JP2012002941A - Light diffusion sheet and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusion sheet with which light of a specific wave length region can be much diffused and then irradiated without using any filter and to provide a manufacturing method for the light diffusion sheet.SOLUTION: In a light diffusion sheet according to the prevent invention, a thermoplastic resin foam sheet includes a luminous body having a peak of light generating spectrum in the wave length region of 570 to 700 nm. As a result, light with different spectrum from that of light irradiated from a light source is diffused and then irradiated. The light irradiated has light with enhanced light of wave length region of 570 to 700 nm (red light). Therefore, red color which is not easily visible for a human eye can be made more observable. The hue of illuminations and display devices and the hue of objects lighted by them can be changed, thereby obtaining the hue which cannot be expressed by using conventional white color reflective plates and silver color reflective plates. The sheet can be preferably used in the usage such as display devices and illuminations for which the hue is highly valued.

Description

  The present invention relates to a light diffusing sheet that can diffuse and emit light in a specific wavelength region, and a method of manufacturing the light diffusing sheet.

  Conventionally, a light diffusing sheet that diffuses light from a light source and irradiates a wider area uniformly in an illumination or a display has been used. As the light diffusion sheet, a sheet containing light diffusing particles, a sheet having a cell structure inside, and the like have been proposed.

  As a light diffusion sheet, Patent Document 1 discloses an anisotropic diffusion sheet in which 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. .

  Furthermore, Patent Document 2 uses a resin as a base material, includes 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 parallel. A light diffusing plate having a line transmittance of 6.5% or less is disclosed.

  However, the light diffusing sheets as disclosed in Patent Documents 1 and 2 are intended to transmit and diffuse light without changing the wavelength spectrum of incident light as much as possible. Therefore, the spectrum of light transmitted through the light diffusing sheet is a light source. In order to change the spectrum, it is necessary to use a filter separately.

JP 2004-79522 A JP 2006-276838 A

  The present invention provides a light diffusing sheet capable of radiating a large amount of light in a specific wavelength region without using a filter and a method for manufacturing the same.

  The light diffusing sheet of the present invention is characterized in that the thermoplastic resin foam sheet contains a luminescent material having an emission spectrum peak in a wavelength region of 570 to 700 nm.

  It does not specifically limit as a thermoplastic resin which comprises the thermoplastic resin foam sheet, For example, polyolefin resin, such as a polypropylene resin and a polyethylene resin, is mentioned, A polypropylene resin is preferable. In addition, a thermoplastic resin may be used independently or 2 or more types may be used together.

  Examples of the polypropylene-based resin include homopolypropylene and propylene-α-olefin copolymers, which are excellent in heat resistance, and are preferably homopolypropylene and propylene-α-olefin block copolymers. Is more preferable. The propylene-α-olefin copolymer may be either a random copolymer or a block copolymer, but a block copolymer is preferred because of excellent heat resistance.

  Examples of the α-olefin include, in addition to ethylene, carbon numbers such as 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, and 1-decene. The alpha olefin which is 4-10 is mentioned.

  The polypropylene resin used in the present invention is preferably a high melt tension polypropylene resin because of its excellent foamability. As high melt tension polypropylene-based resin, high melt tension polypropylene (HMS-PP) having free end long chain branching in molecular structure by electron beam cross-linking, etc., increased melt tension by including high molecular weight component Examples include high melt tension polypropylene.

  The high melt tension polypropylene is commercially available, for example, from Nippon Polypro Co., Ltd. under the trade name “Newstrain SH9000” and from Borealis Co., Ltd. under the trade name “DaployWB135HMS”.

  When the melt flow rate of the polypropylene resin is low, the load on the extruder increases during the production of the light diffusion sheet, resulting in a decrease in productivity, or a decrease in the flowability of the foamable resin composition in the mold. The quality of the light diffusing sheet obtained may be reduced, and if it is high, it will be difficult to maintain the foaming pressure in the mold, and the light diffusing sheet obtained by reducing the foamability of the foamable resin composition will be light. Therefore, 0.2 to 5 g / 10 min is preferable, 0.2 to 4 g / 10 min is more preferable, and 0.3 to 3.5 g / 10 min is particularly preferable.

  Here, the melt flow rate of the polypropylene resin refers to a value measured at a test temperature of 230 ° C. and a test load of 21.18 N in accordance with JIS K7210: 1999, Method B. .

In addition, when several types of polypropylene resin is mixed and used, the melt flow rate of each polypropylene resin is measured in the above-mentioned way. When the polypropylene resin is a mixture of n types of polypropylene resins, the melt flow rate of the mixture is calculated by the following equation.
Melt flow rate of the mixture (g / 10 min)
= (MFR1) × C1 + (MFR2) × C2 +... + (MFRn) × Cn

  The melt flow rate of the polypropylene resin 1 is MFR1, the melt flow rate of the polypropylene resin 2 is MFR2,... The melt flow rate of the polypropylene resin n is MFRn, and the content ratio of the polypropylene resin 1 is C1, polypropylene. The content ratio of the resin 2 is C2, and the content of the polypropylene resin n is Cn. The content ratio Cn of the polypropylene resin n is a value obtained by dividing the weight of the polypropylene resin n by the weight of the entire polypropylene resin n.

