roll production line. Can be manufactured under high productivity. In addition, since one surface of the reflective sheet on which the coating layer not containing the filler is formed faces the light guide plate, the filler does not fall off even when the reflective sheet and the light guide plate come into contact with each other. No scratches occur.

  (9) An edge light type backlight comprising the optical module according to (7) or (8) and a light source for edge light.

  According to the invention of (9), the above-mentioned effect of the invention of (7) or (8) can be enjoyed, and an edge light type backlight having excellent optical characteristics can be produced with good productivity. In addition, in the case of having the constitutional requirements of the invention of (8), since the one surface on which the coating layer not containing the filler of the reflective sheet is formed faces the light guide plate, the contact between the reflective sheet and the light guide plate Also, the filler does not fall off, and the light guide plate is not damaged by the dropped filler and the luminance of the backlight is not uneven.

  (10) A liquid crystal display module in which the backlight according to (8) and a liquid crystal panel are arranged to face each other.

  According to the invention of (10), the liquid crystal display module having excellent optical characteristics can be manufactured with good productivity by enjoying the above effect of the invention of (8).

  According to the present invention, it is possible to improve the quality and productivity of the backlight for the edge light system by maintaining both the optical properties while maintaining both the thermoformability and the optical properties and preferably maintaining the handling properties. A reflective sheet that can be provided can be provided.

It is drawing which shows typically the laminated constitution of the liquid crystal display module which uses the backlight of an edge light system provided with the reflective sheet of this invention. It is drawing which shows typically the laminated constitution of the reflective sheet of this invention. It is a graph which shows the interlayer of the thickness of a coating layer, and a heat contraction rate.

  Hereinafter, first, the basic structure of an edge light type backlight that can suitably use the reflection sheet of the present invention and a liquid crystal display module including the same will be described, and then the details of the reflection sheet of the present invention. Will be explained. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention.

<Edge light type backlight and liquid crystal display module>
FIG. 1 schematically shows a basic configuration of an edge light type backlight 20 using the reflection sheet 1 of the present invention and a liquid crystal display module 100 using the backlight 20. As shown in FIG. 1, the backlight 20 has a light source 3 such as an LED element disposed on the side of an optical module 10 in which a light guide plate 2 and a reflection sheet 1 are laminated or opposed to each other. Further, in the liquid crystal display module 100, the liquid crystal panel 4 is disposed above the light guide plate 2 serving as a light emitting surface of the backlight 20.

  The reflection sheet 1 is disposed to face the lower surface of the light guide plate 2 in the backlight 20 shown in FIG. 1, that is, the surface (back surface) opposite to the light emitting surface of the light guide plate 2. The reflection sheet 1 is used to reflect light traveling toward the back surface of the light guide plate 2 so as to enter the light guide plate 2 again.

  The reflective sheet 1 is a resin sheet having a multilayer structure in which coating layers 12 are laminated on both surfaces of a porous resin layer 11 having light reflectivity. Further, it is preferable that only one of the coating layers 12 on both surfaces contains a filler mainly intended to improve the blocking resistance. When the reflective sheet 1 has an asymmetric layer structure that contains a filler only in one coating layer and does not contain a filler in the other coating layer, a coating layer 12A that does not contain a filler is formed. By arranging the reflective sheet so that the surface on the side facing the light guide plate 2 and the surface on which the coating layer 12B containing the filler is formed faces the opposite side of the light guide plate 2, the reflective sheet 1 The optical characteristics and the productivity of the backlight 20 can be made compatible at a higher level. The details of the reflective sheet 1 and others will be described later.

  The light guide plate 2 has a substantially rectangular flat plate shape, and serves as a light emitting surface and a surface that faces the liquid crystal panel 4, a lower surface that is the opposite surface, and a peripheral edge between these upper and lower surfaces. Are connected to each other. And the one side end surface of the light-guide plate which is one of four side surfaces turns into a light-incidence surface. The light guide plate 2 includes a transparent resin that is a matrix (base material) and phosphor fine particles that are dispersed in the resin. As the transparent resin which is a matrix (base material), a material such as a polycarbonate resin and an acrylic resin which are excellent in transparency and good in light transmittance can be used.

