CA1158704A - Curvilinear type fluorescent lamp - Google Patents
Curvilinear type fluorescent lampInfo
- Publication number
- CA1158704A CA1158704A CA000370811A CA370811A CA1158704A CA 1158704 A CA1158704 A CA 1158704A CA 000370811 A CA000370811 A CA 000370811A CA 370811 A CA370811 A CA 370811A CA 1158704 A CA1158704 A CA 1158704A
- Authority
- CA
- Canada
- Prior art keywords
- glass
- fluorescent lamp
- oxide
- tube
- type fluorescent
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/30—Vessels; Containers
- H01J61/35—Vessels; Containers provided with coatings on the walls thereof; Selection of materials for the coatings
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- Vessels And Coating Films For Discharge Lamps (AREA)
Abstract
Abstract of the Disclosure A curvilinear type fluorescent lamp comprises a curvilinear, light-transmitting sealed tube made of soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 to 720°C and whose coefficient of linear thermal expansion is 92 to 105 x 10-7 cm/cm/°C. On the inner surface of the tube a phosphor layer is formed. The phosphor forming the layer contains a binder consisting chiefly of calcium borate.
Description
0~
Curvilinear type fluorescent lamp This invention relates to a curvilinear type fluorescent lamp comprising a curvilinear, li~ht-transmitting sealed tube made of soda-lime glass or low lead glass.
Various curvilinear type 1uorescent lamps are known. Of these lamps, a circular fluorescent lamp, for example, is manufactured in the following manner.
First, the inner surface of a straiyht, light-transmitting glass tube is coated with a phosphor.Then, a stem holding an electrode coated with an electron-emitting substance is sealed to either end of the straight glass tube. The tube is then heated and softened in a furnace. It is bent about a ~rum, thus being shaped like a circle. Thereafter, the tube is cooled and subsequently evacuated. Finally, an inert gas and mercury are introduced into the tube.
The light-transmitting, sealed tube of the known curvilinear fluorescent lamp is made of lead ~lass which contains 24 to 29 percent by weight of lead oxide and which has a low softening point. The lead glass is used because a tube made of it can easily be bent to form a circle at low temperatures. The glass, however, is expensive because it contains a great quantity of expen-sive lead oxide. A curvilinear type fluorescent lampwill be costly if provided with a curvilinear tube made ~.
of lead glass. Further, lead i5 one of the prominent sources of environmental pollution~ Used and broken fluo-rescent lamps made of lead glass are difficult to dispose of in such a way that the lead does not promote environmen-tal pollution.
Instead of lead glass having the above-mentioned draw-backs, soda-lime glass containing no oxide of lead has been used on trial basis as the material of a straight, light-transmitting sealed tube. A straiyht tube of soda-lime glass cannot be bent easily, however, unless it is heated to a higher temperature than a tube of lead glass. This is because soda-lime glass has a higher softening point than lead glass. While a soda-lime glass tube is being heated to a high temperature and bent, the phosphor laid on the inner surface of the tube migrates into the glass layer.
As the tube is cooled, it may be broken by tension generated due to the difference in thermal expansion coefficient between the phosphor and soda-lime glass. Even if no~ broken at the end of the cooling process, the tube has its strength reduced to an alarming degree. In addition, the radiant efficiency of the phosphor will be reduced, therefore the initial luminous flux of the lamp will be lowexed.
I,ow lead glass which may be used instead of high lead glass or soda-lime glass is disclosed in Japanese Patent Publication No. 50-15804 and Japanese Patent Disclosure (Kokai) NoO 54-60778. The low lead glass disclosed therein has a softening point lower than that of soda-lime glass.
The low lead glass disclosed in Japanese Patent Publication No. 50-15804 contains 1.91 to 10 percent by weight of lead oxide, whereas the low lead glass disclosed in Japanese Patent Disclosure (Kokai) No. 54-60778 contains 4 to 19 percent by weight of lead oxide.
The low lead glass similar to that disclosed in Japanese Patent Publication No. 50-15804 has an oxide com-position (wt. %) such as shown hereinafter in Table 1. The oxide compositions of two examples A, B are shown in Table
Curvilinear type fluorescent lamp This invention relates to a curvilinear type fluorescent lamp comprising a curvilinear, li~ht-transmitting sealed tube made of soda-lime glass or low lead glass.
Various curvilinear type 1uorescent lamps are known. Of these lamps, a circular fluorescent lamp, for example, is manufactured in the following manner.
First, the inner surface of a straiyht, light-transmitting glass tube is coated with a phosphor.Then, a stem holding an electrode coated with an electron-emitting substance is sealed to either end of the straight glass tube. The tube is then heated and softened in a furnace. It is bent about a ~rum, thus being shaped like a circle. Thereafter, the tube is cooled and subsequently evacuated. Finally, an inert gas and mercury are introduced into the tube.
The light-transmitting, sealed tube of the known curvilinear fluorescent lamp is made of lead ~lass which contains 24 to 29 percent by weight of lead oxide and which has a low softening point. The lead glass is used because a tube made of it can easily be bent to form a circle at low temperatures. The glass, however, is expensive because it contains a great quantity of expen-sive lead oxide. A curvilinear type fluorescent lampwill be costly if provided with a curvilinear tube made ~.
of lead glass. Further, lead i5 one of the prominent sources of environmental pollution~ Used and broken fluo-rescent lamps made of lead glass are difficult to dispose of in such a way that the lead does not promote environmen-tal pollution.
Instead of lead glass having the above-mentioned draw-backs, soda-lime glass containing no oxide of lead has been used on trial basis as the material of a straight, light-transmitting sealed tube. A straiyht tube of soda-lime glass cannot be bent easily, however, unless it is heated to a higher temperature than a tube of lead glass. This is because soda-lime glass has a higher softening point than lead glass. While a soda-lime glass tube is being heated to a high temperature and bent, the phosphor laid on the inner surface of the tube migrates into the glass layer.
As the tube is cooled, it may be broken by tension generated due to the difference in thermal expansion coefficient between the phosphor and soda-lime glass. Even if no~ broken at the end of the cooling process, the tube has its strength reduced to an alarming degree. In addition, the radiant efficiency of the phosphor will be reduced, therefore the initial luminous flux of the lamp will be lowexed.
I,ow lead glass which may be used instead of high lead glass or soda-lime glass is disclosed in Japanese Patent Publication No. 50-15804 and Japanese Patent Disclosure (Kokai) NoO 54-60778. The low lead glass disclosed therein has a softening point lower than that of soda-lime glass.
The low lead glass disclosed in Japanese Patent Publication No. 50-15804 contains 1.91 to 10 percent by weight of lead oxide, whereas the low lead glass disclosed in Japanese Patent Disclosure (Kokai) No. 54-60778 contains 4 to 19 percent by weight of lead oxide.
The low lead glass similar to that disclosed in Japanese Patent Publication No. 50-15804 has an oxide com-position (wt. %) such as shown hereinafter in Table 1. The oxide compositions of two examples A, B are shown in Table
2 together with those of the high lead glass and soda-lime ~f ~5~704 glass which are used as the materials of the known curvi-linear and straiyht 1uorescent tubes respectively. The coefficients of linear thermal expansion and softening points of the low lead glasses A and B, the lead glass and the soda-lime glass are shown also in Table 2 The inventors hereof made a number of curvilinear type fluorescent lamps of the same dimensions, whose curvi-linear tubes were made of different glasses, i.e. low lead gLasses A and B, the conventional lead glass and the soda-lime glass. These lamps were tested to determine theircharacteristics. The test showed that the lamps made of glass A and the lamps made of glass B had an initial luminous flux comparable with that of the lamps made of the conventional lead glass and better than that o~ the lamps made of soda-lime glass. ~owever, these lamps were dis-advantageous in the following respects:
~1) These lamps had not a sufficient strength.
(2) Their luminous ~lux over their lifetime deteri-orated further than that of the lamps made of the lead glass.
It is an object of this invention to provide a curvi-linear type fluorescent lamp which comprises a curvilinear, light-transmitting sealed tube made of soda-lime glass or low lead glass and which can have an improved strength and an improved luminous flux performance over its I~fetime.
According to this invention there is provided a flu~rescent lamp comprising a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with electron-emitting substance, said tube being made of soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 tQ 720C and whose coefficient of linear ther mal expansion is 92 to 105 x 10 7 cm/cm/C; and a phosphor layer laid on the inner surface of the tube and containing a binder consisting chiefly of calcium borate.
The lamp of the above-mentioned structure has an initial luminous flux comparable with that of a curvilinear o~
type fluorescent lamp made of the conventionally used high lead glass. The binder melts when a straight tube made of such glass is bent, thus suppressing movement of phosphor particles into the glass layer of the tube. Further it is possible with the lamp to prevent sodium ions ~rom diffus-ing from the glass layer while the lamp is being used.
