WO2013025832A1

WO2013025832A1 - Reflector for light-emitting diode and housing

Info

Publication number: WO2013025832A1
Application number: PCT/US2012/050989
Authority: WO
Inventors: Pham Hoai Nam
Original assignee: E. I. Du Pont De Nemours And Company
Priority date: 2011-08-16
Filing date: 2012-08-15
Publication date: 2013-02-21
Also published as: JP2013058744A

Abstract

Provided is a reflector for a light-emitting diode and a housing containing the reflector that achieves a high reflectance with little drop in reflectance in the 400 nm to 700 nm wavelength range while exhibiting excellent heat resistance, UV light stability, weather resistance, and adhesivity to silicone and epoxy sealants. The reflector is created by molding fluororesin containing a filler having an average particle size less than 1.0 µm and a band gap greater than 3.0 eV. The reflector exhibits reflectance of 85% or higher over the wavelength range of 400 nm to 700 nm.

Description

TITLE OF INVENTION

REFLECTOR FOR LIGHT-EMITTING DIODE AND HOUSING

FIELD OF INVENTION

The present invention relates to a reflector for a light-emitting diode that has excellent heat resistance, UV stability, weather resistance, adhesivity to sealant, and has high reflectance of 85% or higher in the 400 nm to 700 nm wavelength range. The present invention further relates to an LED housing containing this reflector.

BACKGROUND OF INVENTION

Light-emitting diodes (also referred to herein as LED or LED chips) are compact and can be used for lighting for longer periods of time than filament bulbs, and are highly efficient in transforming electrical energy. In recent years there is a rising trend to replace conventional lighting apparatus, including linear fluorescent lamps, with LEDs. As such, they are widely utilized for home electric appliances, LED indicators, and illuminated operation switches. In terms of applications, LEDs are divided into general (visible wavelength) LEDs and ultraviolet LEDs according to the wavelengths used.

Applications of general (near-ultraviolet-visible ray) LEDs includes automobile dashboards, backlighting of display units of display devices (LCD displays, personal computer monitors, compact game devices, and portable telephone units), indoor illumination sources, indoor/outdoor display devices, and traffic display devices, for example. In addition, as applications of ultraviolet LEDs, white LEDs combined with a fluorescent material for achieving a high level of color rendering property include: banknote identifying devices (light sources for banknote

identifying sensors); air cleaners utilizing photocatalysts (for households, vehicles, refrigerators); contaminant treatments; fluorescent light sources for biological, medical, and analytical applications in the medical field; sterilization and retention of freshness of vegetables and food items in the foodstuff field; UV-setting light sources for electronic parts/inks; medical apparatuses; fluorescent-acryl-based illumination; UV light source motors; light sources for ultraviolet actinometers, spectroanalyses, and excitation of fluorescent agents; and sterilization light sources for medical

apparatuses, water and air.

A conventional light-emitting device in which an LED chip is mounted, as shown in Figure 1 , is generally provided with a reflector (3) having a concave aperture part, a LED chip (2) mounted in the concave aperture part, and a curing resin mold (1 ) for sealing the aforementioned concave aperture part. The reflector is mounted on a substrate to form a housing (5). The reflector is a molded product that is obtained by, for example, molding ceramic or white reflecting resin.

Japanese patent no. 4576276 describes an LED housing formed of a porous alumina ceramic. The porous alumina ceramic has excellent heat resistance, UV light stability, and weather resistance and can obtain high reflectance by controlling the pore diameter and the porosity. In molding of the ceramic, since the ceramic was heated to a temperature of 1 ,000°C or higher for a certain time in a batch process, the manufacture cost was high, and the productivity was poor.

Recently, continuously moldable thermoplastic resins have been used to lower the manufacture cost of the LED housing. For example, certain polyamide group resins do not melt even at 300°C.

However, as shown in Comparative Example 5 of the instant application, when such a resin was heated at 150°C for 500 hours, since the resin was oxidized and discolored to a black color, the reflectance was largely lowered. For this reason, even if the reflectance of the LED housing was high at an initial stage, when a high-output operation was continued, since the resin housing reached a high temperature, the LED housing was discolored, and the luminous efficacy was decreased. In addition, since the polyamide group resin is prone to be degraded at high temperature, when the resin was melted and molded, if the residence time in a melting molding machine is lengthened, the resin is thermally decomposed and discolored, so that the manufacture loss is increased, thereby deteriorating the productivity.

Furthermore, as shown in Figure 3, Comparative example 1 , because rutile-type titanium dioxide used as a filler has a refractive index of 2.7, it exhibits a high reflectance in the visible wavelength range, but its reflectance drops when the wavelength is 430 nm or less. Rutile-type titanium dioxide has a 3.0-eV band gap, and according to J. Phys. Chem. B, Vol. 107, pp. 5709-5716 (2003), this is believed to result in low reflectance at wavelengths of 430 nm or less. In addition, transformation of absorbed energy into heat and a photocatalytic action of the titanium dioxide are considered responsible for the progressive deterioration of the resin.

In addition, in recent years, development of white LEDs, which utilize fluorescent materials in three colors, that is, red, green, and blue, combined with a near-ultraviolet LED, is in progress, and its use for general lighting applications is expected due to its superior color rendering property. In this system, because its excitation light source wavelength is further reduced from 460 nm to 400 nm, there is a higher risk that the housing member may be deteriorated, and a long service life of the LED housing cannot be expected. In addition, due to improved luminescence of recent LEDs, the amounts of heat generated are increased,

accelerating the deterioration of the LED housing resins. As such, the link between the LED housing and the sealant is weakened and thereby shortening the service life of such LEDs.

