Fluorescent lamp having phosphor layer

An object of the present invention is to provide a fluorescent lamp including: a hermetically sealed lamp vessel; and a phosphor layer attached to a part of an inner surface of the lamp vessel, where a thickness of the phosphor layer near an edge thereof gradually and smoothly decreases towards the edge.

This application is based on an application No. 2002-221395 filed in Japan, the content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a fluorescent lamp, and particularly relates to a fluorescent lamp that has a phosphor layer formed on an inner surface of its lamp vessel.

(2) Related Art

One kind of fluorescent lamps having a lamp vessel whose inner surface is formed a phosphor layer is electrodeless fluorescent lamp. The electrodeless fluorescent lamp is a fluorescent lamp that literally does not have any electrode. The electrodeless fluorescent lamp is getting attention since it has longer life than other kinds of fluorescent lamps whose life is mainly determined by electrode.

One type of such electrodeless fluorescent lamps has a structure of having a lamp vessel that has a tube-like concave portion whose hollow is formed like a tube, and a coil is provided in the concave portion. If alternating current having a high frequency is fed to the coil, an alternating magnetic field is generated inside the lamp vessel. This alternating magnetic field makes mercury atoms and electrons collide with each other in the lamp vessel, thereby making the mercury atoms emit ultraviolet light. The ultraviolet light emitted in this way will be irradiated on the phosphors applied on an inner surface of the lamp vessel, so as to generate visible light.

In relation to a method of producing the lamp vessel of the aforementioned electrodeless fluorescent lamp, the following mainly describes a process of applying phosphors, a process of drying thereof, and a process of removing unnecessary phosphors.

FIG. 1is a diagram showing a series of steps adopted by the conventional technology.

An object shown in (a)–(d) ofFIG. 1which is formed as a flask having a round-bottom is a glass vessel106, a part of which is used for a glass bulb102(seeFIG. 2) of a lamp vessel100(seeFIG. 2) Note that each glass vessel106in (a)–(d) ofFIG. 1is in a longitudinal sectional view.

First, an application solution110containing phosphor powders is injected into the glass vessel106whose opening is directed upward, with use of an injection nozzle108, up to a level shown inFIG. 1(a) (so far, refer toFIG. 1(a)).

Next, the glass vessel106is made to stand in an inverted position, being rotated in the direction of the arrow D, so as to let out an excess of the application solution110from the glass vessel106(FIG. 1(b)). Here, the reason why the glass vessel106is rotated is to make the thickness of the application solution110attached to the inner surface of the glass vessel106as even as possible.

Then, while the glass vessel106is in an inverted position, a warm-air nozzle112is entered into the glass vessel106, so as to dry the application solution110attached to the inner surface of the glass vessel106(FIG. 1(c)). Here, the reason why the drying step is performed while the glass vessel106is in an inverted position is to prevent the application solution.110from being accumulated at the bottom of the glass vessel106, which results in making the thickness of the formed phosphor layer uneven.

After the application solution110is dried, and so the phosphor layer114is formed, unnecessary phosphor is removed which has been formed on the inner surface of the cylindrical part116of the glass vessel106. For this removing step, a rubber blade118is used for example. This rubber blade118is inserted just before the spherical part120of the glass vessel106. The reason why the rubber blade118is not inserted inside the spherical part120beyond the cylindrical part116will be detailed later. The rubber blade118, by being rotated, scrapes the phosphor layer114off the inner surface of the cylindrical part116(FIG. 1(d)). The following is the reason why the phosphor layer114is removed from the cylindrical part116. That is, an internal tube104(detailed later) will be attached to the cylindrical part116by means of melting. In view of this, if there is phosphor left in the cylindrical part116which will be attached to the internal tube104, a crack will likely occur in the attaching process, and further there is a possibility of leak due to incomplete attachment therebetween.

After the phosphor layer is formed at a predetermined area of the inner surface of the glass vessel106as aforementioned, an internal tube104is inserted therein as shown inFIG. 2, thereby determining the position of the internal tube104. This internal tube104will be a storage of the coil. Then, a burner is used to heat the part of the external surface of the cylindrical part116that corresponds to an opening of the internal tube104, while the internal tube104and the glass vessel106are being rotated around the tube axis of the internal tube, in a same direction and at a same speed. This operation attaches together the internal tube104and the glass vessel106by means of melting (hermetic sealing). Then, the part of the glass vessel which is shown in the broken line is cut, so as to complete the lamp vessel100.

