U.S. patent application number 09/804160 was filed with the patent office on 2001-07-26 for method and apparatus for embossing a precision pattern of micro-prismatic elements in a resinous sheet or laminate.
This patent application is currently assigned to Avery Dennison Corporation. Invention is credited to Pricone, Robert M., Thielman, Scott W..
Application Number | 20010009172 09/804160 |
Document ID | / |
Family ID | 22868151 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009172 |
Kind Code |
A1 |
Thielman, Scott W. ; et
al. |
July 26, 2001 |
Method and apparatus for embossing a precision pattern of
micro-prismatic elements in a resinous sheet or laminate
Abstract
An improved method and apparatus is provided for continuously
embossing a precision pattern of micro-prismatic elements on a
surface of a resinous sheeting material with the aid of an endless
metal embossing belt. The method includes the steps of moving the
belt along a closed path through a heating station and a cooling
station, conveying superimposed resinous film and sheeting material
into proximity with the belt, passing the film and sheeting between
the belt and a series of sonic welding heads to thereby begin to
impress a pattern of micro-prismatic formations of the belt into
one surface of the sheeting, pressing the film and sheeting against
the heated belt until the one surface of the sheeting fully
conforms to the embossing pattern, and stripping the film and
embossed sheeting from the belt.
Inventors: |
Thielman, Scott W.;
(Palatine, IL) ; Pricone, Robert M.;
(Libertyville, IL) |
Correspondence
Address: |
JONES, DAY, REAVIS & POGUE
77 West Wacker Drive
Chicago
IL
60601-1692
US
|
Assignee: |
Avery Dennison Corporation
|
Family ID: |
22868151 |
Appl. No.: |
09/804160 |
Filed: |
March 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09804160 |
Mar 12, 2001 |
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09231197 |
Jan 14, 1999 |
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6200399 |
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Current U.S.
Class: |
156/73.1 ;
156/209; 156/498; 156/499; 156/553; 156/555; 156/580.2;
264/1.9 |
Current CPC
Class: |
B29C 59/046 20130101;
B29L 2011/0083 20130101; B29C 66/81465 20130101; B29C 2791/008
20130101; Y10T 156/1741 20150115; G02B 5/124 20130101; Y10T
156/1023 20150115; B29C 2059/023 20130101; B29C 66/81469 20130101;
B29C 65/00 20130101; B29C 59/022 20130101; B29C 66/024 20130101;
B29C 65/00 20130101; B29C 66/81469 20130101; B29K 2995/003
20130101; B29C 66/81465 20130101; B29L 2009/00 20130101; Y10T
156/1737 20150115 |
Class at
Publication: |
156/73.1 ;
156/209; 156/498; 156/499; 156/553; 156/555; 156/580.2;
264/1.9 |
International
Class: |
B32B 031/16; B29D
011/00 |
Claims
What is claimed is:
1. A method for continuously embossing a precision pattern of
micro-prismatic elements on one surface of a continuous resinous
sheeting material, the method being performed with the aid of a
generally cylindrical metal embossing element having an inner
surface and an outer surface, the outer surface having a precision
embossing pattern which is the reverse of the precision pattern to
be formed on one surface of said sheeting, and wherein the method
includes the steps of: (a) continuously moving the embossing
element through a heating station where said embossing element is
heated to a predetermined temperature and then to a cooling station
where said embossing element is cooled below said predetermined
temperature; (b) continuously conveying into proximity with said
embossing element superimposed resinous film and at least one layer
of sheeting material, said resinous materials of said film and said
sheeting each having different glass transition temperatures; (c)
continuously passing said superimposed resinous film and sheeting
between said embossing element and at least one sonic welding head
with one surface of said sheeting confronting and engaging said
precision pattern of said embossing element to thereby begin to
impress said pattern into said sheeting; (d) heating said embossing
element to said predetermined temperature at said heating station,
said temperature being greater than the glass transition
temperature of said sheeting and less than the glass transition
temperature of said resinous film; (e) pressing said superimposed
film and sheeting against said embossing element at a plurality of
pressure points sequentially spaced along said heating station with
said one surface of said sheeting confronting and engaging said
precision pattern of said embossing element until said one surface
of said sheeting fully conforms to said precision embossing
pattern; and (f) continuously stripping said superimposed layer of
film and embossed sheeting from said embossing element.
