WO2006119791A1

WO2006119791A1 - Ceramic reflector

Info

Publication number: WO2006119791A1
Application number: PCT/EP2005/005143
Authority: WO
Inventors: Paulus Marinus Hermanus Van Den Bergh; Folkert Jan Gideon Tuininga
Original assignee: Van Den Bergh Paulus Marinus H; Folkert Jan Gideon Tuininga
Priority date: 2005-05-10
Filing date: 2005-05-10
Publication date: 2006-11-16

Abstract

The invention relates to a ceramic reflector, comprising a carrier body of which at least one surface is at least partly provided with at least one light-reflecting ceramic cover layer. The invention further relates to a method for manufacturing a ceramic reflector, comprising: applying a suspension of a light-reflecting ceramic material to a carrier body; and then sintering the applied suspension.

Description

CERAMIC REFLECTOR

The present invention relates to a ceramic reflector, in particular to a ceramic reflector for use in a lamp fitting. Reflectors for lamp fittings are usually made of a metal such as aluminum. For a good action of such reflectors, it is desired that they have a good thermal resistance and that the side(s) of the fitting facing the lamp has/have a good light reflection of the desired wavelengths. In general, aluminum lamp fittings carfonly be used safely for lamps with a low to medium high power, namely with a power of maxim ally approximately 600W.

It is an object of the present invention to provide a new reflector, in particular a reflector suitable for use in lamp fittings for horticulture.

The invention relates to a ceramic reflector, comprising a carrier body of the ceramic material known as stoneware or vitreous china of which at least one surface is at least partly provided with a light-reflecting ceramic cover layer.

A reflector according to the invention has good thermal properties compared with conventional metal fittings.

A reflector according to the invention has very good reflecting properties. In particular, the invention provides a ceramic reflector with a total light reflection (more in particular a total reflection of electromagnetic radiation in the visible range, such as white light) of more than 85%, preferably of at least 90%. In particular in (greenhouse) horticulture, this offers advantages since lamps with a higher power can be used and fewer lamps are sufficient for a same lighting.

The light reflection may, for instance, be measured with a commercially available reflectometer in which the reflection of light with a wavelength of 400- 700 nm is determined. A conventional aluminum reflector generally has a reflection of less than 85%.

Compared with metal reflectors, a reflector according to the invention usually has a more diffuse reflection. As a result, a simpler geometry is sufficient than with metal reflectors, which shows specular reflection to a large extent.

Incidentally, it is possible to increase the extent of specular reflection if desired, for instance by applying a high gloss glaze over the light-reflecting cover layer. Due to the good material properties (such as material strength), thermal properties and the light-reflecting properties, the reflector itself can serve as a fitting for a lamp, without a separate casing being necessary. The_invention thus provides inter alia a lamp fitting which at least substantially consists of ceramic material. In this context, "at least substantially" is understood to mean at least a fitting of which, if desired, only the socket(s) for the lamp(s) and the channels (such as wires) for the electricity supply to the lamp consist of non-ceramic material.

A reflector according to the invention is very simply cleanable. A reflector according to the invention is very robust, and is usually less prone to reflection losses with the passage of time than metal reflectors, whose reflection considerably decreases in practice due to gloss losses. A reflector according to the invention can be used in various applications and particularly offers an advantage in a use in demanding environments such as a humid/vapor-containing environment, a warm environment, environments with greatly varying temperatures, a corroding environment and/or an environment rich in dust and/or other dirt. Terms such as "at least substantially free from", "about", "approx" and the like are understood to include at least a deviation of maximally 5%, in particular of maximally 2%.

When terms such as "at least substantially", "mainly" and the like are used herein to indicate the (relative) amount of a component of a substance, material or physical phenomenon and the like, then these are at least understood to mean that this component makes up more than half, preferably 90-100%, in particular 95- 100%, more in particular 98-100% of the substance, the material or physical phenomenon and the like. An at least substantially diffuse reflection is thus at least understood to mean that 50-100%, preferably 90-100%, in particular 95- 100%, more in particular 98-100% of the reflection (i.e. the phenomenon) is diffuse (i.e. the component).