  When the content of the polypropylene resin in the thermoplastic resin is small, the heat resistance of the light diffusing sheet may be lowered, so that it is preferably 20% by weight or more, and preferably 40 to 70% by weight.

  Further, the thermoplastic resin preferably contains a thermoplastic elastomer. Examples of the thermoplastic elastomer include polyolefin-based thermoplastic elastomers and polystyrene-based thermoplastic elastomers, and polyolefin-based thermoplastic elastomers are preferable. In addition, a thermoplastic elastomer may be used independently or 2 or more types may be used together.

  Examples of the polyolefin-based thermoplastic elastomer include: (1) a polymerization type polyolefin-based thermoplastic elastomer that is produced directly in a polymerization reaction vessel by performing polymerization of a monomer serving as a hard segment and a monomer serving as a soft segment in multiple stages. (2) A blend type polyolefin heat produced by physically dispersing a polyolefin resin as a hard segment and a rubber component as a soft segment using a kneader such as a Banbury mixer or a twin screw extruder. By adding a crosslinking agent when physically dispersing the polyolefin-based resin that becomes the hard segment and the rubber component that becomes the soft segment using a plastic elastomer, (3) a kneader such as a Banbury mixer or a twin screw extruder , Polyolefin resin matrix Such as dynamic crosslinking polyolefin thermoplastic elastomer obtainable by fully crosslinked or partially crosslinked rubber is micro dispersion are mentioned in, from the viewpoint of recycling, thermoplastic polyolefin elastomers of the above (2) is preferred.

  When the content of the thermoplastic elastomer in the thermoplastic resin is small, the flexibility of the light diffusion sheet may be reduced. When the content is large, the foamability of the foamable resin composition described later is lowered and the thermoplastic resin foamed. Since the density of the sheet increases and the light transmittance of the light diffusing sheet may decrease, 30 to 80% by weight is preferable, and 30 to 60% by weight is more preferable.

  The thermoplastic resin foam sheet contains a light emitter having an emission spectrum peak in the wavelength region of 570 to 700 nm (hereinafter sometimes simply referred to as “light emitter”). Examples of such light emitters include organic light emitters having an organic dye structure and inorganic light emitters having an inorganic dye structure, but organic light emitters have good light absorption and light emission efficiency. preferable.

  Examples of the light emitter having an emission spectrum peak in the wavelength region of 570 to 700 nm include a pigment that absorbs light in the ultraviolet region or the visible light region and emits fluorescence or phosphorescence in the wavelength region of 570 to 700 nm, the ultraviolet region or the visible light region. A dye that absorbs the light and emits fluorescence or phosphorescence in the wavelength region of 570 to 700 nm is preferable.

  Fluorescence refers to light emitted when transitioning from an excited singlet state to a ground state. Industrially, phosphors using this phenomenon are widely used as fluorescent pigments and fluorescent dyes. Yes.

  Phosphorescence refers to light emitted when transitioning from the excited triplet state to the ground state. Industrially, phosphors utilizing this phenomenon are widely used as phosphorescent pigments and phosphorescent dyes. Yes.

  Examples of the organic light emitter having an emission spectrum peak in the wavelength range of 570 to 700 nm include, for example, xanthene, coumarin, perylene, naphthalimide, acridine, thioflavine, diaminostilbene, imidazole, and thiazole. And phosphors having organic dye structures such as azozine, oxazole, pyrazoline, anthraquinone, methine, benzopyran, thioindigo, azo, and phthalocyanine. An organic light-emitting body may be used independently or 2 or more types may be used together.

Examples of the inorganic light emitter having an emission spectrum peak in the wavelength region of 570 to 700 nm include sulfides such as ZnS and (ZnCd) S, Zn ₂ SiO ₄ , Cd ₂ B ₂ O ₅ , YVO ₃ , and CaWO. Examples include phosphors having an inorganic dye structure such as oxides such as ₄ . An inorganic type light-emitting body may be used independently, or 2 or more types may be used together.

  In addition, as a pigment or dye that absorbs light in the ultraviolet region or visible region and emits fluorescence or phosphorescence in a wavelength region of 570 to 700 nm, for example, trade names “Kayakril Rhodamine FB”, BASF Corporation from Nippon Kayaku Co., Ltd. Trade name “Lumogen F Red 305”, trade name “Shinloicolor FZ-2803”, “Shinloicolor FZ-2801”, “Shinloicolor FZ-2817”, “Sinloicolor FX-301” , “Shinloicolor FX-303”, “Sinloicolor FX-307” and “Shinloicolor FX-327”, trade names “NX-13”, “GPL-13” and “Z-13” from Deigro. And “IPO-13”, which is commercially available from Inagawa Pigment as trade name “Rhodamine B Lake” You can use.

  If the content of the illuminant in the light diffusion sheet is small, the effect of incorporating the illuminant may not be achieved. Therefore, with respect to 100 parts by weight of the thermoplastic resin constituting the thermoplastic resin foam sheet 0.2 parts by weight or more is preferable, 0.5 parts by weight or more is more preferable, and 1 part by weight or more is particularly preferable.

