Note: Descriptions are shown in the official language in which they were submitted.
`` 11;~;~21
This invention relates to apparatus for biaxially orienting
thermoplastic materials, e.g.,polystyrene. More particularly, it relates
to a means for continuously orienting and transferring a continuous web of
material conformingly onto the periphery of a polygonal rotating mold from
an extruder.
This application is a division of application Serial No. 323,052
filed March 9, 1979.
The specifics of the following discussion and specification refers
to oriented polystyrene material, hereinafter referred to as OPS but it
- 10 should be expressly understood that the apparatus constituing the present
invention is applicable to a wide variety of thermoplastic materials,
polymers or mixtures of polymers including other such materials, e.g.,
polymers of ethylene, polypropylene, styrene, vinyl chloride, etc.
While individual materials have problems which are often peculiar
to those materials and hamper commercial exploitation of them, the poly-
styrene materials exhibit low-cost, high stiffness and excellent trans-
parency when properly oriented and the proper molecular orientation further
enhances the polystyrene material by removing its inherent brittleness in
the absence of molecular orientation.
,~
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1133~21
There are various prior art approaches to mitigating
the brittleness factor in polystyrene materials, by the use
of impact modifiers and the like. However, this decreases
the stiffness,eliminates transparency and increases the
cost significantly.
Therefore, prior art approaches to remedy the brittle- ¦
ness problem and increase the impact resistance of poly-
styrene result in certain undesirable properties which did
not exist prior to the addition of such modifiers.
Accordingly, if such materials could be used in a
relatively unmodified state in manufacturing sheets or ,
strips of this material in a continuous extruding ~ethod
in which continuous biaxial orientation is imparted to ,
this m,ate,rial and then, without destroying the continuity or
15 the ~ethod , mold articles or otherwise form articles from
it, all of the desirable physical properties of the material .
could be realized. At the same time all of the desirabili-
ties, speed and efficiencies of a fully continuous process
could be realized in the ultimate product cost.
This integrated approach which combines continuous ,
extrusion, orientation and forming in rapid succession is
the crux of the present invention. n
Heretofore, the conventional approaches " e,g. with
foam sheet materials and non-foamed or non-cellular sheet
25 materials has been to first produce sheeting, store it in .
rolled form and terminate the initial process at that point.
Then, subseguently~ the sheeting is unrolled, reheated and
subsequently for~ed into products or articles in its
reheated state. As ~.ith all thermoplastic techniques,
there are three basic interrelated variables involved in
procéssing thermoplastic materials which affect both the
nature of the operation and the characteristics of the final
product. These variables are temperature, time and ph)~sical
state, with the latter variable dealing with pressure, I _
stress, etc.
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1133~21
As a general rule, temperature and time should be L
minimized variables because extended heat history can
materially affect the properties of an end product. In the
case of OPS, for example, the temperature at which the r
5 material must be oriented represents a compromise between
levels which are best from a flow point of view and levels
which are best from a stress (orientation) point of view. L
Once a stress is imposed at a given temperature, for
example, a molecular orientation is achieved. However, the
10 longer the increment of time involved between the achieve- _
ment of that orientation and a subsequent operation, the
more stress (orientation) will again be relaxed. According-
ly, the degree of orientation of a particular material is
not necessarily a sole function of the amount of heat
15 stretching applied to that material to create the orienta-
tion since relaxation of that orientation may simultaneously
be taking place.
Therefore, a high speed, integrated approach is unique
and important not only from a standpoint of cost but also l ~
20 from the standpoint of results heretofore not otherwise .
attainable.
These inherent advantages of a high speed integrated ~
approach are important in relatively thin products , e.g. l ;-
those with wall thicknesses of ~005 too.010 inches and
25 become increasingly significant with products having wall
thicknesses greater thano.010 inches. This is due to the
fact that conventional systems as heretofore defined,
necessarily involve not only greater time/temperature
exposure during the production of heating from which the
30 ultimate products are formed, but also involve the reheating
and subsequent recooling of the sheet during the subsequent
forming operation. Accordingly, the relief of stress occurs .
during reheating and subsequent recooling as well as during
a possible relaxation during the production of the sheeting _
35 per se.
_
il33Z2~
Theoretically, the ideal method would be to bia~ially
orient the thermoplastic material, form and cook it
simultaneously. In conventional systems, the time factor
is significant and therefore detrimental. Accordingly, the
shorter the time factor the less detrimental the effect
thereof on the maintenance of a stressed or oriented condi-
tion of the material.
Of the conventional methods employed for the production
of articles made from material which is biaxially oriented,
perhaps the most popular and widely used prior art system
involves the extrusion of a sheet from a slot die onto a
roll, the temperature of the said roll being controlled,
and then through a series of additional rolls ~hich first
bring the sheet to an appropriate temperature level for
orientation and then longitudinally stretch the sheet
between tlYO rulls running at different speeds. This longi-
tudinal stretching or drafting orients the material in the
machine direction. ~he material with the longitudinal
orientation is then passed onto a tenter frame to orient it
transversely in a manner well-known in the art. Since con-
ventional tentering involves large, heavy equipment, it is
also necessary that temperatures be ma`intained in the
sheeting through the use of large, expcnsive ovens. After
the sheeting has been oriented both longitudinally and
transversely, it is then rolled and stored for subsequent
use.