Fluororesins, for example, such as polytetrafluoroethylene

(PTFE), tetrafluoroethylene-perfluoro(alkoxy vinyl ether) copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and

tetrafluoroethylene-hexafluoropropylene-perfluoro(alkoxy vinyl ether) copolymer, are widely utilized for piping for transporting acidic and alkaline chemical solutions, solvents, and paints; such chemical industrial products as containers and tanks for storing chemical solutions; and such electrical industrial products as tubes, rollers, and electric wires due to their excellent characteristics such as heat resistance, light resistance, weather resistance, chemical resistance, high-frequency electric characteristics, and flame resistance. As such, they are considered for use as LED reflector resins.

Although an LED reflector made of a fluororesin containing a rutile-type titanium dioxide (DuPont Ti-Pure® R900 titanium dioxide) as a filler is disclosed in US2010/0032702A1 , like in aforementioned Comparative example 1 , because a rutile-type titanium dioxide that absorbs wavelengths of 430 nm and shorter is used as the filler, it creates a problem that the reflectance drops in the near-ultraviolet range (see Comparative example 1 of the instant application). Thus, it cannot be used for a near-ultraviolet LED reflector or a white LED reflector that utilizes fluorescent materials in three colors, that is, red, green, and blue, combined with a near-ultraviolet LED. As such, an LED reflector and a housing containing said reflector that achieve a high reflectance with little drop in reflectance in the 400 nm to 700 nm wavelength range while exhibiting excellent heat resistance, light resistance, weather resistance, and adhesivity to a sealant is in demand.

SUMMARY OF INVENTION

The purpose of the present invention is to provide a reflector and a housing for an LED that achieves a high reflectance with little drop in reflectance in the 400 nm to 700 nm wavelength range while exhibiting excellent heat resistance, UV light stability, weather resistance, and adhesivity to sealants.

In one embodiment, the present invention provides a reflector for a light-emitting diode that is obtained by molding a fluororesin containing a filler having an average particle size less than 1 .0 μιτι and a band gap greater than 3.0 Ev.

In one embodiment, the difference between the maximum value and the minimum value of the reflectance of the reflector in the 380 nm to 400 nm wavelength range is in excess of 25%.

In one embodiment, the reflectance of the reflector over the wavelength range of 400 nm to 700 nm is 85% or greater.

In one embodiment of the reflector for a light-emitting diode, the fluororesin is a homopolymer of tetrafluoroethylene or a copolymer comprising tetrafluoroethylene and at least one monomer selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, perfluoro(a!koxy vinyl ether), vinyiidene fluoride, vinyl fluoride, ethylene, and propylene.

In one embodiment of the reflector for a light-emitting diode, the filler has a refractive index of 1 .5 or greater. In one embodiment of the reflector for a light-emitting diode, the filler has an average particles size greater than 0.01 μιτι but less than 1 .0 μιτι.

In one embodiment of the reflector for a light-emitting diode, the filler is at least one selected from the group consisting of metal oxide and metal sulfide.

In one embodiment of the reflector for a light-emitting diode, the filler is selected from the group consisting of anatase-type titanium dioxide, tin dioxide, niobium pentoxide, and zinc sulfide.

In one embodiment of the reflector for a light-emitting diode, the amount of filler is 0.1 to 50 weight percent based on the combined weights of said filler and said fluororesin.

In one embodiment of the reflector for a light-emitting diode, the fluororesin composition further comprises an adhesion promoter.

In another embodiment, the present invention provides a housing containing the above described reflector for a light-emitting diode.

In another embodiment, the present invention provides a molded article containing a fluororesin and a filler having an average particle size less than 1 .0 μιτι and a band gap greater than 3.0 eV.

In another embodiment, the present invention provides a molded article that is obtained by molding a fluororesin containing a filler having an average particle size less than 1 .0 μιτι and a band gap greater than 3.0 eV.

According to the present invention, an LED reflector and a housing containing said reflector that achieve a high reflectance with little drop in reflectance in the 400 nm to 700 nm wavelength range while exhibiting excellent heat resistance, UV light stability, weather resistance, and adhesivity to a sealant are provided. In addition, the present reflector provides a high reflectance of 85% or higher in the 400 nm to 700 nm wavelength range. Furthermore, because a filler having an average particle size less than 1 .0 μιτι is dispersed evenly inside the reflector of the present invention, the reflectance is higher than ever can be achieved using a smaller amount of filler. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated in the accompanying figures to improve understanding of concepts presented herein.

Figure 1 is a schematic diagram showing the housing having the reflector for LED. In Figure 1 , 1 is the sealant, 2 is the LED chip, 3 is the reflector, 4 is the substrate, and 5 is the housing.

Figure 2 is a schematic diagram showing the reflector for LED in a tape configuration. In Figure 2, 1 is the sealant, 2 is the LED chip, 3 is the reflector, 4 is the substrate, and 6 is the gap.

Figure 3 is a graph showing the wavelength dependency of the reflectance of molded products over the wavelength range of 350 nm to 450 nm.

Figure 4 is a graph showing the wavelength dependency of the reflectance of molded products over the wavelength range of 350 nm to 700 nm.

Figure 5 is a photo obtained using an electron microscope of a fracture cross-section of the fluororesin composition of Application

Example 3.

Figure 6 is a photo obtained using an electron microscope of a fracture cross-section of the fluororesin composition of Comparative Example 2.

DETAILED DESCRIPTION OF INVENTION

In one embodiment the fluororesin used in the present invention is a homopolymer of tetrafluoroethylene (TFE), in another embodiment the fluororesin is a copolymer (TFE copolymer) that comprises TFE and at least one kind of monomer (comonomer) copolymerizable with TFE.

