Sealed lighting element assembly

A sealed or bonded assembly for lighting elements (such as an automobile headlamp) comprising a housing and a cover therefor. The housing and cover have portions (preferably along their respective peripheries) which cooperate to form a seal when a photocurable sealant is disposed therebetween and cured. A preferred photocurable sealant is an epoxy-containing composition, especially one which has been flexibilized by the incorporation of vinyl-terminated acrylonitrile-butadiene polymer.

BACKGROUND OF THE INVENTION 
This invention relates to sealed or bonded assemblies for lighting elements 
and to a novel method for producing same. In another aspect, sealed beam 
lamps and a method for producing same are described. In yet another 
aspect, an actinic light curable composition is utilized to seal a light 
transmissive lens cover to a concave, relfective housing to provide a 
lighting element. 
For many years, the United States Department of Transportation has required 
the use of sealed beam headlamp assemblies on automobiles sold in the U.S. 
These assemblies generally comprise a substantially concave (preferably 
parabolic) lighting element housing and a visible light transmissive cover 
therefor, this cover often being referred to as a lens. The housing 
usually has a concave reflective surface and supports the lighting element 
so as to outwardly direct the light thereby generated through the lens. 
The conventional technique employed to seal a cover (e.g. a lens) to a 
housing involves the application of heat to the respective peripheries 
thereof to fuse or weld the lens to the housing, the lighting element 
being interiorly disposed therein. This conventional technique has a 
tendency to develop internal strain in either the lens or the housing 
(occasionally resulting in breakage of the assembly). The problem of 
breakage has recently become of particular concern due to the now 
fashionable rectangular headlamps employed in the automobile industry. 
Breakage in the range of 10% to 20% has been reported for rectangular 
housing assemblies which are particularly susceptible to generation of 
unequal internal stress during the joining of the housing and its cover by 
the use of heat. 
One possible solution to the aforementioned heat fusing breakage problem 
has been to utilize conventional heat-cured epoxy-containing materials to 
join the perimeters of the housing and the lens. While the temperature at 
which heat-cured epoxy resins may be cured is considerably lower than the 
temperature required to heat fuse the cover and lighting element housing, 
heating the assemblies long enough to bring about epoxy cure is costly. 
SUMMARY OF THE INVENTION 
The present invention provides a sealed assembly for a lighting element 
which overcomes the problems associated with conventional sealing methods 
which require the application of heat. The method of the present invention 
has the additional advantage of having the potential to provide lighting 
element assemblies where the housing or its cover, or both, are comprised 
of heat sensitive polymeric materials such as polymethylmethacrylate and 
polycarbonate. 
In one aspect, the present invention provides a method for sealing a 
lighting element comprising the steps of: 
a. providing a housing and a cover therefor, at least a portion of said 
housing or said cover being light transmissive, said housing or said cover 
being adapted to support a lighting element within said enclosure so that 
said element may be electrically energized, said housing and said cover 
having cooperating portions which are adapted to be joined with a actinic 
light curable adhesive; 
b. placing on one or both said cooperating portions a quantity of actinic 
light curable adhesive sufficient to form a seal between said housing and 
said cover when said sealant is cured; 
c. bonding said cover to said housing at said cooperating portions by 
curing said adhesive therebetween with actinic light. 
In a preferred practice of the present invention an actinic light curable 
epoxy-containing composition is employed to seal the housing to its cover. 
In the most preferred practice of this invention, an actinic light curable 
epoxy-containing composition having improved flexibility by the 
incorporation therein of vinyl-terminated acrylonityrile-butadiene polymer 
is utilized to provide the sealed enclosure. This composition is the 
subject of applicant's copending application Ser. No. 20,312 entitled 
"Photocurable Epoxy Composition Having Improved Flexibility", and 
incorporated by reference herein. 
