JP2005241919A - Optical diffusing sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical diffusing sheet which has high optical transmissivity and emits diffused light with less variations in luminance and is superior in concealing the dots on the light guide plate, while suppressing wrinkles due to heat expansion and contraction, and to also provide an optical diffusion sheet which is able to improve its concealing capability and to further suppress the wrinkles due to heat expansion and contraction. <P>SOLUTION: This optical diffusing sheet 1 is built in a constitution, containing 15-50 mass% of A-glass particles 5 in a single layer sheet 1a made of light transmissive resin. Further, A-glass particles are contained 15-50 mass% in the core layer which is a sheet stacked with a core layer of light transmissive resin and a surface layer, and particles of these A-glass particles are contained in the surface layer at a content smaller or larger than the A-glass particles of the core layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a backlight unit of a liquid crystal display, particularly an edge light type backlight unit, an electric signboard, a lighting cover, an arcade, a daylighting plate, a blindfolding plate for a balcony, and the like.

  A general edge light type backlight unit of a liquid crystal display includes a light guide plate having dots for light diffusion printed on the back surface, and a light source (cold cathode tube, LED disposed at one or both ends of the light guide plate. Etc.), a light diffusion sheet overlaid on the light guide plate, and a lens film (prism sheet) overlaid on or above the light diffusion sheet.

  The light diffusion sheet incorporated in such a backlight unit diffuses the light from the light guide plate uniformly, thereby preventing the dots from being visually recognized on the display screen, and suppressing the light loss to liquid crystal diffused light. It plays the role of releasing uniformly to the panel surface.

  As such a light diffusing sheet, the applicant of the present invention is a single-layer sheet made of a translucent resin having irregularities formed on both sides, and has a specific range of average surface roughness and surface area ratio. A light diffusing sheet in which a light diffusing agent such as talc is further added to the layer sheet has been proposed (Patent Document 1).

This light diffusing sheet has advantages such as reducing light loss and emitting uniform diffused light with little variation in luminance. Especially, a light diffusing sheet containing a light diffusing agent has good dot concealing properties. Thus, generation of wrinkles due to thermal expansion and contraction can be suppressed.

JP 2002-221612 A

  The object of the present invention is to use A glass particles as a light diffusing agent to prevent generation of wrinkles and provide dot concealing properties as well as to significantly improve light transmittance and luminance. Is.

  In order to solve the above-mentioned problems, the first light diffusion sheet according to the present invention is characterized in that 15 to 50% by mass of A glass particles is contained in a single layer sheet made of a translucent resin. .

  And the 2nd light diffusion sheet which concerns on this invention contains 15-50 mass% of A glass particles in the said core layer of the lamination sheet by which the core layer and surface layer which consist of translucent resin were laminated | stacked and integrated. In addition, the surface layer contains A glass particles at a lower content than the content of the A glass particles in the core layer.

  Further, in the third light diffusion sheet according to the present invention, 15 to 50% by mass of A glass particles is contained in the core layer of the laminated sheet in which the core layer and the surface layer made of a translucent resin are laminated and integrated. In addition, the surface layer contains A glass particles at a higher content than the content of the A glass particles in the core layer.

  In the first, second and third light diffusion sheets, fine irregularities are formed on at least one side of the sheet, or an inverted polygonal pyramid, an inverted truncated polygonal pyramid, an inverted cone on at least one side of the sheet It is preferable that the fine recessed part which has either a shape or an inverted truncated cone shape is formed.

  When the first light diffusion sheet according to the present invention is incorporated on the light guide plate of the backlight unit, most of the light traveling while appropriately reflecting the inside of the light guide plate is combined with the light incident surface of the light diffusion sheet. The light enters the sheet from one side (back side) and is sufficiently diffused by the light diffusing action of the A glass particles contained in the sheet in an amount of 15 to 50% by mass to pass through the sheet. Is released from the opposite surface (surface). A glass particle is a particle that has a small difference in optical refractive index from the translucent resin of the sheet and permeates light well, and substantially transmits light even if it is contained in the sheet in an amount of 15 to 50% by mass. Therefore, in addition to dot concealability (light diffusibility), this light diffusing sheet has good light transmittance, luminance, and the like, and there is almost no variation in luminance. The light diffusion sheet is heated by the heat of the light guide plate because the linear expansion coefficient of the sheet decreases and the elastic modulus of the sheet increases due to the A glass particles contained in 15 to 50% by mass of the light diffusion sheet. Even so, the generation of wrinkles is sufficiently suppressed. Therefore, the light diffusing sheet containing the A glass particles is comprehensively determined for various properties required for the light diffusing sheet, such as dot hiding property (light diffusing property), light transmittance, luminance, and antifungal property. For example, it has an overall performance superior to that of a light diffusing sheet containing other light diffusing agents such as calcium carbonate and E glass particles.

