Note: Descriptions are shown in the official language in which they were submitted.
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AMBER VEHICLE LAMP
1. Technical Field
The invention relates to electric lamps and
particularly to electric lamps used in vehicles. More
particularly the invention is concerned with a polymer
coating for a vehicle signal lamp.
2. Background Art
Amber vehicle lamp bulbs are commonly used as
signal lamps in motor vehicles. Historically amber bulbs
were made with a cadmium doped glass to produce the amber
color. For environmental reasons, cadmium has become an
unacceptable material. There is now a market need for an
environmentally sound alternative. Various color coated
lamps have been developed, and their initial color can be
acceptable. Given the specified expected ambient operating
conditions for a vehicle, the bulb surface may have a
temperature ranging from -40 to 350 degrees Celsius, so
durability is difficult to achieve. In fact, the color, or
the adherence of the existing coatings, or both have not
been particularly good over time. Elapsed time for an
automotive signal lamp can appear to be relatively long,
while in fact the actual "on" time can be relatively short.
A signal lamp may be on for only minutes in the day of a
vehicle's operation, so the apparent life of the lamp may
appear to be a year or more, when in fact the lamp has only
been on cumulatively for only a few tens or even several
hundred hours or so. In longer use, known coatings have
been found to peel, or turn into a dust that falls off the
bulb. Similarly the color may fade. The lamp color then
departs from the required specification. There is then a
need for an amber bulb coating material that meets standard
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color specifications, and has a durable life.
Disclosure of the Invention
A durable amber colored lamp may be formed from a
lamp bulb having a coating formed from a silane, a clear
silicone-polyester resin, a yellow iron oxide, and a yellow
anthraquinone.
In one broad aspect, the invention provides an
amber color coated incandescent light bulb comprising an
incandescent light bulb with a light transmissive glass
envelope, the envelope coated with an amber color coating
comprising: a clear silicone-polyester polymer; and colorant
comprising red iron oxide and yellow anthraquinone, wherein
the red iron oxide has a particle size less than 0.01 Vim.
In another broad aspect, there is provided a
method of making an amber coated lamp bulb comprising the
steps of: a) providing a lamp bulb with a glass region to be
coated; b) providing a mixture of a yellow iron oxide, and a
yellow anthraquinone, the mixture having an average particle
size of no more than 0.01 ~m to result in a clear colored
coating; c) mixing the yellow iron oxide, and yellow
anthraquinone mixture with a clear silicone-polyester resin;
d) further including in the mixture a polymer solvent being
in sufficient quantity to form a fluid coating material with
a viscosity convenient for application; e) coating the glass
region to be coated with the coating material to a thickness
sufficient to allow passage of light out from the lamp bulb;
and f) heating the coated lamp to a sufficient temperature,
and for a sufficient time period to cure the resin, to
substantially remove the solvent and to form a colored
polymer layer on the lamp.
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Brief Description of the Drawings
FIG. 1 shows a perspective view of a preferred
embodiment of an amber vehicle lamp.
FIG. 2 shows a perspective view of a preferred
alternative embodiment of an amber vehicle lamp.
FIG. 3 shows a perspective view of another
preferred alternative embodiment of an amber vehicle lamp.
FIG. 4 shows a cross sectional view of a coated
lamp envelope, partially broken away.
FIG. 5 shows a chart of the effects over time of
fading on the color coordinates.
Best Mode for Carrying Out the Invention
FIG. 1 shows a perspective view of a preferred
embodiment of an amber vehicle lamp. Like reference numbers
designate like or corresponding parts throughout the
drawings and specification. The amber vehicle lamp 10 is
assembled from a lamp bulb with a coating 12 comprising a
clear silicone-polyester resin, yellow iron oxide, and a
yellow anthraquinone. A silane coupling agent may be
optionally included in the polyester resin. FIG. 2 shows a
perspective view of a preferred alternative embodiment of an
amber vehicle lamp. FIG. 3 shows a perspective view of
another preferred alternative embodiment of an amber vehicle
lamp. FIG. 4 shows a cross sectional view of a coated lamp
envelope, partially broken away. The amber coating 12
covers substantially all of the light transmitting region of
the glass 14 of the bulb.
The preferred incandescent light bulb is a
spherical bulb with a press seal known generally in the
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industry as an S-8. The bulb has a diameter of about
1 inch, and is made of a SG10 type glass, but other glasses,
including unleaded glasses, may
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be used. The filament is supplied with electricity through two leads sealed
thr~gh
the press seal. Similar, two filament, four lead bulbs are also commonly made,
and
may be similarly coated. A base is attached to the press seal region to
provide a
convenient mechanical coupling and electrical connection for the bulb. Several
base
designs are known. The particular choice of the base design is felt to be
matter of
design choice.
Coated on the exterior of the bulb is an amber colored coating 12 that, apart
from the amber color is substantially transparent. The amber color coating
includes
a clear silicone-polyester polymer and colorant combination including yellow
iron
oxide, and yellow anthraquinone. The preferred coating has a weight ratio
composition of 5.0 percent yellow iron oxide, 5.0 percent yellow anthraquinone
with
the remainder being the silicone-polyester resin. Optionally, a silane
coupling agent,
of 0.5 weight percent silane may be included in the silicone-polyester.
The preferred clear resin is a high silicone content polymer, and in
particular,
high silicone silicone-polyester type polymer resin. The Applicants use a high
silicone content polymer available as Silikoftal HTT from Tega Chemie Service
GmbH.
The preferred silane material (optional) includes silicone-polyester linkages.
