WO2009128003A1

WO2009128003A1 - Colored glass, process for preparing, and article made of, such a glass

Info

Publication number: WO2009128003A1
Application number: PCT/IB2009/051518
Authority: WO
Inventors: Jan M. Hermans; Laetitia Beaujeault; Theodorus H. Ketelaar
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-04-16
Filing date: 2009-04-10
Publication date: 2009-10-22

Abstract

PH009718 15 ABSTRACT: A colored glass defined by the formula R' 2 O-RO-SiO 2, or by a system of formula R' 2 O-RO-SiO 2, wherein R' is an alkali metal element and R is an alkaline earth metal element, is characterized by the addition of: between 0.01% and 1% by weight of molybdenum (Mo) expressed as MoO 3, between 0.01% and 2.5 % by weight of sulfur (S) expressed as SO 3, and between 0.01% and 0.3% by weight of chromium (Cr) expressed as 5 Cr 2 O 3. The tint of the finished glass can be adjusted in a wide range between yellow and amber, preferably a pure clean yellow, by using simple processing techniques such as dilution, control of the thickness of a sheet or envelope of the finished glass, and curing of the finished glass. 10

Description

Colored glass, process for preparing, and article made of, such a glass

FIELD OF THE INVENTION

The present invention relates to a colored glass and an article, for example, an electric lamp bulb comprising a sheet or envelope of such a glass. The invention is particularly relevant to making amber or yellow glass, for example, for signal lighting in automotive applications.

BACKGROUND OF THE INVENTION

EP-A-1193226, the disclosure of which is herein incorporated by reference, describes a colored glass and electric lamp bulb comprising an envelope of such a glass. The glass envelope can be made to a yellow/orange color and the electric lamp made from it may be used as an automotive signal light. Alternatively, the colored glass may be used in, for example, a fog lamp cover for automobiles. The colored glass is defined by the formula R₂O- RO-Siθ2, or by a system of formula R'2θ-RO-Siθ2, wherein R is an alkali metal element and R is an alkaline earth metal element, and is characterized in that 0.01 % to 0.6% by weight of molybdenum (Mo) expressed as Moθ3 and 0.01% to 1.0% by weight of sulfur (S) are added. A method of producing a colored glass bulb for lighting is also described, comprising the steps of forming said glass to a desired hollow shape and heating the shaped hollow article to 400⁰C -620⁰C so as to give it a coloring treatment.

WO-A-2007/034429, the disclosure of which is herein incorporated by reference, describes a colored glass and an electric lamp comprising an envelope of such a glass. The glass envelope can be made to an amber color and the electric lamp made from it is usable as an automotive signal light avoiding, for example, the need for colored plastic covers for the lamp. The colored glass is defined by the formula R₂O-RO-Siθ₂, wherein R is an alkali metal element and R is an alkaline earth metal element, comprising between 0.01% and 1% by weight of molybdenum (Mo) expressed as MOO3 , between 0.01 % and 2.5% by weight of sulfur (S) expressed as SO3, and further comprising between 7.8% and 14% by weight of potassium (K) expressed as K₂O, and between 0.68% and 5.42% by weight of sodium (Na) expressed as Na₂O, wherein the sum of the concentrations of potassium and sodium expressed as K₂O and Na₂O is between 11% and 17% by weight. As described in the prior art, the control of the Na and K concentrations in the glass reduces the presence of crystals in the glass caused by the presence of Mo and S as the chromophores, as compared to the glass described in EP-A-1193226. Reducing the presence of crystals reduces the fragility of the resultant glass and articles made therefrom. It is to be noted that, in this application, the proportion of a constituent is expressed as the oxidic form. Hence, for example, the percentage of Mo is expressed as the weight percentage of MOO3, and the percentage of S is expressed as the weight percentage of SO3. However, this does not mean that this constituent is only present in the glass in this oxidic form. The constituent may be present in various forms, and it is even possible, for example, that the glass does not contain the oxidic form of the element.

