Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND SYSTEMS FOR COATING OBJECTS
FIELD OF THE INVENTION
The present invention relates to apparatus and systems for coating
objects, and, more particularly, relates to continuous belts and systems for
coating objects.
BACKGROUND & DISCUSSION
In the manufacture of products, such as industrial and automotive
components, various small parts, such as stampings, castings, seat and clamp
assemblies, bolts, clamps, conduit, pipes, and the like, are employed that
mainly
serve a functional role in the final assembly. In order to prepare these parts
for
final assembly, a coating material is typically deposited on at least portions
of the
part. In many instances, the entire part is coated to provide a finished
appearance to the part and/or provide protection to the underlying substrate
from
damaging effects as a result of use, wear, and/or environmental conditions.
Because of the substantial number of small parts employed in the
manufacturing industry, various coating techniques have been employed for
depositing material on these parts at high speeds. For example, small parts
can
be spread and loosely placed on a flat metal mesh conveyor belt for high-speed
coating. The parts are transferred to one or more additional belts prior to
the
parts being processed through a drying unit. In many instances, the individual
parts come in close proximity to or engage each other while passing through
the
coating and drying systems such that when the coating is applied over the
parts
and dried or cured, two or more parts may adhere together at the point of
engagement (known as a "touch point"). These coated parts must then be
separated from each other with some degree of force that, typically, results
in the
removal of at least some of the coating from each of the parts at or around
the
touch point. Touch points may also be formed when a part touches the side of
the conveyor. Additionally, even if no contact is made between parts or the
sides of the conveyor, contact is still present between the part and the
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belt that it is resting on, and a touch point is present at each point of
contact with
the belt. This is particularly the case in electrophoretic coating processes
that
require the conveyor belt to be in electrical contact with the part to supply
the
necessary charge prior to or at the time of coating.
At the very least, the touch point provides an unsightly blemish on
the finished product. When the part is formed from a corrosive material, the
touch point, in addition to its reduced appearance, has a substantially
greater
chance of developing premature signs of corrosion following assembly. Because
the parts are randomly positioned on the belt, it is difficult to predict the
locatipn
of the touch points prior to coating.
In the coating process described above, because, for example, the
small parts are randomly placed on the conveyer belt and the parts are
transferred to one or more additional belts prior to the drying unit, it has
been
difficult to minimize the occurrence of touch points. Accordingly, in order to
meet
quality standards, the supplier employing this coating technique may find it
necessary to incur time and cost consuming efforts to sort and scrap non-
conforming parts.
Apparatus and/or systems that can materially reduce or avoid the
shortcomings discussed above and/or improve coating and manufacturing
efficiency, while providing a coated part that meets or exceeds functional and
aesthetic quality requirements, are desired.
SUMMARY OF THE INVENTION
The present invention provides a continuous system for the
application of a coating to an object. The system comprises a continuous belt
comprising at least one supporting member positioned to retain the object
thereon, a drive member in operative engagement with the continuous belt, a
coating unit in communication with the continuous belt, and a drying unit in
communication with the continuous belt and the coating unit and arranged such
that the object is coated and dried on the continuous belt.
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The present invention also provides a continuous belt for coating an
object through a continuous coating system, comprising at least one supporting
member positioned to retain the object thereon, the supporting member
comprising at least one blade member comprising a plurality of projections, at
least one of which is positioned to contact the object.
The present invention also provides a continuous belt for coating an
object through a continuous coating system. The continuous beit comprises: a
first continuous supporting member and a second continuous supporting
member laterally spaced apart from the first continuous supporting member,
each of the first continuous supporting member and the second continuous
supporting member including a plurality of projections configured to support
the
object; a plurality of grounding members coupled to the first continuous
supporting member and the second continuous supporting member at spaced
apart locations, the plurality of grounding members being electrically coupled
to
the plurality of projections; and a pair of side members coupted to the first
continuous supporting member and the second continuous supporting member,
at least one of the side members being electrically coupled to the plurality
of
grounding members.
The present invention is also directed to processes for coating
objects. The processes comprise positioning the objects on a continuous belt
comprising a supporting member positioned to retain the object thereon,
conveying the continuous belt with a drive member such that the continuous
belt
passes through both a coating unit and a drying unit, coating the objects on
the
continuous belt with the coating composition, and drying the objects on the
continuous belt.
In other respects, the present invention provides processes for the
electrophoretic appiication of an aqueous electrodepositable coating
composition
to objects on a continuous belt comprising a supporting member positioned to
retain the objects thereon. These methods comprise: feeding the objects on the
continuous belt; positioning the objects on the continuous belt, wherein the
supporting member comprises a blade member comprising a pluraiity of saw
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teeth arranged to contact the objects; conveying the continuous belt with a
drive
member such that the continuous belt passes through both a coating unit and a
drying unit; electrophoretically coating the objects on the continuous belt
with the
aqueous electrodepositable coating composition; and drying the objects on the
continuous belt.
In another embodiment, the present invention provides a process for
electrical coupling a plurality of projections on a continuous belt to a first
polarity
of an electrode during a continuous electrodeposition coating process wherein
a
plurality of objects and the continuous belt are coated in a tank and
subsequently
cured. The process comprises the steps of: engaging a side member of the
continuous belt to propel the continuous belt; removing a cured coating from
the
side member to provide an electrical contact portion; contacting the
electrical
contact portion of the side member with the first polarity of the electrode at
a
location prior to the side member reentering the tank; and coupling the
electrical
contact portion of the side member to the plurality of projections.
It should be understood that this invention is not limited to the
embodiments disclosed in this summary, but it is intended to cover
modifications
that are within the spirit and scope of the invention, as defined by the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following detailed description
of the preferred embodiments, will be better understood when read in
conjunction with the appended drawings. In the drawings:
FIG. 1A is a perspective view of one embodiment of the continuous
belt of the present invention;
FIG. I B is a perspective exploded view of one portion of the
continuous belt, as illustrated in FIG. 1A;
FIG. 1 C is a perspective exploded view of one portion of the
continuous belt, as illustrated in FIG. 1A;
FIG. 2 is a side elevation view of the continuous belt absent the side
and guide members, as illustrated in FIG. 1A;
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FIG. 3 is a top plan view of the continuous belt, as illustrated in FIG.
1 A;
FIG. 4 is a side elevation view of one embodiment of the blade
member of the continuous belt, as illustrated in FIG. IA;
FIG. 5 is a side elevation view illustrating travel of the continuous
belt of FIG. 1A absent the side and guide members entering or exiting the
coating unit (not shown) of the present invention;
FIG. 6 is a side elevation view illustrating travel of the continuous
belt of FIG. 1A absent the side and guide members around a drive wheel; and
FIG. 7 is a schematic side elevation view of the coating system of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
It is to be understood that the Figures and descriptions of the present
invention have been simplified to illustrate elements that are relevant for a
clear
understanding of the present invention, while eliminating, for purposes of
clarity,
other elements. Those of ordinary skill in the art will recognize that other
elements may be desirable in order to implement the present invention.