Weight percentages are based on the total weight unless stated otherwise. Partly in view of above-mentioned advantages, a reflector according to the invention is also very suitable in one or more uses chosen from photography lighting, projector lighting (for instance for projecting light images, comparable with a slide screen), studio/film set lighting, ship lighting, horticultural lighting, interior lighting, exterior lighting, street lighting, security lighting, construction lighting, laser applications, infrared applications, transport lighting, airplane lighting, car lighting, bicycle lighting, runway lighting, industrial lighting, kitchen lighting, healthcare lighting (for instance operating room lighting or lighting for a dental practice), oven lighting, specific location lighting (such as parking lots, gas stations), stadium lighting, sports center lighting, lighting of water, theater lighting, art/object lighting, handheld lighting (such as a portable lamp, a flashlight and the like), hallway lighting, LEDs (bight -emitting diodes), fume hood lighting, and the like.

In addition to the general advantage of a good light reflection (and accordingly a favorable efficiency), the nature of the reflection can offer specific advantages for specific uses.

It has, for instance, been found that the use of a reflector according to the invention with a high diffuse reflection, in particular with at least substantially diffuse reflection, in water lighting, such as underwater lighting and/or lighting of a water surface, for instance a swimming pool, an aquarium or a waterway, produces less glitters to the water surface than use of an at least substantially specular reflector. There are also indications that growth and/or the wellbeing of living creatures, in particular plants, coral, anemones and the like, can favorably be influenced by exposure to diffuse light which can be produced with the aid of a reflector according to the invention.

A high diffuse reflection, realizable with a reflector according to the invention, is also particularly advantageous in uses such as handheld lighting because a more even light distribution is obtained and thus a better visibility can be created than with a metal reflector.

With uses with an aesthetical aspect, such as with art/object lighting, it has been found that the lighted object gets a higher visual appreciation with light reflected by means of a highly diffusely reflecting reflector according to the invention than with a specularly reflecting reflector.

A reflector according to the invention can further be provided on a surface, such as a wall, ceiling, or another object, in particular a reflection with a large extent of diffuse reflection to bring about diffuse even indirect reflection. This is particularly advantageous for use in a building, a swimming pool or with infrastructural constructions such as bridges, for instance to mark a bridge pillar.

The carrier body is made of a ceramic material known as stone ware or vitreous china. An advantage of this is the high heat resistance compared with metals. Thus, it has been found that a reflector according to the invention with this ceramic carrier body has a very good heat resistance which allows use in, for instance, fittings where the reflector is exposed to temperatures of more than 300⁰C or even 400⁰C or more, whereas conventional aluminum fittings are not well resistant to temperatures of more than 300⁰C.

Preferably, white firing stoneware or vitreous china is used as a carrier body. Preferably, the material has a relatively low thermal expansion coefficient. Very suitable is, a thermal expansion coefficient of less than about 6x10-6 K-I, most preferably from about 3.5x10-6 K-I to about 5.5 xlO-6 K-I.

Very suitable is as mentioned stoneware or vitreous china, in particular very white firing stoneware or vitreous china. Very white firing has been found to have a positive influence on the light reflection. The stoneware or vitreous china has a relatively low thermal expansion coefficient, which has been found to be favorable in view of uses where large temperature changes occur, such as with uses in fittings for high-power lamps such as growth lamps. This is further advantageous in uses in which temperature shocks to the material may occur, for instance by exposure to water. Possibilities are spray water in horticultural greenhouses and outdoor uses in general. Stoneware or vitreous china is also particularly suitable due to the extremely good forming properties.

The terms stoneware and vitreous china are generally known terms in the field.

