SHATTER-RESISTANT LAMP ASSEMBLY AND METHOD

Abstract: A shatter-resistant lamp assembly (1) is formed by encasing a cylindrical lamp bulb (10) in a seamless non-frangible sleeve (18) that is sealed at each end to one end of the lamp. A shatter-resistant lamp assembly (1) is made by applying an adhesive (20) to each end of the lamp, preferably by wrapping double-sided adhesive transfer tape around each metal end cap (14) of the lamp bulb, inserting the bulb into the sleeve (18) with the ends (24) of the sleeve overlapping the tape wound on each end of the bulb, and compressing ends of the sleeve onto the tape by heat-sealing.

Description: Shatter-resistant lamp assembly and method This invention relates to shatter-resistant electric lamps and methods of making such lamps. When a conventional fluorescent lamp breaks, fragments of the glass tube, mercury, and phosphor powders from the lamp can scatter to contaminate a wide area. Such contamina- tion is particularly damaging in areas where food is stored uncovered and to food preparation surfaces. To reduce the possibility of scattered contamination by a broken fluorescent lamp, shatter-resistant lamp assemblies have been developed to contain the contents of a lamp when it breaks. Known lamp assemblies are shown in US Patent Nos. 4,048,537 (Blaisdell et al . ) , 4,924,368 (Northrop, et al . ) , 5,536,998 (Sica) , and 5,173,637 (Sica) . The Sica patents are owned by the assignee of the present invention. The prior art protective assemblies for fluorescent lamps include special molded plastic end fittings that fit onto the terminal caps of the lamp and hold in place a protective sleeve encasing the lamp. In some of the prior art devices, end fittings are intentionally designed to be removed from one lamp and reused on other lamps. This is very unsatisfactory and results in leakage and contamination by the lamp contents which escape when the lamp is broken. The assemblies shown in the two Sica patents are a great improvement, the end fittings are sealed to the protective sleeve and to the lamp itself so that there is lit- tie leakage or contamination; the lamp contents are sealed in the sleeve. A significant disadvantage of the three-component protective assemblies, i.e., sleeve and two end fittings, is the difficulty and expense of making them. The two end fittings can be relatively expensive to make, and the dimen- sions of the end fittings and sleeves should be matched to within relatively close tolerances to ensure a tight fit. Also, there are four seals to be formed, and the greater the number of seals, the greater the chances for leakage. A long-standing problem with the three-component construction is that it gives the lamp bulbs an unnatural appearance and this, in turn, tends to impede their sales. One prior proposal to solve this problem is to coat the entire bulb with a protective coating. However, this is unsatisfac- tory, in that the coating can reduce the useful light output from the bulb, and can become discolored with age, thus adding to the unsightliness. In view of the foregoing, an object of the present in- vention is to provide a shatter-resistant lamp assembly and method which overcome or alleviate the foregoing problems. A further object of the invention is to provide a manufacturing method for making the lamp assembly efficiently and with high quality, while producing a superior product. The above objects are solved by the combination of features of the independent claims. The dependent claims disclose further advantageous embodiments of the invention. The following summary of the invention does not necessarily describe all necessary features so that the invention may also reside in a sub-combination of these described features. The foregoing objects are met, in accordance with the present invention, by the provision of a lamp assembly which includes an elongated lamp having a first end and a second end; a non-frangible sleeve substantially encasing the lamp and -having two ends which are sealed directly to the ends of the lamp. Preferably, the ends of the sleeve are adhered to the end caps of the bulb. If the end caps are of smaller diameter than the bulb, the ends of the sleeve are compressed onto the end caps and adhesive is used to secure the sleeve ends to the end caps. The compression preferably is provided by means of heat-shrinking. Preferably, the adhesive is applied by the use of an adhesive transfer tape which has an adhesive coating on each of its opposed surfaces , together with compression, preferably provided by heat shrinking the ends of the sleeve onto the end caps. Each sleeve end adheres to the outer layer of adhesive on the transfer tape, and the tape adheres to the bulb end. It is believed that the heat shrinking crimps the sleeve ma- terial, reduces the diameter of and shapes the sleeve end to fit on to the bulb end, and presses the sleeve material