The forming of OPS sheeting is usu~lly carried out on
non-rotating thermoforming equipment with special provisions
for the OPS material. It is necessary that the reheating
of the sheetin~ as it is fed into the forming e~uipment
be maintained uniformly througllout its width and length.
As the material reaches a satisfactory forming temperature,
the stretches which have been imposed during the biaxial
orientation must be resisted by ade~uate clamping devices
in order to preclude the sheet from shrinking back to its
original dimensions and losin~ the orientation therein.
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~ 33Z21
Since most non-rotary forming equipment is necessarily
intermittent in its operation, the intermittent feeding of
oriented sheet in such conventional forming equipment im-
- poses inllerent difficulties in the creation and maintenance
5 of uniform temperature conditions throughout the forming
area of the sheet~
There are several other approaches which ]-ave been used
to some extent in the production of biaxially oriented
sheeting. One of these, the bubble process 9 is typically
10 the way much thermoplastic film is produced. By proper
control of temperature and stretching, it is possible to
produce a biaxially oriented film or sheet using this bubble
technique. However, in practice it is proven to be very
critical because of temperature unifoTmity requirements.
15 Also this technique is not usable when it comes to thicker
material such as that used in thermoformed articles or
products on the ordeT of meat trays, containers and table-
ware.
r Further, there is some equipment in use which simul-
20 taneously stretches transversely and longitudinall)r. This
equipment obviates the use of longitudinal stretching rolls
e-g- those previously described, but it has certain
disadvantages, namely, the amount of selvage which must be
discarded due to the increased scalloped effect resulting
25 from clamps which are necessarily moved further apart in
the longitudinal direction in order to achieve such a
simultaneous biaxial stretching action.
The molecular orientation of thermoplastic materials,
as previously indicated, results in significant improve-
30 ments in many of the characteristics of certain of these
materials. Biaxial orientation is essential in most
packaging and disposable products. If orientation is only
in one direction, even though properties may be substan-
tially improved in tl-at direction, they are reduced in tl-e
35 other dimensions. Typical of products which are oriented
in one direction only are monofilaments and fibers.
1133~21
During orientation~ the molecules in the materlal are shifted from random
coil entanglement to a relative alignment parallel to principal axes of
stretch. This results in significant improvements in physical properties,
optical properties and in improved barrier properties and stress crack
resistance.
For example, among the physical property improvements, the impact
strength in materials, e.g., OPS, are improved on the order of ten times
with two to three times the tensile strength of non-oriented polystyrene
and as much as three times the improvement in yield elongation.
By a broad aspect of this invention, means are provided for
continuously orienting and transferring a continuous web of thermoplastic
material conformally onto the peri-pllery of a polygonal rotating mold from
an extruder, the means comprising: web receiving and advancing means
ingesting the web; web stretching means downstream of the web receiving
means for next receiving the web and imparting at least a lateral stretch
to the web and advancing same toward a polygonal rotary mold; and web
transfer means mounted immediately downstream from the web stretching
means in peripheral surface following relationship with the polygonal rota-
ting mold for receiving the laterally stretched web from the web stretch-
ing means and conformally juxtaposing the stretched web with the peripheral
,
-- 6
~33~
surface of the rotating mold; at least one of the web receiving and advan-
cing means and the web transfer means imparting a longltudinal stretch to
the web to impart biaxial orientation thereto prior to its conformal juxta-
position with the peripheral surface of the rotating mold.
By one variant, the web receiving and advancing means comprise
first and second roller means and means driving the roller means at differ-
ent peripheral velocities to impart longitudinal stretch to the web.
By another variant, the web stretching means comprises a pair of
rotating discs, each disc having peripherally disposed teeth engaging a
respective edge of the web when first received therein and the discs being
divergently oriented in a downstream sense such that the teeth constrain
the web to be stretched to a width commensurate with the divergence of
the discs.
By still another variant, the web transfer means comprises:
first, second and third roller means mounted transversely of the web with
the second roller commonly adjacent the other rollers; and a common frame
mounting the roller means for rotation therein on parallel axes of rotation
with the first roller immediately adjacent the web stretching means and the
third roller in rolling juxtaposition with the peripheral surface of the
rotating mold with the oriented web therebetween.
By a further variant, the web receiving and advancing means com-
prise first and second roller means and means driving the roller means at
differential peripheral velocities to impart longitudinal stretch to the
web; the web transfer means comprising: first, second and third roller
means mounted transversely of the web with the second roller commonly adja-
cent the other rollers; and a common frame mounting the roller mcans for
rotation therein on parallel axes of rotation with the first roller immedi--
ately adjacent the web stretching means and the third roller in rolling
juxtaposition with the peripheral surface of the rotating mold with the
113~
oriented web therebetween.
