Note: Descriptions are shown in the official language in which they were submitted.
5~2~i
IM-LINE MANUFACTURE OF PRINTED AND D~E CUT POJ~STYRENE
~OAM SHEETS
.
Background of the Invention
This invention relates generally to the field
of packaging and more particuLarly relates to continuous in~line
process and apparatus for producing thin printed sheets or
boards of expanded polystyrene ~oam which boards are useful,
for example, in the packaging of bacon products.
Although the in~ention will be described with
particular reference to bacon boards it should be understood
that the invention has other applications as well such as in
chocolate box liners, cookie bag liners, place mats, bar
coasters, and tops for frozen foods and the like.
The board presently used in the packaging of bacon
is a printed paperboard which is coated on both sides with
a layer of polyethylene plastic. Although this orm of board
has met with wide acceptance it does possess a number of
disadvantages. For example, the cut edges of the printed
board tend to absorb grease and moisture and furthermore the
composite paperboard products may tend to harbour bacteria.
Furthermore, the present relatively rigid composite paperboard
has a tendency to puncture the overwrapped packaging film both
during shipping and also during store handling and it is
desirable to provide a softer board to assist in eliminating
this problem. It is also considered desirable to provide a
packaging material which is light in weight thus ultimately
resulting in less waste to incinerate or dispose of.
The present invention thus broadly involves the
making of a thin flat sheet of polystyrene foam and thereafter
printing and cutting the sheet in a continuous ln-line
operation while the foam is still in an uncured and somewhat
unstable condition. The process can be carried out very
~15~L826
economically and at a relatively high rate of production.
Summary of the Invention
In accordance with the invention in one aspect
there is provided a method of continuously manufacturing
flexible sheets of cellular polystyrene foam material, including
the steps of: .
(a) passing a molten pol~styrene plastic material
to whi~h a blowing agent has been added through a die oxifice
shaped to al}ow the material to expand into a ribbon of foamed
plastics material;
(b) effecting an initial cooling of the opposing major
surfaces of the ribbon on emergence from the die orifice to
form a thin skin on the surfaces of the ribbon;
(c) biaxially stretching the ribbon of material as it
cools;
(d) effecting further cooling and forming of the
ribbon by passing it on to a surface of a rotating forming drum;
the method being characterized by the steps of:
(e) compressing the partly cooled ribbon to substantially
reduce the thickness thereof by passing the ribbon in pressurized
contact with a surface of a roll means;
(f) before or after step (e), passing the ribbon in a
path of travel to effect further cooling and stabilization of same;
(g) passing the partially cooled and stabilized ribbon
in a further path of travel through a printing press to apply
printing inks to a surface thereof, and
(h) subsequently die cutting printed sheets o a
selected outline shape ~rom ~he ribbon.
In accordance with the product aspect of the
invent~on there is provided a thin flexible sheet of cellular
polystyrene foam, the sheet being in a compressed or crushed
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1~LS~L8~
condition in ~he direction of its thickness and biaxially
oriented in the plane of the ~heet so that the cells of the
foam are in a generally flattened condition and lie with their
major dimensions generally parallel to the major surfaces of
the~sheet. The foam has a density from about 8 to about 12
pounds per cubic foot and at least one of the major surfaces of
the foam sheet has a densified generally continuous skin thereon
having.a thickness of at least abou~ .3 mils.
As noted previously, this thin flexible sheet
is particularly useful as a backing board for use in the
packaging of foodstuff such as bacon although it will be
reali~ed that the product finds use in other applications as
well. The sheet is provided with an outline shape which is
dependent upon its end use and the skin surface will be provided
with printing ink or inksthereon of any desired colours and
pattern arrangement in register with one another.
In the preferred form of the product both of the
major surfaces of the sheet are provided with the continuous
skin. Preferably the skin has a thickness not greater than
about 1.0 mils with the density preferably being from about 10
to about 11.5 pounds per cubic foot.
