Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/38—Exhausting, degassing, filling, or cleaning vessels
  • H01J9/395—Filling vessels
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2209/00—Apparatus and processes for manufacture of discharge tubes
  • H01J2209/38—Control of maintenance of pressure in the vessel
  • H01J2209/387—Gas filling

Definitions

• the present invention is inherent to a novel type of mercury source to precisely dose small amounts of mercury, to its use for lamp manufacturing and to production methods for said mercury source.
• CFL Compact Fluorescent Lamp
• Linear Fluorescent Lamps Linear Fluorescent Lamps
• Circular Fluorescent Lamps a small quantity of mercury (a few milligrams) is dosed by introducing a mercury source in the lamp body.
• CCFL Cold Cathode Fluorescent Lamps
• the mercury source may not be present in the final device, since in the most diffused production process, after mercury release, the source, connected by means of a glass chamber to the main body of the lamp, is discarded and the lamp sealed.
• This production technique is known in the field as double tip-off or double pinch-off, more details may be found in the international patent WO 98/53479 in the applicant's name.
• Another relevant aspect to be considered when dealing with mercury sources is inherent to safety due to the mercury vapor pressure; in this regard it is desirable to have a dispensing solution capable to avoid the mercury release until the required stage in the device manufacturing process.
• the source of mercury is introduced in one of the latest process stages of lamps manufacturing and an ideal source should avoid premature mercury release at low temperatures, up to 70°C and also having an optimized coupling with the lamp production process, meaning that mercury may be fully released at temperatures above 100°C, with times for the mercury release typically ranging from several minutes at temperatures proximate to 150°C, down to tens of seconds for temperature close to 350°C.
• This mercury dispensing solution being more versatile, provides advantages in the manufacturing of the light devices with respect to high temperature sources since the heating phase and the required heating equipments can be simplified and more easily matched with the lamp manufacturing process constraints resulting in a more efficient and leaner process phase.
• European patent application EP 1434249 and Japanese patent application JP 2007273346 disclose the use of composite spheres having an inner metallic core with a mercury coating or a coating with an alloy containing mercury. These solutions pose a series of safety problems since mercury or the mercury containing alloy is on the external part of the dispenser and therefore in direct contact with the environment; furthermore also the metallic core of the sphere, having only a support function, increases the size of the spherical mercury dispenser.
• Chinese patent application CN 101000848 discloses spherical dispensers, where the core is made of a mercury amalgam covered by a membrane of fluorescent powder and a metallic oxide.
• the problem entrained by this solution relates to the low precision in the amount of mercury contained in the amalgam, intrinsic in the amalgam formation process.
• the amalgam may partly re-absorb the mercury after the evaporation.
• Object of the present invention is to provide an improved source for mercury dispensing and precise dosing capable to overcome the problems and drawbacks still present in the prior art with reference to aspects relating to environment, safety, size and releasing temperature and in a first aspect thereof consists in a core-shell mercury source, wherein the core is made essentially by liquid mercury, characterized in that the shell enclosing said mercury core is a composite structure, comprising an organic binder and a filler made by a plurality of solid discrete elements, wherein:
• the core contains at least 95% wt of mercury, since it is tolerable to have impurities, such as traces of other elements not imparting additional features and properties to the mercury liquid source.
• the composite is a composition of the shell from 4 wt% to 35 wt% of an organic binder and between 65 wt% and 96 wt% of a filler made by a plurality of solid discrete elements independently from the true density or nature of the filler.
• the ranges for the wt% of the filler depend on an intrinsic physical property of the filler, its true density that is defined as the density tabulated and characteristic of the element constituting the filler, not including voids or porosities.
• the density averaged over the amount of the fillers that is relevant for the limit determination.
• the average density D will be expressed as follows: wt ⁇ 1 * D ⁇ 1 + wt ⁇ 2 * D ⁇ 2 / wt ⁇ 1 + wt ⁇ 2 .
• the wt% of the organic binder in the shell is comprised between 3% and 70% and the wt% of the filler is comprised between 30% and 97%.
• the thickness of the shell can span from 100 to 1000 micron, and preferably is comprised between 140 and 500 ⁇ m, while the liquid core may contain up to 12 mg of Hg, whereas the lower limit is at 0.1 mg Hg.
• the filler made by a plurality of solid discrete elements it is intended a filler made by discrete particles with no particular restriction on the shape that may be for example spherical, cylindrical, elongated or exhibiting an irregular (corrugated) surface.
• the volume of the discrete elements that shall be comprised between 1*10 -3 and 2*10 6 ⁇ m 3 and preferably is comprised between 4 and 2*10 5 ⁇ m 3 .
• the materials of the discrete elements constituting the filler it is not required to use only one type of material, even though the preferred solution envisages the use of solid discrete elements equal to each other in composition. Particularly preferred is the use of inorganic discrete elements, and even more preferably only one type of inorganic substance is used.
• PTFE polytetrafluoroethylene
• polyolefines such as polyethylene
• acrylic polymers such as polymethylmethacrylate (PMMA), polyetheretherketone (PEEK), polyetherimide (PEI), polybenzimidazole (PBI), polyphenylensulfide (PPS).
• PMMA polymethylmethacrylate
• PEEK polyetheretherketone
• PEI polyetherimide
• PBI polybenzimidazole
• PPS polyphenylensulfide
• Examples of materials suitable to be used as inorganic discrete fillers are silicon, silica, stainless steel, brass, tungsten, molybdenum, bismuth, tin, zinc, their alloys or combinations. Also getter materials, such as zirconium and its alloys, yttrium and its alloys, titanium and its alloys, nickel and its alloys can be adopted.
• hydrocolloid materials also sometimes referred in the field as hydrogels
• hydrogels such as those based on polysaccharides, with particular reference to alginates or celluloses, such as hydroxypropyl-, methyl-, ethyl-, carboxmethylcellulose.
• binders based on crosslinkable gelatins may be employed.