By still another variant, the web stretching means comprises a
pair of rotating discs, each disc hav~ng peripherally disposed teeth
engaging a respective edge of the web when first received therein and .he
discs being divergently oriented in a downstream sense such that the ~eeth
constrain the web to be stretched to a width commensurate with the diver-
gence of the discs; the web transfer means comprising: first, second and
third roller means mounted transversely of the web with the second roller
commonly adjacent the other rollers; and a common frame mounting the roller
means for rotation therein on parallel axes of rotation with the first
roller immediately adjacent the web stretching means and the third roller
in rolling juxtaposition wiih the peripheral surface of the rotating mold
; with the oriented web therebetween.
By yet a further variant, the web receiving and advancing means
comprise first and second loller means and means driving the roller means
at differential peripheral velocities to impart longitudinal stretch to the
web; the web stretching means comprises a pair of rotating discs, each
disc having peripherally disposed teeth engaging a respective edge of the
web when first received therein and the discs being divergently oriented
- 20 in a down stream sense such that the teeth constrain the web to be stretched
to a width commensurate with the divergence of the discs; and the web
transfer means co~prises: first, second and `hird roller means mounted
transversely of the web with the second roller commonly adjacent the other
rollers; and a common frame mounting the roller means for rotation there-
in on parallel axes of rotation with the first roller immediately adjacent
the web stretching means and the third roller in rolling juxtaposition
with the peripheral surface of the rotating mold with the oriented web
therebetween.
By a variation thereof, the web transfer means is mounted
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1133~21
substantially independently of the web stretching means.
By another varlation, the web transfer means is mounted substan
tlally independently of the web stretching means and the means further
includes further means mounting the common frame for rotation on the axis
of rotation of the first roller.
By still another aspect of this invention, means are provided
for continuously manufacturing oriented thermoplastic molded articles from
granulated and comminuted polystyrene material comprising: extruder means
for assimilating raw thermoplastic material and extruding it into a strip;
charging means for providing granulated and comminuted thermoplastic
material to the extruder means; regulating means controlling the
By another aspect of this invention, means are provided for con-
tinuously orienting and transferring a continuous web of thermoplastic
material conformally onto the periphery of a polygonal rotating mold from
an extruder, the means comprising: web receiving and advancing means
ingesting the web; web stretching means downstream of the web receiving
means for next receiving the web and imparting at least a lateral stretch
to the web and advancing same toward a polygonal rotary mold; and web
; transfer means mounted immediately downstream from the web stretching means
in peripheral surface following relationship with the polygonal rotating
mold for receiving the laterally stretched web from the web stretching
means and conformally juxtaposing the stretched web with the peripheral
surface of the rotating mold; at least one of the web receiving and
advancing means and the web transfer means imparting a longitudinal stretch
to the web to impart biaxial orientation thereto prior to its conformal
juxtaposition with the peripheral surface of the rotating mold; the web
transfer means comprising an odd number of three or more roller means
_ g _
32;~1
mounted transversely of the web with the roller means parallel and adjacent
for receiving the web on the peripheral surfaces thereof in a serpentine
path; a common frame mounting the roller means for rotation therein with
an upstream roller means immediately adjacent the web stretching means and
a downstream roller means in rolling juxtaposition with the peripheral
surface of the rotating mold; and the remaining odd number of roller means
being intermediate the upstream and downstream roller means for transpor-
ting the oriented web therebetween in the serpentine path.
By one variant thereof, the web receiving and advancing means
comprise first and second roller means and means driving the roller means
at differential peripheral velocities to impart longitudinal stretch to
the web.
By another variant, the web stretching means comprises a pair of
rotating discs, each disc having peripherally disposed teeth engaging a
respective edge of the web when first received thérein and the discs being
divergently oriented in a downstream sense such that the teeth constrain
the web to be stretched to a width commensurate with the divergence of the
discs.
By still another variant, the web receiving and advancing means
comprise first and second roller means and means driving the roller means
at differential peripheral velocities to impart longitudinal stretch to
the web; and the web stretching means comprises a pair of rotating discs~
each disc having peripherally disposed teeth engaging a respective edge of
the web when first received therein and t11e discs being divergently
oriented in a downstream sense such that the teeth constrain the web to be
stretched to a width commensurate with the divergence of the discs.
The above-identified parent application pr~vided a method which
commenced with the continuous extrusion of a relatively narrow strip of
thermoplastic material from a die at a relatively high linear speed and
which is extruded
".:
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1133;~2~
at the preferred orientation temperature. If the extruslon temperature is
above the desired orientation temperature then it may be passed over
cooling rolls in order to bring it do~n to the desired orientation tem-
perature. The strip is then passed through differential speed rolls, if
desired, to impart a predetermined maximum or partial amount of longitu-
dinal or machine direction stretch orientation thereto and immediately
subsequent to this orientation is passed into a transverse stretching
station which consists basically of a pair of divergently disposed rotating
saw blade-like devices which engage the strip along each edge and divide
it into a series of increments which are then continuously separated trans-
versely to a distance of approximately three times the original dimension
of the extruded strip.
