JP2015050000A - Filament, and light source using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filament having high efficiency for converting electric power to visible light.SOLUTION: A filament includes a base 10 made of a metallic material and a visible light reflectance reducing film 11 covering the base 10 for making the visible light reflectance of the base 10 lower than an infrared reflectance. The film thickness of the visible light reflectance reducing film 11 is set so as to cause a visible light 12 reflected on the surface of the visible light reflectance reducing film 11 and a visible light 13 reflected on the base 10 to interfere with each other and thereby to reduce the strength. The refractive index or extinction coefficient for visible light of the visible light reflectance reducing film 11 is 2.5 or higher. In a visible light reflectance reducing film 11 with a refractive index of 2.5 or higher for visible light, the reflectance of the surface is about 50% therefore, the strength of the visible light 12 reflected on the surface and the strength of the visible light 13 reflected on the base 10 become almost the same and they can be cancelled by each other.

Description

  The present invention relates to a filament with improved energy utilization efficiency, and more particularly to a light source using the filament and a thermionic emission source.

  Incandescent light bulbs are widely used in which a current is passed through a tungsten filament or the like to heat the filament to form a light bulb. An incandescent light bulb has a radiation spectrum excellent in color rendering similar to sunlight, and the conversion efficiency from the power of the incandescent light bulb to light is 95% or more, but the wavelength component of the emitted light is as shown in FIG. The infrared radiation component is 90% or more (in the case of 3000K in FIG. 1). For this reason, the conversion efficiency from the electric power of the incandescent light bulb to visible light is as low as about 15 lm / W. On the other hand, the fluorescent lamp has a conversion efficiency from electric power to visible light of about 90 lm / W, which is larger than the incandescent lamp. For this reason, incandescent bulbs are excellent in color rendering, but have a problem of a large environmental load.

  Various proposals have been made as attempts to increase the efficiency, brightness, and life of incandescent bulbs. For example, Patent Documents 1 and 2 have a configuration in which an inert gas or a halogen gas is sealed inside a light bulb, whereby the evaporated filament material is halogenated and returned to the filament (halogen cycle) to increase the filament temperature. Proposed. These are generally called halogen lamps. Thereby, the effect of the increase in the power conversion efficiency to visible light and the extension of a filament lifetime is acquired. In this configuration, it is important to control the components of the sealed gas and the pressure in order to increase the efficiency and extend the life.

  Patent Documents 3 to 5 disclose a configuration in which an infrared reflection coating is applied to the surface of a bulb glass so that infrared light emitted from the filament is reflected, returned to the filament, and absorbed. As a result, infrared light is used for reheating the filament to increase efficiency.

  Patent Documents 6 to 9 propose a configuration in which a fine structure is produced in the filament itself, and infrared radiation is suppressed and the proportion of visible light radiation is increased by the physical effect of the fine structure.

JP-A-60-253146 Japanese Patent Laid-Open No. 62-10854 JP 59-58752 A JP-T 62-501109 JP 2000-123795 A JP 2001-519079 JP-A-6-5263 JP-A-6-2167 JP 2006-205332 A

F. Kusunoki etal., Jpn. J. Appl. Phys. 43, 8A, 5253 (2004).

  However, the technologies using the halogen cycle as in Patent Documents 1 and 2 can achieve the life extension effect, but it is difficult to greatly improve the conversion efficiency, and the current efficiency is about 20 lm / W. is there.

  In addition, as in Patent Documents 3 to 5, the technology of reflecting infrared radiation with an infrared reflecting coat and reabsorbing the filament to the filament is highly effective in reabsorption because the reflectance of infrared light by the filament is as high as 70%. It does n’t happen well. Further, the infrared light reflected by the infrared reflective coating is absorbed by other parts other than the filament, such as the filament holding part and the base, and is not used for heating the filament. For this reason, it is difficult to greatly improve the conversion efficiency by this technology. At present, the efficiency is about 20 lm / W.

  As described in Patent Documents 6 to 9, a technique for suppressing the infrared radiation by the fine structure is a report showing the radiation enhancement and the suppression effect for the wavelength of the extreme part of the infrared radiation spectrum as in Non-Patent Document 1. However, it is very difficult to suppress infrared radiation over a wide range of infrared light. This is because when one wavelength is suppressed, another wavelength is enhanced. For this reason, it is considered difficult to achieve significant efficiency improvements using this technology. In addition, since a fine microfabrication technique such as electron beam lithography is used for producing a fine structure, a light source using this is very expensive. Furthermore, even if a microstructure is formed on the W substrate, which is a high temperature heat-resistant member, the W substrate surface particles are recrystallized and crystal grains grow at a heating temperature of about 1000 ° C., and the microstructure portion is destroyed due to this recrystallization. There is also the problem of being done.

  An object of the present invention is to provide a filament having high efficiency for converting electric power into visible light.

  In order to achieve the above object, in the present invention, a base formed of a metal material, and a visible light reflectance lowering film that covers the base in order to make the visible light reflectance of the base lower than the infrared light reflectance, A filament comprising: The film thickness of the visible light reflectance lowering film is set so that the visible light reflected from the surface of the visible light reflectance lowering film interferes with the visible light reflected from the substrate to reduce the intensity. The reflectivity of the visible light reflectance lowering film alone is designed to be about 0.5. When realizing this reflectance, the visible light reflectance lowering film has at least one of a refractive index and an extinction coefficient for visible light of 2.5 or more.

