Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
TITLE OF THE INVENTION
LIGHT EMITTING APPARATUS AND METHOD FOR CURING INKS,
COATINGS AND ADHESIVES
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to a method and apparatus for utilizing
ultraviolet (UV)
light emitting diodes in staggered arrays and mechanisms for moving the arrays
to avoid "hot
spots" and provide a uniform application of ultraviolet light to a moving
object including
inks, coatings or adhesives having UV photo initiators for converting, when
exposed to UV
light, monomers in the inks, coatings or adhesives to linking polymers to
solidify the
monomer material. Also, an inert, non-oxygen, gas is injected into the area
where the
staggered arrays of ultraviolet light emitting diodes, UV-LED's are positioned
to apply UV
light to the moving objects to enhance the curing of the ultraviolet activated
UV photo
initiators.
2. Description of the Prior Art.
Heretofore, ultraviolet lamps have been used for the curing of ultraviolet
inks,
coatings and adhesives.
More recently, EXFO and EFOS of Mississauga, Ontario, Canada have developed UV
light emitting diodes (LED's) and gathered them in large numbers for use in
curing ultraviolet
light sensitive monomers to polymerize the monomers and solidify the ink,
coating or
adhesive.
While the.use of a large number of UV-LED's provide many efficiencies, namely
in
cost and energy consumption, there is still the problem of effective curing
with low intensity
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UV-LED's and with respect to "hot spots" which provide more curing at "hot
spots" then at
other locations in the ink, coating or adhesive being cured.
Also, in the UV-LED prior art, the LED is positioned to achieve uniformity for
back
light displays and other lighting applications. The criteria for such
uniformity are primarily
designed to create an appearance that the backlight is uniform for a visual
appearance.
It is, therefore, desirable to provide an improved UV method and apparatus for
applying UV light emitted from UV LED's more uniformly and avoid hot spots to
more
effectively cure UV inks, coatings and adhesives.
BRIEF SUMMARY OF THE INVENTION
As will be described in greater detail hereinafter, the method and device of
the present
invention provide techniques and structures for applying UV light emitted from
UV-LED's
more uniformly so that such light is more effective in curing inks, coatings
and adhesives
and, by applying the UV light more evenly, reducing, if not all together
eliminating, "hot
spots".
According to the present invention there is provided staggered arrays of UV
LED
assemblies on a panel with the UV LED assemblies being arranged in rows with
each row
being staggered from adjacent rows.
In addition to the staggering of the UV LED assemblies in adjacent rows, a UV
curable product, article or other object having a UV ink, coating or adhesive
to be cured, is
moved on or in a web past, and closely adjacent, the arrays.
Further, the panel is moved or translated in an X direction and in a Y
direction, much
like an orbital sander, thereby to cause a slight sweeping of the light from
each UV LED
assembly over an orbital area, e.g., in a circular or elliptical pattern,
thereby minimizing the
creation of "hot spots" and to uniformly apply UV light to the product,
article or other object
having the UV ink, coating or adhesive.
In one preferred embodiment, the web containing the UV curable product,
article or
other object to be cured is arranged to move vertically. A gas having a
molecular weight
heavier than air can be injected at the upper end of the path of movement of
the UV curable
product, article or other object having a UV ink, coating, or adhesive thereon
as it moves past
a panel of arrays of UV LED assemblies. Furthermore, a gas having a molecular
weight
lighter than air can be injected at the lower end of the path of movement of
the UV curable
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product, article or other object having a LJV ink, coating or adhesive thereon
as it moves past
the panel of arrays of UV LED assemblies.
The method and apparatus of the present invention provide uniformity, of light
application from a flat panel having an array of UV-LED's. This result is
obtained when the
product and/or the light fixture is moved relative to and across the UV light
beams from the
UV-LED assemblies. This movement in of itself has the ability to offer one
element of
uniformity. That is, the movement of the product or the movement of the light
array
addresses the problem of providing uniformity in the direction of the product
flow or of the
lamp movement.
The "X Axis" uniformity is addressed by the movement of the product or of the
LED
array.