2. The method according to claim 1, including the step of
preheating said resinous film prior to passing said film and
sheeting between said embossing element and said at least one sonic
welding head.
3. The method according to claim 1, including the step of cooling
said superimposed film and sheeting prior to stripping said film
and sheeting from said embossing element.
4. The method according to claim 1 wherein said path is
substantially cylindrical through said heating station and said
pressure points are provided by at least three spaced pressure
rollers.
5. The method according to claim 1 wherein said precision pattern
is in the form of an array of female microcube corner type elements
whereby the sheeting formed thereby has male microcube corner
elements on one face thereof;
6. The method according to claim 1 wherein said at least one sonic
welding head vibrates at approximately 20,000 cycles per
second.
7. The method according to claim 1 wherein said at least one sonic
welding head vibrates approximately 0.010 inch.
8. The method according to claim 1, including providing multiple
sonic welding heads arranged across a width of said metal embossing
element.
9. The method according to claim 8, wherein said sonic welding
heads are arranged in staggered overlapping relation.
10. Apparatus for continuously embossing a precision pattern of
micro-prismatic elements on one surface of transparent resinous
material, said apparatus comprising: embossing means including an
embossing tool in the form of a thin metal element having an inner
surface and an outer surface, said outer surface having a precision
embossing pattern thereon which is the reverse of the precision
pattern to be formed in the resinous material; means for
continuously moving said embossing element along a closed path;
means for introducing superimposed film and sheeting of resinous
materials onto said embossing element with one face of said
sheeting in direct contact with said pattern on said embossing
element; means for applying sonic vibration to said superimposed
film and sheeting with said one face of said sheeting in direct
contact with said embossing element to thereby begin to heat an
impress said pattern into said sheeting; means for raising the
temperature of said embossing element to the glass transition
temperature of said sheeting and below the glass transition
temperature of said film while said embossing element is in a first
portion of its path; pressure means sequentially spaced along said
first portion of said path for pressing said superimposed film and
sheeting against said embossing element until said one surface
fully conforms to said embossing pattern; and means for stripping
said superimposed film and embossed sheeting from said embossing
element.
11. Apparatus according to claim 10, including means for preheating
said resinous film prior to introducing said film and sheeting onto
said embossing element.
12. Apparatus according to claim 10, including means for cooling
said superimposed film and sheeting prior to stripping said film
and sheeting from said embossing element.
13. Apparatus according to claim 10 wherein said closed path is
substantially cylindrical.
14. Apparatus according to claim 10 wherein said embossing tool is
endless and seamless.
15. Apparatus according to claim 10 wherein said precision pattern
is in the form of an array of female microcube corner type elements
whereby the sheeting formed thereby has male microcube corner
elements on one face thereof.
16. Apparatus according to claim 10 wherein said means for applying
sonic vibration to said superimposed film and sheeting includes at
least one sonic welding head vibrating at approximately 20,000
cycles per second.
17. Apparatus according to claim 10 wherein said means for applying
sonic vibration to said superimposed film and sheeting includes a
sonic welding head vibrating at approximately 0.010 inch.
18. Apparatus according to claim 12 wherein said means for cooling
includes a shoe member having chilled fluid running
therethrough.
19. Apparatus according to claim 18 wherein said embossing element
passes over said shoe member.
20. Apparatus according to claim 12 wherein said means for cooling
includes a cold air plenum.
21. Apparatus according to claim 10 wherein said means for applying
sonic vibration includes a plurality of sonic welding heads
arranged across a width of said embossing element.
22. Apparatus according to claim 20 wherein said sonic welding
heads are arranged in staggered overlapping relation along the
width of the embossing element.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to an improved
method and apparatus for producing sheeting having precision
patterns of micro-prismatic elements formed therein and, more
particularly, to an improved method and apparatus for continuously
embossing the surface of a film or film laminate with a pattern of
precisely formed cube-corner retroreflective elements.