Fluororesin may be used alone or as a mixture comprising two or more fluororesins. The comonomer is contained in the polymer at least in such a sufficient amount that the melting point of the fluororesin becomes substantially lower than the melting point of the TFE homopolymer (poly tetrafluoroethylene (PTFE)). Fluororesin used in the present invention is preferably a melt-moldable fluororesin. Melt molding refers to a molding method that utilizes a known conventional melt molding device; whereby, a molded product, for example, a film, fibers, or a tube, having sufficient levels of strength and durability to suit an intended purpose can be created from a molten substance by letting the polymer flow in its molten state. In one embodiment, the melt-moldable fluororesin used in the present invention is a copolymer comprising 40-98% of repeat unit arising from TFE and 2 to 60 mol% of comonomer that is copolymerizable with TFE. Example of comonomers include hexafluoropropylene (HFP), chlorotrifluoroethylene, perfluoroalkoxytrifluoroethylene, vinylidene fluoride, vinyl fluoride, ethylene, and propylene. Further examples include perfluoroalkene having 3 or more carbon atoms, or preferably, 3 to 6 carbon atoms, and perfluoro(alkyl vinyl ether) having 1 to 6 carbon atoms, for example, are of utility as perfluoroalkoxytrifluoroethylenes. Here, perfluoro(alkyl vinyl ether) (PAVE) alkyl group has 1 to 5 carbon atoms, preferably, linear or branched alkyl group having 1 to 4 carbon atoms. The TFE copolymer may be a copolymer comprising multiple kinds of PAVE monomers and TFE. The amount of repeating units arising from PAVE in the TFE/PAVE copolymer is from 1 to 20 wt%. Example fluororesins include FEP (TFE-HFP copolymer), PFA (TFE-PAVE copolymer), TFE-HFP-PAVE copolymer wherein the PAVE comprises perfluoro(ethy! vinyl ether) (PEVE) and/or peril uoro(propyi vinyl ether), MFA (TFE-perfluoro(methyl vinyl ether)), (PMVE)-PAVE copolymer wherein the alkyl group of the PAVE has 2 or more carbon atoms, and THV (TFE-HFP-vinylidene fluoride (VF2) copolymer. PFA (TFE-PAVE copolymer) is preferred. Fluororesin can include one of the

aforementioned TFE copolymers alone or a mixture comprising two or more such TFE copolymers. Also, a single TFE copolymer or two or more kinds of TFE copolymer can be mixed with a TFE homopolymer.

The TFE copolymer used in the present invention has a melt flow rate (MFR) of approximately 0.5 to 100 g/10 min., preferably, 0.5 to 50 g/10 min., when measured at the standard temperature of the specific TFE copolymer in accordance with ASTM D-1238. In addition, the melt viscosity of the TFE copolymer used in the present invention, as measured at 372^°C using the revised ASTM D-1238 method described in U.S. Patent No. 4,380,618, is at least 10²Pa s, preferably 10²Pa s to 10⁶Pa s, and more preferably from 10³ Pa s to 10⁵ Pa s. The content of the TFE copolymer in the fluororesin composition is 50-99.9 wt%, preferably, 60-99 wt%, or more preferably, 70-95 wt%.

There is no special restriction imposed on the form of the melt- moldable fluororesin as long as it is suitable for melt molding; and a wide variety of forms, such as powder, a granular product of powder, flakes, pellets, and beads, are of utility.

The filler used in the present invention having an average particle size less than 1 .0 μιτι is a light-reflecting compound that has a high refractive index and a high reflectance in the 400 nm to 700 nm

wavelength range. This light-reflecting compound has an average particle size less than 1 .0 μιτι, preferably, greater than 0.01 μιτι but less than 1 .0 μιτι, more preferably, greater than 0.1 μιτι but less than 1 .0 μιτι, or even more preferably, greater than 0.2 μιτι but less than 1 .0 μιτι. It is not desirable for the average particle size of the light-reflecting compound to be 1 .0 μιτι or greater because the light scattering effect is diminished and the reflectance drops. The average particle diameter, for example, can be measured by particle size analyzer (for example, made by CILAS Co., CILAS 990, CILAS 1090, and CILAS 1 190) according to the procedure of ISO 13320.

The filler used in the present invention has a band gap in excess of

3.0 eV. Filler having a band gap of 3.0 eV or less is not desirable in that a sufficient reflectance cannot be achieved in the near-ultraviolet wavelength range because it absorbs light in the 430 nm and shorter wavelength range just like a photocatalysis, as described in The Chemical Society of Japan: Chemistries in Surface Excitation Process, Quarterly Chemical

Reviews No. 12, pp. 132-145 (1991 ). The band gap can be measured, for example, using a UV-3101 PC recording spectrophotometer manufactured by Shimadzu Corporation, in accordance with the method described in Band Gap of Anatase T1O2 3.27 eV in Journal of Molecular Catalysis A Chemical 338, 18 (201 1 ).

The filler used in the present invention has a refractive index of 1 .5 or greater, preferably 2.0 or greater. It is not desirable for the refractive index to be lower than 1 .5 because a high reflectance can not be achieved. Examples of fillers used in the present invention include metal oxides and metal sulfides. Metal oxides are preferred. Example fillers include: anatase-type titanium dioxide (ΤΊΟ2, reflectance: 2.5; band gap: 3.27 eV), tin dioxide (SnO2, reflectance: 2.0; band gap: 3.8eV), niobium pentoxide (Nb₂O₅, reflectance: 2.3; band gap: 3.4eV), zinc oxide (ZnO, reflectance: 2.0; band gap: 3.3eV) and zinc sulfide (ZnS, reflectance: 2.37; band gap: 3.6eV). Anatase-type titanium dioxide is preferred and available commercially, for example, TA-300 manufactured by Fuji Titanium Industry Co., Ltd.