  Since the second and third light diffusing sheets according to the present invention also contain A glass particles in the core layer and the surface layer of the laminated sheet made of a translucent resin, similarly to the first light diffusing sheet, Various performances required for light diffusing sheets such as dot concealment (light diffusibility), light transmittance, brightness, and anti-mold properties are good, and it is comprehensive compared to light diffusing sheets containing other light diffusing agents. Excellent performance.

  The second light diffusion sheet is formed by using a multi-layer coextrusion molding machine to form a core layer by extruding a translucent resin containing 15 to 50% by mass of A glass particles as described later. It is manufactured by a method such as forming a laminated sheet by extruding a translucent resin containing A glass particles at a lower content than the above to form a surface layer. When the translucent resin for forming the surface layer having a low content of the A glass particles is superimposed on the upper and lower sides of the translucent resin for forming the core layer containing 50% by mass, the A glass particles are formed around the extrusion port. Since it becomes more difficult to adhere, it becomes possible to minimize the occurrence of line marks due to the eye-sag phenomenon, and the productivity is greatly improved.

  In the third light diffusion sheet, since the surface layer having a high content of A glass particles is laminated on the core layer containing 15 to 50% by mass of A glass particles, dot concealability (light Performances such as diffusibility, light transmittance, brightness, and antifungal properties can be exhibited, and these various performances are improved as compared with the case of only the core layer.

  In the first, second and third light diffusing sheets, any one of fine irregularities, an inverted polygonal pyramid, an inverted truncated polygonal pyramid, an inverted cone, and an inverted truncated cone on at least one side of the sheet In the case of forming a fine recess having the shape of the above, light easily enters due to these unevenness and recess, or light is diffused well and emitted, so in particular, dot concealment (light diffusibility), light transmittance, Various performances of luminance are further improved.

  Hereinafter, although typical embodiment of this invention is described based on drawing, this invention is not limited only to these embodiment.

  FIG. 1 is a schematic cross-sectional view showing a first light diffusion sheet according to the present invention, and shows a state in which it is incorporated in an edge light type backlight unit indicated by phantom lines.

  The light diffusing sheet 1 is obtained by containing A glass particles 5 in a uniformly dispersed state in a single layer sheet 1a made of a translucent resin and forming fine irregularities on both sides 1c and 1c of the sheet.

  As the translucent resin of the single layer sheet 1a, polycarbonate, polyester, polyethylene, polypropylene, polyolefin copolymer (for example, poly-4-methylpentene-1 etc.), polyvinyl chloride, cyclic polyolefin (for example, high total light transmittance) For example, thermoplastic resins such as cyclopolyolefin, acrylic resin, polystyrene, and ionomer are preferably used.

  Among these, polypropylene has good crystallinity and transparency. When the crystallinity is increased, the elastic modulus is improved and heat deformation and wrinkles are less likely to occur. In particular, polypropylene having a crystallinity of 30 to 80% has rigidity. In addition to being large, it has a refractive index of 1.49 to 1.52 that approximates the refractive index of A glass particles (1.50 to 1.53), so that the total light transmission amount increases and the light diffusion sheet has high luminance. Can be obtained. A more preferable crystallinity of polypropylene is 40 to 70%. The particularly preferred crystallinity is 42 to 65%. The refractive index of polypropylene having a crystallinity in this range is 1.50 to 1.51, which is substantially the same as the refractive index of A glass, and the total light transmittance, luminance. Both increase.

