U.S. patent number 3,596,432 [Application Number 04/842,991] was granted by the patent office on 1971-08-03 for packaging machine.
This patent grant is currently assigned to Possis Machine Corporation. Invention is credited to Thomas L. Schuette, Melvin J. Straub.
United States Patent |
3,596,432 |
Straub , et al. |
August 3, 1971 |
PACKAGING MACHINE
Abstract
A packaging machine wherein a web of paperboard is continuously
drawn along a defined path, under a loading device by which
articles or products to be packaged are successively deposited upon
the web to be carried thereby through a curtain or sheet of molten
thermoplastic resin which debouches from a downwardly opening
nozzle, to lay itself onto and form a covering film on the web and
over any articles or products thereon. The mouth of the nozzle is a
slit which extends transversely across the path of the web and is
arched to have its ends close to the web while its midportion is
spaced much farther from the web. The film-covered web then travels
across a vacuum chamber by which any space between the covering
film and the web is evacuated and the film drawn tightly over the
articles or products and against the web. A series of closely
spaced parallel rollers across the top of the vacuum chamber with
their axes transverse to the web supports the web, and certain of
the rollers are driven to draw the web through the machine. Beyond
the vacuum chamber, the web with the covered articles or products
thereon enters a guillotine-type cutoff station where it is cut
into discrete units each of which is a complete package.
Inventors: |
Straub; Melvin J. (Minnetonka,
MN), Schuette; Thomas L. (Osseo, MN) |
Assignee: |
Possis Machine Corporation
(Minneapolis, MN)
|
Family
ID: |
25288771 |
Appl.
No.: |
04/842,991 |
Filed: |
July 18, 1969 |
Current U.S.
Class: |
53/133.7;
118/303; 427/420; 53/140; 118/DIG.4; 118/324 |
Current CPC
Class: |
B05C
5/005 (20130101); B05C 5/002 (20130101); B65B
33/00 (20130101); B29C 48/001 (20190201); Y10S
118/04 (20130101); B29C 48/08 (20190201) |
Current International
Class: |
B29C
47/00 (20060101); B65B 33/00 (20060101); B05C
5/00 (20060101); B65b 061/18 (); B65b 033/00 () |
Field of
Search: |
;53/112A,133,140,141
;18/15F,15R,15S ;117/12L,105.3,120 ;118/303,603,323--325
;156/244,390 ;264/90,238,259 ;99/166,171,174 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Condon; Theron E.
Assistant Examiner: Spruill; Robert L.
Claims
We claim:
1. A machine for applying a film of thermoplastic material onto a
substrate and over an article of any description laid onto the
substrate, comprising:
A. means for advancing the substrate with such an article thereon
along a defined horizontal path;
B. a nozzle having an elongated downwardly opening mouth positioned
above and extending transversely across the path of the
substrate;
C. means for delivering pressurized molten thermoplastic material
to the nozzle for discharge therefrom as a descending curtain which
impinges upon and lays itself as a form-retaining film of said
thermoplastic material onto the substrate and anything on the
substrate as the latter passes under the nozzle; and
D. the nozzle mouth being so shaped that the opposite ends thereof
are closer to the path of the substrate than its lengthwise
intermediate portion,
so that despite substantial elevation of said intermediate portion
above the path of the substrate, the molten thermoplastic material
issuing from the end portions of the nozzle mouth contacts a
passing substrate before the edges of the curtain have a chance to
waver.
2. The machine of claim 1 further characterized by:
A. suction means in the form of a pan-shaped vacuum chamber located
beneath the path of the substrate downstream of the nozzle to have
the substrate pass thereover, said vacuum chamber being connected
with a source of suction;
B. a plurality of closely spaced rollers collectively forming a
supporting surface across the top of the pan-shaped member and by
which the substrate is supported as it passes over the suction
means,
the axes of the rollers being transverse to the path of the
substrate; and
C. drive means drivingly connected with at least one of said
rollers to drive the same in the direction to advance the substrate
as a consequence of the tractive engagement between the driven
roller and the substrate which results from the effect of suction
on the substrate.
3. The machine of claim 2, further characterized by means for
supplying the substrate in the form of a continuous web of
indescriminate length so that the driven roller pulls the web
successively past the nozzle and the suction means.
4. The machine of claim 3 further characterized by:
A. loading apparatus for depositing articles upon the moving
substrate; and
B. perforating means positioned to act upon the web as it
approaches the loading apparatus
whereby an otherwise impervious web material is rendered air
permeable to enable the effect of suction applied at the underside
of the web to be manifested at the top side of the web.
5. The machine of claim 4 further characterized by seal-coating
means positioned to act upon and apply a seal coat to the underside
of the web after the suction means has acted thereon, and thereby
close the perforations formed in the web.
6. The machine of claim 3 further characterized by seal-coating
means positioned to act upon and apply a seal coat to the underside
of the web after the suction means has acted thereon, to thereby
seal the underside of the web and render it impervious to air.