The dispersed condition of the filler in the molded product can be observed using a field-emission-type scanning electron microscope, for example, and S-4500 SEM manufactured by Hitachi, Ltd.

The amount of filler in the fluororesin composition is from 0.1 to 50 weight percent, preferably from 1 to 40 weight percent, and more preferably from 5 to 30 weight percent, based on the combined weight of filler and fluororesin. It is not desirable for the filler to be less than 0.1 wt% because the reflectance of the obtained reflector is poor. Also, it is not desirable for the amount of filler to exceed 50 wt% because injection molding of the fluororesin composition becomes difficult due to its high melt viscosity, and the strength and the durability of the obtained molded product will deteriorate.

The fluororesin of the present invention optionally further contains an adhesion promoter for the purpose of improving the adhesivity of the fluororesin composition to an LED sealant such as silicone, epoxy resin, or a mixture of these materials. There is no special restriction imposed on the adhesion promoter as long as it improves the adhesion of the fluororesin to sealants such as silicone, epoxy resin, or their mixture. In one embodiment, the adhesion promoter is an inorganic compound or an organic polymer. In this embodiment, the inorganic compound is hydrophilic in order to enhance the wettability of the fluororesin

composition to the silicone or epoxy. The surface of the inorganic compound adhesion promoters can also include functional groups such as hydroxyl groups, vinyl groups, or silane groups (e.g., from silane coupling agents) that promote bonding with silicone or epoxy during curing. Alumina is an example of an inorganic compound type adhesion promoter. The organic polymer can be any polymer that shows high thermal resistance and adhesion to sealant such as silicone or epoxy. Example such polymers include thermal resistant silicone powder, or polar polymers such as polyimide, Nafion®, PEI (polyetherimide), PES (polyethersulfone), and the like.

The amount of adhesion promoter in the fluororesin composition is from 0.1 to 20 weight percent, preferably from 0.5 to 10 weight percent, and more preferably from 1 to 5 weight percent, based on the combined weights of fluororesin, filler and adhesion promoter. When alumina is used as the adhesion promoter, if the alumina is less than 0.1 weight percent, a sufficient level of adhesivity of the fluororesin to the sealant can not be achieved. It is not desirable for the alumina to exceed 20 weight percent because the reflectance of the obtained reflector will decrease.

The fluororesin and the filler may be mixed either before the melt molding or simultaneously with the melt molding. Also, a commonly utilized mixing method can be used as a method for mixing them; and a known conventional disperser/blender, for example, a co-coagulation method as disclosed in Japanese Kokai Patent Application No. 2007- 1 19769, a planetary mixer, a high-speed impeller disperser, a rotary drum- type mixer, a screw-type mixer, a belt conveyor mixing method, a ball mill, a pebble mill, a sand mill, a roll mill, an attritor, and a bead mill, may be utilized for this purpose. A device that is capable of evenly dispersing the fluororesin and the filler is preferred.

The fluororesin composition obtained by mixing the fluororesin and the filler before the melt molding may take a variety of forms, for example, a powdery material, a granular product of a powdery material, flakes, pellets, and beads.

In addition to the aforementioned mixing method, a wet mixing of the kind described below is also of utility. For example, a fluororesin coated with a filler can be obtained by dissolving a filler into an aqueous solution or an organic solvent functioning as a carrier and then spraying the filler solution onto a fluororesin. Here, light drying is desirable in order to let the aforementioned aqueous solution or the organic solvent to evaporate. Although no special restriction is imposed on the organic solvent, methanol, ethanol, chloroform, and toluene, for example, are of utility. In addition, an organic solvent that allows the filler to be dissolved easily is desirable.

Any known conventional molding method may be used as a method for melt-molding the fluororesin composition. Compression molding, extrusion molding, transfer molding, flow molding, injection molding, rotational molding, lining molding, foam extrusion molding, and film molding, are of utility. Extrusion molding and injection molding are preferred.

The molded product obtained through the aforementioned melt molding method has a high reflectance with little drop in reflectance in the 400 nm to 700 nm wavelength range, and exhibits excellent heat resistance, UV light stability, and weather resistance. The molded product exhibits a reflectance of 85% or higher in the 400 nm to 700 nm

wavelength range when measured using a measuring method to be described later herein, whereby a stable reflectance can be achieved.

When said molded product is used as an LED reflector, the reflector and therefor a light-emitting diode housing utilizing the reflector achieves a high reflectance of 85% or higher in the 400 nm to 700 nm wavelength range while exhibiting excellent heat resistance, US light stability, and weather resistance.

Reflectances of the molded products shown in Figure 3 in the 350 nm to 700 nm wavelength range can be obtained by measuring

reflectances of roughly 1 .5-mm thick samples that are produced by melt compression molding. In this method, light having wavelength of 350 nm to 700 nm is emitted to a reflective fluororesin layer formed on the front surface of a sample at an incident angle of 10^°, and the transmitted light is let go without providing any reflector on the back surface of the sample. Then, a spectral reflectance (relative reflectance in contrast to a standard white board) with the inclusion of a regular reflection component and a diffused reflection component was measured for each wavelength using a spectrophotometer having an integrating sphere mounted on a detector (for example, a U-4500 manufactured by Hitachi, Ltd.). No special restriction is imposed on the shape of the LED reflector in the present invention. As shown in Figure 2, when multiple LED elements are provided on a tape-shaped or sheet-shaped flexible substrate, a single layer of said reflector can be utilized also as a cover layer equipped with insulating, adhering, and reflecting functions in addition to the concave-shaped reflector shown in Figure 1 .

The housing of the present invention refers to a housing wherein a reflector mounted with an LED chip is attached to a substrate. In this case, the LED chip is sealed off using a sealant.