  The A glass particles 5 contained in the single-layer sheet 1a have a role of diffusing light and a role of preventing the occurrence of wrinkles by suppressing thermal expansion and contraction of the sheet, and have an average particle diameter of 5 to 50 μm. The smooth spherical fine particles are preferably used. A glass particles having an average particle size of less than 5 μm are disadvantageous in that the particles themselves are difficult and expensive to manufacture, and A glass particles having an average particle size of more than 50 μm are sheared or compressed by screws during extrusion. This is not preferred because there are inconveniences such as poor appearance and little improvement in tensile elastic modulus at high temperatures due to breakage.

A glass is a glass having an alkali (Na ₂ O, K ₂ O) content of 0.8 to 20%, and is also called alkali-containing glass or soda-lime glass. This A glass has a refractive index of 1.50 to 1.53 as described above, and other light diffusing agent, for example, an E glass having an alkali (Na ₂ O, K ₂ O) content of less than 0.8%. Those with a smaller refractive index than other glass particles such as (alkali-free glass), inorganic particles such as calcium carbonate, and metal oxide particles such as titanium oxide, and a slight difference in refractive index from the translucent resin In addition, since the glass particle itself is transparent and transmits light well, when the A glass particles are contained in the single-layer sheet 1a of the translucent resin, the light diffusing sheet 1 having a large amount of light transmission and high luminance is obtained. be able to. In addition, when the A glass particles 5 are contained in the single layer sheet 1a, the rigidity of the single layer sheet 1a is increased and the linear expansion coefficient is lowered, so that the light diffusing sheet 1 (single layer sheet 1a) has an antifungal property. improves. In addition, since the A glass particles 5 are spherical fine particles with a smooth surface, for example, compared to a fine scaly light diffusing agent such as talc, the eye-gear phenomenon at the time of extrusion molding is suppressed, and it is difficult to form linear traces. Become.

As a preferable specific example of the A glass particle 5, GB210 [trade name, average particle diameter of 18 μm, manufactured by Potters Ballotini Co., Ltd.] (composition: SiO ₂ (72%), Al ₂ O ₃ (2.0%)) Fe ₂ O ₃ (0.1%), Na ₂ O + K ₂ O (13.5%), MgO (3.4%), CaO (9.0%)) and EMB20 [Potters Barotini Product name, average particle size 10 μm] (composition: SiO ₂ (55.5%), Al ₂ O ₃ (14.0%), Fe ₂ O ₃ (0.2%), Na ₂ O + K ₂ O (0.5%), MgO (1.0%), CaO (23.1%)) and the like.

  The content of the A glass particles 5 in the single layer sheet 1a needs to be 15 to 50% by mass. If the amount is less than 15% by mass, light diffusion becomes insufficient, so that the dot concealing property is lowered and thermal expansion and contraction is also insufficiently suppressed, so that the light diffusion sheet 1 is likely to be wrinkled. On the other hand, if the A glass particles 5 are more than 50% by mass, the light transmittance and luminance of the light diffusing sheet 1 are reduced due to scattering, reflection, and absorption by the A glass particles 5, so that a back incorporating such a light diffusing sheet is incorporated. Even if the light unit is used to illuminate the display from behind, the display is difficult to see. The more preferable content rate of the A glass particles 5 is 25 to 45% by mass.

  The thickness of the light diffusion sheet 1 (single layer sheet 1a) may be determined according to the application. For example, when it is incorporated in an edge light type backlight unit, the thickness is suitably 60 to 300 μm. If the thickness is less than 60 μm, the light transmittance and luminance are improved, but the dot hiding property (light diffusibility) may be lowered, and the sheet rigidity may be lowered and the anti-mold property may be lowered. On the other hand, if the thickness is greater than 300 μm, the light diffusing sheet 1 has improved anti-molding and concealing properties, but the light transmittance and luminance are reduced, and the display on the display is difficult to see. A more preferable thickness of the light diffusion sheet 1 (single layer sheet 1a) is 100 to 250 μm.

  Moreover, when incorporating in the direct type backlight unit which arrange | positions a light-diffusion sheet just above a light source, it is suitable to set to 1-3 mm. This is because if the thickness is 1 mm or less, the rigidity is insufficient and the light can be seen through, and if it is 3 mm or more, the light transmittance and the luminance are lowered.