,
1133'~Zl
Since the longitudinal direction is also desirably
oriented by stretching on an order of ma~nitude of three
times the original dimension, if this has not been
achieved by the stretching rolls upstream from the trans-
verse stretching mechanism, the balance of the longitudinal
` stretching may be taken care of downstream from the
transverse stretching apparatus. All of the foregoing
steps, however, are performed on a continuous and uninter-
rupted basis. `
After the proper degree of orientation has been
biaxially imparted to the extruded and now lengthened and
widened strip of material, the material is continuously
transferred onto the perimeter of a rotating polygon mold,
each segment of ~hich contains a forming cavity and reten-
tion devices to hold the stretched sheet to its new
dimensions at the point of transfer.
The sheet is then thermoformed onto the mold cavities
on the rotating polygon sequentially and is chilled against
the mold surface below the distortion point of the oriented
sheeting to thereby set the material and retain the orien-
-; tation therein.
Downstream from the rotating polygon mold device is a
continuous and sequential severing apparatus which contin-
uously and sequentially severs the formed articles from
the selvage and then accumulates the articles for stac~ing
and packaging while gathering the selvage for reuse. The
selvage is reused by recycling it to the ra~ material
processor which includes a device Ior admixing thermoplastic
i pellets and chopped up selvage.
In order to enhance the operation and the quality
control, the biaxial orientation equipment must be
physically engaged, in some part, at its output point with
the rotating polygon mold means and therefore, problems
of inertial interaction bet~een these two devices have
been noted. Novel means are provided herein forprecluding the full
inertial effect ~ taking place and includes a structure which in
fact minimizes,
- 12 -
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11~3~21
to an optimum degree, the equipment inertia present at the mold-orientation
equipment interface thereby to preclude uneven longitudinal stresses from
being imparted to the material because of this inertialproblem at the
interface.
In the accompanying drawings,
Figure 1 is a schematic of a continuous extrusion, biaxial orien-
tation and forming system wherein the extrudate is ext~uded at orientation
temperature;
Figure 2 is another embodiment of another continuous system in
which the extrudate is at a higher temperature than is considered optimum
for orientation and in which a series of cooling rolls are provided for
establishing the desirable orientation temperature downstream from the
extruder;
Figure 3A is an enlarged schematic of the biaxial orientation
apparatus of the system of .Figure 2 illustrating the several positions at
which orientation can occur;
Figures 3B, 3C and 3D are schematic stretch diagrams showing the
several modes of biaxial orientation of the extrude which is possible in
correlation with the relative position of the extrudate in the orientation
20 apparatus of Figure 3A;
Figure 4 is a schematic of a low inertia e~odiment;
Figure 5A is a top pL~n schematic illustrating the transverse
stretching blades used in a means set at maximum divergence;
Figure 5B is a top plan schematic illustrating the trc~nsverse
stretching blades used in a means set at minimum divergence (mutually
parallel); and
Figure 6 is a top plan partial schematic of the embodl~ent of
Figure 4.
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- 13 -
` 11~3Z21
Referring in detail to the drawings and with particular
reference to Figure 1, an extruder 10 is illustrated as
having an output to a die 12 which forms a narrow web 14 of
polystyrene or other thermoplastic extrudate at a tempera-
ture approximating the optimum temperature for subsequent
biaxial orientation of the extrudate 14.
From tlle die 12, the web-like extrudate 14 is shown as .
passing over an input roller means 16, beneath a transverse
stretcher blade assembly 18, and subsequently, over an out-
put roller assembly Z0, the latter being juxtaposed with
the periphery of a mold wheel assembly 22 which is of poly-
gonal cross-sectional shape and which is rotated about a r
central axis 22A. The web of extrudate 14 passes beneath
15 the mold wheel 22 which rotates clockwise as shown in the
drawing. Each flat on the periphery of the mold wheel 22 r
includes a mold cavity MC, a plurality of which are shown
in dotted lines in Figure 1.
Suitable vacuum means or a combination of positive
20 pressure, vacuum and/or male die members are provided to
cooperate with the mold cavities MC to form predetermined
shapes corresponding to those initially imparted to the ~ .
.mold cavity in the web 14 and these products 24 are
schematically shown in cross-section leaving the uppeTmost .
` 25 portion of the mold wheel 22 and passing in a reverse
; direction back over the extruder 10 as illustrated by the
directional arrow 26.
The rotational velocity of the input roller assembly 16
relative to the transverse stretching blade assembly 18 may
be set differentially to impart a longitudinal stretch or a
machine direction stretch to the web 1~ and a similar
differential rotational velocity between the peripheries Of r
. the output roller assembly ~0 and the transverse stretcher
blade assembly 18 may also be provided to impart additional
machine direction stretch or orientation to the .leb 14.