EXAMPLES

Next, the present invention will be explained in further detail by application examples and comparative examples; however, the present invention is not limited by this explanation.

Each property in the present invention was measured by the following methods.

A. Measurements of properties

(1 ) Melting point (peak melting temperature)

A differential scanning calorimeter (Pyris 1 Type DSC manufactured by PerkinElmer, Inc.) was used. After approximately 10 mg of sample was weighed, put in a special aluminum pan, and crimped using a special crimper, the sample was placed in a DSC body and heated to 360^°C from 150^°C at the rate of 10^°C/min. Its peak melting point (Tm) was obtained based on a melting curve obtained then.

(2) Melt flow rate (MFR)

A melt indexer equipped with a corrosion-resistant cylinder, a die, and a piston in compliance with D-1238-95 (manufactured by Toyo Seiki Co., Ltd.) was used. After 5 g of sample powders were filled in the cylinder that was maintained at 372 ± 1 ^°C and held for 5 minutes, they were extruded through a die orifice under the load of 5 kg (the piston and a weight); and the extrusion rate then (g/10 min.) was obtained as an MFR.

(3) Measurements of reflectance

Reflectance of an approximately 1 .5-mm thick sample produced by means of melt compression molding was measured under the following condition. A method in which light having a wavelength of 350 nm-700 nm was emitted to the reflective layer formed on the front surface of a sample at an incident angle of 10^°, and the transmitted light was let go without providing any reflector on the back surface of the sample was used. Then, a spectral reflectance (relative reflectance in contrast to a standard white board) with the inclusion of a regular reflection component and a diffused reflection component was measured for each wavelength using a spectrophotometer having an integrating sphere mounted on a detector (U-4500 manufactured by Hitachi, Ltd.).

(4) Heat treatment test

An approximately 1 .5-mm thick sample produced by means of melt compression molding was placed inside a circulating hot air oven (ESPEC SUPER-TEM. OVEN STPH-101 ), which had been preheated to 150^°C, in order to apply a heat treatment.

(5) Melt-blending test

A fluororesin and a filler were melt-blended according to the composition shown in Table 1 at 350^°C, which was approximately 40^°C higher than the melting point (approximately 308^°C) of the fluororesin, at 100 rpm for 5 minutes using a melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a

fluororesin composition.

(6) Observation of filler dispersion state

An even dispersion state of a filler was checked by observing a fracture cross-section of an approximately 1 .5-mm thick sample, which was produced from the aforementioned fluororesin at 350^°C by means of melt compression molding, using a scanning electron microscope (S-4500, an SEM manufactured by Hitachi, Ltd.). Average particle sizes of the fillers are also shown in Table 1 .

(7) Measurement of shear/bonding strength

Shear/bonding strength was measured (25^°C, tension speed of

1 mm/min.) in accordance with JIS K 6850, except that sample length of 187.5 ± 0.25 mm was changed to 60 ± 0.25 mm, lap length of 12.5 ± 0.25 mm was changed to 40.5 ± 0.5 mm, and the distance of the sample from the end of the lap part was changed from 50 mm ± 1 mm to 10.5 mm ± 0.5 mm.

(B) Raw materials

Raw materials used in the application examples and the comparative examples of the present invention are as follows.

(1 ) Resins

a) Perfluororesin (TFE/PAVE copolymer, PFA) PFA 440 HPJ manufactured by DuPont-Mitsui Fluorochemical Co., Ltd. (Melting point 308^°C; melt flow rate 15 g/10 min.)

b) Polyphthalamide (PPA) complex. AMODEL (registered trademark) A-4122NLWH905 manufactured by Solvay Advanced

Polymers K.K. (Melting point 324^°C, 22 wt% of glass fibers contained)

(2) Fillers

a) Anatase-type titanium dioxide. TA-300 manufactured by Fuji Titanium Industry Co., Ltd. (Average particle size 0.3 μιτι)

b) Niobium pentoxide. Nb₂O₅ powder from Kojundo Chemical Lab. Co., Ltd. (Average particle size 0.4 μιτι)

c) Rutile-type titanium dioxide. Ti-Pure (registered trademark) R-900 manufactured by E. I. DuPont de Nemours and Company (Average particle size 0.41 μιτι)

d) Zinc dioxide. FINEX-30 powder manufactured by Sakai Chemical Industry Co., Ltd. (Average particle size 0.04 μιτι)

(3) Adhesion promoter: a-alumina. A31 manufactured by Nippon Light Metal Co., Ltd.; average particle size 5.2 μιτι

(4) LED sealant: Silicone. ASP-1010 (A B) manufactured by

Shin-Etsu Chemical Co., Ltd.

Application Example 1

First, 12.2 g of anatase-type titanium dioxide (TA-300 manufactured by Fuji Titanium Industry Co., Ltd) and 100 ml of pure water were put into a beaker (2L) and stirred at 150 rpm for 10 minutes using a downflow propeller-type 4-blade mixer. Then, 372.9 g of PFA aqueous dispersion obtained by means of emulsion polymerization was added so that the titanium dioxide content became 10 wt% with respect to fluororesin PFA (PFA440HPJ manufactured by DuPont-Mitsui

Fluorochemical Co., Ltd.) and stirred for another 30 minutes. After the stirring, 1 .2 ml of 60% nitric acid was added and stirred until the mixture became gelatinized so much that it could not be stirred any longer in order to co-coagulate PFA primary particles and anatase-type titanium dioxide particles together at once. After excessive water was removed by separating the obtained gel aggregate from the aqueous medium, the remaining aggregate was dried at 150^°C for 10 hours in order to obtain dry powders of the aggregate. The obtained dry powders were melt-blended at 350^°C and 100 rpm for 5 minutes using the melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a fluororesin composition. When the dispersion state of the anatase-type titanium dioxide was checked in a fracture cross-section of the obtained fluororesin composition using an electron microscope, the titanium dioxide was found dispersed evenly. Also, reflectances of an approximately 1 .5-mm thick sample, which was produced from the fluororesin at 350^°C by means of melt compression molding, were measured. The results obtained are summarized in Table 1 .