7. The machine of claim 1, further characterized by means mounting
the nozzle for rotation about a vertical axis that intersects the
nozzle medially of its end, so that the nozzle may occupy a
position squarely transverse to the path of the substrate or
oblique to said path.
8. The machine of claim 1, wherein the downwardly opening mouth of
the nozzle from which the molten thermoplastic material issues is
concave from end to end.
9. The machine of claim 8, further characterized by means mounting
the nozzle for rotation about a vertical axis that intersects the
nozzle medially of its ends, so that by rotary adjustment of the
nozzle about said axis, the ends of the nozzle mouth can be
positioned contiguous to the side edges of substrates of different
widths.
10. The machine of claim 1, wherein the bottom of the nozzle in
which its mouth is located is arched with the top of the arch
curved and its sides substantially straight.
11. The machine of claim 10, wherein the straight sides of the arch
are inclined and the included angle therebetween is approximately
90.degree..
12. In a machine for packaging articles by applying a film of
plastic material onto a surface of a carrier for the article and
over an article on the carrier, wherein the film is formed by
discharging a liquid resinous plastic material in the form of a
descending curtain from the downwardly facing mouth of a stationary
nozzle onto the carrier with the article thereon while the carrier
moves along a horizontal path below the stationary nozzle, so that
said material lays itself onto the upwardly facing surfaces of the
carrier and article, the improvement which comprises:
the mouth of the stationary nozzle being elongated and transverse
to the path along which the carrier moves, and from end-to-end
having a concave shape, so that the ends of the nozzle mouth are
closer to the path of the carrier than the middle portion
thereof,
whereby the material issuing from the nozzle mouth has a shorter
distance to travel in reaching the carrier than the material which
issues from the middle portion of the nozzle mouth.
13. The machine set forth in claim 12, further characterized by
means incorporated in the nozzle for causing the material to issue
from the middle portion of the nozzle mouth at a velocity less than
that at which the material issues from the end portions of the
nozzle.
14. The packaging machine of claim 12, further characterized by
means providing a supply of cord; and means for directing the cord
onto the advancing carrier upstream from the nozzle so that the
cord will be interposed between the carrier and the thermoplastic
covering film to provide a tear strip to facilitate stripping the
film from the carrier.
15. The packaging machine of claim 12, further characterized by
means to govern the velocity of the molten thermoplastic material
debouching from the concave nozzle mouth and to effect a
differential in said velocity along the length of the nozzle mouth
with said velocity at the ends of the nozzle mouth being greater
than at the middle portion thereof.
16. The packaging machine of claim 15 wherein the nozzle mouth is a
slit, and wherein said velocity governing means comprises a
difference in the width of the slit along the length thereof with
the slit width being least at the mid point in the length of the
slit and increasing towards the ends of the slit.
17. The packaging machine of claim 15 wherein the nozzle has a
manifold chamber extending throughout substantially the length of
the nozzle mouth, and the mouth of the nozzle is a slit opening
into said manifold chamber and defined by opposing walls; and
wherein said velocity governing means comprises a difference in the
width of the walls which define the slit, along the length thereof,
with the greatest width of said walls being at the middle of the
concave nozzle mouth and becoming progressively narrower towards
the ends of the slit, so that greater frictional flow retardation
exists at the middle of the concave nozzle mouth than at its
ends.
18. A machine for packaging articles by means of a plastic film
adhered to a substrate which has at least some air permeability and
upon which the article has been laid, with the film overlying and
tightly embracing the article, said machine comprising the
combination of:
A. means for supporting the substrate with an article resting
thereon, for movement along a horizontal path;
B. a stationary nozzle above said supporting means and hence above
the path of the substrate, said nozzle having a downwardly opening
elongated discharge mouth that extends transversely across the path
of the substrate and from end-to-end has a concave shape, so that
the ends of the nozzle mouth are closer to a substrate passing
therebeneath than its middle portion;
C. means for delivering pressurized liquid resinous plastic
material to the nozzle for discharge from its mouth as a descending
curtain wide enough to encompass the article on the substrate and
extend far enough therebeyond to assure that the resulting film
laid onto the substrate and article as the substrate passes beneath
the nozzle will have marginal portions adhered to the
substrate,
the closer proximity of the ends of the elongated nozzle mouth to
the substrate assuring substantially straight edges for the
marginal portions of the film; and
D. suction means beneath the path of the substrate downstream from
the nozzle and operable to draw air through the substrate and
evacuate any space between the substrate and the plastic film.
19. The machine of claim 18, further characterized by means to
cause the liquid plastic material issuing from the middle portion
of the nozzle mouth to flow at lower velocity than the material
which issues from the ends of the nozzle mouth,
so that across its entire width the descending curtain of material
lays itself smoothly onto the substrate and the article thereon
without tendency to bunch up in spots.
Description
This invention relates to a machine for packaging articles by the
so-called "skin packaging" technique.
