CA1135021A - Means for interfacing web with rotating surface - Google Patents
Means for interfacing web with rotating surfaceInfo
- Publication number
- CA1135021A CA1135021A CA000386352A CA386352A CA1135021A CA 1135021 A CA1135021 A CA 1135021A CA 000386352 A CA000386352 A CA 000386352A CA 386352 A CA386352 A CA 386352A CA 1135021 A CA1135021 A CA 1135021A
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- Prior art keywords
- web
- peripheral surface
- roller means
- roller
- upstream
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
Means are provided herein for interfacing a web of continuously formed thermoplastic material with a continuously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in the web and conform a surface of the web with the peripheral surface, the web being in continuous longitudinal motion. The means includes elongated bracket means extending longitudinally of the web and pivotally mounted on a trans-verse axis at its upstream end for rotation toward and away from the peri-pheral surface. A plurality of parallel roller means are mounted for rotation in the bracket means transversely of the web and mutually parallel with the peripheral surface, with the web being threaded in a serpentine manner through the roller means. Downstream roller means are provided in the plurality of roller means, constrained by the bracket means to follow the peripheral surface throughout its undulations and driven by the latter at a like peripheral speed transferring the web directly onto the peri-pheral surface. Finally, upstream roller means are provided in the plura-lity of roller means initially receiving the web on its peripheral surface and having an axis of rotation substantially coincident with the trans-verse pivotal axis of the bracket means. Such system which is provided is very facile and variable with regard to unique and unusual shapes.
Means are provided herein for interfacing a web of continuously formed thermoplastic material with a continuously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in the web and conform a surface of the web with the peripheral surface, the web being in continuous longitudinal motion. The means includes elongated bracket means extending longitudinally of the web and pivotally mounted on a trans-verse axis at its upstream end for rotation toward and away from the peri-pheral surface. A plurality of parallel roller means are mounted for rotation in the bracket means transversely of the web and mutually parallel with the peripheral surface, with the web being threaded in a serpentine manner through the roller means. Downstream roller means are provided in the plurality of roller means, constrained by the bracket means to follow the peripheral surface throughout its undulations and driven by the latter at a like peripheral speed transferring the web directly onto the peri-pheral surface. Finally, upstream roller means are provided in the plura-lity of roller means initially receiving the web on its peripheral surface and having an axis of rotation substantially coincident with the trans-verse pivotal axis of the bracket means. Such system which is provided is very facile and variable with regard to unique and unusual shapes.
Description
V~l ~ is invention r~lates to appara-tus For biaxially orienting thelmoplastic materials, e.g., polystyrene. More particularly, it relates to mecms for interfacing a web of continuously formed thermoplastic mater-ial with a continuously undulating and rotating peripheral surface to mini~ize resulting longitudinal stresses in the web and conform a surface of the web with the peripheral surface, the web being in continuous longi-tudinal motion.
This application is a division of pending 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 should be expressly understood that the apparatus constituting the present invention is applicable to a wide variety of t~ermoplastic mater-ials, 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 remDving its inherent brittleness in the absence of molecular orientation.
There are various prior art approac}-es to mitigating the brittleness factor in pol)~styrene 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 ~hen, without destroying the continuity or t 15 the method , mold articles or otherwise form articles from it) all of the desirable physical properties of the material could be reali~ed. At the same time all of the de~irabili-ties, speed and efficiencies of a full~ 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 in~ention.
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, subse~uently, the sheeting is unrolled, reheated and subsequently formed into products or articles in its reheated state. As with all thermoplastic techniques, there are three basic interrelated variables involved in processing thermoplastic materials whicll affect both the nature of the operation and the characteristics of the final product. These variables are temperature, time and physical state, with the latter variable dealing with pressure, stress, etc.
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This application is a division of pending 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 should be expressly understood that the apparatus constituting the present invention is applicable to a wide variety of t~ermoplastic mater-ials, 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 remDving its inherent brittleness in the absence of molecular orientation.