  In the liquid crystal display module 100 or the edge light type backlight 20, various other optical sheets such as various prism sheets and polarized light reflecting sheets (all not shown) are further provided between the light guide plate 2 and the liquid crystal panel 4. Are appropriately arranged.

  The light source 3 configured using an LED element or the like constitutes the edge light type backlight 20 by being disposed at a position where light can be incident on the light incident surface of the light guide plate 2 described above, that is, one end surface. .

<Reflection sheet>
As shown in FIG. 2, the reflective sheet 1 has a porous resin layer 11 having an olefin resin as a base resin as a core layer, an indentation elastic modulus (Young's modulus) of 2000 MPa to 2800 MPa, and a thickness of 0. A three-layer structure in which the coating layers 12 (12A, 12B) having a thickness of 5 μm or more and 5 μm or less are directly laminated on both surfaces of the porous resin layer 11 is a basic layer structure. The coating layer 12 can be formed by forming a coating solution for a coating layer containing each resin, which will be described in detail below, as a main resin, on each surface of the porous resin layer 11 by a known coating method.

  The total thickness of the reflection sheet 1 is preferably 55 μm or more and 100 μm or less, and more preferably 85 μm or less. When the total thickness of the reflection sheet 1 is less than 55 μm, the stretchability and flexibility of the resin film constituting each layer are excessive, and therefore workability at the time of integration as a backlight is lowered. On the other hand, by being 100 μm or less, more preferably 85 μm or less, it is possible to respond in a preferable manner to a request for thinning in a final product such as a smartphone that is finally incorporated in the form of an edge light type backlight or the like. .

  The thickness of the porous resin layer 11 in the reflection sheet 1 is preferably 50 μm or more and 95 μm or less in order to ensure the preferable optical characteristics described later and also maintain good workability. More preferably, it is 80 μm or less.

  The thickness of each coating layer 12 (12A, 12B) in the reflection sheet 1 does not hinder the good optical properties of the porous resin layer 11, and the thermoformability, heat resistance, and handling properties of the reflection sheet 1 Is preferably 0.5 μm or more and 5 μm or less, and more preferably 1 μm or more and 3 μm or less.

  The porous resin layer 11 disposed to provide the necessary optical characteristics as the main layer of the reflection sheet 1 has an appropriate thickness of the foamed resin film using an olefin resin such as polypropylene as the base resin. It can be configured by adjusting. The material of the foamed resin film constituting the porous resin layer 11 is not particularly limited as long as it is a foamable resin base material mainly made of an olefin resin and capable of ensuring the optical characteristics of the reflective sheet 1. As an example, a resin film having the same composition as the “foamed resin film” disclosed in International Publication WO2007 / 132826, wherein the resin film is adjusted to a desired thickness unique to the present invention, Preferable specific examples can be given. This foamed resin film can be obtained by stretching a resin composition containing polypropylene as a base resin and containing a filler, as disclosed in the above-mentioned document.

  As the base resin of the resin composition used for producing the foamed resin film constituting the porous resin layer 11, it is preferable to use a polypropylene resin such as a propylene homopolymer or a propylene-ethylene copolymer among olefin resins. it can. In addition, ethylene resins such as high-density polyethylene can also be used. These may be used in combination of two or more. Among these, it is more preferable to use a propylene resin from the viewpoint of water resistance, water repellency, chemical resistance, production cost, and the like.

  Copolymerization of propylene homopolymer, propylene as a main component, and α-olefin such as ethylene, 1-butene, 1-hexene, 1-heptene, 4-methyl-1-pentene as the propylene resin Coalescence can be used. The stereoregularity is not particularly limited, and isotactic or syndiotactic and those showing various degrees of stereoregularity can be used. The copolymer may be a binary system, a ternary system, or a quaternary system, and may be a random copolymer or a block copolymer.