It was found that the cured prior-art glass produces lamps emitting an acceptable orange or amber light when illuminated, but when attempts are made to produce yellow-emitting lamps from the same glass by diluting the orange or amber glass, or using a thinner sheet or envelope, the results are not satisfactory and an orange or amber tinge remains.

It would be desirable to provide a glass having a chromophore which can be used to prepare purer yellow, amber, as well as intermediate mixed tint lamps or other glass articles, by one or more of the following simple controlled adjustments in the manufacturing process: (a) control of the degree of dilution of the glass in clear glass; (b) control of the thickness of the glass sheet or envelope; and (c) control of the degree of curing the glass.

SUMMARY OF THE INVENTION

The present invention is based on the inventors' surprising findings that, by adding a controlled amount of chromium (Cr) to the prior-art glass defined by the formula R'2θ-RO-Siθ2, or by a system of formula R'2θ-RO-Siθ2, wherein R is an alkali metal element and R is an alkaline earth metal element, and having an addition of between 0.01% and 1% by weight of Mo and between 0.01 % and 2.5% by weight of S, a glass is obtained from which finished batches in sheet or envelope form having one of amber, yellow and a mixed intermediate tint, are achievable with a purer yellow color than the prior art, by selection of the Cr and the Mo-S chromophore and using one or more of the following simple controlled adjustments during the manufacturing process: (a) control of the proportion of chromophore by the degree of dilution of the glass in other, e.g. colorless, glass; (b) control of the thickness of the glass sheet or envelope; and (c) control of the degree of curing the glass sheet or envelope. A first aspect of the present invention provides a colored glass defined by the formula R'₂O-RO-SiO₂, or by a system of formula R'2θ-RO-Siθ2, wherein R is an alkali metal element and R is an alkaline earth metal element, and is characterized by the addition of: between 0.01% and 1% by weight of molybdenum (Mo) expressed as MOO3, between 0.01% and 2.5% by weight of sulfur (S) expressed as SO₃, and between 0.01% and 0.3% by weight of chromium (Cr) expressed as Cr₂O₃.

The glass preferably comprises between 7.8% and 14% by weight of potassium (K) expressed as K₂O, and between 0.68% and 5.42% by weight of sodium (Na) expressed as Na₂O, wherein the sum of the concentrations of potassium and sodium expressed as K₂O and Na₂O is between 11% and 17% by weight.

The amount of molybdenum expressed as MoO₃ is preferably between 0.01% and 0.6% by weight, for example, between 0.05% and 0.6% by weight.

The amount of sulfur expressed as SO₃ is preferably between 0.01% and 1.0% by weight, for example, between 0.02% and 0.75% by weight. The colored glass may further contain one or more additives selected, for example, from iron oxide (Fe₂O₃), rare earth oxides and titanium dioxide (TiO₂). At least one selected from La₂O₃ (lanthanum oxide) and Nd₂O₃ (neodymium oxide) may be used as rare earth oxide.

If present, the amount of iron expressed as Fe₂O₃ is preferably between 0.001 % and 0.05% by weight, for example, between 0.01 % and 0.05% by weight.

The composition of the glass before curing is preferably selected to provide a 0.5 mm thick sheet of the glass at color point X-coordinate CpX of the CIE chromaticity diagram (CIE 1931 standard colorimetric system established by the Commission Internationale de l'Eclairage (CIE)) in the range of 0.45 - 0.6, for example, 0.52 - 0.6, preferably 0.525 - 0.575.

For example, when iron is present, the amounts of Mo, S, Cr, K, Na and Fe are preferably selected to provide a 0.5 mm thick sheet of the glass at color point X-coordinate CpX of the CIE chromaticity diagram (CIE 1931 standard colorimetric system established by the Commission Internationale de l'Eclairage (CIE)) in the range of 0.525 - 0.6 as defined by the following relation:

CpX = 0.5283 + 0.172 w(Fe ₂O₃) + 0.417 W(MoO₃) + 0.0377 w(SO₃) - 0.002477 w(K₂0) + 0.00881 W(Na₂O) wherein w(— ) is the amount of the particular oxide stated in brackets in weight %. For any other thickness T of the glass sheet, the total amount A (weight %) of the Mo-S chromophore should be adjusted so that the product of T and A (T.A) is the same as at T = 0.5mm.