The "Y Axis" uniformity is addressed by how the LED chips are arranged. To
achieve
the cure rates that are associated with typical UV curing applications, a very
large number of
UV-LED chips are arranged to deliver, the amount of UV energy necessary to
cure the
polymers.
The first step in building these arrays is to create either a series or
parallel electrical
circuit either in series or in which the LED chips are placed in a linear
fashion of equal
distance from each other. (Lets say a distance of X). The second row would
start its row at a
distance %2 X and each LED chip would then be spaced from adjacent LED chips
in the row
by the distance X.
The third row would start at a distance %2 X in from the start of the second
row. This
offset would continue for each row of LED chips in the array. Two things
happen when this
is done. First the light uniformity is increased because of the alternating
position of the UV-
LED chips. This creates an overlap of light emissions. Then, having each row
begin half the
distance of the row it precedes will create a stair case effect. This will
allow uniformity in the
Y Axis as the array grows in size.
There is another way to position the LED chips, and achieve the same
uniformity.
This would be to use 3 rows to achieve the uniformity. That is, to have the
LED chips
arranged at a distance of X, and to have the next row (row 2) start at a
distance 1/3 in from
the start of the first row and the next row (row 3) start at a distance 2/3 in
from the start of the
first row or at a distance 1/3 in from the start of the second row.
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Still another way is to provide 4 rows to create the uniformity, with the LED
chips in
the first row being spaced at a distance of X from each other. The second row
starts its first
LED chip at a distance '/4 X in from the first LED chip in the first row. The
third row starts
its row at a distance '/2 X in from the first LED chip in the first row or at
a distance '/4 X in
from the start of the previous row.
The method and apparatus of the present invention also address a very large
number
of LEDs that are mounted in long multiple rows, and still have a uniform
distribution of light.
Additionally, in situations where UV curable ink or adhesive may splatter onto
the
array of LED's, a thin transparent plastic sheet or layer is positioned over
the array to protect
the array, and the sheet or layer is periodically cleaned or replaced.
A more detailed explanation of the invention is provided in the following
detailed
description and claims taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan elevational view of an LTV LED assembly including a pad
for a
cathode and an anode mounting an UV LED chip in accordance with the teachings
of the
present invention;
FIG. 2 is a top plan elevational view of a design of mating building blocks or
substrates which can be blank or have an anode and cathode mounted thereon in
accordance
with the teachings of the present invention;
FIG. 3 is a front elevational view of one array of UV LED assemblies wherein
rows of
UV LED assemblies are arranged in the array with alternate rows of UV LED
assemblies in
one row being staggered from the UV LED assemblies in the adjacent rows in
accordance
with the teachings of the present invention;
FIG. 4 is front elevational view of a panel of six arrays of UV LED assemblies
shown
in FIG. 3 in accordance with the teachings of the present invention and shows
schematically a
first eccentric cam which moves against one side edge of the panel against a
spring at the
opposite side edge of the panel so as to move, reciprocate or translate the
panel in an X
direction and a second eccentric cam which acts against an upper edge of the
panel and
against a spring bearing against a lower edge of the panel to cause movement
of the panel in
the Y direction and thereby cause all the arrays to move in a orbital,
circular, or elliptical path
when the first and second cams are rotated about their axes;
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FIG. S is a block schematic diagram of a web made of, or carrying products,
articles
or other objects to be UV cured trained over rollers to move in a generally
vertical path past
the panel of arrays of UV LED assemblies shown in FIG. 4 such that the
products, articles or
other objects with UV photo initiators therein can be cured as each product,
article or other
object moves past the arrays of UV LED assemblies while a non-oxygen, heavier
than air gas
is injected from a gas tube located near the top of the path of movement of
the web; and
FIG. 6 is a block schematic view of a web made of, or carrying, products,
articles or
other objects to be UV cured trained over rollers to move in a generally
vertical path past the
panel of arrays of UV LED assemblies shown in FIG. 4 such that each product,
article or
other object with UV photo initiators therein can be cured as each product,
article or other
object moves past the arrays of UV LED assemblies while a non-oxygen gas is
injected from
a gas tube located near the bottom of the path of movement of the web.