There are two ways in which skin packaging has been practiced. In
one, a thermoplastic sheet--usually transparent--after being heated
to soften it, is draped over the article which has been placed upon
an air pervious panel, such as a piece of cardboard and then by
means of suction applied to the underside of the panel, the
thermoplastic sheet is drawn down over the article and into firm
engagement with the top of the panel.
To assure good adhesion between the panel and those portions of the
thermoplastic sheet in contact therewith, it is customary to coat
the panel surface or selected areas thereof with a coating which
has an affinity for the material of which the thermoplastic sheet
is made. The Groth U.S. Pat. No. 2,855,735 and the Grinrod et al.
U.S. Pat. No. 3,228,168 are examples of this skin-packaging
method.
The other approach to skin packaging is an outgrowth of curtain
enrobing, wherein articles to be enrobed are carried through a
falling curtain of the coating or enrobing material. This packaging
method is described in an article which appeared in the May, 1965,
issue of Modern Packaging, under the heading "Skin Pack That Flows
On." As explained in that article, the curtain is molten
thermoplastic resin extruded from a nozzle and deposited onto the
article to be packaged and the surrounding surface of the card on
which it is placed. As the flowing thermoplastic material contacts
the article and its carrying card, it solidifies and forms the
desired covering film; and, again, as in the other method, suction
applied to the underside of the card draws the covering film
tightly about the article and onto the card.
The present invention also uses an extruded molten thermoplastic
film and, in a general way, produces packages in the manner
described in the Modern Packaging article, but does so far more
efficiently.
To gain the utmost efficiency and speed, the machine of this
invention operates in a continuous manner. To that end, the
articles or products to be packaged are sequentially deposited upon
a traveling substrate which may be a web of paperboard drawn from a
roll, to be carried thereby through the descending curtain or sheet
of liquid thermoplastic material and covered by the thermoplastic
film which forms as the molten material contacts the web and the
articles thereon. Directly downstream from the nozzle by which the
curtain is formed, the machine has an upwardly opening suction
nozzle or vacuum chamber across which the web passes. As it does,
any space between the web and the covering thermoplastic film is
evacuated, causing the covering film to be drawn tightly over the
article and against the web, it being understood that the web is
either inherently air permeable or specially made so.
The traveling web with the now covered articles thereon next passes
through a cutting station where a "flying guillotine" severs the
web into individual packages.
In the development of the machine of this invention, it was
observed that the phenomenon known as "necking"--which is a
convergent narrowing of the width of the curtain debouching from
the nozzle, and which in the past was thought to be
inescapable--caused the side edges of the ribbon of film laid onto
the web to take a very irregular shape. To eliminate this unsightly
result, it would be necessary to trim off the side edge portions of
the finished packages, which of course would create waste and take
time, unless some way of preventing necking could be found. This
has been accomplished by the present invention.
As will be more fully explained hereinafter, one of the features of
this invention stems from the discovery that if the elongated
nozzle orifice from which the curtain of molten thermoplastic
material issues, is arched or concave in its lengthwise dimension
so that the ends of the nozzle can be brought close to the side
portions of the web while its middle is spaced far enough above the
web to accommodate the articles or products being carried through
the curtain issuing from the nozzle, the side edges of the applied
film are straight and can be held directly contiguous to the edges
of the substrate web.
But with the solution of the necking problem, another difficulty
was encountered. The medial portion of the applied film did not lie
flat along the length of the web, even when the web was devoid of
articles or products, but instead was doubled or piled up on itself
at spaced intervals. This objectionable condition known as
"cascading" results from the wavering that is characteristic of a
falling sheet or curtain of liquid resin. Because of it, the
deposited material folds back and forth upon itself, unless the
advance of the surface onto which the curtain is deposited and the
velocity of the falling curtain are correctly coordinated. If the
distance between the web and all portions of the nozzle orifice is
uniform--which of course requires that the nozzle be
straight--adjustment of the web speed is the easiest way of gaining
this needed coordination. But the concave or arched nozzle shape
rules out this obvious solution to the cascading problem.
Because of the arched shape of the nozzle, the distance the curtain
drops or travels before it impinges upon the surface being coated
is not uniform. It falls farther at the middle than it does at the
side edges of the curtain, and because it falls farther, its
velocity at the moment of impact with the web--due to gravitational
acceleration-- is faster than it is at the side edges. Hence, with
the web speed correct for proper deposition of the film at the side
edges, which is essential to the attainment of a neat package, it
is too slow for proper deposition at the middle and this causes the
objectionable cascading.
The elimination of this objectionable cascading which resulted from
the use of the arched or concave nozzle is another object of this
invention. Its attainment, broadly stated, resides in so governing
or controlling the velocity of the material issuing from the nozzle
that the material leaves the medial portion of the nozzle at a
slower rate than it does at the ends of the nozzle. There are
different ways of accomplishing this result and alternatives
readily suggested themselves once it was discovered what caused the
cascading and why the problem could not be corrected by simply
adjusting the speed of web travel.
