Electric lamp and discharge devices – With gas or vapor – Having a particular total or partial pressure
Reexamination Certificate
1999-07-29
2002-12-31
Moore, Margaret G. (Department: 1712)
Electric lamp and discharge devices
With gas or vapor
Having a particular total or partial pressure
C525S478000, C427S387000, C313S634000, C313S635000, C313S578000, C313S489000, C313S315000
Reexamination Certificate
active
06501219
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an environmentally safe method for applying a single coating of an optically clear transparent silicone containment composition onto the surface of an incandescent lamp bulb. More particularly, the present invention relates to a silicone coating composition useful for imparting shatter resistance to incandescent lamps and to shatter resistant lamps made thereby.
As shown by Robertson et al, Canadian Patent 914265, an incandescent lamp bulb is coated by dipping it into a silicone dispersion consisting of 75% of xylene and 25% silicone rubber. After treating the lamp, removal of excess solvent is necessary. In a related patent, U.S. Pat. No. 3,715,232, to Audesse et al, a method is described to make a shatter-resistant incandescent lamp, by initially coating the lamp bulb with an organic solvent silicone composition as shown by Robertson et al, followed by treating the coated lamp bulb surface with a solvent containing silicone overcoat.
Gagnon et al, Canadian Patent 1,243,723 is directed to an electric lamp having a pressurized light source capsule in a glass, light transmissive bulb. A containment coating is described for the bulb in the form of a fluoropolymer, such as Teflon resin of E. I. duPont de Nemours, or a multi-layer silicone rubber. It is reported that the silicone rubber multi-layer is applied by dip coating.
Lamoreaux U.S. Pat. No. 3,529,035, relates to high strength silicone elastomers. These silicone elastomers are formed by reacting a copolymer of SiO
2
units and (CH
3
)
2
SiO units, in a toluene solvent, with a silanol end stopped polydimethylsiloxane in toluene. Reaction is effected with a catalyst in the form of an organic carboxylic acid salt of a metal, such as tin. Coating of an incandescent lamp bulb was achieved by dipping the lamp in the solvent blend, and upon lamp removal, allowing the solvent to evaporate from the treated bulb surface overnight. The silicone coating on the lamp's surface was then oven cured for 1 hour.
A transparent shatter-resistant platinum catalyzed silicone coating composition suitable for use on a glass surface is described by Maguire et al U.S. Pat. No. 5,034,061. An example of the Maguire et al composition includes the use of a 60% by weight in toluene solution of a benzene soluble copolymer of SiO
2
units and (CH
3
)
3
SiO
0.05
units, in combination with a siloxane hydride fluid and vinyldimethylsiloxane fluid.
While various silicone coating compositions are described in the prior art for treating the bulbs of incandescent lights to enhance their shatter resistance, significant environmental concerns have often been advanced as a result of the necessity of organic solvent disposal during the cure of the silicone coating composition. Alternative silicone coating compositions and methods for incandescent lamp treatment are therefore needed to offset such environmental concerns while continuing to maintain the physical properties of the applied silicone coating of interest to the incandescent lamp industry.
BRIEF SUMMARY OF THE INVENTION
The present invention is based on the discovery that a substantially organic solvent-free, platinum catalyzed heat curable silicone mixture, comprising by weight (a) a blend of a low molecular weight, and a high molecular weight vinyl containing polydimethylsiloxane fluid, (b) a siloxane hydride, and (c), a vinyl resin comprising chemically combined trimethylsiloxy units and SiO
2
units, can be used in an environmentally safe manner as an effective incandescent lamp bulb containment coating composition. The heat curable silicone composition has an extended shelf life, and can be applied as a single coating onto the surface of a lamp bulb by dip coating or spraying. Upon application and curing on the lamp bulb's surface, of the platinum catalyzed heat curable silicone mixture of the present invention, the lamp shows improved shatter resistance, weather resistance, and optical clarity.