There are various prior art approac}-es to mitigating the brittleness factor in pol)~styrene 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 ~hen, without destroying the continuity or t 15 the method , mold articles or otherwise form articles from it) all of the desirable physical properties of the material could be reali~ed. At the same time all of the de~irabili-ties, speed and efficiencies of a full~ 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 in~ention.
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, subse~uently, the sheeting is unrolled, reheated and subsequently formed into products or articles in its reheated state. As with all thermoplastic techniques, there are three basic interrelated variables involved in processing thermoplastic materials whicll affect both the nature of the operation and the characteristics of the final product. These variables are temperature, time and physical state, with the latter variable dealing with pressure, stress, etc.
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As a gcneral rule, temperature and time should be 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 5 material must be oriented represents a compromise between levels whicl~ are best from a flol~ point of view and levels ~hich are best from a stress (orientation~ point of view.
Once a stress is imposed at a givcn 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 20 from the standpoint of results heretofore not otherwise attainable.
These inherent advantages of a high speed integrated t approach are important in relatively thin products , e g those with wall thicknesses of ~005 too.010 inches and 25 become increasingly significant ~ith products having ~all 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 F
during reheating and subsequent recooling as well as during a possible relaxation during the production of the sheeting _ 35 per se.
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!
As a gcneral rule, temperature and time should be 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 5 material must be oriented represents a compromise between levels whicl~ are best from a flol~ point of view and levels ~hich are best from a stress (orientation~ point of view.
Once a stress is imposed at a givcn 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 20 from the standpoint of results heretofore not otherwise attainable.
These inherent advantages of a high speed integrated t approach are important in relatively thin products , e g those with wall thicknesses of ~005 too.010 inches and 25 become increasingly significant ~ith products having ~all 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 F
during reheating and subsequent recooling as well as during a possible relaxation during the production of the sheeting _ 35 per se.
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11~5~2~1 Theoretically, the ide~l meth~d ~ould be to biaxially orient the thermoplastic material, orm and cook it simultaneously. In conventional systems, the time factor is signiicant and therefore detrimcntal. Accordingly, the 5 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 oricnted, 10 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 which first bring the sheet to an appropriate temperature level for 15 orientation and then lo3lgitlldinally stretch the sheet between two rulls running at different s~eeds. This longi-tudinal stretching or drafting orients the material in the machine direction. The material with the longitudinal orientation is then passed onto a tenter frame to oricnt it 20 transversely in a manner well-kno~n in the art. Since con-ventional tentering involves large, heavy equipment, it is also necessary that temperatures be maintained in the sheeting through the use of large, expensive ovens. After t}le sheeting has been oriented both 1O3lgitudinally and 25 transversely, it is then rolled and stored for subsequent use.
The forming of OPS sheeting is usually carried out on non-rotating thermoforming equipment with special pro~isions for the OPS material. It is necessary that the reheating 30 of the sheeting as it is fed into the formin~ equipmcllt be maintained uniformly througllout its ~idth and length.
As the material reac}-es a satisfactory forming temperature, the stretches ~hich ha~e bcen imposed during the biaxial orientation must be resisted by adequate clamping devices F
35 in order to preclude the sheet from shlin~ing bac~ to its original dimensions and losing the orientation therein.
~ 0 2 1 j Since most non-rotary forming e(~uipment is necessarily intermittent in its operation, the intermittent feeding of oriented sheet in such conventional forming equipment im-poses inherent difficulties in the creation and maintenance of uniform temperature conditions throughout the forming area of the sheet.
There are several other approaches which have been used to some extent in the production of biaxially oriented sheeting. One of these, the bubble process, is typically the way mucll thermoplastic film is produced. By proper control of temperature and stretching, it is possible to produce a biaxially oriented film or sheet usin~ this bubble technique. However, in practice it is proven to be very critical because of temperature uniformity requiTements.