Application Example 2

First, 19.4 g of anatase-type titanium dioxide (TA-300 manufactured by Fuji Titanium Industry Co., Ltd) and 150 ml of pure water were put into a beaker (2L) and stirred at 150 rpm for 10 minutes using the downflow propeller-type 4-blade mixer. Then, 372.9 g of PFA aqueous dispersion obtained by means of emulsion polymerization was added so that the titanium dioxide content became 15 wt% with respect to

fluororesin PFA (PFA440HPJ manufactured by DuPont-Mitsui

Fluorochemical Co., Ltd.) and stirred for another 30 minutes. After the stirring, 1 .3 ml of 60% nitric acid was added and stirred until the mixture became gelatinized so much that it could not be stirred any longer in order to co-coagulate PFA primary particles and anatase-type titanium dioxide particles together at once. After excessive water was removed by separating the obtained gel aggregate from the aqueous medium, the remaining aggregate was dried at 150^°C for 10 hours in order to obtain dry powders of the aggregate. The obtained dry powders were melt-blended at 350^°C and 100 rpm for 5 minutes using the melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a fluororesin composition. When the dispersion state of the anatase-type titanium dioxide was checked in a fracture cross-section of the obtained fluororesin composition using an electron microscope, the titanium dioxide was found dispersed evenly. Also, reflectances of an approximately 1 .5-mm thick sample, which was produced from the fluororesin at 350^°C by means of melt compression molding, were measured. The results obtained are summarized in Table 1 .

Application Example 3

First, 27.5 g of anatase-type titanium dioxide (TA-300 manufactured by Fuji Titanium Industry Co., Ltd) and 200 ml of pure water were put into a beaker (2L) and stirred at 150 rpm for 10 minutes using the downflow propeller-type 4-blade mixer. Then, 372.9 g of PFA aqueous dispersion obtained by means of emulsion polymerization was added such that the titanium dioxide content became 20 wt% with respect to

fluororesin PFA (PFA440HPJ manufactured by DuPont-Mitsui

Fluorochemical Co., Ltd.) and stirred for another 30 minutes. After the stirring, 1 .4 ml of 60% nitric acid was added and stirred until the mixture became gelatinized so much that it could not be stirred any longer in order to co-coagulate PFA primary particles and anatase-type titanium dioxide particles together at once. After excessive water was removed by separating the obtained gel aggregate from the aqueous medium, the remaining aggregate was dried at 150^°C for 10 hours in order to obtain dry powders of the aggregate. The obtained dry powders were melt-blended at 350^°C and 100 rpm for 5 minutes using the melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a fluororesin composition. When the dispersion state of the anatase-type titanium dioxide was checked in a fracture cross-section of the obtained fluororesin composition using an electron microscope, the titanium dioxide was found dispersed evenly in the PFA matrix with a grain size of approximately 0.3 μιτι (primary particle state) as shown in Figure 5. Also, reflectances of an approximately 1 .5-mm thick sample, which was produced from the fluororesin at 350^°C by means of melt compression molding, were measured. The results obtained are summarized in Table 1 . Application Example 4

Niobium pentoxide particles (Nb₂O₅ powder from Kojundo Chemical Lab. Co., Ltd.) and fluororesin PFA (PFA440HPJ manufactured by DuPont-Mitsui Fluorochemical Co., Ltd.) were melt-blended according to the composition shown in Table 1 at 350^°C and 100 rpm for 5 minutes using the melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a fluororesin composition. When the dispersion state of the niobium pentoxide particles was checked in a fracture cross-section of the obtained fluororesin composition using an electron microscope, the niobium pentoxide particles were found to be dispersed evenly. Also, reflectances of an approximately 1 .5-mm thick sample, which was produced from the fluororesin at 350^°C by means of melt compression molding, were measured. The results obtained are summarized in Table 1 .

Application Example 5

Zinc dioxide particles (FINEX-30 powder manufactured by Sakai Chemical Industry Co., Ltd.) and fluororesin PFA (PFA440HPJ manufactured by DuPont-Mitsui Fluorochemical Co., Ltd.) were melt- blended according to the composition shown in Table 1 at 350^°C and 100 rpm for 5 minutes using the melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a fluororesin composition. When the dispersion state of the zinc dioxide particles was checked in a fracture cross-section of the obtained fluororesin composition using an electron microscope, the zinc dioxide particles were found to be dispersed evenly. Also, reflectances of an approximately 1 .5-mm thick sample, which was produced from the fluororesin at 350^°C by means of melt compression molding, were measured. The results obtained are summarized in Table 1 .

Application Example 6

An approximately 1 .5-mm thick sample was created from the fluororesin obtained in Application example 3 by means of melt

compression molding at 350^°C. After the obtained sample was applied with a heat treatment for 100 hours inside a circulating hot air oven, which had been preheated to 150^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 2.

Application Example 7

compression molding at 350^°C. After the obtained sample was applied with a heat treatment for 500 hours inside the circulating hot air oven, which had been preheated to 150^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 2.

Application Example 8

compression molding at 350^°C. After the obtained sample was applied with a heat treatment for 72 hours inside a circulating hot air oven, which had been preheated to 180^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 3.

Application Example 9

compression molding at 350^°C. After the obtained sample was applied with a heat treatment for 140 hours inside a circulating hot air oven, which had been preheated to 180^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 3.