The method recited above is carried out by a novel
system for continuously manufacturing flexible
sheets of foamed thermo-plastics material, which system includes:
(a) an extruder for extruding and expanding a continuous
flat ribbon of foamed plastic material;
~b) means adjacent the extruder for rapidly cooling
the opposing major surfaces of ~he ribbon to produce a skin on
both of such surfaces;
(c) means for biaxially stretching the extruded
ribbon of plastics material;
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~5~82~i
(d) a rotatable forming drum for engaging the biaxially
stretched ribbon and means to rotate the forming drum at a speed
sufficient to accommodate the advancing ribbon;
the improvement characterized by:
- (e) the drum having a surface acting to smooth and
flatten the ribbon surface as the ribbon cools;
(f) gauge roll means for compressing the partially
cooled ribbon to substantially reduce the thickness thereof and
to effect a consequent densification of such foam; and
(g) printing press means downstream of the forming
drum and gauge rol} means to receive the advancing ribbon and to
apply printing inks to a major surface of the partially cooled
and stabilized ribbon.
In a further feature means are provided to cause the
ribbon to pass along an elongated path of travel between the
forming drum and the printing press means, with the length of such
path of travel being selected to allow a degree of stabilization
and cooling of the ribbon to take place prior to the ribbon
entering the printing press means.
Preferably, the printing means comprises a plurality of
rolls around which the ribbon passes and one of which rolls in-
cludes means for applying printing ink in a preselected
pattern to a major surface of the ribbon.
In a typical opexation~ a plurality of said printing
press means are provided, each of which is arranged to apply
a different ink colour to the ribbon surface whereby to build
up multi-colour images on the ribbon.
According to a still further feature a
die cutter assembly is located after said plurality
of printing press means and is adapted to sever the ribbon all
around each of the multi-colour images printed thereon; the die
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cutter assembly being arranged such that the remaining ink
free waste ribbon portion emerges in a continuous fashion for
collection and re-use.
During operation,the printing press units are
dri-~en in synchronism thereby to match the speed of advance of
the thermoplastic ribbon being fed thereto. Suitable tensioning
means are provided to maintain a desired tension in the ribbon
as it passes from the forming drum toward the first press unit.
In order to establish the desired degree of tension in the
ribbon r and in order to eliminate the slack in the ribbon which
occurs at start-up or after the ribbon has been spliced, the
apparatus, in accordance with a further aspect of the invention,
is provided with a drive system which can be activated to cause the
printing units to operate at a speed som~what higher than the speed
of the incoming ribbon. After all slack in the ribbon has been
taken up and the ribbon is at the desired tension, the overspeed
drive is deactivated and the printing units thereafter operate at
a speed which is synchronized with the speed of the incoming ribbon.
Brief Description of the Drawings
Typical embodiments of the invention will now
be described by way of example with reference to the accompanying
drawings wherein:
Figs. lA, lB, and lC illustrate a portion of the
production line including the extruder die assembly, the biaxial
orientor, the forming drum assembly, and the downstre~am printing
units and die cutter unit;
Fig~ 2 is a somewhat diagrammatic plan view of
the screw extruder, homogenizer, cooler, and extruder die
arrangement as in the T.W.Winstead process;
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Fig. 3 is an end view of the extrusion die and
mandrel showing an extruded ribbon of foamed plastic passing
over the mandrel as in the T.W.Winstead process;
Fig. 4 is a longitudinal section view of the
extruder die and mandrel assembly as in the T.W.Winstead process;
Figs. 5 and 6 are side elevation and plan views
respectively of the biaxial orientor as in the T.W.Winstead
process;
Fig. 7 is a side elevation view of apparatus for
maintaining ribbon tension as it passes toward the printing
section;
Fig. 8 illustrates a portion of the printing press
drive mechanism including the overspeed mechanism;
Fig. 9 is an illustration of the product i.e. a
backing board for bacon products.
Fig. 10 is a perspective view showing the foam
ribbon cell structure.
Detailed Description
Referring first to Fig. 2 of the drawings, there is
shown a more or less conventional extruding machine 10 having a
hopper 12 and a screw 14 operating in a barrel 16. The screw 14
is rotated at a speed determined by the desired output by a
suitable drive means (not shown). The barrel 16 discharges through
an outlet screen assembly 18 via heated insulated conduit 20
into the inlet end of a homogenizer 22 which may be of the
type well known in the art under the trademark KENICS
THERMGGENIZER. This device mixes or scrambles the polystyrene
material after it leaves the extruder 10. It will of course
be understood that the inner surface oc the extruder barrel 16
is very hot and the particles of the polystyrene mixture that
are against the inner surface are hotter than the ones midway
between the inner surface oE the barrel and the outside surface of
the screw. The REMICS THERMOGENIZER includes therein
a series of static metal ribbon-like parts alterna-tely
twisted in the left hand and right hancl directiond and
which are held in the center of the melt stream and thus
326
scramble the melt as it flows through the homogenizer~ This
serves to mix ithe hotter particles with ~he less hot particles
thus giving uni~orm temperature throughout the melt as well as
providing for uniform mixing of the various ingredients of the
mel.t.
