U.S. patent application number 16/857324 was filed with the patent office on 2020-08-13 for apparatus for applying protective films.
The applicant listed for this patent is EXEL INDUSTRIES. Invention is credited to Michael DeFillipi, Vipin Patel.
Application Number | 20200254745 16/857324 |
Document ID | 20200254745 / US20200254745 |
Family ID | 1000004782782 |
Filed Date | 2020-08-13 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200254745 |
Kind Code |
A1 |
DeFillipi; Michael ; et
al. |
August 13, 2020 |
APPARATUS FOR APPLYING PROTECTIVE FILMS
Abstract
An improved method of protecting finished surfaces of, for
example, automobiles replaces the prior art methods of spraying and
hand laying large plastic sheets. In this method a slotted die
extrudes a ribbon of a polymeric emulsion onto the surface to be
protected under robotic control so as to maintain a constant
spacing between die and surface. The die can be moved quickly and
with great precision. The applied film is cured and, at a later
time, is peeled from the surface.
Inventors: |
DeFillipi; Michael;
(Plymouth, MI) ; Patel; Vipin; (Livonia,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EXEL INDUSTRIES |
Paris |
|
FR |
|
|
Family ID: |
1000004782782 |
Appl. No.: |
16/857324 |
Filed: |
April 24, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15910367 |
Mar 2, 2018 |
10696033 |
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16857324 |
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14311533 |
Jun 23, 2014 |
10000049 |
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15910367 |
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15349349 |
Nov 11, 2016 |
10315405 |
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14311533 |
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14311533 |
Jun 23, 2014 |
10000049 |
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15349349 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B05C 5/0254 20130101;
B05D 1/325 20130101; B29C 48/07 20190201; B29C 48/305 20190201;
B05D 1/26 20130101; B32B 37/0046 20130101; B05C 5/0283 20130101;
B05D 1/42 20130101; B05D 5/00 20130101; B05C 5/0216 20130101; B32B
37/153 20130101; B29C 48/154 20190201 |
International
Class: |
B32B 37/15 20060101
B32B037/15; B32B 37/00 20060101 B32B037/00; B05D 1/42 20060101
B05D001/42; B29C 48/154 20060101 B29C048/154; B05D 5/00 20060101
B05D005/00; B05C 5/02 20060101 B05C005/02; B05D 1/26 20060101
B05D001/26; B29C 48/07 20060101 B29C048/07; B29C 48/305 20060101
B29C048/305 |
Claims
1. A method of applying a peelable film of a cured polymeric
emulsion to the painted surface of an article of manufacture
comprising the steps of: a. supplying an emulsion of a polymer to
an extrusion die having a body with a long, narrow slot-shaped
outlet; b. robotically moving the die over said surface while
maintaining a constant distance between the die outlet and the
surface; c. extruding said emulsion onto said surface in the form
of a non-atomized ribbon of said material through said outlet while
moving the die relative to the surface and maintaining said
predetermined distance to adhere one or more ribbons to said
surface; and thereafter, d. curing the applied ribbon or ribbons of
film.
2. The method defined in claim 1 wherein the viscosity of the
emulsion is between about 3,000 and 12,0000 centipoise at a
predetermined operating temperature.
3. The method defined in claim 1 wherein the distance between the
die outlet and the finished surface is about 15 mm.
4. The method defined in claim 1 including the further step of
maintaining the temperature of the body at said predetermined
operating temperature.
5. The method defined in claim 1 including the further step of
peeling the cured applied ribbon from the article.
6. The method defined in claim 1 wherein the thickness of the
applied ribbons is about 200 microns.
7. The method defined in claim 1 wherein the robot moves the die
body during application of said ribbons at a speed of between 1,500
mm and 2,000 mm per second.
8. The method defined in claim 1 wherein the robot applies multiple
ribbons in overlapping strokes.
9. The method defined in claim 1 wherein the polymer is PVA.
10. The method defined in claim 1 wherein the article of
manufacture is a painted automobile body component.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/910,367 filed Mar. 2, 2018, which is a
divisional of U.S. patent application Ser. No. 14/311,533, filed
Jun. 23, 2014 (U.S. Pat. No. 10,000,049), and a divisional of U.S.
patent application Ser. No. 15/349,349, filed Nov. 11, 2016 (U.S.
