JP2011075890A - Light diffusion sheet, method for manufacturing light diffusion sheet and light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion sheet having high light diffusion and high light transmission. <P>SOLUTION: The light diffusion sheet contains polystyrene resin, with number of bubbles per cm<SP>2</SP>of a sheet face of 1×10<SP>7</SP>, and a thickness of 0.3-1.0 mm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light diffusion sheet, a method for manufacturing a light diffusion sheet, and a light emitting device.

  Conventionally, this type of light diffusion sheet has been used as, for example, an illumination cover, a light diffusion plate of a display, or the like.

  As such a light diffusion sheet, for example, rod-shaped bubbles are dispersed, and the axial direction of the rod-shaped bubbles is parallel to the sheet surface and directed in one direction (for example, Patent Documents). 1) or using a resin as a base material, including bubbles having an expansion ratio of 1.5 or less and an average particle diameter of 0.5 to 50 μm, a total light transmittance of 40 to 80%, and a parallel light transmittance A light diffusion plate (for example, Patent Document 2) of 6.5% or less is known.

JP 2004-079522 A JP 2006-276838 A

  By the way, when the light diffusion sheet is used as, for example, a cover of an indoor lighting fixture, high light diffusibility is required to irradiate the entire room, and light from a light source can be emitted from the viewpoint of energy efficiency. As long as it can be irradiated indoors, a high light transmittance is required.

  However, in recent years when conventional light diffusing sheets are required to have higher light diffusibility and higher light transmittance, it is possible to sufficiently satisfy such demands. Can not.

  In view of the above problems, an object of the present invention is to provide a light diffusion sheet having high light diffusibility and high light transmittance.

The present invention relates to a light diffusing sheet characterized in that it contains a polystyrene resin, has a number of bubbles of 1 × 10 ⁷ or more per 1 cm ^{2 of} the sheet, and has a thickness of 0.3 to 1.0 mm. It is in.

In the present invention, the light diffusion sheet is contained so that the polystyrene resin is contained, the number of bubbles per 1 cm ^{2 of} the sheet is 1 × 10 ⁷ or more, and the thickness is 0.3 to 1.0 mm. It exists in the manufacturing method of the light-diffusion sheet | seat characterized by manufacturing.

  Furthermore, this invention exists in the light-emitting device provided with the said light-diffusion sheet and a light source.

  ADVANTAGE OF THE INVENTION According to this invention, the light-diffusion sheet and light-emitting device which have high light diffusibility and high light transmittance can be provided.

1 is a schematic cross-sectional view of an annular die according to an embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

Furthermore, in the light diffusion sheet of the present invention, the number of bubbles per 1 cm ^{2 of} the sheet surface is 1 × 10 ⁷ or more. The light diffusing sheet of the present invention has an advantage of having high light diffusibility because the number of bubbles per 1 cm ^{2 of} the sheet surface is 1 × 10 ⁷ or more.
The surface of the sheet means a surface perpendicular to the thickness direction, and also means a surface irradiated with light from a light source.
In the light diffusion sheet of the present invention, the number of bubbles per 1 cm ^{2 of} the sheet surface is preferably 1 × 10 ^{7 to} 5 × 10 ⁷ , more preferably 2 × 10 ^{7 to} 3 × 10 ⁷ . Since the light diffusion sheet of the present invention has 2 × 10 ⁷ or more bubbles per 1 cm ^{2 of} the sheet surface, the illuminance from the light emitting device is increased when the light diffusion sheet of the present invention is attached to the light emitting device. There is an advantage that it becomes more uniform. Further, the light diffusion sheet of the present invention has an advantage that the decrease in illuminance from the light emitting device can be suppressed because the number of bubbles per 1 cm ^{2 of} the sheet surface is 5 × 10 ⁷ or less.

The “number of bubbles per 1 cm ^{2 of the} sheet surface” can be determined by the method described in Examples.

  The light diffusion sheet of the present invention has a thickness of 0.3 to 1 mm, preferably 0.5 to 1 mm. The light diffusion sheet of the present invention has an advantage that the light diffusibility is high because the thickness is 0.3 mm or more, and further has an advantage that the strength of the sheet itself is high. Further, the light diffusion sheet of the present invention has an advantage that the total light transmittance is high and the light transmittance is high because the thickness is 1 mm or less.