  Both surfaces 1c and 1c of the light scattering sheet 1 are formed with fine irregularities so that the arithmetic average roughness Ra is 0.5 to 10.0 [mu] m, preferably 0.6 to 8.0 [mu] m. As described above, both surfaces having an arithmetic average roughness Ra of 0.5 to 10.0 μm are easy to allow light to enter uniformly from the light guide plate and have high light transmittance, so that light loss is greatly reduced and uniform. Strongly diffused diffused light can be emitted. It is desirable to form the unevenness in a shape with a rounded tip, and in this way, when the light scattering sheet 1 is incorporated in the backlight unit, the upper and lower lens films 3 and the light guide plate 2 may be damaged. There will be nothing. The arithmetic average roughness Ra on the front surface and the arithmetic average roughness Ra on the back surface may be the same or different.

  The light diffusing sheet 1 having the above-described configuration is a raw material translucent resin containing 15 to 50% by mass of A glass particles using, for example, an extrusion molding machine (mixed with various additives as necessary). Is extruded into a film or sheet to form a single-layer sheet 1a, and the single-layer sheet 1a is passed between a pair of upper and lower embossed rolls or pressed with a press plate having fine irregularities. The sheet is manufactured by forming fine irregularities on both surfaces 1c and 1c of the sheet. The A glass particles contained in the translucent resin are spherical fine particles with a smooth surface and are less likely to cause the eye discoloration phenomenon than other light diffusing agents such as talc in the above extrusion molding process. This makes it possible to improve the productivity by reducing the frequency of the above.

  As shown in FIG. 1, the light diffusing sheet 1 is placed on a light guide plate 6 on a reflection sheet 7, and a lens film 8 is overlaid thereon, and a light source 9 is provided on the side of the light guide plate 6 to provide an edge. When a light type backlight unit is assembled and light is incident on the light guide plate 6 from the light source 9, as described above, the back surface 1c on which the unevenness of the light diffusion sheet 1 is formed has an arithmetic average roughness suitable for incident light. Therefore, most of the light traveling while appropriately reflecting and emitting light inside the light guide plate 6 enters the sheet 1 from the entire back surface 1c of the sheet 1 substantially uniformly. And the light which entered into the sheet | seat 1 is fully spread | diffused with the A glass particle 5 contained in 15-50 mass% in the sheet | seat 1, and also on the sheet | seat surface 1c which has arithmetic mean roughness suitable for a spreading | diffusion. Since it is strongly and uniformly diffused and emitted toward the lens film 8, dot concealability (light diffusibility) is good. In particular, the A glass particle 5 is a particle that has a small difference in light refractive index from the light-transmitting resin of the sheet 1 and permeates light well. Even if it is contained in the sheet in an amount of 15 to 50% by mass, Since the transmission is not substantially hindered, the light diffusing sheet 1 has good light transmittance and luminance, and hardly causes variations in luminance. The light diffusing sheet 1 is excellent in antifungal property because the linear expansion coefficient is lowered and the elastic modulus at high temperature is improved by the A glass particles 5 contained in 15 to 50% by mass. Even with heat, wrinkles are unlikely to occur in the light diffusion sheet 1. Therefore, this light diffusion sheet 1 can be used for other light diffusions if the various properties required for the light diffusion sheet such as dot hiding property (light diffusion property), light transmittance, luminance, and anti-mold properties are comprehensively determined. The overall performance is superior to that of a light diffusion sheet containing an agent.

  FIG. 2 is a schematic cross-sectional view showing a second light diffusion sheet according to the present invention.

  In this light diffusion sheet 2, 15 to 50 mass% of A glass particles 5 are contained in the core layer 2 a of the laminated sheet 2 d in which the core layer 2 a made of a translucent resin and the surface layers 2 b and 2 b are laminated and integrated. The surface layers 2b and 2b contain the A glass particles 5 at a lower content than the content of the A glass particles 5 in the core layer 2a, and fine irregularities are formed on the sheet surfaces 2c and 2c. Has been.