and tape together so that the adhesive fills any creases in the sleeve material and tightly secures and seals the sleeve to the bulb ends . The resulting assembly is tightly sealed but has seams only at the end caps, where the visibility of the seams is low. It is a relatively simple, good-looking, shatter- resistant lamp. It is also preferred that the adhesive be resistant to deterioration at relatively high temperatures, such as 82 °C (180°F) for an extended length of time. The tape used preferably is a relatively soft acrylic tape with relatively high-tack adhesive. -Use of such double-sided adhesive tape greatly facilitates the manufacturing method. The tack and dimensions of the adhesive layer used can be controlled easily, and the tape is readily adaptable to being applied by automated or semi-automated equipment. The invention can be summarized as follows. A shatter- resistant lamp assembly is formed by encasing a cylindrical lamp bulb in a seamless non-frangible sleeve that is sealed at each end to one end of the lamp. The lamp assembly is made by applying an adhesive to each end of the lamp, preferably by wrapping double-sided adhesive transfer tape around each metal end cap of the lamp bulb, inserting the bulb into the sleeve with the ends of the sleeve overlapping the tape wound on each end of the bulb, and compressing ends of the sleeve onto the tape by heat-sealing. Other objects, aspects, features, and advantages of the present invention will be set forth in or become apparent from the following detailed description and the drawings which represent preferred embodiments of the invention and which by no means should be regarded as being limiting the gist of the present invention. The single Figure of the drawings is a side elevation view, partially broken-away and partially cross-sectional, of a shatter-resistant lamp assembly constructed in accordance with the present invention. The drawing illustrates one end of a shatter-resistant lamp assembly 1. The other end of the assembly (not shown) is simply a mirror image of the end shown. Lamp assembly 1 comprises a conventional fluorescent lamp bulb 10, a protective sleeve 18, and pressure-sensitive adhesive 20. Lamp bulb 10 includes a substantially cylindrical glass tube 12 that tapers slightly at each end and is terminated with a cup-like metal end cap 14 having a peripheral flange portion 16 of a diameter less than that of the tube 12. Cap 14 contains a conventional lamp base portion (not shown) coupled to conventional electrical contact prongs or electrodes 22. Any conventional contact apparatus can be used, such as a single prong connector, a recessed double contact connector, etc. The lamp bulb 10 is inserted into the sleeve 18, and the ends 24 of the sleeve are compressed, preferably by heat-shrinking, to make intimate contact with the adhesive 20 to seal the ends of the sleeve onto the flanges 16. Protective sleeve 18 preferably is a non-frangible transparent heat-shrinkable polymer sleeve, such as a polycarbonate sleeve, for example. A particularly suitable transparent, heat-shrinkable tubular polycarbonate material is sold by 3M, Inc. under the designation PC-3207, T-13 version. This material has an interior diameter of approxi- ately 3.85 cm (1.517 inches), an external diameter of approximately 3.93 cm (1.547 inches), and a wall thickness of approximately 0.04 cm (0.015 inches). This preferred material is transparent to visible light but substantially opaque to ultra-violet radiation having a wavelength of up to 390 nm. It does not turn yellow with age, to any appreciable degree. Optionally, sleeve 18 comprises a translucent material having a predominant color, such as gold, red, blue, green, or the like. Whether transparent or translucent, sleeve 18 substantially retains its clarity during extended exposure to ultraviolet radiation and heat produced by the lamp 12. Additionally, it is preferred that the inner radius of sleeve 18 be slightly larger than the outer radius of lamp 12. Such difference in radii provides a small annular gap „C" along much of the length of lamp assembly 1. The gap is large enough to permit the bulb to be inserted into the sleeve easily, but small enough to insure adequate dissipation of heat from the bulb. Adhesive 20 is a high-temperature-resistant adhesive that provides a mechanical seal between the inner surface of sleeve 18 and the outer surface of flange 16. Preferably, adhesive 20 is a soft acrylic pressure-sensitive adhesive. Adhesive 20 also serves as a moisture barrier and assists in preserving an air tight seal. A particularly advantageous adhesive is provided on a „transfer" tape produced by 3M, Inc. which is available un- der the designation ,,969 Tape", a type of „ATG tape". This double-sided adhesive tape is approximately 0.013 cm (0.005 inches) thick and features an adhesive designated „A-60" which has a very high initial adhesion along with good shear holding power. Adhesive A-60 bonds to most metals and plas- tics and a variety of other materials. 