According to a further aspect of the invention, a curvilinear type fluorescent lamp is provided, which com-prises a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with electron-emitting substance, said tube being made of soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 to 720C and whose coefficient of linear thermal expansion is 92 to 105 x 10 7 cm/cm/C; a metal oxide layer coated on the inner surface of the tube in an amount of 0.6 to 6.2 mg per square centi-meter and made of at least one of the group consisting of aluminum oxide, magnesium oxide, silicon oxide and titanium oxide; and a phosphor layer laid on the metal oxide layer and containing binder consisting chiefly of calcium borate.
The curvilinear sealed tube of the latter-mentioned lamp is stronger than that of ~he first-mentioned lamp, owing to the use of the metal oxide layer. The metal oxide layer can operate effectively to suppress movement of phos phor particles into the glass layer and thus suppress cre-ation of radicals in the glass. Moreover, it tends to pre-vent the receptor sites, if any, from trapping Hg , thereby improving the luminous flux performance of the lamp over its lifetime. Still further, the metal oxide layer tends to suppress reaction between Hg and sodium ions diffused from the glass layer.
It is preferred that calcium borate is used in an amount of 0.2 to 2.0 percent by weight on the basis of the amount of phosphor used so that the phosphor layer is strengthened and the initial luminous flux of the lamp is improved. Further, it is preferred that the phosphor con-taining the binder is coated on the inner surface of the ~J
~ (3 glass tube or on the metal oxide layer coated on the inner surface of the tube in an amount of 2.9 to 3.9 my per square centimeter.
Preferably also the glass contains 12 to 17 percent by weight of sodium oxide (Na2O~. In addition, the glass preferably contains 3 to g percent by weight o~ calcium oxide, whereby to suppress diffusion of sodium iQnS .
Moreover, with a view to both the initial luminous flux and life performance of luminous flux of the lamp being further enhanced, it is prefarred that the calcium borate contained in the binder is obtained from a mixture of CaO and B2O3, the mol ratio of CaO to B2O3 being 1/~ to
~1) These lamps had not a sufficient strength.
(2) Their luminous ~lux over their lifetime deteri-orated further than that of the lamps made of the lead glass.
It is an object of this invention to provide a curvi-linear type fluorescent lamp which comprises a curvilinear, light-transmitting sealed tube made of soda-lime glass or low lead glass and which can have an improved strength and an improved luminous flux performance over its I~fetime.
According to this invention there is provided a flu~rescent lamp comprising a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with electron-emitting substance, said tube being made of soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 tQ 720C and whose coefficient of linear ther mal expansion is 92 to 105 x 10 7 cm/cm/C; and a phosphor layer laid on the inner surface of the tube and containing a binder consisting chiefly of calcium borate.
The lamp of the above-mentioned structure has an initial luminous flux comparable with that of a curvilinear o~
type fluorescent lamp made of the conventionally used high lead glass. The binder melts when a straight tube made of such glass is bent, thus suppressing movement of phosphor particles into the glass layer of the tube. Further it is possible with the lamp to prevent sodium ions ~rom diffus-ing from the glass layer while the lamp is being used.
According to a further aspect of the invention, a curvilinear type fluorescent lamp is provided, which com-prises a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with electron-emitting substance, said tube being made of soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 to 720C and whose coefficient of linear thermal expansion is 92 to 105 x 10 7 cm/cm/C; a metal oxide layer coated on the inner surface of the tube in an amount of 0.6 to 6.2 mg per square centi-meter and made of at least one of the group consisting of aluminum oxide, magnesium oxide, silicon oxide and titanium oxide; and a phosphor layer laid on the metal oxide layer and containing binder consisting chiefly of calcium borate.
The curvilinear sealed tube of the latter-mentioned lamp is stronger than that of ~he first-mentioned lamp, owing to the use of the metal oxide layer. The metal oxide layer can operate effectively to suppress movement of phos phor particles into the glass layer and thus suppress cre-ation of radicals in the glass. Moreover, it tends to pre-vent the receptor sites, if any, from trapping Hg , thereby improving the luminous flux performance of the lamp over its lifetime. Still further, the metal oxide layer tends to suppress reaction between Hg and sodium ions diffused from the glass layer.
It is preferred that calcium borate is used in an amount of 0.2 to 2.0 percent by weight on the basis of the amount of phosphor used so that the phosphor layer is strengthened and the initial luminous flux of the lamp is improved. Further, it is preferred that the phosphor con-taining the binder is coated on the inner surface of the ~J
~ (3 glass tube or on the metal oxide layer coated on the inner surface of the tube in an amount of 2.9 to 3.9 my per square centimeter.
Preferably also the glass contains 12 to 17 percent by weight of sodium oxide (Na2O~. In addition, the glass preferably contains 3 to g percent by weight o~ calcium oxide, whereby to suppress diffusion of sodium iQnS .
Moreover, with a view to both the initial luminous flux and life performance of luminous flux of the lamp being further enhanced, it is prefarred that the calcium borate contained in the binder is obtained from a mixture of CaO and B2O3, the mol ratio of CaO to B2O3 being 1/~ to
3/2, deposited on the inner surface of the glass tube or on the metal oxide layer.
The lamp of either structure mentioned above can be manufactured at a reduced cost. Further, since the glass used contains only a small amount of lead, the lamp of this invention is preferred from the point of view of environ-mental pollution.
Other objects and advantages of the invention will become apparent during the following discussion of the accompanying drawings.
This invention can be more fully understood fxom the following detailed description when taken in conjunction wi~h the accompanying drawings, in which:
Figure 1 shows a known circular type fluorescent lamp after continuous use for 3000 hours;
Figure 2(a) is an enlarged sectional view of the wall of a known glass tube and a phosphor layer coated on the glass wall;
Figure 2(b) is an enlarged sectional view of the wall of the known glass tube now bent in the form o~ a circ~e and the phosphor layer coated on the glass wall;
Figure 2(c~ is an enlarged sectional view of a portion 26 of the circular type fluorescent lamp shown in Yigure 1, taken along line II-II' in Figure l;
Figure 3 shows a circular type fluorescent lamp ,~, ~S~ 4 according to this invention;
Figure 4 is a cross sectional view oE the lamp shown in Figure 3, taken alony line IV-IV' in Figure 3;
Figure 5 is a graph showing the relationship between the strength of a phosphor layer and the mixing ratio of a binder consisting chiefly of calcium borate;
Figure 6 is a ~raph illustrating the relationship between total luminous flux and the mixing ratio of a binder consisting chiefly of calcium borate;
Figure 7 is a graph showing the relationship between the quantity of phosphor coated, on one hand, and initial luminous flux and ratio of blackening during use, on the other;
Figure 8 shows another circular type fluorescent lamp according to this invention;
Figure 9(a3 is an enlarged sectional view of the wall of a glass tube of this invention and a phosphor layer coated on the glass wall;
Figure 9(b) is an enlarged sectional view`of the wall of a glass tube of this invention, now bent in the form of a circle, and the phosphor layer coated on the glass wall;
and Figure 9(c) is an enlar~ed sectional view of a portion of the lamp shown in Figure 8 after continuous use for 3000 hours.
It will first be discussed why the prior art lamps already discussed above and made of glasses A and B were disadvantageous despite their good initial luminous flux.
Table 3 shows the initial luminous flux, luminous flux at 3000 Hr and luminous flux at 5000 ~r of various curvilinear type fluorescent lamps made by the in~entors and subsequently tested. "Initial luminous flux" was measured at the 100th hour of use, in accordance with the re~ulation JISC7601.
All the la~ps were circular fluorescent lamps of lOOV, 30W.
The numerical data given in Table 3 were the average of 50 lamps of each type tested.
Fig. 1 sho~s the typical outer appearance of a circular '7~
fluorescent lamp mad~ of the conventional low lead glass, after 3000 hours of continuous use. A portion 24 of the circular tube 22 made of the low lead glass, which con-tained 12 percent by weight or less of lead oxide ~PbO), was yellow brown. It was ascertained that in general this colour change occurred at ~hat portion 24 of the tube 22 which was heated to the highest temperature during the bending process, i.e. that portion 24 which was positioned highest in the furnace.
It may reasonably be assumed that this colour change was caused partly by sodium amalgam formed by reaction between Na+ diffused from the glass and mercury vapor and partly by bonding of Hg to receptor sites in the glass, which were ~enerated as the phosphor moved into t~le glass.
As shown in Table 2, Na~ was diffused in a small amount from the conventionally used lead glass because the glass contained a small amount of sodium oxide (Na2O). The tubes of the lead glass were bent in a desired fashion at a relatively low temperature, an~ since the phosphor moved into the glass in but a small amount, no marked generation of receptor sites tended to occur.
The above-mentioned test further revealed that, the more the phosphor moved into glass, the weaker became the tubes made of the glass. The reason why so will be dis-cussed.
Binders generally contained in the phosphor forfluorescent lamps contains boron oxide (B2O3). The boron oxide therefore is partly in contact with soda-lime glass or low lead glass. A portion of the boron oxide therefore melts when the tubes of either soda-lime glass or low lead glass are heated and bent in the fuxnace. The molten borate is fused with the glass, thus forming a B2O3-Sio2-Na2O glass. The viscosity of the glass thus formed sharply decreases when the glass is heated to about æoooc. When the glass tubes are heated to about 800C, the inner surfaces as well as their outer sur~aces are softened, whereby the phosphor moves into them. As a result, when the bent tubes -~L~lS870~
~ 8 --are cooled, the inner surface portion of each tube has fine cracks due to the difference in thermal expansion coeffici-ent between the phosphor and the glass. The fine cracks seem to weaken the tubes.