Also this technique is not usable ~hen it comes to thicker material such as that used in thermoformed articles or products on the order of meat trays, containers and table-ware. I
Further, there is some eguipment in use which simul- !
taneously stretches transversely and longitudinally. This equipment obviates the use of longitudinal stretching rolls e-g- those previously described, but it has certain disadvantages, namely, tle amount of selvage which must be discarded due to the increased scalloped effect resulting 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-ments in many of the characteristics of certain of thesematerials. Biaxial orientation is essential in most packaging and disposable ~roducts. If orientation is only j.
in one direction, even though properties may be substan-tially improved in that direction, they are reduced in the other dimensions. Typical of products which are oriented in one direction only are monofilaments and fibers.
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~uring orielltation, the molecu]es in the material are shifted from random coil entanglemcnt to a relative alignlllellt parallel to principal axes of stretch. This results in significant improvements in physical properties, opt;cal properties and in improved barrier properties and stress crack resistance.
For example, among the physical property impro~ements, the impact strength in materials, e.g., OPS, are improved on the order of ten items with two to three times the tensile strength of non-oriented polystyrene and as much as three times the improvement in yield elongation.
0 ~7 a broad aspect of this inventlon, means are provided for inter-facing a web of col~tinuously formed thermoplastic material with a continu-ously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in the web and to conform a surface of the web with the peripheral surface, the web being in continuous longitudinal motion, the means comprising: elongated bracket means extending longitudinally of the web and pivotally mounted on a transverse axis at its upstream end for rotation toward and away from the peripheral surface; a plurality of parallel roller means mounted for rotation in the brac~et means transverse-ly of the web and mutually parallel with the peripheral surface; the web being threaded in a serpentine manner through the roller means; down-stream roller means in the plurality of roller means, constrained by the bracket means to follow the peripheral surface througllout its undulations and driven by the latter at a like peripheral speed, transferrin~ the web directly onto the peripheral surface; and upstream roller means in the plurality of roller means initially receiving the web on its peripl-eral surface and having an axis of rotation substantially coincident with the transverse pivotal axis of the bracket means.
il3~021 By another aspect of this invention, means are provided for inter-facing a web of continuously formed thermoplastic material with a continu-ously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in the web and conform a surface of the web with the peripheral surface, the web being in continuous longitudinal motion, the means comprising: elongated bracket means extending longitudinally of the web and pivotally mounted on a transverse axis at its upstream end for rotation toward and away from the peripheral surface; a plurality of parallel roller means mounted for rotation in the bracket means trans-versely of the web and mutually parallel with the peripheral surface; the web being threaded in a serpentine manner through the roller means; down-stream roller means in the plurality of roller means, constrained by the bracket means to follow the peripheral surface throughout its undulations and driven by the latter at a like peripheral speed, transferring the web directly onto the peripheral surface; and upstream roller means in the pluralii:y of roller means initially receiving the web on its peripheral surface and having an axis of rotation substantially coincident with the transverse pivotal axis of the bracket means; and an odd number of inter-mediate roller means between the upstream and downstream roller means.
By a variant thereof, the upstream roller means includes drive means maintaining a differential peripheral speed between the upstream and downstream roller means to impart longitudinal orientation to the web in the interfacing means.
The above-identified parent application provided 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 ~13~02~
at the preferred orientation t~nperature. If the extrusion temperature ls above the desired orientation temperature then it may be passed over cooling rolls in order to bring it do~n to the deslred 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 iDto 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.
~ incc tllc lol~itn~lin.ll direction is also desirably oriented by stretc}~ g on an ord~r of magnitude of three times the origillal dimension, if this has not been ~chieved by the stretchin~ rolls upstream from the trans-S verse stretching mechanism, the balance of the longitudinalstretching 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 which 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 ~hich contin-uously and sequentially severs the formed articles from the selvage and then accumulates the articles for stacking and packaging while gathe~ing the selvage for reuse. The selvage is reused by recycling it to the raw material processor which includes a device for admixing thermoplastic 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 betl~een these tWG devices have been noted. Novel means are provided herein for precluding the full inertial effect from tak ~ placeand includesa structure ~hich in fact minimizes, _ g _ . ~
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to an opti~lm clegree, the equipment inertia present at the ld-orientation equipment interface thereby to preclude uneven longitudinal stresses from being imparted to the material because of this inertial problem 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 extruded 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 fc~r 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. sever21 positions at which orientation can c~ccur;
Figures 3B, 3C and 3D are schematic stretch diagrams showing the several modes of biaxial orientation of the extrudate which is possible in correlation with the relative position of the extrudate in the orienta-tion apparatus of Figure 3A;
Figure 4 is a schematic of a low inertia embodiment;
Figure 5A is a top plan schematic illustrating the transversestretching blade used in a means set at maximum divergence;
Figure 5B is a top plan schematic illustrating the transverse stretching blades used in a means set at minimum divergence (mutually parallel); and Figure 6 is a top plan partial schematic of the embodiment of Figure 4.
