Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2000-04-21
2001-09-18
Bell, Bruce F. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S164000, C422S186130, C422S186180, C422S186220
Reexamination Certificate
active
06290823
ABSTRACT:
TECHNICAL FIELD
The invention relates to rollers and electrodes for use in corona treating systems.
BACKGROUND ART
The prior art includes treatment of plastic films, papers, metal foils, and other materials using a high frequency, high voltage, electrical discharge, or corona. Early equipment employed a spark gap to generate the high frequency required. In the late 1960's, solid state generators were introduced which used SCR's (silicon controlled rectifier). The latest equipment uses IGBT's (insulated gate bipolar transistors) to provide high frequency switching within the power supply, also referred to herein as the “corona treatment generator.”
Referring to
FIG. 1
a
, a “conventional” corona treatment station
10
a
of the prior art is composed of a corona treatment generator
11
a
, providing high frequency and high voltage, a stationary metal electrode
12
a
, and an electrode roller
13
a
covered with a thin layer of dielectric material
14
a
. The electrode
12
a
and roller
13
a
are separated by a small gap
15
a
, usually about sixty mils, where the corona
16
a
is formed. Although the elements
12
a
,
13
a
are formed as cylinders, only their walls next to the corona gap
15
a
have been shown in section, it being understood that a full section would show a second thickness of layer
14
a
, for example. The surface energy of a plastic web of material
17
a
is raised by direct contact with the corona
16
a
. This improves the wetting and adhesion of inks or coatings applied in subsequent operations.
The electrode
12
a
in a conventional system is normally bare aluminum, steel, or stainless, in bar, tube, or flat-sided form. The electrode may be shaped (shoe form) to match the curvature of the covered roller. The electrode may also be one piece, for full-width treatment of the web, or broken into sections (segments) to allow adjustment of the area being treated.
Many types of materials have been used for the dielectric covering
14
a
on the roller in a conventional system. The oldest types are rubber compounds made from silicone and Hypalon™ polymers. Other coverings are made of epoxy and other thermoset resins (solid resin or composites with fibers), glass, and ceramics.
Inorganic coatings, such as glass and ceramic, provide durability and can also provide tolerance to the highest power densities in the corona since they are not combustible. These are more expensive than rubber coverings, for example. Epoxy and ceramic coverings are the most popular dielectrics for conventional systems. The thickness of the polymer coatings is typically 100 to 125 mils, while the thickness of glass and ceramic coatings is much lower, 40 to 80 mils (mainly due to cost). The practical range for all possible dielectric materials is from 20 mils to 500 mils in thickness.
Referring to
FIG. 1
b
, a bare roll form of corona treatment system
10
b
is shown. In this system
10
b
, the roller
13
b
does not have a covering, so the system
10
b
is referred to as “bare roll”. The original dielectric on the upper electrode
12
b
was quartz but has been replaced with ceramic
18
b
(aluminum oxide) for improved temperature resistance. The bare roll electrode
12
b
is usually a tube (or several tubes connected in parallel) of ceramic
18
b
, filled with metal powder
21
b
, to avoid the thermal expansion problems of a solid metal electrode. The packed metal powder is connected directly to a high voltage lead from the generator.
The corona
16
b
of a bare roll electrode system
12
b
is always full width and cannot be adjusted. The bare roll system
10
b
has the advantage that the web
17
b
is in contact with a grounded roller
13
b
. If a metallic web is being treated, the web
17
b
will not become energized, due to the grounding. The bare roll system
10
b
has the disadvantage that it is less efficient than other prior systems. Less input power is delivered from the corona treatment generator
11
b
to the web
17
b
. Consequently, the power of a bare roll system
10
b
must be increased to equal the treatment of other systems, or the line speed must be reduced to reach the desired treatment level.
To overcome or reduce the limitations of the bare roll system, a dielectric cover
19
c
has been applied to the “bare” electrode roller
13
c
. The covers
18
c
,
19
c
on both the electrode
12
c
and roller
13
c
are typically ceramic, although other materials could be used for the roller covering. The added dielectric
19
c
on the roller
13
c
shifts the power distribution toward the web
17
c
, which increases the percentage of the input power actually used to treat the film, however, it does not provide a grounded web.
SUMMARY OF THE INVENTION
The present invention is directed to improvements in corona treatment systems having all of the advantages of prior systems, including favorable power efficiency and grounding of the web, without the limitations of the prior systems. The invention provides a covered electrode roller, and a switching arrangement in which the corona treater system can be switched between a first operating mode as a bare roll system and a second operating mode as a dual dielectric system.
The covering on the convertible electrode roller is preferably made of ceramic such as alumina, zirconia, or a blend of ceramic materials. Other embodiments may employ coverings of other inorganic materials, elastomers including silicone, and thermoset resins and composites, including epoxy and polyester resins.
The convertible electrode roller of the present invention an outer layer over the dielectric layer. This outer layer is conductive. The outer layer can either be grounded (bare roll mode) or ungrounded (dual dielectric mode). This outer layer behaves like a grounded bare metal roller while in the bare roll mode. The bare roll mode can be used for treating conductive or non-conductive webs, papers, films, and foils. While in the dual dielectric mode, the outer layer behaves like a metal foil web wrapped around a dielectric covered roller.
With the outer conductive layer connected to ground, the roller appears to the system to be a grounded metal roller. The capacitance of the roller-web combination is the same as in a bare roll system. The corona also appears the same as it does in a bare roll system with the same characteristics of smoothness or spikiness.
With the outer conductive layer isolated from ground, the system behaves like a dual dielectric treater system, using a ceramic covered electrode, of course. Normally, the corona in a dual dielectric system appears to be smoother than a bare roll or conventional system. In the case of the convertible roller electrode, the corona looks the same in either mode. The corona appears like a corona in a bare roll system.
Other objects and advantages of the invention, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of the preferred embodiments which follow. In the description, reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. Such examples, however, are not exhaustive of the various embodiments of the invention, and therefore, reference is made to the claims which follow the description for determining the scope of the invention.
REFERENCES:
patent: 4946568 (1990-08-01), Kalwar et al.
patent: 5169450 (1992-12-01), Opad et al.
patent: 5268151 (1993-12-01), Reed et al.
Butters Gary S.
Hyllberg Bruce E.
American Roller Company
Bell Bruce F.
Quarles & Brady LLP
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