~ fter leaving the homogenizer 22, the melt passes
via insulatea heated conduit 24 into a cooling unit 26. Various
types of cooling units for hot plastic melts are commercially
available. The cooler should be selected to provide uniform
cooling of the melt as substantial uniformity of temperature
across the width of the ribbon being extruded is required. No
more than about a 5F. variation across the width of the ribbon
being extruded is permissible as otherwise brittle streaks may
appear in the thin ribbon which can cause cracking or breakage
therealong in the final product.
The melt, after Ieaving the cooler 26, then passes
into the extruder die 28 which will be described in detail
hereinafter.
With continued reference to Figure 2 and in a typical
process operation, the hopper 12 of the extruder is supplied with
any suitable general purpose polystyrene resin, a particularly
preferred resin being one produced by Monsanto Chemical Co.,
under the trademark LUSTREX polystyrene resin and designated as
"yellow 500". A suitable blowing agent is "Freon ll''(Reference
may be made to Canadian Patent 843,838, June 9, 1970 of
T. W. Winstead).
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*Trademark
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The blowing agent is injected at an intermediate
point of the extruder by means o~ a pump 30 and inlet pipe 32.
The injection pressure will be in the order of 3500 pounds per
square inch which figure will, of course, vary somewhat depending
upon process conditions. The melt pressure at the outlet of
the extruder is between about 6000 and 7000 pounds per square
inch. The temperature of the melt at this same point is typically
about 370F. By the time the melt reaches the extruder die 28
it will have been cooled down to a temperature of about 29~-295F.
Temperature control is of considerable importance, it being
noted here that overly high temperatures tend to produce a
brittle ribbon.
Reference will now be had to Figures 3 and 4 which
show the extruder die and mandrel assembly 28 in detail. For
a detailed description of this part of the apparatus, reference
may be had to Canadian Patent No. 834,029 issued February 10th,
1970 to Thomas W. Winstead. Basically the extruder embodies a
die lip arrangement wherein the discharge slot is arcuate in
shape and fed from a feed chamber which diverges from a
substantially central inlet point to the arcuate lips. This
arrangement provides a uniform distribution of pressure flow
at all points along the lip of the die and thereby eliminates
strains or distortions in the extruded material and accommodates
maximum width-wise expansion of the extruded material thus
preventing formation of wrinkles therein. As best seen in
Figure 4, the extrusion die assembly includes a main body 36
with a feed passage 38 extending longitudinally through the
body. A die head 40 is located at one end of the body. A
first die lip 42 is secured to the die head in radial relation
to the passageway 38. An end cap 44 is secured to the die
head with its inner face adjacent to but longitudinally spaced
s~
from the first die lip 42 to thereby form a complementary
second die lip 4~ spaced from the irst die lip. ~n extrusion
chamber 48 is bounded by a rear wall which converges from a
point adjacent the axis of the plastic feeding passage toward
the die lips, and by side walls 50 (see Flg.3) which diverge
from said axis toward the die lips. The end cap 44 is provided
with a substantially conical recess 51 which is concentric
with the feeding passage. An adapter 53 is disposed in the
recess and is contoured to define the diverging side walls 50
of the chamber. The extrusion orifice be~ween the spaced die
lips 46 and 42 is transversely arcuate with respect to the die
head whereby the extruded material from chamber 48 may be
extruded radially in a diverging path.
As described in detail in the above noted Canadian
patent 834,029, a spreading mandrel 52 is provided adjacent
the die lips. The spreading mandrel 52 comprises a vertically
disposed transversely arcuate tube mounted on a cross bar 54
which, in turn, is mounted on a threaded adjustment device 56
thereby to permit the elevation of same to be varied relative
to the die lips. Mandrel 52 is in the form of a tube through
which a cooling fluid is passed to prevent sticking of the
extruded material to the tube as it passes over the mandrel.