Rcferring in detail to thc drawin~s and with particular . reference to Figure 1 an extruder 10 is illustrated as having an Oltput to a di.e 12 which forms a narrow web 14 of polystyrene or other tllermoplastic extrudate at a tempera-ture approximating the optimum temperature for subsequent biaxial orientation of the extrudate 14.
From the die 12 the web-like extrudate 14 is shown as passing over an input roller means 16 beneath a transverse 5tretcher blade assembly 18 and subsequently over an out-put roller assembly 20 the latter being juxtaposed ~ith the periphery of a mold ~heel assembly 22 which is of poly-gonal cross-sectional shape and which is rotated about a central axis 22A. The web of extrudate 14 passes beneath lS the mold wheel 22 which rotates clockwise as shown in the drawing. Each flat on the periphery of the mold w}leel 22 includes a mold cavity MC a plurality of which are shoh~n in dotted lines in Fi ~ e 1.
Suitable vacuum means or a combination of positive pressure vacuum and/or male die members are provided to cooperate with the mold cavities ~C to form predetermined shapes corresponding to those initially imparted to the .mold cavity in the web 14 and t]lese products 24 are schematically shown in cross-section leaving the uppermost 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 asse]nbly 18 may be set diffeTentially to impart a longitudinal stretch or a machine direction stretch to the web 14 and a similar differential rotational velocity between the l~eripheries of the output roller assembly 20 and the transverse ~tretcher blade assembly 18 may also be provided to impart additional machine direction stIetch or oricntation to the ~eb 14.
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I`lle trallsverse stretcher blade assembly 18 is best illustrated by joint reerence to Figures 1, SA and 5B in . which the transverse stretcher blade assembly 18 is illus-trated as including first and second circular saw blades 5 18A and 18B, respectively, ~hich 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 10 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 15 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 output side t 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 25 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 schematical.ly illustrated at 28 and 30 which post 28 is biased by suitable means 30 such that the output roller assembly 20 closely follows the peripheral contours of the polygon shaped mold wheel 22.
As a result, the oscillation of the vertical sul)port 28 P
about its center point 28C occurs as shown by the arcuate 35 arrow 28D in Figure 1. L
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~ O 2 'I`herefore, if the speed of the mold wheel 22 is increased to a point where production speeds of a highly desirable level are obtained, the inertial forces in the combined integrated input-tIansverse orientation-output roll S 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 and in some cases, an improper alignment on the mold wheel 22. This results, of course, in products which are inferior and which defy efforts to provide satisfactory quality -control. At sl'ower speeds, however, the continuity of the method and apparatus of Figure 1 provides a highly desirable process with high quality end products 24. t In the event that the extruder 10 emits material from the die 12 which is at a higher temperature than the optimum r 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 machine direction or longitudinal orientation to the extrudate web 14.
As illustrated in Figure 2, the extruder 10 and the die 12 feed an extrudate web 14 first into a bank of cooling rolls CR which are provided, as is well-known 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 temperature for orientation. r - , . . I
r - -' Tl~e i~ ut roller assembly 16 is illustratcd as including a first roller 16A and a second roller 16B which receives the web 14 in a serpentine path th~rebetween and which rolls 16A
and 16B are driven at differential rotational velocities to impart a longitudinal or machine direction oricntation 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 dri~ing 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 2Z 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-g- serrations, vacuum orifices or the like, schematically shown as upstanding teeth 22T on one of the flats of the mold wlleel 22 for piercing or otherwise securely engaging theweb to hold it against a relaxation of the imparted orientation therein during the molding process i~
- 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 towards the direction of the extTuder 10.