Furthermore, when the light diffusion sheet of the present invention is attached to a light box, the average luminance measured by a two-dimensional color luminance meter is preferably 1300 cd / m ² or more, more preferably 1500 cd / m ² or more. When the light diffusion sheet of the present invention is attached to a light box, the measured value of average luminance by a two-dimensional color luminance meter is 1300 cd / m ² or more, so that necessary illuminance can be ensured.
The “average luminance by a two-dimensional color luminance meter when attached to a light box” can be obtained by the method described in the examples.

  The light diffusion sheet of the present invention has a total light transmittance of preferably 20% or more, more preferably 25% or more. Since the light diffusion sheet of the present invention has a total light transmittance of 20% or more, there is an advantage that the illuminance from the light emitting device is further increased when the light diffusion sheet of the present invention is attached to the light emitting device. .

The light diffusion sheet of the present invention has a density of preferably 30 to 60 kg / m ³ , more preferably 35 to 50 kg / m ³ .
The light diffusing sheet of the present invention has an advantage that it is easy to produce because the density is 30 kg / m ³ or more.
In addition, the light diffusion sheet of the present invention has an advantage that it is lightweight and has high flexibility when the density is 60 kg / m ³ or less. Further, the light diffusion sheet of the present invention is advantageous in that it can be easily installed with respect to various light sources by being lightweight and having high flexibility.

Furthermore, the light diffusion sheet of the present invention preferably has a bubble cross section exposed on at least one side of the sheet surface, and more preferably a bubble cross section exposed on both sides of the sheet surface. The light diffusing sheet of the present invention is such that, when the light diffusing sheet of the present invention is attached to the light emitting device, the light irradiated to the sheet surface from the light source when the bubble cross section is exposed on at least one surface of the sheet surface. Can be prevented from being reflected, so that there is an advantage that the illuminance is further increased, and there is also an advantage that light can be diffused efficiently.
In addition, this sheet | seat surface means the surface of a surface perpendicular | vertical to the thickness direction.

Furthermore, the light diffusion sheet of the present invention contains a polystyrene-based resin.
Examples of the polystyrene resin include those obtained by mixing one or more known polystyrene resins such as polystyrene, high impact polystyrene, styrene-α-methylstyrene copolymer, and the like. The light diffusing sheet of the present invention is preferably polystyrene as a polystyrene-based resin from the viewpoint of cost reduction and good foamability.
The polystyrene-based resin preferably contains 50% by mass or more of styrene monomer units, more preferably 70% by mass or more, and still more preferably 90% by mass or more.

The light diffusion sheet of the present invention is configured as described above. Next, a method for manufacturing the light diffusion sheet of the present invention for manufacturing the light diffusion sheet of the present invention will be described.

The method for producing a light diffusing sheet of the present invention contains a polystyrene resin, the number of bubbles per 1 cm ^{2 of} the sheet is 1 × 10 ⁷ or more, and the thickness is 0.3 to 1.0 mm. A light diffusing sheet is manufactured.

  Below, the manufacturing method of the light-diffusion sheet of this embodiment is demonstrated.

  In the light diffusing sheet manufacturing method of this embodiment, the polystyrene-based resin and the cell nucleating agent are melt-kneaded with an extruder to obtain a cell nucleating agent-containing resin composition.

  Examples of the extruder include a single-screw extruder, a twin-screw extruder, and a tandem extruder. In the present embodiment, a tandem type extruder is preferably used from the viewpoint of easy adjustment of the extrusion conditions.