Another feature of this invention resides in the design of the
vacuum chamber or suction nozzle, and especially in the fact that
as the web passes across its mouth, it is supported on a series of
parallel closely spaced rollers, certain of which are driven to
draw the web through the machine.
The machine of this invention lends itself well to the
incorporation of optional features for special treatment of the
substrate. For instance, as the web-substrate is drawn off the
supply roll, it can be passed under a perforating roll by which a
multiplicity of tiny perforations can be formed in the web to
render an otherwise imperforate substrate air permeable. Also, by
means of an appropriately located coating roller, a seal coat can
be applied to the underside of the web after the covering film has
been drawn down onto the articles or products. Die cutting of the
web before the articles or products are loaded onto it, to provide
means to facilitate opening the finished packages can be
incorporated, or for the same purpose a tear strip or cord can be
introduced between the substrate and the covering film as the
packages are being formed.
With these observations and objects in mind, the manner in which
the invention achieves its purpose will be appreciated from the
following description and the accompanying drawings. This
disclosure is intended merely to exemplify the invention. The
invention is not limited to the particular structure or method
disclosed, and changes can be made therein which lie within the
scope of the appended claims without departing from the
invention.
The drawings illustrate several complete examples of the physical
embodiment of the invention constructed according to the best modes
so far devised for the practical application of the principles
thereof, and in which:
FIG. 1 is a perspective view of the front side of the machine,
viewing the same from its loading end;
FIG. 2 is a perspective view of the same side of the machine taken
from its discharge end;
FIG. 3 is a cross-sectional view through the machine on the plane
of the line 3-3 in FIG. 2;
FIG. 4 is a cross-sectional view through the curtain forming
nozzle, on the plane of the line 4-4 in FIG. 3;
FIG. 5 is a view similar to FIG. 3, but showing an alternate way of
delivering the molten thermoplastic material to the nozzle;
FIG. 6 is a perspective view of the two plates which together form
the curtain forming nozzle, the plates being separated to
illustrate their inner mating faces;
FIG. 7 is a perspective view showing a curtain or sheet of liquid
resin issuing from a conventional slit-type discharge nozzle and
illustrating the necking that occurs as the curtain descends and
the irregular edges of the applied film that are caused by the
necking;
FIG. 8 is a perspective view showing a curtain or sheet of liquid
resin issuing from the nozzle of this invention, but without the
benefit of its feature that eliminates the cascading problem, and
showing the effects of cascading on the covering film laid onto the
traveling substrate;
FIG. 9 is a bottom view of the discharge nozzle illustrating in an
exaggerated manner one way in which the velocity of the material
issuing from the nozzle can be controlled to eliminate the
cascading problem;
FIG. 10 is a front view of the nozzle illustrating another way of
gaining a differential in the velocity of the material issuing from
the nozzle at different locations along the length thereof to
eliminate the cascading effect;
FIG. 11 is a front view of the discharge nozzle illustrating still
another way of achieving a reduced velocity for the material
issuing from the middle portion of the nozzle as compared to the
velocity of the material leaving its end portions;
FIG. 12 is a side view of the vacuum chamber or suction nozzle by
which the covering film is drawn down onto the articles or products
and tightly against the substrate, with parts broken away and in
section;
FIG. 13 is a cross-sectional view through the vacuum chamber or
suction nozzle, taken on the plane of the line 13-13 in FIG.
12;
FIG. 14 diagrammatically illustrates the adaptation to the machine
of a web-perforating device by which an otherwise impervious web
can be rendered air permeable;
FIG. 15 diagrammatically illustrates one way in which the machine
can be equipped with a seal-coating device to enable the underside
of the substrate to be sealed;
FIG. 16 diagrammatically illustrates a modification of the machine
to incorporate a tear-strip or cord in the packages;
FIG. 17 diagrammatically illustrates the optional incorporation of
a die cutter by which the substrate may be die cut to provide for
easy opening of the packages;
FIG. 18 diagrammatically illustrates a modification to the machine
to adapt it to making plastic blisters for use in packaging
materials or products that cannot very well be packaged by the
skin-packaging technique; and
FIG. 19 is a more or less diagrammatic top view of that portion of
the machine at which the plastic extrusion nozzle is located, to
illustrate how a single nozzle can be adapted to substrate webs of
different width.
THE MACHINE GENERALLY
Referring to the accompanying drawings, the numeral 3 designates
the general frame structure of a packaging machine embodying this
invention. The frame supports a table 4 over which a web 5 of
paperboard may be drawn from a supply roll 6 suitably mounted at
the loading end of the machine where an idler roll 7 guides the web
onto the table. The web provides the substrate for the packages to
be produced.
As the web travels along the table 4 it first passes under a
loading chute 8 down which the articles or products to be packaged
slide to be deposited on the web in regularly spaced sequence. The
timing of their placement and the spacing of the articles or
products on the web is controlled by a pair of pneumatically
actuated plungers 9 and 10, the alternate actuation of which allows
the articles or products to drop one at a time, at the right
instant, from the bottom of the chute onto the web.
