U.S. patent number 3,870,015 [Application Number 05/408,617] was granted by the patent office on 1975-03-11 for method and apparatus for applying plastisol coating of uniform thickness to glass containers.
This patent grant is currently assigned to Anchor Hocking Corporation. Invention is credited to William L. Brown, Francis J. Shonebarger.
United States Patent |
3,870,015 |
Brown , et al. |
March 11, 1975 |
METHOD AND APPARATUS FOR APPLYING PLASTISOL COATING OF UNIFORM
THICKNESS TO GLASS CONTAINERS
Abstract
An apparatus and method are described for coating a glass
container with a substantially uniform thickness of a viscous
curable plastic coating material. The article being coated is first
dipped into a bath of the plastic coating material while gripped at
the finish or closure portion, and is drawn upwardly through an air
knife apparatus in accordance with the invention, which provides a
shaped air flow that removes the excess coating material from the
surface of the article, and leaves a coating of uniform thickness
thereon. The coating is then cured to a hardened state.
Inventors: |
Brown; William L. (Amanda,
OH), Shonebarger; Francis J. (Lancaster, OH) |
Assignee: |
Anchor Hocking Corporation
(Lancaster, OH)
|
Family
ID: |
27020325 |
Appl.
No.: |
05/408,617 |
Filed: |
October 23, 1973 |
Current U.S.
Class: |
118/63; 118/56;
427/430.1 |
Current CPC
Class: |
B05D
1/18 (20130101); B05D 3/042 (20130101); C03C
17/00 (20130101) |
Current International
Class: |
C03C
17/00 (20060101); B05D 1/18 (20060101); B05D
3/04 (20060101); B05c 011/06 () |
Field of
Search: |
;118/21,56,63,423,100,120 ;117/12R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stein; Mervin
Assistant Examiner: Salser; Douglas A.
Attorney, Agent or Firm: Wood, Herron & Evans
Claims
What is claimed is:
1. An air knife apparatus for forming an air knife to remove excess
liquid coating material from glass containers passing therethrough,
comprising, in combination:
means for connection in use to a source of pressurized gas;
an annular fixture with an inwardly and downwardly angulated
annular orifice;
a gas conduit communicating between said means for connection to a
source of pressurized gas and said annular orifice, to permit gas
to flow through said annular orifice to form a thin conical sheet
of gas moving toward an apex; and
means for gripping said containers at a finish portion thereof and
moving the containers thus gripped upwardly through said annular
fixture.
2. The air knife apparatus of claim 1 wherein said annular orifice
is angled downwardly at an angle of less than 45.degree..
3. The air knife apparatus of claim 1 wherein said annular orifice
is angled downwardly at an angle of approximately 15.degree..
4. The air knife apparatus of claim 1 including an annular plenum
chamber inside said annular fixture, said plenum chamber
communicating with said gas conduit and said orifice to
substantially provide a uniform flow of gas through said
orifice.
5. The air knife fixture of claim 4 wherein said gas conduit
communicates with said annular plenum chamber so that the gas
entering said plenum chamber from said conduit enters at an angle
approximately perpendicular to the plane of said annular fixture,
the uniformity of gas flow through said orifice thereby being made
substantially uniform.
6. The air knife fixture of claim 5 wherein said gas conduit
communicates with said plenum chamber at least at two locations
uniformly distributed around said annular plenum chamber.
7. The air knife fixture of claim 1 wherein said orifice is
approximately 5 mils in height.
8. An apparatus for uniformly coating a plastic material onto a
glass container having a finish portion for receiving a closure,
said apparatus comprising, in combination:
means for immersing the container in a bath of liquid uncured
plastic material;
a source of pressurized gas;
a fixture including an inwardly and downwardly directed annular
orifice;
a gas conduit communicating between said source and said orifice to
permit gas to flow through said orifice to form a thin conical
sheet of gas moving toward an apex; and
moving means for gripping the container at the finish portion
thereof and for withdrawing the container from the bath and passing
it upwardly through said annular orifice so as to move through the
thin conical sheet of gas.
9. The apparatus of claim 8 wherein said annular orifice is angled
downwardly at an angle of less than 45.degree..