In this context, reference 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 shown in Figure 4.
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11 ~ 5~2 1 While the severed products travel to a stack 24S, the selvage 14S travels to a selvage recycling means 34 whi~h cooperates with a source of new plastic granules or pellets 36 to place both reground selvage and the pellets 36 into a mi~er 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 more fully describedat a later ~
l~*S~ point here;n. FOT 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 common feature of all of the preferred embodiments of the present invention 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 no~
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 Ol 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, any other ratio of initial machine direction stretch and final machine direction stretch is also feasible. ~he degree of transverse or longitudinal orientation can be varied to suit a particular product which may have depth or shape requiring less initial orientation of the sheeting in one or another direction. Therefore, a system is provided which is very facile and variable with regard to unique and unusual m~lded shapes. .
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ii3~(~21 The ~l~lt of selvdge which falls outside of the transverse stretcher blades 18A and 18B is the same as that amount of selvage which falls outside of the llolding devices 22T about the periphery of 5 the mold wheel 22. These holding devices 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 view in Figure 6.
In practice, the holding devices or ~ripping devices 10 2~T about the periphery of the mold wheel can be made r effective on tlle 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 r stripping or molded product removal side or stations of 15 the mold wheel polygon 22 such that the stripping 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 20 transverse stretching zone TS which is preceeded on the upstream side by a machine stretch zone MSl and on the down-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 stretch has been 25 effectuated in the zone MS2 as indicated by the wider spacing between the edge adjacent dots 14I which are uti-lized to designate equal increments of unbiased web 14 in F
the initial spacing shown in the zone MSl of Figure 3B
which is a totally unoriented configuration and spacing.
30 Thi~ spacing is incremental in both the longitudinal and transverse directions of the web, i.e., the dots 14I
define biaxial lncre-ents of th- web 14 , - .:
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Referrin~ next to Figure 3C, it can be seen that the rotational velocity of the transverse stretcher blades 18A
is such that the web travels faster in the transverse stretching zone TS and therefore has imparted to it both S transverse and longitudinal stretch and has no additional longitudinal stretch imparted to it in the doh~nstream 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 r 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 transverse stretching is achieved within the i 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 impart machine direction stretch to the web 14 in the upstream zone MSl.
Referring furtller 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 roll 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. .
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~ 02 1 The surface speed of the second roll 16B is usually faster than the surface speed of the first roll 16A so as to achieve longitudinal stretch in the upstream area MSl and preferably, the surface speed of the roller 16B as compared to that of the roller 16A is such that 50% of the longitudinal or machine direction orientation OCCUTS in the transfer of material from the roller 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 ofthe second roller 16B and t:he 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-trate the edge of the web OT strip 14 50 as to hold thematerial 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 SA and 5B.
The third or initial output roller 20A is also posi-20 tioned very close to the teeth 18T of the blades 18A and 18Bso 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 25 the perimeter speed of the transverse stretching blades 18A and 18B and the fourth roller 20B is maintained close to the third roller 20A in order to minimize shrinl;back during the transfer from one roller to another. Usually, the fourth roll 20B is run faster than the third roller 20A with the~preferred speed being such as to accomplish the Temain-ing 50% of the longitudinal or machine direction orientation in the web 14. The web 14, as it leaves the lourth or interfacing Toller 20B onto the mold w]leel 22, is thus fully biaxially oriented.
_ _ _, _ _ _ _ _ , - . .
- , ~ ' As cliscloscd with reference to Fi~ures 1 and 2~ the entire orientation device 16-18-20 in thc 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 ;n Fgiure 1 or a pneumatic cylinder schematically shown in Figure 2 is provided to bias the final output or interfacing roller 20B against the peri- -pheral shoulders of the mold wheel 22 such tllat the teeth 22T on the mold wheel will avoid contact with the rolleT
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 ~C therein.