  According to the present invention, the visible light reflectance of the filament can be effectively made lower than the infrared light reflectance by the visible light reflectance lowering film in which at least one of the refractive index and the extinction coefficient for visible light is 2.5 or more. Therefore, infrared light radiation of the filament can be suppressed and visible light radiation can be enhanced. Therefore, a filament with high visible light radiation efficiency can be obtained.

The graph which shows the wavelength dependence of the radiant energy in each temperature of the conventional tungsten filament. In the filament of this invention, explanatory drawing which shows that visible light cancels out by interference by the visible light reflectance fall film | membrane 11 of high refractive index. In the filament of this invention, explanatory drawing which shows that infrared light does not cancel out by the visible light reflectance fall film | membrane 11 of high refractive index. The graph which shows the relationship between the reflectance of the filament of this invention, an emissivity, and an emission spectrum. The graph which shows the theoretical curve of the reflectance and radiation | emission spectrum which are requested | required of a filament in order to produce the light beam efficiency exceeding 50 lm / W in the temperature range of 3000K. In the filament of a comparative example, explanatory drawing which shows that visible light weakens by interference by the visible light reflectance fall film | membrane 11 of a low refractive index. Explanatory drawing which shows melting | fusing point of the material which can be used for the visible light reflectance fall film | membrane 11, a refractive index, and an extinction coefficient in a table | surface form. The graph which shows the reflectance curve of the base | substrate 10 (HfN / W) of Embodiment 1, and the W filament of a comparative example. The graph which shows the reflectance curve of the filament (Os / HfN (1000 nm) / W) whose film thickness of the Os film | membrane of Embodiment 1 is 0, 5, 13, 20, 50, 200 nm. The graph which shows the relationship between the reflectance of the filament (Os (13nm) / HfN (1000nm) / W) of Embodiment 1, the emissivity, and the radiation spectrum. The graph which shows the relationship between the reflectance of W filament, an emissivity, and an emission spectrum. The graph which shows the relationship between the reflectance of the filament (Re (10nm) / HfN (1000nm) / W) of Embodiment 2, the emissivity, and the radiation spectrum. Graph showing reflectance curves of the filament coated with WSi ₂ film with a thickness of 4nm embodiment _{3 (WSi 2 (4nm) /} HfN (1000nm) / W). Graph showing reflectance curves of the third embodiment of the WSi ₂ film having a film thickness of the filament _{(WSi 2 / HfN (1000nm)} / W) coated with 5,6,7,8,9,10Nm. Graph showing respectively the reflectivity curve of the filament thickness of the HfO ₂ film of Embodiment 4 is _{5,10,20,30nm (Os (3nm) / HfO} 2 / HfN (1000nm) / W). Graph showing the reflectivity and emissivity of the relationship between the emission spectrum of the filaments embodiment _{4 (Os (3nm) / HfO} 2 (30nm) / HfN (1000nm) / W). Graph showing the reflectivity and emissivity of the relationship between the emission spectrum of the filaments embodiment _{5 (SiC (20nm) / HfO} 2 (200nm) / Ta). Sectional drawing of the incandescent lamp of Embodiment 6. FIG.

  An embodiment of the present invention will be described. As shown in FIGS. 2 and 3, the filament of the present invention covers the base 10 formed of a metal material and the base 10 so that the visible light reflectance of the base 10 is lower than the infrared light reflectance. And a visible light reflectance lowering film 11. The film thickness of the visible light reflectance lowering film 11 is such that the visible light 12 reflected on the surface of the visible light reflectance lowering film 11 interferes with the visible light 13 reflected by the substrate 10 as shown in FIG. Is set to At least one of the refractive index and extinction coefficient with respect to visible light of the visible light reflectance lowering film 11 is 2.5 or more.

  The film thickness of the visible light reflectivity lowering film 11 of the present invention is set so as to reduce visible light by interference, and therefore hardly affects the phase of infrared light having a wavelength longer than that of visible light. Therefore, as shown in FIG. 3, the infrared light 14 reflected by the surface of the visible light reflectance lowering film 11 and the infrared light 15 reflected by the substrate 10 do not interfere with each other, and the intensity hardly decreases. Therefore, the visible light reflectance of the filament can be made lower than the infrared light reflectance.

  Further, by using a visible light reflectance lowering film 11 having at least one of a refractive index and an extinction coefficient of 2.5 or more for visible light, the reflectance of the surface of the visible light reflectance lowering film 11 is 50%. Can be back and forth. As a result, the intensity of the visible light 12 reflected from the surface of the visible light reflectance lowering film 11 and the intensity of the visible light 13 reflected from the substrate 10 are substantially equal, and can be almost canceled out. The reflectance can be effectively reduced.

  When at least one of the refractive index and extinction coefficient for visible light of the visible light reflectance lowering film 11 is 3.0 or more, the reflectance of the visible light reflectance lowering film 11 can be close to 50%. More preferred.

  Due to the action of the visible light reflectance lowering film 11, it is preferable that the reflectance of at least part of the visible light region of the filament is 40% or less and the reflectance of at least part of the infrared light region is 80% or more. Thereby, the efficiency of visible light radiation of the filament can be significantly increased as compared with the conventional case.

The visible light reflectance lowering film 11 can include a film formed of any one of Os, Re, Ru, W, Mo, SiC, and WSi ₂ . These materials can achieve 2.5 or more of at least one of a refractive index and an extinction coefficient with respect to visible light. However, the material of the visible light reflectance lowering film 11 is different from the material of the base material 10 in contact with the visible light reflectance lowering film 11.