  The arithmetic average roughness of the translucent resin, the A glass particles 5, and the sheet surfaces 2c and 2c of the core layer 2a and the surface layers 2b and 2b of the light diffusion sheet 2 is the same as that of the single layer sheet 1a of the light diffusion sheet 1 described above. Since it is the same as the arithmetic average roughness of the translucent resin, the A glass particles 5, and the sheet surfaces 1c and 1c, the description is omitted.

  The content of the A glass particles 5 in the core layer 2a is 15 to 50% by mass, similar to the content of the light diffusion sheet 1 described above, but the content of the A glass particles 5 in the surface layers 2b and 2b is as described above. Thus, it is set as the content rate lower than the content rate of the A glass particle 5 of the core layer 2a. Thus, when the content rate of the A glass particles 5 in the surface layers 2b and 2b is lower than the content rate of the core layer 2a, when the light diffusing sheet 2 is manufactured, in the step of multilayer coextrusion molding, the A glass There is an advantage that the particles 5 are less likely to adhere to and grow around the extrusion port and the productivity can be improved by further suppressing the eye stain phenomenon. From the viewpoint of suppressing the eye stain phenomenon, the lower the content of the surface layer 2b and the A glass particles 5 of 2b, the better. However, if it is too low, the linear expansion coefficient of the surface layers 2b and 2b increases. In addition, since the elastic modulus is lowered and the anti-mold property of the light diffusion sheet 2 may be lowered, it is preferable to contain at least 3% by mass, preferably 10% by mass or more.

  The thickness of the core layer 2a, the thicknesses of the surface layers 2b and 2b, and the total thickness of the light diffusion sheet 2 may be appropriately determined according to the application. For example, when incorporated in an edge light type backlight unit, The thickness of the layer 2a is set to 50 to 200 μm, the total thickness of the light diffusing sheet 2 is set to 60 to 300 μm, and the thickness of the surface layer 2b is determined within a range that satisfies the thickness condition of the core layer 2a and the thickness of the entire sheet at the same time. It is preferable to do. If the thickness of the core layer 2a is less than 50 μm, and the thickness of the entire sheet 2 is less than 60 μm, the elastic modulus at high temperature is lowered, which may lead to a decrease in the fender, and the light diffusion is also weakened so that it is concealed. There is also a risk of lowering. On the other hand, when the thickness of the core layer 2a is greater than 200 μm and the thickness of the entire sheet 2 is greater than 300 μm, the light transmittance and luminance are reduced, and the display on the display is difficult to see. A more preferable thickness of the core layer 2a is 60 to 180 μm, a further preferable thickness is 70 to 120 μm, a more preferable thickness of the entire sheet 2 is 80 to 200 μm, and a further preferable thickness is 100 to 150 μm. The thickness of the surface layer 2b may be determined within a range that satisfies the thickness condition of the core layer 1a and the thickness condition of the entire sheet as described above, but is usually about 4 to 50 μm, preferably about 5 to 30 μm, Preferably it is about 6-15 micrometers.

  On the other hand, when incorporated in a direct type backlight unit, the core layer has a thickness of 0.8 to 2.5 mm, the surface layer has a thickness of 0.1 to 0.2 mm, and the light diffusion sheet 2 has a thickness of 1.0 to It is appropriate to set it to 3.0 μm.

  The light diffusing sheet 2 having the above-described configuration is obtained by using a three-layer coextrusion molding machine, for example, a raw material translucent resin containing 15 to 50% by mass of A glass particles (if necessary, various additives). The mixture layer is extruded into a film or a sheet, and at the same time, the raw translucent resin containing A glass particles at a lower content than the above is overlapped and extruded. A laminated sheet 2d having a three-layer structure in which the surface layers 2b and 2b are laminated integrally is formed, and the laminated sheet 2d is passed between a pair of upper and lower embossing rolls, or a press plate having fine irregularities. By pressing, it is manufactured by forming fine irregularities on both surfaces 2c, 2c of the sheet. When the three-layer coextrusion molding as described above, the A glass particle content in the translucent resin for forming the upper and lower surface layers is low, so that the A glass particles are more difficult to adhere and grow around the extrusion port, It is possible to minimize the line marks due to the eye-sag phenomenon, and the productivity is greatly improved.