After thermal curing of the glass, described in more detail below, the CpX will generally rise within the range of 0.525 - 0.6. In both cured and uncured glasses, the CIE CpX and CpY coordinates of a 0.5mm thick glass sheet within the CpX range of 0.525 - 0.6, using illuminant A as used in the CIE 1931 test method, are found to be generally situated on the line L as shown in Figure 3 of the accompanying drawings.

If present, the titanium dioxide and/or one or more rare earth oxide can serve as colorants in addition to Mo, S and Cr, so as to obtain a dense and clear orange, amber or yellow color. For further details of the amounts of titanium dioxide and rare earth oxides that may be used, reference is made to EP-A-1193226, for example, paragraph [0023].

The colored glass may be obtained by forming a batch of glass defined by the formula R^O-RO-SiCh in conventional manner (see, for example, US Patent No. 5470805; WO-A-02/46116; WO-A-02/075777, the disclosures of which are herein incorporated by reference) and including also the required amount of Mo (molybdenum), S (sulfur) and Cr (chromium), or compounds or any of them, and fusing the batch mixture so as to obtain the colored glass. This preparation procedure constitutes a second aspect of the present invention.

From this glass, differently colored glasses, and sheets and envelopes thereof for use in articles such as automotive lamp bulbs, may be prepared batchwise by means of a variety of processing techniques. These include selection of the Cr and the Mo-S chromophore and using one or more of the following simple controlled adjustments during the manufacturing process: (a) control of the proportion of Cr and the Mo-S chromophore by the degree of dilution of the glass in other, e.g. colorless, glass; (b) control of the thickness of the glass sheet or envelope; and (c) control of the degree of curing the glass sheet or envelope.

The yellow glass achievable by the present invention has a clear transparency and a clean yellow color without an amber tinge when transmitting light.

Intermediate tints of finished glass between amber and yellow are achievable by processing from the initially prepared glass under correspondingly adjusted processing conditions.

The finished colored glass composition, preparable as generally described above, constitutes a third aspect of the present invention, and the process for preparing the individual finished glasses constitutes a fourth aspect of the present invention. It is alternatively possible to prepare a finished glass having a required chromaticity, e.g. amber or yellow glass, by direct mixing of the appropriate composition without a step of diluting an initially prepared glass with a colorless glass. Such a manufacturing process for preparing the glass articles having the desired tint directly from a mixture of the components without dilution of an initial glass constitutes a fifth aspect of the present invention, and a finished glass prepared in this way constitutes a sixth aspect of the present invention. However, for large-scale manufacture, the advantage provided by the present invention in making a large batch from which tints can be finely controlled in one or more subsequent processing batches will generally be preferable. According to a seventh aspect of the present invention, an article is provided, comprising a sheet or envelope formed of a finished glass according to the third or the sixth aspect of the present invention. Such an article may be, for example, an electric lamp bulb, e.g. for automotive use, comprising a glass envelope made from a colored glass according to the third or the sixth aspect of the present invention. The various aspects of the present invention are defined in and by the appended claims.

The glass according to the present invention is preferably free of toxic or banned components such as lead, antimony, selenium or cadmium and their compounds. The expression "free of refers at least to maximum levels within legal requirements, and preferably to the essential absence of these elements according to available tests.

The recognition that a glass composition from which such a wide range of chromaticities, with clear transparency and cleanness of color in the yellow range, is achievable through simple processing steps is remarkable and unexpected, and has the potential to provide significant cost savings and other manufacturing advantages.

DETAILED DESCRIPTION OF THE INVENTION

A glass defined by formula R'₂O-RO-Siθ₂, or by a system of formula R'₂O- RO-SiO₂ (both options hereinafter collectively referred to as "defined by formula R'₂0-R0- SiO₂" and similar expressions), was conventionally used for preparing lamps and covers for lighting. The glass generally has desirable properties including satisfactory workability, insulation and sealing properties with dumet wires and the like.