  The reflectance of the substrate 10 itself is desirably 90% or more in at least a part of the visible light region and at least a part of the infrared light region. This is because the reflectance of the infrared light region of the filament is increased and the reflectance of the visible light region is reduced. In particular, it is desirable that the reflectance is 80% or more at a wavelength of 1000 nm.

  In order to achieve high reflectivity, it is desirable that the surface of the substrate 10 be processed into a mirror surface. Specifically, the surface roughness of the substrate satisfies at least one of center line average roughness Ra of 1 μm or less, maximum height Rmax of 10 μm or less, and ten-point average roughness Rz of 10 μm or less. It is desirable.

  In addition, the substrate 10 may have a structure in which the surface of a core material made of metal is covered with a metal layer having a higher reflectance than the core material. Thereby, the reflectance of a base | substrate can be raised.

  The visible light reflectance lowering film 11 may be configured to further include a dielectric layer disposed between the base 10 and the substrate 10. In this case, the refractive index of the dielectric layer with respect to visible light may be smaller than 2.5. The total film thickness of the visible light reflectance lowering film 11 and the dielectric layer causes the visible light reflected on the surface of the visible light reflectance lowering film 11 to interfere with the visible light reflected by the substrate 10 to reduce the visible light intensity. As long as it is designed as such.

Materials constituting the substrate (core material) 10 include Ta, Os, Ir, Mo, Re, W, Ru, Nb, Cr, Zr, V, Rh, C, B ₄ C, SiC, ZrC, TaC, and HfC. , AlN, BN, ZrN, HfN, TiN, LaB ₆ , ZrB ₂ , HfB ₂ , or an alloy thereof can be used.

  Further, it is desirable to use a substrate (core material) 10 that is preliminarily heated at a high temperature to complete crystal grain growth of the material constituting the substrate 10 and mirror-polished the substrate 10 that has completed the crystal grain growth. . Thereby, when the substrate 10 is heated at a high temperature, crystal grains grow and the surface becomes rough, and as a result, the infrared reflectance is lowered, and the film disposed on the surface of the visible light reflectance preventing film 11 or the like. It can be prevented from causing damage at high temperatures.

The metal layer having a higher reflectance than the core material that covers the substrate (core material) 10 is composed of a metal film having a melting point of 2000K or higher, a metal carbide film, a nitride film, a boride film, and an oxide film. It is also possible to form either. For example, Ta, Os, Ir, Mo, Re, W, Ru, Nb, Cr, Zr, V, Rh, C, B4C, SiC, ZrC, TaC, HfC, AlN, BN, TiN, ZrN, HfN, LaB ₆ , ZrB2, HfB2, CaO, CeO2, MgO, ZrO ₂ , Y ₂ O ₃ , HfO ₂ , Lu2O ₃ , Yb ₂ O ₃ , ThO ₂ , or a mixture thereof, To do.

  Next, the principle that the filament of the present invention having a visible light reflectance lower than the infrared light reflectance can emit visible light with high efficiency will be described with reference to the drawings.

  The filament of the present invention ideally has a low reflectance close to 0% in the visible light region with a wavelength of 700 nm or less as shown by a solid line in FIG. 4, and close to 100% in the infrared light region. Although it is desirable to have a reflectivity, a reflectivity curve that can be realized using a material that is practically available has a low reflectivity of 40 nm or less at a wavelength of 500 nm, as shown in FIG. The reflectance of the above long wavelength infrared light region shows a high reflectance of 80% or more. As for the wavelength dependence of the reflectance between the low reflectance and the high reflectance, it is desirable that the reflectance monotonously increases from the short wavelength side to the long wavelength side as shown in FIGS. . By heating a filament having reflectivity characteristics as shown in FIG. 5 to 3000 K, it is possible to increase the luminous efficiency of 30 lm / W, which has been conventionally realized, to a value exceeding 50 lm / W.

  First, Kirchhoff's law for blackbody radiation is based on the principle that filaments with high reflectivity in the infrared light region and low reflectivity in the visible light region emit visible light with high efficiency when heated by current supply etc. Based on this, it will be described below.

The energy loss with respect to the input energy of the material (here, the filament) under conditions without natural convection heat transfer (for example, in a vacuum) is given by the following equation (1) in an equilibrium state.
(Equation 1)
P (total) = P (conduction) + P (radiation) (1)
Where P (total) is the total input energy, P (conduction) is the energy lost through the lead that supplies current to the filament, and P (radiation) is the temperature at which the filament is heated It is the energy lost by radiating light.

  When the filament is heated to a high temperature of 2500 K or more, the energy lost through the lead wire is only about 5%, and the remaining 95% or more is lost to the outside by light radiation. Almost all the electric energy can be replaced by light. However, of the radiated light emitted from the conventional general filament, the proportion of the visible light component is only about 10%, and most of it is the infrared radiated light component. Don't be.

式（２）においてε（λ）は、各波長における放射率、αλ^-5／（ｅｘｐ（β／λＴ）−１）の項は、プランクの放射則を示す。α＝３．７４７×１０^８ Ｗμｍ^４／ｍ^２、β＝１．４３８７×１０^４ μｍＫ、である。また、ε（λ）は、キルヒホッフの法則によって反射率Ｒ(λ)と式（３）の関係にある。
（数３）
ε(λ)＝１−Ｒ(λ) ・・・(3) In general, the term of P (radiation) in the above formula (1) can be described by the following formula (2).