  In addition, if the content of the luminescent material in the light diffusion sheet is large, the light transmittance of the light diffusion sheet may be reduced, and the foaming ratio of the light diffusion sheet may be reduced to reduce lightness or flexibility. Therefore, the amount is preferably 10 parts by weight or less, more preferably 6 parts by weight or less, and particularly preferably 4 parts by weight or less with respect to 100 parts by weight of the thermoplastic resin constituting the thermoplastic resin foam sheet.

  The light diffusion sheet preferably has a bubble cross section exposed on at least one side thereof, preferably the light incident surface, and preferably has a bubble cross section exposed on at least one whole surface, preferably the entire light incident surface. More preferred. The bubble cross section may be exposed on both surfaces of the light diffusion sheet, preferably on both surfaces.

  This is because when a foam sheet is manufactured, a non-foamed layer called a skin layer is usually formed on the surface of the foam sheet, and this skin layer reflects a part of the light incident on the light diffusion sheet and diffuses the light. There is a possibility that the amount of light incident on the sheet may decrease. Therefore, the skin layer is removed on at least one surface of the light diffusion sheet, preferably the light incident surface, so that the cell cross section of the thermoplastic resin foam sheet is exposed, and light can easily enter the light diffusion sheet. The light diffusion effect can be improved.

  In the light diffusion sheet of the present invention, a part of the light emitted from the light source and incident on the light diffusion sheet is absorbed by the light emitter, and the light emitter emits light in a wavelength region of 570 to 700 nm. In the light diffusion sheet, the light transmittance at a wavelength of 610 nm is preferably 2% or more, more preferably 5% or more, higher than the light transmittance at a wavelength of 550 nm. By configuring in this way, red is more emphasized in the emitted light from the light diffusing sheet, the light emitted from the light source is changed to light more emphasized in red, and the light is emitted after being diffused. be able to.

  In addition, the light transmittance in the specific wavelength in a light-diffusion sheet says the value measured based on JISZ8722. Specifically, the light transmittance at a specific wavelength in the light diffusion sheet is based on JIS Z8722, for example, using a spectrophotometer (trade name “UV-2450” manufactured by Shimadzu Corporation) and an integrating sphere accessory device. Can be measured.

  If the total light transmittance of the light diffusion sheet is low, the proportion of the light emitted from the light source and incident on the light diffusion sheet is absorbed by the light diffusion sheet, and the amount of light emitted from the light diffusion sheet is small. Therefore, 23% or more is preferable.

  If the haze value of the light diffusion sheet is low, there is a possibility that the light emitted from the light source cannot be diffused over a wide range, so 80% or more is preferable, and 90% or more is more preferable.

  Here, in the light diffusion sheet, the total light transmittance and the haze value can be measured according to JIS K7361. Specifically, a flat square test piece having a side of 50 mm is cut out from the light diffusion sheet, and the total light transmittance or haze value of the test piece can be measured according to JIS K7361 using a haze meter. As the haze meter, for example, an apparatus commercially available from Murakami Color Research Laboratory under the trade name “HM-150” can be used.

If the density of the light diffusing sheet is low, it becomes difficult for light to enter the light diffusing sheet, and the light diffusing property of the light diffusing sheet may be reduced. If the density is high, the lightness or flexibility of the light diffusing sheet is reduced. Therefore, 30 to 100 kg / m ³ is preferable, 30 to 90 kg / m ³ is more preferable, and 35 to 80 kg / m ³ is particularly preferable.

In addition, the density of a light-diffusion sheet can be measured based on JISK7222-1999. Specifically, a test piece of 50 cm ³ or more was cut out from the light diffusing sheet while keeping the bubble structure unchanged, and the weight W (kg) and volume V (m ³ ) of the test piece were measured. Based on this, the density of the light diffusion sheet is calculated.
Light diffusion sheet density (kg / m ³ ) = W / V

Further, in the light diffusion sheet, if the number of bubbles per 1 cm ² of the light incident surface is small, the light diffusion property of the light diffusion sheet is deteriorated, so 1 × 10 ⁵ or more is preferable. Since total light transmittance may fall, 1 * 10 < ⁵ > -1 * 10 < ⁷ > pieces are preferable.

Here, in the light diffusion sheet, the number of bubbles per 1 cm ² of the light incident surface is measured as follows. First, the average bubble diameter in the direction along the light incident surface in the light diffusion sheet is measured. The average cell diameter of the light diffusion sheet is measured according to the test method of ASTM D2842-69.

  Specifically, the light diffusion sheet is cut along MD (extrusion direction) and TD (direction orthogonal to the extrusion direction), and an enlarged photograph of the central portion of each cut surface is taken using a scanning electron microscope. In addition, as a scanning electron microscope, the apparatus marketed with the brand name "S-3000N" from Hitachi, Ltd. can be used.

  Next, a straight line having a length of 60 mm is drawn on each of the enlarged photograph images so as to be parallel to each cutting direction. That is, a straight line is drawn parallel to MD for the enlarged photograph of the cut surface cut along MD, and a straight line is drawn parallel to TD for the enlarged photo of the cut surface cut along TD. The magnification of the scanning electron microscope is adjusted so that 10 to 20 bubbles are present on the straight line. When drawing a straight line, the straight line should penetrate as much as possible without making point contact with the bubbles.