FIG. 7 is a plan view of another way of positioning UV LED assemblies in at
least
three rows where the spacing between UV LED assemblies in each row is
increased to
establish a three tier staggering of UV LED assemblies.
DETAILED DESCRIPTION OF THE INVENTION-
A detailed description of the preferred embodiments and best modes for
practicing the
invention are described herein.
Refernng now to the drawings in greater detail, there is illustrated in FIG. 1
a prior art
ultraviolet light-emitting diode (UV LED) assembly 10 including a cathode pad
12 and an
anode 14 mounting a chip 16, which comprises a UV LED chip 16. Each cathode
pad 12
(FIG. 1 ) is connected to a wire conductor as is each anode 14.
Referring now to FIG. 2, there is illustrated therein a building block 20
having a first
array 21 of the UV LED assemblies 10 thereon, namely, pads 12 and anodes 14,
which
provide a plurality of UV LED chips 16. The building block 20 is designed to
mate with
similar building blocks to form a group 22 of arrays 21, 23 and 25 as shown in
FIG's 3 and 4.
In this way, several of the blocks 20 can matingly engage each other and be
arranged in a
pattern ( e.g. like tiles on a floor) on a panel 28 (FIG. 4).
As shown in FIG. 3, the UV LED assemblies 10 in each array 21, 23 and 25 are
spaced apart in a first lower row 36 of UV LED assemblies 10. Then, in a
second adjacent
row 38, the UV LED assemblies 10 are arranged in a staggered manner so that
they are
located above the spaces between the UV LED assemblies 10 in the first row. In
the same
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manner, the next upper row 40 of UV LED assemblies 10 is staggered and a total
of twenty
(20) staggered rows are provided in the UV LED array 21 shown in FIG. 3.
Also, as shown in FIG. 3 the beginning of the first UV LED assembly 10 in the
lowest
row 36 in the first array 21 is aligned with the end of the last UV LED
assembly 10 at the end
of the lowest row 42 in the second, lower left, array 23.
Then, the beginning of the first UV LED assembly 10 in the uppermost row 44 in
the
first array 21 is aligned with the end of the last UV LED assembly 10 in the
uppermost row
46 in the second, lower left array 23. Next, the end of the last UV LED
assembly 10 in the
lowest row 36 in the first array 21 is aligned with the beginning of the first
UV LED
assembly 10 in the lowest row 48 in the third, lower right array 25. Finally,
the end of the last
UV LED assembly 10 in the uppermost row 44 in the first array 21 is aligned
with the
beginning of the first UV LED assembly 10 in the uppermost row 49 in the
third, lower right
array 25, as shown in FIG. 3.
As shown best in FIG. 4, the three arrays 21, 23 and 25 can be arranged on the
panel
28 in a staggered manner so that the UV light from each UV LED assembly 10 is
not only
spaced and staggered relative to adjacent rows in the array but also spaced
and staggered
relative to the rows in the other arrays. Also more than three arrays 21, 23
and 25 can be
provided, such as six arrays, not shown.
Also shown in FIG. 4, are mechanisms, preferably eccentric cams 50 and 52,
that can
be provided for moving, translating or reciprocating the panel 28 back and
forth in the X
direction and up and down in the Y direction, much like in an orbital sander.
The first, x
axis, eccentric cam 50 is mounted for rotation about a shaft 54 to act against
one side edge 56
of the panel 28 with a spring 58, such as a helical tension spring, positioned
to act against the
other side edge 60 of the panel 28.
Then the second, y axis, eccentric cam 52 (FIG. 4) is mounted for rotation on
a shaft
64 to act against an upper edge 66 of the panel 28 against the action of a
spring 68, such as a
helical tension spring, positioned to act against a lower edge 70 of the panel
28.