As a starting material for the light-reflecting cover layer, usually, a light- reflecting ceramic material is used. The suitable materials include pure or complex mixtures of alumina, silicondioxides, zirconiasilicates, zirconiaoxides, tinoxides, ceriumoxide, calcium pyrophosphates, barium sulfates, magnesium oxides, titanium dioxides and aluminosilicates (oxides which, in addition to oxygen, mainly_contain silicon and aluminum). The light-reflecting material preferably has a relatively low expansion coefficient, in particular of less than about 6x10-6 K-I, more in particular of less than about 5x10-6 K-I. Preferably, the reflecting cover layer has a thermal expansion coefficient which is approximately equal to or lower than the expansion coefficient of the body on which the cover layer has been applied.

In this respect, very good results have been obtained with a reflecting cover layer of an aluminosilicate, in particular in the case that the body comprises a (hard) porcelain material. It has been found that a reflection of white light of 93% and more is achievable with this.

Preferably, the light-reflecting cover layer (and if desired the carrier body) comprises an aluminosilicate with a molecular ratio of AI2O3 to Siθ2 of about 3^2. Preferred weight percentages for these oxides are shown in Table 2b (see Example 1).

Examples of particularly suitable alumino silicates for use in the reflecting cover layer are mullite and zirconium mullite. Mullite is an inorganic oxide with the overall formula 3 AI2O3.2 Siθ2. Zirconium -mullite is_an inorganic oxide based on oxides of zirconium, aluminum and silicon. Herein, Zrθ2 is usually present in a content of about 34-38 wt. %, AbCton a content of about 43.8-47.8 wt.% and Siθ2in a content of about 16.5-18.5 wt.%.

Most preferably, the light-reflecting cover layer consists at least substantially of sintered mullite. This has been found to have a very good reflection for light. It has further been found that a cover layer of mullite is very suitable for manufacturing a reflector which is well resistant to temperature changes.

Another reflecting ceramic material is alumina. However, alumina has been found to be less suitable for use in ceramic reflectors for high-power lamps than an aluminosilicate. This is because it has been found that the durability of the reflecting cover layer is relatively low and already begins to show cracks after relatively short heating by lighting, compared with an aluminosilicate cover layer.

There is a possibility to use formulations in which, in addition to mullite or another ceramic light-reflecting material, one or more substances have been added which reduce the transparency of the cover layer and/or contribute to the reflection of light. In this manner, for instance, the reflected intensity can be set.

The reflection of light may, for instance, be improved with an additive chosen from the group of zirconium, tin oxide and cerium oxide, in particular in a cover layer based on an aluminosilicate. The thickness of the cover layer can simply be determined experimentally, depending on the desired reflection properties, commercial considerations and the like. Inter alia because of commercial considerations (the material for the cover layer is usually relatively expensive), the average thickness of the reflecting cover layer is preferably less than about 1.5 mm, most preferably less than 0.7 mm. With a view to a high reflection, the layer thickness is preferably at least about 100 μm.

Very good results have been obtained with an average layer thickness in the range of 100-500 μm. If desired, over the light-reflecting cover layer, a glazing has been applied. A glazing contributes to the smoothness of the surface and simplifies the cleaning of a reflector.

Such a layer* is particularly desired in an embodiment in which the assembly of carrier body and light-reflecting cover layer is open-porous, more in particular in the case that the open porosity is such that the saturation moisture absorption (at approx 25°C) is less than 0.1 wt. % based on the weight of the .. reflector.

The glazing may be based on the usual materials for glazing ceramic, in particular for glazing stoneware or vitreous china. Very suitable are glazings based on analuminosilicate.

With regard to the thermal expansion coefficient of preferably used glazings, the same considerations apply as for the light-reflecting cover layer (see above).

The glazing may be transparent or opaque. In the case of an opaque glazing, the glazing may have been applied on a light-reflecting cover layer or serve as a light-reflecting cover layer itself and optionally be applied directly to the carrier body, without intermediate light-reflecting layer.