However, in the aforementioned lamp vessel100, the edge of the phosphor layer114is square-cornered, as shown in “details of part E” ofFIG. 2. This is because the phosphor layer114is removed by the rubber blade118. Accordingly, at this angular part122, some portions thereof are likely to fall off (chipping). When the electrodeless fluorescent lamp is illuminated, the pieces of the phosphor having fallen off will be seen as a shadow, from outside the electrodeless fluorescent lamp, which is a quality problem.

Note here that the reason why the rubber blade118is not inserted inside the spherical part120beyond the cylindrical part116is as follows. That is, if the phosphor layer is scraped off by inserting the rubber blade in such a way, the phosphor that has been scraped off will be stuck, in-powder forms, in the slope part124which is arc-shaped, the slope part124positioning between the cylindrical part116and the spherical part120. If such remaining phosphor powders enter into the attaching part in the aforementioned attaching process, a crack or a leak occurs at the attaching part.

SUMMARY OF THE INVENTION

The object of the present invention, in order to solve the stated problems, is to provide a fluorescent lamp whose phosphor layer is prevented from falling off near the edge thereof.

The above object is achieved by a fluorescent lamp including: a hermetically sealed lamp vessel; and a phosphor layer attached to a part of an inner surface of the lamp vessel, where a thickness of the phosphor layer near an edge thereof gradually and smoothly decreases towards the edge.

According to the stated construction, the phosphor will not fall off, which tends to happen with conventional fluorescent lamps that have a phosphor layer whose edge is square-cornered. As a result, the fluorescent lamp of the present invention will be unlikely to have the problem that phosphor having fallen off will be seen from outside during the lamp illumination.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As follows, the present invention is described by way of an electrodeless fluorescent lamp.

FIG. 3is a partly broken view of the electrodeless fluorescent lamp10of the present embodiment that uses the electromagnetic induction-coupling discharge (H discharge) This electrodeless fluorescent lamp10is hereinafter simply referred to as “electrodeless lamp10”.

The electrodeless lamp10has a lamp vessel12which is made of translucent glass and which has been hermetically sealed. A phosphor layer14is formed at a predetermined area of the inner surface of this lamp vessel12, and a discharge material that includes mercury and an inert gas composed of such as argon and krypton is filled in the lamp vessel12.

The lamp vessel12has a glass bulb16in a spherical shape and an internal tube18. The internal tube18is not only used as a material for hermetically sealing the glass bulb16, but also as a storage of a core24which will be detailed later. The glass bulb16is attached to the internal tube18, at a position shown by the reference sign19.

The internal tube18has a concave portion20that is in a tube-like shape, and the core24is provided in the concave portion20. The core24has a coil wound around the outer surface of the core24. The core24is made of a magnetic material and is shaped as a tube.

A cylindrical part28of an aluminum heat sink26is inserted in the core24, towards the side of the inner radius of the core24. The heat sink26is used to dissipate heat from the core24, so as to prevent overheat of the core24, and has a cup part30as an extension from the cylindrical part28, and this cup part30is fixed to a circuit case32made of a synthetic resin.

The circuit case32stores therein a high frequency driving circuit34that is connected to the coil22, so as to supply a high-frequency alternating current to the coil22.

Furthermore, a base36having the same standard as general incandescent lamps is attached to the circuit case32. Power from the commercial power source is supplied to a high frequency driving circuit34via this base36.

In the electrodeless lamp10having the stated structure, an exciting current having a high frequency is fed to the coil22from the high frequency driving circuit34, so as to have the mercury-including gas which has been enclosed in the lamp vessel12to generate a plasma discharge, at areas mainly shown by the reference sign38. This plasma, working as a secondary coil, is then electrically coupled with the coil22, so as to stabilize the state of discharge. This discharge causes mercury to emit ultraviolet light, and the emitted ultraviolet light is then irradiated on the phosphor included in the phosphor layer14on the inner surface of the lamp vessel12, so as to generate visible light.

The phosphor layer14is formed on the substantially entire inner surface of the glass bulb16, and the edge of the phosphor layer14positions a little behind the sealing part19of the glass bulb16. Note here that the average thickness of the phosphor layer14, which is formed substantially even, is about 20 μm, as opposed to the thickness of the glass bulb16which is around 1 mm. As can be inferred from this, the thickness of the phosphor layer14in the drawings is exaggerated, for convenience in explaining.

As shown in the details of Part A inFIG. 3, the thickness of the phosphor layer14in the vicinity of the edge thereof gradually and smoothly decreases towards the edge40; that is, the vicinity of the edge of the phosphor layer14is formed to have a slope having an acute angle with respect to the inner surface of the glass bulb16. In other words, the edge of the phosphor layer14is not square-cornered. As a result, the phosphor in the edge is prevented from falling off, and furthermore there is less possibility of the aforementioned problem that is attributable to the phosphor falling-off.