Pat. No. 10,315,405); the entire contents of both are incorporated
herein.
FIELD OF THE INVENTION
[0002] Disclosed herein is a method and apparatus for producing and
applying ribbons of polymeric film to the surfaces of an article of
manufacture, such as but not limited to an automobile body or a
portion thereof, wherein the method includes using an extrusion die
with a slot opening configured to hydraulically deliver a ribbon of
polymer-based film with controlled width, thickness and edge
characteristics. The die is roborically controlled to maintain a
constant spacing from the target surface and ribbons may be applied
in parallel overlapping manner to cover a surface with a high level
of spacing with respect to edges and gaps. The ribbons may be cured
and, in the case of an automobile, peeled from the surface at the
time of sale or before a showing.
BACKGROUND OF THE INVENTION
[0003] It is known to protect the painted exterior surfaces of
glass and automobile parts with pre-formed, laminated sheets or
sprayed-on polymeric films for various purposes; e.g., to reduce
the likelihood of damage during shipment, storage and use or to act
as spacers for stacking. There have been numerous problems
associated with the application of such films. Spraying invokes the
need to deal with environmental issues as well as overspray, both
in the air and on parts of the article which are not to be coated.
For non-permanent applications, it is often necessary to use
solvents to remove the film. Lamination involves, first, the
extrusion of a thin sheet of plastic film and, second, the step of
joining the plastic film to a paper backing so it can be rolled up
for shipment or storage. When the time comes to apply the film to,
for example, an automobile body, several laborers are required to
unroll the paper-backed film, lay the film over the automobile,
remove the paper backing, and smooth the film. The result is a
peelable film requiring no solvents or detergents for removal, but
the manufacturing and application processes are labor intensive
and, therefore, creates substantial expense.
[0004] It is also known to apply a film or coating of resilient
protective polymeric material such as PVC to the rocker panels and
other locations on automobile bodies to serve as an anti-chip
coating. The coating is typically sprayed onto the vehicle rocker
panel during the painting phase and dried or cured using, for
example, standard paint oven convection heating. This sprayed-on
method of application requires carefully masking of the body of the
vehicle for overspray protection, which is labor-intensive. The
masking must also be removed and disposed of, adding further cost
to the process.
SUMMARY OF THE INVENTION
[0005] In general, this document discloses a device and a method of
use as described above in which large and small areas of fully or
partially finished surfaces of manufactured products can be coated
with polymer-based protective films, which films can be applied by
the controlled hydraulic "extrusion" o ribbons of polymer-based
material such as polyvinyl acetate without atomization and with
controlled width, thickness and edge characteristics. This
apparatus can create, for example, ribbons of polymeric film that
have a desired thickness profile from edge to edge that promotes
peelability and that can be applied extremely close to a part edge
or a seam between adjacent assembled parts without crossing or
bridging the seam. This virtually eliminates the problems
associated with prior art spray methods as well as the
labor-intensive steps of applying protectant from a paper backed
roll of pre-extruded film. The device can also be used to apply
ribbons of polymeric film for other purposes.
[0006] An aspect of the subject matter described herein is an
applicator die for producing a ribbon or film of fluidized
polymeric material directly onto a surface to be protected without
atomization or other division of the film leaving the die. The
applicator die can be robotically guided and controlled as to
spacing from the target surface to dynamically and consistently lay
down a polymeric film of the desired width, length, thickness and
edge characteristics in a precise fashion, i.e., coming very close
to seams and part edges, and at low labor cost. Although the
examples described herein involve fairly flat surfaces, the
applicator can be configured to conform to curved or complex
surfaces. The applicator described herein may be said to
"hydraulically extrude" a film of laminarized, emulsified polymeric
material in a ribbon with such well controlled edge-to-edge
consistency and thickness as to be suitable for masking as well as
protection. A preferred emulsion thickness for protecting painted
auto body surfaces is 200 microns (wet) with slight beads on the
edges to promote peelability. This is readily distinguished from
sound-deadening material which is generally 2000 or more microns
thick and is not peelable. When used to produce a protective layer
for an automobile body, the prior art steps of pre-extruding and
backing a film are eliminated because the robotic arm guiding the
applicator can be indexed to produce multiple overlapping ribbons
that together cover large uninterrupted areas right up to edges or
seams. Moreover, the applicator hereinafter described in detail can
be "ambidextrous" in that it is capable of producing adjacent
parallel ribbons of plastic film without indexed rotation for
reversal; i.e., the applicator can be reversed in its direction of
travel. In addition, the applicator can be used to apply different
materials for different purposes to horizontal, vertical and
inverted surfaces, whether flat, concave or convex.