  Content of said base resin in the material resin composition used for the foamed resin film which comprises the porous resin layer 11 should just be 25 mass% or more and 99 mass% or less, and is 30 mass% or more and 80 mass% or less. It is preferable. If the content is 25% by mass or more, there is a tendency that the surface is not easily scratched when the foamed resin film is stretch-molded. If the content is 80% by mass or less, a sufficient number of pores contributing to light diffuse reflection can be obtained. There is a tendency to be easily.

  The foamed resin film constituting the porous resin layer 11 preferably contains 20% by mass to 75% by mass of filler. If the filler contained in the foamed resin film is 75% by mass or less in total, the foamed resin film has a high strength, and it is easy to obtain one that can withstand practical use. When the filler content is 20% by mass or more, it is easy to form sufficient pores, and preferable diffuse reflectance is easily obtained.

  As said filler contained in a foamed resin film, various inorganic fillers or organic fillers can be used. Examples of the inorganic filler include heavy calcium carbonate, precipitated calcium carbonate, calcined clay, talc, titanium oxide, barium sulfate, aluminum sulfate, silica, zinc oxide, magnesium oxide, diatomaceous earth, and the like.

  In order to adjust the pore size generated in the foamed resin film constituting the porous resin layer 11, the average particle size of the inorganic filler is preferably 0.05 μm or more and 2.0 μm or less, preferably 0.1 μm or more. A range of 1.5 μm or less is more preferable. When a filler having an average particle size of 0.05 μm or more is used, desired pores tend to be easily obtained. Moreover, the uniformity of pore size can be enhanced by using a filler having an average particle size of 2.0 μm or less.

  The foamed resin film constituting the porous resin layer 11 can be formed by a method in which uniaxial stretching or biaxial stretching is combined with general extrusion molding. As an example of a specific forming method of uniaxial stretching or biaxial stretching, after extruding the molten resin into a film using a single layer or multilayer T die or I die connected with a screw type extruder, A method of uniaxially stretching by longitudinal stretching using the peripheral speed difference of the roll group, and then a sequential biaxial stretching method that combines transverse stretching using a tenter oven, and simultaneous biaxial stretching by a combination of a tenter oven and a linear motor Examples thereof include an inflation molding method in which air is blown after a molten resin is extruded into a cylindrical shape using a single layer or multilayer die connected to a screw type extruder. The stretching temperature is a temperature that is 2 ° C. or more and 60 ° C. or less lower than the melting point of the base resin used as a material, and a temperature that is 2 ° C. or more and 60 ° C. or less higher than the glass transition point. Or less) is preferably 95 ° C. or more and 165 ° C. or less. The stretching speed is preferably 20 m / min or more and 350 m / min or less. The foamed resin film can be obtained by a method combining the above laminating method and stretching method.

The amount of pores per unit volume of the porous resin layer 11 is expressed as “porosity” and means a value calculated according to the following formula (1). The porosity of the porous resin layer 11 is preferably in the range of 25% to 80%, more preferably 30% to 58%. If the porosity is in the range of 25% or more and 80% or less, it is easy to suppress a decrease in reflectance. In the following formula (1), d1 represents the true density of the porous resin layer 11, and d0 represents the density of the porous resin layer 11 (JIS-P-8118). The true density d1 of the porous resin layer 11 is equal to the density unless the resin composition before stretching contains a large amount of air.
Porosity (%) = (1−d1 / d0) × 100 (1)

The porous resin layer 11 has a large number of fine irregularities formed on the surface due to pores formed in the vicinity of the surface. The unevenness contributes to diffuse reflection. Further, such a surface state that can contribute to diffuse reflection can be grasped as glossiness. The glossiness of the porous resin layer 11 is preferably 100 or less, more preferably 60 or less, as measured by the following method. If the glossiness is 100 or less, a desired diffuse reflectance tends to be obtained. In addition, the glossiness of the porous resin layer 11 shall be equal to the glossiness of the foamed resin film which comprises the said layer.
Glossiness: HORIBA, Ltd. Measured with a high gloss gloss checker IG-410 at a measurement angle of 60 degrees.