R'₂O in formula R'₂O-RO-SiO₂ is an alkali metal oxide such as Li₂O (lithium oxide), Na₂O (sodium oxide), K₂O (potassium oxide) and the like, and any mixture of two or more alkali metal oxides. RO in formula R'₂O-RO-Siθ₂ is an alkaline earth metal oxide such as MgO (magnesium oxide), CaO (calcium oxide), SrO (strontium oxide), BaO (barium oxide) and the like, and any mixture of two or more alkaline earth metal oxides.

According to the present invention, Mo, S and Cr are added to the master batch in controlled amounts. Independently of the other two, each of Mo, S and Cr can be used in the form of the element or in the form of a compound thereof.

For example, the elemental metal Mo (metal molybdenum) or a molybdenum compound such as Moθ3 (molybdenum trioxide), M0S2 (molybdenum disulfide) or the like, or any combination thereof, may be used as the raw material for molybdenum. Irrespective of the type of raw material for Mo to be used, an amount of molybdenum should be added, providing 0.01% to 1% by weight of Mo in the glass on the converted basis to MOO3 (molybdenum trioxide) (i.e. 0.01% to 1% by weight of Mo expressed as MOO3).

For example, the elemental substance S (flowers of sulfur) or a sulfur compound such as Na₂S (sodium sulfide), K₂S (potassium sulfide) or the like, or any combination thereof, may be used as the raw material for sulfur. Irrespective of the type of raw material for S to be used, an amount of sulfur should be added, providing 0.01% to 2.5% by weight of S in the glass on the converted basis to SO3 (sulfur trioxide) (i.e. 0.01% to 2.5% by weight of S expressed as SO3).

For example, the elemental substance Cr (chromium metal) or a chromium compound such as Cr₂θ3 (chromium (III) oxide) or the like, or any combination thereof, may be used as the raw material for chromium. Irrespective of the type of raw material for Cr to be used, an amount of chromium should be added, providing 0.01% to 0.3% by weight of Cr in the glass on the converted basis to Cr₂θ3 (chromium (III) oxide) (i.e. 0.01% to 0.3% by weight of Cr expressed as Cr₂O₃). Care should be taken to avoid adding excess Mo and S, because this can cause the formation and precipitation of black crystals of MoS in the glass. This adversely affects the desired coloring and light transparency of the glass.

According to the present invention, the colored glass may be obtained by forming a batch of glass defined by formula R'₂O-RO-SiO₂ in conventional manner (see, for example, US Patent No. 5470805; WO-A-02/46116; WO-A-02/075777) and including also the required amount of Mo (molybdenum), S (sulfur) and Cr (chromium), or compounds or any of them, and fusing the batch mixture so as to obtain the colored glass.

In glass of this type, SiO₂ serves as a network former in the glass. The SiO₂ content is typically limited to 60% -75% by weight, which, in combination with the other constituents, leads to a readily meltable glass. Aluminum oxide (AI₂O3) may be included to improve the chemical resistance and the corrosion resistance of the glass. The batch mixture may also include sodium sulfate (Na2SO4). The alkali metal oxide(s) R'20 are used as a melting agent and reduce the viscosity of the glass. If all of the three alkali metal oxides Li₂O, Na₂O and K₂O are used in a given composition, the electrical resistance is sufficiently high (the "mixed- alkali" effect). BaO as the alkaline earth metal oxide RO has the favorable property that it increases the electrical resistance of the glass and reduces the softening temperature (T_soft). The other alkaline earth metal oxides SrO, MgO and CaO have the favorable property that they reduce the liquefying temperature and the melting temperature of the glass. The raw materials used for glass batches of this type are well known to those skilled in this art and include, for example, Calumite™ (Calumite Limited, http://www.calumite.co.uk).

The glass may contain a number of additional elements. These elements include iron (e.g. up to about 0.05% by weight as Fe₂Os), titanium (e.g. up to about 0.05% by weight as TiO₂), fluorine (e.g. up to about 0.05% by weight as F) or chlorine (e.g. up to about 0.05% by weight as Cl).