Indeed a binder will more strongly bind phosphor par-ticles if it contains barium oxide (BaO). But barium oxide will lower the melting point of the binder, and the binder may possibly melt before the glass softens. If this happens, more phosphor particles wi~l move into the glass layer of a tube while the tuhe is being heated, softened and bent.
With reference to Figs. 2(a), 2(b) and 2(c), it will be described how phosphor particles containing a binder con-sisting of barium calcium borate move into the glass layer of the tube.
Fig. 2(a) shows the particles 28 of phosphor coated on the inner surace of the glass tube 22 and subsequently baked. Fig. 2(b) illustrates the phosphor particles 28, some of which lie in the glass layer of the tube 22 which has been already heated, softened and bent. In the recesses 30 between the glass layer and each phosphor particle 28 that lies partly or wholly within the glass layer, receptor sites will be formed. Fig. 2~c) illustrates a part 26 of the portion 24 of the tube 22 which has been used for 3000 hours (see Fig. 1). Since mercury vapor has flowed into the recesses 30 through the spaces among the phosphor par-ticles 28, the portion 24 of the tube is turned into yellow brown by reaction at the receptor sites of the glass with this mercury.
Japanese Utility Model Disclosure (Kokai) No. 53-92976 discloses the technique of providing a metal oxide layer between the inner surface of a curvilinear glass tube and a phosphor layer thereby to reinforce the glass tube. This technique may indeed be effective if the tube is made of glass having a softening point of about 60aoc. However, the technique does not seem to work if the tube is made of soda-lime glass or low lead glass which has a relatively high softening point ranging from 640C to 720C. Japanese ~8'~
Utility Model Disclosure (Kokai) No. 53-92976 further teaches that on the metal oxide layer there is formed a layer of phosphor containing 0.1 to 4 percent by weight of a B2O3-containing binder and that the binder may be a barium calcium borate binder. A barium calcium borate binder, however, melts before soda-lime glass or low lead glass softens which has a high softening point. If the tube according to Disclosure (Kokai) No. 53-92976 is made of soda-lime glass or low lead glass, the binder will help many phosphor particles move into the glass layer of the tube and hence will create many receptor sites when the tube is heated, softened and bent. The receptor sites thus formed will eventually reduce the luminous flux of the resultant curvilinear fluorescent lamp.
Japanese Patent Disclosure (Kokai) No. 49-20972 dis-closes a method of improving the luminous flux performance over the lifetime of a curvilinear fluorescent lamp. More specifically, a titanium dioxide film 0.02 to 0.2 micron thick is laid on the inner surface of a glass tube. Patent Disclosure (Kokai) No. 49-20972 teaches that, unless the titani~un dioxide film is provided, the sodium ions liberated from the glass reacts with mercury vapor to form amalgam after a certain duration of use of the lamp and that the amalgam, if formed, causes the phosphor (e.g. Ca5(PO4)3X;
Sb, Mn, where X = F, Cl) to turn gray. The above~mentioned titanium dioxide film is too thin to prevent the aforemen-tioned yellow brown change of coloux taking place in a curuilinear fluorescent lamp which is made of soda-lime glass or low lead glass.
Japanese PatentPublication No. 35-12085 discloses a binder consisting of CaO and B2O3 in weight ratio of 3:1 to 1:2. The binder is mixed with phosphor, and the mixture is coated on the inner surface of a glass tube and subsequently baked, thereby forming calcium borate. This technique aims to enhance the strength of the phosphor layer without reduc-ing the luminous efficacy of a fluorescent lamp comprising the glass tube. In contrast, the binder used in the present {)~
invention consists chiefly of calcium borate. It is used in order to prevent phosphor particles from entering a layer of soda-lime glass or low lead glass having a high softening point, while a tube made of such glass is being heated, softened and bent, thereby to improve the strength of the glass tube. It is used also in order to suppress diffusion of sodium ions into the glass layer, thereby to enhance the luminous efficacy of the lamp.
Fig. 3 shows the outer appearance of a circular type fluorescent lamp 32 according to the present invention.
Fig. 4 is a cross sectional view of the lamp 32, taken along line IV-IV' in Fig. 3. The lamp 32 comprises a ring-shaped sealed glass tube 34 and a phosphor layer 36 coated on the inner surface of the glass tube 34. The tube 32 is made of low lead glass containing 12 percent by weight or less of lead oxide (PbO) and having a softening point of 640 to 720C and a coefficient of linear thermal expansion of 92 to 105 x 10 cm/cm/C. The --'.1 ' ~J
58~(3~L
layer 36 is made of calcium halophosphate phosphor acti-vated by manganese and antimony (CaS(YO4)3X; Sb, Mn, where X = F, Cl) containing a binder consisting of calcium borate.
Fifty circular fluorescent lamps of the structure shown in Figs. 3 and 4 were made which were provided with phosphor layers of the same thickness. These were 100 V - 30 W fluorescent lamps. They were continuously used for 3000 hours. Upon lapse of these hours all the fifty lamps were found to have performance of luminous flux ranging from 92 to 94 %. Further, their sealed glass tubes 34 had almost never turned yellow brown, unlike the conventionally used glass tubes inner sur-faces of which are coated with phosphor containing barium-calcium borate binder.
~t was found that calcium borate should be used in mixing ratio of 0.2 to 2.0 percent by weight with respect to the phosphor. If calcium borate is used in mixing ratio outside this specific range, the phosphor layer will not be sufficiently strong and the initial luminous flux of the lamp will not be suf-ficiently high.
Fig. 5 illustrates the relationship between the strength of phosphor layer and the mixing ratio of a binder. Curve a indicates this relationship observed in the above-mentioned another fifty fluorescent lamps according to this invention. Curve ~ shows this rela-tionship observed in fifty circular fluorescent lamps of the same size and structure but using a known binder consisting of barium calcium borate. Curve y indicates said relationship observed in fifty circular fluorescent lamps of the same size and structure but using a known binder consisting of calcium phospha-te and thus having an extremely high melting point. The binders used in the lamps of the three categories have melting pointSas given in Table ~. This melting point was obtained by detecting the maximum - 12 - ~5~70~
heat-absorption temperature of the respective binders, using differential thermal analysis.
The phosphor layers of all the fluorescent lamps of the three categories were formed by coating the S phosphors on the inner surEaces of the respective glass tubes and subsequently baking the phosphor thus coated.
The strength of each of the phosphor layer was detected by blowing air at the rate of 300 Torr-Q/sec against the layer through a nozzle spaced from the layer by lO mm.
The strength of the layer is the reciprocal of the ratio of the diameter of the largest flake of phosphor exfo-liated from the inner surface of the glass tube to the diameter of the largest flake of known phosphor exfo-liated from the inner surface of a tube made of the con-ventionally used lead glass, said known phosphor con-taining a binder consisting of barium calcium borate and calcium phosphate in weight mixing ratio of 2:1. In Fig. 6 said reciprocal is given in percentage.
Fig. 6 illustrates the relationship between the total luminous flux of each fluorescent lamp tested and the mixing ratio of a binder used. Curve ai indicates this relationship observed in the fifty fluorescen-t lamps according to this invention. Curve ~' shows the relationship observed in fifty fluorescent lamps using the known binder consisting of barium calcium borate.
Curve y' shows the relationship observed in the fifty fluorescent lamps using the known binder consisting of calcium phosphate.
As evident from Figs. 5 and 6, the circular 3~ fluorescent lamps using calcium b~t~e in a mixing ratio of 0.2 to 2.0 % exhibited performance of luminou~s flux better than that of the fluorescent lamps made of the conventionally used lead glass and exhibited a total luminious flux greater than the fluorescent lamps using the known binder consisting of barium calcium borate or calcium phosphate~ The fluorescent lamps using calcium borate in a mixing ratio of more than 2.0 % exhibited a ~S87~
t~
poor performance ~ luminous flux, and the phosphor containing calcium borate in a mixing ratio of less than 0.2 ~ was found llkely to exfoliate from the inner sur-face of the glass tubes.
As Table 4 shows, barium calcium borate has a melting point 44C to 77jC ~ ower than the softening points of the soda-lime glass A and glass B - all given in Table 2. Barium calcium borate, iE used as a binder, will melt before any of these glasses softens.
While the sealed glass tube is being heated, softened and bent, Na+ diffused from the glass used will enter the molten barium calcium borate. This may be why the lamps using barium calcium borate as a binder exhibited a total luminous flux smaller than the lamps using calcium borate as a binder.
As Table 4 further shows, calcium phosphate has an extremely high melting point, 1670C. For this reason, the layer of the phosphor containing calcium phosphate did not adhere to the glass layer so strongly as did the layer of the phosphor containing calcium borate and the layer of the phosphor containing barium calcium borate.