  According to the reflection sheet 1 in which the porous resin layer 11 having the characteristics described above is arranged as an inner layer having a three-layer structure, the light reflectance is 95% or more by setting the thickness of the porous resin layer 11 to about 70 μm. In addition, optical properties with a regular reflectance of 30% or less can be imparted to the reflective sheet 1. Further, if necessary, the reflective sheet 1 can be given a higher reflectance by further increasing the thickness of the porous resin layer 11.

  The coating layer 12 includes a base resin and a solvent as the base resin of the same layer, and if necessary, prepares a coating liquid to which other additives such as a curing agent are added, and this is used as the porous resin layer 11. It can form by the coating process (For example, the process by the well-known gravure coating method etc.) which forms a coating film by apply | coating to both both surfaces directly. The base resin in this case refers to a resin having a content ratio of 50% by mass or more in the resin layer of the same layer after molding and having the largest content ratio among the resin components of the same layer.

  The base resin of the coating layer 12, that is, the main resin of the coating liquid used in the coating process, is a resin that is used for general-purpose coating materials such as urethane and acrylic and can be coated by dissolving in a solvent. Of these, the indentation elastic modulus defined above may be selected on the condition that the indentation elastic modulus is within the above defined range in the state after the reflection sheet is formed. The main resin thus selected is mixed with a solvent and, as necessary, other additives such as a curing agent and various fillers as described above to form a coating liquid for a coating layer, which is used as a porous resin layer. The coating layer 12 having a thickness of 5 μm or less can be efficiently formed on the surface of the porous resin layer 11 while maintaining good quality stability by forming a coating film on the surface of the coating layer 11 by a known coating treatment method. it can.

  The main resin of the coating liquid used as the base resin of the coating layer 12 is particularly preferably one of an acrylic resin, a urethane resin, and an acrylic urethane resin, and among these, the above-described indentation elastic modulus Those satisfying the above conditions can be used as appropriate. Among these, acrylic resins such as urethane and PMMA can be particularly preferably used from the viewpoint of flexibility.

  Since the coating layer 12 is a layer having flexibility within a predetermined range as described above, specifically, the indentation elastic modulus of the coating layer is required to be 2000 MPa or more and 2800 MPa or less. Unlike the hard coating for improving the scratch resistance, a curing agent is not essential, and a one-component type coating solution can be preferably used. However, a necessary amount of a curing agent may be further added in an appropriate amount range in which the indentation elastic modulus of the coating layer 12 can be maintained within the above range. When a curing agent is added in an appropriate amount range to the coating liquid used when forming the coating layer 12 by a coating treatment, for example, a polyisocyanate compound having an NCO group, preferably an aliphatic or alicyclic polyisocyanate. Isocyanate compounds can be used.

  Further, when the coating layer 12 is formed by a coating process, the solvent of the coating liquid is not particularly limited, and the base resin can be dissolved or dispersed to impart applicability to the porous resin layer 11 to the coating liquid. If there is no particular limitation. Examples of such solvents include water-insoluble solvents such as toluene, xylene, butyl acetate, ethyl acetate, and ethylbenzene, and water-soluble solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. .

  In order to improve the blocking resistance of the reflective sheet 1, the coating layer 12 has 8% by mass or more of one coating layer 12B of the coating layers 12A and 12B formed on both surfaces with respect to the total resin components. It is preferable to contain a filler in the ratio of 25 mass% or less. When the filler content of the coating layer 12B is 10% by mass or more, preferable blocking resistance is easily obtained. Further, when the content is 25% by mass or less, it is possible to prevent the reflectance and the glossiness from being lowered.

  As the filler to be contained in one coating layer 12B, various inorganic fillers or organic fillers can be used. As inorganic filler, heavy calcium carbonate, precipitated calcium carbonate, calcined clay, talc, titanium oxide, barium sulfate, aluminum sulfate, silica, zinc oxide, magnesium oxide, diatomaceous earth, etc., and as organic filler, acrylic beads, Examples thereof include urethane beads.