The bubble nucleating agent promotes the generation of bubble nuclei when foaming the polystyrene-based resin, and has an effect on the refinement and uniformity of bubbles.
Examples of the bubble nucleating agent include inorganic compounds, organic compounds, inert gases, and the like. Examples of the inorganic compound include talc, mica, silica, diatomaceous earth, alumina, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, and potassium sulfate. , Barium sulfate, sodium bicarbonate, glass beads and the like. Examples of the organic compound include polytetrafluoroethylene, azodicarbonamide, a mixture of sodium hydrogen carbonate and citric acid, and the like. Nitrogen etc. are mentioned as said inert gas. Among the bubble nucleating agents, talc is preferable as the inorganic compound, and polytetrafluoroethylene is preferable as the organic compound. As the cell nucleating agent, one kind may be used alone, or two or more kinds may be used.
The amount of the cell nucleating agent is preferably 0.01 to 5 parts by weight, more preferably 0.1 to 3 parts by weight with respect to 100 parts by weight of the polystyrene resin.
In the light diffusing sheet manufacturing method of the present embodiment, the cell nucleating agent may be mixed with the polystyrene resin in its own form, or may be mixed with the polystyrene resin in the form contained in the masterbatch. Good.
Further, in the method for producing a light diffusion sheet of the present embodiment, the cell nucleating agent may be mixed with the polystyrene resin and then supplied to the extruder, and the cell nucleating agent and the polystyrene resin may be mixed. You may supply to an extruder, without mixing.
The base resin of the masterbatch is not particularly limited as long as it has good compatibility with the polystyrene resin. For example, polystyrene, high impact polystyrene, and the like can be suitably used.

The manufacturing method of the light diffusing sheet of this embodiment may use various additives usually used for foam molding as an optional component.
Examples of the additive include a weather resistance stabilizer, a light stabilizer, a pigment, a dye, a flame retardant, a crystal nucleating agent, a plasticizer, a lubricant, a surfactant, a dispersant, an ultraviolet absorber, an antioxidant, and a filler. , Reinforcing agents, antistatic agents and the like. Among these, the surfactant improves the slip property and the anti-blocking property. Moreover, a dispersing agent improves the dispersibility of an inorganic filler. Examples of the dispersant include higher fatty acids, higher fatty acid esters, higher fatty acid amides, and the like.
The addition amount of the additive can be appropriately set as long as it does not impair the effects of the present invention. For example, the addition amount used for foam molding of a normal thermoplastic resin can be employed.
The additive is contained in the masterbatch from the viewpoint of easy handling, and from the viewpoint of suppressing the possibility of production environment contamination due to powder scattering when the additive is in powder form. It is preferable to use in.

  In addition, the light diffusing sheet manufacturing method of the present embodiment is obtained by mixing and kneading the cell nucleating agent-containing resin composition and the foaming agent with an extruder to obtain a foaming agent-containing resin composition, and using an extrusion foaming method. The foaming agent-containing resin composition is foamed by a mold attached to the extruder and a foam is obtained.

In the present embodiment, carbon dioxide is preferably used as the foaming agent.
Further, in the present embodiment, from the viewpoint that the foam bubbles can be formed more finely than when other foaming agents are used, as the carbon dioxide, supercritical carbon dioxide, subcritical carbon dioxide. Or liquefied carbon dioxide is preferably used.
In this embodiment, the amount of the foaming agent is appropriately adjusted according to the density of the foam to be formed (that is, the density of the light diffusion sheet to be formed).
The amount of the foaming agent is preferably 1 to 12 parts by weight, more preferably 2 to 10 parts by weight, and even more preferably 3 to 8 parts by weight with respect to 100 parts by weight of the polystyrene resin. In this embodiment, since the amount of the foaming agent is 1 part by weight or more with respect to 100 parts by weight of the polystyrene-based resin, the density of the foam can be kept low, and the light-diffusing sheet formed is lightweight. And has the advantage of increased flexibility. In addition, in the present embodiment, when the amount of the foaming agent is 12 parts by weight or less with respect to 100 parts by weight of the polystyrene resin, foaming occurs in the mold, and bubble breakage occurs. Or there exists an advantage that it is suppressed that a big space | gap arises in a foam.

As the mold, an annular die as shown in FIG. 1, that is, a bubble generating part 2 formed by constricting a resin flow path, and a foam for growing the generated bubbles and smoothing the foam surface An annular die having the molding part 1 is preferably used. In the present embodiment, by using the annular die as the mold, it is possible to suppress the generation of corrugation in the bubble generation unit 2 by an appropriate slip resistance in the foam molding unit 1, and the surface is smooth. A foam can be obtained.
The corrugate is a large number of ridges and valleys formed by undulation of the foam from the annular die to absorb the circumferential linear expansion due to the deposition expansion.