Application Example 10

Approximately 1 .6 ± 0.1 mm thick, 60 mm long, and 25 mm wide samples were created from the fluororesin obtained in Application example 3 by means of melt compression molding at 350^°C. Silicone (ASP-1010 (A/B) manufactured by Shin-Etsu Chemical Co., Ltd.) serving as an LED sealant was coated between two lapped samples and subjected to cross-linking reactions first at 100^°C for two hours and then at 150^°C for three hours. Shear/bonding strengths of the cross-linked samples at 25^°C were measured at the tension speed of 1 mm/min. The results obtained are summarized in Table 4.

Application Example 1 1

First, a-alumina (A31 manufactured by Nippon Light Metal Co., Ltd.) was added to the complex composition obtained in Application example 3 until the alumina content became 1 wt% with respect to fluororesin PFA and melt-blended at 350^°C and 100 rpm for 5 minutes using the melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a fluororesin composition.

Approximately 1 .6 ± 0.1 -mm thick, 60-mm long, and 25-mm wide samples were created from the obtained fluororesin by means of melt compression molding at 350^°C. Silicone (ASP-1010 (A B) manufactured by Shin-Etsu Chemical Co., Ltd.) serving as an LED sealant was coated between 2 lapped samples and subjected to cross-linking reactions first at 100^°C for 2 hours and then at 150^°C for 3 hours. Shear/bonding strengths of the cross-linked samples at 25^°C were measured at the tension speed of 1 mm/min. The results obtained are summarized in Table 4.

Comparative Example 1

Rutile-type titanium dioxide (Ti-Pure® R-900 manufactured by E. I. DuPont de Nemours and Company) and fluororesin PFA

(PFA440HPJ manufactured by DuPont-Mitsui Fluorochemical Co., Ltd.) were melt-blended according to the composition shown in Table 1 at 350^°C and 100rpm for 5 minutes using the melt blender (KF-70V compact segment mixer manufactured by Toyo Seiki Co., Ltd.) in order to obtain a fluororesin composition. When the dispersion state of the rutile-type titanium dioxide was checked in a fracture cross-section of the obtained fluororesin composition using an electron microscope, the titanium dioxide was found dispersed evenly in the PFA. Also, reflectances of an approximately 1 .5-mm thick sample, which was produced from the fluororesin at 350^°C by means of melt compression molding, were measured. The results obtained are summarized in Table 1 .

Comparative Example 2 After anatase-type titanium dioxide (TA-300 manufactured by Fuji Titanium Industry Co., Ltd.) and fluororesin PFA (PFA440HPJ manufactured by DuPont-Mitsui Fluorochemical Co., Ltd.) were put in a polyester bag and shaken for 5 minutes, and a sheet was created from the mixture by means of melt compression molding at 350^°C, this sheet was cut into small pieces, and the same melt compression molding was carried out again in order to create an approximately 1 .5-mm thick sample. When the dispersion state of the anatase-type titanium dioxide was checked in a fracture cross-section of the obtained fluororesin composition using an electron microscope, many titanium dioxide aggregates having a diameter of 80 μιτι to 200 μιτι were found formed and dispersed as shown in Figure 6. When reflectances were measured at 3 different positions of the sample, reflectances indicated the same values. The results obtained are summarized in Table 1 .

Comparative Example 3

Reflectances of an approximately 1 .5-mm thick sample, which was created from a PPA complex (AMODEL (registered trademark) A- 4122NLWH905 manufactured by Solvay Advanced Polymers K.K.) containing glass fibers as a filler by means of melt compression molding at 340^°C, were measured. The results obtained are summarized in Table 2. Comparative Example 4

After a sample created under the same conditions as those in Comparative example 3 was applied with a heat treatment for 100 hours inside the circulating hot air oven, which had been preheated to 150^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 2.

Comparative Example 5

After a sample created under the same conditions as those in Comparative example 3 was applied with a heat treatment for 500 hours inside the circulating hot air oven, which had been preheated to 150^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 2.

Comparative Example 6

After a sample created under the same conditions as those in Comparative example 3 was applied with a heat treatment for 72 hours inside the circulating hot air oven, which had been preheated to 180^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 3.

Comparative Example 7

After a sample created under the same conditions as those in Comparative example 3 was applied with a heat treatment for 140 hours inside the circulating hot air oven, which had been preheated to 180^°C, its reflectances were measured at room temperature. The results obtained are summarized in Table 3.

Reference Example 1

An approximately 1 .5-mm thick sample was created from fluororesin PFA440HPJ by means of melt compression molding at 350^°C. Reflectances measured of the obtained sample at room temperature are summarized in Table 1 .

Dependency of reflectance of reflector on anatase-type titanium dioxide, niobium pentoxide, and zinc oxide added

In Application example 1 , reflectances of 90% and higher were exhibited without absorbing any light at the wavelengths measured when 10 wt% of anatase-type titanium dioxide particles (particle size 0.3 μιτι) were dispersed evenly in the PFA. In addition, as shown in Application examples 1 -3, because the reflectances did not change much from the reflectances measured at the respective wavelengths in Application example 1 even when the amount of the titanium dioxide added was increased up to 20 wt%, it was found that 10 wt% of filler was sufficient for achieving reflectances of 90% and higher. In addition, in Application example 4 and Application example 5, when 10 wt% of niobium pentoxide (particle size 0.4 μιτι) and 20 wt% of zinc dioxide (particle size 0.04 μιτι) were dispersed evenly in the PFA, reflectances of 85% and higher were exhibited in the 400 nm-700 nm wavelength range. On the other hand, as shown in Table 1 , Figure 3, and Figure 4, the fluororesin containing no filler (Reference example 1 ) exhibits high transmittances, but it exhibits low reflectances in the visible ray range in particular.