F
- 14 - _
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~33Z~
The transverse stretcher blade assembly 18 is best
illustrated by joint reference to Figures 1, 5A and 5B in
which the transverse stretcher blade assembly 18 is illus-
trated as including first and second circular saw blades
18A and 18B, respectively, which are mounted on downstream
pivots PA and PB, respectively, which in turn, are suitably
- mounted by any well-known means on a machine frame such
that the saw blades 18A and 18B are adjustable about the
pivot means PA and PB between a maximum divergence of 45
to the machine direction or product center line illustrated
- in Figures 5A and 5B as produce center line 14CL and which
are driven about central blade axes by means of drive pulleys
DA and DB which are also positioned for movement with the
blades l8A and 18B about the said respective pivot means
PA and PB.
The teeth 18T about the periphery of each blade engage
the outermost edges of the web 14 and cause it to change
from its initial extruded dimension at the input side of
the blades to a much wider dimension commensurate with the
20 divergence at which the blades are set at the outyut side - I
thereof. In this manner, a transverse orientation is
imparted to the web 14 in a continuous manner as it
traverses the transverse orientation blade assembly 18
from the input roll assembly 16 to the output roll assembly
20.
In the schematic of Figure 1, the entire assembly of
the input rollers 16, transverse orientation rollers 18 and
` output rollers 20 is a unitary structure mounted on a common
vertical post which is schematically illustrated at 28 and
whiçh post 28 is biased by suitable means 30 such that the
output roller assembly 20 closely follo~s the peripheral
contours of the polygon shaped mold IYheel 22.
As a result~ the oscillation of the vertical support ~8
about its center point 28C occurs as sho~Yn by the arcuate
arrow 28D in Figure 1.
-
`j.
-
~ . . . . . .
Therefore, if the speed of the mold whcel 22 isincreased to a point where production speeds of a highly
- .desirable level are obtainedJ the inertial forces in the
' combined integrated input-transverse orientation-output roll ¦'
assembly 16-18-20 are such that the roller assembly 20 at
the output will not properly follow the contour of the mold
wheel 22 and will place uneven longitudinal stresses in the
biaxially oriented material, resulting in inferior products I .
and in some cases, an improper alignment on the mold wheel.
; 10 22. This results, of course, in products which are inferior I
and which defy efforts to provide satisfactory quality
control. At slower speeds, however, the continuity of the
method and apparatus of Figure 1 provides a highly desirable I r
process with high quality end products 24.
In the event that the'extruder 10 emits material from
the die 12 which is at a higher temperature than the optimum
one for imparting biaxial orientation to the material in
the web 14, then the system schematically illustrated in
Figure 2 is utilized to bring the extrudate web 14 down to
the proper orientation'temperature. The-embodiment of
Figure 2 also illustrates the use of another preferred . .
embodiment of input and output roller assemblies to impart~ I .
machine direction or longitudinal orientation to the
extrudate web 14.
As illustrated in Figure 2, the e~truder 10 and the :
-j die 12 feed an extrudate web 14 first into a bank of cooling
rolls CR whicll are provided, as is well-kno~n in the art,
: with a suitable heat exchange medium and control therefor,
'. or which simply provide the proper reach of web material 14
for ~ given temperature of extrusion to permit it to cool
sufficiently in the ambient conditions of the process
equipment, such that when it reaches the input roll assembly. .
16 it is at the proper t-mperature for ori~ntation.
' - 16 -
_ . . . . . .......... . ..... . . . . . . . . . . . .
,
- : ;
" 1133~1
The inl~ut roller assembly 16 is illustrated as including
a first roller 16A and a second roller 16B which receives the
web 14 in a serpentine path therebetween and which rolls lGA
` and 16B are driven at differential rotational velocities to
impart a longitudinal or machine direction orientation or
stretch to the web 14 prior to the engagement of the said
web 14 with the teeth 18T of the transverse stretcher blade
' assembly 18.
Similarly to the input roller assembly 16, the output
roll assembly 20 is shown as comprising first and second
output rolls 20A and 20B extending downstream, in that order,
from the transverse blade assembly 18 and which further
includes the concept of driving these rollers at selectively
differential rotational velocities to impart further longi-
tudinal stretch, if desired, to the web 14 downstream of andsubsequent to the impartation of transverse orientation
thereto. The downstream output roller 20B is engaged with
the periphery of the polygon mold wheel ~2 such that in its
rotation about the center 22A, the oriented web material 14
will be immediately placed upon the periphery of the mold
wheel 22, the latter being provided with suitable gripping
means e-~- . serrations, vacuum ori-fices or the like,
schematically shown as upstanding teeth 22T on one of the
; flats of the mold wheel 22 for piercing OT otherwise
securely engaging theweb to hold it against a relaxation of-
the imparted orientation therein during the molding process
- on the periphery of the mold wheel 22.
As in Figure 1, the web 14 is shown leaving the mold
wheel 22 with formed products 24 therein heading back
towa,rds the direction of the extruder 10.
In this context, re~erence is now made to Figure 4 in
which the molded products 24 travelling in the return
direction 26 are delivered tn ~ cutter means 32 which scvers
the molded products 24 from the selvage of the web 14 and
causes the - severed products 24 to be stacked in a
suitable product stack 24S which is schematically sho-~n in
Figure 4.