According to this invention, the calcium halophosphate phosphor containing calcium borate in a mixing ratio of 0.2 to 2.0 % is coated on the inner sur-face of the glass tube in an amount of, preEerably, 2.9 to 3.9 mg per square centimeter. Curve ~ in Fig. 7 shows the relationship between the initial luminous flux of the lamps using calcium borate in a mixing ratio in said range and the amount of the phosphor used (mg/cm2). And curve ~ in Fig. 7 illustrates the rela-tionship between the amount of phosphor used (mg/cm2) and the ratio of generated blac~ening of the glass tubes. As curve ~ clearly shows, the lamps using the phosph~r in an amount of less than 2.g mg per square centimeter exhibited an initial luminous flux smaller than that of a circular fluorescent lamp made of the conventionally used lead glass. ~s curve ~ clearly - 14 _ ~ S~70~
shows, the la~ps using the phosphor in an amount of more than 3.9 mg per square centimeter encountered the blackening of the glass tubes.
According to this invention it is preferred that the binder be prepared by calcium oxide (CaO) and boric anhydride (B2O33 in mol ratio of 1:2 to 3:2. A number of 100 V - 30 W white circular fluorescent lamps were made which comprised a circular sealed tube made of glass A and phospher layer coated on the inner surface of the tube and made of the above-mentioned calcium halophosphate phosphor containing a binder prepared by calcium oxide and boric anhydride in mol ratio (CaO/B2O3) ranging from 0.28 to 1~82. These fluorescent lamps were put to an impact strength test. More precisely, a steel ball having a diameter of 10 mm and weighing 3.5 g was dropped from different levels onto that portion of each fluorescent lamp which was about 100 mm from the exhaust tube of the lamp. The results of the test were as shown in Table 5. The impact strength of the circular fluorescent lamps made of the conventionally used lead glass is approximately 50 g--cm or more. If the fluorescent lamps of this invention are to have comparable impact strength, the mol ratio o calcium oxide to boric anhydride has to be 0.5 or more as well understood from Table 5. But, when the mol ratio exeeded 3/2 as in tests Nos. 9 and 10, the phospor layer exfoliated from the inner surface of the glass tube as the steel ball hit the tube, though the tube had a great impact strength.
Fig. 8 shows a cross sectional view of another circular type fluorescent lamp accoraing to this invention. As shown in Fig. 8, this lamp comprises a ring-shaped sealed glass tube 34, metal oxide layer 38 formed on the inner surface of the tube 34 and a phosphor layer 36 formed on the metal oxide layer 38. The tube 34 is made of the same low lead glass as the tube of the lamp shown in Figs. 3 and 4. The phosphor layer - 1 s - ~ '7~
36 is made of the same phosphor as the phosphor layer oE
the lamp shown in Figs. 3 and 4. The metal oxide layer 38 is made of y-alumina and 0.1 to 1.0 micron thick.
The thickness of the layer 38 may be detected by a scanning electron microscope.
Fifty circular fluorescent lamps of the struc-ture shown in Fig. 8 were made which were provided with phosphor layer o~ the same thickness within said range and of different mixing ra~ios of calcium borate con-tained in the phosphor. These were 100 V - 30 W
fluorescent lamps. They were continuously used for 3000 hours. Upon lapse of these hours it was found that their sealed glass tubes 34 has turned far li~hter yellow brown than those of the lamps shown in Figs. 3 and A. Further it was found that less phosphor par~
ticles were partly embedded in the glass layer while the glass tube was being heated, softened and bent.
Fig. 9(a) schematically shows metal oxide layer 38 formed on the inner surface of a straight glass tube and phosphor layer 36 formed on the metal oxide layer 3~.
Fig. 9(b) schematically shows the metal oxide layer 38 and the phosphor layer 36 of the glass tube now bent in the form of circle. Fig. 9(c) schematically illustra-tes the metal oxide layer 38 and the phosphor film 36 of the lamp ~7hich has been continuously used for 3000 hours. As evident from Fig. 9(b), far less phosphor particles were partly embedded in the g~ass layer while the glass tube was being heated, softened and bent.
Further, as Fig. 9(c) shows, no mercury did not enter the recess 30 between the phosphor particles and the metal oxide layer 38~ This is perhaps because the ~`eC~pta r S ,-~e~, creation of ~ b~ was effectively suppressed as is proved by the fact that the glass tube did not turn yellow brown.
Needless to say, the metal oxide layer 38, i.e. y-alumina layer successfully prevented the diffusion of Na+ from the glass tube 22. As mentioned above, the ~ 16 - ~5~'704 metal oxide layer 38 is 0.1 to l.0 micron thick according to this invention. This i5 because it was found that the layer 38 failed to effectively suppress the creating r~cC~Dto f ~ l tes of d~n~ii~g-~n~ and failed to prevent Na~ diffusion when it was less than 0.1 micron thick and that the phosphor layer 36 exfoliated from lt when it was more than l.0 micron thick. The metal oxide layer 38 may be formed 0.1 to l.0 micron thick if y-alumina is used in an amount of 0.6 to 6.2 mg per square centimeter.
As mentioned above, it is preferred that calcium borate be used in an amount of 0.2 to 2.0 percent of the phosphor used. In case the metal oxide layer 38 is 0.5 micron thick, the phosphor layer 36 will exfoliate from the layer 38 if it is made of phoshor containing less than 0.2 percent by weight of calcium borate. If the phosphor layer 36 is made of phosphor containing more than 2.0 percent by weight of calcium borate, boron oxide will increase and thus promote Na~ diffusion despite the metal oxide layer 38 and will wrap up the phosphor particles, whereby the radiant efficiency of the phosphor is inevitably degraded.
The above-described impact strength test was con-ducted on lO0 V - 30 W circular fluorescent lamps of the following ive categories:
I: Lamps each comprising a curvilinear tube of the conventionally used lead glass and phosphor layer coated on the inner surface of the tube and made of phosphor containing a binder consisting of barium calcium borate alone.
II: Lamps each comprising a circular tube of the conventionally used lead glass, an alumina film formed on the inner surface of the tube and a phosphor layer coated on the alumina film and made of phosphor containing a binder consisting of barium calcium borate alone.
III: Lamps each comprising a circular tube of soda-lime or low lead glass and a phosphor layer ~s~t7~)~
coated on the inner surface of the tube and made of phosphor containing a binder consisting of barium calcium borate alone.
IV. Lamps each comprising a circular tube of soda-lime or low lead glass, an alumina layer coated on the inner surface of the tube, and a phosphor layer coated on the alumina layer and made of phosphor containing binder consisting of barium calcium borate alon~.
V. La~ps each comprising a circular tube of soda-lime or low lead glass, an alumina layer coated on the inner surface Qf the tube and a phosphor layer coated on the alumina film and made of phosphor containing a binder consisting of calcium borate alone.
In the lamps of categories II and IV the alumina layer was 0.5 micron thick. In the lamps of category of V the phosphor contained 1.0 percent by weight o calcium borate. The results of the impact strength test were as shown in Table 6.
As Table 6 shows, the lamps of category IV, which were made of soda-lime or low lead glass and provided with an alumina layer, proved stronger than the lamps of category III which were made of soda-lime glass or low lead glass but not provided with an alumina layer.
~urprizin~ly, the lamps of cate~ories IV and V, the lamps made of soda-lime glass or low lead glass and provided with an alumina layer, proved far stronger than those made of the conventionally used lead glass.
Further, as will be evident by comparing the lamps of categories IV and V, lamps made of soda lime glass or low lead glass will become stronger if their phosphor layer contains a binder consisting of calcium borate.
The metal oxide layer used in the second embodiment of this invention is not limited to an alumina layer.
Use may be made of other metal oxide such as magnesium ~S87~)~
~ 18 -oxide, silicon oxide, titanium oxide and the mixture o them to bring forth the same effect as does alumina.
Both embodiments thus far described use soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide. If the tube is made of soda-lime glass which contains 12 to 17 percent by weight of Na2O or low lead ~lass which contains the same amount of Na2O, the effect of the present invention will become apparent. The more the content of Na2O in the glass is, the more the diffusion of Na+ is. Soda-lime glass containing 12 to 17 percent by weight of Na2O and low lead glass containing the same amount of Na2O in addi-tion to 12 percent by weight or less of lead will more effectively prevent diffusion of Na~~ if they contain further 3 to 8 percent by wei~ht of calcium oxide (CaO).
As mentioned above, the phosphor used in this invention contains binder consisting of calcium borate alone. In view of this it is desired that the phosphor be antimony-manganese activated calcium halophosphate.
The basic idea of this invention may be applied to~
a U-shaped fluorescent lamp a~ a W~shaped fluorescent lamp, besides a circular fluorescent lamp.