All of the longitudinal stretching rollers 16A, 16B,, , 20A a,nd 20B,are,preferably coated with fluorocarbon e-g- ~hat known by the Trade Mark TEFLON to avoid sticking of the web 14 the~eto. 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 149 the ro.lls reach about the .same temperature as that of the web itself.
A low inertia orientation ap~tus 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 outl~ut roller set 120 which is comprised of three rollers 120A, 170B and 120C mounted on a common frame 120D which is biased by suitable means 120E toward the mold wlleel 22 SUC]I tlnat the fi~al output or interfacing roller 120C is engaged with ' the mold wheel 22 in a manner similar to that of the final roller 20B in the previous embodiments.
The biasing means 120E can be any suitable device such as a compression spring or a pneumatic spring or cylinder such as already described in re~erence to the embodiments of Figure 1 and Figure 2, respectively.
` 19 -113~i021 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 input 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 t~o rollers. The gap between the three rollers 120A - 120C is kept very small to avoid shrinXback of the now biaxially oriented web traversing these rolls. Because the inertia of this particular output stretch and interface roll means has 'oeen minimized, 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 which engages drive pulleys or sprockets Sl and S2 mounted on the shafts of the rollers 120A and 16B, respectively.
Further, the roller 16B includes a passive output gearing Gl whic~ is engaged with compatible gearing ~of a predetermined ratio) G2 mounted on the shaft of the initial input roller 16A such that the differential speed between the rollers 16A and 16B can be effectuated from the same common drive means DC that drives both the rollers 16B
and 12OA.
., _ 20 -O~l Tl~us,the ratio of the gears Gl and G2 can be changed to vary the amount of longitudinal stretch achieved between the initial input rollers 16A and 16B.
The last two rolls 120B an(~ 120C on the downstream side of the transverse stret~heT blades 18 are not driven from the stretcher apparatus. Tl~e 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 pro~ide the proper longitudinal orientation when measured against the fixed speed of the initial output roll 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 12~A and 120C of the set 12~.
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 center 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 d'irection 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 of the latter.
- Suitable stop means or bosses are provided on the saw blade adj~stment brackets to interact with the mounting of t]le various input rollers 16A and 16B to preclude engagement of the rolls with the saw blade but maintaining the desired immediate' proximity thereof.
The mat:Cl`ial tellS iOIl Or thc wcb 14 proceedin~ bcncath the roller lGA l-ack over tlle roller 16B and thcrlce bcncath the saw blades 18A ancl 18B is sufficient, since tl~e web 14 initially approaches the roll 16A from above, to cause the roll 16A to track the movements of the roll 16B ~nd thereby maintain the desired minimum spacing by l~ay of the material tension in the web 14.
Suitable means are also provided ~ithin the mounting bracket 120D of the output roll set 120 to provide for moving the t}-ree rollers 120A, 120B and 120C apart and back 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-of ordinary sXill 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 orientation of the l~eb 14, by way of an exemplary process parameter. In this case, the die opening would be on the order f 0 090 inches of ~.eb 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 roo]s CR before enteTing the initial rollers 16A and 16B of the stretcher apparatus of ~n aspect of the prese,nt invention.
At an output rate of approximately 600 pounds of wcb material per hour, the speed of the extrudate ~.~ould be 90 feet per minute before entering the initial rolls 16 of the stretcher assembly and ~ 270 feet per mintlte leaving the last or interfacing roller 120C of the stretch~r assembly. This 270 foot per minute speed ~.ould m~tch the speed of the mold surface OT mold polygon 22.
.
, Zl Fifty percent of the longitudinal orientation in the web 14 would probably be accomplished between the rollers 16A and 16B, all of the transverse orientation between the transverse stretcher blades 18A and lBB 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. ~he plate 24 would weight 10 grams and 324 plates per minute would be produced at a mold wheel speed of 21rpm.