A batch of the glass to which Mo, S and Cr are added is melted so as to prepare the composition of the colored glass as described above. The composition of the glass may be adjusted by diluting the glass with colorless or other glass, preferably a glass defined by formula R'₂O-RO-SiO₂. Then, for preparing a lamp bulb, a glass tube is made from the melted colored glass by stretching the melted glass by means of a conventional drawing process, such as hand-drawing and down-drawing, etc.

The glass tube obtained in the manner as described above is heated by a burner and then formed into a glass bulb having a desired shape obtained by means of a conventional method such as blowing. The thickness of the glass in the shaped form is suitably selected to provide, after any optional curing, the desired tint.

In the glass of the present invention, the color owing to Mo-S-Cr tends to be enhanced when the colored glass is cured by subjecting it to a heat treatment in a certain temperature range, in comparison with the case in which the colored glass is melted and then immediately cooled. If necessary, the curing treatment may therefore be applied to the colored glass or the colored glass bulb formed as described above, so as to give a desired color. The curing treatment is preferably performed by using a batch-type or continuation- type electric furnace at about 400⁰C to about 620⁰C for about 10 to about 300 minutes, preferably at about 450⁰C to about 580⁰C for about an hour. If the curing temperature is lower than 400⁰C, a longer time will be required which accordingly raises production costs. If the temperature is higher than 620⁰C, the colored glass bulb may be deformed, or clear coloring is not obtainable.

Such a curing treatment is effective in that it prevents the formation and precipitation of black crystals of Mo-S in the glass due to addition of an excess amount of colorant, and in that stable colored glass or a colored glass bulb for lighting is obtained, particularly the colored glass bulb used for turn signal lamps of automobiles. Moreover, for producing covers used for fog lamps of automobiles, the curing treatment has the advantage that the chromaticity of the colored glass can be easily controlled. The glass of the present invention, suitably modified by using a selection of the Cr and the Mo-S chromophore within the proportion ranges stated above, makes color tints ranging from yellow to amber available by means of one or more of the following simple controlled adjustments during the process of manufacturing a glass sheet or envelope or an electric lamp having such an envelope: (a) control of the proportion of the chromophore by the degree of dilution of the glass in other, e.g. colorless, glass; (b) control of the thickness of the glass sheet or envelope; and (c) control of the degree of curing the glass sheet or envelope.

Control of the proportions of Cr and Mo and S relative to each other is achievable by selecting the amounts of ingredients that contribute to these elements in the initial mixing process. Control of the total amount of Cr and Mo and S relative to the total composition is achievable by diluting the glass of the initial fusion with other, e.g. colorless, glass.

It was found that there is a relationship between the amount of chromium

(expressed as Cr₂Os) in the glass composition and the amount of CIE 1931 chromaticity y units (Illuminant A) (Δ CpY) by which the CpY of the glass sheet or envelope is raised above the Amber chromophore line (see Figure 2, representing a chromium-free yellow glass), defined by the following relation:

Δ CpY = 0.0484 [Cr] wherein [Cr] is the percentage by weight of Cr in the glass composition, expressed as Cr₂C^. Control of the thickness T of the glass sheet or envelope has the effect that the

CpX of the glass sheet or envelope is raised as the thickness T increases. It was found that, at least in the thickness range from 0 to 0.2 cm, CpX is related to thickness T (in cm) in approximately the following way:

CpX = 0.3634.T⁰⁴ + 0.4484. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, without limitation and solely by way of example, with reference to the accompanying drawings, in which : Fig. 1 shows an electric lamp according to the invention; Fig. 2 shows a CIE chromaticity graph in the amber-yellow color range, showing the amber and yellow glasses of the present invention, in comparison with other glasses, as described below; and

Fig. 3 shows a CIE chromaticity graph in the amber-yellow color range of the yellow glass of the present invention, in comparison with other glasses, as described below.

DESCRIPTION OF EMBODIMENTS All percentages herein are by weight unless stated otherwise.