• the binder may contain also additional organic compounds, to impart better properties to the shell, such as an improved strength; in this regard example of suitable additives are Shellac, Gellan gum, Xanthan gum, Guar Gum, special polysaccharides, polyvinyl alcohol and their combination.
• suitable additives are Shellac, Gellan gum, Xanthan gum, Guar Gum, special polysaccharides, polyvinyl alcohol and their combination.
• the amount of these additional organic compounds is usually not higher than 10% wt, calculated over the overall shell weight.
• a structure made by a plurality of shells particularly advantageous is a two shells enclosing structure, with the outer shell having a different composition with respect to the composition of the shell in direct contact with liquid mercury.
• This solution enables to split the required property of the shell into two different composite structures.
• Particularly advantageous is providing for the composite material in direct contact with mercury a good wettability and adhesion, thereby a good mercury enclosure, while the outer shell is chosen to provide mechanical resistance to the shell, for example by modulating its breaking properties.
• the outer shell may be without filler, while the inner shell is the structure containing the filler made by a plurality of solid discrete elements.
• the filler might be in the inner shell and the outer shell shall be of a lower filler content, preferably 0-50% of the filler content of the inner shell, and providing diffusion strength or elasticity.
• One of the advantages of the mercury sources according to the present invention is their stability, i.e. the lack of mercury release, for temperatures up to 70° C, and the full release of mercury at a temperature such as 150° C.
• the mercury releasing mechanism is evaporation from cracks and fissures of the shell structure, whereas for a higher temperature, such as 300° C, the shell breakage (fragmentation) and a more sudden mercury release process takes place.
• Shell thickness influences the releasing mechanism, with thinner shell being more subject to breakage.
• the mercury sources according to the present invention satisfy the safety requirement in lamp manufacturing with regard to the handling without mercury losses at temperatures up to 70° C and also show a high versatility in the releasing mechanism enabling the adoption of the very same solution for a wide range of production processes, each one with its own temperature limit and characteristics.
• the invention is related to the use of a core-shell mercury source, wherein the core is made essentially by liquid mercury, characterized in that the shell enclosing said mercury core is a composite structure comprising an organic binder and a filler made by a plurality of solid discrete elements, wherein:
• the mercury source is sealed within the device; in this case after the sealing process and opening of the core-shell structure only the shell may be found within the lamp, while mercury is present in the lamp in form of vapors or deposits being spread on the lamp components.
• the dispenser is just used in an intermediate manufacturing production step and not present within the sealed lamp.
• the invention relates to a production process for core-shell mercury source, wherein the core is made essentially by liquid mercury, characterized in that the shell enclosing said mercury core is a composite structure comprising an organic binder and a filler made by a plurality of solid discrete elements, wherein:
• the Rotary Die process is based on the formation of an organic band used to create the capsules: a warm liquid cellulose (e.g. hydroxypropyl methylcellulose) or gelatin is spread over a slowly revolving stainless steel drum. It is solidified on the rotating drum in such a way to form an elastic band rolling off of the other end. This thin band is then filled with the core material and automatically formed into capsules.
• a warm liquid cellulose e.g. hydroxypropyl methylcellulose
• gelatin e.g. hydroxypropyl methylcellulose
• This thin band is then filled with the core material and automatically formed into capsules.
• a Drip Casting process allows the production of spherical core-shell structures characterized by an envelope covering the core by using a microcapsule technology, which can be based e.g. on a vibrating nozzle suitable for droplets formation.
• the Spraying process can be exploited to create an envelope or shell around already formed droplets covering them with a coating applied starting from a suitable suspension based on a combination of binder and solid filler.
• the shell is produced by coating mercury with a slurry containing the organic binder and the filler preferably in form of powders.
• the slurry is an aqueous suspension containing at least 50% of water.
• non aqueous slurries such as alcohol or solvent based ones may be employed.
• composition of the different batches/groups is shown in Table 1, showing for each of them the binder, the filler type, the wt% composition of the shell, its thickness, and the size of the filler powders.
• Spheres from groups 1 to 9 have a composition according to the present invention, made with silicon, that has a true density of 2.33 g/cm 3 , as inorganic filler; group 10 core-shell mercury spheres have a composition according to the present invention but in this case the inorganic filler is tungsten, that has a true density of 19.3 g/cm 3 .
• Spheres from groups C1-C3 are comparative examples of compositions not covered by the present invention.
• the core-shell spheres from the different groups were tested in order to determine their mechanical strength according to the following procedure: for each group, 20 spheres were closed in a plastic cylindrical container having height of 30 mm and base diameter of 20 mm; then the container was placed in rotation on an axis perpendicular to the cylinder axis at a speed of 30 rounds/min for 15 minutes to simulate severe stresses during handling. At the end of the tests visual inspections were carried out under a microscope with a 50X magnification and the percentage of cracked or broken capsules was determined per each batch.
• the groups were divided in the following three categories according to the induced defective rate: "bad" for a defective rate induced by the rotation of more than 60%, "acceptable” for an induced defective rate between 40% and 10%, "good” for a defective rate lower than 10%.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Vessels And Coating Films For Discharge Lamps (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (1)

Family

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Family Applications (1)

Country Status (2)

Citations (9)

• 2010
  • 2010-12-24 EP EP10425390A patent/EP2469576A1/de not_active Withdrawn
• 2011
  • 2011-12-15 WO PCT/EP2011/072882 patent/WO2012084679A1/en active Application Filing

Patent Citations (9)

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