10. The apparatus of claim 8 wherein said annular orifice is angled
downwardly at an angle of approximately 15.degree..
11. The apparatus of claim 8 including an annular plenum chamber
inside said fixture, said plenum chamber communicating with said
gas conduit and said orifice to provide a substantially uniform
flow of gas through said orifice.
12. The apparatus of claim 11 wherein said gas conduit communicates
with said annular plenum chamber so that the gas entering said
plenum chamber from said conduit enters at an angle approximately
perpendicular to the plane of said plenum chamber so that the gas
flow through said orifice is substantially uniform.
13. The apparatus of claim 12 wherein said gas conduit communicates
with said plenum chamber at least at two locations uniformly
distributed around said annular plenum chamber.
14. The apparatus of claim 8 wherein said orifice is approximately
5 mils in height.
15. The apparatus of claim 8 wherein the minimum clearance between
the article and the annular orifice as the article passes
therethrough is approximately 1/2 inch.
16. The apparatus of claim 8 wherein said moving means moves the
article through said annular orifice at a constant velocity.
17. The apparatus of claim 16 wherein said constant velocity is
approximately 1/3 an inch per second.
18. The apparatus of claim 8 wherein said source provides gas at a
pressure of approximately 14 pounds per square inch.
Description
BACKGROUND OF THE INVENTION
This invention relates to the field of coating articles and more
particularly to applying a uniform coating of a viscous plastic
material such as a plastisol on glass containers.
It is known in the art to apply a plastic coating to glass
containers in order to reduce the danger of abrasion of the glass
and the chance of shattering and fragmentation. The plastic may be
applied as a plastisol, that is, colloidal dispersion of a
synthetic resin in a plasticizer, with or without solvent, in the
form of a viscous liquid. The article is dipped into a bath of the
plastisol and the excess is allowed to drain. The plastisol is then
hardened or cured, usually by heating.
When tall objects, such as beverage bottles, are dipped into a
plastisol bath, the liquid drains downwardly on the bottom from the
top toward the heel or base. That amount which is grossly excessive
will drain off, but the layer that remains on the bottle tends to
be thicker near the heel than at the top. As a result, the final
cured coating will display a thickness at the lower part of the
sidewall which is substantially thicker than at the top, and it may
even be several times thicker than the top. This results in higher
material costs, without commersurate improvement in protection for
the glass article. Such nonuniform thicknesses do not cure
uniformly, and a cure cycle which is appropriate for a median
thickness may over- or under-cure coatings which are too thin or
too thick.
Moreover, gravity drain of excess plastisol after the bottle has
been dipped into it requires an undesirably long time. A period of
90 minutes or more after dipping may be required before coating
drains by gravity to a desired nominal or mean thickness of say 3
mils. This slows rate of production, or (if the excess if not
allowed drain before curing) results in a coating which is
unnecessarily heavy, improperly cured, and which increases coating
material costs.
Coating uniformity can be improved by inverting the article after
dipping, so that an excess accumulation of coating near the heel
will flow toward the finish. However, such inversion is
mechanically difficult at useful line speeds, and is very sensitive
to timing, temperature and viscosity.
One prior art approach for eliminating the excess material which
accumulates on the lowermost surfaces of a previously dipped
article has been to contact these lower surfaces with an absorbent
roller wetted with a liquid solvent. This approach does remove
excessive material, however, it does not assure that the remaining
coating is uniform in thickness.
OBJECTIVES OF THE INVENTION
In view of the foregoing difficulties experienced in prior art
approaches for coating glass bottles with a plastic coating, it is
a primary objective of this invention to provide a method and
apparatus for coating glass containers such as narrow neck bottles
and wide mouth jars with a substantially uniform coating of
plastisol material, and further wherein the time and handling
required is less than previously required by other methods and
apparatus.