The sealed enclosure for a lighting element produced in the practice of the 
present invention comprises a housing and a cover therefor. At least a 
portion of the housing or the cover must be visible light transmissive (to 
permit light egress from said lighting element) and either the housing or 
the cover must be adapted to support a lighting element within the 
enclosure, preferably so that said lighting element may be exteriorly 
energized, such as by means of leads passing through said housing to a 
source of electricity. Further, the housing and the cover have cooperating 
portions (usually on their respective peripheries) which are adapted to be 
joined with an actinic light curable adhesive. Disposed between the 
cooperating portions of the housing and the cover is a photocured 
composition which is preferably derived from an actinic light curable 
epoxy-containing composition, especially one which also includes therein 
vinyl-terminated acrylonitrile butadiene polymer. 
The present invention contemplates the joining or sealing of all manner of 
housings and covers therefor which cooperate to provide a lighting element 
enclosure. The sealed assembly or enclosure may be adapted to receive a 
lighting element (i.e. the assembly may have replaceable lighting 
elements) or the enclosure may already have the lighting element supported 
or mounted within. Optionally associated with the assemblies of the 
invention is a reflector means. In a preferred practice of the invention a 
concave, interiorly reflective housing (including therein a lighting 
element) is joined to a generally flat transparent cover or lens so as to 
provide a hermetic lighting element enclosure. The cover may, of course, 
have a curved surface or body if desired.

DETAILED DESCRIPTION OF THE INVENTION 
Thus in FIG. 1 there is shown an enclosed lighting element assembly 10 
which is useful, for example, as an automobile headlamp. In the embodiment 
depicted the assembly comprises a generally concave housing 12 and a 
cooperating transparent cover or lens 14 therefor. 
Housing 12 is interiorly reflective, (i.e., having a concave reflective 
surface) there being a thin metal vapor deposited coating 16 (e.g. 
aluminum) therein. Also disposed within the housing is a lighting element 
or capsule 18 which comprises a transparent envelope 20 having therein a 
filament 22. Filament 22 is connected by leads 24 and 26 to the exterior 
backside of housing 12, there being hermetic seals around leads 24 where 
they exit envelope 20 and where leads 26 exit through the backside of 
housing 12. Leads 26 may in turn be connected to an external source of 
electrical energy such as an automobile alternator (not shown) which 
provides electrical energy to cause filament 22 to incandesce. "Lighting 
element" as the term is used herein is meant to include the light 
producing capsules shown herein, open filaments (i.e. metallic filaments 
without an envelope), and various bulbs which are optionally replaceable. 
The capsule 18 shown herein when manufactured from quartz and having 
therein an amount of a halogen gas, (e.g. bromine) is referred to in the 
art as a quartz-halogen capsule. The backside of housing 12 may be adapted 
to be fitted into the front portion of an automobile (such as by support 
means 28) to provide illumination therefor. 
Around the periphery of housing 12 is a substantially male cooperating 
surface 30 which cooperates with a female surface 32 around the periphery 
of transparent cover 14. Cooperating surfaces 30 and 32 are adapted to 
form a joint therebetween when suitably affixed to each other. 
Conventionally, of course, cooperating surfaces 30 and 32 would be heat 
fused to each other. As more clearly seen in FIGS. 2 and 3, in a practice 
of this invention a quantity or bead 34 of actinic light curable sealant 
or adhesive is disposed along the entire length of either of cooperating 
surfaces 30 and 32 usually after cleaning the cooperating surfaces using a 
volatile solvent such as methylethyl ketone. Application techniques 
include syringes, manual or air-operated caulking guns or automated 
sealant application techniques. After the sealant has been disposed along 
either of the peripheries (to a coverage generally in the range of 0.01 to 
0.3 grams sealant per lineal inch of periphery), the cooperating surfaces 
are mated so as to dispose the sealant/adhesive therebetween. 