The average chord length (t) of the bubbles is calculated based on the following formula from the number of bubbles existing on the straight line for each enlarged photograph, and the average chord length (t) is calculated as the average bubble diameter D _MD or D _{TD in} each cutting direction. And
Average chord length (t) = 60 / (number of bubbles × photo magnification)

  If some of the bubbles are in point contact with a straight line, the number of bubbles that are in point contact with the straight line is included in the number of bubbles, and both ends of the straight line are positioned within the bubble without penetrating the bubbles. In this case, the number of bubbles is also included in the number of bubbles.

And let the arithmetic mean value of the average bubble diameter ( _DMD ) of obtained MD and the average bubble diameter ( _DTD ) of TD be the average bubble diameter C of the direction along the light-incidence surface in a light-diffusion sheet.
Average bubble diameter C (mm) in the direction along the light incident surface = (D _MD + D _TD ) / 2

Next, the density ρ (kg / m ³ ) in the non-foamed state of the thermoplastic resin constituting the thermoplastic resin foam sheet of the light diffusion sheet is measured based on JIS K7112-1999. Furthermore, the apparent density D (kg / m ³ ) of the light diffusion sheet is measured based on JIS K7222-1999, and the bubble density E (number / cm ³ ) in the light diffusion sheet is calculated based on the following formula.
Bubble density E (pieces / cm ³ )
= (Ρ / D-1) / {(4/3) × π × [(C / 10) / 2] ³ }

The thickness of the light diffusing sheet was measured at any 10 locations, and the arithmetic average value was defined as the thickness T of the light diffusing sheet. The number of bubbles per 1 cm ² of the light incident surface in the light diffusion sheet can be calculated based on the following formula.
Number of bubbles per 1 cm ^{2 of} light incident surface = bubble density E (number / cm ³ ) × thickness T (cm)

  And if the thickness of the light diffusion sheet is thin, the light diffusion property of the light diffusion sheet may be reduced, and if it is thick, the total light transmittance of the light diffusion sheet may be reduced. 0.5 mm is preferable, and 0.5 to 1.5 mm is more preferable.

  The light diffusing sheet has a weather resistance stabilizer, a light stabilizer, a flame retardant, a crystal nucleating agent, a plasticizer, a lubricant, a surfactant, a dispersant, an ultraviolet absorber, an oxidation, within a range not impairing its physical properties. Additives such as an inhibitor, a filler, a reinforcing agent, and an antistatic agent may be contained. Examples of the dispersant include higher fatty acids, higher fatty acid esters, higher fatty acid amides, and the like.

  Next, the manufacturing method of a light-diffusion sheet is demonstrated. The method for producing the light diffusing sheet is not particularly limited. For example, a thermoplastic resin and a light emitting body are supplied to an extruder and melt kneaded, and a foaming agent is press-fitted into the molten thermoplastic resin and melt kneaded. The foamable resin composition is made into a foamable resin composition, and then the foamable resin composition is extruded and foamed from a mold attached to the tip of the extruder to produce a thermoplastic resin foam sheet. The manufacturing method which makes it a diffusion sheet is mentioned. Examples of the extruder include a single-screw extruder, a twin-screw extruder, and a tandem extruder, and a tandem extruder is preferably used because the extrusion conditions can be easily adjusted.

  It is preferable to supply a cell nucleating agent to the extruder. The cell nucleating agent promotes the generation of cell nuclei when foaming the foamable resin composition, and has an effect on the refinement and uniformity of the cells. Examples of the cell 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, potassium sulfate, Examples thereof include barium sulfate, sodium hydrogen carbonate, and glass beads, and talc is preferable. Examples of the organic compound include polytetrafluoroethylene, azodicarbonamide, a mixture of sodium hydrogencarbonate and citric acid, and polytetrafluoroethylene is preferable. In addition, a bubble nucleating agent may be used independently or 2 or more types may be used together.

  If the amount of the cell nucleating agent supplied to the extruder is small, the effect of the cell nucleating agent may not be manifested.If the amount is large, the foaming property of the foaming resin composition may be impaired. 0.01-10 weight part is preferable with respect to 100 weight part of a thing, and 0.1-8 weight part is more preferable.

  In supplying the cell nucleating agent to the extruder, the cell nucleating agent may be directly supplied to the extruder or may be supplied to the extruder after making a master batch. Further, the cell nucleating agent may be mixed with the thermoplastic resin and then supplied to the extruder, or the cell nucleating agent may be supplied to the extruder separately from the thermoplastic resin and the light emitting body.

  When the cell nucleating agent is used as a master batch, the base resin of the master batch is not particularly limited as long as it is compatible with the thermoplastic resin, but homopolypropylene, block polypropylene, random Polypropylene, low density polyethylene and high density polyethylene are preferred.

  The foaming agent is not particularly limited, and examples thereof include nitrogen, carbon dioxide, butane, and propane. Carbon dioxide is preferable, and in terms of bubbles becoming finer, carbon dioxide in a supercritical state and subcritical state. Carbon dioxide and liquefied carbon dioxide are more preferable.