[0007] A specific use of the subject matter described herein is the
use of the applicator die described above to apply a protective
film of a polymeric material, such as an aqueous solution of
polyvinyl acetate (PVA), to the fully or partially finished
surfaces of an automobile body or component part therefor. As
stated above, this may be for masking or protection purposes, in
which case the film is temporary and must be peelable. The film is,
after curing, readily and easily peelable without the use of
solvents of detergents in large part because it is of its thickness
profile across its width. For the reasons described above, this
process is highly efficient due in part to the fact that the
application of overlapping polymeric ribbons, applied in a back and
forth fashion to cover large areas, can be carried out simply by
indexing the applicator between parallel rows and without the need
to rotate the applicator 180.degree. for the next run. The
applicator can essentially be moved relative to the application
surface at about the velocity at which the applied material is
emitted from the applicator die. Velocities of about 1500 to 2000
mm/second have been achieved. However, translation speed will vary
from application to application.
[0008] As further described herein, the preferred applicator die
comprises a two-part body with an inlet, an internal gallery, a
bottom edge in which a long, narrow, outlet groove is created by a
spacer or shim placed between the two mirror-image body parts, and
the shim thickness controls the thickness of the film or ribbon to
be extruded. The preferred gallery includes internal grooves in the
two body parts that face each other and run parallel to and
adjacent the bottom edge, although a one-sided groove arrangement
is also feasible. The gallery groove or grooves create an internal
volume for material received from the inlet and emit or "extrude"
that material through the slot between the facing surfaces of the
two body parts. The shim geometry relative to the gallery groove
has been found to be important in controlling film edge qualities;
i.e., the gallery grooves are radiused, i.e., 180.degree. rounded
at their ends and the shim is designed with a top edge that lies
along the top edge of a gallery groove and with side edges that
flare out at an angle of about 5.degree. to 50.degree. but
preferably 17.degree. to create a slightly broadening film.
Importantly, the length of the extrusion slot surfaces over which
the film material passes between the gallery slot and the die exit
edge is constant from one edge of the slot to the other and we have
found that this ensures a substantially uniform film flow velocity
across the entire width of the extrusion slot.
[0009] For peelable protective film or for masking, a film with a
uniform thickness of 200 microns from edge to edge is preferred.
This results from the shim geometry shown in FIG. 11B and described
below. An exemplary film width is 75-
[0010] Other advantages, features and characteristics of the
subject matter disclosed herein, as well as methods of operation
and functions of the related elements of the structure, and the
combination of parts and economies of manufacture, will become more
apparent upon consideration of the following detailed description
and the appended claims with reference to the accompanying
drawings, the latter being briefly described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The description herein makes reference to the accompanying
drawings wherein like reference numerals refer to like parts
throughout the several views and wherein:
[0012] FIG. 1 is a perspective view of an applicator die as
described herein mounted on a robot arm and used to apply a
protective film to the hood of an automobile;
[0013] FIG. 2 is a schematic view of a representative pattern of
runs of the robotically moved applicator die in fully covering an
automobile hood;
[0014] FIG. 3 is a plan view of the ribbons laid down by the run
pattern of FIG. 2;
[0015] FIG. 4 is a perspective view of another application of the
teachings herein as applied to the use of permanent protective
films on rocker panels;
[0016] FIG. 5 is an exploded view of an applicator as described in
the following specification;
[0017] FIG. 6 is a sectional view through the application of FIG.
4;
[0018] FIGS. 7A, 7B, 7C, and 7D are diagrams of a material ribbon
emerging from applicator dies of different design;
[0019] FIG. 8 is a block diagram of one of the methods described
herein;
[0020] FIG. 9 is a block diagram of another method;
[0021] FIG. 10 is a schematic diagram of a complete system; and
[0022] FIGS. 11A and B are full and partial plan views of the shim
26 of FIG. 5 overlying a die block 20 wherein FIG. 11 B indicates a
flow pattern found to be advantageous.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0023] Referring to FIG. 1, an applicator die 10 is shown mounted
on the end of an arm 12 of a numerically controlled multi-axis
robot 14 capable of moving the applicator die in three-dimensional
space as well as rotating the applicator die about multiple axes.