In the light diffusing sheet manufacturing method of the present embodiment, when extrusion foaming is performed, the resin discharge speed V in the bubble generation unit 2 is preferably 30 to 200 kg / (cm ² · hr), more preferably 40 to 150 kg / (Cm ² · hr), more preferably 40 to 100 kg / (cm ² · hr). Moreover, in the manufacturing method of the light-diffusion sheet of this embodiment, when extrusion-foaming, the resin pressure just before an annular die becomes like this. Preferably it is 7-30 Mpa, More preferably, it is 10-25 Mpa. The production method of the light diffusing sheet of this embodiment has the advantage that the foaming property of the foaming agent-containing resin composition can be improved by extrusion foaming under these conditions, and further, the foam of the foam obtained is removed. There is also an advantage that the strength of the film of the bubbles can be further increased while being miniaturized. In the present embodiment, these conditions improve the processability when processing the obtained foam, and there is an advantage that, for example, slicing processing for exposing the cell cross section can be easily performed.

The light diffusing sheet manufacturing method of the present embodiment has an advantage that bubbles can be easily miniaturized when the discharge speed V is 30 kg / (cm ² · hr) or more. There is also an advantage that it is easy to reduce the density of the film.
Further, in the method of manufacturing the light diffusing sheet of the present embodiment, when the discharge speed V is 200 kg / (cm ² · hr) or less, the resin generates heat in the bubble generating section 2 of the mold, and the bubble breaks. This has the advantage that the foam density can be reduced, and the corrugated corrugation is less likely to occur, the bubble diameter is uniform, and the foam surface is more smooth. There is also.
The discharge speed V is appropriately adjusted according to the cross-sectional area of the bubble generating portion 2 of the annular die and the extrusion discharge amount.
In the manufacturing method of the light diffusing sheet of this embodiment, as a method for adjusting the cross-sectional area of the bubble generating unit 2, the length (in the case of a flat mold) of the bubble generating unit 2 of the mold or the aperture (of the annular die) And a method of changing the interval (in the case of a flat die or an annular die) between the bubble generating portions 2 of the die.
The bubble generating part 2 is a narrow resin flow path (foaming agent-containing resin composition flow path part 3) formed by the annular die-out side mold 5 and the annular die-in side mold 4 and the foam molding part. This is the part where the interval between the channels following 1 is the smallest.
Moreover, it is preferable that the mold surface of the foam molded part 1 has a satin-like shape that has been subjected to blasting and then plated in order to prevent high-temperature resin from adhering and to have appropriate slip resistance. . The surface roughness (Ra) of the satin is preferably 0.4a to 3.2a, more preferably 0.5a to 2.0a.

Furthermore, in the method of manufacturing the light diffusion sheet according to the present embodiment, when the resin pressure immediately before the annular die is 7 MPa or more, bubbles start to be generated in the portion before the bubble generating portion 2 of the annular die. There is an advantage that a good foam can be obtained. In addition, the light diffusing sheet manufacturing method of the present embodiment has the advantage that the load on the extruder can be suppressed because the resin pressure immediately before the annular die is 30 MPa or less, and the foaming agent There is also an advantage that it is possible to suppress the possibility that the foaming agent is difficult to press-in due to the pressure when the slag is injected becomes too high.
The resin pressure immediately before the annular die is appropriately adjusted according to the molten resin viscosity, the extrusion discharge amount, and the cross-sectional area of the bubble generating portion 2 of the annular die.
The molten resin viscosity is appropriately adjusted depending on the viscosity of the resin composition in the extruder, the amount of foaming agent added, and the molten resin temperature.
In this specification, the molten resin temperature is a temperature measured by a thermocouple attached in a direct contact with the molten resin in a straight pipe mold for measuring the resin pressure immediately before the annular die. means.
The molten resin temperature is preferably in the range of 30 ° C. to 50 ° C. higher than the glass transition temperature of the polystyrene resin used in the present embodiment, from the viewpoint of enhancing foamability. In the method for producing a light diffusing sheet of this embodiment, by making the molten resin temperature 30 ° C. or more higher than the glass transition temperature, the viscosity is not excessively increased and the extrusion conditions are easily stabilized, thereby suppressing the extruder load. There is an advantage that can be. In addition, the light diffusing sheet manufacturing method of the present embodiment has a molten resin temperature that is 50 ° C. or less higher than the glass transition temperature. There is an advantage that the possibility of occurrence is suppressed and the density of the foam can be lowered.