  In order to improve the blocking resistance as the reflective sheet 1 without reducing the good optical properties of the porous resin layer 11 by dispersing it in the coating layer 12B, which is a thin film layer having a thickness of 5 μm or less, The average particle size of the inorganic filler contained in the coating layer 12B is preferably 0.05 μm or more and less than 6.0 μm, and more preferably 0.5 μm or more and 5.5 μm or less.

  The reflection sheet 1 having the above configuration has a light reflectance of 95% or more of light having a wavelength of 450 nm or more and 650 nm or less when light is input from at least the surface on which the coating layer 12A containing no filler is formed. Preferably, it is 96% or more, more preferably 97% or more, and the regular reflectance is 30% or less, preferably 25% or less. The reflective sheet 1 can have such optical characteristics by configuring the porous resin layer 11 and the coating layer 12A on the reflective surface side as described above.

In addition, the definitions of the light reflectance, diffuse reflectance, and regular reflectance in this specification are as follows.
The reflectance at 450 nm to 650 nm was measured, and the numerical values at each wavelength were averaged to obtain the reflectance and diffuse reflectance. Further, the regular reflectance was calculated from the reflectance and diffuse reflectance at each wavelength by the following formula (2), and the numerical values at each wavelength were averaged to obtain the regular reflectance. In addition, since it is difficult to strictly measure the absolute reflectance, the relative reflectance with the reference standard sample is usually used for the reflectance. In the present invention, barium sulfate is used as a comparative standard sample. The reflectance in the present invention is determined by attaching an integrating sphere attachment device (for example, integrating sphere unit ISN-723) to a spectrophotometer (for example, JASCO Corporation V-670DS), using barium sulfate as a standard plate, and using 100 as the standard plate. It is a value obtained by measuring the relative reflectance in%.

  Regular reflectance (%) = reflectance (%) − diffuse reflectance (%) (2)

  If the above-mentioned light reflectance of the reflection sheet 1 is 95% or more, most of the light leaking to the back side of the light guide plate 2 out of the light emitted from the light source 3 constituted by LED elements or the like is on the light emitting surface side. It is possible to efficiently use the light reflected from the light source 3 and emitted from the light source 3.

  The diffuse reflectance measured by the above method of the reflective sheet 1 is the average value of the reflectance of each wavelength measured in the wavelength range of 450 nm to 650 nm using an optical trap according to the method described in JIS-Z-8722. Means.

  The regular reflectance calculated by the above method of the reflective sheet 1 is 30% or less, preferably 1% or more and 25% or less. By increasing the ratio of the diffuse reflectance to the light reflectance as much as possible, the light emitted from the light source 32 is uniformly diffused over the entire screen of a liquid crystal display device such as a smartphone incorporating the liquid crystal display module 100, and the luminance Unevenness can be reduced and image quality can be improved. From the viewpoint of improving the diffuse reflectance, the smaller the regular reflectance, the better. However, since a special material such as a filler having a very narrow particle size distribution or a manufacturing method is required, it is not preferable from the viewpoint of cost. When the regular reflectance exceeds 30%, the ratio of the diffuse reflectance decreases, and the halation due to light reflection becomes too strong, which is not preferable because the display screen feels dazzling.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