The robot itself is conventional. The applicator die 10 is shown
engaged in a process of applying 85 mm wide and 200 micron thick
ribbons 16, 17 of polymeric film to the hood of an automotive
vehicle which has been painted and essentially fully assembled,
ready for shipment to a dealer. In FIG. 1, a first ribbon 16 has
been applied across the rearmost portion of the hood 18; i.e., the
portion closest to the windshield of the automobile, by moving the
robot from right to left along a slightly curved path as shown in
FIG. 1. The robot then indexed the arm 12 toward the front of the
vehicle and is shown in the process of applying a second ribbon 17
moving from left to right across the hood 18 as seen in FIG. 1.
Each ribbon is approximately 85 mm wide, and with an overlap with
the adjacent ribbon or ribbons of about 1-7 mm. The preferred
thickness profile for this particular application is uniform from
edge to edge at about 200 microns.
[0024] The material being applied is an aqueous solution of
polyvinyl acetate (PVA) at a temperature between about 70.degree.
and 120.degree. F. and with a viscosity of about 3000 to 12,000
centipoise. Material is supplied to applicator die 10 under close
temperature and flow rate control conditions via supply conduit 20;
temperature-controlled liquid is supplied via conduit 21. The
velocity of the material ribbon from the applicator can, for
example, be as much as about 2000 mm/second and the robot 14 moves
the applicator die 10 relative to the surface of the hood 18 at
about that same speed. The spacing between the material outlet,
i.e., the bottom edge of the applicator die 10 and the surface of
the hood 18 is about 5 to 15 mm. The ratio of polymer to water in
the applied material in an illustrative case is approximately 50/50
but will vary with the application. These figures are given by way
of example. Robot speed, extrusion rate, spacing and emulsion
ratios can all vary.
[0025] Referring now to FIGS. 2 and 3, the complete coverage of the
hood 18 is achieved using crosswise movements to produce ribbons
16a, 16b, 16c and 16d in a back-and-forth fashion, the robot
serving to index the applicator forward by just less than the width
of the applied ribbon but without the need to rotate the applicator
die 10 through 180.degree. as the applicator die 10 is entirely
ambidextrous; i.e., it has no "forward" side and operates in a
spatial orientation nearly or completely orthogonal to the surface
upon which material is being applied.
[0026] As shown in FIGS. 2 and 3, the material is applied to the
surface of the hood in back-and-forth, overlapping ribbons until
the forward-most ribbon 16d is applied at which time the applicator
is rotated 90.degree. and moved along the ribbon 16e to cover the
left edge of the hood and the lateral ribbon ends, as shown in FIG.
2. The applicator is then moved to the top right portion of the
hood, as shown in FIG. 3 to apply the final ribbon 16f. It will be
noted that material is not applied across vehicle body seams. The
pattern of ribbons in FIGS. 2 and 3 is illustrative only.
[0027] Looking now to FIGS. 5 and 6, an applicator die 10 is shown.
It is referred to as an "applicator die" because the film ribbons
issued from it are essentially hydraulically extruded as opposed to
atomized or aerated and sprayed. There is no "spray" of particles
or droplets. The term "hydraulic extrusion" is used herein to mean
a laminar flow of non-atomized fluid propelled by hydraulic
pressure rather than by air or other compressible propellant. The
applicator die 10 is shown to comprise blocks 23 and 28 which are
machined out of solid stainless steel, for example, about 31/2''
long by 2'' high with rounded bottom corners and mitered top
corners for weight reduction. Placed between the two blocks 23 and
28 in the assembled condition is a shim or spacer 26 made of brass,
stainless steel, plastic or other suitable material having locator
holes 22 so that it may be precisely located on guide pins 40 which
are inserted into precisely located holes in the interior surface
41 of the block 23. A fourth element of the applicator die
combination is a valve 30 which helps to produce sharper cutoffs as
hereinafter explained.