969 Tape has the further advantages of being clear, and being resistant to ultraviolet light. It has been found that 969 Tape retains its clarity even after extended exposure to light and heat produced by the lamp 12. It is rated as being resistant to te - peratures up to 82°C (180°F) over a period of weeks or months . According to the new manufacturing method, the shatter- resistant lamp assembly 1 is made by wrapping the double- sided adhesive tape 20 twice around each of flanges 16 and inserting lamp 12 through sleeve 18 until the ends of the sleeve 18 are substantially aligned with the ends of lamp 12. By wrapping twice, the existence of any gaps in the coverage of the tape can be minimized. Next, at each end of lamp 12, the portion of sleeve 18 extending over flange 16 is heat-shrunk and compressed to form an adhesive seal between sleeve 18 and flange 16. The heat-shrinking process preferably comprises applying heat at a temperature of approximately 82°C (180°F) to the ends of sleeve 18 for approximately twelve to fifteen seconds. The shrinkage applies moderate pressure sufficient to compress each sleeve end and reduce its diameter to ap- proximately that of the flange 16 plus the thickness of the tape 20. Since the heat-sealing temperature is relatively low, the sleeve ends shrink but are not believed to melt. This is an advantage in that the sleeve is not weakened by melting a thin spot or a hole through it. The pressure applied by shrinkage bonds the sleeve ends to the adhesive on the tape 20. Since the adhesive also bonds well to metal, a secure bond and seal is formed at each end of the lamp. Although it is preferred that the sleeve ends be shrunk by the process, it is not essential. Simple clamping or crimping may be sufficient, depending on the dimensions of the bulb and the flanges 16, the flexibility of the sleeve material, and the type of adhesive used. Heat-shrinking can be done by slipping a heat- shrinkable plastic collar over each end of the sleeve, applying heat to the collars with a hot-air blower, thus causing both the collars and the sleeve ends to shrink, and removing the collars. Alternatively and preferably, a heater block is provided with a hole slightly larger than the outside diameter of the flanges 16. The sleeve and one end of the lamp are pushed longitudinally into the hole in the heater block and the block heats the sleeve end to heat-shrink the sleeve end onto the tape. This is done for each end of the lamp assem- bly. The foregoing method is amenable to hand-work, full automation, or full or semi-automation. In an automated or semi-automated production method, at a first station, the tape is separated from the liner material and a strip of tape is wound around each flange and cut. A winding machine (not shown) can be used or the strip can be applied by hand. Alternatively, an even coating of adhesive can be applied all of the way around each flange 16. Lamp bulbs, with adhesive applied, and sleeves, pre-cut to the proper length, are fed to a second station location where a pusher mechanism (not shown) pushes each bulb into a sleeve. Alternatively, the insertion can be done by hand. Next, the sleeve-protected bulb is conveyed or carried to a heating fixture which has two spaced-apart heated clamps or heater blocks which receive the sleeve ends and heat-shrink both sleeve ends simultaneously for 12 to 15 seconds. Alternatively, this step also can be done by hand. After that, the lamp assemblies are packaged for shipment. Conveyor belts or other conveying equipment can be used to move the lamp assembly parts between stations. In a typical accident situation, the application of a blow to the lamp assembly 1 may cause the lamp 12 to shatter within sleeve 18. However, sleeve 18 itself will not shatter and will contain the fragments and fluorescent materials of the lamp, thus preventing the escape of contamination outside of the assembly 1. The shatter-resistant lamp assembly has fewer parts and seams, and has a sleek, seamless look so important to many users. Although illustrative embodiments of the present invention and modifications thereof have been described in detail herein, it is to be understood that this invention is not limited to these precise embodiments and modifications, and that other modifications and variations may be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims . Advantages of the present invention comprise: • An assembly is provided which has a minimum of separate parts and seams, has no unsightly seams, is transparent to desirable light, and does not discolor with heat and/or age. • A device is provided that is structurally simpler, more readily adaptable to automated or semi-automated manufacture, and can be made at a lower cost than prior devices.