  And also this 2nd light-diffusion sheet 2 contains 15-50 mass% of A glass particles 5 in the core layer 2a which consists of translucent resin, and contains A glass particles 5 lower than it in the surface layers 2b and 2b. As with the first light diffusing sheet, the properties required for the light diffusing sheet such as concealment (light diffusibility), light transmittance, luminance, and anti-mold properties are good. The overall performance is superior to the light diffusing sheet containing other light diffusing agents.

  FIG. 3 is a schematic cross-sectional view showing a third light diffusion sheet according to the present invention.

  This light diffusion sheet 3 contains 15 to 50% by mass of A glass particles 5 in the core layer 3a of the laminated sheet 3d in which the core layer 3a made of a translucent resin and the surface layers 3b and 3b are laminated and integrated. The surface layers 3b and 3b contain the A glass particles 5 at a content higher than the content of the A glass particles 5 in the core layer 3a, and fine irregularities are formed on the sheet surfaces 3c and 3c. Has been.

  Translucent resin forming the core layer 3a and the surface layers 3b, 3b of the third light diffusion sheet 3, A glass particles 5, arithmetic average roughness of the sheet surfaces 3c, 3c, the thickness of the core layer and the surface layer, The total thickness of the light diffusion sheet 3 is the above-described translucent resin of the light diffusion sheet 2, the A glass particles 5, the arithmetic average roughness of the sheet surfaces 2c and 2c, the thickness of the core layer 2a and the surface layer 2b, and the light diffusion sheet. Since the thickness of each of the two is the same, description thereof is omitted.

  The third light diffusing sheet 3 is different from the second light diffusing sheet 2 in that the content of the A glass particles 5 contained in the surface layer 3b is higher than that of the core layer 3a. When the content in the surface layer 3b is increased, light diffusion occurs intensively by the surface layer 3b, dot concealability (light diffusibility) is improved, rigidity is improved, and rigidity of the entire light diffusion sheet 3 is also improved. improves. In addition, wrinkles are less likely to occur due to the improved rigidity of the surface layer 3b. Thus, the A glass particles 5 contained in the core layer 3a and the A glass particles 5 contained in the surface layer make it possible to conceal the dot of the light diffusion sheet 3 (light diffusibility), the light transmittance, the brightness, and the fender. Various performances such as properties can be further improved.

  If the content of the A glass particles 5 to be contained in the surface layer 3b is too large, the A glass exposed or protrudes from the surface layer 3b will increase, so that it will fall off, reduce the strength of the light diffusion sheet 3, Inconveniences such as lowering the temperature occur, and therefore, it is preferably up to 70% by mass. More preferably, it is 25-60 mass%.

  This third light diffusing sheet 3 is produced in the same manner as the second light diffusing sheet 2 except that the content of the A glass particles 5 contained in the translucent resin forming the surface layer 3b is increased. Therefore, description of the manufacturing method is omitted.

  FIG. 4 is a schematic cross-sectional view showing another embodiment of the first light diffusion sheet according to the present invention.

  This light diffusing sheet 4 contains A glass particles 5 in a uniformly dispersed state in a single-layer sheet 4a made of a translucent resin, and arrayed with fine recessed portions 4d having inverted polygonal pyramids on one side 4b of the sheet, Fine irregularities are formed on the other surface 4c.

  The concave portion 4d has an inverted regular quadrangular pyramid shape in FIG. 4, and the inclination angle of the inclined surface is about 15 to 70 °. The concave portion 4d is not limited to the above-described inverted regular quadrangular pyramid shape, but may have other shapes such as an inverted polygonal pyramid shape, an inverted truncated polygonal pyramid shape, an inverted cone shape, and an inverted truncated cone shape. In the case of the inverted polygonal cone or inverted truncated polygonal pyramid-shaped recess 4d, the inclination angle of the inclined surface is preferably about 15 to 70 ° as described above, and the inverted cone or inverted truncated cone In the case of the shaped recess 4d, it is preferable that the inclination angle of the ridge line is 15 to 70 °. The inverted truncated polygonal pyramid refers to a shape obtained by cutting the top of the inverted polygonal pyramid, and the inverted truncated cone refers to a shape obtained by cutting the top of the inverted cone.