Figure 1 shows an electric automotive signal lamp 1 , also called indicator lamp, comprising: a lamp envelope or bulb 2 made of colored glass, having a wall thickness of between, for example, 0.3 mm and 1.3 mm, a mount 3 comprising two lead-in wires 3a and 3b held by a bead 4 mounted inside the glass bulb 2 for supporting a coiled filament 5, a metal cap 9 fitting in a lamp holder, a location pin 7 extending from the metal cap 9 to fit in the lamp holder, the relative positioning of said location pin 7 being such that it is impossible to mount the wrong lamp type in a specific luminary (e.g. it is impossible to mount a clear lamp in a luminary intended for an amber lamp), and an electric contact 8 connected to the mount 3 for the lamp to be electrically supplied by the electric circuits of the car.

The envelope 2 of the electric lamp shown in Fig. 1 is made of a colored glass according to the invention.

A master batch of glass is prepared by weighing and mixing all required raw materials mentioned above. The batch is fed to a conventional continuous melting tank. Standard process settings are used for melting, refining and conditioning of the tube-forming process. The master batch may have, for example, the following nominal composition (percentages by weight):

Basic Glass Composition - Si (SiO₂) 64.8596; Al (Al₂O₃) 0.6249; Li (Li₂O) 1.5800; Na (Na₂O) 1.8501; K (K₂O) 12.4100; Mg (MgO) 2.4400; Ca (CaO) 4.4899; Sr (SrO) 2.1200; Ba (BaO) 8.5800;

Chromophore - Mo (MoO₃) 0.1200; S (SO₃) 0.7500; Cr (Cr₂O₃) 0.0700;

Others - Fe (Fe₂O₃) 0.0205; Mn (MnO) 0.0126; Ti (TiO₂) 0.0424; F 0.0126; Cl 0.0051.

This nominal composition produces a yellow glass, the color of which can be enhanced by thermal curing of the sheet or envelope initially formed. Furthermore, the tint of the glass may be adjusted as desired under fine control within the amber-to -yellow range by dilution of a batch with another, e.g. colorless, glass, preferably a glass defined by the formula R'₂O-RO-SiO₂. The thickness of a sheet or envelope of the glass will also affect the transmitted light color, and the degree of curing the glass sheet or envelope will also affect the color within the amber -to-yellow color range. A glass tube is made from the glass batch by means of standard tube-drawing techniques. From the glass tube, a glass bulb having the desired envelope wall thickness is prepared in conventional manner.

Especially where a finished amber bulb is desired, the glass bulb can be subsequently cured by using a batch-type or continuation-type electric furnace at about 400⁰C to about 620⁰C for about 10 to about 300 minutes, preferably at about 450⁰C to about 580⁰C for about an hour.

Referring to Figure 2, a CIE chromaticity graph is shown for the following glasses at a glass thickness of 0.6mm: a range of "Amber" cured glass lamps, representing (chromium- free) glass according to WO-A-2007/034429, having different thicknesses and compositions, and therefore different colors in the yellow range. The points are shown and are joined by a line referred to as the "Amber chromophore line"; a range of conventional commercially available Philips HiPer yellow lamp bulbs, prepared by varnishing clear lamps with yellow varnish. All points for these lamps are in the yellow area of the graph, as shown; a range of conventional commercially available Philips P21 yellow lamp bulbs, prepared by varnishing clear lamps with yellow varnish. All points for these lamps are in the yellow area, as shown by the lines representing the spec parameters for the yellow lamp; a range of yellow lamps according to the present invention, having colors situated on a chromophore line (shown as a broken line in Figure 2) which closely tracks the line of the Amber chromophore line but extends further than it into the yellow region to the left side of Figure 2, as shown. The color coordinates of the standard color lamp "illuminant A", conventionally used in CIE tests, are also shown in Figure 2.

Figure 2 also shows the spec parameters for the relatively yellow-green PY21 lamps.

Interestingly, the chromophore line ( ) on which the glass of the present invention is situated, passes close to all of the comparative lamps, across a wide range of yellow to amber colors.