An opaque glazing preferably comprises one or more opacifying agents, preferably chosen from the group consisting of tin oxide, cerium oxide or zirconium oxide. An advantage of an opaque glazing, in addition to the above-mentioned advantages of glazings in general, is that it can contribute to the reflection or can even completely serve as light-reflecting cover layer.

The thickness of the glazing can be chosen within a wide range. Good results have inter alia been achieved with an average glazing thickness of 400 μm or less (in combination with a separate light-reflecting cover layer) or with an average layer thickness as stated for the light-reflecting cover layer (when the glaze has been applied directly on the carrier body and no separate light-reflecting cover layer is present). For practical reasons, the glazing is preferably at least 100 μm, if present. To increase the specular reflection, on the glazing, a (top) layer may have been applied which improves the specular properties. Very suitable for this is a layer based on vanadium pentoxide. Such a layer has been found to contribute to very good specular properties of the reflector. Very suitable is a specular reflection- improving layer with a thickness of about 10-100μm. The surface of a reflector according to the invention may be uniform, i.e. consist of one type of material. It is also possible to provide a multiform surface, that is, a surface built up from different types of materials next to one another and/or over one another. Thus, the surface of a reflector according to the invention may be built up from different types of material, which may have been applied next to one another and/or over one another, with optionally different light- reflecting properties. In this manner, the specular/diffuse reflection ratio, the total extent of reflection and/or the reflection pattern can be set. The surface may, for instance, be formed by different types of materials chosen from transparent glaze, opaque glaze, light-reflecting material (such as mullite), specularly reflecting material (such as vanadium oxide) and the like. The invention further relates to a method for manufacturing a ceramic reflector, such as a reflector described hereinabove, comprising applying a suspension of a light-reflecting material to a carrier body! and then sintering the applied suspension, thereby forming a light-reflecting cover layer. Most preferably, the carrier body (with optionally one or more layers already applied to it) is, at least at some moment, exposed to a sintering temperature of approx 1300⁰C, more in particular to a sintering temperature of approx 1250-^* 1350⁰C. This is particularly advantageous for_obtaining stoneware and vitreous china. Fig. 1 shows seven preferred processes (processes A-F).

The invention further relates to a lamp fitting comprising a reflector according to the invention. At least during use, a fitting according to the invention also comprises a lamp, such as a growth lamp for making plants grow, for instance in (greenhouse) horticulture. Very good results '■ have been achieved with a lamp with a power of more than 600 W.

The invention further relates to use of a reflector or fitting according to the invention in street lighting.

By means of the invention, street lighting can be provided with a high intensity. This is inter alia interesting with a view to street safety.

The invention further relates to the use of a reflector according to the invention as a thermal insulator.

Here, a reflector according to the invention with high reflection of infrared radiation, preferably of more than 85%, most preferably of at least 90% is particularly suitable (for instance measured with infrared with a wavelength of 800-1000 nm). The purpose of the thermal insulation may be to better retain heat, for instance for an oven of which one or more inner walls are wholly or partly provided with a reflector according to the invention. In addition, the thermal insulation may serve to cool a space or goods, for instance with a cool box of which one or more outer walls are wholly or partly provided with a reflector according to the invention.

Further, a reflector according to the invention may serve as insulating construction material, for instance as (sun-protective) thermal insulation of a building. For this purpose, one or more outer walls of a building and/or the roof may be wholly or partly provided with a reflector according to the invention. Thus, the invention also relates to an oven, a cool box and a building, respectively, provided with a reflector according to the invention.

Further, a reflector according to the invention is suitable as reflector in a photodiode, in particular in a photovoltaic cell, more in particular in a solar cell. Preferably, the reflector has at least substantially diffusely reflecting properties in this.