  When the light diffusion sheet 4 having such a fine recess 4d formed on one side 4b is incorporated into an edge light type backlight unit so that the recess 4d becomes a light exit surface, the light transmitted through the light diffusion sheet 4 is recessed. Since the light that is refracted by the 4d inclined surface and exits is condensed at the center, a sheet with high luminance can be obtained.

  Since other structures, such as translucent resin, A glass particle, content rate, and unevenness on the other surface, are the same as those of the first light diffusion sheet 1, description thereof is omitted.

  The light diffusing sheet 4 is manufactured in the same manner as the first light diffusing sheet 1 except that the shape of the upper embossing roll is changed to a roll in which the projections of regular square pyramids are aligned. A description of the method is omitted.

  Needless to say, the recess 4 d can be applied to the second light diffusion sheet 2 or the third light diffusion sheet 3.

  Next, more specific examples and comparative examples of the present invention will be described.

[Example 1]
Using an extrusion molding machine, the thickness of 130 μm of polypropylene containing 30% by mass of the above-mentioned GB210 [trade name, average particle diameter of 18 μm, refractive index of 1.51] manufactured by Potters Ballotini Co., Ltd.] as A glass particles A single-layer sheet was formed by extruding into a sheet shape, and the single-layer sheet was passed between upper and lower embossing rolls to produce a light diffusion sheet having fine irregularities on both sides.

  When DEKTAK II [manufactured by Nippon Vacuum Technology Co., Ltd.] was used and the above-mentioned light diffusion sheet was measured for arithmetic average roughness Ra within a measurement range of 5 mm in length, Ra on the back surface serving as the light incident surface was 1. The Ra of the surface to be 1 μm and the light exit surface was 2.7 μm.

  About said light-diffusion sheet, when total light transmittance and haze were measured using haze meter NDH2000 [made by Nippon Denshoku Industries Co., Ltd.], total light transmittance was 81.2% and haze was 90.6%. Met.

Further, the linear expansion coefficient at 20 ° C. of the above light diffusion sheet was measured using TMA8140C (manufactured by Rigaku Corporation), and it was 4.1 × 10 ⁻⁵ / ° C.

  Furthermore, the storage elastic modulus at 60 ° C. of the above light diffusion sheet was measured using DMS6100 [manufactured by Seiko Instruments Inc.] and found to be 1180 MPa.

  Moreover, when the crystallinity degree of the polypropylene of the said sheet | seat was measured by the method of the differential thermal analysis (DSC) (measurement conditions: temperature rising 10 degree-C / min, -20-220 degreeC), the degree of crystallinity was 43%. .

Next, the above light diffusion sheet is placed on the light guide plate of the edge light type backlight unit for liquid crystal display, the light source is turned on, and a luminance meter [Minolta Co., Ltd. manufactured at a distance of 20 cm from the light diffusion sheet. Ft-1 ° p] and the luminance was measured to be 1284 cd / m ² . At the same time, it was visually observed whether or not the dots on the back surface of the light guide plate were concealed. As a result, the dots were concealed and could not be visually recognized, and the dot concealability was good. Furthermore, when the presence or absence of wrinkles was visually observed, no wrinkles were generated.

  These measurement results and observation results are listed in Table 1 below.

[Comparative Examples 1 and 2]
130 μm in the same manner as in Example 1 except that 30% by mass of E glass particles [EMB20 manufactured by Potters Ballotini Co., Ltd., average particle size 10 μm, refractive index 1.54] was contained instead of A glass particles. A light diffusing sheet having a single layer structure of Comparative Example 1 having a thickness of 10 mm was prepared. Moreover, it replaced with A glass particle and carried out similarly to Example 1 except having contained 30 mass% of acrylic beads [MB20X-5 made from Sekisui Plastics Co., Ltd., average particle diameter of 5 micrometers, refractive index 1.49]. A light diffusing sheet having a single layer structure of Comparative Example 2 having a thickness of 130 μm was prepared.

  About the light-diffusion sheet | seat of these comparative examples 1 and 2, it carried out similarly to Example 1, and the total light transmittance, haze, the linear expansion coefficient in 20 degreeC, the storage elastic modulus in 60 degreeC, a brightness | luminance, dot hiding property, arithmetic average The roughness and the presence of wrinkles were examined. The results are also shown in Table 1 below.