SUMMARY OF THE INVENTION
In accordance with this invention, the glass container which is to
be coated is dipped into a bath of liquid plastisol material so
that the area to be coated is wetted with the material. The liquid
coated article is withdrawn from the liquid bath. Some gravity
draining of excess coating material occurs as the article is
raised. The article is drawn upwardly through a fixture of a form
to be described, out of which an air jet or "air knife" is directed
radially inwardly towards the article passing therethrough, and at
a downward angulation, so as to define a thin conical sheet of air,
moving toward an apex point. This jet of air is operative to remove
the excess liquid plastisol material from the surface of the
container and substantially uniformly to distribute the remaining
material over the container surface. Once the container has been
drawn through the air knife fixture, it may then be cured in
conventional manner, for example in an oven at elevated
temperature, so that the liquid plastisol material is converted to
a solid plastic coating on the container.
More particularly, the air knife fixture comprises a ring through
which the liquid coated article is drawn while being gripped by a
chuck or clamp at the finish or closure portion thereof. An annular
plenum chamber inside the ring communicates with an annular orifice
located on the inner surface of the ring. A pressurized air supply
communicates with the plenum chamber so that air will flow
uniformly from the annular orifice towards the article passing
through the ring. The annular orifice itself communicates with the
plenum chamber in a manner so that the air passing through the
orifice is angled downwardly to form a thin conical sheet of moving
air directed toward an apex point disposed downwardly of the
orifice. The optimum downward angulation of the thin conical sheet
of air is less than 45.degree. and greater than 0.degree. to the
horizontal. In one preferred embodiment, the downward angulation of
the conical sheet of air is approximately 15.degree..
The foregoing and other objects, advantages and features of this
invention will become more clear from the following detailed
description of the preferred embodiment therefor taken in
connection with the drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation of a typical carbonated beverage
container made of glass.
FIGS. 2a, 2b and 2c are a sequence of elevations showing
schematically three steps in the coating of glass bottles of the
types shown in FIG. 1 with a liquid plastisol material, in
accordance with the invention.
FIG. 3 is a plan view from below of the upper half of the air knife
fixture of this invention.
FIG. 3a is a vertical sectional view taken along section line
3a--3a of FIG. 3.
FIG. 4 is a plan view from above of the mating lower half of the
air knife fixture of this invention.
FIG. 4a is a vertical sectional view taken along line 4a--4a of
FIG. 4.
FIG. 5 is a vertical sectional view of the assembled air knife
fixture, showing the two halves thereof disposed in their
interfitting positions.
DETAILED DESCRIPTION
Referring now to FIG. 1, a glass container in the form of a typical
carbonated beverage bottle is shown with a finish 10 at the top,
which comprises the threaded or ribbed portion for engaging and
holding a cap or other closure. Extending downwardly from the
finish 10 is a relatively narrow neck portion 12 which flares
outwardly with a gradually increasing circumference below the
finish 10. The bottle has a so-called shoulder, generally at 14,
which forms a transition region between the neck 12 and the side
wall shown generally at 16. At the lower end of the side wall 16 is
a heel portion 18 which presents a rounded corner surface between
the side wall 16 and the bottom 20 of the bottle. The bottom 20 is
"domed" or recessed at the center, as indicated by the dotted line
at 21.
According to this invention, glass articles including (by way of
illustration and not limitation) bottles of the type shown in FIG.
1, are coated with a plastisol by the process generally shown in
FIGS. 2a, 2b and 2c. This plastisol coating is shown as a thin
coating over the bottle shown in FIG. 1.
In FIG. 2a, a bottle 21 of the type generally shown in FIG. 1 is
gripped at the finish 10 by a bottle gripping apparatus or chuck
shown generally at 22. Chucks for this purpose are known in the art
and do not comprise the invention. The chuck need only grip the
bottle finish to thereby support the bottle or movement in the
manner described below.
The chuck 22 is mounted on the lowermost end of a chuck support
member 24 which is movable generally in a vertical direction to
permit the bottle 21 to be raised and lowered between the positions
shown in FIG. 2a and FIG. 2b.
Located directly below the bottle 21 is an air knife fixture 26
according to this invention. The air knife fixture generally is in
the shape of a ring with a central opening located directly beneath
the bottle 21 thereby permitting the bottle to be lowered
vertically by the movable chuck support member 24 through the air
knife fixture 26 into the liquid plastic material contained in the
tank 28, as shown in FIG. 2b. The liquid plastic material 30 in the
tank 28 preferably comprises a liquid plastisol material which will
wet to the surface of the bottle 21. Numerous plastisols are
available, however, one particularly useful type is known as No.