Jv c~
'7~
Table 1 SiO2 _ ~ -60 ~ 72 A Q 23 0 . 5 ~- 4 O X I DE K2O _0 . 2 ~ 3 COMPOSITION CaO 3 ~ 8 MgO
(WIT %) PbO 0.5 ^~ 12 B aO 0 ~ 3 _ O ^~ O. S
. Sb23 0 ~ 0. 5 Na2+K2+Li213 ~ 17. 5 CaO+Mgo 5 ~ 10 PbO+BaO2 . 5 ~ 13 _ AS203+Sb203 O. 02 ~- - 59 - 20 - ~ ~ 5 8'7 Tab1e 2 ~~~~---__ IGLASS-AIGLASS-B LEAD SODA-LIME
~~----____ I I GLASS GLASS
_ ~
SiO2 61.7 67.1 56.569.5 _AQ2O3 1.7 1.6 1.23 2.0 Fe23 0.04 0.04 0.04 0.1 ~XI~E
Na2O 14.0 15.3 4.55 15.5 COMPOSITION _ _ _ K2O 1.1 1.0 8.46 1.5 (W'T %) C aO 6 . 8 6.0 6.7 M9O 1 2.5 2.7 3.5 PbO 10.8 4.628.4 -B2O3 0.55 0.56 AS2O3 0.2 0.20.27 _ Sb23 0.34 0.350.30 0.2 COEFFICIENT OF LINEAR
(X 10 7 CM/CM/C) _ . _ SOFTENING POINT 664 ¦ 680 617 697 ( c) I
.
Table 3 ` C,"'~ LEAD GLASS GLASS-A ¦ GLASS
ACTERISTICS
F LUX ( L M ) AT 3000 Hr (LM) (92.9) (91.2) (89-4) (89~4) _ ____ AT 5000 Hr (LM) (88.0) (85.6) ~83.9) (82.7) _ .
(x) denotes life performance of luminous flux Table 4 BINDERMELTING POINT ~C) _ Table 5 _ TEST NO. l 2 3 4 5 _ MOL RATIO CaO/B2O3 0.28 0.45 0.500.73 0.91 FLUORESCENT LAMP (G - CM) 28 1 40 ¦ 53 58 60 -T EST NO. 6 7 a 9 1 o MOL RATIO CaO/B2O3 1.08 1.23 1.501.67 1.82 FLUORESCENT LAMP ( G-C M ) 63 64 65 67 69 Table 6 (UNIT; G-CM) TEST NO. I l .
I I II III IV I V
_ :
STRENGTH OF ¦ 46 45 44 50 ¦55
The lamp of either structure mentioned above can be manufactured at a reduced cost. Further, since the glass used contains only a small amount of lead, the lamp of this invention is preferred from the point of view of environ-mental pollution.
Other objects and advantages of the invention will become apparent during the following discussion of the accompanying drawings.
This invention can be more fully understood fxom the following detailed description when taken in conjunction wi~h the accompanying drawings, in which:
Figure 1 shows a known circular type fluorescent lamp after continuous use for 3000 hours;
Figure 2(a) is an enlarged sectional view of the wall of a known glass tube and a phosphor layer coated on the glass wall;
Figure 2(b) is an enlarged sectional view of the wall of the known glass tube now bent in the form o~ a circ~e and the phosphor layer coated on the glass wall;
Figure 2(c~ is an enlarged sectional view of a portion 26 of the circular type fluorescent lamp shown in Yigure 1, taken along line II-II' in Figure l;
Figure 3 shows a circular type fluorescent lamp ,~, ~S~ 4 according to this invention;
Figure 4 is a cross sectional view oE the lamp shown in Figure 3, taken alony line IV-IV' in Figure 3;
Figure 5 is a graph showing the relationship between the strength of a phosphor layer and the mixing ratio of a binder consisting chiefly of calcium borate;
Figure 6 is a ~raph illustrating the relationship between total luminous flux and the mixing ratio of a binder consisting chiefly of calcium borate;
Figure 7 is a graph showing the relationship between the quantity of phosphor coated, on one hand, and initial luminous flux and ratio of blackening during use, on the other;
Figure 8 shows another circular type fluorescent lamp according to this invention;
Figure 9(a3 is an enlarged sectional view of the wall of a glass tube of this invention and a phosphor layer coated on the glass wall;
Figure 9(b) is an enlarged sectional view`of the wall of a glass tube of this invention, now bent in the form of a circle, and the phosphor layer coated on the glass wall;
and Figure 9(c) is an enlar~ed sectional view of a portion of the lamp shown in Figure 8 after continuous use for 3000 hours.
It will first be discussed why the prior art lamps already discussed above and made of glasses A and B were disadvantageous despite their good initial luminous flux.
Table 3 shows the initial luminous flux, luminous flux at 3000 Hr and luminous flux at 5000 ~r of various curvilinear type fluorescent lamps made by the in~entors and subsequently tested. "Initial luminous flux" was measured at the 100th hour of use, in accordance with the re~ulation JISC7601.
All the la~ps were circular fluorescent lamps of lOOV, 30W.
The numerical data given in Table 3 were the average of 50 lamps of each type tested.
Fig. 1 sho~s the typical outer appearance of a circular '7~
fluorescent lamp mad~ of the conventional low lead glass, after 3000 hours of continuous use. A portion 24 of the circular tube 22 made of the low lead glass, which con-tained 12 percent by weight or less of lead oxide ~PbO), was yellow brown. It was ascertained that in general this colour change occurred at ~hat portion 24 of the tube 22 which was heated to the highest temperature during the bending process, i.e. that portion 24 which was positioned highest in the furnace.
It may reasonably be assumed that this colour change was caused partly by sodium amalgam formed by reaction between Na+ diffused from the glass and mercury vapor and partly by bonding of Hg to receptor sites in the glass, which were ~enerated as the phosphor moved into t~le glass.
As shown in Table 2, Na~ was diffused in a small amount from the conventionally used lead glass because the glass contained a small amount of sodium oxide (Na2O). The tubes of the lead glass were bent in a desired fashion at a relatively low temperature, an~ since the phosphor moved into the glass in but a small amount, no marked generation of receptor sites tended to occur.
The above-mentioned test further revealed that, the more the phosphor moved into glass, the weaker became the tubes made of the glass. The reason why so will be dis-cussed.
Binders generally contained in the phosphor forfluorescent lamps contains boron oxide (B2O3). The boron oxide therefore is partly in contact with soda-lime glass or low lead glass. A portion of the boron oxide therefore melts when the tubes of either soda-lime glass or low lead glass are heated and bent in the fuxnace. The molten borate is fused with the glass, thus forming a B2O3-Sio2-Na2O glass. The viscosity of the glass thus formed sharply decreases when the glass is heated to about æoooc. When the glass tubes are heated to about 800C, the inner surfaces as well as their outer sur~aces are softened, whereby the phosphor moves into them. As a result, when the bent tubes -~L~lS870~
~ 8 --are cooled, the inner surface portion of each tube has fine cracks due to the difference in thermal expansion coeffici-ent between the phosphor and the glass. The fine cracks seem to weaken the tubes.
Indeed a binder will more strongly bind phosphor par-ticles if it contains barium oxide (BaO). But barium oxide will lower the melting point of the binder, and the binder may possibly melt before the glass softens. If this happens, more phosphor particles wi~l move into the glass layer of a tube while the tuhe is being heated, softened and bent.
With reference to Figs. 2(a), 2(b) and 2(c), it will be described how phosphor particles containing a binder con-sisting of barium calcium borate move into the glass layer of the tube.
Fig. 2(a) shows the particles 28 of phosphor coated on the inner surace of the glass tube 22 and subsequently baked. Fig. 2(b) illustrates the phosphor particles 28, some of which lie in the glass layer of the tube 22 which has been already heated, softened and bent. In the recesses 30 between the glass layer and each phosphor particle 28 that lies partly or wholly within the glass layer, receptor sites will be formed. Fig. 2~c) illustrates a part 26 of the portion 24 of the tube 22 which has been used for 3000 hours (see Fig. 1). Since mercury vapor has flowed into the recesses 30 through the spaces among the phosphor par-ticles 28, the portion 24 of the tube is turned into yellow brown by reaction at the receptor sites of the glass with this mercury.
Japanese Utility Model Disclosure (Kokai) No. 53-92976 discloses the technique of providing a metal oxide layer between the inner surface of a curvilinear glass tube and a phosphor layer thereby to reinforce the glass tube. This technique may indeed be effective if the tube is made of glass having a softening point of about 60aoc. However, the technique does not seem to work if the tube is made of soda-lime glass or low lead glass which has a relatively high softening point ranging from 640C to 720C. Japanese ~8'~
Utility Model Disclosure (Kokai) No. 53-92976 further teaches that on the metal oxide layer there is formed a layer of phosphor containing 0.1 to 4 percent by weight of a B2O3-containing binder and that the binder may be a barium calcium borate binder. A barium calcium borate binder, however, melts before soda-lime glass or low lead glass softens which has a high softening point. If the tube according to Disclosure (Kokai) No. 53-92976 is made of soda-lime glass or low lead glass, the binder will help many phosphor particles move into the glass layer of the tube and hence will create many receptor sites when the tube is heated, softened and bent. The receptor sites thus formed will eventually reduce the luminous flux of the resultant curvilinear fluorescent lamp.