<Manufacture of reflective sheet>
[Examples 1-5, Comparative Examples 1-2]
(Porous resin layer)
A foamed resin film (described as “foamed PP” in Table 1) having a thickness of 70 μm and constituting the porous resin layer of the reflective sheet of each example and comparative example was produced by the following method.
Propylene homopolymer (manufactured by Nippon Polychem Co., Ltd., trade name “Novatech PP: MA-8”, melting point 164 ° C.) 65.5% by mass, high density polyethylene (manufactured by Nippon Polychem Co., Ltd., trade name “Novatech HD: HJ580”) , Melting point 134 ° C., density 0.960 g / cm ³ ) 6.5% by mass and an inner layer composition having an average particle size of 1.5 μm and 28% by mass of calcium carbonate powder, using an extruder An unstretched film was obtained. This unstretched film was stretched 4 times in the flow direction (MD) to obtain a uniaxially stretched film. In this reference example, the flow direction (MD) means the extrusion direction when the composition is extruded using an extruder.
51.5% by mass of propylene homopolymer (Nippon Polychem Co., Ltd., trade name “Novatech PP: MA-8”, melting point 164 ° C.), high density polyethylene (Nippon Polychem Co., Ltd., trade name “Novatech HD: HJ580”) Melting point 134 ° C., density 0.960 g / cm ³ ) 3.5 mass%, calcium carbonate powder 42 mass% with an average particle diameter of 1.5 μm, titanium oxide powder 3 mass% with an average particle diameter of 0.8 μm, The outer layer composition was extruded using a die on both sides of the uniaxially stretched film obtained above using an extruder to obtain a laminate having a three-layer structure (outer layer, inner layer, and outer layer).
The laminate is stretched seven times in the width direction (direction perpendicular to the flow direction of the uniaxially stretched film laminated on the inner layer, TD), so that the total thickness is 70 μm (outer layer 15 μm, inner layer 40 μm, outer layer 15 μm). A foamed resin film (foamed PP) was obtained. The porosity of this foamed resin film was 55%.
(Coating layer)
A coating layer of 1 to 3 μm was formed on one surface (described as “reflecting surface” in Table 1) of the foamed resin film (foamed PP) by a gravure coating method. Next, a coating layer of 1 to 3 μm was formed by the gravure coating method on the other surface of the above-described foamed resin film (described as “back surface” in Table 1), and Examples 1 to 5 and Comparative Examples 1 to 2 were formed. Each reflective sheet was used. The main resin of the coating layer used at this time was as shown in Table 1 below. As a solvent for liquefying each main resin, ethyl acetate was used in Example 3, and MEK was used in Examples 1, 2, 4, 5 and Comparative Examples 1 and 2. The drying conditions were 70 ° C. and 20 to 40 seconds. Further, as shown in Table 1, only in the coating layers of Examples 4 and 5, a filler made of non-spherical pulverized fine powder silica having an average particle diameter of 5.2 μm was used as an additive at a ratio of 12.5% by mass. Added.
[Comparative Example 3]
(Joining of polyethylene terephthalate film)
Two polyethylene terephthalate films (A5-AF48, manufactured by Toray Industries, Inc., 4.5 μm thick) were prepared, and an adhesive layer was formed on one surface of the polyethylene terephthalate film by a gravure coating method. The adhesive layer used at this time was a polyurethane-based adhesive (manufactured by Rock Paint Co., Ltd., main agent Adlock RU-77T, manufactured by Rock Paint Co., Ltd., hardener lock bond JH-7, main agent: hardener = 10: 1). Including. Next, one polyethylene terephthalate film was bonded to one surface of the foamed resin film (foamed PP) used in the above-described example via an adhesive layer. Furthermore, one polyethylene terephthalate film was bonded to the other surface of the foamed resin film (foamed PP) via an adhesive layer. The reflective sheet thus obtained was used as the reflective sheet of Comparative Example 3.
[Comparative Example 4]
Comparative Example 4 was obtained by forming a reflective sheet with a single layer configuration consisting of only foamed PP without providing a coating layer on the foamed resin film (foamed PP).