However, because such elements are well known in the art, and because they
do not facilitate a better understanding of the present invention, a
discussion of
such elements is not provided herein.
In the descriptions of the present invention, the invention will be
described and illustrated in the form of an apparatus for depositing a coating
on
an object having a particular configuration. To the extent that this
configuration
gives size and structural shape to the object, it should be understood that
the
invention is not limited to embodiment in such form and may have application
in
whatever size, shape, and configuration of objects desired to be coated. Thus,
while the present invention is capable of embodiment in many different forms,
this detailed description and the accompanying drawings disclose only specific
forms as examples of the invention. Those having ordinary skill in the
relevant
art will be able to adapt the invention to application in other forms not
specifically
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presented herein based upon the present description. For example, in the
descriptions of the present invention, the invention will be illustrated as a
system
and/or apparatus for coating an object, such as, for example, a bolt. It
should be
understood that the detailed description in this form is only illustrative of
the
present invention, and that the present invention may be employed with objects
of other shapes and configurations that are not specifically described herein.
Also, the present invention and devices to which it may be attached
may be described and/or illustrated herein in a normal operating position, and
terms such as upper, lower, front, back, horizontal, proximal, distal, etc.,
may be
used with reference to the normal operating position of the referenced device
or
element. It will be understood, however, that the apparatus of the invention
may
be manufactured, stored, transported, used, and sold in orientations other
than
those described and/or illustrated herein.
Other than in the operating examples, or where otherwise indicated,
all numbers expressing quantities of ingredients, reaction conditions and so
forth
used in the specification and claims are to be understood as being modified in
all
instances by the term "about". Accordingly, unless indicated to the contrary,
the
numerical parameters set forth in the following specification and attached
ciaims
are approximations that may vary depending upon the desired properties sought
to be obtained by the present invention. At the very least, and not as an
attempt
to limit the application of the doctrine of equivalents to the scope of the
claims,
each numerical parameter should at least be construed in light of the number
of
reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting
forth the broad scope of the invention are approximations, the numerical
values
set forth in any specific examples are reported as precisely as possible. Any
numerical values, however, inherently contain certain errors necessarily
resulting
from the standard deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein
is intended to include all sub-ranges subsumed therein. For example, a range
of
"1 to 10" is intended to include all sub-ranges between and including the
recited
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minimum value of 1 and the recited maximum value of 10, that is, having a
minimum value equal to or greater than I and a maximum value of equal to or
less than 10.
AII patents and publications set forth herein are incorporated herein
by reference. Any patent, publication, or other disclosure material, in whole
or in
part, that is said to be incorporated by reference herein is incorporated
herein
only to the extent that the incorporated material does not conflict with
existing
definitions, statements, or other disclosure material set forth in this
disclosure.
As such, and to the extent necessary, the disclosure as explicitly set forth
herein
supersedes any conflicting material incorporated herein by reference.
The present invention is directed to apparatus and systems for
depositing at least one coating on an object, such as, for example, via
electrophoretic coating techniques. As used herein, the phrase "deposited on"
a
substrate and like terms means deposited or provided above or over but not
necessarily adjacent to the surface of the substrate. For example, a coating
can
be deposited directly on the substrate or one or more other coatings can be
applied therebetween.
As used herein, the term "object" is meant to include all articles that
may suitably be placed on the continuous belt as set forth herein,
particularly
those that may be coated for subsequent use. The term "object" is meant to
include, for example, industrial, automotive, and aerospace small parts that
may
be used in the final assembly of products, such as, for example, stampings,
castings, seat and clamp assemblies, bolts, clamps, conduit, pipes, and any
other bodies employed in manufacturing. For illustration purposes only, and
without intending to limit the scope of the present invention, the object is
illustrated as a bolt with integral washer.
As used herein, the term "retain" and like terms means to keep or
support.
The present invention provides continuous systems for the
application of a coating to an object comprising a continuous belt having in
certain nonlimiting embodiments at least one supporting member positioned to
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retain the object thereon, a drive member in operative engagement with the
continuous belt, a coating unit in communication with the continuous belt, a
rinse
unit in communication with the continuous belt, and a drying unit in
communication with the continuous belt and the coating unit, arranged such
that
the object is coated and dried on the continuous belt. In the discussion
below,
the coating system may be, for example, an electrophoretic coating system. The
continuous systems may inciude a movable belt to which the objects are
situated
thereon for movement with the belt. Although the Figures illustrate one
embodiment of the continuous belt apparatus that can be used to convey an
object, such as a bolt, from a point of origin to a destination point through
a
coating and/or drying unit of a coating system, it should be understood that
the
invention is not limited to embodiment in such form and may have application
in
whatever design, size, shape, and/or configuration of continuous belt desired
to
be employed. Thus, while the present invention is capable of embodiment in
many different forms,. this detailed description and the accompanying drawings
disclose only specific forms of continuous belts as examples of the invention.
Those having ordinary skill in the relevant art will be able to adapt the
invention
to application in other forms not specifically presented herein based upon the
present description. For example, in one belt embodiment discussed in detail
below, the belt may be formed from a series of belt segments that are affixed
to
one another by means of coupling devices to form a continuous belt of a
desired
length. The belt segments can be of any desired length, and the belt segments
that form the belt need not be of a uniform length. At least one supporting
member, such as a blade member, and in some embodiments a plurality of
blade members, may be affixed to the belt and act to accept, retain, and/or
convey, objects. The supporting members may include projections taking the
shape of, for example, a saw tooth cross-sectional profile that contact
portions of
the object. In embodiments where the object is a bolt, for example, surfaces
of
the bolt, including the bolt shaft, need only be in contact with the belt
apparatus
at one or more relatively fine projection points along the length of the bolt.
Therefore, relatively small and, possibly, substantially invisible or
unrecognizable
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points are created on the surfaces of the object at the points of contact with
the
belt apparatus. It should be noted, however, that other forms of continuous
belts
that are not specifically set forth herein may be employed in the systems of
the
present invention.
Turning now to the drawings, FIGS. 1A-1C illustrate embodiments of
the continuous belt 10 employed in the systems of the present invention. Belt
10
supports and/or retains one or more objects 20 thereto for subsequent
treatment
through a coating and/or drying process, described below. Belt 10 may be
continuous, i.e., it is, or may be, attached end-to-end to form an endless
loop
when positioned on a drive mechanism. Belt 10 may be generally formed of any
durable material known in the art for withstanding the temperatures and
conditions associated with the continuous coating of objects. In embodiments
of
the present invention, belt 10 may be formed of a resilient, durable, and/or
conductive material, such as, for example, aluminum, stainless steel, or mild
steel. Although belt 10 is shown in a horizontal configuration, it is
understood
that other configurations, such as, for example, an angled configuration, may
be
employed and that such modifications are intended to be included within the
scope of the present invention. On belt 10 may be attached at least one
supporting member 12. The supporting member 12 may be in the form of
various conveying surfaces such as, for example, at least one and, typically,
a
plurality of, blade members 14 to retain and/or electrically contact objects
20.