- 17 -
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~133ZZ~
While the severed products travel to a stack 24S, the
selvage 14S travels to a selvage recycling means 34 which
cooperates with a source of new plastic granules or pellets
;i - 36 to place both reground selvage and the pellets 36 into
a mixer assembly 38 of a type well-known in the art to
redirect both fresh raw material and recycled selvage into
the extruder 10.
Figure 4 also includes a low inertia embodiment apparatus
; which will be m,ore fully described ata later
~*~r point herein. For the present, the foregoing des-
`~ cription of Figure 4 is to illustrate that the recycling
of the selvage after separation of the selvage 14S from
the products 14 is a com,mon feature ofall of preferred
embodiments and is to be
considered as included in the description of the embodi-
ments of Figures 1 and 2.
In order to fully explain at this point in time the
orientation process in the biaxial mode, reference is now -
made to Figures 3A, 35B, 3C and 3D, with Figure 3A being
an enlarged partial schematic.of the biaxial orientation
portion of Figure 2.
. In practice, the longitudinal stretching or machine
direction stretching or orientation can be carried out
immediately before or immediately after the transverse
stretching or half before or half after the said trans-
verse stretching. Furthermore, an~ other ratio of initial
machine direction stretch and final machine direction
stretch is also feasible. The degree of transverse or
longitudinal orientation can be varied to suit a particular
pro~uct which may have depth or shape re~uiring less
initial orientation of the sheetin~ in one or another
direction. Therefore, a system is provided which is very facile and
variable with regard to uniqueand unusual molded shapes.
- 18 -
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1~33Z ~
The amDunt of selvage which
falls outside of the transverse stretcher blades 18A and
18B is the same as that amount of selvage which falls
outside of the holding devices 22T about the periphery of
the mold wheel 22. These holding de~ices 22T, as
; illustrated, for example, in Figure 6, are along both
peripheral edges of the mold wheel 22 which is shown in
partial top-plan ~iew in Figure 6.
In practice, the holding devices or gripping devices
22T about the periphery of the mold wlleel can be made
effective on the mold wheel station where the web 14 is
initially engaged and where molding initially takes place
and can be deactivated or rendered ineffective on the
stripping or molded product removal side or stations of
the mold wlleel polygon 22 such that the strip~ing of the
finished products 24 and selvage 14S from the mold wheel 22
is facilitated.
In Figures 3A - 3D, the zone subtended in the web 14
by the transverse stretcher assembly 18 is identified as a
transverse stretching zone TS which is preceeded on the
upstream side by a machine stretch zone MSl and on the do~n-
stream side by a machine stretch zone MS2.
Referring now to Figure 3B, it can be seen that all of
the machine orientation or longitudinal st~etch has been
effectuated in the zone MS2 as indicated by the wider
spacing between the edge adjacent dots 14I whic~l are uti-
lized to designate equal increments of unbiased web 14 in
the initial spacing shown in the zone MSl of Figure 3B
which is a totally unoriented configuration and spacing.
This spacing is incremental in both the longitudinal and
transverse directions of the web, i.e., the dots 14I
define biaxial increments of the web 14.
-- 19 --
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li33Z21
Referring next to Figure 3C, it can be seen that the
rota~ional velocity of the transverse stretcher blades 18A
is such that the web travels faster in the transverse
stretching zone TS and therefoTe has imparted to it both
transverse and longitudinal stretch and has no additional
longitudinal stretch imparted to it in the downstream or
second machine stretch zone MS2. The zone MSl upstream of
the transverse stretching zone TS illustrates no biaxial
orientation upstream of the transverse zone TS.
Referring next to Figure 3D, it can be seen that in the
- initial upstream zone MSl that no biaxial orientation is
imparted to the web 14, that in the zone TS both transverse
and partial machine direction stretch are imparted to the
web 14 and in downstream zone MS2 additional longitudinal
or machine direction stretch is imparted to the web 14.
The foregoing clearly illustrates the wide variety
of lon~itudinal and t~ansverse stretch modes which can be
effectuated. In all cases, of
~ course, the tTansverse stretcnlng lS achleved withln tne
zone TS and not within the upstream and downstream zones
MSl and MS2, respectively.
If in the zone MSl in either of the foregoing diagrams
of Figures 3B, 3C or 3D, the dots 14I in the upstream zone
MSl were to vary in spacing longitudinally of the web 14,
then that would be indicative of a differential peripheral
velocity of the rollers 16A and 16B which would impar~
machine direction stretch to the web 14 in the upstream
zone MSl.
Referring further to Figure 3A, the diameter of the
rolls 16A, 16B, 20A and 20B are kept as small as is consis-
tent with minimizing the deflection of these rolls under
load. Also, the distance between the rolls in the respec-
tive Toll pairs 16 and 20 is preferably no greater than to
allow for slight clearance of the web or extrudate 14
which minimizes the shrinkback which otherwise occurs as
the material is transferred from one roll to another.