As mentioned above, there is a relationship between the amount of chromium (expressed as Cr₂Os) in the glass composition and the amount of chromaticity y units (Δ CpY) by which the chromophore line of a comparable glass sheet or envelope of the invention is raised above the Amber chromophore line, defined by the following relation:

Δ CpY = 0.0484 [Cr] wherein [Cr] is the percentage by weight of Cr in the glass composition, expressed as Cr₂C^.

This general raising of the chromophore line ( ) of the glass of the present invention is shown in Figure 2. This indicates that the glass of the present invention can make very good approximations of a wide range of commercial yellow and amber glasses available for use in lamps and the like, through simple manufacturing processing adjustments of dilution, thickness control and curing.

Referring to Figure 3, a CIE chromaticity graph is shown for the following glasses at a glass thickness of 0.5mm: the spec range of conventional commercially available Philips HiP er yellow lamp bulbs; the spec range of conventional commercially available Philips P21 yellow Chartres lamp bulbs; a range of yellow glass according to the present invention (referred to as

"amber production glass"), having colors situated on a chromophore line L in Figure 3, as shown, both before and after thermal curing; a range of yellow test glasses, also having colors situated on a chromophore line L in Figure 3; and the chromaticity of black body radiation in a range of temperatures, showing that Illuminant A (X on the black body radiation chromaticity line) has the spectrum of black body radiation at 2856 K.

This again shows that the glass of the present invention can make very good approximations of a range of commercial yellow glasses available for use in lamps and the like, through simple manufacturing processing adjustments of dilution, thickness control and curing.

As is clear from the drawings and the above description, the present invention provides a very versatile glass composition from which a relatively wide range of finished glasses and articles in the yellow- to -amber color range can be readily prepared. The glasses are of the type defined by the formula R'₂O-RO-Siθ₂, with the associated advantages of this type of glass in terms of relatively low fragility of the glass and articles made therefrom, satisfactory workability, insulation and sealing properties with dumet wires and the like.

Any reference sign in the appended claims should not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements other than those defined in any claim. Use of the indefinite article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:

1. A colored glass defined by the formula R₂O-RO-SiO₂, or by a system of formula R'2θ-RO-Siθ2, wherein R is an alkali metal element and R is an alkaline earth metal element, characterized by the addition of: between 0.01% and 1% by weight of molybdenum (Mo) expressed as MOO3, between 0.01% and 2.5% by weight of sulfur (S) expressed as SO3, and between 0.01% and 0.3% by weight of chromium (Cr) expressed as Cr₂O₃.

2. A glass according to claim 1, wherein the amount of molybdenum is between 0.01% and 0.6% by weight.

3. A glass according to claim 1 or 2, wherein the amount of sulfur is between

0.01 % and 1.0% by weight.

4. A glass according to any one of the preceding claims, wherein the amount of chromium is between 0.01% and 0.1% by weight.

5. A yellow glass according to any one of claims 1 to 4.

6. A process for preparing a glass as defined in any one of the preceding claims, comprising the steps of mixing conventional ingredients under conventional conditions for forming a glass defined by the formula R'₂O-RO-SiO₂, including ingredients which introduce Mo (molybdenum), S (sulfur) and Cr (chromium), and fusing the mixture to obtain the colored glass.

7. A process according to claim 6, wherein the colored glass is obtained as a glass sheet or envelope and the glass as defined in any one of claims 1 to 5 is obtained by providing one or more of the following: (a) control of the total amount of Mo (molybdenum), S (sulfur) and Cr (chromium) in the glass by the degree of dilution of the glass in other, e.g. colorless, glass; (b) control of the thickness of the glass sheet or envelope; and (c) control of the degree of curing the glass sheet or envelope.

8. A process according to claim 7, wherein one or more of controls (b) and (c) are used without control (a).

9. A glass prepared by means of a process according to any one of claims 6 to 8.

10. An article comprising a sheet or envelope of a glass according to any one of claims 1 to 5 and 9.

11. An article according to claim 10, which is an electric lamp bulb, e.g. for automotive use.