As follows, parts of the production process for the electrodeless lamp10structured as above are described, with reference toFIG. 4andFIG. 5.

The glass vessel42in a round-bottom flask shape is a glass vessel, a part of which will become of the aforementioned glass bulb16. The glass vessel42is made up of a cylindrical part44and a spherical part46.

First, an injection nozzle48is entered in the glass vessel42whose opening is directed upward. Then the injection nozzle48injects an application solution50into the glass vessel42(FIG. 4(a)). The application solution50is obtained by mixing phosphor powders in an aqueous solution obtained by dissolving, in pure water, polyethylene oxide that is an adhesive polymeric material. The application solution50to be injected into the glass bulb16should be in an amount that is sufficient for coating the inner surface of the glass bulb16, and should not be too much. That is, the amount of the application solution50should be small, relative to the volume of the glass vessel42.

Next, the glass vessel42is gradually made to stand in an inverted position, while being rotated in the direction of the arrow B (FIG. 4(b)). The reason why the glass vessel42is rotated is to apply the small amount of injected application solution to the entire inner surface of the glass vessel42, and also to prevent the application solution from remaining in stripes within the glass vessel42.

Finally, the glass vessel42is completely in an inverted position (FIG. 4(c)). After a while, the rotation of the glass vessel42is stopped (FIG. 4(d)). Below the glass vessel42, an application solution collection container52is provided, which will collect an application solution having dropped from the glass vessel42.

Next, drying and partial removal of the application solution are performed. The partial removal is directed to the most part of the application solution attached to the cylindrical part44. The purpose of this partial removal is, as aforementioned, to prevent any crack or leak, in sealing the glass bulb26with the internal tube18.

The drying and the partial removal of the application solution are performed by going through the four steps ({circle around (1)}–{circle around (4)}) shown inFIG. 5.

The glass vessel42is moved, keeping an inverted position, below the hot-air duct62composed of four outlets54,56,58, and60. The location of the glass vessel42is determined directly below each of the outlets54–60. The glass vessel42, at each determined location, is subjected to a hot air of about 200° C. blown from the corresponding outlet, for a predetermined period of time (e.g. about 40 seconds) and at the external round-bottom thereof. At the same time, at each location, the glass vessel42is subjected to a steam suction by which steam generated within the glass vessel42is removed by suction. In addition to these, in Step {circle around (1)} and Step {circle around (3)}, an excess of the application solution is removed by cleansing.

FIG. 6is a sectional view of the head part64of the cleansing-suction apparatus that is used for cleansing the application solution and removing the steam by suction. The entire body of the cleansing-suction apparatus is not shown in the drawing. The head part64has: a nozzle66for injecting the cleansing solution fed through the pump (not shown in the drawing); and a suction tube68for sucking in the steam. Note that pure water is used for the cleansing solution. The suction tube68is connected to a pipe70connected to the inlet of the blower (now shown in the drawing). The removal of the steam from the glass vessel42into the suction tube68is realized by the power of suction of the blower.

The end of the nozzle66is directed downward, so as to inject pure water to the inner surface of the cylindrical part44, with an angle α. The range of the angle α is detailed later. The injection position from which the pure water is injected is preferably as upper as possible within the cylindrical part44. If the injection position is beyond the cylindrical part44and the injected pure water reaches the slope72situated above the cylindrical part44, the inside of the spherical part46will be splattered with the injected pure water, thereby making the phosphor layer within the spherical part46uneven. On the other hand, if the injection position is too low, the sealing position should be accordingly lower in position. This will lead to a longer lamp vessel12, and further to a longer electrodeless lamp10.

Now, returning toFIG. 5, in Step {circle around (1)}, while the glass vessel42is being rotated in the direction of the arrow C, the application solution is removed by cleansing, with the pure water injected from the nozzle66of the aforementioned head part64, and the steam is removed from the glass vessel42by suction of the suction tube68. This cleansing is a rough cleansing. Note that until the later operations {circle around (2)}, {circle around (3)}, {circle around (4)} have been complete, the glass vessel42is kept rotated in the direction of the arrow C.

In Step {circle around (2)} that follows, only drying of the application solution is performed. Therefore, only removal of the steam is performed by sucking the steam through the suction tube74. The suction tube74is in a cylindrical shape, and the lower end thereof is connected to the inlet of the aforementioned blower, via the pipe76.

In Step {circle around (3)}, cleansing and sucking are performed with use of the head part78, just as in Step {circle around (1)}. This cleansing is the finishing process in cleansing. Note here that the head part78is the same kind as the head part64used in Step {circle around (1)}.