In equation (2), ε (λ) represents the emissivity at each wavelength, and the term αλ ⁻⁵ / (exp (β / λT) −1) represents Planck's radiation law. α = 3.747 × 10 ⁸ W μm ⁴ / m ² and β = 1.4387 × 10 ⁴ μmK. Also, ε (λ) has a relationship of the reflectance R (λ) and the equation (3) according to Kirchhoff's law.
(Equation 3)
ε (λ) = 1−R (λ) (3)

  When the equations (2) and (3) are discussed in association, a material whose reflectance is 1 over all wavelengths is ε (λ) = 0 from the equation (3), and hence the equation (2). Since the integral value at becomes zero, no loss due to radiation occurs. This physical meaning means that since P (total) = P (conduction), there is no loss due to light emission even with a small amount of input energy, and the filament reaches a very high temperature. On the other hand, a material having a reflectance of 0 over all wavelengths is called a complete black body, and ε (λ) = 1 from equation (3). As a result, the integral value in the equation (2) is maximized, and consequently the amount of loss due to radiation is maximized. In ordinary materials, the emissivity ε (λ) exists between 0 <ε (λ) <1, and the wavelength dependence thereof does not change dramatically (wavelength λ, slowness with respect to temperature T). There is a major dependency). Therefore, light emission in the infrared to visible light region occurs uniformly from substantially visible to the infrared light region as shown by the two-dot chain line in FIG. In FIG. 4, the black body radiation spectrum is plotted with ε (λ) = 1 in the entire wavelength region in order to simplify the discussion.

On the other hand, as shown by a one-dot chain line in FIG. 4, a material having approximately 0% emissivity in the infrared light region and approximately 100% emissivity in the visible light region of 700 nm or less was heated in vacuum. Thermal radiation can be expressed by the following equation (4).

In equation (4), θ (λ−λ ₀ ) has an emissivity of ₀ from a long wavelength to a wavelength λ _{0 of} visible light, and an emissivity of 1 in a region shorter than a certain wavelength λ _0. It is a function that shows some step function behavior. The obtained radiation spectrum has a shape obtained by convolving the stepwise emissivity and the blackbody radiation spectrum, and the calculation result is a spectrum indicated by a broken line in FIG. In other words, the physical meaning of equation (4) is that the radiation loss is suppressed in the low temperature region where the input energy to the filament is small, and the P (radiation) term of equation (4) is 0, so the energy loss is Only the P (conduction), and the filament temperature rises very efficiently. On the other hand, the filament temperature is a high temperature, the peak wavelength of black-body radiation spectrum is a temperature region as shorter than lambda _0, as a visible light emission as the spectrum that shows an energy input to the filament by a broken line in FIG. 4 To lose.

In the equation (4), θ (λ−λ ₀ ) has an emissivity of ₀ from a long wavelength to a wavelength λ ₀ where visible light is present as described above, and an emissivity in a region shorter than a certain wavelength λ _0. Is a material that is 1. Such a material has a reflectivity of 0 at a wavelength λ ₀ or less and a reflectivity of 1 in a wavelength region longer than the wavelength λ ₀ as shown by a solid line in FIG. 4 according to Kirchhoff's law of Equation (3). It becomes. Therefore, the present invention suppresses the emission of infrared light by producing a filament having a reflectance close to 0 at a wavelength λ ₀ or less and having a reflectance close to 1 in a longer wavelength region than the wavelength λ ₀ , thereby making visible light visible. Light can be emitted with high efficiency. Further, as shown in FIG. 5, the reflectance at a wavelength λ _S = 500 nm or less is a low reflectance of 40% or less, the reflectance monotonously increases from a wavelength of 500 nm, and an infrared having a wavelength longer than the wavelength λ _L = 1000 nm. Even a highly reflective filament with a reflectance of 80% or more in the light region can suppress the emission of infrared light and emit visible light with high efficiency, which is more efficient than a conventional tungsten filament. It can be increased by 40% or more. For example, at a heating temperature of 3000 K, the conventional tungsten filament is 36.7 lm / W, whereas the filament having the reflectance characteristic of FIG. 5 improves the luminous efficiency up to 51.5 lm / W. This makes it possible to provide a highly efficient incandescent light source.

  Further, since the filament for the light source has a high temperature of 2000K to 3000K, also in the present invention, as shown in FIG. A filament for a light source that exhibits a high reflectance of 80% or more in the infrared light region having a longer wavelength than that of the light source.

  In the present invention, as described above, the visible light reflectance is made lower than the infrared light reflectance by coating the base 10 with the visible light reflectance lowering film 11. Hereinafter, the optical characteristics and the like of the visible light reflectance lowering film 11 and the substrate 10 will be described more specifically.

(1) Refractive index and extinction coefficient of visible light reflectivity lowering film 11 Visible light reflectivity lowering film 11 is formed of visible light 13 reflected by substrate 10 and the surface of visible light reflectivity lowering film 11 as shown in FIG. The visible light reflectivity is lowered by using the interference with the visible light 12 reflected in step 1 so that the visible light 12 and the visible light 13 cancel each other. As a result of the interference, the electric field intensity of the visible light 12 reflected by the surface of the visible light reflectivity lowering film 11 is equal to the electric field intensity of the visible light 12 reflected by the interface with the substrate 10 in order to bring the reflected light of the visible light closer to zero. It is desirable that they are approximately the same. Therefore, it is preferable that the visible light reflectance on the surface of the visible light reflectance lowering film 11 is about 0.5. Thereby, half of the incident visible light is reflected on the surface of the visible light reflectance lowering film 11, and the remaining half of the visible light is incident on the visible light reflectance lowering film 11 to be interfaced with the substrate 10. Can be reflected. As a result, the electric field strengths of the visible light 12 reflected by the surface of the visible light reflectivity lowering film 11 and the visible light 13 reflected by the substrate 10 are equal, so that it is theoretically possible to cancel almost completely. .