  The amount of the foaming agent supplied to the extruder may be appropriately adjusted according to the density of the light diffusion sheet. However, if the amount is small, the lightness or flexibility of the light diffusion sheet may be reduced. Occasionally, foam breakage or a large gap may occur in the light diffusion sheet, so that 1 to 12 parts by weight is preferable with respect to 100 parts by weight of the thermoplastic resin, more preferably 2 to 10 parts by weight, and 3 to 8 parts by weight. Part is particularly preferred.

  The mold is not particularly limited, but by using an annular mold as shown in FIG. 1, a thermoplastic resin foam sheet having excellent surface smoothness and a uniform thickness can be obtained. A light diffusing sheet having uniform light diffusibility can be obtained.

  An annular mold 1 shown in FIG. 1 includes an outer die 2 and an inner die 3 disposed in the outer die 2, and a cross-section between opposing surfaces of the outer die 2 and the inner die 3. An annular resin flow path 4 is formed.

  The resin flow path 4 includes a first resin flow path part 41 and a second resin flow path part 42 communicating with the tip of the first resin flow path part 41. The first resin flow path portion 41 has a narrow path portion 41a in which the flow path is gradually narrowed and reduced in diameter from the proximal end side toward the distal end side, that is, in the resin flow direction. Have.

  The proximal end of the second resin flow path portion 42 is connected to and communicated with the distal end of the narrow path portion 41a of the first resin flow path portion 41. The second resin flow path portion 42 has, at its base end portion, a wide path portion 42a in which the flow path gradually widens and expands from the front end side toward the base end side, that is, in the resin flow direction. The base end of the wide path part 42a and the front end of the narrow path part 41a of the first resin flow path part 41 are connected and communicated with each other. In addition, the front-end | tip part of the inner die 3 which comprises the 2nd resin flow-path part 42 protrudes in the conveyance direction of an annular | circular foam from the front-end | tip of the outer die 2 which comprises the 2nd resin flow-path part 42. It was formed on the protruding portion 3a.

  When extrusion foaming is performed using the annular mold 1, the foamable resin composition discharged from the extruder flows into the first resin flow path portion 41 in the resin flow path 4 of the annular mold 1, and the first It flows into the narrow passage portion 41a of the resin flow passage portion 41.

  The narrow passage portion 41a of the first resin flow passage portion 41 has a narrow passage and a reduced diameter from the base end to the distal end, and the foamable resin composition does not foam in the narrow passage portion 41a. The first resin flow channel portion 41 is circulated.

  Then, the foamable resin composition that has reached the tip of the narrow passage portion 41a of the first resin flow passage portion 41 continuously flows into the wide passage portion 42a of the second resin flow passage portion. The wide channel portion 42a has a gradually wider and larger diameter from the base end toward the distal end, and the flow area of the foamable resin composition than the distal end portion of the narrow channel portion 41a of the first resin flow channel portion 41. The foamable resin composition foams at the same time as it flows into the wide path part 42a of the second resin flow path part 42.

  At this time, the annular foam obtained by foaming the foamable resin composition has its inner and outer peripheral surfaces received by the second resin flow path portion 42, and the annular foam has an inner and outer peripheral surface that is second. While flowing through the resin flow path portion 42, the second resin flow path portion 42 is smoothed.

  Furthermore, since the diameter of the second resin flow path portion 42 is gradually increased in the resin flow direction, the volume increase due to the foaming of the annular foam is smoothly absorbed, and the circumference of the annular foam is There is no so-called corrugation that undulates in the direction.

  Then, after the annular foam is discharged from the front end opening of the second resin flow path portion 42 into the atmosphere and further expanded in diameter, it is supplied to the cooling mandrel and cooled, and then the annular foam Is continuously cut in the extruding direction between the inner and outer peripheral surfaces to be developed into a thermoplastic resin foam sheet, and a thermoplastic resin foam sheet containing this luminous body can be obtained as a light diffusion sheet. . The light diffusing sheet thus obtained has excellent light diffusibility because the bubbles of the thermoplastic resin foamed sheet are made fine and uniform.

  Further, the surface of the second resin flow path portion 42 of the annular mold 1 is blasted to prevent the annular foam from adhering and to impart an appropriate slip resistance to the annular foam. It is preferable to use a satin-like shape plated after the treatment. The surface roughness (Ra) of the second resin flow path portion 42 is preferably 0.4 to 3.2 μm, and more preferably 0.5 to 2.0 μm.

Moreover, if the discharge speed of the foamable resin composition at the tip of the narrow passage portion 41a in the first resin flow passage portion 41 of the annular mold 1 is slow, the bubbles of the light diffusion sheet become coarse, and the light diffusion sheet The light diffusibility may decrease, or the density of the light diffusion sheet may increase, and the flexibility or lightness of the light diffusion sheet may decrease. In this case, bubbles are broken and the density of the light diffusing sheet is increased or the air bubbles are non-uniformized, so that the light diffusibility of the light diffusing sheet may be lowered. Therefore, 50 to 300 kg / cm ² · hour is preferable, 70 ˜250 kg / cm ² · hour is more preferable, and 100 to 200 kg / cm ² · hour is particularly preferable. In addition, the discharge speed of the foamable resin composition at the tip of the narrow path portion 41a in the first resin flow path portion 41 of the annular mold 1 is the narrow path in the first resin flow path portion 41 of the annular mold 1 It can be controlled by adjusting the cross-sectional area at the tip of the portion 41a or the extrusion discharge amount of the foamable resin composition from the extruder.