A reflector according to the invention is particularly advantageous for use in a solar cell with one or more diodes with at least two light sensitive sides (the so- called bifacial cells). A suitable diode is known by the brand name Sliver®. A suitable design of such a cell is for instance known from Weber et al. http7/solar.anu.edu.au/pages/publications2004/2CV _l_36.pdf. The contents of this publication are incorporated herein by reference.

An example of such a solar cell is diagrammatically shown in Fig. 2. One or more diodes 1 are embedded in a transparent material 2, for instance divided into multiple layers 2a (overlying layer), 2b (encapsulating layer) and 2c (underlying layer). The surface b of the transparent material which faces away from the light source during use is provided with the reflector 3. During use, light enters via surface a, where a part of the light reaches the side of the diode facing the light source and a part of the light reaches the reflector. The reflector reflects the light. Of this light, one part reaches the side of the diode facing away from the light source and another part is reflected from the surface a. With such a setup, a very good efficiency can be achieved.

The invention will now be illustrated in more detail in and by a number of examples.

Example l: preferred formulations

Tabel l: Carrier body (hard) -porcelain

Table 2- suspension for reflecting cover layer

Table 2Ά- ceramic materials and sintering auxiliaries

A suspension is usually obtained by mixing 100 parts by weight of dry inorganic matter (light-reflecting material plus any sintering auxiliaries) with 20- 60 parts by weight of water and 20-60 parts by weight of additives.

In the examples described hereinafter, 42.8 parts by weight of water and 36.7 parts by weight of polyglycols were added.

Table 2b: composition of cover layer after sintering (Preferred and in Exam le 2)

Table 3: transparant glazing

Example T- preparation of an aluminosilicate reflector

A number of ceramic carrier bodies in the form of a test plate (80 x 80 mm) were, in a usual manner, manufactured from a porcelain standard type 1 (ST l) and from a porcelain standard type 2 (ST 2), with a composition as shown in Table 1. Example 2a' open-porous carrier

A part of the carrier bodies was biscuit-fired at approx 1000⁰C, which resulted in an open-porous carrier. After biscuit firing, the suspension (as shown in Table 2) was applied. The applied amount was about 10.5 g/dm2. A part of the carrier bodies was sintered at 1000⁰C, subsequently glazed and then fired at 1400⁰C; another part was sintered at 1400⁰C and not provided with a glazing,^' again another part was sintered at 1400⁰C, glazed and then gloss-fired at 1200 or 1350⁰C. Fig. 1 shows suitable processes in block diagram. The reflectors had a reflection for white light of 93% or more. They had no visible cracks in the cover layer after prolonged exposure to varying temperatures between room temperature and a temperature of 400⁰C or more.

Of a reflector whose cover layer had been sintered at 1300⁰C, without glazing, a reflection of up to 97% was measured.

Example 2b: non-porous carrier

The other carrier bodies were biscuit -fired at approx 1400⁰C, thereby forming a carrier which was free from open pores (saturation moisture absorption <0.1 %). The suspension was applied as described under Example 2a. After this, sintering took place at 1100⁰C, 1300⁰C or 1400⁰C. A part of the reflecting layers was then provided with a glazing which was gloss-fired at 1200 - 1350⁰C.

The reflectors had a reflection for white light of 93% or more. They had no visible cracks in the cover layer after prolonged exposure to varying temperatures between room temperature and a temperature of 400⁰C or more.

Claims

1. A ceramic reflector, comprising a carrier body of which at least one surface is at least partly provided with at least one light-reflecting cover layer.

2. A ceramic reflector according to claim 1, wherein the carrier body is made of stoneware.

3. A ceramic reflector according to anyone of the preceding claims, whose reflecting layer has a total light reflection of more than 85%, preferably of at least 90%.

4. A ceramic reflector according to anyone of the preceding claims, wherein the light-reflecting cover layer comprises a calcium pyrophosphate, a barium sulfate, a magnesium oxide, a titanium dioxide, an aluminosilicate or a combination of one or more of these compounds.