Moreover, the manufacturing method of the light-diffusion sheet of this embodiment cuts the said foam with a cutter etc., obtains a foam sheet, and removes the skin of this foam sheet by slicing, and obtains a slice foam sheet.
In the method for producing a light diffusing sheet of this embodiment, the cell cross section of the sheet can be exposed by removing the skin of the foamed sheet by slicing.
As the slicing machine used in the slicing process, a known machine such as a type in which a blade rotates can be used.

In the light diffusing sheet manufacturing method of the present embodiment, one sliced foam sheet may be used as a light diffusing sheet, or a plurality of sliced foam sheets may be used as a light diffusing sheet.
In the manufacturing method of the light diffusing sheet of this embodiment, when a plurality of sliced foam sheets are stacked, the number of sheets is preferably 4 or less from the viewpoint of improving light transmittance.

Next, the light emitting device of the present invention will be described.
The light emitting device of the present invention is a light emitting device comprising the light diffusion sheet and the light source of the present invention.
Examples of the light source include an LED, a fluorescent lamp, a light bulb, and the like.

  The light diffusing sheet of the present invention, the method for producing the light diffusing sheet of the present embodiment, and the light emitting device of the present invention have the above-mentioned advantages due to the above configuration. The manufacturing method of a diffusion sheet is not limited to the said structure, A design change is possible suitably.

  For example, the light diffusing sheet manufacturing method of the present embodiment uses a cell nucleating agent-containing resin composition, but the light diffusing sheet manufacturing method of the present invention may be an embodiment that does not use a cell nucleating agent. In that case, a polystyrene-based resin and a foaming agent may be mixed and kneaded to obtain a foaming agent-containing resin composition.

  Next, the present invention will be described more specifically with reference to examples and comparative examples.

Example 1
First, a tandem extruder in which a second extruder having a diameter of 75 mm was connected to the tip of a first extruder having a diameter of 65 mm was prepared.
Next, polystyrene resin (PS Japan, GPPS P9305) and 0.05 parts by weight of zinc stearate as a sheet surface smoothing agent with respect to the polystyrene resin (PS Japan, GPPS P9305) and Was supplied to the first extruder and melt-kneaded to obtain a surface smoothing agent-containing resin composition.
Then, with respect to 100 parts by weight of the polystyrene-based resin, 6.0 parts by weight of carbon dioxide in a supercritical state as a foaming agent is press-fitted into the first extruder, and a surface smoothing agent-containing resin composition in a molten state and the foaming agent Were uniformly mixed and kneaded to obtain a foaming agent-containing resin composition, and the molten foaming agent-containing resin composition was continuously supplied to the second extruder and cooled to a resin temperature suitable for foaming while being melt-kneaded. .
Next, from the annular die of the die attached to the tip of the second extruder (the diameter φ of the bubble generation part: 62 mm, the diameter φ of the outlet part of the foam molding part: 89 mm), the discharge amount is 30 kg / hr, the resin The foaming agent-containing resin composition was extruded and foamed under the conditions of a temperature of 140 ° C. and a resin pressure of 18.5 MPa immediately before the annular die, and a foam on the cylinder was formed in the foam forming part of the annular die.
Then, the foam was cooled and molded by applying the foam onto the cooled mandrel and blowing air from the air ring to the outer surface portion of the foam.
Next, the cooled cylindrical foam was cut by a cutter at one point on the mandrel to obtain a foam sheet.
Next, the obtained foamed sheet is sliced by a splitting machine (“AB-320D” manufactured by Fortuner) to remove the skin portion on both sides, and the slice foam in which the cell cross section is exposed on both sides having a thickness of 0.5 mm. A sheet was obtained.
Then, various tests (density, total light transmittance, haze value, average cell diameter, sheet thickness, melt flow rate, average luminance (B), and luminance between light sources are described below for the sliced foam sheet as a light diffusion sheet. Difference (ΔB)).
Note that the average luminance (B) and the difference in luminance between light sources (ΔB) are adjusted so that the extrusion direction during foam molding is parallel to the longitudinal direction of the fluorescent lamp of the light box. It was installed in a box and measured.