[0028] Block 23 is thicker than block 28 and includes a threaded
material entry port 22 which extends downwardly to approximately
the center of the block where it communicates with a forwardly
directed passage 32 which, in turn, feeds material into a gallery
of machined grooves comprising diverging legs 34, 36 and a
horizontal cross-groove 38, all of which are of the same depth. A
horizontal groove 50 is formed in the inside surface 31 of block 28
in full face-to-face registry with groove 38 in block 23 to create
a gallery volume parallel to and adjacent the bottom edge surface
of the die. The spacer 26 fits flush against the inside surface 41
of the block 23 to cover most of the grooves 34 and 36 of the
gallery; the shim has a lower cutout or "relief" 44 with 15.degree.
flared side edges 46, which terminate at points 47 on the radiused
corner arc of the die block which is 36-degrees from the vertical
centerline. The shim provides a gap between the inside surfaces 41,
31 of blocks 28 and 23, respectively, of uniform thickness for
material to flow downwardly from the horizontal grooves 38 and 50
and out through the bottom outlet 58 of the die, as shown in FIG.
11. A preferred shim design is shown in detail in FIG. 11B. The
ribbon of film preferably meets the target surface at a distance of
between 5 and 15 mm from the bottom edge of the die 10, i.e., where
the opposite sides of the ribbon have become essentially
parallel.
[0029] Block 28 has locator holes 52 which receive the guide pins
40 and locate the block relative to the face 42 of the opposing
block 23, as well as the hidden face of the spacer 26. Block 28 has
a single horizontal gallery groove 50 which is opposite but
co-extensive with the groove 38 within the relief 44 of the spacer
26 to allow the horizontal fluid chamber created by the two grooves
38, 50 to fill with the PVA material while preventing lateral
outflow as well as upflow between the spacer and the inside surface
41 of the block 23. An aperture 56 cooperates with the valve 30 to
pull the pin 61 out of the flow chamber when cutoff is desired.
This rapidly increases chamber volume and correspondingly reduces
chamber pressure, resulting in a slight negative pressure with
material pull-back. This feature is optional.
[0030] When applied to a fully finished painted surface for
temporary protective purposes, the material applied is polyvinyl
acetate in an emulsion containing, for example, about 50% water and
50% polymer. When dispensed, the material is extruded from the
applicator die 10 with a width of about 85 mm. Thereafter, it has
been found that the material begins to converge due to surface
tension. Accordingly, the spacing between the outlet 58 of the
applicator die 10 and the surface upon which the ribbons are being
applied is preferably held such that the material is applied at or
near the point of maximum width where the opposite edges are
parallel. See FIG. 7.
[0031] As indicated above, the applicator die 10 can be moved at
the selected rate over the target surfaces while material is
dispersed or extruded therefrom. When placed in an infrared oven,
drying time of about 15 minutes has been shown to be possible at a
temperature of 180.degree.. Convective and/or microwave drying can
also be used.
[0032] It will be noted that the applicator die 10 is operated in a
position which is orthogonal to the target surface rather than
angled or tipped in the direction of flow as is the case with
typical spray-type, deflective applicators. It will also be noted
that the extruded ribbon of material being applied is not particled
or atomized; rather, it is a full, continuous film of material
moving outwardly and downwardly in laminar form and at a desired
rate. Because the applicator is ambidextrous, it does not have to
be turned around by rotation between parallel passes in opposite
directions and this too, increases the rate at which an automobile
body part, for example, a hood, can be covered. After coating, the
component goes to an oven for faster curing. FIG. 7A shows how the
film behaves as it leaves the applicator die 10. Because of the
diverging or flared shape of the die exit slot, the ribbon diverges
at 53 but quickly converges due to surface tension. The
die-to-target spacing is preferably such as to apply the ribbon to
the target surface at about the point of maximum ribbon width.
[0033] FIG. 7B shows how the extruded material behaves when using a
spacer that defines the die outlet slot 59 with straight sided,
parallel edges A5. The material converges immediately upon
departing the die slot due to surface tension; see ribbon edges 53
and becomes difficult to control.
[0034] FIG. 7C shows in profile two ribbons that can be created
using the dies of FIGS. 7A and 7B. The top ribbon A-8 is 300
microns thick and has 500 micron thick edge beads, measured at a
distance of 10 mm from the die outlet. This is undesirable.