Japanese Patent Disclosure (Kokai) No. 49-20972 dis-closes a method of improving the luminous flux performance over the lifetime of a curvilinear fluorescent lamp. More specifically, a titanium dioxide film 0.02 to 0.2 micron thick is laid on the inner surface of a glass tube. Patent Disclosure (Kokai) No. 49-20972 teaches that, unless the titani~un dioxide film is provided, the sodium ions liberated from the glass reacts with mercury vapor to form amalgam after a certain duration of use of the lamp and that the amalgam, if formed, causes the phosphor (e.g. Ca5(PO4)3X;
Sb, Mn, where X = F, Cl) to turn gray. The above~mentioned titanium dioxide film is too thin to prevent the aforemen-tioned yellow brown change of coloux taking place in a curuilinear fluorescent lamp which is made of soda-lime glass or low lead glass.
Japanese PatentPublication No. 35-12085 discloses a binder consisting of CaO and B2O3 in weight ratio of 3:1 to 1:2. The binder is mixed with phosphor, and the mixture is coated on the inner surface of a glass tube and subsequently baked, thereby forming calcium borate. This technique aims to enhance the strength of the phosphor layer without reduc-ing the luminous efficacy of a fluorescent lamp comprising the glass tube. In contrast, the binder used in the present {)~
invention consists chiefly of calcium borate. It is used in order to prevent phosphor particles from entering a layer of soda-lime glass or low lead glass having a high softening point, while a tube made of such glass is being heated, softened and bent, thereby to improve the strength of the glass tube. It is used also in order to suppress diffusion of sodium ions into the glass layer, thereby to enhance the luminous efficacy of the lamp.
Fig. 3 shows the outer appearance of a circular type fluorescent lamp 32 according to the present invention.
Fig. 4 is a cross sectional view of the lamp 32, taken along line IV-IV' in Fig. 3. The lamp 32 comprises a ring-shaped sealed glass tube 34 and a phosphor layer 36 coated on the inner surface of the glass tube 34. The tube 32 is made of low lead glass containing 12 percent by weight or less of lead oxide (PbO) and having a softening point of 640 to 720C and a coefficient of linear thermal expansion of 92 to 105 x 10 cm/cm/C. The --'.1 ' ~J
58~(3~L
layer 36 is made of calcium halophosphate phosphor acti-vated by manganese and antimony (CaS(YO4)3X; Sb, Mn, where X = F, Cl) containing a binder consisting of calcium borate.
Fifty circular fluorescent lamps of the structure shown in Figs. 3 and 4 were made which were provided with phosphor layers of the same thickness. These were 100 V - 30 W fluorescent lamps. They were continuously used for 3000 hours. Upon lapse of these hours all the fifty lamps were found to have performance of luminous flux ranging from 92 to 94 %. Further, their sealed glass tubes 34 had almost never turned yellow brown, unlike the conventionally used glass tubes inner sur-faces of which are coated with phosphor containing barium-calcium borate binder.
~t was found that calcium borate should be used in mixing ratio of 0.2 to 2.0 percent by weight with respect to the phosphor. If calcium borate is used in mixing ratio outside this specific range, the phosphor layer will not be sufficiently strong and the initial luminous flux of the lamp will not be suf-ficiently high.
Fig. 5 illustrates the relationship between the strength of phosphor layer and the mixing ratio of a binder. Curve a indicates this relationship observed in the above-mentioned another fifty fluorescent lamps according to this invention. Curve ~ shows this rela-tionship observed in fifty circular fluorescent lamps of the same size and structure but using a known binder consisting of barium calcium borate. Curve y indicates said relationship observed in fifty circular fluorescent lamps of the same size and structure but using a known binder consisting of calcium phospha-te and thus having an extremely high melting point. The binders used in the lamps of the three categories have melting pointSas given in Table ~. This melting point was obtained by detecting the maximum - 12 - ~5~70~
heat-absorption temperature of the respective binders, using differential thermal analysis.
The phosphor layers of all the fluorescent lamps of the three categories were formed by coating the S phosphors on the inner surEaces of the respective glass tubes and subsequently baking the phosphor thus coated.
The strength of each of the phosphor layer was detected by blowing air at the rate of 300 Torr-Q/sec against the layer through a nozzle spaced from the layer by lO mm.
The strength of the layer is the reciprocal of the ratio of the diameter of the largest flake of phosphor exfo-liated from the inner surface of the glass tube to the diameter of the largest flake of known phosphor exfo-liated from the inner surface of a tube made of the con-ventionally used lead glass, said known phosphor con-taining a binder consisting of barium calcium borate and calcium phosphate in weight mixing ratio of 2:1. In Fig. 6 said reciprocal is given in percentage.
Fig. 6 illustrates the relationship between the total luminous flux of each fluorescent lamp tested and the mixing ratio of a binder used. Curve ai indicates this relationship observed in the fifty fluorescen-t lamps according to this invention. Curve ~' shows the relationship observed in fifty fluorescent lamps using the known binder consisting of barium calcium borate.
Curve y' shows the relationship observed in the fifty fluorescent lamps using the known binder consisting of calcium phosphate.
As evident from Figs. 5 and 6, the circular 3~ fluorescent lamps using calcium b~t~e in a mixing ratio of 0.2 to 2.0 % exhibited performance of luminou~s flux better than that of the fluorescent lamps made of the conventionally used lead glass and exhibited a total luminious flux greater than the fluorescent lamps using the known binder consisting of barium calcium borate or calcium phosphate~ The fluorescent lamps using calcium borate in a mixing ratio of more than 2.0 % exhibited a ~S87~
t~
poor performance ~ luminous flux, and the phosphor containing calcium borate in a mixing ratio of less than 0.2 ~ was found llkely to exfoliate from the inner sur-face of the glass tubes.
As Table 4 shows, barium calcium borate has a melting point 44C to 77jC ~ ower than the softening points of the soda-lime glass A and glass B - all given in Table 2. Barium calcium borate, iE used as a binder, will melt before any of these glasses softens.
While the sealed glass tube is being heated, softened and bent, Na+ diffused from the glass used will enter the molten barium calcium borate. This may be why the lamps using barium calcium borate as a binder exhibited a total luminous flux smaller than the lamps using calcium borate as a binder.
As Table 4 further shows, calcium phosphate has an extremely high melting point, 1670C. For this reason, the layer of the phosphor containing calcium phosphate did not adhere to the glass layer so strongly as did the layer of the phosphor containing calcium borate and the layer of the phosphor containing barium calcium borate.
According to this invention, the calcium halophosphate phosphor containing calcium borate in a mixing ratio of 0.2 to 2.0 % is coated on the inner sur-face of the glass tube in an amount of, preEerably, 2.9 to 3.9 mg per square centimeter. Curve ~ in Fig. 7 shows the relationship between the initial luminous flux of the lamps using calcium borate in a mixing ratio in said range and the amount of the phosphor used (mg/cm2). And curve ~ in Fig. 7 illustrates the rela-tionship between the amount of phosphor used (mg/cm2) and the ratio of generated blac~ening of the glass tubes. As curve ~ clearly shows, the lamps using the phosph~r in an amount of less than 2.g mg per square centimeter exhibited an initial luminous flux smaller than that of a circular fluorescent lamp made of the conventionally used lead glass. ~s curve ~ clearly - 14 _ ~ S~70~
shows, the la~ps using the phosphor in an amount of more than 3.9 mg per square centimeter encountered the blackening of the glass tubes.
According to this invention it is preferred that the binder be prepared by calcium oxide (CaO) and boric anhydride (B2O33 in mol ratio of 1:2 to 3:2. A number of 100 V - 30 W white circular fluorescent lamps were made which comprised a circular sealed tube made of glass A and phospher layer coated on the inner surface of the tube and made of the above-mentioned calcium halophosphate phosphor containing a binder prepared by calcium oxide and boric anhydride in mol ratio (CaO/B2O3) ranging from 0.28 to 1~82. These fluorescent lamps were put to an impact strength test. More precisely, a steel ball having a diameter of 10 mm and weighing 3.5 g was dropped from different levels onto that portion of each fluorescent lamp which was about 100 mm from the exhaust tube of the lamp. The results of the test were as shown in Table 5. The impact strength of the circular fluorescent lamps made of the conventionally used lead glass is approximately 50 g--cm or more. If the fluorescent lamps of this invention are to have comparable impact strength, the mol ratio o calcium oxide to boric anhydride has to be 0.5 or more as well understood from Table 5. But, when the mol ratio exeeded 3/2 as in tests Nos. 9 and 10, the phospor layer exfoliated from the inner surface of the glass tube as the steel ball hit the tube, though the tube had a great impact strength.
Fig. 8 shows a cross sectional view of another circular type fluorescent lamp accoraing to this invention. As shown in Fig. 8, this lamp comprises a ring-shaped sealed glass tube 34, metal oxide layer 38 formed on the inner surface of the tube 34 and a phosphor layer 36 formed on the metal oxide layer 38. The tube 34 is made of the same low lead glass as the tube of the lamp shown in Figs. 3 and 4. The phosphor layer - 1 s - ~ '7~
36 is made of the same phosphor as the phosphor layer oE
the lamp shown in Figs. 3 and 4. The metal oxide layer 38 is made of y-alumina and 0.1 to 1.0 micron thick.