The reflectance R of the surface of the visible light reflectance lowering film 11 is represented by the formula (5).
(Equation 5)
R = [(n ₀ −n (λ)) ² + k (λ) ² ] / [(n ₀ + n (λ)) ² + k (λ) ² ]
···(Five)
In equation (5), n ₀ is the refractive index of vacuum, 1 is the refractive index of the visible light reflectance lowering film 11, k is the extinction coefficient of the visible light reflectance lowering film 11, and λ is incident. It is the wavelength of visible light.

  Using the above formula (5), when the refractive index n for which the reflectance R = 0.5 is obtained for visible light, when the extinction coefficient k is 0, it becomes approximately n = 6. Since there is no material having such a high refractive index and an extinction coefficient k of 0, the reflectivity is actually designed by taking into account the effect of the extinction coefficient k. Considering the extinction coefficient, the visible light reflectance lowering film 11 is preferably such that at least one of the refractive index and extinction coefficient for visible light is 2.5 or more, more preferably 3.0 or more. .

  As a comparative example, the electric field strength when the refractive index of the visible light reflectance lowering film 11 is lower than 2.5 is shown in FIG. When the refractive index is smaller than 2.5, the reflectance of the surface of the visible light reflectance lowering film 11 becomes lower, so that the electric field intensity of the visible light 12 reflected by the surface of the visible light reflectance lowering film 11 becomes the substrate 10. It becomes smaller than the electric field intensity of the visible light 13 reflected by. Therefore, although the visible light intensity can be reduced, it cannot be canceled out, so the effect of reducing the visible light reflectance is reduced.

(2) Film thickness of the visible light reflectance lowering film 11 The film thickness D of the visible light reflectance lowering film 11 is such that the phase of the visible light 13 reflected by the substrate 10 is reflected by the surface of the visible light reflectance lowering film 11. The visible light 12 is set to be shifted by π radians (that is, inverted).
(Equation 6)
D = (1/4) (λ / n ² ) (6)
Where λ is the wavelength of visible light 13 in vacuum.

Thereby, the visible light 12 reflected by the surface of the visible light reflectance lowering film 11 and the visible light 13 reflected by the substrate 10 can be canceled by interference. Therefore, the optimum film thickness D is obtained in consideration of the refractive index of the visible light reflectance lowering film 11 and the visible light wavelength region to be lowered. As an example, when the visible light reflectance lowering film thickness D is determined by selecting 555 nm having the highest visibility, the film thickness D = 15.4 nm when the refractive index n = 3. Since the refractive index of the above-mentioned material suitable for the visible light reflectance lowering film 11 has a refractive index and an extinction coefficient as shown in FIG. 7, the visible light reflectance lowers except for WSi ₂ (refractive index of 20 or more). A suitable film thickness of the film 11 exists in the range of about 5 to 30 nm.

  On the other hand, since the refractive index of the visible light reflectance lowering film 11 is lower in the infrared light region than in the visible light region, the infrared light reflectance of the visible light reflectance lowering film 11 is higher as visible light. Absent. Therefore, the electric field strengths of the infrared light 14 reflected by the surface of the visible light reflectance lowering film 11 and the infrared light 15 reflected by the substrate 10 are not equal. Moreover, since the film thickness D is a film thickness suitable for canceling out visible light by interference, the film thickness is too thin for infrared light having a wavelength longer than that of visible light, and absorption and phase. Almost no effect of shifting. Therefore, as shown in FIG. 3, the infrared light 14 reflected by the surface of the visible light reflectance lowering film 11 and the infrared light 15 reflected by the base 10 do not cancel each other and strengthen each other. Thereby, the reflectance of infrared light is not lowered even if the visible light reflectance lowering film 11 is arranged.

(3) Reflectance of the substrate 10 The substrate 10 desirably reflects the light transmitted through the visible light reflectance lowering film 11 without reducing as much as possible. Therefore, as described above, the reflectance of the substrate 10 is desirably 90% or more in at least a part of the visible light region and at least a part of the infrared light region. In particular, the reflectance is preferably 80% or more at a wavelength of 1000 nm.

  Hereinafter, embodiments of the present invention will be specifically described.

(Embodiment 1)
In the first embodiment, the base 10 has a structure in which the core is made of W, and the core is covered with a layer of metal (HfN or ZrN) having a higher reflectance than W. An Os film is used as the visible light reflectance lowering film 11.

  The core material (W) of the base 10 is produced by a known process such as sintering or drawing of a metal material. The base is formed in a desired shape such as a wire, a bar, or a thin plate.

  Since the substrate manufactured by a process such as sintering or drawing has a rough surface, the reflectance is low. Therefore, the surface of the core material of the substrate 10 is polished to increase the reflectance. Specifically, the core material (W) of the substrate 10 is preliminarily heated to complete crystal grain growth, and the core material that has completed the crystal grain growth is polished with a plurality of diamond abrasive grains, and the center line average The mirror surface is processed into a mirror surface satisfying at least one of a roughness Ra of 1 μm or less, a maximum height (Rmax) of 10 μm or less, and a ten-point average roughness (Rz) of 10 μm or less. Of course, other methods can be used as long as the reflectance of the filament surface can be improved without being limited to mechanical polishing. For example, wet or dry etching, a method of contacting a smooth die during drawing, forging or rolling can be employed.