Light-reflecting behavior of anatase-type titanium dioxide In Application Example 1 , when 10 wt% of anatase-type titanium dioxide was dispersed evenly in the PFA, reflectances of 90% and higher were exhibited without absorbing any light in the 400 nm-700 nm wavelength range. On the other hand, it can be seen in Table 1 and Figure 3, although reflectances of 90% and higher were exhibited in the visible ray range (440 nm-700 nm) when 10 wt% of rutile-type titanium dioxide was dispersed evenly in the PFA (Comparative example 1 ), the reflectances dropped in the range of 430 nm and lower because the light was absorbed by the rutile-type titanium dioxide at wavelengths of 430 nm and lower. As shown in Table 2 and Figure 3, it was also found that the reflectances of the PPA complex (Comparative example 3) dropped in the range of 430 nm and lower, just like the aforementioned PFA rutile-type titanium dioxide.

Dependency of reflectance on grain size of anatase-type titanium dioxide

In Application Example 3, reflectances of 90% and higher were exhibited in the 400 nm-700 nm wavelength range when 20 wt% of anatase-type titanium dioxide was dispersed evenly in the PFA. On the other hand, although the same crystals (anatase-type titanium dioxide) as those of the titanium dioxide used in Application example 3 were used in the same amount (20 wt%) in Comparative example 2, because

insufficient shearing force was applied during the melt compression molding, the titanium dioxide ended up having grain sizes of 80 μηη-200 μιτι due to coagulation, and only reflectances as high as 70% were exhibited in the same wavelength range. As such, in one embodiment the present invention involves dispersing the anatase-type titanium dioxide evenly in its primary particle state such as by applying a shearing force during the melt blending, thereby resulting in high levels of reflection in the 400 nm-700 nm wavelength range.

Dependency of reflectance on 150^°C heat treatment time

In Application Examples 5 and 6, it was found that the reflectances hardly changed even when the fluororesin compounds were thermally treated continuously at 150^°C for 100 hours and 500 hours, respectively. On the other hand, in the case of the PPA complexes in Comparative Examples 4 and 5, the reflectances dropped in the visible wavelength range due to discoloration of the samples as shown in Table 2 when they were thermally treated under the same conditions as those in Application Examples 5 and 6.

Dependency of reflectance on 180^°C heat treatment time

In Application Examples 7 and 8, it was found that the reflectances hardly changed even when the fluororesin compounds were thermally treated continuously at 180^°C for 72 hours and 140 hours, respectively. On the other hand, in the case of the PPA complexes in Comparative Examples 6 and 7, the reflectances dropped in the visible ray range due to discoloration of the samples as shown in Table 3.

Improvement of adhesivity to silicone sealant

As it is clear from Table 4, while the bonding strength to the silicone sealant was 0.04 MPa in Application example 9, the bonding strength was improved to 0.15 MPa when 1 wt% of alumina was added in Application example 10. Furthermore, it was also found that high reflectance (90% or higher) was able to be maintained in the 400 nm-700 nm wavelength range even when 1 wt% of alumina was added.

Table 1

Table 1 : Reflectance of molded products and filler dispersed s :ate

Table 2

Table 2: Reflectances of non-heat-treated products and molded products heat-treated at 150^°C

Table 3

Table 3: Reflectances of non-heat-treated products and molded products heat-treated at 180^°C

Table 4

Table 4: Shear/bondin stren ths and reflectances

Claims

1 . A reflector for a light-emitting diode that is obtained by molding a fluororesin containing a filler having an average particle size less than 1 .0 μιτι and a band gap greater than 3.0 eV.

2. The reflector for a light-emitting diode of claim 1 , wherein the difference between the maximum value and the minimum value of the reflectance of the reflector in the 380 nm to 400 nm wavelength range is in excess of 25%.

3. The reflector for a light-emitting diode of claim 1 , wherein the reflectance over the wavelength range of 400 nm to 700 nm is 85% or greater.

4. The reflector for a light-emitting diode of claim 1 , wherein said fluororesin is a homopolymer of tetrafluoroethylene or a copolymer comprising tetrafluoroethylene and at least one monomer selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, perfluoro(alkoxy vinyl ether), vinylidene fluoride, vinyl fluoride, ethylene, and propylene.

5. The reflector for a light-emitting diode of claim 1 , wherein said filler has a refractive index of 1 .5 or greater.

6. The reflector for a light-emitting diode of claim 1 , wherein said filler has an average particle size greater than 0.01 μιτι but less than 1 .0 μιτι.

7. The reflector for a light-emitting diode of claim 1 , wherein said filler is at least one selected from the group consisting of metal oxide and metal sulfide.

8. The reflector for a light-emitting diode of claim 1 , wherein said filler is selected from the group consisting of anatase-type titanium dioxide, tin dioxide, niobium pentoxide, and zinc sulfide.

9. The reflector for a light-emitting diode of claim 1 , wherein said filler is anatase-type titanium dioxide.

10. The reflector for a light-emitting diode of claim 1 , wherein the amount of said filler is 0.1 to 50 weight percent based on the combined weight of said filler and said fluororesin.

1 1 . The reflector for a light-emitting diode of claim 1 , wherein said fluororesin composition further comprises an adhesion promoter.

12. A housing containing a reflector for a light-emitting diode

described in claim 1 .

13. A molded article comprising fluororesin and a filler having an average particle size less than 1 .0 μιτι and a band gap greater than 3.0 eV.

14. A molded article that is obtained by molding a fluororesin containing a filler having an average particle size less than 1 .0 μιτι and a band gap greater than 3.0 eV.