The Applicants have used a known silane with polyester linkages comprising
gamma-
methacryloxypropyltrimethoxysilane available as Z-6030 from Dow Corning
Corporation. The silane material may be applied separately, or mixed with the
silicone-polyester resin. One recent test procedure indicates that while the
coating
composition that includes the silane material can achieve an existing
specification, the
same composition without the silane results in greater durability. The
composition
with the silane included is now considered a less preferred alternative.
A solvent is mixed with the colorants, silane (optional) and resin in
sufficient
quantity to form a fluid coating material with a viscosity convenient for the
chosen
form of application. Dipping the lamp is one convenient method of applying the
coating. The Applicants prefer spraying, so the mixture needs to be diluted
with the
solvent sufficiently to result in a sprayable fluid. The preferred polymer
solvent is
acetone but others may be used, such as methoxypropylacetate.
The preferred colorant material is a mixture of a yellow iron oxide and an
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anthraquinone. The preferred anthraquinone is Filester yellow RNB, available
from
Ciba Specialty Chemicals and has a more particular chemical formula of 9,10-
arithraceneedione, 1,1'-{(6-phenyl-1,3,5-triazine-2,4diy1)diiminof bis-. The
colorants
are prepared to provide particle sizes of O.OI~.m or less. The very small size
particle
size enables a transparent bulb, that still has an amber color.
The yellow iron oxide colorant may be dispersed in a media mill using
solvent, and milled to the small size. The anthraquinone may be dispersed
separately,
again using a media mill, and milled to the small size (particle sizes of
O.Ol~cm or
less). The two colorants are then combined in the mill, and then milled
together.
The two colorants are then thoroughly mixed. The silane (optional) and
silicone-
polyester resin are then added by using a planetary mixer. A solvent is added
to
achieve the desired viscosity for the chosen form of application. The
resulting
mixture, immediately after mixing, does not necessarily show the proper amber
color.
Nonetheless, the resulting mixture is ready for application to the clean glass
lamp
surface.
The Applicants coat previously manufactured, clear lamp bulbs. The chosen
bulb is known as a 3157 S-8 wedge. The bulbs are held by their bases so the
bulb
portions face down, and the bases and electrical connections are shielded from
any
spray. This leaves the light transmissive portion of the bulb exposed. The
exposed
glass portions of the bulb are then sprayed, bulb side up, with the coating
mixture at
ambient temperature, leaving a thin fluid coating. Alternatively, the exposed
glass
portions may be dipped (bulb down) in the coating material, and any excess
coating
material may drip off. In either case, the viscosity is such that the coating
material
as applied leaves a uniform thin layer which may be approximately 0.0127
millimeters (5.0 10-0inches). Measured variations were about 0.0015
millimeters (5.9
10's inches). This thickness is sufficient to allow light to exit the bulb
with an amber
color that meets the ECE specification for vehicle amber signal lamps.
The coated bulb is then baked at 250 to 300 degrees Celsius for 15 minutes
in a dust free atmosphere to form an amber colored polymer layer. During the
baking process a number of events occur. The colored coating layer is bonded
to the
glass. The yellow iron oxide changes from Fe00H to Fe,02 and which in
combination with the yellow anthraquinone pigment gives the desired amber
color.
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The silicone-polyester polymer is cross linked around the
colorant particles to entrap them in a complex network of
resin material. The baking also drives off any residual
solvent.
5 The resulting coated bulbs were tested and found
to have the following characteristics: The bulb had a thin
hard, transparent amber coating. The amber color meets the
SAE and ECE color coordinate requirements for vehicle amber
signal lamps. In particular, when the bulb is on, it
produces an amber color light with color coordinates (X, Y)
within the 1931 CIE chromaticity region wherein a) 0.398
(the red boundary) is equal to or less than Y, b) Y is also
equal to or less than 0.429 (the green boundary), and c)
0.993 - X is equal to or less than Y (the white boundary).
Coated bulbs (with silane) under test have been operated
continuously for over 840 hours. This is 70 percent of the
rated life of 1200 hours for a 3157 S-8 wedge bulb. Coated
bulbs (with silane) have been found to have complete coating
adherence and a color maintenance of 96 percent measured by
spherical integration methods. Coated bulbs (with silane)
are expected to have a color maintenance of 94.3 percent at
100 percent of rated bulb life.
FIG. 5 shows a chart of the effects over time of
fading on the color coordinates. In this test, the bulbs
were exposed to normal operating environment of 90 flashes
per second for 1315 hours. The initial color coordinates
were approximately, (0.579, 0.415), and after 1315 hours the
color had shifted to approximately (0.573, 0.422). Both the
initial and the final coordinates were within the EC
(region 16) and SAE (region 18) defined regions for amber.
The coated bulbs, with silane and without silane, were
tested according to a schedule of 24 hours of the lamp being
on under varying conditions of heat, and humidity. In
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summary, during the test, the temperature was varied from
-40 to 80 degrees Celsius, with the humidity reaching as
much as 93 percent. Meanwhile, the lamps were turned on and
off according to a schedule. The coated lamps were to
achieve a B10 (90 percent success, 10 percent failure) of 10
cycles (10 days). The bulbs with silane passed with a B10
of about 10 or 12 cycles. The bulbs without the silane
achieved a B10 of 18 cycles. The coated bulb has proven to
have a better amber color, and a longer color maintenance
than any other coated product known to the applicants. The
disclosed operating conditions, dimensions, configurations
and embodiments are as examples
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only, and other suitable configurations and relations may be used to
implemer~,.the
invention.
While there have been shown and described what are at present considered to be
the preferred embodiments of the invention, it will be apparent to those
skilled in the
art that various changes and modifications can be made herein without
departing from
the scope of the invention defined by the appended claims:
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