To further prevent sticking the surface of the mandrel is coated
with a suitable non-sticking material such as polytetrafluoro-
ethylene. When the mandrel 52 is suitably adjusted with
respect to the die head, it will be found that in the space
between the arcuate die orifice and the mandrel that the
corrugations or wrinkles of the expanding cellular sheet are
very efficiently and quickly removed. Optimum efficiency is
achieved when the rate of lateral expansion of the extruded
material coincides with the rate of flow ~etween the die orifice
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326
and the mandrel; when this condition is achieved no wrinkles
or corrugations even begin to form. For best results, the
mandrel should be maintained at a temperature between 60 and
70F
With further reference to Figures 3 and 4 it will
be seen that currents of cool air are applied to the opposing
surfaces of the ribbon immediately after emergence thereof from
the arcuate die orifice. These currents of cool air serve to
quickly cool the opposing major surfaces of the ribbon thus
inhibiting the development of cells on the foam surfaces, which
action, in turn, is responsible for the appearance on the foam
surfaces of a substantially continuous skin, the thickness of
which is from about 0.3 mils to about 1.0 mils with the skin
thickness preferably being kept on the low side of this range
for best results. The means for sup~lying the currents of cool
air comprise a pair of air lips 55 located on opposing sides of
the arcuate die orifice and being co-extensive therewith.
Air lips 55 each include a curved slit-like opening 57 which
directs air from a source (not shown) on to the opposing ribbon
surfaces just as the ribbon emerges from the die oriflce. ~he
curved slit-like openings 56 are parallel to the die openings
and direct the cool air generally downwardly toward the die
orifice. The air is maintained at a temperature of about 70F.
The operator observes the emerging ribbon and adjusts the air
pressure to get the desired skin thickness i.e. the greater the
air pressure and flow, the greater the skin thickness. The
rapid cooling effec~ solidifj.es the ribbon surface before it
expands. The "freezing" of the surfaces can be observed readily
i.e. a so-called "frost line" can be observed along the line
where the air strikes the ribbon surfaces. The operator can
adjust the air flows to obtain a "frost line" on the surface
and can, w_~h a little practice, obtain the desired skin
thickness. For a further teaching of this aspect of the process
reference may be had to U.~. patents 3,461,496; 3,632,266;
3,670,059 and 3,676,537, of T.W.Winstead.
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31 ~S~826
After passing over khe mandrel S2 the ribbon Rof extruded material passes toward the bia~ial orienter 60
illustrated in Figs. lA, 5 and 6. ~he biaxial orienter employs
a first pair of rolLs 62, a pair of toothed wheels 64 positioned
immediately after rolls 62, and a plurality of transfer rolls
66 disposed after the toothed wheels 64. It will be seen that
the toothed wheels 64 are of relatively large diameter in
comparison to rolls 62, 66 and that the teeth 68 on the periphery
thereof are arranged to bite into opposing marginal edges of
ribbon R as the latter travels therearound. As best seen in
Fig. 6, these toothed wheels 64 are arranged in a diverging
relationship relative to one another such that as the ribbon R
travels therearound, it is stretched in the transverse direction.
An adjustment means 70 is provided thereby to permit the degree
of transverse stretch of the ribbon to be varied somewhat.
Preferably the amount of transverse stretch is in a two to one
ratio. The sets of rolls 62 and 66 are also driven at a speed
such that the ribbon R is stretched in the longitudinal direction
to provide a stretch ratio of about two to one as well. This
stretching takes place primarily between the mandrel 52 and the
first roll of the set of rolls 62. The rolls 66 of the transfer
roll system are divided into upper and lower groups, each group
being mounted to a respective support frame 72, the support frames
72 being adjustable toward and away from one another thereby
to allow the angle of wrap of the ribbon around the individual
rolls of the system to be varied. The upper frame 72 can also
be swung u~ to allow the ribbon R to be threaded through the
rolls at start up. By causing the ribbon to travel in an undu-
lating path between the sets of rolls, the ribbon is allowed to
cool and stabilize somewhat thus preventing shrin~age of theribbon in the lateral direction. It should be noted at this point
that the ribbon temperature is about 230F. at the point where
longitudinal stretching begins to take place. In order to
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promote more rapid stabilization of the ribbon,
it is highly desirable to cool the first three or
four rolls of the transfer roll set 66. This
may be accomplished by passing fluid through such rolls in the
manner well known generally in the art. The mean temperature
of the ribbon as it emerges from the transfer roll system 66
should not be greater than about 180F. If the temperature
is significantly greater than thls, a substantial amount of
llshrinkback" of the web may occur ln the transverse direct.ion.