Downstream of the loading station the web passes under a nozzle 11
from which a curtain or sheet S of molten thermoplastic material
debouches to lay itself onto the passing web and the articles or
products thereon. As it does so, it congeals or solidifies and
forms a film which covers the entire top surface of the web and, of
course, any articles or products thereon. The thermoplastic
material employed may be any one of several which lend themselves
to the "skin-packaging" technique. The useable materials are
characterized by high molecular weight and a viscosity in excess of
20,000 centipoises in the molten condition. Included among such
materials are polyolefins, cellulose esters, vinyl polymers, and
the like. Among the preferred materials are cellulose acetate
butyrate and cellulose acetate propionate because of their ease of
handling and ability to produce a clear transparent film which
greatly enhances the appearance of the finished package.
The table is interrupted beneath the nozzle 11 so that during
warmup periods before the web has been fed into the machine, or
when for some reason or other no substrate is present under the
nozzle, the molten resin extruded from the nozzle can drop into a
melt tank or pot 12 located below the table level. Directly after
passing under the nozzle 11, the coated web crosses a vacuum
chamber or suction nozzle 13, the mouth of which faces upwardly and
is wide enough to encompass the full width of the web. To enable
subjecting the web to the negative pressure maintained in the
vacuum chamber or suction nozzle, the table 4 is, of course,
interrupted and its web supporting function is taken over by a
series of closely spaced rollers 14 that form a grid over the mouth
of the vacuum chamber or suction nozzle.
The rollers are transverse to the web and at least some of them are
power driven in the direction to draw the web off the roll and
through the machine. Since the web is held down on the rollers by
suction, the traction between the driven rollers and the web is
quite adequate to assure a uniform rate of travel of the web at
whatever speed the rollers are driven.
In accordance with the skin-packaging technique which this
invention follows, the web material is either inherently porous or
air permeable, or is specially made so. Hence, the suction applied
to its underside as the web passes over the vacuum chamber or
suction nozzle draws the thermoplastic covering film tightly over
the articles or products and against the web.
As is well known in the art, some of the previously identified
thermoplastic materials in the molten state will adhere to the
naked surface of ordinary paperboard stock, such as that known in
the trade as "patent coated." This paperboard is only lightly
calendared so as to preserve its inherently porous, gas-permeable
nature. Its face or top layer is composed essentially of virgin
pulp and high grade waste free of ground wood, and presents an
attractive finish and appearance.
Where the chosen thermoplastic material is of the type that does
not adhere readily to the naked surface of paperboard stock, the
board is coated or suitably treated with an adhesive which has an
affinity for the chosen thermoplastic. One example of the practice
will be found in the Groth U.S. Pat. No. 2,855,735.
In any event, after the web crossed the vacuum chamber or suction
nozzle, the covering film should be securely adhered to it, and
with this accomplished, only one operation remains to be performed
by the machine. The web, with its plastic covered articles or
products thereon, must be severed transversely between the
successive articles or products thereon, to form separate units or
pieces, each of which constitutes a complete package. This is done
by a flying guillotine-type knife 15 located at the discharge end
of the machine. A carrier 16 mounts the knife for up and down
movement and the carrier rides on horizontal rails 17 that are
fixedly secured to the frame of the machine. Suitable drive
mechanism (not shown for sake of clarity) effects reciprocation of
the carrier along the rails 17, and imparts up and down motion to
the knife, in proper timed relation with the advance of the
web.
If desired, a punch can be operated along with the knife, to
provide a hanging hole in each package as it is cut from the web,
and by the same token, the knife can be shaped to impart any
desired configuration to the edges of the package.
Also, as will be readily understood, one or more slitting couples
can be provided to slit the web into two or more strips before it
reaches the flying guillotine knife 15. The provision of such
slitters permits forming a plurality of packages with each
operation of the flying guillotine knife, by simply loading the
articles or products in side-by-side relation across the width of
the web.
THE RESIN HANDLING SYSTEM
As best seen in FIG. 3, and as briefly mentioned before, a melt
tank or pot 12 located beneath the nozzle 11 catches the descending
curtain of molten plastic material whenever there is no substrate
under the nozzle. The tank or pot, like the nozzle, is heated to
keep the material molten. Electric heating elements 18 inserted
into bores or pockets in the walls of the nozzle and the pot
provide a convenient heat source for this purpose. Obviously, of
course, these heating elements are connected with a current source
and are appropriately controlled to maintain a predetermined
temperature, but for sake of clarity these details are not shown in
the drawings.
During operation of the machine, a pump 19 diagrammatically
illustrated in FIG. 3, draws molten thermoplastic material from the
melt tank or pot and delivers it under pressure to the nozzle 11,
it being understood that the ducts through which the material
reaches the nozzle are suitably heated, and preferably the material
is passed through a dearerator 20 like that of the Chenoweth U.S.
Pat. No. 3,299,195 in its passage to the nozzle.