.--- i
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Z21
The surface speed of the second roll 16B is usually L
faster than the surface speed of the first roll 16Aso as
to achieve longitudinal stretch in the upstream area MSl and
preferably, the. surface speed of the roller 16Bas
compared to that of the roller 16Ais such that 50% of
the longitudinal or machine direction orientation occurs in
the transfer of material from the Toller 16A onto the roller
16B.
Also, as shown in Figure 3A, the teeth 18T on the trans-
verse stretcher blade 18A are very close to the surface of
the second roller 16B and the perimeter speed of the blades
is preferably slightly faster than the surface speed of the
roller 16B thereby making the transfer of material from one
to the other more effective. The teeth 18T actually pene-
15 trate the edge of the web or strip 14 so as to hold the
material securely as transverse stretching takes place due
to the angular orientation of the blades 18A and 18B, the
latter being best shown with reference to Figures 5A and 5B.
The third or initial output rolleT 20A is also posi-
tioned very close to thé teeth 18T of the blades 18A and 18B
so as to minimize shrinkback at this particular transfer
point comprised by the interface between the said roll 20A
and the blades 18A and 18B. The surface speed of the
roller 20A is usually and preferably slightly faster than
the perimeter speed of the transverse stretching blades
18A and 18B and the fourth roller 20B is maintained close to
the t]lird roller 20A in order to minimi~e shrinXback during
the transfer from one roller to another. Usually, the`
fourth roll 20B is run faster than the third roller 20A ~ith
the preferred speed being such as to accomplish the remain-
ing 50% of the longitudinal or machine direction oricntation
in the web 14. The web 14, as it leaves the fourth or
interfacing roller 20B onto the mold wheel 22,isthus
fully biax~ally oriented.
- 21 -
.
J
~33221
As disclosed with reference to Figures 1 and 2, the
entire orientation device 16-18-20 in the particular
embodiments of Figures 1, 2 and 3A is pivoted about the
pivot points 28C and a suitable means 30. e-g- a spring
schematically shown in Fgiure 1 or a pneumatic cylinder
schematically shown in Figure 2 is provided to bias the
final output or interfacing roller 20B against ~he peri-
pheral shoulders of the mold wheel 22 such that the teeth
22T on the mold l~heel will avoid contact with the roller
surface~ but will penetrate and retain the web 14 in its
biaxially oriented condition over each face of the mold
wheel 22 such that a uniform web is presented to each mold
cavity ~5C therein.
All of the longitudinal stretching rollers 16A, 16B,, ,
20A a,nd 20B,are,preferably coated with fluorocarbon e-g- that
known by the Trade Mark TEFLON to avoid sticking of the web 14 thereto- Also
such rollers are usually made with thin-walled steel tubes
in order to minimize the heat retention capacity and heat
transfer to the ends of the rollers. Therefore, in the
area of contact with the web 14, the rolls reach about the
same temperature as that of the web itself.
A low inertia orientation apparatus will now be described
with further reference to Fig~s 4, 5A,5B and 6.
In this embodiment, the output rollers 20 of the
previous embodiments are replaced by an output roller set
120 which is comprised of three rollers 120A, 120B and
120C mounted on a common frame 120D which is biased by
suitable means 120E to~ard the mold wheel 22 SUC]I that the
fi~al output or interfacing roller 120C is engagcd ~ith
the mold wheel 22 in a manner similar to that of the final
roller 20B in the previous embodimcnts.
The biasing means 120E can be any suitable dcvice such
as a compression spring or a pneumatic spring or cylinder
such as already described in reference to the embodiments
of Figure 1 and Figure 2, res~ectively.
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..
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,
~133'~2~
The common support 120D for the downstream output
roller set 120 is pivoted on the center line of the upstream
roller 120A of that set and the transverse stretching saw
blades 18 and the inpùt stretch rolls 16 are fixedly mounted
in the embodiments of Figures 4 and 6 as opposed to being
mounted for movement about a central point 28C such as
previously described in Figures 1 and 2.
Thus, only the inertia of the three output stretching
and interface rollers 120A - 120C and the frame 120D on
which these are mounted is involved in the interfacing of
the biaxially oriented web 14 and the undulating peripheral
surface of the rotating mold polygon 22. Through the use of
three rollers, disproportionate elongation due to oscilla-
tion is avoided and a more uniformly elongated web 14 will
result than would result with the use of two rollers. The
gap between the three rollers 120A - 120C is kept very
small to avoid shrinkbac~ of the now biaxially oriented ~eb
traversing these rolls. Because the inertia of this
particular output stretch and interface roll means has been
minimi~ed, the mass and inertia of the remaining portions of
the biaxial orientation equipment is not critical.
The drive means DA and DB on the transverse stretch saw
blades 18A adn 18B, respectively, and the nearest rollers
thereto, namely, the upstream interface roller 16B and the
downstream initial roller 120A are all driven preferably
from a common drive motor through various drive belts or
chains and the rollers 16B and 120A are illustrated in
Figure 6 as being driven by a common drive belt DC ~.hich
engages drive pulleys or sl~rockets Sl and S2 mounted on
the shafts of the rollers 120A and 16B, respectively.