  As shown in FIG. 8, the mirror-polished W core material has a reflectance of 90% or more for infrared light longer than a wavelength of 2000 nm, but the reflectance for a wavelength of 2000 nm or less decreases. Therefore, in the first embodiment, a metal film (HfN or ZrN or the like) having high temperature heat resistance and high reflectivity up to the visible light region is formed on the surface of the W core material of 100 nm or more (1000 nm in FIG. 8). And coat. Thereby, as shown in FIG. 8, the base | substrate 10 whose reflectance of infrared light with a wavelength of 1000 nm or more is 80% or more can be obtained.

  If the thickness of the highly reflective metal film (such as HfN or ZrN) is less than 100 nm, light is transmitted to the underlying W, and the reflectance in the infrared region cannot be increased. It is preferable that

  As a film formation method for HfN or ZrN, various methods such as an electron beam evaporation method, a sputtering method, and a CVD method can be used. In addition, after the film formation, it is possible to perform an annealing treatment in a temperature range of 1500 ° C. to 2500 ° C. in order to improve the adhesion to the substrate and to improve the film quality (optical characteristics and the like).

  Next, an Os film having a thickness of 5 to 20 nm is formed as the visible light reflectance lowering film 11 on the substrate 10 (HfN or ZrN). As shown in FIG. 7, the Os film has a high melting point of 3306K and a high refractive index of 4.67 at a wavelength of 555 nm, which has high visibility. As a method for forming the Os film, various methods such as an electron beam evaporation method, a sputtering method, and a CVD method can be used. In addition, after the film formation, it is possible to perform an annealing process in a temperature range of 1500 ° C. to 2500 ° C. in order to improve the adhesion to the substrate 10 and to improve the film quality (crystallinity, optical characteristics, etc.).

  In addition, in order to find the film thickness of the visible light reflectivity lowering film (Os film) 11 that minimizes the visible light reflectivity of the filament, a plurality of filament samples are obtained by changing the film thickness to 5, 13, 20, 50, and 200 nm. Was made. When the reflectance of the prepared filament sample was determined by simulation or actual measurement, as shown in FIG. 9, it was determined that the thickness of the Os film of 13 nm minimized the visible light reflectance. Therefore, in this embodiment, the film thickness of the visible light reflectance lowering film (Os film) 11 is set to 13 nm.

  FIG. 10 shows the reflectance, emission spectrum, and emission spectrum of the substrate within the visibility of the filament (Os / HfN / W) obtained by coating the HfN / W substrate 10 with an Os film having a thickness of 13 nm. Indicates. As a comparative example, FIG. 11 shows the reflectance, the emission spectrum, and the emission spectrum of the substrate within the visual sensitivity of the W-only filament that does not include the Os / HfN film. When the reflectance of FIG. 10 of Embodiment 1 is compared with the reflectance of the W filament of FIG. 11 of the comparative example, the reflectance is greatly reduced in the visible light region and the reflectance is greatly increased in the infrared light region. I understand that. For example, at a wavelength of 500 nm, it can be seen that the reflectivity, which was around 50% in the W filament state, is reduced to about 10% by coating with an Os / HfN film. It can also be seen that at a wavelength of 1000 nm, the reflectivity, which was about 60% in the W substrate state, is improved to nearly 90% by coating with an Os / HfN film. As a result, the visible light luminous flux efficiency of 36.7 lm / W (heating temperature 3000 K) that can be realized with the conventional W filament can be improved 2.4 times or more to 89.4 lm / W.

  The HfN film covering the core material of the substrate 10 has the property of being easily oxidized when heated at a high temperature, but the visible light reflectivity lowering film 11 covers HfN and prevents HfN from coming into contact with oxygen. It also plays a role in protecting the membrane.

  In the first embodiment, an example in which an Os film is used as the visible light reflectance lowering film 11 has been described. In addition to this, a metal film, a carbide film, a boride film, or an oxide film as shown in FIG. Or a multilayer film obtained by laminating a plurality of types of single-layer films of these materials, or a single-layer film formed of these composite materials and a multilayer film, and the visible light reflectance lowering film 11 is formed. It can also be configured.

(Embodiment 2)
In the second embodiment, a case where a metal Re film is used as the visible light reflectance lowering film 11 will be described.

  The configuration of the base 10 is HfN / W as in the first embodiment. The method for forming the metal Re film and the method for obtaining the optimum film thickness were performed in the same manner as the Os film of the first embodiment. Thereby, the film thickness of the Re film was set to 10 nm.

  FIG. 12 shows the reflectance, emission spectrum, and emission spectrum of the substrate within the visual sensitivity of the filament (Re / HfN / W) obtained by coating the HfN / W substrate 10 with a 10 nm thick Re film. Indicates. As shown in FIG. 12, the Re / HfN / W filament has a greatly reduced reflectance in the visible light region and a significantly increased reflectance in the infrared light region as compared with the W filament of FIG. For example, at a wavelength of 500 nm, it can be seen that the reflectivity of the W filament, which was around 50%, is reduced to about 25% by coating with a Re / HfN film. It can also be seen that at a wavelength of 1000 nm, the reflectivity, which was about 60% in the W substrate state, is improved to nearly 80% by coating with a Re / HfN film. As a result, the visible light luminous efficiency of 36.7 lm / W (heating temperature 3000 K) that can be realized by the conventional W filament can be improved by 80% or more to 64.8 lm / W.

(Embodiment 3)
As a third embodiment, the case where tungsten silicide (WSi ₂ ) shown in FIG. 7 is used as the visible light reflectance lowering film 11 will be described. This material (WSi ₂₎ has a refractive index for visible light, very large 22.4, set the film thickness to 1 to 10 nm. For this reason, the film is formed by a film forming method (for example, MBE (molecular beam evaporation) or the like) capable of precisely controlling the film thickness.