In acllieving 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 n~ethod with a relatively high speed of production and high quality control with a low~inertia apparatus is readily effectuated by the embodiments of ~igures 4, 5A, 5B and 6.
,
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11~5~2~1 Theoretically, the ide~l meth~d ~ould be to biaxially orient the thermoplastic material, orm and cook it simultaneously. In conventional systems, the time factor is signiicant and therefore detrimcntal. Accordingly, the 5 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 oricnted, 10 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 which first bring the sheet to an appropriate temperature level for 15 orientation and then lo3lgitlldinally stretch the sheet between two rulls running at different s~eeds. This longi-tudinal stretching or drafting orients the material in the machine direction. The material with the longitudinal orientation is then passed onto a tenter frame to oricnt it 20 transversely in a manner well-kno~n in the art. Since con-ventional tentering involves large, heavy equipment, it is also necessary that temperatures be maintained in the sheeting through the use of large, expensive ovens. After t}le sheeting has been oriented both 1O3lgitudinally and 25 transversely, it is then rolled and stored for subsequent use.
The forming of OPS sheeting is usually carried out on non-rotating thermoforming equipment with special pro~isions for the OPS material. It is necessary that the reheating 30 of the sheeting as it is fed into the formin~ equipmcllt be maintained uniformly througllout its ~idth and length.
As the material reac}-es a satisfactory forming temperature, the stretches ~hich ha~e bcen imposed during the biaxial orientation must be resisted by adequate clamping devices F
35 in order to preclude the sheet from shlin~ing bac~ to its original dimensions and losing the orientation therein.
~ 0 2 1 j Since most non-rotary forming e(~uipment is necessarily intermittent in its operation, the intermittent feeding of oriented sheet in such conventional forming equipment im-poses inherent difficulties in the creation and maintenance of uniform temperature conditions throughout the forming area of the sheet.
There are several other approaches which have been used to some extent in the production of biaxially oriented sheeting. One of these, the bubble process, is typically the way mucll thermoplastic film is produced. By proper control of temperature and stretching, it is possible to produce a biaxially oriented film or sheet usin~ this bubble technique. However, in practice it is proven to be very critical because of temperature uniformity requiTements.
Also this technique is not usable ~hen it comes to thicker material such as that used in thermoformed articles or products on the order of meat trays, containers and table-ware. I
Further, there is some eguipment in use which simul- !
taneously stretches transversely and longitudinally. This equipment obviates the use of longitudinal stretching rolls e-g- those previously described, but it has certain disadvantages, namely, tle amount of selvage which must be discarded due to the increased scalloped effect resulting 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-ments in many of the characteristics of certain of thesematerials. Biaxial orientation is essential in most packaging and disposable ~roducts. If orientation is only j.
in one direction, even though properties may be substan-tially improved in that direction, they are reduced in the other dimensions. Typical of products which are oriented in one direction only are monofilaments and fibers.
v'~
~uring orielltation, the molecu]es in the material are shifted from random coil entanglemcnt to a relative alignlllellt parallel to principal axes of stretch. This results in significant improvements in physical properties, opt;cal properties and in improved barrier properties and stress crack resistance.
For example, among the physical property impro~ements, the impact strength in materials, e.g., OPS, are improved on the order of ten items with two to three times the tensile strength of non-oriented polystyrene and as much as three times the improvement in yield elongation.
0 ~7 a broad aspect of this inventlon, means are provided for inter-facing a web of col~tinuously formed thermoplastic material with a continu-ously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in the web and to conform a surface of the web with the peripheral surface, the web being in continuous longitudinal motion, the means comprising: elongated bracket means extending longitudinally of the web and pivotally mounted on a transverse axis at its upstream end for rotation toward and away from the peripheral surface; a plurality of parallel roller means mounted for rotation in the brac~et means transverse-ly of the web and mutually parallel with the peripheral surface; the web being threaded in a serpentine manner through the roller means; down-stream roller means in the plurality of roller means, constrained by the bracket means to follow the peripheral surface througllout its undulations and driven by the latter at a like peripheral speed, transferrin~ the web directly onto the peripheral surface; and upstream roller means in the plurality of roller means initially receiving the web on its peripl-eral surface and having an axis of rotation substantially coincident with the transverse pivotal axis of the bracket means.