If shrinkback problems are encountered, the frames 72 can be
moved closer toward one another thus increasing the degree of
surface contact between the ribbon and the rolls 66 thus
increasing the amount of lateral friction between the rolls and
the ribbon to eliminate lateral shrinkback.
The ribbon then passes toward a rorming drum 80~ The
forming drum comprises an aluminum drum having a smooth cylindrical
surface with which the ribbon comes into contact. As seen in
Fig. lA, the forming drum 80 is of relatively large diameter,
for example, about 5 feet in diameter, such drum being mounted ;~
for rotation about a horizontal axis 82 and being driven at a
constant rate of rotation via a suitable motor and gear reduction
drive (not shown) at a speed commensurate with the speed of
~advance of the ribbon as it passes from the biaxial orienter
and transfer roll system. The forming drum 80 is preferably
mounted in a partial enclosure 84 within which are disposed
fans 86 and 88 which project currents of air toward the ribbon
which is being carried around the periphery of the drum thereby
to effect further cooling and stabiliza~ion of the ribbon. By
.
adjusting these air currents, the forming drum surface can be
maintained at a temperature of about 110-120F.
32~
With further reference to Fig. lA it will be seen
that the ribbon R moves toward and onto the surface of the
forming drum 80 by way of guide rolls 90 with -the ribbon then
passing through a nip 92 defined between the forming drum surface
and a chill roll 94O This roll 94 is maintained at a surface
temperature o about 65F. and its primary purpose is to effect
further cooling of the ribbon while at the same time effecting
a partial calendaring of such ribbon. By way-of example, it
i5 noted here that the ribbon thickness out of the forming die
assembly 28 is approximately 0.125 inch in thickness. After
the biaxial orientation, ribbon thickness is about .08 inch i.e.
80 mils. After passing through nip 92 between forming drum 80 and
chill roll 94, the ribbon thickness is approximately 0.050 inch.
The ribbon subsequently enters a further nip 96
defined between forming drum 80 and a gauging roll 98. This
gauging roll 98 is positioned relative to the forming drum
surface such that the ribbon can be brought toward its final
thickness of approximately 0.020 inch. The final thickness
is achieved later on at the first press unit
at the nip between rolls 150, 152. Those skilled in the art will
of course appreciate that these figures are given by way of
example only and the amount of calendering or transverse
compression can be varied somewhat thereby to provide the
desired degree of ribbon thickness.
With particular reference to Figs. lA, lB and lC,
it will be seen that the ribbon R moves away from the forming
drum 80 in an elongated path of travel defined by guide rolls 100,
102, 104 over a splicing table 106 and thence via infeed tension
unit 108 and draw roll system 150, 152 into the printing assembly
110. Th~ printing assembly 110 comprises a plurality of serially
arranged printing units of which only two, i.e. 112 and 114 are
illustrateZ. The number of printing units is, of course, dependent
upon the number of colours to be applied to the ribbon surface.
It .s noted here that in a typical operation a
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ribbon speed of about 150 feet per minute is common. By way
of example the distance between the forming drum 80 and the
first press unit 112 may be about 30 feet. The travel time
of ribbon R from forming drum 80 to the first press unit 112
provides additional time which allows the uncured ribbon to
further stabilize and cool. It will of course be kept in mind
that ribbon R has relatively low thermal conductivity and thus
this additional cooling time is desirable thereby to allow the
interior portions of the ribbon to become more stable. If
1~ insufficient time is allowed between the forming drum 80 and
the first press unit 112, the ribbon may be overly soft and
the printing unit may tend to emboss the ribbon surface in an
undesirable manner and the ribbon may elongate thus causing
registration problems as the ribbon passes through the several
press units.