Supporting members 12 may include projections 21, as outward extensions,
from its base. In one embodiment, supporting members 12 have a thickness of
about 0.06 inches (about 0.15 cm). Belt 10 may have an open bottom portion,
as illustrated, to, for example, provide a greater degree of belt flexibility,
to aid in
drying and cooling the coated object, and/or to avoid retention of coating
material
as belt 10 travels through the coating system 50, described below.
When employed, blade members 14 may be positioned on belt 10
and may include a plurality of projections 21 (FIGS. I B and 1 C), at least
one of
which acts to at least partially support or contact objects 20 at points of
relatively
small surface area to minimize touch points. When coating system 50 is an
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electrophoretic coating system, projections 21 may also act as electrical
contact
points to pass charge to objects 20. In addition, projections 21 may provide
points of added friction in order to more securely retain objects 20 to belt
10 as
belt 10 moves through the various sections of coating system 50. Blade
members 14 may be any size or shape to contact objects 20 and/or to aid in the
retention of objects 20 to belt 10. For example, the contact points of blade
members 14 may have a repeating saw tooth cross-sectional profile in the form
a
plurality of contact points positioned along the blade members 14 to contact
objects 20 when objects 20 are properly oriented on belt 10. In one
embodiment, best illustrated in FIGS. 2 and 4, the cross-sectional profile of
the
contact points of blade members 14 may be in the form of a pruning blade.
Various commercial blades may be employed, such as those manufactured
under the tradename MILWAUKEE SAWZALL pruning blade, Model 48-00-1303,
from Milwaukee Electric Tool Corporation, Milwaukee, Wisconsin. Blade
members 14 may be formed of any resilient material that supports objects 20 on
belt 10, and may be formed of a resilient electrically conductive material. In
certain embodiments of the present invention, blade members 14 may be formed
of a resilient, durable, and conductive material, such as stainless steel or
mild
steel, which may, if desired, be further hardened by heat treatment. Blade
members 14 may be secured to beit 10 by any manner known in the art. For
example, and as illustrated, belt 10 may include one or more coupling devices,
such as elongated pins 22 passing through blade members 14, with elongated
pins 22 engaging side members 16 by, for example, tabs 19 extending
therefrom. Any suitable fasteners may be employed to affix elongated pins 22
to
side members 16 such as, for example, rivets, bolts, screws, and the like.
Blade members 14 may be arranged in any orientation suitable for
electrically contacting and/or retaining objects 20, such as, for example, in
an
orientation substantially parallel to each other, as illustrated. The blade
members 14 may be spaced apart such that the distance between any two blade
members 14 is less than the length, width, or height of objects 20 to be
coated,
to prevent passage of objects 20 through belt 10. When beit 10 includes side
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members 16, blade members 14 may be oriented relative to side members 16 in
any suitable arrangement thereto such as, for example, diagonal, parallel,
perpendicular, or combinations thereof. It is contemplated that various angles
or
orientations may be employed, based on, for example, the size, shape, and
placement of objects 20 to be coated, or the operation of belt 10 through
coating
system 50. Guide members 23 that are shaped and oriented in a manner similar
to blade members 14 may also be employed. When employed, guide members
23 may be slightly larger than blade members 14 so that objects 20 on belt 10
do
not slide from belt 10 due to forces on belt 10 as belt 10 travels through
coating
system 50.
As best illustrated in FIGS. 1A-1C and FIG. 4, each blade member
14 may include a pivotable portion 15 and a slotted portion 17 for operative
movement of belt 10 through continuous system 50. The pivotable portion 15
may include an opening passing through the blade member 14 for receipt of
coupling device 22, which, as illustrated, is an elongated pin 22. In this
embodiment, the cross sectional diameter of elongated pin 22 may be sized
slightly smaller than the diameter of the opening to allow blade members 14 to
freely rotate around pin 22 at pivotable portion 15 as belt 10 changes its
direction
of travel from, for example, a generally horizontal to an angled direction of,
for
example, 150 to 20 from horizontal, such as when belt 10 travels into or out
of
coating unit 74, described below. In addition, each blade member 14 may
include a slotted portion 17 that may be an open or closed notch at an end
opposite pivotable portion 15. Slotted portion 17 may have any height suitable
for receipt of elongated pin 22. The notch height may be slightly larger than
the
cross sectional diameter of elongated pin 22, and the notch length may be any
length that allows relatively free pivotable and/or lateral movement of blade
members 14 of belt 10 at an end opposite pivotable portion 15. For example,
elongated pin 22 may allow blade members 14 at slotted portion 17 to freely
pivot, expand, or contract as belt 10 changes direction, such as when belt 10
- travels around bends through coating system 50.
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As illustrated in FIGS 1A-1C and FIG. 3, belt 10 may have a plurality
of blade members 14 in the form of individual belt segments for operative
movement through continuous coating system 50. As illustrated, and by way of
example, blade members 14 may have at least one overlapping section 18 such
that pivotable portion 15 of one segment of blade members 14 engages the
same coupling device 22 as the slotted portion 17 of an adjacent segment of
blade members 14. This arrangement provides a staggered blade orientation,
as illustrated, such that blade members 14 are retained in their orientation
by
coupling device 22, in the form of, for example, elongated pin 22. If removal
of
one segment of belt 10 is desired, removal of elongated pin 22 from side
members 16 allows the segment of blade members 14 having their pivotable
portion 15 engaging the removed elongated pin 22 to be separated from belt 10,
by sliding the opposite ends of blade members 14 engaging adjacent elongated
pin 22 from the open end of slotted portion 17. In this manner, the staggered,
overlapping arrangement of blade members 14 allows relative and, at least,
partial independent movement of individual segments of belt 10 through the
coating system 50.
It is contemplated that the belt components, such as blade members
14 and elongated pin 22, may be adjustable and positionable to retain objects
of
varying sizes such that a single belt 10 may be employed on a production line
to
coat a series of different sized objects having, for example, differing
diameters,
lengths, and the like. In this form, belt replacement could be reduced or
substantially eliminated between runs of various sized objects (e.g. bolts of
differing diameters or lengths) or entirely different objects (e.g. a run of
bolts
immediately followed by a run of clamps).