The thickness of the layer 38 may be detected by a scanning electron microscope.
Fifty circular fluorescent lamps of the struc-ture shown in Fig. 8 were made which were provided with phosphor layer o~ the same thickness within said range and of different mixing ra~ios of calcium borate con-tained in the phosphor. These were 100 V - 30 W
fluorescent lamps. They were continuously used for 3000 hours. Upon lapse of these hours it was found that their sealed glass tubes 34 has turned far li~hter yellow brown than those of the lamps shown in Figs. 3 and A. Further it was found that less phosphor par~
ticles were partly embedded in the glass layer while the glass tube was being heated, softened and bent.
Fig. 9(a) schematically shows metal oxide layer 38 formed on the inner surface of a straight glass tube and phosphor layer 36 formed on the metal oxide layer 3~.
Fig. 9(b) schematically shows the metal oxide layer 38 and the phosphor layer 36 of the glass tube now bent in the form of circle. Fig. 9(c) schematically illustra-tes the metal oxide layer 38 and the phosphor film 36 of the lamp ~7hich has been continuously used for 3000 hours. As evident from Fig. 9(b), far less phosphor particles were partly embedded in the g~ass layer while the glass tube was being heated, softened and bent.
Further, as Fig. 9(c) shows, no mercury did not enter the recess 30 between the phosphor particles and the metal oxide layer 38~ This is perhaps because the ~`eC~pta r S ,-~e~, creation of ~ b~ was effectively suppressed as is proved by the fact that the glass tube did not turn yellow brown.
Needless to say, the metal oxide layer 38, i.e. y-alumina layer successfully prevented the diffusion of Na+ from the glass tube 22. As mentioned above, the ~ 16 - ~5~'704 metal oxide layer 38 is 0.1 to l.0 micron thick according to this invention. This i5 because it was found that the layer 38 failed to effectively suppress the creating r~cC~Dto f ~ l tes of d~n~ii~g-~n~ and failed to prevent Na~ diffusion when it was less than 0.1 micron thick and that the phosphor layer 36 exfoliated from lt when it was more than l.0 micron thick. The metal oxide layer 38 may be formed 0.1 to l.0 micron thick if y-alumina is used in an amount of 0.6 to 6.2 mg per square centimeter.
As mentioned above, it is preferred that calcium borate be used in an amount of 0.2 to 2.0 percent of the phosphor used. In case the metal oxide layer 38 is 0.5 micron thick, the phosphor layer 36 will exfoliate from the layer 38 if it is made of phoshor containing less than 0.2 percent by weight of calcium borate. If the phosphor layer 36 is made of phosphor containing more than 2.0 percent by weight of calcium borate, boron oxide will increase and thus promote Na~ diffusion despite the metal oxide layer 38 and will wrap up the phosphor particles, whereby the radiant efficiency of the phosphor is inevitably degraded.
The above-described impact strength test was con-ducted on lO0 V - 30 W circular fluorescent lamps of the following ive categories:
I: Lamps each comprising a curvilinear tube of the conventionally used lead glass and phosphor layer coated on the inner surface of the tube and made of phosphor containing a binder consisting of barium calcium borate alone.
II: Lamps each comprising a circular tube of the conventionally used lead glass, an alumina film formed on the inner surface of the tube and a phosphor layer coated on the alumina film and made of phosphor containing a binder consisting of barium calcium borate alone.
III: Lamps each comprising a circular tube of soda-lime or low lead glass and a phosphor layer ~s~t7~)~
coated on the inner surface of the tube and made of phosphor containing a binder consisting of barium calcium borate alone.
IV. Lamps each comprising a circular tube of soda-lime or low lead glass, an alumina layer coated on the inner surface of the tube, and a phosphor layer coated on the alumina layer and made of phosphor containing binder consisting of barium calcium borate alon~.
V. La~ps each comprising a circular tube of soda-lime or low lead glass, an alumina layer coated on the inner surface Qf the tube and a phosphor layer coated on the alumina film and made of phosphor containing a binder consisting of calcium borate alone.
In the lamps of categories II and IV the alumina layer was 0.5 micron thick. In the lamps of category of V the phosphor contained 1.0 percent by weight o calcium borate. The results of the impact strength test were as shown in Table 6.
As Table 6 shows, the lamps of category IV, which were made of soda-lime or low lead glass and provided with an alumina layer, proved stronger than the lamps of category III which were made of soda-lime glass or low lead glass but not provided with an alumina layer.
~urprizin~ly, the lamps of cate~ories IV and V, the lamps made of soda-lime glass or low lead glass and provided with an alumina layer, proved far stronger than those made of the conventionally used lead glass.
Further, as will be evident by comparing the lamps of categories IV and V, lamps made of soda lime glass or low lead glass will become stronger if their phosphor layer contains a binder consisting of calcium borate.
The metal oxide layer used in the second embodiment of this invention is not limited to an alumina layer.
Use may be made of other metal oxide such as magnesium ~S87~)~
~ 18 -oxide, silicon oxide, titanium oxide and the mixture o them to bring forth the same effect as does alumina.
Both embodiments thus far described use soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide. If the tube is made of soda-lime glass which contains 12 to 17 percent by weight of Na2O or low lead ~lass which contains the same amount of Na2O, the effect of the present invention will become apparent. The more the content of Na2O in the glass is, the more the diffusion of Na+ is. Soda-lime glass containing 12 to 17 percent by weight of Na2O and low lead glass containing the same amount of Na2O in addi-tion to 12 percent by weight or less of lead will more effectively prevent diffusion of Na~~ if they contain further 3 to 8 percent by wei~ht of calcium oxide (CaO).
As mentioned above, the phosphor used in this invention contains binder consisting of calcium borate alone. In view of this it is desired that the phosphor be antimony-manganese activated calcium halophosphate.
The basic idea of this invention may be applied to~
a U-shaped fluorescent lamp a~ a W~shaped fluorescent lamp, besides a circular fluorescent lamp.
Jv c~
'7~
Table 1 SiO2 _ ~ -60 ~ 72 A Q 23 0 . 5 ~- 4 O X I DE K2O _0 . 2 ~ 3 COMPOSITION CaO 3 ~ 8 MgO
(WIT %) PbO 0.5 ^~ 12 B aO 0 ~ 3 _ O ^~ O. S
. Sb23 0 ~ 0. 5 Na2+K2+Li213 ~ 17. 5 CaO+Mgo 5 ~ 10 PbO+BaO2 . 5 ~ 13 _ AS203+Sb203 O. 02 ~- - 59 - 20 - ~ ~ 5 8'7 Tab1e 2 ~~~~---__ IGLASS-AIGLASS-B LEAD SODA-LIME
~~----____ I I GLASS GLASS
_ ~
SiO2 61.7 67.1 56.569.5 _AQ2O3 1.7 1.6 1.23 2.0 Fe23 0.04 0.04 0.04 0.1 ~XI~E
Na2O 14.0 15.3 4.55 15.5 COMPOSITION _ _ _ K2O 1.1 1.0 8.46 1.5 (W'T %) C aO 6 . 8 6.0 6.7 M9O 1 2.5 2.7 3.5 PbO 10.8 4.628.4 -B2O3 0.55 0.56 AS2O3 0.2 0.20.27 _ Sb23 0.34 0.350.30 0.2 COEFFICIENT OF LINEAR
(X 10 7 CM/CM/C) _ . _ SOFTENING POINT 664 ¦ 680 617 697 ( c) I
.
Table 3 ` C,"'~ LEAD GLASS GLASS-A ¦ GLASS
ACTERISTICS
F LUX ( L M ) AT 3000 Hr (LM) (92.9) (91.2) (89-4) (89~4) _ ____ AT 5000 Hr (LM) (88.0) (85.6) ~83.9) (82.7) _ .
(x) denotes life performance of luminous flux Table 4 BINDERMELTING POINT ~C) _ Table 5 _ TEST NO. l 2 3 4 5 _ MOL RATIO CaO/B2O3 0.28 0.45 0.500.73 0.91 FLUORESCENT LAMP (G - CM) 28 1 40 ¦ 53 58 60 -T EST NO. 6 7 a 9 1 o MOL RATIO CaO/B2O3 1.08 1.23 1.501.67 1.82 FLUORESCENT LAMP ( G-C M ) 63 64 65 67 69 Table 6 (UNIT; G-CM) TEST NO. I l .
I I II III IV I V
_ :
STRENGTH OF ¦ 46 45 44 50 ¦55
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A curvilinear type fluorescent lamp comprising:
a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with an electron-emitting substance, said tube being made of soda-lime glass or low Lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 to 720°C and whose coefficient of linear thermal expansion is 92 to 105 x 10-7 cm/cm/°C; and a phosphor layer laid on the inner surface of the tube and containing a binder consisting chiefly of calcium borate.
a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with an electron-emitting substance, said tube being made of soda-lime glass or low Lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 to 720°C and whose coefficient of linear thermal expansion is 92 to 105 x 10-7 cm/cm/°C; and a phosphor layer laid on the inner surface of the tube and containing a binder consisting chiefly of calcium borate.