Further, the roller 16B includes a passive output
gearing Gl ~hick is engaged l~lith compatible gearing ~of a
predetermined ratio) G2 mounted on the shaft of the initial
input roller 16A such that the differential speed bet~.~een
the rollers 16A and 16B can be effectuated from the same
common drive means DC that drives both the rollers 16B
and 120A.
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1~33ZZ~
~ hus,the ratio of the gears Gl and G2 can be cllanged
to vary the amount of longitudinal stretch achieved between
the initial input rollers 16A and-16B.
The last two rolls 120B an~l 120C on the downstream
side of the transverse stretcher blades 18 are not driven
from the stretcher apparatus. The last output or interface
roll 120C is driven by the surface speed of the mold wheel
or polygon 22 with which it is in contact and this speed is
established and selected to provide the proper longitudinal
orientation when measured against the fixed speed of the
initial output Toll 120A. The middle roll 120B of the
output roller group 120 merely idles and reaches a speed
in between that of the toher two rolls 120A and 120C of the
set 120.
-In order to maintain a constant dimensional relation-
ship between the transverse stretch saw blades 18A and 18B
and the initial output roller 120A, the blades 18A and 18B
are pivoted at their downstream edge on the pivots PA and
PB, respectively, rather than at the centeT of the said
blades 18A and 18B. Therefore, the relationship between
these blades 18A and 18B and the output roller 120A remains
constant during adjustment of the blades between a direction
parallel to the machine direction oriented at 45 with
respect to the machine direction.
The second roller 16B and its companion input roll 16A
in the input stretch roll set 16 move in and out to adjust
to the position of the transverse stretch saw blades 18A
and 18B depending upon the adjusted position Gf the latteT.
Suitable stop means or bosses are provided on the saw blade
adj~stment brackets to interact wi~h the mounting of the
various input rollers 16A and 16B to preclude ~engagement
of the rolls with the saw blade but maintaining the desired
immediate proximity thereof.
- 24 -
- 1133;Z2i
The material tension of the web 14 proceeding beneath
the roller 16A back over the roller 16B and thence beneath
the sa~ blades 18A and 18B is sufficient, since the web 14
initially approaches thé roll 16A from above, to cause the
roll 16A to track the movements of the roll 16B and thereby
maintain the desired minimum spacing by way of the material
tension in the web 14.
Suitable means are also provided within the mounting
bracket 120D of the output roll set 120 to provide for
moving the three rollers 120A, 120B and 120C apart and bac~
together again to provide for the threading of material
- therethrough at the beginning of an extrusion and orientation
and molding cycle and then placing the rollers under a suffi-
cient bias to provide a predetermined minimum spacing and
pressure thereon such as by small air cylinders or the like,
all of which is within the purview of one-o ordinary skill
in the art.
If the molded products 24 are desired to be nine inch
plates having a material thickness on the order of~.010
inches, a stretch ratio of 3 to 1 is established for
both the transverse and longitudinal oTientation of the web
14, by way of an exemplary process parameter. In this case,
the die opening would be on the order f 0 090 inches of web
thickness and 3 inches inwidth plus perhaps a one-quarter
inch allowance for selvage. The polystyrene resin which
is to be converted to OPS resin would be extruded at
preferably, 425F. The extrudate would be cooled to
280F by the cooling rools CR before entering the initial
rollers 16A and 16B of the stretcher apparatus of an aspect of the
present invention.
At an output rate of approximately 600 pounds of ~eb
material per hour, the speed of the extrudate~would be
90 feet per minute before entering the initial rolls
16 of the stretcher assembly and ~ 270 feet per minute
3s leaving the last or interfacing roller 120C of the stretchcr
assembly. This 270 foot per minute speed would match the
speed of the mold surface or mold polygon 22.
- 25 -
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~133221
Fifty percent of the longitudinal orientation in the
web 14 would yrobably be accomplished between the rollers
16A and 16B, all of the transverse orientation between the
transverse stretcher blades 18A and 18B and the remaining
50% of the longitudinal orientation established between the
roll 120A at the input of the group 120 and the roll 120C
interfacing the biaxially oriented web material with the
mold polygon 22.
The mold polygon or mold wheel 22, for example, might
have 15 mold cavities MC and would be in that event, four
feet in diameter. The ratio of selvage to finished product
would be - 50-50. The plate 24 would weight ~ 10
grams and 324 plates per minute would be produced at a mold
wheel speed of 21rpm.
In achieving the transverse orientation with the
blades 18A and 18B, these blades would be gapped at
three and one-eighth inches on their upstream side and
nine and three-eighth inches on their downstream
side to effectuate the three for one transverse stretch
desired.
Accordingly it can be seen that a continuous ~eth~d
with a relatively high speed of production and high qualit~
control with a low~inertia apparatus is readily effectuated
by the embodiments of Figures 4, 5A, 5B and 6.