2342 manufactured by the G & S Plastic Company. While this
particular plastisol material has been used successfully, other
plastisols which cure at elevated temperatures are also usable to
form a uniform hardened plastic coating for bottles according to
the invention.
As shown in FIG. 2c, after the bottle 21 has been wetted in the
liquid 30 for a short period of time and preferably about 3 seconds
the bottle 21 is raised upwardly by the chuck support member 24
through the air knife fixture 26. According to this invention, the
air knife fixture 26 is connected to a pressurized air supply 32 by
air tubing 34. The flow of air through an annular orifice in the
air knife fixture 26, as will become more clear later, forms a thin
conical sheet of air directed downwardly and inwardly towards the
bottle 21 as it is raised upwardly therethrough. This thin
conically shaped sheet of air is operative to remove excess liquid
plastic material from the surface of the bottle and leave a
substantially uniformly thick residue of liquid material on the
surface after the bottle has passed through the air knife fixture
26. The bottle is then moved into an oven to cure the plastic
material. The actual curing process required depends entirely on
the specific coating material used, however, in one preferred form
of the invention, No. 2342 plastisol is used with a curing
temperature of approximately 460.degree. to 500.degree. F. and a
curing time is approximately 6 to 6 1/2 minutes.
Referring to FIG. 5, the air knife fixture 26 in its preferred form
is shown in section. As indicated generally above, the air knife
fixture 26 is formed in the shape of a ring with a central circular
opening, shown generally at 35, through which a bottle or other
article being coated is drawn. The central opening 35 has a
substantially cylindrical shaped wall 36 in which an annular
orifice 37 is provided. This annular orifice 27, in its preferred
form, comprises an opening in the wall 36 which is approximately 5
mils high. Additionally, as will become more clear later, the
annular orifice communicates with a pressurized air supply and is
shaped to form a thin conical sheet of moving air which is angled
downwardly in a direction shown generally by the arrow 38. This
downward angulation of the air flow is operative to remove excess
plastisol material from the surface of a bottle drawn upwardly
therethrough and also to uniformly distribute the residue remaining
on the surface of the bottle.
The air knife fixture of this invention is preferably formed in two
halves. The upper half 40, in one preferred form, is shown in FIGS.
3 and 3a. The lower half 42 is shown in FIGS. 4 and 4a. Both the
upper and lower half 40 and 42 of the air knife fixture are
preferably made of a metalic material such as aluminum or other
material easily machined to close tolerances and are shaped, as
described below, to interfit in the manner shown in FIG. 5.
The upper half 40 of the air knife fixture is generally ring shaped
and includes a centrally located cylindrically shaped passageway
therethrough having a diameter indicated at 44. In its preferred
form, the diameter 44 is approximately 1 inch larger than the
maximum diameter of bottles which are moved upwardly through the
air knife fixture. The upper half 40 includes an upper surface 46
which comprises a substantially planar surface with a plurality of
uniformly distributed holes 48 passing perpendicularly
therethrough. These holes 48, provide a passageway for threaded
screws 50 (as shown in FIG. 5), which secure the upper half 40 to
the lower half 42 of the air knife fixture. Two threaded holes 52
also pass perpendicularly through the upper half 40. These threaded
holes 52 are aligned, as will be described later, with their axia
arranged perpendicularly to the upper surface 46 and are threaded
to receive threaded air tubes through which pressurized air is
admitted to the air knife fixture.
The lower surface of the upper half 40, as best shown in FIG. 3a,
is shaped to interfit with the lower half 42 of the air knife
fixture. Disposed nearest the circumference of the upper half 40 is
an annular shaped surface 54 which when the upper half 40 is
interfitted with the lower half 42, as shown in FIG. 5, rests on an
annular shaped surface 56 of the lower half 42. The surface 56
includes a plurality of equally spaced threaded holes 58 which are
located in alignment with the holes 48 of the upper half 40 so as
to permit bolts 50, as viewed in FIG. 5, to pass through the upper
half 40 and engage the threaded holes 58 in the lower half 42
thereby securing the two halves of the air knife fixutre together
in their interfitting position.