[0003] 2. Description of the Related Art
[0004] Cube-corner type reflectors have long been in use in such
applications as pavement markers, automobile reflectors and
retroreflectors for use in highway signage construction, for
example. The phrases "cube-corner," or "trihedral" or "tetrahedron"
are well recognized terms in the art for structure consisting of
three mutually perpendicular faces, without regard to the size or
shape of each face, or the optical axis of the element so provided.
One early example of a cube-corner type reflector is disclosed in
the patent to Stimson, U.S. Pat. No. 1,906,655, issued May 2,
1933.
[0005] In more recent times, cube-corner retroreflective elements
have been used advantageously not only in pavement markers and
automobile reflectors, but also in flexible retroreflective
sheeting suitable for use in highway signage construction, for
example. Retroreflective sheeting requires, among other things, a
drastic reduction in the size of the cube-corner elements by
comparison to the elements used typically in pavement markers and
automobile reflectors. Cube-corner type reflectors, to retain their
functionality of reflecting light back generally to its source,
require that the three reflective faces be maintained flat and
within several minutes of 90.degree. relative to each other.
Spreads beyond this, or unevenness in the faces, results in
significant light spread and a drop in intensity at the location
desired. A more detailed description of the optics of cube and
microcube structures are found in commonly assigned copending
application U.S. Ser. No. 08/655,545 (as published in PCT case
US97/08806), the disclosure of which is incorporated herein by
reference.
[0006] For many years, it was suggested that cube-corner
retroreflective sheeting could not be manufactured successfully
using embossing techniques (e.g., Rowland, U.S. Pat. No. 3,684,348,
column 5, lines 30-42). However, embossing techniques were
perfected such that embossed microcube retroreflective sheeting is
now readily available. An example of a successful method for
embossing sheeting is disclosed in U.S. Pat. No. 4,601,861, issued
to Pricone et al. and assigned to the common assignee herein, the
disclosure of which is incorporated specifically herein by
reference.
[0007] While the method and apparatus disclosed in the
aforementioned Pricone et al. patent performs effectively in
continuously producing high quality microcube retroreflective
sheeting, a disadvantage of such a system is the time involved in
forming the prismatic elements. Generally, such a system is only
capable of producing the embossed film at a rate of no more than
thirty lineal inches per minute. The principal time factor in this
system is that required to heat the film to its glass temperature,
to enable formation of the microprismatic elements. This requires
multiple embossing machines if high volume production is desired.
Consequent cost in terms of machine maintenance and floor space,
for example, also is therefore required. Accordingly, it is
desirable to provide a method and apparatus capable of increasing
production capacity of microcube retroreflective sheeting over
prior known technology. Further, it is desirable to provide such a
method and apparatus which produces a high quality finished
product. It is further desirable to provide such a method and
apparatus which is practical and relatively inexpensive to use.
Still further, it is desirable to provide for the high production
of embossed sheeting or laminates formed with precise patterns of
micro-prismatic cells which can serve functions other than in
retroreflective sheeting.
SUMMARY OF THE INVENTION
[0008] The present invention improves over the prior art by
providing an improved method for continuously embossing a precision
pattern of micro-prismatic elements on a surface of a resinous
sheeting material with the aid of an endless metal embossing belt.
The method includes the steps of moving the belt along a closed
path through a heating station and a cooling station, conveying
superimposed resinous film and sheeting material into proximity
with the belt, passing the film and sheeting between the belt and a
series of sonic welding heads to thereby begin to impress a pattern
of micro-prismatic formations of the belt into one surface of the
sheeting, pressing the film and sheeting against the heated belt
until the one surface of the sheeting fully conforms to the
embossing pattern, and stripping the film and embossed sheeting
from the belt.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The foregoing and other novel features and advantages of the
invention will be better understood upon a reading of the following
detailed description taken in conjunction with the accompanying
drawings in which:
[0010] FIG. 1 is a fragmentary plan view, greatly enlarged, of the
embossed surface of one form of microcube retroreflective sheeting
produced by the present invention;
[0011] FIG. 2 is a fragmentary side schematic view, greatly
enlarged, showing the embossing pattern of one form of an embossing
tool for embossing the retroreflective pattern of the sheeting of
FIG. 1, as though taken along the line 2-2 of FIG. 1, except that
the tool is of female microcubes and the finished film is of male
microcubes;
[0012] FIG. 3 is a schematic perspective view of one form of
retroreflective sheeting produced by the present invention, after
further processing has rendered the sheeting ready for
installation;
[0013] FIG. 4 is a schematic view of one form of apparatus
constructed in accordance with the principles of the invention for
producing the retroreflective sheeting of FIGS. 1 and 3;
[0014] FIG. 5 is a schematic view of a second form of apparatus
constructed in accordance with the principles of the invention for
producing the retroreflective sheeting of FIGS. 1 and 3;
[0015] FIG. 6 is a top schematic view of an embossing roller in
accordance with the invention showing one form of orientation of
multiple ultrasonic vibration heads;
[0016] FIG. 7 is a side schematic view of a micro-prismatic
laminated product other than retroreflective sheeting; and
[0017] FIG. 8 is a side schematic view of another micro-prismatic
laminated product other than retroreflective sheeting.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The present invention will first be described in connection
with the production of high quality retroreflective sheeting,
although other sheeting applications will be discussed
hereinafter.