<Indentation elastic modulus of coating layer>
The indentation elastic modulus of the coating layers of each Example and Comparative Example was measured by the following measurement method.
(Measuring method)
A resin layer made of the same resin as the main resin for the coating layer of each example to be measured is formed on a clean glass substrate with a thickness (50 μm) necessary for the test, and the test load F [mN] is from 0 mN. Push the Vickers indenter into the surface of the coating layer while increasing to 1 mN over 10 seconds, hold the Vickers indenter for 5 seconds at a test load of 1 mN, unload the tester from 1 mN to 0 mN over 10 seconds, and push the Vickers indenter back. Measure the displacement of the indentation depth h [μm] due to, and divide the test load F by the indentation depth h (F / h) [mN / μm] = [10 ³ N / m] = [10 ⁻³ MPa] Determined by Further, the indentation elastic modulus was measured using a Picodenter HM-500 manufactured by Fischer Instruments. The test resin layers were formed under the same drying conditions by using the same coating solution as that used for forming the film layers in the respective Examples and Comparative Examples. The results were as shown in Table 1. In addition, about the filler of the particle size range used for each Example, since there is almost no influence which has on the handleability (flexibility) by the presence or absence of the addition, about Example 4, it is a reflective surface which does not contain a filler. The indentation elastic modulus was measured for the coating layer on the side.

<Evaluation Example 1: [Evaluation of Handling (Flexibility)]>
About the reflective sheet of Example 1 to Example 5 and Comparative Example 1 to Comparative Example 4, a cylindrical metal mandrel (mandrel) of 2 mm to 32 mm imitating the cylindrical mandrel described in JIS-K5600-5-1 A sample piece (100 mm × 50 mm) was wrapped around a load of 500 g, and the handling property (flexibility) of the reflective sheet was evaluated. When the light reflecting member was wound around the cylinder, the minimum diameter of the bar where the “irreversible fold” did not occur on the light reflecting member was recorded. The evaluation criteria were as follows.
A: Minimum diameter of the bar is less than 6 mm B: Minimum diameter of the bar is 6 mm or more and less than 12 mm C: Minimum diameter of the bar is 12 mm or more

<Evaluation Example 2: [Evaluation of anti-blocking]>
The anti-blocking property was evaluated about the reflective sheet of each comparative example except Example 1 to Example 5 and the comparative example 3 whose handling property evaluation was C. Evaluation of blocking resistance was made by superimposing two light reflecting members and applying a load of 20 kg to each 5 cm x 5 cm area for 72 hours at room temperature to check whether there was blocking on the two overlapping sheets. It was done by doing. In addition, about Example 4, evaluation was performed in the state with which the reflective surface and back surface of each sheet | seat were overlapped. The evaluation criteria were as follows.
A: Blocking did not occur at all B: No material breakage, but resistance when peeling C: Blocking occurred, material broke

<Evaluation Example 3: [Evaluation of Heat Resistance (Heat Shrinkage)]>
About the reflective sheet of the comparative example (comparative example 4) except Examples 1 to 5 and Comparative Examples 1 to 3 in which the evaluation of handling property or blocking resistance was C, the heat resistance (heat shrinkage rate) was evaluated. . The heat resistance (heat shrinkage rate) was measured by the following measuring method.
(Measurement method of thermal shrinkage)
The measurement was performed as follows based on JIS C2151 (21. Dimensional change).
Samples are prepared by punching the reflective sheets of Examples and Comparative Examples into 100 mm × 100 mm squares using a small punch and a Thomson blade. Next, the dimension before heating of a sample is measured using a dimension automatic measuring device. The sample is then warmed at 90 ° C. for 30 minutes using a thermostat. The sample is then removed from the incubator and allowed to cool slowly to room temperature by placing it in an atmospheric environment. Next, the dimension after heating of a sample is measured using a dimension automatic measuring device. Then, the thermal contraction rate of the sample is calculated by dividing the dimension after heating of the sample by the dimension before heating of the sample. In addition, the following apparatus was used for the measurement of this thermal contraction rate.
Small punching machine Tester Sangyo Co., Ltd. SA-1008III type Thomson blade Koike Manufacturing Co., Ltd.
Dimensional automatic measuring device Chuo Denki Keiki Seisakusho GS-6040N
Incubator Enomoto Kasei HT320
The evaluation criteria were as follows.
A: Heat shrinkage rate less than 0.6% B: Heat shrinkage rate 0.6% or more and less than 1% C: Heat shrinkage rate 1% or more