FIG. 13 shows the reflectance obtained by wave optical calculation for a filament (WSi ₂ / HfN / W) in which the HfN / W substrate 10 is coated with a 4 nm-thickness WSi ₂ film. As is apparent from FIG. 13, the reflectance in the visible light region is reduced at a wavelength of 500 nm or less.

In addition, as shown in FIG. 14, the WSi ₂ / HfN / W filament is a WSi ₂ film having a film thickness of 5 to 10 nm (in FIG. 14, the film thickness is 5, 6, 7, 8, 9, 10 nm). It can be seen that a region where the reflectance is reduced in a narrow band in the infrared light region is generated depending on the film thickness. Therefore, a radiation spectrum is obtained in this infrared light region.

Further, as described in the following fourth embodiment, a dielectric layer may be disposed between the visible light reflectance lowering film (WSi ₂ ) 11 and the substrate 10.

(Embodiment 4)
As Embodiment 4, a filament in which a dielectric layer is disposed between the visible light reflectance lowering film 11 and the substrate 10 will be described. The refractive index of the dielectric layer with respect to visible light may be smaller than 2.5. By disposing the dielectric layer, the optical path length of the light transmitted through the visible light reflectance lowering film 11 and reaching the substrate 10 can be adjusted. Therefore, the film thickness control of the visible light reflectance lowering film 11 can be easily performed. Become. In this case, with the optical path length of the total film thickness of the visible light reflectance lowering film 11 and the dielectric layer, the visible light reflected on the surface of the visible light reflectance lowering film 11 and the visible light reflected on the substrate 10 are made to interfere with each other and visible. Designed to reduce light intensity. The dielectric layer is preferably made of a material having a low absorption rate for visible light and infrared light.

Here, an Os film having a thickness of 3 nm is used as the visible light reflectance lowering film 11, and an HfO ₂ film is used as a dielectric layer disposed between the visible light reflectance lowering film 11 and the substrate 10. As in the first embodiment, HfN / W is used for the substrate 10.

The reflectance was obtained by simulation for four types of filament samples in which the film thickness of the HfO ₂ film as the dielectric film was changed to 5, 10, 20, and 30 nm, respectively. The result is shown in the graph of FIG. As shown in FIG. 15, the reflectance in the visible light region is significantly reduced to 40% or less, and a high reflectance film thickness dependency of 80% or more is observed in the infrared light region. In particular, a filament having a HfO ₂ film thickness of 30 nm has the lowest visible light reflectance.

This thickness of the HfO ₂ film is 30nm filament _{(Os (3nm) / HfO 2} (30nm) / HfN (1000nm) / W), the wave optics calculations, reflectance, emission spectra, as well as radiation in the luminosity The spectrum was determined. The result is shown in FIG. When the reflectance of FIG. 16 is compared with the reflectance of the W filament of FIG. 11, the reflectance is greatly reduced in the visible light region, and the reflectance is greatly increased in the near-infrared light region (800 to 1100 nm). I understand that. For example, at a visible light wavelength of 500 nm, the reflectance of the W filament is around 50% as shown in FIG. 11, but the reflectance of the Os / HfO ₂ / HfN / W filament in FIG. It turns out that it has fallen. Further, at a wavelength of 1000 nm, the W filament in FIG. 11 has a reflectivity of about 60%, whereas the Os / HfO ₂ / HfN / W filament in FIG. 16 has an improved reflectivity to 80%. As a result, the visible light luminous efficiency of 36.7 lm / W (heating temperature 3000 K) is obtained with the conventional W filament, and 2.3 times or more up to 82.8 lm / W with the Os / HfO ₂ / HfN / W filament. Can be improved.

(Embodiment 5)
As Embodiment 5, another example of a filament in which a dielectric layer is disposed between the visible light reflectance lowering film 11 and the substrate 10 will be described. In the filament of the fifth embodiment, a SiC film having a thickness of 20 nm is used as the visible light reflectance lowering film 11, and a HfO ₂ film having a thickness of 200 nm is used as the dielectric layer. The substrate 10 is made of Ta.

  With respect to the filament of Embodiment 5, the reflectance, the emission spectrum, and the emission spectrum within the visibility were obtained by wave optics calculation. The result is shown in FIG. The reflectivity in FIG. 17 is greatly reduced in the visible light region with a wavelength of 400 to 700 nm, and high in the near infrared and infrared light regions with a wavelength of 1000 nm or more. For example, at a visible light wavelength of 550 nm, the reflectivity of the filament of FIG. Further, at a wavelength of 1000 nm, the filament of FIG. 17 has a reflectance close to 90%. As a result, with the conventional W filament, the visible light luminous efficiency of 36.7 lm / W (heating temperature 3000 K) is improved about 3.4 times to 124.7 lm / W with the filament of the fifth embodiment. Can do.

(Embodiment 6)
As Embodiment 6, a light source using the filament of the present invention will be described.

  FIG. 18 shows a cross-sectional view of an incandescent bulb as a light source of the present embodiment. The incandescent lamp includes a translucent airtight container 2, a filament 3 disposed inside the translucent airtight container 2, and a pair of lead wires 4 that are electrically connected to both ends of the filament 3 and support the filament 3. 5 and an anchor 6 that supports the filament 3. The lead wires 4 and 5 and the anchor 6 are supported by an insulating mount 7 disposed in the translucent airtight container 2. The base portion of the mount 7 is supported by the sealing portion 8 of the translucent airtight container 2. Sealing metal (metal foil) 114 and 115 and lead rods 16 and 17 are arranged in the sealing portion 8.