[0019] Referring now to the drawings, and initially to FIG. 1, a
portion of retroreflective sheeting is designated generally by the
reference numeral 12. The sheeting 12 is preferably of
thermoplastic material having embossed on one surface thereof a
repeating pattern of retroreflective microcube-corner type
reflector elements 14. The thermoplastic material may
advantageously be acrylic. Sheeting 12 initially had smooth front
and back surfaces and was on the order of 0.006 inch (0.15 mm)
thick. Alternatively, the sheeting 12 may consist of a laminate of
different thermoplastic materials having different characteristics,
as hereinafter described.
[0020] The retroreflective pattern of elements 14 was formed with
the aid of embossing tool 16 of a thin flexible belt or cylinder of
the type produced in accordance with that invention entitled
Embossing Tool and Method of Producing Same, U.S. Pat. No.
4,478,769, and assigned to applicant's assignee. Other shapes and
arrays of microcube elements may be formed on the tool. Such shapes
may be hexagons, triangles, rectangles or the like as disclosed in
aforesaid U.S. Ser. No. 08/655,545.
[0021] As shown in FIG. 2, the embossing tool 16 has on one surface
an embossing pattern 18, the depth of which is indicated by
dimension A. One example for dimension A may be 0.00338 inch (0.085
mm). Dimension B of FIG. 1 represents the distance between parallel
grooves which, for the "A" dimension provided, would be on the
order of 0.0072 inch (0.18 mm).
[0022] FIG. 3 shows one form of sheeting 12 produced by the present
invention, after further processing and ready for use. More
specifically, the retroreflective pattern of cube corner elements
14 may be covered with a metalized layer 19, which in turn may be
covered by a suitable backing material 20, in turn covered by a
suitable adhesive 22 for mounting, in turn covered by release paper
24. The thickness of the metalizing layer 19 is essentially
immeasurable. Backing material 20 may have a thickness, dimension
C, of about 0.001 inch (0.025 mm) and the thickness of the adhesive
layer 22 may be about 0.0015 inch (0.038 mm). The total thickness
of the complete structure 25 is about 0.010 inch (0.25 mm) and the
structure 25 is flexible enough so it can be rolled and readily
stored on a supply reel 26. Another version may consist of air
cells formed by sonic welding of a rear film layer to the embossed
layer, as disclosed in applicants' copending application Ser. No.
08/566,006, commonly assigned.
[0023] In accordance with the invention, one form of machine 30 for
producing the cube corner sheeting 12 is shown schematically in
elevation in FIG. 4. A supply reel 32 of unprocessed acrylic web 34
is mounted above the machine as is a supply reel 36 of transparent
plastic film 38, such as Mylar. In the illustrated embodiment, the
web 34 may be 0.006 inch (0.15 mm) thick and the film 38 may be
0.002 inch (0.05 mm) thick. The flat web 34 and the film 38 are fed
from the reels 32 and 36, respectively, to a guide roller 40
positioned in close proximity to the embossing means 16.