When the process for coating objects 20 is an electrophoretic
coating process, belt 10 of the present invention may include at least one
electrical grounding member 28, and typically includes a plurality of
grounding
members 28 positioned along belt 10 to insure a satisfactory ground for the
electrical circuit in the process. When employed, electrical grounding members
28 may be positioned at a bottom portion of belt 10 below blade members 14
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and electrically connected thereto through any means known in the art, such as
by use of fasteners or by welding. In certain embodiments of the present
invention, and as illustrated in the FIGS. IA-IC, grounding members 28 may
each be an electrically conductive plate or bar and positioned in a notch in
blade
members 14 and secured to an underside thereto. The grounding members 28
may be oriented on belt 10 in any manner that provides suitable electrical
contact therewith, such as in a substantially perpendicular orientation to
blade
members 14, as illustrated. Typically, grounding members 28 may be formed of
an electrically conductive material that is compatible with the material that
forms
blade members 14. In certain embodiments of the present invention, grounding
members 28 are formed of a resilient, durable, and/or conductive material,
such
as aluminum, stainless steel, or mild steel.
Grounding members 28 may provide electrical contact through belt
10 by any means known in the art. For example, grounding members 28 may be
electrically connected to elongated pin 22 by grounding connectors 29, such as
grounding cabies, that provide electrical conductivity through grounding
members 28 to elongated pin 22 and through side members 16. Suitable
grounding cables may be lug-to-lug flexible braided grounding cables
identified
as Model 69925K32, commercially available from McMaster-Carr Supply
Company, Atlanta, Georgia. Grounding connectors 29 may be held in place by,
for example, rivets, bolts, screws, and the like to provide electrical contact
through belt 10. Grounding connectors 29 may also be formed of an electrically
conducting material, such as mild steel, stainless steel or aluminum, so that
as
belt 10 is conveyed, such as by rotation, by a drive mechanism, grounding
members 28 may contact one or more components of coating system 50 to
electrically ground belt 10.
It is contemplated that various other support members 12, as
conveying surfaces, may be employed in the present invention in place of, or
in
addition to, blade members 14. Suitable support members 12 may include, for
example, grating strips having a plurality of projections, such as those
commercially available under the tradename GRIP STRUT, from McNichols
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Company, Tampa, Florida which include diamond shaped openings edged with
serrated teeth. Support members 12 may also include a series of trays engaging
belt 10 with small gaps therebetween. The series of trays may be arranged such
that objects 20 are loaded so as not to bridge from one tray to another. In
these
alternative embodiments, the supporting members 12 may be arranged and
configured on belt 10 by various means, such as, for example, in a manner
similar to those described herein.
In one embodiment, supporting member 12, illustratively blade
members 14, are arranged in a plurality of laterally spaced apart continuous
supporting members each forming a continuous loop of belt 10, such as loops
13A and 13B illustratively shown in Fig. 3. In the illustrated embodiment,
each
row of blade members 14 is coupled to a respective coupling device 22,
illustratively pin 22, and is coupled to a respective grounding member 28.
Grounding member 28 is electrically coupled to at least one coupling device 22
through connectors 29. Coupling devices 22 are electrically coupled to at
least
one of side members 16.
At least one of side members 16 is electrically coupled to conductor
72. As such, objects 20 being conveyed by belt 10 may be electrically charged
by conductor 72 due to the electrical coupling of conductor 72 to the
projections
21 supporting object 20 through side member 16, pins 22, connectors 29,
grounding member 28, and supporting members 12. As shown in Fig. 7,
conductor 72 is electrically coupled to side member 16 prior to side member 16
entering the electrodeposition tank of coating unit 74. In one embodiment,
conductor 72 is electrically coupled to side member 16 through one or more
wipers (not shown), such as copper leaf springs. Exemplary wipers are
disclosed in U.S. Patent No. 3,669,870 and U.S. Patent No. 3,607,711, the
disclosures of which are expressly incorporated by reference herein. In one
embodiment, electrode 72 maintains electrical continuity with side member 16
through the wipers.
In one embodiment, belt 10 is a component of a continuous coating
process wherein objects 20 and belt 10 are moved through a coating unit 74 and
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subsequently through a drying unit 80. As stated herein, the portion of belt
10
including projections 21 may be cleaned with a cleaning unit 88 to remove any
buildup of coating, such as dried and/or cured coating, and/or to promote
electrical contact between blade members 14 and objects 20 prior to receiving
additional objects 20 for coating. Further, as stated herein an additional
cleaning
unit and/or cleaning unit 88, such as a rotatable brush, may be used to remove
any buildup of coating from side members 16, such as dried and/or cured
coating, and/or to promote electrical contact between electrode 72 and side
member 16 prior to side member 16 being passed through coating unit 74.
In one embodiment, a dried and/or cured coating is removed from
side member 16 to provide an electrical contact portion, such as bare metal.
The electrical contact portion of side member 16 is contacted with a first
polarity
of electrode 72 at a location prior to the side member 16 reentering the tank
of
coating unit 74. As explained herein, since the electrical contact portion of
side
member 16 is electrically coupled to electrode 72 the plurality of projections
21,
and hence objects 20, are electrically coupled to electrode 72. In one
example,
electrical contact between side member 16 and electrode 72 is proximate to a
position just prior to wherein side member 16 is reentering the tank of
coating
unit 74.
Turning now to FIG. 7, the continuous belt 10 of the present
invention may be employed in a continuous coating system 50 that may include
a drive mechanism or system 60, 82 in operative engagement with belt 10 for
rotation as an endless system through an optional pretreatment unit 70,
coating
unit 74, rinse unit 76, and drying unit 80. Coating system 50 employed in the
present invention may be any system for coating objects 20 known to those of
ordinary skill in the art and may include, for example, electrophoretic or
electrodeposition coating systems or processes. Although any continuous
coating system may be employed, for illustrative purposes only, and without
intending to be limited to any particular embodiment, the continuous system 50
will be described and illustrated in the form of an electrodeposition coating
system for coating metallic objects 20.
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Although objects 20 may be manually fed onto belt 10, continuous
coating system 50 typically includes an object feeding mechanism 52 for
receiving, orienting, and/or feeding objects to be coated. Feeding mechanism
52
typically includes a hopper 54, for receiving a bulk load of objects 20, and
one or
more conveyors 56 for transporting objects from hopper 54 in a streaming queue
to a pick-up point at belt 10. Conveyor 56 may be of any conventional type,
such
as, but not limited to, a belt conveyor, a chain conveyor, a platform
conveyor, a
gravity conveyor and the like. Feeding mechanism 52 may also include a
conventional sorting device 58 for orienting or distributing objects 20 from
conveyor 56 onto belt 10. Feeding mechanism 52, and, more specifically,
conveyor 56 may feed a plurality of objects 20 onto belt 10 by methods well
known to those of ordinary skill in the art, such as, for example, in a
streaming,
random manner that may avoid piling of objects 20 on belt 10. Feeding
mechanism 52 employed in the present invention may be one that is well known
in the art, or may be assembled from various conventional hopper, sorting, and
conveying components. For example, if objects 20 to be coated are threaded
bolts, suitable bolt hopper, bolt sorter and bolt conveyor mechanisms are
commercially available from Spectrum Automation Company, Livonia, Michigan.