The space provided also has another practical purpose
in that it provides the necessary room for an elongated spllcing ;~
table 106 which facilitates manual splicing of the continually
extruded foam ribbon to the stationary leader which has been pre-
threaded along the ribbon path through the printing and die sections
At this point it is desirable to refer to Figs. 7and 8 which illustrate the ribbon tensioning device and the
printing section overspeed drive assemblies respectively. The
infeed tensioning assembly includes a spaced apart pair of rolls
116, 118 mounted between opposing ends of a pair o~ arms 120,
~only one arm being shown in Fig. 7). Arms 120, in turn, are
rotatably mounted at their mid-point for rotation on
a support member 122 which is affixed to the frame of the
first printing unit 112. The rolls 116 and 118 are back
pressured by an air cylinder ~24 and lin~age assembly 126 in
a clockwise direction to resist the counter-clockwise torque
caused by tightenlng ribbon tension. A pressure regulating
valve (not shown) can preset the air pressure to regulate the
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tension in the ribbon. By observing the position and direction
of rot~tion OI arms 120~ the operator can determine if the
ribbon is tightening or loosening or is remaining at the
predetermined ribbon tension.
Reference may now be had to Fig. 8 which shows a
portion of the press assembly drive train. There is shown a
main drive unit 130 which is of any suitable conventional
construction and having mounted on its output shaft a pair of
axially spaced drive sprockets 132 and 134. The drive sprocket
134 is of somewhat larger diameter than drive sprocket 132;
sprocket 134 may have 48 teeth,for example, while sprocket 132
may have, for example,40 teeth. The sprocket 132 is coupled
to the drive shaft via a one-way overrunning clutch 136 of any
desired standard construction. The sprocket 134 is coupled
to drive shaft 134 via an air cylinder operated clutch 138,
such air actuated clutch also being of any standard commerclally
available variety. The sprocket 134 is coupled to sprocket 140
while sprocket 132 is coupled to sprocket 142. Sprockets 140
and 142 are of the same diameter and they are both affixed to
line shaft 144, such line shaft 144 extending alongside the
several printing units and the die cutting unit 170 and being
coupled thereto in a conventional manner (not shown). During
ordinary operation of the system, the main drive 130
drives the printing units via sprocket 132 which in
turn drives sprocket 1~2 to rotate line shaft 144 at
a predetermined speed thereby driving the various press units
at a speed which is synchronized with the speed of travel of the
incoming ribbon R. During this mode of operation the air
operated clutch 138 is deactivated so that sprocket 134 simply
free-wheels on the main drive shaft. Howevex, during start-up
operations, as will be described more ~ully hereinaEter, it is
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desired to operate the printing press and ~ie cutting sections at a higher
than normal rate of speed and in this instance, the air operated clutch is
activated thereby to engage sprocket 134 with the main drive shaft. Since
sprocket 134 is larger than sprocket 132 it obviously drives sprocke-t 140 at
a higher rate of speed thus resulting in a higher speed of operation of the
printing and die cutting u~its. For example, when the ribbon splice is made
with the continuously moving ribbon to the stationary ribbon leader in the
press section, a press start-up button is manually operated and the press
section runs at a speed synchronized with the speed of the inccming ribbon
i.e. the a~ove described sprocket 132 drives sprocket 142. At this point,
there is usually a considerable degree of slackness in the ribbon before the
draw rolls 150 and 152 and scm.e slackness in the ribbon going through the
press section. At the start-up point this can be observed by the position
of the arms 120 of the infeed tension assembly 108. At this point,
the operator presses a press speed-up button which serves to activate the
air operated clutch 138 thus automatically shifting the press and die cutting
sections into the overspeed mode of operation. m is overspeed may be about
10% higher than the speed of the incoming ribbon. The operator holds the
speed-up button down until the slackness in the ribkon disappears and the
arm 120 revolves to its medial position. m e operator then releases the
speed-up button and the press section returns to synchronous speed, matching
the speed of the incc~ing extruded rib~onO
~ ith further reference to Figs. lB and lC, it is noted here
that the several prlnting units 112 are sc~ewhat modified flexigraphic
printing units utilizing rubber printing plates. The modifications basically
concern anti-backlash gears in the plate cylinder gear train to cc~pensate
for the thickness of -the ribbon being printed ard to maintain inter-colour
register, and the use of large diameter ribbon carrier rolls to reduce curl
effects in the uncured rib~on. The carrier rolls are designed for relatively
lcw inertia, are well balanced, and use 1GW friction bearings to reduce
drag on the ribbon and avoid stretching of ~he ribbon. Since other aspects
of this flexographic printing process are well knawn in the art of printing
a detailed description is considered unnecessary. Other printing processes,
such as rotogravure, etc. can be used.