The system is kept supplied with thermoplastic material by
periodically introducing fresh material into the melt tank or pot
12 by means of a conventional extruder, not shown, which, as is
customary, has a hopper to receive the additional material, and
also serves as a premelter so that by the time the fresh material
reaches the melt tank it is almost in its molten state.
As an alternate for the material supply system just described, the
more direct arrangement illustrated in FIG. 5 may be employed. In
this system there is no pump and no melt tank. Instead, an
extruder-melter unit EM converts the pelletized material that is
loaded into the hopper of the unit into molten thermoplastic
material and forces it into and from the nozzle. It is to be
understood that the ducts leading to the nozzle are suitably heated
and that the flow of molten plastic material to the nozzle can be
terminated, if desired, by either stopping the extruder or
providing a valve-controlled bypass for the material leaving the
extruder. Since no melt tank or collecting hopper is employed in
the alternate system, it is to be understood that no material would
be delivered to the nozzle until the web has been started through
the machine and was traveling under the nozzle.
THE EXTRUSION NOZZLE
The most significant aspect of the nozzle is the arched or concave
shape of its bottom edge in which the mouth 21 of the nozzle is
located. The nozzle mouth is a slit which extends for practically
the entire length of the nozzle. Because of the arched or concave
shape of the nozzle mouth its ends can be located quite close to
the level of the table over which the web substrate travels, while
the medial or middle portion thereof is spaced far enough above
that level to permit unrestricted passage of the articles or
products being packaged.
Because of the close proximity of the ends of the nozzle mouth to
the level of the table, the thermoplastic material issuing
therefrom has but a very short distance to travel before it
impinges the web. Accordingly, the descending curtain reaches its
destination, i.e. the passing web and the articles or products
thereon, without being affected by the necking which characterizes
falling curtains or sheets of liquid resin, and which is
illustrated in FIG. 7. In fact, the curtain or sheet which
debouches from the nozzle mouth 21 is practically devoid of
necking, and because of this the side edges of the curtain do not
waver toward and from one another. Accordingly the edges of the
deposited film are straight and directly contiguous to the edges of
the web, as shown in FIG. 8, Obviously, of course, for this desired
contiguity to exist, the nozzle dimensions must comport with the
width of the web.
The specific shape of the arch or concavity defined by the bottom
edge of the nozzle while subject to modification, has been found to
be very effective if the side portions of the arch are straight and
at an angle of about 45.degree. to the horizontal for a substantial
distance and the medial or upper portion thereof has a compound
curvature. With this formation the included angle between the
straight side portions of the arched nozzle is 90.degree..
The nozzle is formed by joining two plates 22 which, as best seen
in FIG. 6, are mirror images of one another. The mating inner faces
of these plates have grooves 23 above their bottom edges 24 and
leading from a groove 25 which opens to the top edge of the plates.
Thus when the plates are secured together, as by capscrews 26, the
grooves coact to provide a manifold passage which leads from an
inlet formed by the grooves 25 to the mouth 21 of the nozzle.
The mouth of the nozzle is a slit between the lower edge portions
or lands 27 of the plates which is that part thereof between the
grooves 23 and the bottom edges of the plates. If the plates are in
direct surface-to-surface engagement, it is of course necessary
that the lands 27 be at a level below that of the remaining flat
inner faces of the plates in order to provide the slit.
Alternatively shims 28 of a size and shape to cover all but the
lower edge portions 27 of the plates, can be clamped therebetween.
The use of shims without also cutting the lands 27 below the plane
of the flat faces of the plates will result in a nozzle mouth of
uniform width for its entire length.
To obtain the needed differential in velocity of the material
issuing from the nozzle so that the flow is slower from the medial
portion of the nozzle mouth than it is at the end portions of the
nozzle mouth, one of several things must be done. With or without
the shims 28, the lands 27 can be cut to a progressively deeper
level below the plane of the flat inner face of the plates, so that
the slit which forms the mouth is wider at its ends than at its
middle as shown in an exaggerated way in FIG. 9, where--for sake of
clarity--the nozzle appears as a monolith. This difference in width
of the nozzle mouth results in a greater flow capacity at the ends
than at the middle of the nozzle mouth; and as a consequence the
velocity of the material debouching from the middle portion of the
nozzle mouth is less than it is at the ends.
The same differential flow capacity and resultant velocity
difference can be obtained with a uniform width slot, by making the
lands 27 wider at the center than at the ends of the slot, as shown
in FIG. 10, also in an exaggerated way.
Another way of gaining the needed velocity differential as
illustrated in FIG. 11, involves bringing the liquid resin
simultaneously into both ends of the manifold formed by the grooves
23, through inlet ports 30, and having the manifold-forming grooves
progressively smaller in cross section from both ends thereof
towards the middle.
Still another way of achieving the desired velocity differential is
to employ two sources of molten resin, one at a higher temperature,
and hence lower viscosity, than the other. The latter is introduced
into the central portion of the manifold and the lower viscosity
material into the ends of the manifold.