Rotation of the shafts 54 and 64 (FIG. 4) each by a prime mover such as a
variable
speed motor (not shown) can cause the panel 28 to move in a generally orbital,
annular,
circular, or elliptical path of movement. This will result in orbital movement
of each UV
LED assembly 10 in each of the rows in each of the arrays 21, 23 and 25
mounted on the
panel 28 so as to spread out the emitted UV light and uniformly apply the UV
light to the
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products, articles or other objects to be UV cured. This spreading of the UV
light also
minimizes, if not altogether eliminates the creation of, so called "hot spots"
of UV light .
As shown in FIG. 5, where a schematic block diagram of one UV curing
apparatus,
assembly, mechanism or device constructed according to the teachings of the
present
invention is shown, the panel 28 of UV LED arrays 21, 23 and 25 is positioned
generally
vertically and closely adjacent the path of movement of a conveyor belt
comprising web 74
which is trained over rollers 76, 78 and 80 to move generally upright and
vertically past and
closely adjacent and in proximity to the panel of UV LED arrays 21, 23 and 25.
For this
purpose, at least one of the rollers 76, 78 and/or 80 of a conveyor can be a
drive roller.
UV curable products, articles or other objects, such as labels, positioned in
or on the
web 74 (FIG. 5), can have one or more UV curable inks, coatings and/or
adhesives between a
plastic cover layer and the label. The UV curable ink, coating, and/or
adhesive can have UV
photo initiators therein which will polymerize the monomers in the UV curable
ink, coating,
or adhesive when subjected to UV light within a predetermined UV wavelength
range.
The UV curable ink, coating and/or adhesive is preferably located on the side
of the
web 74 (FIG. 5) that is closest to and faces the panel 28. Preferably, the
spacing between the
UV LED assemblies and the ink, coating or adhesive is between 0.001 inch and
0.3 inch to
enhance the effectiveness of the UV emitted light which dissipates
exponentially as the
distance to the product, article or other UV curable object to be treated
increases.
Preferably, the shafts 50 and 52 (FIG. 4) are rotated to cause orbital
movement of the
panel 28 and UV LED assemblies as the web 74 containing the product, article
or other UV
curable object moves past the panel 28. Such movement also minimizes "hot
spots" and
provide uniform sweeping, distribution, and application of the UV light from
the UV LED
assemblies 10.
The block schematic diagram of the assembly or device, shown in FIG. 5 is
provided
to minimize exposure of the products, articles or other objects during curing
to oxygen, which
inhibits UV curing. A gas tube 84 providing an upper gas injection is provided
on the
assembly and device for injecting heavier-than-air, non-oxygen-containing gas,
e.g., carbon
dioxide, near an upper end 86 of a path of downward movement, indicated by the
arrow 88,
of the web 74, so that the gas can flow downwardly in the space between the
panel 28 and the
web 74 to provide an anaerobic area between the UV LED assemblies 10 on the
panel 28 and
the web 74 having UV curable products, articles or other objects to be cured.
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A wiper blade 90 (FIG. S) providing a lower inhibitor go can be positioned
adjacent
the lower edge 70 of the panel 28 for holding, compressing, collecting and/or
blanketing the
gas in the area between the orbiting UV LED arrays 21, 23 and 25 (FIG. 4) and
the moving
web 74 (FIG. 5). Preferably the wiper blade 90 is fixed to the lower edge 70
of the panel 28
and has an outer edge 92 that is positioned to wipe against the moving web 74.
In this way,
the injected gas can be inhibited from escaping the curing area.
FIG. 6 is a block schematic diagram of a UV curing apparatus, assembly,
mechanism
or device constructed according to the teachings of the present invention
where the moving
web 74 is trained about rollers 94, 96 and 98, at least one of which can be a
drive roller, to
cause the web 74 with the UV curable products, articles or other objects
thereon or therein to
move upwardly, as shown by the arrow 100, past the panel 28 mounting arrays
21, 23 and 25
(FIG. 4) of UV LED assemblies, much the same as in the UV curing apparatus,
assembly and
device shown in FIG. S.