<Evaluation Example 4: [Evaluation of Optical Properties (Light Reflectance)]>
The reflective sheet of Example 1 to Example 5 was evaluated for optical characteristics (light reflectance). The optical characteristics (light reflectance) were measured by the following measuring method.
(Measurement method of light reflectance)
An integrating sphere attachment device (integrating sphere unit ISN-723) is attached to a spectrophotometer (Spectrophotometer V-670DS manufactured by JASCO Corporation), and the light reflectance is measured in 1 nm increments in the wavelength range of 400 nm to 800 nm. The light reflectance at a wavelength of 550 nm was extracted. In addition, barium sulfate is used as the standard plate, and the light reflectance is a relative value of barium sulfate.
The evaluation criteria were as follows.
A: Light reflectivity 97% or more B: Light reflectivity 95% or more and less than 97% C: Light reflectivity less than 95%

<Evaluation Example 5: [Relationship Between Film Thickness of Coating Layer and Thermal Shrinkage Ratio]>
For the reflective sheet of Example 1, the effect of the thickness of the coating layer on the heat shrinkage resistance was evaluated. FIG. 3 shows the thermal contraction rate when the thickness of the coating layer is changed between 0.5 μm and 5 μm. The heat shrinkage rate did not exceed 0.7 at any coating layer thickness, and the heat shrinkage resistance was good.

  From the results of the evaluation examples 1 to 5, the reflective sheet of the present invention has both the thermal formability and the heat resistance while maintaining the optical characteristics, and also maintains the good handling properties, so that the backlight of the edge light system is used. It was confirmed that it is a reflective sheet that can also contribute to the improvement of quality and productivity.

DESCRIPTION OF SYMBOLS 1 Reflection sheet 11 Porous resin layer 12, 12A, 12B Cover layer 2 Light guide plate 3 Light source 4 Liquid crystal panel 10 Optical module 20 Backlight 100 Liquid crystal display module

Claims (10)

A porous resin layer based on an olefin resin,
A reflective sheet comprising a coating layer laminated on both surfaces of the porous resin layer,
A reflective sheet having a thickness of the coating layer of 0.5 μm or more and 5 μm or less, and an indentation elastic modulus of the coating layer of 2000 MPa or more and 2800 MPa or less. The base resin of the porous resin layer is a polypropylene resin,
The reflective sheet according to claim 1, wherein a base resin of the coating layer is one of an acrylic resin, a urethane resin, and an acrylic urethane resin. The thickness of the porous resin layer is 50 μm or more and 95 μm or less,
The thickness of each layer of the coating layer laminated on both surfaces of the porous resin layer is 0.5 μm or more and 5 μm or less,
The reflective sheet according to claim 1, wherein the total thickness of all layers is 100 μm or less.   Among the coating layers, the coating layer laminated on one surface of the porous resin layer contains a filler, and the coating layer laminated on the other surface of the porous resin layer does not contain a filler. The reflective sheet according to any one of claims 1 to 3.   The reflection sheet according to any one of claims 1 to 4, wherein the porous resin layer is a stretched resin film containing a filler, and the porosity of the porous resin layer is 25% or more and 80% or less. It is a manufacturing method of the reflective sheet according to claim 1,
A method for producing a reflective sheet, in which a coating liquid comprising a base resin of a coating layer and a solvent is directly applied to both surfaces of the porous resin layer to form the coating layer.   An optical module for an edge light type backlight, wherein the reflection sheet according to any one of claims 1 to 5 is disposed opposite to a light guide plate. The reflective sheet according to claim 5 is an optical module for backlight of an edge light system, which is disposed to face the light guide plate,
The reflective sheet has one surface on which a coating layer containing no filler is formed facing the light guide plate, and the other surface on which the coating layer containing a filler is formed faces away from the light guide plate. The optical module is arranged as follows.   An edge light type backlight comprising the optical module according to claim 7 and a light source for edge light.   A liquid crystal display module in which the backlight according to claim 9 and a liquid crystal panel are arranged to face each other.

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