[0024] The embossing means 16 includes an embossing tool in the
form of an endless metal belt 44 which may be about 0.020 (0.5 mm)
inch in thickness and 54 inches in circumference and 22 inches
wide. The width and circumference of the belt 44 will depend in
part on the width of the material to be embossed, as well as on the
desired embossing speed and the thickness of the belt 44. The belt
44 is mounted on and supported for rotation by a heating roller 46
and a post-cooling roller 48 having parallel axes. Rollers 46 and
48 may be driven by chains (not shown) to advance the belt 44 in
the direction of the arrow. Belt 44 is provided on its outer
surface with a continuous female embossing microprismatic pattern
such as the cubes 18 (FIG. 2).
[0025] Evenly spaced around the belt for about 180.degree. around
the heating roller 46 are a plurality, at least three, and as shown
five, pressure rollers 60 of a resilient material, preferably
silicone rubber, with a durometer hardness ranging from Shore A 20
to 90, and preferably from Shore A 60 to 90. While the rollers 46
and 48 could be the same size, the diameter of heating roller 46 is
about 101/2 inches (26.6 cm) and the diameter of the post-cooling
roller is about 8 inches (20.3 cm). The diameter of each pressure
roller 60 is about 6 inches (15.2 cm). The heating roller 46 or the
post-cooling roller 48 may have axial inlet and outlet passages
joined by an internal spiral tube for circulation therethrough of
hot oil (in the case of the heating roller) or other liquid (as in
the case of the cooling roller) supplied through appropriate
lines.
[0026] The web 34 and film 38 are fed over guide roller 40 where
they are superimposed to form a laminate 62 which then is conveyed
over the belt 44. In preferred form, the machine 30 is provided
with a series of infrared heaters 64 which serve to preheat the
laminate 62 after it has passed around the guide roller 40. In
accordance with the invention the laminate 62 then passes between
heating roller 46 and a series of sonic welders 70. The sonic
welders 70 may be of a type operated by a 120 volt 60 Hertz power
supply designed to vibrate at 20,000 cycles per second with horns
72 that move through 0.010 inch. Although only one sonic welder 70
is shown, in practice, the machine 30 will comprise several welders
70 positioned in staggered relation to cover the full width of the
laminate 62. The welders 70 serve to essentially drive the heated
web 34 into the embossing tool 44 to initiate formation of the
microcube corner retroreflective elements 14.
[0027] The laminate 62 then passes under pressure rollers 60 and is
moved with the belt 44 around the heating roller 46 and then along
the belt 44 through a generally planar cooling station 76. The film
38, which has a higher glass transition temperature than the web
34, performs several functions during this operation. First, it
serves to maintain the web 34 under pressure against the belt 44
while traveling around the heating roller 46, thus assuring
conformity of the web 34 with the precision pattern 16 of the tool
during the change in temperature gradient as the web 34 drops below
the glass transition temperature of the material. Second, the film
38 maintains what will be the outer surface of the sheeting in a
flat and highly finished surface for optical transmission. Finally,
the film 38 acts as a carrier for the web 34 in its weak "molten"
state and prevents the web 34 from otherwise adhering to the
pressure rollers as the web 34 is heated above the glass transition
temperature. The cooling station 76 is preferably of a type
disclosed in the aforementioned U.S. Pat. No. 4,601,861 which
operates with chilled fluid.
[0028] The machine 30 includes a stripper roller 80 around which
the laminate 62 passes to remove the laminate 62 from the belt 44
shortly before the belt 44 itself contacts the post-cooling roller
48. The laminate 62 then is fed from stripping roller 80 over
further guide rollers 82 to an annealing means 84. The laminate 62
then emerges from the annealing means 84 guided by additional guide
rollers 86 with the film 38 facing outwardly, past a monitoring
device 88 which continuously monitors the optical performance of
the sheeting. From there, the finished laminate 62 having the
embossed sheeting 13 may be transferred to a wind-up roller (not
shown) for removal and further processing.
[0029] A second form of embossing machine constructed in accordance
with the principles of the invention is illustrated in FIG. 5 and
designated generally by the reference numeral 100. The machine 100
includes as a principal component a heated roller 102 which is much
larger than the roller 46 and is preferably on the order of 34
inches (86.4 cm) in diameter. As in the machine 30, an endless
metal belt 104 provided with an embossing pattern passes around the
roller 102 and is heated thereby. The machine 100 also includes a
cooling shoe 106 over which the belt 104 passes, as will be
described in detail hereinafter.