In the apparatus, assembly or device shown in FIG. 6, a gas tube 104 providing
a
lower gas injector is positioned near a lower end 106 of the path 100 of
movement of the web
74 for injecting an inert lighter-than-air, non-oxygen-containing gas, e.g.,
helium, in the area
between the orbiting panel 28 (FIG. 4) and the upwardly moving web 74 (FIG. 6)
thereby
provide an anaerobic area to enhance and facilitate curing of the UV photo
initiators in the
UV curable products, articles or other objects that are carried by the web 74.
A wiper blade 108 (FIG. 6) providing an upper inhibitor 108 is positioned near
the
upper edge 68 of the panel 28 as shown in FIG. 6 to minimize the escape of the
lighter-than-
air gas and hold, compress, collect and/or blanket the injected gas in the
curing area between
the orbiting panel 28 (FIG. 4) and the moving web 74 (FIG. 6), much the same
as in the UV
curing apparatus, assembly and device shown in FIG. 5. Again, the wiper blade
108 (FIG. 6)
can be fixed to the upper edge 68 and arranged to wipe against the web 74.
To avoid overheating the UV LED assemblies 10, i.e., to control the heat
generated by
the UV LED assemblies 10, the power supplied to the UV LED assemblies can be
periodically or sequentially activated and deactivated, i.e. can be turned on
and off, at a
relatively high frequency. Also, the duty cycle of the on-off cycle can be
varied to adjust the
UV light intensity.
In FIG. 7 is illustrated another way to position the UV LED assemblies,
namely, the
LED chips 16, and achieve the same uniformity as shown in FIG's. 2 and 3. This
would be to
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use 3 rows to achieve the uniformity. That is, to have the LED chips 16 in a
first row 112
arranged at a distance of X, and to have the next row 114 (row 2) start at a
distance 1/3 in
from the start of the first row 112 and the next row 116 (row 3) start at a
distance 2/3 in from
the start of the first row 112 or at a distance 1/3 in from the start of the
second row 114.
It will be understood that the space X can be equal to the width of 1, 2, 3,
4, 5, etc. of
an UV LED assembly 10 to provide a desired staggering of the light beams from
the UV LED
assemblies 10.
Also, in situations where UV curable ink or adhesive might splatter on the UV
LED
assemblies 10, a clear/transparent sheet or layer of plastic material can be
placed over the
arrays 21, 23 and 25 to protect the UV LED assemblies 10. Then, the sheet or
layer is
cleaned or replaced periodically.
From the foregoing description it will be apparent that the method and device
of the
present invention have a number of advantages, some of which have been
described above
and others of which are inherent in the invention. For example, the panel 28
of UV LED
assemblies 10 can be arranged closely adjacent the web 74 carrying UV curable
products,
articles or other objects which enables UV light from UV LED assemblies 10 to
better effect
curing of the UV curable ink, coating and/or adhesive.
. Further, the moving of the web 74, carrying the UV curable products,
articles or other
objects past staggered rows of UV LED assemblies 10 in staggered arrays 21, 23
and 25 of
UV LED assemblies 10 on the panel 28 ensures uniform application of UV light
to all of the
ink, coating and/or adhesive to be cured in the UV curable product, article or
object.
Still further, the oscillating or orbital movement of the UV LED assemblies 10
adjacent the moving web containing the UV curable products, articles or other
objects to be
cured ensures a more uniform sweeping of the UV light over the UV curable
products,
articles or other objects on or in the web 74.
Finally, the application of a heavier-than-air or a lighter-than-air, non-
oxygen-
containing gas to the area between the oscillating or orbiting panel 28 of UV
LED assemblies
and the web 74 carrying the UV curable products, articles or other objects
having
monomer material to be cured or polymerized enhances the emission and
application of more
uniform UV light upon the UV curable products, articles, or other objects.
Although embodiments of the invention have been shown and described, it will
be
understood that various modifications and substitutions, as well as
rearrangements of
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components, parts, equipment, apparatus, process (method) steps, and uses
thereof, can be
made by those skilled in the art without departing from the teachings of the
invention.
Accordingly, the scope of the invention is only to be limited as necessitated
by the
accompanying claims.