[0035] The bottom ribbon A-7 shows the ribbon profile produced by
the invention die of FIGS. 5 and 11B. It is 200 microns thick with
250 micron edge beads at 10 mm from the slot outlet. This is a
desirable profile. The very shallow edge beads promote clean
peeling without excess material in the overlap areas or along the
edges of the anti-chip coat.
[0036] FIG. 8 is a schematic diagram of a method of applying a
protective film of an automobile. The first step 100 as indicated
by the legend is to apply the emulsion in overlapping and
alternating strokes. The second step 102 is to dry the emulsion
with infrared radiation. The third step 104, in the case of a
manufactured automobile, is to ship the protected vehicle and the
final step 106, typically performed by the dealer, is to peel the
coating off of the vehicle and dispose of it in an environmentally
appropriate fashion. It peels in one piece and the material can be
recycled.
[0037] An alternative or additional method of using the applicator
die 10 is shown in FIGS. 4 and 9. This method comprises a first
step 200 of applying primer to a rocker panel of an automotive body
300 in conventional fashion. Thereafter, a robot 302 carrying an
applicator die 10 essentially as shown in FIGS. 5 and 6 and
described above is used in step 202 to apply a PVC emulsion to the
primed rocker panel as an anti-chip coating. It will be understood
that the applicator die 10 has material and coolant supply lines
running to it as is the case for the film applicator in FIG. 1. In
this case, the polyvinyl chloride solution or emulsion comprises a
polymer in an organic solvent applied in a ribbon of the
appropriate thickness while the rocker panel is essentially
vertical. Temperatures, spacing and application rates are
empirically determined in view of the fact that the material has a
viscosity of about 50,000 centipoise. It has been found that
additional primer and body color paint can be applied over the PVC
ribbon in step 204 before it is dried; i.e., paint can be applied
"wet-on-wet." The PVC surface produced by the applicator is glossy
and uniform in thickness. In this embodiment, only one pass along
the rocker panel is required.
[0038] There are numerous advantages to the use of this process for
the anti-chip coating relative to the prior art process of spraying
the coating on the car. Spraying requires the entire vehicle to be
masked to protect it against overspray which is highly detrimental
to paint finishes. Therefore, this method eliminates the need to
mask the vehicle and to remove and dispose of the masking
materials. In addition, the laminar ribbon offers a smooth, glossy
appearance as compared to the rough appearance caused by
spraying.
[0039] FIGS. 11A and B show the preferred embodiment of the
extrusion die and especially the geometry of the relief 44 in the
shim 26 relative to the groove 38 and the 180.degree. rounded ends
A-1 thereof. FIG. 11A shows the shim 26 overlying the die block 28
with the top edge 300 of the shim relief overlying and coextensive
with the top edge of the gallery groove 38. The right and left
corner or inside edges 46 of the shim partially follow the curve of
the gallery groove end, but flare downward to a point 47 which is
located at the 36-degree point along the arc of the outer die block
28 corner radius. Both the right and left inside edge lines 46 of
the shim, which begin at the outer radius point 47, terminate at
point 48 where they intersect the tangent of the half-circle (A-1)
of the right and left ends of gallery groove 38. The right and left
end-points of the shim at 47 define the endpoints of the extrusion
slot which will therefore determine the width of the ribbon as it
emits from the slot. In FIG. 11B, the gallery groove radius (A-1)
and the outer die block corner radius at point 47 share the same
co-radial center point 59. Therefore, the internal extrusion slot
surface distance 57 over which the material exiting the die flows
in contact with the slot surfaces 58 is a constant width 57 from
inlet edge to outlet edge, including the curved portions at the
right and left ends of the slot which arc upward to the 36-degree
endpoint of the slot, as terminated by the 46 edge of the shim.
This allows a uniform velocity of material emitting from the slot
outlet face A-9 on the die block from ribbon edge to edge, all
across the width of the slot. The ribbon trajectories will emit at
an angle normal (perpendicular) to the slot face A-9 of the die
block, which means that ribbon trajectories emitting at any point
along the straight segment of the slot will all be parallel, but in
the curved ends of the slot at the right and left corners of the
die block, the trajectories will gradually diverge from zero
degrees to 36-degrees at the right and left slot end-points at 47.