It is contemplated that various object feeding mechanisms 52 may be employed
in the present invention.
In particular, the path of each object 20 on conveyor 56 is along a
path that is in general alignment and engagement with belt 10, such that
objects
20 may be placed and retained on one or more projections 21 of blade members
14. The projections 21, such as in the form of saw teeth, act to support
and/or
retain objects 20 on belt 10 and provide contact therewith at one or more fine
points along their length. As objects 20 are fed from feeding mechanism 52
onto
belt 10, objects 20 travel along a path of the belt 10 as it is conveyed, such
as by
rotation, by drive mechanism 60 and/or 82. The drive mechanism employed in
the present invention may be any known mechanism for driving known
continuous belt conveyor systems, or it can be of the type that is shown in
the
Figures. The drive mechanism 60, 82 may be in operative rotational
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engagement with belt 10 by any means known to those of ordinary skill in the
art,
such as, for example, by a conventional sprocket arrangement wherein one or
more toothed drive wheels 82 engage links in side members 16 that are in the
form of chain members extending substantially the length of belt 10 to provide
movement to belt 10 and, consequently, to objects 20. The speed of belt 10, as
conveyed by drive mechanism 60, 82, may be at any speed that is in operative
association with the speed at which objects 20 are being fed from conveyor 56.
Although the rate of travel of belt 10 through coating system 50 may be at any
rate, in certain non-limiting embodiments, continuous line production may be
performed at 5.0 feet per minute (1.5 meters per minute).
As discussed above, when the process for coating objects 20 is an
electrophoretic coating process, such as an electrodeposition coating process,
belt 10 of the present invention may include at least one electrical grounding
member 28, and typically a plurality of grounding members 28, positioned on
belt
10 to insure a satisfactory ground for the electrical circuit in the process.
Before depositing coatings on the surface of the object 20, it may be
necessary to remove foreign matter from the-metal surface by thoroughly
cleaning and/or degreasing the object surface. In this regard, optional
pretreatment unit 70 may include a cleaning system that prepares the surface
of
objects 20 for coating. The surface of the object 20 can be cleaned by any
physical or chemical means known in the art, such as mechanically abrading the
surface or, as is typical, cleaning/degreasing with commercially available
alkaline
or acidic cleaning agents that are well known to those skilled in the art,
such as
sodium metasilicate and sodium hydroxide. Non-limiting examples of suitable
cleaning agents include CHEMKLEEN 163 and CHEMKLEEN 177 phosphate
cleaners, both of which are commercially available from PPG Industries, Inc.
of
Pittsburgh, Pennsylvania.
Following, or in lieu of, the cleaning step, the surface of the object 20
may be rinsed with water, typically deionized water, in order to remove any
residue. Optionally, the metal surface can be rinsed with an aqueous acidic
solution after cleaning with the alkaline cleaners. Examples of rinse
solutions
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include mild or strong acidic cleaners such as the dilute nitric acid
solutions
commercially available and conventionally used in, for example, metal
pretreatment processes. The object 20 may be air-dried using an air knife, by
flashing off the water by brief exposure of the object 20 to a high
temperature.
Optionally, a phosphate-based pretreatment or conversion coating
can be applied to the object 20 when object 20 includes a metallic substrate.
Suitable phosphate conversion coating compositions include those known in the
art, such as zinc phosphate, optionally modified with nickel, iron, manganese,
calcium, magnesium or cobalt. Useful phosphating compositions are described
in U.S. Patent Nos. 4,793,867 and 5,588,989; 4,941,930; 5,238,506 and
5,653,790.
A drying/preheating mechanism may be employed to dry and/or
preheat objects 20 as they pass through pretreatment unit 70 prior to being
charged for coating in coating unit 74. Any drying and/or preheating method
known to those skilled in the art may be employed in pretreatment unit 70,
such
as for example, infrared, electron beam, actinic radiation, convection,
induction,
and combinations thereof. Pretreatment. unit 70 may also be hooded, as
illustrated, depending on the cleaning solution employed.
Objects 20 to be pretreated with a cleaner and/or a conversion
coating can be conveyed through pretreatment unit 70 by any of the
mechanisms known to those skilled in the art, such as any chain driven
conventional flat-wire or chain linked continuous belt, a barrel, and/or a
basket,
among other means. In certain embodiments, objects 20 are conveyed through
pretreatment unit 70 by a chain driven balanced weave belt (which comprises
alternating left and right hand spirals joined with crimped connectors), such
as is
supplied by Cambridge International, Inc., and Ashworth Brothers, Inc. In
certain
embodiments, the balance weave belt has elongated loops which allow a
supporting member to pass through the balanced weave.
Following the optional pretreatment stage, and prior to or upon
entering coating unit 74, objects 20 may be charged by a conductor 72.
Electrical current is applied on one polarity from conductor 72 to the
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electrodeposition bath and in the opposite polarity to the conductive belt 10,
and
thereby to objects 20. In the process of the present invention, object 20
serves
as an electrode, typically the cathode, in an electrical circuit comprising
the
electrode and a counter-electrode that are immersed in an aqueous
electrodepositable coating composition.
Generally, in the process of applying the electrodepositable coating,
the aqueous dispersion of the electrodepositable composition is placed in
contact with an electrically conductive anode and cathode. Upon passage of an
electric current between the anode and cathode, an adherent film of the
electrodepositable composition will deposit in a substantially continuous
manner
on the object 20 serving as either the anode or the cathode depending on
whether the composition is anionically or cationically electrodepositable.
Although any suitable voltage may be employed to charge conductive belt 10,
the voltage employed may be dependent on the size and shape of object 20 to
.15 be coated, and the applied coating material. Electrodeposition is usually
carried
out at a constant voltage ranging from 1 volt to 7,000 volts, and typically
between
50 and 500 volts. Current density is usually between about 1.0 ampere and 15
amperes per square foot (10.8 to 161.5 amperes per square meter). If the
coating material used is anionic, belt 10 is supplied with an anionic charge,
whereas if the coating material used is cationic, belt 10 is supplied with a
cationic
charge.
Coating unit 74 may contain an electrodepositable coating material,
drawing such material from, for example, a pump well, a storage unit, such as
a
feed tank, and may be positioned to coat all or a portion of objects 20 on
belt 10.
Coating system 50 may also employ a recirculation system that allows coating
unit 74 and the storage unit to be in fluid communication. Any electrophoretic
coating unit may be employed in continuous coating system 50 of the present
invention, such as, for example, an electrodeposition tank, and the like. As
illustrated, coating unit 74 includes an electrodeposition tank. In addition,
in
certain embodiments, coating unit 74 may comprise an electrodeposition tank
that includes means for agitation of the electrodepositable coating material
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stored therein. For example, agitation may be provided at or near the bottom
of
the electrodeposition tank by feeding the electrodepositable coating material
into
eductors positioned along the bottom portion of the coating unit 74. In
addition,
agitation may be directed near coating belt 10, at or near the top of the
electrodeposition tank, by including risers arranged to discharge the
electrodepositable coating material towards the top and bottom of coating belt
10.