Whichever approach is used to gain the needed velocity
differential, the important consideration is that the velocity of
the material issuing from the middle portion of the nozzle mouth
must be sufficiently slower than that which issues from the ends
thereof to assure that the velocity of the flowing material will be
uniform across the entire width of the curtain at the moment the
film forming material contacts the web and the articles or products
thereon. With such uniform impingent velocity, cascading can be
prevented by simply adjusting the rate of travel of the web.
The specific structure by which the nozzle 11 is supported and
connected with the pump is a matter of design and not important to
this invention, but for sake of completeness of the disclosure, the
connected plates 22 are bolted to the underside of an arm 31 which
in turn is supported on an upright pedestal, both of which units
are provided with the passages necessary to conduct the material
from the pump to the nozzle, and one of them may contain the
dearerator 20.
With the nozzle mounted in a manner just described, a change in
width of the web entails removal of the nozzle and replacement
thereof with one that is correct for the different web width.
However, by mounting the nozzle as shown in FIG. 19 so that is can
be rotated or swiveled about a vertical axis passing through the
inlet to the nozzle, a nozzle of a size that is correct for the
widest web handled by the machine can be swung to a position
oblique to the path of the web. This enables adjusting the
effective width of the descending curtain to a narrower web. Thus
by that simple adjustment, the machine can be adapted to webs of
different width.
THE VACUUM CHAMBER OR SUCTION NOZZLE
(FIGS. 12 and 13)
The vacuum chamber or suction nozzle 13 is essentially a
rectangular pan with end walls 34-34', sidewalls 35-35', and a
bottom wall 36, the latter having a port 37 through which the
chamber is connected with a source of suction, not shown. Across
the top of the pan is the grid formed by the series of closely
spaced rollers 14. The ends of these rollers are journaled in the
sidewalls 35-35' at a level such that their peripheral surfaces are
tangent to the plane of the table 4. Collectively, therefore, the
tops of the rollers form a continuation of the table.
In the structure illustrated every other roller is driven in the
direction to draw the web through the machine. The drive for the
rollers may be provided by any suitable variable speed prime mover,
as for instance, an adjustable speed electric motor or a variable
speed hydraulic motor, but whatever form of prime mover is
employed, it is drivingly connected with a gear 38 that is secured
to a stub shaft 39 journaled in the sidewall 35. The wall 35 is
hollow and provides a transmission chamber 40 through which the
shaft 39 extends, and inside this chamber the shaft 39 has a
sprocket 41 fixed thereto.
Every other roller 14 has an extension of its shaft extending
across the chamber 40 and provided with a sprocket 43. All of the
sprockets 43 are aligned with one another and with the sprocket 41
and a chain 44 meshes with all of the sprockets to transmit driving
torque from the shaft 40 to all of the driven rollers. As seen in
FIG. 13 a removable cover 46 which closes the top of the
transmission chamber, holds the chain 44 in meshing engagement with
all of the sprockets 43, and though not shown, an adjustable idler
may be provided if necessary to keep the chain taut.
By driving only every other roller, the sprockets 43 can be larger
in diameter while at the same time the space between adjacent
rollers can be held to a bare minimum.
If it is desired to drive all of the rollers, the illustrated and
described drive mechanism can be duplicated at the opposite side of
the vacuum chamber. In this case half the rollers would be driven
from one end thereof and the other half from the opposite end.
As will be readily understood, the negative pressure maintained in
the vacuum chamber or suction nozzle, acting through the inherently
porous substrate, or specifically produced "porosity" of the
substrate, evacuates any space between the substrate and the
covering thermoplastic film as the web crosses the chamber, and at
the same time assures good traction between the driven rollers and
the web.
The adjustability of the drive for the rollers enables the rate of
advance of the web to be properly coordinated with the velocity of
the falling curtain to assure the attainment of a fine appearing
package in which the transparent plastic film tightly hugs the
packaged article or product and all portions of the film are smooth
and free from the effects of cascading.
As noted hereinbefore, after the web with the plastic covered
articles or products thereon crosses the suction chamber it is cut
transversely by the flying guillotine knife 15 whereupon the
packages are complete and can be taken from the machine in any
desired manner. Since this flying guillotine is quite conventional,
it need not be specifically illustrated or described; on the
contrary it is sufficient to note that the operation of the knife
must be timed with the advance of the web and coordinated with the
placement of the articles or products onto the web at the loading
station of the machine.
MODIFICATIONS
The continuity which characterizes the operation of the machine of
this invention, adapts it very nicely to the incorporation of
optional features. One of these which is diagrammatically
illustrated in FIG. 14, enables perforation of the web to render an
otherwise impervious web, air permeable. This can be done by having
the web pass between a perforating roll 50 with many sharp pins
projecting therefrom, and a bed roll 51 which has a rubber surface.
The location of this perforating couple can be any where upstream
of the loading station.