The lower surface of the upper half 40 (FIG. 3a) additionally
includes a downwardly projecting cylindrical wall 60 which has a
diameter just small enough to interfit with the cylindrical wall 62
(FIG. 4a) located on the upper surface of the lower half 42.
Referring again to FIG. 3a, extending inwardly of the lowermost
portion of the cylindrical wall 60 is a flat annular surface shown
generally as 64 through which the threaded holes 52 pass. As viewed
in FIG. 4a, the half 42 includes an annular support surface 66
disposed inwardly of the cylindrical wall 62 on which the outermost
portions of the surface 64 of the upper half 40 rests when the two
halves are in their interfitting position. The flat surface 64
extends inwardly of the cylindrical wall 60 to a line shown
generally at 68 from which a downwardly sloped inwardly projecting
surface 70 extends. This surface 70 is angled downwardly as
indicated by the angle 72 and defines the upper wall for the
annular orifice 37. As has already has been indicated, in its
prefered form the angle 72 is approximately 15.degree. although the
angle may take on other values depending on numberous system
variables discussed later.
Referring again to FIG. 4a, an annular slot or chamber 74 is cut
downwardly into the support surface 66. This annular slot 74, when
the two halves of the air knife are in their interfitting position,
as shown in FIG. 5, comprises an annular plenum chamber for
receiving pressurized air.
Disposed inwardly of the annular slot 74 is a downwardly sloping
surface 76 which slopes downwardly at an angel indicated at 78
which, in its preferred form, is also approximately 15.degree.. The
downwardly sloping surface 76 forms the lower wall of the annular
orifice 37 as viewed in FIG. 5.
A downward angulation of 15.degree. for the thin conically shaped
sheet of air formed by the air knife fixture has proved to be
highly desirable. The results for three different tests using an
air knife fixture having a downward angulation of 15.degree. for
the thin conically shaped air sheet has been tabulated in Tables 1,
2 and 3.
Table 1 ______________________________________ Test Conditions
Bottle Air Withdrawal Bake Bake No. Pressure Speed Temp. .degree.F.
Time Min. ______________________________________ 1 12 psi .33
in./sec. 460 7 2 14 psi .33 in./sec. 460 6.5 3 16 psi .33 in./sec.
460 6.5 ______________________________________ Minimum clearance
between bottle and air knife fixture approximately .5 inches.
Orifice height -- 5 mils
Table 2 ______________________________________ Vertical Coating
Distributions Bottle N.sub.1 N.sub.2 N.sub.3 SW.sub.1 SW.sub.2
SW.sub.3 No. ______________________________________ 1 -- 4.5 5 3 3
4.5 2 2.5 3.5 2.75 2.5 2.5 2.5 3 3 3 2.25 2 2 3.25
______________________________________
Table 3 ______________________________________ Horizontal Coating
Distribution at SW.sub.2 Bottle P.sub.1 P.sub.2 P.sub.3 P.sub.4
P.sub.5 P.sub.6 No. ______________________________________ 1 3 3.5
3.25 3 3.75 3.5 2 2.5 2.5 3 3 2.75 2.5 3 2 2.5 3 2.5 2 2
______________________________________
As is apparent from Table 2, the vertical coating distribution of
cured plastisol on three different bottles is substantially uniform
for all of the positions measured. The measuring points N.sub.1,
N.sub.2, N.sub.3, SW.sub.1, SW.sub.2 and SW.sub.3 are indicated
generally in FIG. 1. Table 3 shows that the horizontal distribution
around the midpoint of the side wall of the bottle, that is, at
position SW.sub.2, is also substantially uniform at all points
around the bottle.