After the cooperating surfaces have been mated, cure of the sealant 
therebetween is initiated by exposing the sealant to actinic light. The 
sealant may be exposed to actinic light (e.g., for a period of 5 to 300 
seconds) by directing an actinic light source, (e.g. a medium pressure 
mercury vapor lamp) through lens 14 (if the lens is appropriately 
transmissive to actinic light). Alternatively, actinic light may be 
focused laterally around the outside of the assembly coplanar with the 
sealant to expose the exteriorly disposed sealant to radiation. In either 
case the completed assembly will appear in cross-section substantially as 
shown in FIG. 3, with the cured adhesive 34' between the cooperating 
portions. 
In a further practice of the present invention, a delayed curing 
epoxy-containing composition is employed. In this method, the delayed 
curing epoxy-containing composition is applied to one or the other or both 
of the cooperating portions and exposed to actinic light for a brief 
period of 0.02 to about 10 seconds. At this point, the cooperating 
portions are brought together and maintained in registration until the 
epoxy composition cures to form a seal. The time required for the delayed 
curing epoxy to completely cure is generally from 30 seconds to 24 hours. 
The use of the delayed curing epoxy-containing composition is particularly 
advantageous in those situations where actinic light absorptive substrates 
(e.g., metals and various polymers) are joined. As more completely 
described in applicant's above noted copending application, the 
polyoxyalkylene mono, di, or polyepoxides, such as polyoxypropylene 
diepoxide, are a particularly useful class of delayed curing epoxides 
especially when used in admixture with other epoxy-containing materials. 
FIGS. 4, 5, 6 and 7 depict alternative configurations or designs for the 
cooperating surfaces of the cover or the housing. FIGS. 4 and 5 show a 
tongue 40 and groove 42 arrangement (uncured sealant 34 and cured sealant 
34' being disposed therebetween) while FIGS. 6 and 7 show lapping sections 
46, 46', 48 and 48' which overlap to form lap joints. 
Of particular note in FIGS. 4 through 7 are protrusions or spacers 44 which 
have been molded into one or the other of the cooperating surfaces which 
form the joints. These spacers are molded into the material of the housing 
(or cover), there being from 6 to 10 generally hemispherical spacers 
evenly distributed around the perimeter formed by the cooperating 
surfaces. The spacers project above the adjacent surface from which they 
are molded to a height generally equal to the desired thickness of the 
sealant 34 which is to be disposed between the cooperating portions. A 
sealant thickness of about 0.010 inch (250 micrometers) is usually 
desirable and hence the height of the spacers is preferably about 0.010 
inch (250 micrometers) with spacer height in the range of about 0.002 inch 
(50 micrometers) to 0.050 inch (1250 micrometers) being contemplated. The 
spacers serve to provide a uniform sealant thickness as well as reducing 
the difficulty of obtaining proper registration between housing and its 
cover. Proper registration and sealant thickness between the housing and 
its cover is obtained merely by pressing the housing and its cover 
together until the spacers engage the opposing cooperating surface. 
The sealant which is preferred in the practice of the present invention is 
an actinic light curable epoxy composition having improved flexibility, 
the composition comprising in admixture: 
a. epoxy-containing material; 
b. vinyl-terminated acrylonitrile-butadiene polymer, and; 
c. actinic-light-activatable epoxy cure initiator, the composition 
optionally including therein; 
d. hydroxyl-containing organic material and 
e. filler. 
Preferably the composition used in this invention comprises: (a) 100 parts 
by weight epoxy-containing materials, (b) 5 to 200 parts by weight 
vinyl-terminated acrylonitrile-butadiene polymer, (c) 0.5 to 80 parts by 
weight actinic-light-activatable epoxy cure initiator, (d) 5 to 400 parts 
by weight of hydroxyl-containing organic material, (e) 0.5 to 100 parts by 
weight adhesion promoter and (f) 0.5 to 400 parts by weight filler. 