The electrodeposition bath composition may be employed in a tank
as one embodiment in the systems of the present invention, may be polymeric,
and may comprise a resinous phase dispersed in an aqueous medium. The
resinous phase includes a film-forming organic component which can comprise
an anionic electrodepositable coating composition, or, as is typical, a
cationic
electrodepositable coating composition. The electrodepositable coating
composition typically comprises an active hydrogen group-containing ionic
resin
and.a curing agent having functional groups reactive with the active hydrogens
of the ionic resin.
As used herein, the term "reactive" refers to a functional group that
forms a covalent bond with another functional group under suitable reaction
conditions.
Non-limiting examples of anionic electrodepositable coating
compositions include those comprising an ungelled, water-dispersible
electrodepositable anionic film-forming resin. Examples of film-forming resins
suitable for use in anionic electrodeposition coating compositions are base-
solubilized, carboxylic acid containing polymers, such as the reaction product
or
adduct of a drying oil or semi-drying fatty acid ester with a dicarboxylic
acid or
anhydride; and the reaction product of a fatty acid ester, unsaturated acid or
anhydride and any additional unsaturated modifying materials which are further
reacted with polyol. Also suitable are the at least partially neutralized
interpolymers of hydroxy-alkyl esters of unsaturated carboxylic acids,
unsaturated carboxylic acid and at least one other ethylenically unsaturated
monomer. Yet another suitable electrodepositable anionic resin comprises an
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alkyd-aminoplast vehicle, i.e., a vehicle containing an alkyd resin and an
amine-
aldehyde resin. Yet another anionic electrodepositable resin composition
comprises mixed esters of a resinous polyol. These compositions are described
in detail in U.S. Pat. No. 3,749,657 at col. 9, lines 1 to 75 and col. 10,
lines 1 to
13. Other acid functional polymers can also be used such as phosphatized
polyepoxide or phosphatized acrylic polymers as are well known to those
skilled
in the art.
By "ungelled" is meant that the polymer is substantially free of
crosslinking and has an intrinsic viscosity that can be measured when
dissolved
in a suitable solvent. The intrinsic viscosity of a polymer is an indication
of its
molecular weight. A gelled polymer, on the other hand, since it is of
essentially
infinitely high molecular weight, will have an intrinsic viscosity too high to
measure.
With reference to the cationic resin, a wide variety of cationic
polymers are known and can be used in the compositions of the invention so
long as the polymers are "water dispersible," i.e., adapted to be solubilized,
dispersed, or emulsified in water. The water dispersible resin is cationic in
nature, that is, the polymer contains cationic functional groups to impart a
positive charge. Typically, the cationic resin also contains active hydrogen
groups.
Examples of cationic resins suitable include onium salt group-
containing resins such as ternary sulfonium salt group-containing resins and
quaternary phosphonium salt-group containing resins, for example, those
described in U.S. Patent Nos. 3,793,278 and 3,984,922, respectively. Other
suitable onium salt group-containing resins include quaternary ammonium salt
group-containing resins, for example, those that are formed from reacting an
organic polyepoxide with a tertiary amine salt. Such resins are described in
U.S.
Patent Nos. 3,962,165; 3,975,346; and 4,001,101. Also suitable are the amine
salt group-containing resins such as the acid-solubilized reaction products of
polyepoxides and primary or secondary amines such as those described in U.S.
Patent Nos. 3,663,389; 3,984,299; 3,947,338 and 3,947,339.
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Usually, the salt group-containing resins described above are used
in combination with a blocked isocyanate curing agent. The isocyanate can be
fully blocked as described in U.S. Patent No. 3,984,299 or the isocyanate can
be
partially blocked and reacted with the resin backbone such as is described in
U.S. Patent No. 3,947,338.
Also, one-component compositions as described in U.S. Patent No.
4,134,866 and DE-OS No. 2,707,405 can be used as the cationic resin. Besides
the epoxy-amine reaction products, resins can also be selected from cationic
acrylic resins such as those described in U.S. Patent Nos. 3,455,806 and
3,928,157. Also, cationic resins which cure via transesterification such as
described in European Application No. 12463 can be used. Further, cationic
compositions prepared from Mannich bases such as described in U.S. Patent
No. 4,134,932 can be used. Also useful in the electrodepositable coating
compositions of the present invention are those positively charged resins that
contain primary and/or secondary amine groups. Such resins are described in
U.S. Patent Nos. 3,663,389; 3,947,339; and 4,115,900. U.S. Patent No.
3,947,339 describes a polyketimine derivative of a polyamine such as
diethylenetriamine or triethylenetetraamine with the excess polyamine vacuum
stripped from the reaction mixture. Such products are described in U.S. Patent
Nos. 3,663,389 and 4,116,900.
In one embodiment of the present invention, the cationic resins
suitable for inclusion in the electrodepositable coating compositions useful
in the
present invention are onium salt group-containing acrylic resins.
The cationic resin described above is typically present in the
electrodepositable coating compositions in amounts of 1 to 60 weight percent,
preferably 5 to 25 weight percent based on total weight of the composition.
As previously discussed, the electrodepositable coating
compositions which are useful in the present invention typically further
comprise
a curing agent which contains functional groups which are reactive with the
active hydrogen groups of the ionic resin.
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Aminoplast resins, which are typically used as curing agents for
anionic electrodeposition, are the condensation products of amines or amides
with aidehydes. Examples of suitable amine or amides are melamine,
benzoguanamine, urea and similar compounds. Generally, the aldehyde
employed is formaldehyde, although products can be made from other
aldehydes such as acetaldehyde and furfural. The condensation products
contain methylol groups or similar alkylol groups depending on the particular
aldehyde employed. Preferably, these methylol groups are etherified by
reaction
with an alcohol. Various alcohols employed include monohydric alcohols
containing from 1 to 4 carbon atoms such as methanol, ethanol, isopropanol,
and n-butanol, with methanol being preferred. Aminoplast resins are
commercially available from American Cyanamid Co. under the trademark
CYMEL and from Monsanto Chemical Co. under the trademark RESIMENE.
The aminoplast curing agents are typically utilized in conjunction with
an active hydrogen-containing anionic electrodepositable resin in amounts
ranging from about 5 percent to about 60 percent by weight, preferably from
about 20 percent to about 40 percent by weight, the percentages based on the
total weight of the resin solids in the electrodeposition bath.
Curing agents that can be employed for cationic electrodepositable
coating compositions include blocked organic polyisocyanates. The
polyisocyanates can be fully blocked as described in U.S. Patent No. 3,984,299
column 1 lines I to 68, column 2 and column 3 lines 1 to 15, or partially
blocked
and reacted with the polymer backbone as described in U.S. Patent No.