  The lower ends of the lead wires 4 and 5 are welded to the metal foil sealing metals 114 and 115. The upper ends of the lead rods 16 and 17 are welded to the sealing metals 114 and 115, and the lower ends are drawn out from the sealing portion 8. The sealing portion 8 has a structure in which the lower end portions of the sealing metals 114 and 115 and the lead wires 4 and 5 and the upper end portions of the lead rods 16 and 17 are pinch-sealed (melted and sealed by melting glass). Thereby, current can be supplied from the lead rods 16 and 17 to the filament 3 from the outside. The reason why the sealing metals 114 and 115 are arranged in the sealing portion to perform pinch seal sealing is that when the filament is used at a high temperature of 3000 K or more, the translucent airtight container 2 is broken (the glass is broken). Is to prevent. That is, the material of the translucent airtight container 2 has a low coefficient of thermal expansion, whereas the metal lead wires 4 and 5 and the metal lead rods 16 and 17 generally have a high coefficient of thermal expansion. Although the difference in expansion occurs, the sealing metals 114 and 115 relieve the stress caused by the difference in thermal expansion depending on the thickness and material.

As the filament 3, the filament of the present invention is used. In FIG. 18, as an example, filaments in the form of wire rods are spirally wound. However, the filament shape is not limited to this shape, and may be a desired shape such as a rod shape or a plate shape. Moreover, the inside of the translucent airtight container 2 is in a pressure state of 10 ⁻³ to 10 ⁺⁷ Pa.

  Since the filament 3 of the present invention has a high reflectance in the infrared wavelength region and a low reflectance in the visible light region as described in Embodiments 1 to 4, it can suppress the emission of infrared light. Therefore, a light source with high visible light emission efficiency, that is, a light source with high energy conversion efficiency into visible light can be obtained. Thereby, an inexpensive and efficient energy saving type lighting bulb can be provided.

The filament 3 of the present invention may cause sublimation of the visible light reflectance lowering film 11 or the like when the hermetic container 2 is in a high vacuum state such as 10 ⁻³ Pa. An inert gas such as Ar may be sealed at a high pressure of about 10 ⁵ to 10 ⁷ Pa to suppress sublimation of the film. Further, in place of an inert gas such as Ar, the film can be sublimated as appropriate by using about several percent oxygen gas, nitrogen gas, halogen gas, carbon-based gas, or a mixed gas thereof. Therefore, it is possible to achieve a long life.

  In Embodiment 6 described above, the use of the filament of the present invention as a filament of an incandescent bulb has been described. However, it is also possible to use the filament other than an incandescent bulb. For example, it can be employed as a heater wire, a welding wire, a thermionic emission electron source (such as an X-ray tube or an electron microscope), and the like. Also in this case, since the filament can be efficiently heated to a high temperature with a small amount of input power due to the suppression effect of infrared light radiation, the energy efficiency can be improved.

DESCRIPTION OF SYMBOLS 1 ... Incandescent light bulb, 2 ... Translucent airtight container, 3 ... Filament, 4 ... Lead wire, 5 ... Lead wire, 6 ... Anchor, 8 ... Sealing part, 9 ... Base

Claims (10)

A substrate formed of a metal material;
In order to make the visible light reflectance of the substrate lower than the infrared light reflectance, a visible light reflectance lowering film covering the substrate is provided,
The film thickness of the visible light reflectance lowering film is set so that the visible light reflected by the surface of the visible light reflectance lowering film interferes with the visible light reflected by the substrate to reduce the intensity,
At least one of a refractive index and an extinction coefficient with respect to visible light of the visible light reflectance lowering film is 2.5 or more.   2. The filament according to claim 1, wherein at least one of a refractive index and an extinction coefficient of the visible light reflectance lowering film with respect to visible light is 3.0 or more.   3. The filament according to claim 1, wherein the reflectance of at least a part of the visible light region is 40% or less and the reflectance of at least a part of the infrared light region is 80% or more. In the filament according to any one of claims 1 to 3, the visible light reflectance reduction film, Os, Re, Ru, W , Mo, SiC, and, formed in one of WSi ₂ A filament comprising a membrane.   5. The filament according to claim 1, wherein the reflectance of the substrate itself is 90% or more in at least a part of the visible light region and at least a part of the infrared light region. Filament.   6. The filament according to claim 5, wherein the substrate has a mirror-finished surface.   The filament according to claim 5 or 6, wherein the base has a structure in which a surface of a core material made of metal is covered with a metal layer having a higher reflectance than the core material. .   The filament according to any one of claims 5 to 7, wherein the surface roughness of the substrate is a center line average roughness Ra of 1 µm or less, a maximum height Rmax of 10 µm or less, and a ten-point average roughness Rz. Satisfy | fills at least 1 of 10 micrometers or less. The filament according to any one of claims 1 to 8, wherein the visible light reflectance lowering film further includes a dielectric layer disposed between the substrate and the refraction of the dielectric layer with respect to visible light. The rate is less than 2.5,
The total film thickness of the visible light reflectivity lowering film and the dielectric layer reduces the visible light intensity by causing the visible light reflected on the surface of the visible light reflectivity lowering film to interfere with the visible light reflected by the substrate. Filament characterized by being set to let A light source having an airtight container, a filament disposed in the airtight container, and a lead wire for supplying current to the filament;
The light source according to claim 1, wherein the filament is one according to claim 1.

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