  Furthermore, if the resin pressure of the foamable resin composition immediately before the annular mold 1 is small, the foamable resin composition may start to foam before being supplied to the annular mold. However, if it is too large, there is a possibility that the load applied to the extruder becomes too large, or it becomes difficult to press-fit the foaming agent into the extruder, so 8-30 MPa is more preferable. By controlling the resin pressure in this way, the bubbles of the obtained light diffusion sheet are made finer and the strength of the bubble film is increased, and as will be described later, the surface layer of the thermoplastic resin foam sheet constituting the light diffusion sheet When the portion is removed, the cell cross section can be exposed without impairing the cell structure of the thermoplastic resin foam sheet. The resin pressure of the expandable resin composition immediately before the annular mold 1 is the melt viscosity of the thermoplastic resin, the discharge amount of the expandable resin composition from the extruder, or the narrowness of the first resin flow path portion. It can be controlled by adjusting the cross-sectional area of the tip in the passage. The melt viscosity of the thermoplastic resin can be adjusted by the amount of foaming agent added, the resin temperature in the extruder, and the like.

  If the resin temperature of the foamable resin composition in the extruder is low, the load on the extruder may become too large, and crystallization of the polypropylene resin will occur when the thermoplastic resin contains a polypropylene resin. Extrusion foam may become unstable due to a sudden increase in viscosity, and if it is high, when the foamable resin composition is foamed, the cooling speed of the annular foam cannot keep up with the foaming speed of the foamable resin composition and breaks. Since there exists a possibility that a bubble may be produced, the temperature below 10 degreeC higher than the melting point of a thermoplastic resin and 20 degrees C or less higher than the melting point of a thermoplastic resin are preferable.

  A non-foamed layer called a skin layer is formed on the surface of the thermoplastic resin foam sheet constituting the light diffusion sheet obtained as described above. The skin layer of the thermoplastic resin foam sheet, preferably the skin layer on the light incident side of the thermoplastic resin foam sheet, more preferably the skin layers on both sides in the thickness direction of the thermoplastic resin foam sheet are removed to remove the thermoplastic resin foam sheet. By exposing the cross section of the bubbles, it is possible to facilitate the incidence of light into the light diffusion sheet and to improve the light diffusibility by the light diffusion sheet.

  Examples of the method for removing the skin layer of the thermoplastic resin foam sheet constituting the light diffusion sheet include a method of cutting the skin layer of the thermoplastic resin foam sheet using a general-purpose cutting means such as a cutter. .

  In the light diffusing sheet thus obtained, the thermoplastic resin foam sheet constituting the light diffusing sheet has a large number of bubbles inside, so that the light incident on the light diffusing sheet collides with the bubble wall. The direction of travel is changed by refracting when reflected or transmitted through the bubble wall, and as a result, light is emitted in a state of being uniformly diffused from the entire light diffusion sheet, and the light diffusion sheet has excellent light diffusibility. have.

  And since the light-diffusion sheet contains the light-emitting body which has the peak of an emission spectrum in the wavelength range of 570-700 nm, among the light which injected into the light-diffusion sheet, the light of the absorption wavelength area | region of a light-emitting body is contained. Part of the light is absorbed by the light emitter, and light in the wavelength region of 570 to 700 nm is emitted from the light emitter. Accordingly, light having a spectrum different from that of the light incident on the light diffusing sheet is emitted from the light diffusing sheet. Therefore, according to the light diffusing sheet of the present invention, a spectrum different from that of the light source can be obtained without using a filter. The light which it has can be made to radiate | emit in the state diffused uniformly, and the light-diffusion sheet of this invention can be used suitably for uses, such as an illuminating device and a display. In addition, it does not specifically limit as a light source, For example, LED, a fluorescent lamp, a light bulb etc. are mentioned.

  The light diffusing sheet of the present invention may be used singly or in a state in which a plurality of sheets are laminated. However, if the number of laminated layers is increased, the light transmittance is lowered. It is preferable to use a light diffusing sheet laminated.

  Since the light diffusing sheet of the present invention has the above-described configuration, it radiates after diffusing light having a spectrum different from the spectrum of the light emitted from the light source, and the emitted light is The light in the wavelength region of 570 to 700 nm (red) is emphasized. Therefore, it is possible to easily recognize red color that is difficult to be recognized by human eyes, change the hue of lighting and display devices, and objects illuminated by them, and hue that could not be expressed by conventional white and silver reflectors. And can be suitably used in applications in which hue is important, such as display devices and illumination applications.

It is the schematic cross section which showed the annular mold used when manufacturing the light-diffusion sheet of this invention.