Another optional feature, provides for seal coating the underside
of the web after it leaves the vacuum chamber or suction nozzle. As
diagrammatically shown in FIG. 15, this can be done by an
applicator roll 53 positioned to contact the underside of the web
and to have a coating substance transferred to it by a transfer
roll 54 which in turn dips into a bath of the coating material
maintained in a pan or fountain 55.
Seal coating the underside of the web may be especially desirable
if perforated material is used for the substrate, so that where the
perforating fixture of FIG. 14 is employed it would be advantageous
to also equip the machine with the seal coater, the combination
being shown in FIG. 15.
To facilitate opening the formed packages, a tear strip or cord 55
can be incorporated in each package. This requires only providing a
supply of the strip or cord material as indicated at 56 in FIG. 16,
and feeding the same onto the web before the web reaches the
curtain forming nozzle. The location of the tear strip or core
transversely of the web would of course depend upon the nature and
size of the article or product being packaged; and to facilitate
grasping an end of the strip or cord, the cutoff knife can be
shaped to form a tab in line with the strip or cord either on the
leading or trailing edge of the packages as they are formed.
It is also possible to equip the machine with a die cutter 57 as
shown in FIG. 17, by which the web can be slit to provide a freely
displaceable tab to facilitate opening of the package.
While it is undoubtedly best from the standpoint of ease and speed
of operation to supply the substrate in the form of a web drawn
continuously off a roll, the significant advantages and
improvements of the invention are not limited to the use of a web,
but can also be utilized if the substrate consists of discrete
cards or styrofoam cradles fed successively into the machine. In
this case it would of course be necessary to provide a conveyor to
carry the individual cards or cradles through the machine, but of
course only to the cutoff knife.
As shown in FIG. 18, it is also possible to adapt the machine to
the production of plastic blisters which can be adhered to cards to
form packages for materials and products that do not lend
themselves to being packaged by the skin-packaging technique. For
this purpose, an endless belt conveyor 60 of a suitable
gas-pervious material to which the thermoplastic material does not
adhere, carries molds 61 through the machine and to the cutoff
knife. The molds 61 which are also of material to which the plastic
material does not adhere, may be deposited on the conveyor in the
same way the articles or products are loaded onto the traveling
substrate web, and as they pass under the nozzle the curtain of
molten thermoplastic material issuing therefrom lays itself onto
the molds and the surrounding surface of the conveyor to be drawn
tightly about the molds and against the conveyor by the vacuum
chamber. The result is a plastic ribbon with integral blisters of a
shape defined by the molds. Since the plastic film does not adhere
to the conveyor, it continues smoothly beyond the discharge end of
the conveyor and into the cutoff knife by which it is supported as
it is cut into separate units, each of which comprises a blister 62
of a shape determined by the mold over which it was drawn and an
encircling flat flange 63. The molds either drop out of the
blisters as the separate units leave the machine, or are easily
removed therefrom with the result that the separate units may be
used in blister packaging by adhesively securing their flanges to
carrying cards.
It will also be apparent that in addition to providing an improved
packaging machine, the invention encompasses a new method of (1)
utilizing the skin-packaging technique (2) coating a surface of a
substrate with a plastic film that is uniformly thin and smooth
across the entire area of the coated surface ans has straight side
edges directly contiguous to the side edges of the substrate, and
(3) forming a plastic strip having a nonplanar shape and straight
side edges. This method, in its specifically different embodiments
can be practiced with tools and structure other than the machine
herein disclosed. The novel and characterizing steps of this method
which are generic to its specifically different embodiments
are:
1. providing an air permeable conveyor or traveling substrate;
2. discharging molten thermoplastic material from a downwardly
facing elongated orifice that has an endwise concave shape so that
its ends are at a lower elevation than its medial portion, to
produce a descending curtain of the molten thermoplastic
material;
3. laying that curtain of molten thermoplastic material onto the
conveyor traveling substrate as a form-retaining film by advancing
the conveyor substrate along a substantially horizontal path
through the descending curtain;
4. so controlling the path of the conveyor or substrate that as it
passes beneath the orifice the top surface thereof is close to the
ends of the orifice, so that the material forming the side edge
portions of the curtain travels but a short distance before it
impinges upon the conveyor or substrate;
5. coordinating the rate at which the conveyor or substrate passes
through the descending curtain with the flow rate of the
thermoplastic material forming the side edge portions of the
curtain to assure that the side edge portions of the curtain lay
themselves smoothly and uniformly onto the conveyor or
substrate;
6. effecting a differential in the discharge rate of the molten
thermoplastic material along the length of the orifice to cause the
material to issue sufficiently slower from the middle portion of
the orifice than it does from the end portions thereof so that
across its full width the film is laid smoothly and uniformly onto
the conveyor or substrate and has a substantially uniform
thickness; and
7. passing the conveyor or substrate with the film of thermoplastic
material covering its upper surface across a source of suction to
draw the film tightly down onto the conveyor substrate.
From the foregoing description taken in connection with the
accompanying drawings, it will be apparent to those skilled in this
art that the machine of this invention will be a tremendous boom to
the packaging industry.
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