In the last step (Step {circle around (4)}), the suction tube80is used to suck the steam, so as to perform only drying of the application solution.

Note that below the route where the glass vessel42passes, a collection bath82is set for collecting the cleansed off application solution.

By going through the steps {circle around (1)}–{circle around (4)}, unnecessary application solution is cleansed and removed off the glass vessel42, and the application solution applied is dried, so as to form a phosphor layer at the desirable area described above.

The drying operation performed in the steps {circle around (1)}–{circle around (4)} makes the application solution becomes solid gradually from the side of the bottom of the glass vessel42to the side of the cylindrical part42, and at the same time, the drying operation makes a small amount of the application solution in liquid form which is not yet solid go underneath along the glass vessel42(i.e. going along the spherical part46to the cylindrical part44). The edge of the phosphor layer is formed by being cleansed with a liquid (pure water) under such a situation. This is the reason why this edge is shaped as aforementioned (details of part A, inFIG. 3). Furthermore, in view of preventing the phosphor from falling off, the vicinity of the edge of the phosphor layer14preferably forms a slope having an acute angle, relative to the inner surface of the cylindrical part44of the glass vessel42. Accordingly, it is appropriate that the injection angle α (FIG. 6) of the pure water (cleansing solution) is smaller than 90° C.

Note that in the glass vessel42, the final average thickness of the phosphor layer formed on the inner surface of the spherical part46is determined by the viscosity of the application solution and the drying speed at which the application solution is dried.

That is, the phosphor layer becomes thick, as the viscosity becomes high (i.e. as the fluidity of the application solution becomes low), and as the drying speed becomes fast. On the contrary, the phosphor layer becomes thin, as the viscosity thereof becomes low (i.e. as the fluidity of the application solution becomes high), and as the drying speed becomes slow. This is because the application solution applied on the inner surface of the spherical part46flows downward under its own weight, until becoming solid. Accordingly, the thickness of the layer of application solution (i.e. thickness of the phosphor layer) decreases.

The drying speed is, for example, adjustable by how deep the suction tube is entered into the glass vessel42. The reason is as follows. The purpose of providing the suction tube is to suck mainly the steam generated inside the spherical part46, so as to promote drying of the application solution on an inner surface of the spherical part46. Therefore, as the opening of the suction tube (upper opening) gets close to the spherical part46(i.e. as it entered deep), the ratio of the steam becomes high in relation to the total amount sucked by the suction tube, thereby promoting the drying. On the contrary, as the opening gets close to the vicinity of the opening of the glass vessel42(i.e. as it enters shallow in the glass vessel42), the ratio of the air (air outside the glass vessel42) becomes high in relation to the total amount sucked by the suction tube, so as to decrease the ratio of the steam in relation to the total amount sucked by the suction tube. This will slowdown the drying.

In the aforementioned Step {circle around (1)}, the application solution is simultaneously cleansed and dried under a condition where the application solution is substantially non-dry. In this Step {circle around (1)}, it is impossible to enter the suction tube deep enough into the glass vessel42, from the following reason. That is, if the suction tube is entered too deep, an air current yielded by the air sucked by the suction tube makes the cleansing solution wind up inside the spherical part46, and drop on the inner surface of the spherical part46. This will result in an uneven thickness of the application solution having been applied.

Therefore, at Step {circle around (1)}, the drying speed of the application solution is slower than that in Step {circle around (2)} (or in Step {circle around (4)}) where the suction tube is inserted deeper into the glass vessel42.

In view of the above, in order to make the final phosphor layer thick, it is possible to perform only sucking of steam in Step {circle around (1)}, just as in Step {circle around (2)}, and to enter the suction tube deep into the glass vessel42. Or, it is further possible to omit Step {circle around (1)}, and to perform Step {circle around (2)} for a period of time which is a summation of the time required for Step {circle around (2)} and the time required for Step {circle around (1)}.

In addition, in the aforementioned embodiment, the aqueous solution made of polyethylene oxide is used for the liquid into which the phosphor is mixed. However, not limited to this, the aqueous solution may be butyl acetate. That is, an application solution maybe obtained by mixing phosphor powders into butyl acetate. Note that in this case, the cleansing solution has to be butyl acetate.

The fluorescent lamp to which the present invention is applied is not limited to the aforementioned electrodeless fluorescent lamp. The essential point is that the fluorescent lamp has to have a hermetically sealed lamp vessel, and that a phosphor layer is on a part of the inner surface of the lamp vessel (i.e. there is an edge of the phosphor layer), for the present invention to be applicable thereto.