The results tabulated in Tables 1, 2 and 3 show that a downward
angulation of 15.degree. for the conically shaped air sheet
provides a desirable cutting action wherein the excess plastisol is
sheared or stripped from the surface of the bottle leaving a
substantially uniform coating on the surface of the bottle. By way
of comparison, if no air knife is employed, the coating thickness
varies from 3 1/2 mils at the neck to 15 mils at the heel. Other
tests were performed where the air jet formed by the air knife
fixture was not downwardly angulated at all, that is, the air was
directed towards the bottle in a direction substantially
perpendicular to the direction of bottle movement through the air
knife fixture while that configuration effected some plastisol
removal, the distribution of plastisol on the exterior surface of
the bottle after curing was highly irregular and, indeed, there
appeared to be a bulge of plastisol material located near the upper
portion of the bottle side wall. Other experiments were conducted
with downward angulation of 45.degree. for the conically shaped air
sheet. The results for this particular test indicated no
perceptible cutting action at all. When the air knife had a
downward angulation of approximately 30.degree. the cutting action,
while improved over a 45.degree. angle, was not as satisfactory as
the 15.degree. angle.
While the foregoing results suggest that downward angulation of
approximately 15.degree. is near optimum for the particular coating
and parameters involved, it will be recognized by those skilled in
the art that there are a number of variables which will effect the
end result. For example, the air pressure in the air knife will
affect the thickness of material remaining on a bottle after it has
passed through the fixture of this invention. Additionally, the
rate of bottle travel as it passes through the air knife fixture
will also affect the coating thickness. A further variable is the
particular shape of the article being coated as well as the minimum
clearance between that article and the air knife fixture. Further,
the viscosity of the coating material prior to curing also has an
effect on the thickness of the material remaining on the article.
Therefore, in view of the large number of variables, the actual
test results shown in Table 1, 2 and 3 suggest that the downward
angulation of 15.degree. for the conically shaped air sheet is
advantageous but is by no means assuredly optimum for all cases.
Indeed, it is reasonably clear from the tests performed to date
that the optimum downward angulation for the conically shaped air
sheet be greater than 0.degree. and less than 45.degree. and that
the exact optimum angle depends on each of the variables indicated
above. As such, once each of the variables has been set, a certain
amount of experimentation may be necessary to determine the most
optimum downward angulation for that particular configuration,
which can be done by comparison of uniformity of coating
thickness.
As indicated generally above, there are advantages to introducing
the air into the plenum chamber 74 in a direction which is
substantially perpendicular to the plane of the plenum chamber 74.
Experimentation has shown, for example, that if the air is
introduced into the plenum chamber 74 in a direction which is
substantially parallel to the plane of the plenum chamber 74, the
air flow through the orifice 37 is not uniform around the plenum
and this lack of uniformity gives rise to an uneven distribution of
coating material on the surface of the bottle. By introducing the
air into the plenum chamber perpendicularly in the manner described
above, advantageous results are achieved as indicated in Tables 1,
2 and 3. It will be clear to those skilled in the art that the
pressurized air supply can also be introduced perpendicularly into
the plenum chamber 74 at more than two locations. In this matter,
the air pressure within the plenum chamber 74 is substantially
uniform thereby assuring that the flow of air through the orifice
37 is also uniform.
The air knife provides a surprising advantage in respect to coating
of the dome 21 of the bottom of the bottle. When the bottle is
dipped into the plastisol bath, an air bubble or pocket is usually
caught in the dome which prevents that part of the bottle surface
from being contacted and uniformly wetted with coating material. If
left to drain in the conventional manner, this area would be poorly
coated.
However, when the bottle is passed through the air knife, the
coating is spread around the heel 18 and over the dome area 21,
even though that area may previously have been incompletely wetted
by the bath. The air knife thus distributes the coating onto a
bottom area which otherwise would not have been coated
properly.
The foregoing description has specifically referred to coating of a
bottle, for purposes of explanation, but the technique and
apparatus of the invention are also useful in coating jars, and the
term container is used generically herein and refers to and means
both bottles (i.e., narrow neck items) and jars (wide mouth
items).
While the foregoing description has been made with particular
emphasis on a preferred embodiment, it will be clear to those
skilled in the art that certain modifications in form only can be
readily made without departing from the spirit and scope of this
invention as defined in the following claims.
* * * * *