This enables the outer right and left edges of the material ribbon
53 to exit the die slot at a trajectory of 36-degrees from the
centerline of the ribbon. Immediately as the ribbon emerges and
flows out from the slot however in FIG. 7, the inherent surface
tension A6 of the ribbon material will pull across the ribbon width
to gradually arc the right and left edge trajectories inward toward
each other an angle at first parallel (or zero degrees) to the
centerline of the ribbon, and then will continue to arc inward to a
final trajectory having a negative angle to the centerline of the
ribbon (about -20 degrees). If allowed to continue, both ribbon
edges would finally intersect and the ribbon would undesirably
coalesce into a rod or cylinder of free-flowing material, instead
of a ribbon.
[0040] The zone of the emerging ribbon where the right and left
ribbon edges are substantially parallel to the ribbon centerline at
A-2, is designated the "zone of controlled film width and
thickness" A-3, which is where the process of this disclosure is
carried out. This sector of the ribbon extrusion, which is
generally 5 to 15 mm from the face of the die block, has a
substantially uniform edge-to-edge width (about 85 mm wide in this
embodiment) and a constant film thickness of about 0.2 mm or 200
microns edge to edge. This ribbon zone of 5 to 15 mm from the slot
face of the applicator, therefore defines the ideal range of
distance (same 5-15 mm) for the applicator to dispense an optimum
ribbon shape onto a surface. For this reason, robotic motion for
dispensing ribbons is programmed such that the slot face of the
applicator is taught a nominal 10 mm distance from the substrate
surface. This will produce a wet ribbon extrusion on the substrate
surface which will be of uniform width (85 mm, plus or minus 1 mm)
and of uniform wet film thickness (0.2 mm). The only variance in
wet film thickness across the width of the ribbon, are found at the
edges, for no more than 1 mm inside the ribbon edge, where the wet
material thickness is measured to be about 0.25 mm. (A-7 in FIG.
7C). This increased thickness (0.05 mm) which occurs within a
millimeter from the right and left edges of the ribbon, is an
advantage which enhances the peelability of the dry film when it is
removed from the car body. Conversely, ribbon edges which are
tapered under the 0.2 mm wet film thickness are a detriment in this
application, since the tensile strength of the thinner film will be
weaker than the adhesive strength holding the dry film to the
substrate, and the dry film will tear at the edges during removal,
leaving troublesome lines of dried film residue along the perimeter
boundary of the ribbon pattern on the car body.
[0041] FIG. 7B shows the ribbon edge profile A4 produced by
conventional extrusion means which are considered prior art, where
the shim is trimmed at A5 (instead of at 46) which is at the right
and left termini of the straight segment of the slot. This is a
straightforward design which insures that all points of the ribbon
emerging from the straight slot face are at the same velocity and
in a parallel trajectory normal to (or perpendicular to) the slot
face. Often, and especially with higher viscosity materials like
clays and ductile metals, this will produce a ribbon of material
having the same extruded width as the slot opening width of the die
block. In the case of polymer emulsions however, which are
relatively low viscosity liquids, the force of surface tension A6
in the liquid ribbon shape as it emerges from the die slot will
immediately draw the ribbon edges together A4 as described above.
This ribbon produced from the conventional design will have no
parallel edges A2 for creating a "zone of controlled width and
thickness" and can only emit a ribbon of constant width ribbon
length and thickness at a distance no more than 1 mm from the die
face A-9. The consequence of robotically applying transit coating
from a die block only 1 mm from the car body surface is impractical
and dangerous and therefore unfeasible. Applying a transit coating
emulsion with this conventional die block design at the standard 10
mm distance (as used in the invention) would produce a narrower
ribbon where the overall thickness of the ribbon will be greater
than the specified 0.25 mm limit, and the ribbon edges will have
grown considerably to 0.5 mm thick for a width of 3 mm or more (see
A-8, FIG. 7B), will propagate drips and runs, and require
considerably longer drying times for the thicker edge portions,
which would also be unfeasible in production.