(Example 2)
A light diffusion sheet was prepared in the same manner as in Example 1 except that the thickness of the slice foam sheet was 0.6 mm, and various tests were performed in the same manner as in Example 1.

(Example 3)
A slice foam sheet as a light diffusing sheet is installed in the light box so that the extrusion direction at the time of forming the foam and the longitudinal direction of the fluorescent lamp of the light box are perpendicular to each other. Various tests were carried out in the same manner as in Example 1 except that the inter-brightness brightness difference (ΔB) was measured.

(Comparative Example 1)
Two sliced foam sheets produced by the same method as in Example 2 were overlapped to form a 1.5 mm light diffusion sheet so that the extrusion direction during foam molding was the same direction, and the foam was molded. Place the light diffusion sheet in the light box so that the direction of extrusion and the longitudinal direction of the fluorescent lamp in the light box are perpendicular to each other, and measure the average brightness (B) and the difference in brightness between light sources (ΔB) Except for the above, a light diffusion sheet was produced in the same manner as in Example 1, and various tests were carried out in the same manner as in Example 1.

(Comparative Example 2)
A light diffusing sheet was produced in the same manner as in Example 1 except that polystyrene paper (manufactured by Sekisui Plastics Co., Ltd., Eslen sheet H350A-200) was used instead of the foamed sheet produced in Example 1. Various tests were conducted in the same manner as in Example 1.

  The foam sheets and light diffusion sheets of Examples and Comparative Examples were subjected to the following tests.

(density)
The density was measured based on the method described in JIS K 7222-1999.
Specifically, a test piece of 10 cm ³ or more (100 cm ³ or more in the case of semi-hard and soft-hard materials) is cut from the foamed sheet so as not to change the original cell structure of the sample, and its mass is measured. The density was calculated by the following formula.
Density (kg / m ³ ) = Test piece mass (g) / Test piece volume (cm ³ ) × 10 ³

(Total light transmittance and haze value)
The total light transmittance and haze value were measured according to the method described in JIS K 7361.
Specifically, three 50 × 50 mm test pieces were cut out from the foamed sheet, and the test pieces were used in a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) to measure the total light transmittance and haze value. did. What averaged the measured value of the light transmittance and haze value of three test pieces was made into the light transmittance and haze value of a foam sheet.

(Average bubble diameter)
The average cell diameter was measured according to the test method of ASTM D2842-69.
Specifically, the foamed sheet is cut along the MD direction (extrusion direction) and the TD direction (direction orthogonal to the extrusion direction), and the center part of each cut surface is a scanning electron microscope (S-3000N, Hitachi, Ltd.). ) And enlarged.
Next, the photographed image was printed on A4 paper, and one straight line having a length of 60 mm was drawn on the image. In addition, about the cut surface cut | disconnected in MD direction, the straight line was drawn in parallel with MD direction, and about the cut surface cut | disconnected in TD direction, the straight line was drawn in parallel with TD direction.
The magnification of the electron microscope was adjusted so that 10 to 20 bubbles were present on the straight line.
The average chord length (t) of the bubbles was calculated from the number of bubbles present on the straight line by the following formula, and the average chord length (t) was defined as the average bubble diameter in each direction (MD direction, TD direction).
Average chord length (t) = 60 / (number of bubbles × photo magnification)
When drawing a straight line, the straight line should be penetrated as much as possible without making point contact with the bubbles. Also, if some of the bubbles are in point contact with a straight line, this bubble is included in the number of bubbles, and if both ends of the straight line are located in the bubble without penetrating the bubbles Includes the bubbles in which both ends of the straight line are located in the number of bubbles.
Then, as shown in Equation, the arithmetic mean value of the cell diameters of the obtained MD direction cell diameter (D _MD) and TD direction (D _TD) was defined as the average cell diameter of the foamed sheet.
Average bubble diameter = (D _MD + D _TD ) / 2

(Bubble density)
The bubble density (pieces / cm ³ ) is the average bubble diameter (C: mm) and the density (ρ: kg / m ³ ) when a polystyrene resin is measured in a non-foamed state based on JIS K7112-1999. From the apparent density (D: kg / m ³ ) of the foamed sheet measured based on JIS K7222-1999, the following formula was used.
Bubble density (pieces / cm ³ ) = (ρ / D−1) / {(4/3) × π × (C / 10/2) ³ }