2. A curvilinear type fluorescent lamp according to Claim 1, wherein said phosphor layer contains 0.2 to 2.0 percent by weight of calcium borate.
3. A curvilinear type fluorescent lamp according to Claim 2, wherein said phosphor layer is coated on the inner surface of said tube in an amount of 2.9 to 3.9 mg per square centimeter.
4. A curvilinear type fluorescent lamp according to Claim 3, wherein said soda-lime glass or low lead glass contains 12 to 17 percent by weight of sodium oxide (Na2O).
5. A curvilinear type fluorescent lamp according to Claim 4, wherein said soda lime or low lead glass further contains 3 to 8 percent by weight of calcium oxide (CaO).
6. A curvilinear type fluorescent lamp according to Claim 5, wherein said low lead glass consists of the following components in the following weight percentages:
SiO2 ..... 60 - 72 CaO ..... 3 - 8 Na2O ..... 12 - 17 PbO ..... 0.5 - 12 Li2O ..... 0 - 1 As2O3 ..... 0 - 0.5 MgO ..... 1 - 5 Na2O+K2O+Li2O ..... 13 - 17.5 BaO ..... 0 - 3 CaO+MgO ..... 5 - 10 Sb2O3 ..... 0 - 0.5 PbO+BaO ..... 2.5 - 13 A?2O3 ..... 0.5 - 4 As2O3+Sb2O3 ..... 0.02 - 0.59 K2O ...... 0.2 - 3.
SiO2 ..... 60 - 72 CaO ..... 3 - 8 Na2O ..... 12 - 17 PbO ..... 0.5 - 12 Li2O ..... 0 - 1 As2O3 ..... 0 - 0.5 MgO ..... 1 - 5 Na2O+K2O+Li2O ..... 13 - 17.5 BaO ..... 0 - 3 CaO+MgO ..... 5 - 10 Sb2O3 ..... 0 - 0.5 PbO+BaO ..... 2.5 - 13 A?2O3 ..... 0.5 - 4 As2O3+Sb2O3 ..... 0.02 - 0.59 K2O ...... 0.2 - 3.
7. A curvilinear type fluorescent lamp according to Claim 6, wherein the calcium borate is obtained from a mix-ture of calcium oxide (CaO) and boron oxide (B2O3), the mol ratio of calcium oxide (CaO) to boron oxide (B2O3) being 1/2 to 3/2.
8. A curvilinear type fluorescent lamp according to Claim 7, wherein said binder contains no barium oxide (BaO).
9. A curvilinear type fluorescent lamp comprising:
a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with an electron-emitting substance, said tube being made of soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 to 720°C and whose coefficient of linear thermal expansion is 92 to 105 x 10-7 cm/cm/°C;
a metal oxide layer coated on the inner surface of the tube in an amount of 0.6 to 6.2 mg per square centi-meter and made of at least one of the group consisting of aluminum oxide, magnesium oxide, silicon oxide and titanium oxide; and a phosphor layer laid on the metal oxide layer and containing a binder consisting chiefly of calcium borate.
a curvilinear, light-transmitting sealed tube having an electrode attached to either end and coated with an electron-emitting substance, said tube being made of soda-lime glass or low lead glass containing 12 percent by weight or less of lead oxide, whose softening point is 640 to 720°C and whose coefficient of linear thermal expansion is 92 to 105 x 10-7 cm/cm/°C;
a metal oxide layer coated on the inner surface of the tube in an amount of 0.6 to 6.2 mg per square centi-meter and made of at least one of the group consisting of aluminum oxide, magnesium oxide, silicon oxide and titanium oxide; and a phosphor layer laid on the metal oxide layer and containing a binder consisting chiefly of calcium borate.
10. A curvilinear type fluorescent lamp according to Claim 9, wherein said phosphor layer contains 0.2 to 2.0 percent by weight of calcium borate.
11. A curvilinear type fluorescent lamp according to Claim 10, wherein said phosphor layer is coated on the inner surface of said tube in an amount of 2.9 to 3.9 mg per square centimeter.
12. A curvilinear type fluorescent lamp according to Claim 11, wherein said soda-lime glass or low lead glass contains 12 to 17 percent by weight of sodium oxide (Na2O).
13. A curvilinear type fluorescent lamp according to Claim 12, wherein said soda-lime or low lead glass further contains 3 to 8 percent by weight of calcium oxide (CaO).
14. A curvilinear type fluorescent lamp according to Claim 13, wherein said low lead glass consists of the following components in the following weight percentages:
SiO2 ..... 60 - 72 CaO ..... 3 - 8 Na2O ..... 12 - 17 PbO ..... 0.5 - 12 Li2O ..... 0 - 1 AS2O3 ..... 0 - 0.5 MgO ..... 1 - 5 Na2O+K2O+Li2O ..... 13 - 17.5 BaO ..... 0 - 3 CaO+MgO ..... 5 - 10 Sb2O3 ..... 0 - 0.5 PbO+BaO ..... 2.5 - 13 A?2O3 ..... 0.5 - 4 As2O3+Sb2O3 ..... 0.02 - 0.59 K2O ..... 0.2 - 3.
SiO2 ..... 60 - 72 CaO ..... 3 - 8 Na2O ..... 12 - 17 PbO ..... 0.5 - 12 Li2O ..... 0 - 1 AS2O3 ..... 0 - 0.5 MgO ..... 1 - 5 Na2O+K2O+Li2O ..... 13 - 17.5 BaO ..... 0 - 3 CaO+MgO ..... 5 - 10 Sb2O3 ..... 0 - 0.5 PbO+BaO ..... 2.5 - 13 A?2O3 ..... 0.5 - 4 As2O3+Sb2O3 ..... 0.02 - 0.59 K2O ..... 0.2 - 3.
15. A curvilinear type fluorescent lamp according to Claim 14, wherein the calcium borate is obtained from a mixture of calcium oxide (CaO) and boron oxide (B2O3), the mol ratio of calcium oxide (CaO) to boron oxide (B2O3) being 1/2 to 3/2.
16. A curvilinear type fluorescent lamp according to Claim 15, wherein said binder contains no barium oxide (BaO).
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1657880A JPS56114275A (en) | 1980-02-15 | 1980-02-15 | Curved fluorescent lamp |
| JP16578/80 | 1980-02-15 | ||
| JP26519/80 | 1980-03-05 | ||
| JP2651980A JPS56123661A (en) | 1980-03-05 | 1980-03-05 | Curved fluorescent lamp |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1158704A true CA1158704A (en) | 1983-12-13 |
Family
ID=26352944
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000370811A Expired CA1158704A (en) | 1980-02-15 | 1981-02-13 | Curvilinear type fluorescent lamp |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0034494B1 (en) |
| AU (1) | AU530404B2 (en) |
| CA (1) | CA1158704A (en) |
| DE (1) | DE3161854D1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| HU214130B (en) * | 1994-03-29 | 1997-12-29 | Ge Lighting Tungsram Rt | Low-pressure mercury vapour discharge lampe pinched on one side |
| CN1363113A (en) | 2000-02-01 | 2002-08-07 | 皇家菲利浦电子有限公司 | Low-pressure mercury vapor discharge lamp and small fluorescent lamp |
| EP1734563A3 (en) * | 2005-06-17 | 2009-08-12 | Toshiba Lighting & Technology Corporation | Fluorescent lamp comprising a protective film, and illuminating apparatus therewith |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2905572A (en) * | 1958-10-02 | 1959-09-22 | Gen Electric | Phosphor coating of improved adherence and preparation thereof |
| US3012168A (en) * | 1960-03-23 | 1961-12-05 | Sylvania Electric Prod | Fluorescent lamp |
| US3094641A (en) * | 1960-04-27 | 1963-06-18 | Sylvania Electric Prod | Fluorescent lamp |
| US3377494A (en) * | 1965-05-24 | 1968-04-09 | Westinghouse Electric Corp | Fluorescent lamp envelope with transparent protective coatings |
| GB1176211A (en) * | 1966-05-27 | 1970-01-01 | Matsushita Electronics Corp | A Method of Manufacturing Fluorescent Lamps |
| US3599029A (en) * | 1969-10-31 | 1971-08-10 | Gen Electric | Fluorescent lamp envelope with transparent protective coating |
| US3890530A (en) * | 1973-01-22 | 1975-06-17 | Gen Electric | Precoat for fluorescent lamp |
-
1981
- 1981-02-11 AU AU67202/81A patent/AU530404B2/en not_active Ceased
- 1981-02-13 CA CA000370811A patent/CA1158704A/en not_active Expired
- 1981-02-16 DE DE8181300626T patent/DE3161854D1/en not_active Expired
- 1981-02-16 EP EP19810300626 patent/EP0034494B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU530404B2 (en) | 1983-07-14 |
| AU6720281A (en) | 1983-03-10 |
| DE3161854D1 (en) | 1984-02-16 |
| EP0034494A1 (en) | 1981-08-26 |
| EP0034494B1 (en) | 1984-01-11 |
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