[0042] FIG. 11B shows the exit trajectory of the ribbon edge at 47
aligned with the internal flow trajectory of the material 55
passing across the slot distance 57. The angle of flow trajectory
55 is defined by two points on this line: the radius centerpoint
59, and the shim termination point at 47. This line of trajectory
(shown in this embodiment as 36-degrees from centerline) is also
the shortest flow path for the material travelling across the slot
distance 57, which will pass by the shim terminus at point 47 to
form the edge of the ribbon when it exits the slot. The difference
between the 36-degree flow trajectory angle at the end of the slot,
and the angle of the shim edge 46 creates a triangular area 49
within the slot 57 where comparatively little material flow takes
place. The triangular area 49 does however create an area of
"laminar relief" adjacent to the flow path of the material which
will form the edge of the ribbon. This feature of the triangular
area 49 containing material adjacent to the main flow path for the
ribbon edge contributes less resistance to the flow path than if
the shim edge 46 were aligned directly along that path way at a
36-degree angle. When the shim edges at 46 are aligned with the
36'' degree material path, they present a hard boundary adjacent to
material flow across the slot distance 57, which slows the ribbon
velocity at the edges when emerging from the slot face, causing
increased thickness of the ribbon edge (>0.3 mm or 300 microns)
when dispensed on the substrate surface, which is undesirable. The
laminar relief created by area 49 creates less boundary impedance
and consequently higher velocity for the adjacent faster-flowing
material which will form the ribbon edge when it exits the slot,
and thereby produces the ideal ribbon edge thickness (0.25 mm) on
the substrate.
[0043] The ribbon edge exit angle which is controlled by the shim
edge 46 and endpoint 47 were optimized at 36-degrees in the present
embodiment to create the optimum "zone of controlled film width and
thickness" for transit coating material application, and this was
determined from observation and experimentation. However, other
polymer emulsion formulas for other types of application, which may
have a lower or higher viscosity, and/or a greater or lesser ribbon
thickness requirement, may require a greater or lesser ribbon edge
exit angle to optimize the zone of controlled width and thickness
for that material and application. For this reason the active range
of this invention for the possible exit angles of the ribbon edge
which will produce the optimized zone of controlled width and
thickness will lie between 5 degrees and 50 degrees relative to the
applicator centerline. Likewise, although the width of the ribbon
of the present embodiment is 85 mm, the straight segment of the
applicator gallery and slot can be elongated considerably while
preserving the radiused slot endpoint geometry to produce ribbon
widths of 200 mm or even wider, or narrower ribbon widths could be
produced by shortening the straight slot segment down to a ribbon
width of about 25 mm. The scalability of ribbon width (25 mm or
greater), and the range of viable ribbon edge exit angles (5 to 50
degrees) are inherent to the invention.
[0044] FIG. 10 is a schematic diagram of a representative system,
in this case, for the application of the PVA film as a protective
coating. However, the essentials of the system are the same for all
applications. As shown in the drawing, material is supplied from
drums 60, 62 through lines 64 and 66 which are connected into a Y
conduit 68 and from there through parallel legs 70, 72 with drains.
Conduit 74 flows from the leg 72 through a filter 76 and from there
into a heat exchanger 78 which is controlled by a temperature
controller 82. Finally, the material flows into the conduits 80
which supply the applicator die 10. Adjacent the applicator die 10
in a standby position is a liquid-filled cleaning standby station
84 with an interior brush which can be activated as necessary. The
fluid in the case of the aqueous PVA emulsion is water. Next to the
cleaning standby station 84 is a cleaning station 86 where the
applicator can be blow-dried. A purge station 90 may be used where
desired.
[0045] Summarizing, the applicator die 10 uniquely dispenses a
ribbon of material of uniform thickness at a controlled speed and
with improved edge control. PVA in a water emulsion is used in the
protective film application process of FIG. 8 or for masking. PVC
in an organic emulsion is used for the anti-chip coating. The two
examples demonstrate that the film ribbons can be applied to
horizontal as well as vertical surfaces. They can also be applied
to inverted and curved surfaces. Although a shim between the two
body parts is shown, the objective is to shape the die outlet slot
so that the side and bottom edges are such that (a) the film ribbon
flares outwardly at about 36.degree. and (b) the distance the film
travels from the center of the gallery grooves to the bottom edge
of the slot is constant across the slot width; i.e., from left
radiused edge to the right radiused edge, thereby promoting a
constant exiting film velocity across the ribbon.
[0046] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiments but, on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims, which
scope is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures as is
permitted under the law.
* * * * *