Example 1
A tandem extruder was prepared by connecting a second extruder having a diameter of 75 mm to the tip of a first extruder having a diameter of 65 mm. High melt tension polypropylene (trade name “Newstrain SH9000” manufactured by Nippon Polypro Co., Ltd., melt flow rate: 0.3 g / 10 min) 60% by weight and thermoplastic elastomer (trade name “Thermo Run Z101N” manufactured by Mitsubishi Chemical Co., Ltd., melt flow rate) : 14 g / min) 40 wt% thermoplastic resin (thermoplastic resin composition density: 892 kg / m ³ ) 100 parts by weight, master batch containing 70 wt% talc having an average particle size of 12 μm (Nippon Talc Co., Ltd.) Product name “Talpet 70P”, 10 parts by weight of base resin: polypropylene, and 0.5 parts by weight of fluorescent pigment (product name “Shinloicolor FX-307” manufactured by Sinloihi Co., Ltd.) as the light emitter are supplied to the first extruder. Then, it was melt-kneaded at 210 ° C. to obtain a thermoplastic resin composition. The fluorescent pigment absorbed light in the wavelength region of 470 to 570 nm and emitted fluorescence in the wavelength region of 570 to 700 nm.

  Then, supercritical carbon dioxide as a foaming agent is injected into the first extruder so as to be 4.2 parts by weight with respect to 100 parts by weight of the thermoplastic resin, and the molten thermoplastic resin composition and the supercritical A foamable resin composition was produced by uniformly mixing carbon dioxide in a state.

  The foamable resin composition was continuously supplied to the second extruder, melted and kneaded, and then supplied to an annular mold connected to the second extruder at a resin temperature of 175 ° C. The annular mold had the structure shown in FIG.

  Then, the foamable resin composition is extruded and foamed from an annular mold to produce an annular foam, and the annular foam is expanded while cooling by blowing cold air to the outer peripheral surface thereof. After being cooled and supplied to a cooling mandrel, the annular foam is continuously cut in the extruding direction between the inner and outer peripheral surfaces and expanded to provide a thermoplastic containing a fluorescent pigment as a light emitter. A resin foam sheet was obtained as a light diffusion sheet.

  The skin layers on both sides in the thickness direction of the thermoplastic resin foam sheet constituting the light diffusion sheet are cut using a splitting machine (trade name “AB-320D” manufactured by Fortuner) and foamed with thermoplastic resin on both sides. A light diffusing sheet having a thickness of 1.0 mm, in which the bubble cross section of the sheet was completely exposed, was obtained.

The annular die has a diameter F ₁ of the outer die 2 at the tip of the narrow passage portion 41a of the first resin flow passage portion 41 of 35 mm, and the inside and outside at the tip of the narrow passage portion 41a of the first resin flow passage portion 41. The distance between the dies 3 and 2 was 0.25 mm, and the diameter F ₂ of the protrusion 3a of the inner die 3 was 70 mm.

The discharge rate of the foamable resin composition at the tip of the narrow passage portion 41a in the first resin flow passage portion 41 of the annular mold 1 was 109 kg / cm ² · hour. The resin pressure of the foamable resin composition immediately before the annular mold 1 was 10.1 MPa.

(Example 2)
An annular mold in which a fluorescent pigment (trade name “Shinloicolor FX-307” manufactured by Sinloihi Co., Ltd.) was 1 part by weight, and the foamable resin composition was connected to a second extruder at a resin temperature of 176 ° C. A light diffusing sheet having a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the bubble cross section of the thermoplastic resin foam sheet was exposed on both sides. The discharge rate of the foamable resin composition at the tip of the narrow passage portion 41a in the first resin flow passage portion 41 of the annular mold 1 was 109 kg / cm ² · hour. The resin pressure of the foamable resin composition immediately before the annular mold 1 was 10.7 MPa.

(Example 3)
The amount of the fluorescent pigment (trade name “Shinloicolor FX-307” manufactured by Sinloihi Co., Ltd.) was 2 parts by weight, and the foaming resin composition was connected to the second extruder at a resin temperature of 176 ° C. A light diffusing sheet having a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the bubble cross section of the thermoplastic resin foam sheet was exposed on both sides. The discharge rate of the foamable resin composition at the tip of the narrow passage portion 41a in the first resin flow passage portion 41 of the annular mold 1 was 121 kg / cm ² · hour. The resin pressure of the foamable resin composition immediately before the annular mold 1 was 11.1 MPa.

Example 4
7 parts by weight of a master batch containing 70% by weight of talc having an average particle size of 12 μm (trade name “Talpet 70P” manufactured by Nippon Talc Co., Ltd., base resin: polypropylene), and fluorescent pigment (trade name “Shinloihi Co., Ltd. The same as Example 1 except that the color FX-307 ") was 3 parts by weight and the foamable resin composition was supplied to the annular mold connected to the second extruder at a resin temperature of 177 ° C. Thus, a light diffusing sheet having a thickness of 0.5 mm was obtained by exposing the entire cell cross section of the thermoplastic resin foam sheet on both sides. The discharge rate of the foamable resin composition at the tip of the narrow passage portion 41a in the first resin flow passage portion 41 of the annular mold 1 was 121 kg / cm ² · hour. The resin pressure of the foamable resin composition immediately before the annular mold 1 was 11.5 MPa.