(Thickness of slice foam sheet and light diffusion sheet)
The thickness of the slice foam sheet and the light diffusion sheet was measured with a thickness gauge manufactured by Mitutoyo Corporation.
Specifically, the average value of the thickness measured using a thickness gauge at a point where the sheet width is divided into 12 equal parts in the TD direction of the sheet every 10 m in the MD direction of the sliced foam sheet (at two ends when less than 10 m). The thickness of the sliced foam sheet was used, and the light diffusion sheet calculated from the thickness of the slice sheet used was the thickness of the light diffusion sheet.

(Number of bubbles per 1 cm ^{2 of} sheet surface)
Regarding the light diffusion sheet, the number of bubbles per 1 cm ^{2 of} the sheet surface (number) was calculated from the bubble density (number / cm ³ ) and the thickness (cm) of the light diffusion sheet.
Number of bubbles per 1 cm ² surface of the sheet (number) = cell density (number / cm ³ ) × thickness (cm)

(Average luminance (B))
The average luminance (B) was measured under the following conditions using a light box (NEW5000 inverter, manufactured by Fuji Film Imaging) and a two-dimensional color luminance meter (CA2000, manufactured by Konica Minolta).
First, the milky white light diffusion plate on the upper surface of the light box was removed and placed on a flat surface, and the lens position of the CCD camera of the two-dimensional color luminance meter was set 50 cm above the upper surface of the light box. At this time, the light box and the CCD camera were set so that their central axes coincide.
Before starting the measurement, turn on the light box for about 1 hour in advance, and fix the light diffusion sheet so that it does not sag on the top surface of the light box (distance about 20 mm from the top of the fluorescent lamp) after the illuminance stabilizes. Then, the average luminance in the light-emitting surface of the light box was measured with a two-dimensional color luminance meter.

(Brightness difference between light sources (ΔB))
Simultaneously with the measurement of the average brightness, the brightness difference between the light sources of the two fluorescent lamp tubes in the light box was measured. That is, the light emitting surface is divided into 50 sections in the center of the light box and in the direction perpendicular to the longitudinal direction of the fluorescent lamp, and the luminance on a 4 mm rectangular surface is measured with a spot. And the difference between the minimum luminance generated between fluorescent lamps is the luminance difference between the light sources. This luminance difference between light sources was used as an index of light diffusion performance.

  The results of the above test are shown in Table 2. The comprehensive evaluations in Tables 2 to 4 are based on the criteria in Table 1.

As shown in Table 2, in Examples 1 to 3, which are within the scope of the present invention, the brightness between the light sources is higher than that of Comparative Example 2 in which the number of bubbles in a sheet per 1 cm ² is smaller than within the scope of the present invention. It was shown that the difference was low, that is, the light diffusibility was high. Further, Examples 1 to 3, which are within the scope of the present invention, have a higher average luminance than that of Comparative Example 1 having a thickness larger than that within the scope of the present invention, that is, a high light transmittance. Indicated.

  1: foam forming part, 2: bubble generating part, 3: foaming agent-containing resin composition flow path part, 4: ring die-in side mold, 5: ring die-out side mold

Claims (5)

A light diffusing sheet comprising a polystyrene-based resin, having a number of bubbles of 1 × 10 ⁷ or more per 1 cm ^{2 of} the sheet, and having a thickness of 0.3 to 1.0 mm. The light diffusion sheet according to claim 1, wherein when attached to the light box, a measured value of average luminance by a two-dimensional color luminance meter is 1300 cd / m ² or more.   The light diffusion sheet according to claim 1 or 2, wherein the light diffusion sheet is produced using carbon dioxide as a foaming agent. A light diffusing sheet is produced so that a polystyrene resin is contained, the number of bubbles per 1 cm ^{2 of} the sheet surface is 1 × 10 ⁷ or more, and the thickness is 0.3 to 1.0 mm. A manufacturing method of a light diffusion sheet.   The light-emitting device provided with the light-diffusion sheet and light source of any one of Claims 1-3.

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