It will be seen from
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the drawings that the incoming ribbon R passes between a draw
roll 150 and a chilled roll 152. ~s noted previously, these rolls
may be used to further compress the ribbon to control the web
thickness. The ribbon then passes downwardly around a series of
rolls 15~ and thence upwardly through a nip defined between a plate
cylinder 156 and an impression roll 158. An engraved inker roll
160 rotates in contact with the plate cylinder 156, the inker
roll 160 being i~mersed in a bath of ink contained in trough 162,
with a suitable doctor blade 164 being provided to remove excess
ink from the inker roll. The printed ribbon then passes upwardly
around guide roll 166 and through a conventional dryer arrangement
168 which serves to dry the applied ink following which the ribbon
passes on to the next printing uni~. The printing units are all
o~ essentially the same construction as that described above and
the number of such printing units is, of course, dependent on the
number of colours to be applied. A simple two colour system would
require the use of only two printing units but for most purposes
four or five printing units will be required.
Insofar as the printing inks are concerned, various
conventional printing inks based on nitrocellulose or acrylic
resins were found to be reasonably satisfactory. The best
combination of properties insofar as flexibility, adhesion,
slip, abrasion resistance and odour are concerned was obtained
using the "Flexo Styrene" series of inks produced by General
Printing Ink Company, Toronto,Canada. This series of inks is
based on a combination of nitrocellulose and cellulose acetate
propionate. The solvents used with the ink are denatured
anhydrous ethyl alcohol, normal propyl acetate and normal
propyl alcohol. The addition of one percent micronized
polyethylene to the ink provides additional slip~
After the ribbon e~erges from the printing section
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110 it enters into a die cutter and delivery unit 170. ~his unit is
illustrated diagra~matically in Figure lC. Again, since units of this nature
are basically well known in the art a detailed description of same is
considered unnecessary. The ribbon first passes around a cooled roll 172,
around guide roll 174 and thence between the rolls of a scoring unit 176. At
this point it is advisable to refer to Fig. 9 which illustrates a segment of
the ribbon R and illustrates the outline shape of the die cut bacon board
blanks thereon. It will be seen that each bacon board includes a flap portion
F and a body portion B. Between the flap portion F and body portion B there
is a continuous score line S which has a series of spaced apart fine slits P
therealong. These slits facilitate folding of the flap portion relative to
the bcdy portion. Th~ score line S is provided by scoring unit 176. Followlng
the scoring unit, the ribbon passes dcwnwardly into the nip b~tween cutter
roll 180 and anvil roll 182.- The cutter roll is provided with a raised sharp
edged lip which, r~hen it comes into contact with the ribbon R, penetrates
therethrough and severs such ribbon all around the outline contour of the
bacon board which has been printed on the ribbon surface. At the same time
the roll 180 also cuts the above noted slits P along the score line S. After
this operation, the ribbon passes dcwnwardly around delivery roll 184 and be-
20 tween guide rolls 186 following which the ribkon waste is drawn vertically up-
wardly at a sharp angle with such action causing the cut bacon koards to pass
outwardly onto a slowly moving surface 188 of a delivery table r,~th the
result being that the bacon boards are deposited on such takle in an over-
lapping shingle-like fashion. The remaining ladder-like waste portion of
the ribbon is then forwarded to a waste cutter with the waste material being
ultimately collected and ultimately fed back into the extruder hopper 12
with the result being that there is virtually no wastage of materials.
This is possible since the printed design is spaced about 1/8 of
an inch inwardly of the die cut edge all around the die cut edge
thus avoiding ink contamination of the waste ribbon material,
which contamination would otherwise ultimately adversely dis-
colour the extruded ribbon webs.