It is especially important (where glass to glass bonds are being formed) 
that the sealants used herein include 0.5 to 100 parts by weight (based 
upon 100 parts by weight epoxy-containing material), preferably 5 to 50 
parts by weight adhesion promoter. By "adhesion promoter" herein it is 
meant a material which has an affinity for both the substrate and the 
adhesive, sealant or coating being used. For example, conventional silane 
compounds such as beta-3,4-(epoxycyclohexyl)ethyltrimethoxy-silane, and 
gamma glycidoxypropyltrimethoxysilane, (both commercially available from 
Union Carbide Corporation under the trade designation "A-186" and "A-187" 
respectively) can be utilized as adhesion promoters where a glass-to-glass 
bond is intended. Other adhesion promoters or primers are well known to 
those skilled in the art. 
The sealed lighting assemblies produced in the practice of the present 
invention are sufficiently integral so that they may be evacuated or 
pressurized. A dry inert gas such as dry air or nitrogen at atmospheric 
pressure may be introduced into the housing if substantially ambient 
pressure inside the housing is desired. In operation interior temperatures 
of the housing may reach 200.degree. F. to 250.degree. F. (90.degree. C. 
to 120.degree. C). These temperatures are easily withstood by the present 
assemblies, there being no significant adhesive degradation. 
Objects and advantages of this invention are illustrated in the following 
examples which should not be construed to limit the scope of this 
invention. All parts are by weight unless otherwise specified. 
EXAMPLE 
Illustrating the preparation of an assembly of the invention. 
A 1/2 pint (250 ml) epoxy-lined friction top metal container (a 
conventional paint container) metal container was charged with 71.8 g of 
cycloaliphatic epoxy "ERL 4221", 30 g of previously melted (heated to 
about 160.degree. F., 70.degree. C.) polytetramethyleneether glycol 
"Polymeg 1000", 10 g vinyl terminated acrylonitrile-butadiene polymer 
"Hycar 1300.times.23", 10 g gamma-glycidoxypropyltrimethoxy silane "A187" 
and 11.7 g of a 30% by weight solution of triarylsulfonium 
hexafluoroantimonate in "ERL 4221". The room temperature mixture was 
maintained under normal lighting conditions (i.e., in the absence of 
sunlight) and was stirred at low speed using an air driven 4 bladed 
impeller ("High Lift" 1.5 inch diameter impeller commercially available 
from M. F. Fawcett Company) until a uniform mixture was obtained, e.g., 5 
min. Four grams of fumed silica ("Cab-O-Sil") was added to the admixture 
while increasing the impeller speed to ensure complete dispersal of the 
silica, thus completing the formulation of the composition. At this point 
the composition was degassed in a vacuum chamber by evacuating to a 
pressure of about 1 psi (6.9 kPa), this pressure being maintained for 30 
minutes at which time no further dissolved gas evolved from the admixture 
(i.e., bubbling ceased). A dry nitrogen line was attached to an inlet to 
the vacuum chamber and the chamber was backfilled to atmospheric pressure. 
The composition then was removed from the vacuum chamber. The cooperating 
peripheral portions of an assembly depicted in FIG. 1 were cleaned using a 
clean dry cloth saturated with methylethyl ketone. The photocurable 
mixture was drawn into a disposable 3 cc syringe. The syringe was fitted 
with an 18 gauge by two inch hypodermic needle. Using the filled syringe 
and needle the photocurable mixture was applied to the cooperating portion 
of the housing of the headlamp assembly. The lens portion of the assembly 
was positioned over the peripherally coated housing, the cooperating 
portions of the housing and the cover being brought together with the 
photocurable composition therebetween. The composition spreads uniformly 
over (coats or wets) both cooperating portions to form a seal. The 
assembly then was irradiated by exposure to a 200 watt/inch mercury vapor 
lamp for a period of 30 seconds. Distance from the arc tube to headlamp 
lens was 5 inches. The arc tube was parallel to the long dimension of the 
headlamp and equidistant from the two long sides of the lens. Exposure was 
through the lens of the headlamp assembly. 
Various modifications and alterations of the invention will become apparent 
to those skilled in the art without departing from the scope and spirit of 
the invention, and it should be understood that this invention is not to 
be limited to the illustrative embodiments and examples set forth herein.