3,947,338 column 2 lines 65 to 68, column 3 and column 4 lines I to 30. By
"blocked" is meant that the isocyanate groups have been reacted with a
compound so that the resultant blocked isocyanate group is stable to active
hydrogens at ambient temperature but reactive with active hydrogens in the
film
forming polymer at elevated temperatures, usually between 90 C and 200 C.
Suitable polyisocyanates include aromatic and aliphatic
polyisocyanates, including cycloaliphatic polyisocyanates; representative
examples include diphenylmethane-4,4'-diisocyanate (MDI), 2,4- or 2,6-toluene
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diisocyanate (TDI), including mixtures thereof, p-phenylene diisocyanate,
tetramethylene and hexamethylene diisocyanates, dicyclohexylmethane-4,4'-
diisocyanate, isophorone diisocyanate, mixtures of phenylmethane-4,4'-
diisocyanate and polymethylene polyphenylisocyanate. Higher polyisocyanates
such as triisocyanates can be used. An example would include
triphenylmethane-4,4',4"-triisocyanate. Isocyanate prepolymers with polyols
such as neopentyl glycol and trimethylolpropane and with polymeric polyols
such
as polycaprolactone diols and triols (NCO/OH equivalent ratio greater than 1)
can also be used.
The polyisocyanate curing agents are typically utilized in conjunction
with the cationic resin in amounts ranging from 1 weight percent to 65 weight
percent, such as from 5 weight percent to 45 weight percent, based on the
weight of the total resin solids present composition.
The aqueous compositions of the present invention are in the form of
an aqueous dispersion. The term "dispersion" is believed to be a two-phase
transcoating, translucent or opaque resinous system in which the resin is in
the
dispersed phase and the water is in the continuous phase. The average particle
size of the resinous phase is generally less than 1.0 and usually less than
0.5
microns, and may be less than 0.15 micron.
The concentration of the resinous phase in the aqueous medium is
at least 1 and usually from about 2 to about 60 percent by weight based on
total
weight of the aqueous dispersion. When the compositions of the present
invention are in the form of resin concentrates, they generally have a resin
solids
content of about 20 to about 60 percent by weight based on weight of the
aqueous dispersion.
Electrodeposition baths useful in the present invention are typically
supplied as two components: (1) a clear resin feed, which includes generaily
the
active hydrogen-containing ionic electrodepositable resin, i.e., the main film-
forming polymer, the curing agent, and any additional water-dispersible, non-
pigmented components; and (2) a pigment paste, which generally includes one
or more pigments, a water-dispersible grind resin which can be the same or
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different from the main-fiim forming polymer, and, optionally, additives such
as
wetting or dispersing aids. Electrodeposition bath components (1) and (2) are
dispersed in an aqueous medium which comprises water and, usually,
coalescing solvents.
The electrodeposition bath of the present invention has a resin and
pigment solids content usually within the range of about 5 to 25 percent by
weight based on total weight of the electrodeposition bath.
Besides water, the aqueous medium may also contain a coalescing
solvent. Useful coalescing solvents include hydrocarbons, alcohols, esters,
ethers and ketones. The preferred coalescing solvents include alcohols,
polyols
and ketones. Specific coalescing solvents include isopropanol, butanol, 2-
ethyihexanol, isophorone, 2-methoxypentanone, ethylene and propylene glycol
and the monoethyl, monobutyl and monohexyl ethers of ethylene glycol. The
amount of coalescing solvent can be between about 0.01 and 25 percent such
as from about 0.05 to about 5 percent by weight based on total weight of the
aqueous medium.
As discussed above, a pigment composition and, if desired, various
additives such as surfactants, wetting agents or catalyst can be included in
the
dispersion. The pigment composition may be of the conventional type
comprising pigments, for example, iron oxides, strontium chromate, carbon
black, coal dust, titanium dioxide, talc, barium sulfate, as well as color
pigments
such as cadmium yellow, cadmium red, chromium yellow and the like.
The pigment content of the dispersion is usually expressed as a
pigment-to-resin ratio. In the practice of the invention, when pigment is
employed, the pigment-to-resin ratio is usually within the range of about 0.02
to
1:1. The other additives mentioned above are usually in the dispersion in
amounts of about 0.01 to 3 percent by weight based on weight of resin solids.
The present invention may also employ non-electrophoretic coating
compositions. Suitable non-electrophoretic coating compositions can be any of
a variety of coating compositions well known in the art and the specific
composition utilized is generally based upon the final appearance and
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performance properties desired by the user. For example, the non-
electrophoretic coating composition can be a liquid coating composition or in
solid particulate form, e.g., a powder coating composition. Suitable non-
electrophoretic coating compositions are those set forth in U.S. Patent No.
6,676,820, which is incorporated herein by reference in its entirety.
Referring again to Fig. 7, as belt 10 carries objects 20 from optional
pretreatment unit 70 into coating unit 74, belt 10, and particularly blade
members
14, may be pivotably rotated, for example, from a horizontal position to a
slightly
angled position, such as at a 15-20 degree angle from horizontal, to enter
coating unit 74. As best illustrated in FIG. 5, pivotable portion 15 and
slotted
portion 17 of blade members 14 allow blade members 14 to pivot around
elongated pins 22 to provide relatively free angular movement thereto such
that
belt 10 freely enters and exits coating unit 74 when the coating unit 74
employs a
coating tank, as illustrated. As a result, coating materials in coating unit
74 may
be readily applied to each object 20 positioned on belt 10.
Coating unit 74 may also serve as a reservoir to collect excess
coating material from the exterior surface of objects 20 as the coated objects
20
are carried away by belt 10 after coating, to prevent waste thereof. In this
manner, the electrophoretic coating may be deposited upon objects 20 to a
desired thickness based on various factors, such as the speed of belt 10, the
composition of the coating material, the temperature of coating unit 74, and
the
like. Typically, the temperature of coating unit 74 and coating material is
maintained in the range of 21 to 38 C. Coating times through coating unit 74
may vary considerably and depend on voltage, temperature and composition of
the coating material, desired film thickness, and the like. Typical coating
time is
2 minutes, and may range from 30 seconds to 5 minutes.
The excess coating material may be rinsed from coated object by
one or more rinsing units 76 positioned downstream from coating unit 74. Air
knives (not shown) may be employed to remove excess rinse water from objects
20. Rinsing unit 76 may include a recycle system for returning excess material
to the mother tank for reuse. Deionized water, municipal water, and/or
permeate
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from an ultrafiltration system 78 may be used for rinsing the excess material
from
objects 20. The rinse water may be filtered and expelled from coating system
50, or may be recycled back through the system for reuse in order to provide a
closed, non-polluting system.