[Comparative Example 3]
A A single-layer sheet of Comparative Example 3 having a thickness of 130 μm was prepared in the same manner as in Example 1 except that polypropylene containing no A glass particles was used. The total light transmittance, haze, linear expansion coefficient at 20 ° C., storage elastic modulus at 60 ° C., luminance, dot hiding property, arithmetic average roughness, presence of wrinkles, arithmetic average roughness, presence of wrinkles were examined. The results are also shown in Table 1 below. The refractive index of this polypropylene was calculated to be 1.51.

  In Table 1, ◯ indicates that the dot concealability is good and it is difficult to visually recognize the dots, Δ indicates that the dot concealability is slightly poor and the dots are slightly visible, and × indicates that the dot concealability is poor and the dot Indicates that visual recognition is possible.

  As can be seen from Table 1, Comparative Example 3, which does not contain a light diffusing agent such as A glass, E glass, and acrylic beads, has poor haze, linear expansion coefficient, elastic modulus, and so on. It turns out that it cannot be used as a diffusion sheet.

In Comparative Example 2 containing acrylic beads as a light diffusing agent, although there is no dot hiding property and wrinkle generation, the linear expansion coefficient is twice that of Example 1 and Comparative Example 1, and also in terms of elastic modulus. It can be seen that the sheet is about 200 MPa worse and expands and contracts. It can also be seen that the luminance is about ²⁰ cd / m ² worse than that in Example 1. Therefore, it can be seen that Comparative Example 2 is worse than the light diffusion sheet of Example 1 in terms of antifungal properties and luminance.

On the other hand, it can be seen that Comparative Example 1 containing E glass as a light diffusing agent is slightly better in total light transmittance than Example 1, but the luminance is about 30 cd / m ² worse. This indicates that when incorporated in the backlight unit, the light diffusing sheet of Example 1 provides a brighter screen than the light diffusing sheet of Comparative Example 1.

  From these facts, the light diffusing sheet containing 30% by mass of the A glass particles in the single layer sheet has dot hiding property (light diffusing property), light transmittance, light transmittance at 550 nm, luminance, anti-mold property and the like. Comprehensively determining various properties required for the light diffusion sheet, it can be seen that it has an overall performance superior to that of the light diffusion sheet containing E glass particles and acrylic beads.

It is a schematic cross section which shows the 1st light diffusion sheet which concerns on this invention, Comprising: The state integrated in the backlight unit shown with a virtual line is shown. It is a schematic cross section which shows the 2nd light-diffusion sheet which concerns on this invention. It is a schematic cross section which shows the 3rd light-diffusion sheet which concerns on this invention. It is a schematic cross section which shows other embodiment of the 1st light-diffusion sheet which concerns on this invention.

Explanation of symbols

1, 2, 3, 4 Light diffusing sheet 1a Single layer sheet 1c, 2c, 3c, 4c Sheet both sides 2a, 3a Core layer 2b, 3b Surface layer 2d, 3d Laminated sheet 4d Recessed part 5 Light diffusing agent 6 Light guide plate 8 Lens film (Prism sheet)
9 Light source

Claims (5)

  A light diffusing sheet comprising 15 to 50% by mass of A glass particles in a single layer sheet made of a translucent resin.   The core layer of the laminated sheet in which the core layer and the surface layer made of a translucent resin are laminated and integrated contains 15 to 50% by mass of A glass particles, and the A glass particles are contained in the core layer in the surface layer. A light diffusion sheet, which is contained at a lower content than the content of the A glass particles.   The core layer of the laminated sheet in which the core layer and the surface layer made of a translucent resin are laminated and integrated contains 15 to 50% by mass of A glass particles, and the A glass particles are contained in the core layer in the surface layer. A light diffusion sheet, which is contained at a higher content than the content of the A glass particles.   The light diffusion sheet according to any one of claims 1 to 3, wherein fine irregularities are formed on at least one surface of the sheet.   2. A fine recess having any one of an inverted polygonal pyramid shape, an inverted truncated polygonal pyramid shape, an inverted cone shape, and an inverted truncated cone shape is formed on at least one surface of the sheet. The light-diffusion sheet in any one of -3.

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