[0030] A supply reel 108 of unprocessed acrylic web 110 is mounted
over the machine as is a supply reel 112 of transparent Mylar 114.
In this embodiment of the invention, an intermediate supply reel
116 of UV stabilized face film 118 is also provided. The resulting
composite 120 passes around a guide roller 122 and beneath a series
of essentially aligned sonic welders 124, only one of which can be
seen, which essentially begins to drive the web 110 into the
embossing belt 104. The laminate 120 then passes around the heater
roller 102 beneath a series of pressure rollers 126 where the web
110 is fully impressed into the belt 104.
[0031] The cooling shoe 106 is an arcuate, hollow member through
which chilled fluid flows. The shoe 106 serves to lower the
temperature of the laminate to preferably on the order of
100.degree. F. aided by a cold air plenum 128 which blows on the
laminate 120. The laminate 120 then passes around a stripper roller
130 and is drawn to a wind-up roller 132. As in the machine 30, a
series of infrared heaters 134 may be provided to preheat the web
110.
[0032] FIG. 6 shows a top schematic view of a heated roller 102
illustrating one form of orientation of multiple ultrasonic welders
124 spaced along the width of the roller 102. Preferably, the
welders 124 are positioned in staggered overlapping relation so
that the welders 124 act on the laminate 120 continuously across
its entire width.
[0033] Referring now to FIG. 7, another form of laminate, shown
greatly enlarged, is designated by the reference numeral 140. This
form of laminate 140 has a layer of thermoplastic material 142
embossed with a pattern of microprismatic type channels 144
defining upstanding support portions 146. A cover layer 148 is
later thermally welded to the support portions 146. The channels
144 may in this form of laminate contain a deposit of a suitable
chemical composition 150 which changes color in the presence of a
bodily fluid, which is drawn into the channels 144 by capillary
action. An application for such a device may, for example, be a
home pregnancy test kit. The layer 142 is readily embossed using
the ultrasonic technique as hereinabove described.
[0034] FIG. 8 illustrates yet another laminate 160 comprising two
sheets of spaced thermoplastic material 162 embossed with a pattern
of microprismatic type projections 164. This structure 160 is
suitable for use as a fuel cell in accordance with well-known
electrochemical technology and the sheets 162 are also readily
embossed using the ultrasonic technique hereinabove described.
[0035] It can now be appreciated that embossing machines 30 and 100
constructed in accordance with the invention provide considerable
improvement over prior art devices in terms of production output
capacity. A typical embossing machine of the type disclosed, for
example, in aforementioned U.S. Pat. No. 4,601,861 has a sheeting
production rate of three feet (0.91 m) per minute. In contrast,
with the present machines, production rates as high as 30 feet (9.1
m) per minute are believed readily attainable. This production rate
increase is directly attributable to the preheating of the film
together with the initial forming of the cube corner
retroreflective elements by the sonic welding heads prior to
conveying the laminate under the pressure rollers and around the
heated roller.
[0036] In preferred form, the machines 30 and 100 may use five
welding heads 124 having a nominal width each of 11.5 inches (29.2
cm) as are presently commercially available. An embossing belt 104
may thereby be used having a width on the order of 52 inches (1.32
m) to form finished film 120 having a width on the order of 481/2
inches (1.123 m).
[0037] It can further be appreciated that the machines 30 and 100
are also capable of producing sheeting of high optical intensity at
considerably greater speed than heretofore known. One advantage of
the machine 100 is that the large diameter roller 102 and shoe 106
arrangement greatly increases the life of the generally cylindrical
metal embossing belt 104 by reducing bending stresses on the belt
104 as are present in the machine 30. The large roller 102 also
increases the working area of the belt 104 to help speed
production.
[0038] While the present invention has been described in connection
with preferred embodiments thereof, it will be apparent to those
skilled in the art that many changes and modifications may be made
without departing from the true spirit and scope of the present
invention. Accordingly, it is intended by the appended claims to
cover all such changes and modifications as come within the true
spirit and scope of the invention.
* * * * *