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*Trademark - 2 0 - `
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~1S~1 32~
Reference may now be had to Table 1 which
illustrates the physical characteristics of a number of foam
products. Samples No. 2-5 were made generally in accordance
with the principles of the present invention. Samples No. 3
and 4 were considered to have the best properties insofar as
the purposes of the present invention are concerned. Sample No.
6 which was included here for purposes of comparison is a
relatively low density foam meat tray; this foam was not bi-
axially oriented after extrusion, nor was it provided with skin
surfaces nor was the foam compressed or calendared thereby to
control the thickness thereof as in the other samples. Table 1
should be reviewed in conjunction with ~igure 10 which illustrates
the cellular structure of the foam as well as the manner in
which cell size is measured and determined.
It will be seen from a review of Table l and Fig.
10 that the cells of the bacon board samples have a relatively
squashed or flattened appearance with diameters in the machine
direction ranging from about .23 to .28 mm. and diameters in
the cross machine direction varying from about .2~ to about .30
2~ mm. With reference to skin thickness, all samples with the
exception of Sample No. ~ i.e. the meat tray, which had no skin,
were found to have about 0.3 to about 1.0 mils of skin on the
surface. Two samples, iOe. samples 3 and 4 had skins on both
major surfaces, i.e. on the inside and outside surfaces. These
two samples were found to have the highest tensile strength in
the machine direction. The cross machine direction tensile
strength for these two samples was not the highest observed but
this may be accounted for by the lower cross machine direction
orientations observed. The skinned surfaces give rise to a
number of benefits. The skinned surfaces make for a tougher foam
- 21
5~326
due to the biaxial orientation of the skin surfaces. The skin
also protects the surfaces during the crushing or compressing
operation. The biaxial orientation appears to have a beneficial
effect on cell structure during the crushing as cell structure
is well defined near both surfaces. In the absence of a skin
surface on the foam, the cell structures tend to rupture thus
producing a poorly defined structure which may be susceptible
to premature aging and loss of strength. It might be noted here
that care has to be taken to prevent excessive cooling at the
die during the skin forming step or the foam will split.
Although there is no need for the skins on opposing sides o~ the
foam ribbon to be exactly the same thickness, there should be
a reasonable degree of balance between them thereby to mlnimize
warping of the final product.
In the preferred form of the invention, the final
density is achieved by crushing or compressing a 2.5 lb./ft.3
foam to achieve a final density of the foam ribbon in the range
of 10.5 lb./ft.3. In other words, the foam which initially has
a thickness of about 80 mils is crushed or compressed back
to a recovered value of approximately 20 mils. This represents
a four to one crush ratio. These figures,may of course, be
varied considerably. At the same time i~ should be kept in
mind that overly high crush ratios may cause rupturing of
an undue number of the cells of the foam in turn adversely
affecting the aging characteristics.
It has previousiy been observed that the orientation
levels are relatively high, particularly in the cross-machine
or transverse direction. In the example described previously
the amount of orientation or stretch was in about a two to one
-22-
3Z6
ratio in both the machine direction (longitudinal direction)
and in the cross-machine (transverse) direction. This relatively
high degree of orientation is considered to be ~ery beneficial
and is believed to be responsible for much of the improvement
in ~he properties of the foam ribbon observed. With reference
to Table 1, in comparing Sample No. 1 with Samples Nos. 3 and 4,
the increase in orientation in the cross-machine direction is
quite obvious. The dramatic increase in tensile strength,
particularly in the cross-machine direction, is attributable
in a large measure to the increase in orientation.
With reference to Samples Nos. 2-5 it will be
seen that they range in density from a low, in the case of
Sample No.2, of 8.1 lb./ft.3 to a high, in the case of Sample No.
3, of 11.4 lb./ft.3. Generally speaking, it is recommended
that the density of the final product be maintained within the
range from about 8 to about 12 lb./ft.3. For best overall
results, it is considered desirable to maintain the final
density in the order of about 10-11.5 lb./fto3 and this, of
course, can be controlled by controlling the degree of
crushing or compression being effected by the gauge roll
means previously described.
From the foregoing, it is believed that the
invention may be readily understood by those skilled in the art
without further description 7 it being borne in mind that
numerous changes may be made in the details disclosed without
departing from the spirit of the invention set forth in the
following claims.