In addition, if desired, a second substantially organic solvent-free heat curable platinum catalyzed silicone coating composition can optionally be applied at thicknesses up to about a mil onto the cured silicone treated lamp surface as a dust repellent. The dust repellent composition can comprise a platinum group metal catalyzed mixture of a vinyl resin comprising chemically combined dimethylvinylsiloxy units and SiO
2
units, a low molecular weight vinyl containing polydimethylsiloxane fluid, and a silicon hydride cross-linker.
In a further aspect of the present invention, there is included an incandescent lamp exhibiting improved containment of glass shards resulting from external impact. The incandescent lamp exhibiting improved impact resistance can be made by applying a single coating of the aforementioned heat curable platinum catalyzed silicone coating composition onto the incandescent lamp's glass bulb surface, extending beyond the hermetic seal between the glass bulb and the metallic base. Preferably, application of the silicone composition onto the surface of the incandescent lamp's metallic base can extend up to the threaded portion.
SUMMARY OF THE INVENTION
A substantially volatile organic solvent-free, platinum group metal catalyzed, heat curable silicone coating composition comprising by weight,
(a) 100 parts of an alkenyl terminated polydiorganosiloxane mixture consisting essentially of a (i) a low molecular weight alkenyl terminated polydiorganosiloxane having a viscosity of about 500 centipoise to about 15000 centipoise at 25° C. and (ii) a high molecular weight alkenyl terminated polydiorganosiloxane having a viscosity of about 40,000 centipoise to about 220,000 centipoise at 25° C., where there can be present by in the alkenyl terminated polydiorganosiloxane mixture, from about 0.02 to 0.5 part of (i), per part of (ii),
(b) 5 to 50 parts of a silicone resin, referred to hereinafter sometimes as MQ, or MQD, having ratio of organo radicals to silicon which has a value of about 0.5 to 2, where the organo radicals are selected from the group consisting of C
(1-6)
organo radicals, C
(2-6)
alkenyl radicals, and a mixture thereof, and the silicone resin comprises “Q” units having the formula,
SiO
2
,
chemically combined with a member selected from the group consisting of “M” units having the formula,
(R)
a
(R
1
)
b
SiO
0.5
,
and a mixture of M units and “D” units having the formula,
(R
2
)
2
SiO,
where R is a C
(1-6)
organo radical, R
1
is a C
(2-6)
alkenyl radical, R
2
is selected from R, R
1
, and a mixture thereof, “a” is an integer having a value of 2 or 3, “b” is a whole number having a value of 0 or 1, and the sum of a+b is equal to 3, referred to hereinafter sometimes as an “MQ”, or “MQD” resin,
(c) 0.1 to 10 parts of a silicon hydride cross-linking agent, and,
(d) an effective amount of an inhibited platinum group metal catalyst.
An environmentally favorable method for making a shatter resistant incandescent lamp having a substantially transparent tack-free silicone coating on the incandescent lamp bulb, comprising the steps of:
(1) treating the surface of the bulb of the incandescent lamp with the above described substantially volatile organic solvent-free, platinum group metal catalyzed, heat curable silicone coating composition comprising (a),(b), (c) and (d) above, and
(2) heating the treated incandescent lamp at a temperature in the range of about 100° C. to about 180° C. until the silicone treated incandescent lamp bulb surface is substantially tack-free.
An environmentally favorable method for making a shatter resistant incandescent lamp having a substantially transparent dust repellent tack-free silicone coating on the surface of its bulb, comprising the steps of:
(1) treating the surface of the incandescent lamp bulb with the substantially volatile organic solvent-free, platinum group metal catalyzed, heat curable silicone coating composition comprising (a),(b), (c) and (d) above,
(2) heating the treated incandescent lamp at a temperature in the range of about 100° C. to about 200° C. until
Bigio Laurence
Horkay Ferenc
Reisman Juliana Piukaso-Vich
Striker Richard Albert
Uriarte Richard Joseph
Bennett Bernadette M.
General Electric Company
Johnson Noreen C.
Moore Margaret G.
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