Belt 10 may carry the coated and, optionally, rinsed objects 20
through drying unit 80 to dry the coating deposited on objects 20. As used
herein the terms "dry", "dried", or "drying" are intended to include both
drying and
curing. In one embodiment, the electrodeposited coating is dried by driving
substantially all the solvent and/or water from the coating either by
evaporation
at ambient temperature or by forced drying at elevated temperatures (for
example 150 F to 600 F (82 C to 316 C)). The term "dried" is also intended to
include exposing the electrocoated object 20 to thermal conditions sufficient
to
crosslink the co-reactive film components.
Also, as used herein, the term "cure" as used in connection with a
composition, e.g., "a cured composition," shall mean that any crosslinkable or
co-reactive components of the composition are at least partially crosslinked
or
co-reacted. In certain embodiments of the present invention, the crosslink
density of the crosslinkable components, i.e., the degree of crosslinking,
ranges
from 5% to 100% of complete crosslinking. In other embodiments, the crosslink
density ranges from 35% to 85% of full crosslinking. In other embodiments, the
crosslink density ranges from 50% to 85% of full crosslinking. One skilled in
the
art will understand that the presence and degree of crosslinking, i.e., the
crosslink density, can be determined by a variety of methods, such as dynamic
mechanical thermal analysis (DMTA) using a Polymer Laboratories MK III DMTA
analyzer conducted under nitrogen. This method determines the glass transition
temperature and crosslink density of free films of coatings or polymers. These
physical properties of a cured material are related to the structure of the
crosslinked network.
Generally, the electrodepositable coating compositions which are
useful in the present invention are applied under conditions such that a
substantially continuous coating having a dried film-thickness ranging from
0.3 to
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2.0 mils (7.6 to 50.8 micrometers), usually from 0.6 to 1.0 mils (15.2 to 25.4
micrometers) is formed upon the surfaces of objects 20.
Any method known to those skilled in the art of drying the applied
coating may be employed, such as, for example, infrared, electron beam,
actinic
radiation, convection, induction, and combinations thereof. For example,
drying
unit 80 of continuous system 50 may employ heat treatment to the coating by
the
combination of infrared radiation and convection. In one embodiment of the
present invention, after the coating has been applied by electrodeposition, it
is
cured, usually by heating, at elevated temperatures ranging from 82 C to 316 C
for a period ranging from 60 to 2400 seconds. Alternatively, the coating can
be
cured using infrared curing techniques as are well known in the art, typically
for a
period ranging from 5 to 300 seconds or a time sufficient to obtain a peak
metal
temperature ranging from 300 F to 550 F (149 C to 288 C). For non-metallic
substrates, the times and temperatures may be adjusted and depend, at least in
part, on the particular substrate employed.
In one embodiment of the present invention, a cooling unit, such as a
refrigeration unit, a series of blowers (not shown), water misting nozzles,
and/or.
a water bath, may be positioned after drying unit 80 to lower the temperature
of
objects 20 for handling and transport. Air may be blown over objects 20 at any
suitable velocity and temperature, and may range from, for example, 150 to
10,000 ft/min (0.8 to 51 m/s) at ambient. Typically, the cooling unit reduces
the
surface temperature of objects 20 to below 120 F (49 C).
After exiting drying unit 80 and passing through the optional cooling
unit, objects 20 may be released from belt 10 by manual or automated means.
Suitable releasing means include mechanical assistance and/or gravity assisted
means wherein as belt 10 is conveyed over drive wheel 82, the movement of belt
10 around drive wheel 82, with the aid of gravity, acts to release each object
20
from belt 10. As belt 10 is conveyed around drive wheel 82, belt 10 may be
rotated, for example, from a horizontal position to an angled position, such
as,
for example, at a 90 to 180 degree angle, as belt 10 make its return to the
feeding mechanism 52. Although belt 10 may be conveyed around drive wheel
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82 at any angle, in one embodiment of the present invention, the angle of
rotation may be 135 degrees, so that objects 20 may fall clear of belt 10 as
belt
conveyed around drive wheel 82. As illustrated in FIG. 6, pivotable portion 15
and slotted portion 17 of blade members 14 allow blade members 14 to
5 substantially freely rotate around elongated pin 22 via relative movement
thereto
provide a means for belt 10 to expand and contract as belt 10 freely rotates
around drive wheel 82 and other return wheels, as illustrated. The released
and
coated objects 20 may then be deposited in receptacle 84 for packing or for
further processing. Continuous rotation of belt 10 returns belt 10 back to the
10 feeding mechanism 52 for receipt of additional objects 20 for support and
retention therewith for coating and drying.
Coating system 52 may include a cleaning unit 88, such as a
rotatable brush, as illustrated, that cleans the surface of belt 10 to reduce
buildup
of coating on the belt surface and/or to promote electrical contact between
blade
members 14 and objects 20 prior to receiving additional objects 20 for
coating.
In embodiments of the present invention that employ a rotatable brush, as
illustrated, the rotatable brush may be formed of any suitable material that
effectively cleans the surface of the belt 10, and may include individual
resilient
bristles, such as carbon steel wire bristles, that provide effective cleaning
of, for
example, the tips of the saw teeth and therebetween. One or more additional
cleaning units, such as a rotatable brush, may be employed after the release
of
objects 20 to reduce coating buildup on, for example, side chains 16, to
enhance
belt 10 to conductor 72 contact.
Although the coating system 50 set forth above has been described
as applying a single coating over objects 20, it is contemplated that more
that
one coating may be deposited on objects 20. For example, two or more layers
of coating may be deposited on objects 20 by adding additional coating and
drying units to the coating system 50 described above, or by running coated
objects 20 through the coating system 50 one or more additional times, or by
running objects 20 through a combination of coating system 50 (when
electrophoretic) in conjunction with one or more non-electrophoretic coating
29
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WO 2006/020857 PCT/US2005/028721
systems either prior or subsequent to coating system 50. Accordingly, the
description of the coating system 50 set forth above is merely illustrative of
one
method of employing the coating system 50, and is not intended to limit the
scope of the present invention.
The present invention allows objects to be coated at high speeds
through various coating processes, while reducing the risk that those coated
surfaces will be marred or, otherwise damaged, by providing a supporting
member having one or more, and in some embodiments a plurality of, small
contact points along the length of the object. The relatively small contact
points
may minimize the touch points on the object, promote electrical ground after
repeated coating cycles, and/or promote the application of a smoother coating
on the surface of the object. In addition, the present invention provides a
system
for coating objects on a single continuous belt through the coating and drying
units without the need for belt transfer. As a result, the deposited coating
on the
surfaces of the object may be more uniform and include fewer defects than
previous prior art coating techniques.
Whereas particular embodiments of this invention have been
described above for purposes of illustration, it will be evident to those
skilled in
the art the numerous variations of the details of the present invention may be
made without departing from the invention as defined in the appended claims.