Claims: Claims 1. A shatter-resistant lamp assembly (1) comprising: • a substantially cylindrical lamp bulb (10) having a first lamp end and a second lamp end; each of said lamp ends being smaller in diameter than said bulb; • a substantially cylindrical non-frangible flexible sleeve (18) substantially encasing said lamp and hav- ing an integral first sleeve end (24) and an integral second sleeve end, said sleeve ends being compressed onto said lamp ends; • a first seal sealing said first sleeve end directly to said first lamp end; and • a second seal sealing said second sleeve end directly to said second lamp end. 2. The lamp assembly according to claim 1, wherein said first seal and said second seal are adhesive seals. 3. The lamp assembly according to claim 1, wherein said first seal and said second seal are heat-shrink and adhesive seals. 4. The lamp assembly according to any one of claims 1 to 3, wherein each of said seals comprises at least one layer of double-sided adhesive tape wrapped around one of said ends of said lamp, with one end of said sleeve compressed onto said tape. 5. The lamp assembly according to claim 4 in which each of said seals includes at least two layers of said tape. 6. The lamp assembly according to any one of claims 1 to 5, wherein said sleeve (18) is transparent. The lamp assembly according to any one of claims 1 to 5, wherein said sleeve (18) is translucent and has a predominantly non-white color. The lamp assembly according to any one of claim 1 to 7 in which said lamp (10) includes a pair of end caps (14) at each of said lamp ends, a length of double-sided adhesive tape wound around each of said end caps and each end of said sleeves is heat-shrunk onto said tape. 9. A shatter-resistant lamp assembly (1) consisting of: • a substantially cylindrical lamp bulb (10) having a first lamp end and a second lamp end, a metal cap (14) at each of said first and second lamp ends, said metal caps being smaller in diameter than said lamp bulb; • a substantially cylindrical non-frangible sleeve (18) substantially encasing said lamp (10) and having an integral first sleeve end (24) and an integral second sleeve end, said sleeve ends being heat-shrunk onto one of said lengths of tape; • two lengths of double-sided adhesive tape, each extending around one of said end caps (14) ; • a first seal sealing said first sleeve end to one of said end caps (14) ; and • a second seal sealing said second sleeve end to the other of said end caps. 10. A method of manufacturing a lamp assembly (1) comprising the steps of: • providing a substantially cylindrical lamp bulb (10) with first and second lamp ends of a diameter less than that of said bulb; • applying a pressure-sensitive adhesive to each of said first and second lamp ends; • inserting said bulb into a substantially cylindrical lamp through a substantially cylindrical non- frangible sleeve (18), said sleeve having an integral first sleeve end (24) and an integral second sleeve end; • compressing said first sleeve end (24) onto said first lamp end and forming a first seal between said first sleeve end and said first lamp end; and • compressing said second sleeve end onto said second lamp end and forming a second seal between said second sleeve end and said second lamp end. 11. The method according to claim 10 in which said step of applying a pressure-sensitive adhesive (20) to said first lamp end and to said second lamp end comprises wrapping a length of double-sided adhesive tape around each of said lamp ends. 12. The method according to claim 10 or 11 in which said compressing step comprises heat-shrinking said sleeve ends onto said lamp ends. 13. The method according to any one of claims 10 to 12 in which said step of applying a pressure-sensitive adhe- sive (20) to said first lamp end and to said second lamp end comprises wrapping a length of double-sided adhesive tape around each of said lamp ends, and said steps of forming a seal include heating each of said sleeve ends (24) for a predetermined length of time while co press- ing the adjacent one of said sleeve ends. 14. A method of making a shatter-resistant lamp structure, said method comprising the steps of: • providing an elongated lamp bulb (10) having end caps providing an elongated hollow sleeve (18) made of plastic and slightly larger in internal lateral dimension than the outside of said bulb, said sleeve having a length such that its ends overlie said end caps when said bulb is inserted into said sleeve; compressing each of said sleeve ends (24) when it overlies one of said end caps (14) and adhering each of said sleeve ends to one of said end caps to form a sealed enclosure about said bulb. 15. A method as in claim 14 in which said plastic is heat- shrinkable and said compressing step includes heat- shrinking said sleeve ends (24) onto said end caps (14) . 16. A method as in claim 14 or 15 in which said adhering step is performed by wrapping double-sided adhesive tape around said end caps (14) before said compressing step. 17. A method as in any one of claims 14 to 16 in which plas- tic is heat-shrinkable and said adhering step is performed by wrapping double-sided adhesive tape around said end caps (14) before said compressing step and including the step of heating said sleeve ends (24) to compress them.

Inventors: SICA MICHAEL F, SICA, MICHAEL, F.
Applicants: SICA MICHAEL F, SICA, MICHAEL, F.
Application year: 1998
Main classification: H01J61
IPC codes: F21V3, F21V17, F21Y103, H01J5, H01J61