5. A ceramic reflector according to anyone of the preceding claims, wherein the light-reflecting cover layer comprises sintered mullite.

6. A ceramic reflector according to anyone of the preceding claims, provided with a high gloss glaze, which has been applied to the light-reflecting cover layer on the side facing away from the carrier body.

7. A ceramic reflector according to anyone of the preceding claims, wherein the carrier body, the light-reflecting cover layer and, if desired, the glaze each comprise an alumino silicate.

8. A ceramic reflector according to anyone of the preceding claims, wherein the reflecting cover layer comprises an alumino silicate whose molecular ratio of AlzO3 to SiO2 in the aluminum silicate is about 3^2.

9. A ceramic reflector according to anyone of the preceding claims, wherein the ratio of the thermal expansion coefficient of the carrier body to the thermal expansion coefficient of the light-reflecting ceramic cover layer and/or the ratio of the thermal expansion coefficient of the carrier body to the thermal expansion coefficient of the glazing is at least about 1, preferably 1-1.5, most preferably 1.1- 1.4.

10. A method for manufacturing a ceramic reflector, if desired a reflector according to anyone of the preceding claims, comprising: applying a suspension of a light -reflecting ceramic material to a carrier body; and then sintering the applied suspension, thereby forming a light-reflecting cover layer.

11. A method according to claim 10, wherein the sintering takes place at a temperature in the range of 1000 to 1420⁰C, preferably at a temperature of 1200- 1350⁰C.

12. A method according to anyone of claims 10 or 11, wherein the suspension comprises an additive, preferably an additive for modifying a suspension property chosen from the group consisting of viscosity, rheology, suction behavior to the body, flow behavior, spray behavior and liquation behavior.

13. A method according to anyone of the preceding claims, wherein the suspension is applied by immersion and/or spraying.

14. A method according to anyone of claims 10-13, wherein the suspension comprises at least one sintering agent, preferably at least one sintering agent chosen from the group consisting of zeolites, magnesium silicates, sodium aluminum silicates, potassium aluminum silicates, alkaline -earth aluminum silicates, aluminum boron silicates and (complex) synthetic glass frits.

15. A method according to anyone of claims 10-14, wherein at least 90% of the particles of the light -reflecting material (at least before sintering) have a size of less than 50 /μm.

16. A reflector obtainable by means of a method according to anyone of claims 10 to 15.

17. A lamp fitting comprising a reflector according to anyone of claims 1- 10 or 16.

18. A lamp fitting according to claim 17, provided with a lamp, preferably a growth lamp.

19. A lamp fitting according to claim 18, which at least substantially, consists of ceramic material.

20. A streetlamp, comprising a reflector or a lamp fitting according to anyone of claims 1-10, 16 or 17-19.

21. A solar cell, comprising a reflector according to anyone of claims 1-10 or 16.

22. An oven or cool box, of which at least one surface is at least partly provided with a layer of a reflector according to anyone of claims 1-10 or 16.

23. Use of a reflector according to claims 1-10 or 16 or a lamp fitting according to anyone of the claims 17-19 in a use chosen from photography lighting, projector lighting (for instance for projecting light images, comparable with a slide screen), studio/film set lighting, ship lighting, horticultural lighting, interior lighting, exterior lighting, street lighting, security lighting, construction lighting, laser applications, infrared applications, transport lighting, airplane lighting, car lighting, bicycle lighting, runway lighting, industrial lighting, kitchen lighting, healthcare lighting (for instance operating room lighting or lighting for a dental practice), oven lighting, specific location lighting (such as parking lots, gas stations), stadium lighting, sports center lighting, lighting of water, theater lighting, art/object lighting, handheld lighting (such as a portable lamp, a. flashlight and the like), hallway lighting, LEDs (light-emitting diodes) and fume hood lighting.