(Example 5)
A master batch containing 70% by weight of talc having an average particle size of 12 μm (trade name “Talpet 70P” manufactured by Nippon Talc Co., Ltd., base resin: polypropylene) is 4 parts by weight, and a fluorescent pigment (trade name “Shinloihi Co., Ltd. The same as Example 1 except that the color FX-307 ") was 4 parts by weight, and the foamable resin composition was supplied to the annular mold connected to the second extruder at a resin temperature of 174 ° C. Thus, a light diffusing sheet having a thickness of 0.5 mm was obtained by exposing the entire cell cross section of the thermoplastic resin foam sheet on both sides. The discharge rate of the foamable resin composition at the tip of the narrow passage portion 41a in the first resin flow passage portion 41 of the annular mold 1 was 121 kg / cm ² · hour. The resin pressure of the foamable resin composition immediately before the annular mold 1 was 11.7 MPa.

(Comparative Example 1)
A light diffusing sheet having a thickness of 1.0 mm, in which the cellular cross section of the thermoplastic resin foam sheet is completely exposed on both sides in the same manner as in Example 1 except that the fluorescent pigment is not supplied to the first extruder. Got. The discharge rate of the foamable resin composition at the tip of the narrow passage portion 41a in the first resin flow passage portion 41 of the annular mold 1 was 109 kg / cm ² · hour. The resin pressure of the foamable resin composition immediately before the annular mold 1 was 9.8 MPa.

In the obtained light diffusion sheet, the density, the number of bubbles per 1 cm ^{2 of} the light incident surface, the light transmittance at a wavelength of 610 nm, the light transmittance at a wavelength of 550 nm, the total light transmittance, and the haze value were measured as described above. The results are shown in Table 1. In Table 1, the number of bubbles per 1 cm ² of the light incident surface is simply expressed as “number of bubbles”.

1 annular mold 2 outer die 3 inner die
3a Protrusion 4 Resin channel
41 First resin flow path
41a Narrow part
42 Second resin flow path
42a Broadway

Claims (14)

The light-diffusion sheet characterized by including the light-emitting body which has the peak of an emission spectrum in the wavelength range of 570-700 nm in a thermoplastic resin foam sheet. The light diffusing sheet according to claim 1, wherein the illuminant is a pigment or a dye that absorbs light in an ultraviolet region or a visible light region and emits fluorescence or phosphorescence in a wavelength region of 570 to 700 nm. The light diffusion sheet according to claim 1, wherein a bubble cross section is exposed on at least one side. The light diffusion sheet according to any one of claims 1 to 3, wherein the thermoplastic resin contains a polypropylene-based resin. The light diffusion sheet according to any one of claims 1 to 3, wherein the thermoplastic resin contains a polypropylene-based resin and a thermoplastic elastomer. The light diffusion according to any one of claims 1 to 5, wherein the density is 30 to 100 kg / m ³ and the number of bubbles per 1 cm ^{2 of the} light incident surface is 1 × 10 ⁵ or more. Sheet. The light diffusion sheet according to any one of claims 1 to 6, wherein the light transmittance at a wavelength of 610 nm is 2% or more higher than the light transmittance at a wavelength of 550 nm. The light diffusion sheet according to any one of claims 1 to 7, wherein a total light transmittance is 20% or more and a haze value is 80% or more. A thermoplastic resin and a phosphor having an emission spectrum peak in the wavelength region of 570 to 700 nm are supplied to an extruder and melt-kneaded in the presence of a foaming agent to obtain a foamable resin composition. A method for producing a light diffusing sheet, wherein the composition is extruded and foamed to produce a thermoplastic resin foamed sheet, and the thermoplastic resin foamed sheet containing the phosphor is used as a light diffusing sheet. 10. The light diffusing sheet according to claim 9, wherein the illuminant is a pigment or dye that absorbs light in the ultraviolet region or visible light region and emits fluorescence or phosphorescence in a wavelength region of 570 to 700 nm. Method. The luminescent material having an emission spectrum peak in a wavelength region of 570 to 700 nm with respect to 100 parts by weight of a thermoplastic resin is supplied to the extruder by 0.2 to 10 parts by weight. The manufacturing method of the light-diffusion sheet of description. The method for producing a light diffusing sheet according to any one of claims 9 to 11, wherein the foaming agent is carbon dioxide. An annular die is attached to the tip of the extruder, and this annular die has an outer die and an inner die disposed in the outer die, and the outer die and the inner die. A resin channel having an annular cross section is formed between the first resin channel and the first resin channel having a narrow channel part with a narrow channel gradually narrowed at the tip. A second resin flow path portion at the base end portion that communicates with the distal end of the path portion and gradually expands the flow path, and is narrow in the first resin flow path portion of the annular mold. A method for producing a light diffusing sheet, wherein the discharge rate of the foamable resin composition at the tip of the road portion is 50 to 300 kg / cm ² · hour. The method for producing a light diffusing sheet according to any one of claims 9 to 13, wherein a surface layer portion of at least one surface of the thermoplastic resin foam sheet is removed to expose a cell cross section.

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