il3~021 By another aspect of this invention, means are provided for inter-facing a web of continuously formed thermoplastic material with a continu-ously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in the web and conform a surface of the web with the peripheral surface, the web being in continuous longitudinal motion, the means comprising: elongated bracket means extending longitudinally of the web and pivotally mounted on a transverse axis at its upstream end for rotation toward and away from the peripheral surface; a plurality of parallel roller means mounted for rotation in the bracket means trans-versely of the web and mutually parallel with the peripheral surface; the web being threaded in a serpentine manner through the roller means; down-stream roller means in the plurality of roller means, constrained by the bracket means to follow the peripheral surface throughout its undulations and driven by the latter at a like peripheral speed, transferring the web directly onto the peripheral surface; and upstream roller means in the pluralii:y of roller means initially receiving the web on its peripheral surface and having an axis of rotation substantially coincident with the transverse pivotal axis of the bracket means; and an odd number of inter-mediate roller means between the upstream and downstream roller means.
By a variant thereof, the upstream roller means includes drive means maintaining a differential peripheral speed between the upstream and downstream roller means to impart longitudinal orientation to the web in the interfacing means.
The above-identified parent application provided 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 ~13~02~
at the preferred orientation t~nperature. If the extrusion temperature ls above the desired orientation temperature then it may be passed over cooling rolls in order to bring it do~n to the deslred 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 iDto 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.
~ incc tllc lol~itn~lin.ll direction is also desirably oriented by stretc}~ g on an ord~r of magnitude of three times the origillal dimension, if this has not been ~chieved by the stretchin~ rolls upstream from the trans-S verse stretching mechanism, the balance of the longitudinalstretching 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 which 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 ~hich contin-uously and sequentially severs the formed articles from the selvage and then accumulates the articles for stacking and packaging while gathe~ing the selvage for reuse. The selvage is reused by recycling it to the raw material processor which includes a device for admixing thermoplastic 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 betl~een these tWG devices have been noted. Novel means are provided herein for precluding the full inertial effect from tak ~ placeand includesa structure ~hich in fact minimizes, _ g _ . ~
li;~SO~
to an opti~lm clegree, the equipment inertia present at the ld-orientation equipment interface thereby to preclude uneven longitudinal stresses from being imparted to the material because of this inertial problem 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 extruded 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 fc~r 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. sever21 positions at which orientation can c~ccur;
Figures 3B, 3C and 3D are schematic stretch diagrams showing the several modes of biaxial orientation of the extrudate which is possible in correlation with the relative position of the extrudate in the orienta-tion apparatus of Figure 3A;
Figure 4 is a schematic of a low inertia embodiment;
Figure 5A is a top plan schematic illustrating the transversestretching blade used in a means set at maximum divergence;
Figure 5B is a top plan schematic illustrating the transverse stretching blades used in a means set at minimum divergence (mutually parallel); and Figure 6 is a top plan partial schematic of the embodiment of Figure 4.
Rcferring in detail to thc drawin~s and with particular . reference to Figure 1 an extruder 10 is illustrated as having an Oltput to a di.e 12 which forms a narrow web 14 of polystyrene or other tllermoplastic extrudate at a tempera-ture approximating the optimum temperature for subsequent biaxial orientation of the extrudate 14.
From the die 12 the web-like extrudate 14 is shown as passing over an input roller means 16 beneath a transverse 5tretcher blade assembly 18 and subsequently over an out-put roller assembly 20 the latter being juxtaposed ~ith the periphery of a mold ~heel assembly 22 which is of poly-gonal cross-sectional shape and which is rotated about a central axis 22A. The web of extrudate 14 passes beneath lS the mold wheel 22 which rotates clockwise as shown in the drawing. Each flat on the periphery of the mold w}leel 22 includes a mold cavity MC a plurality of which are shoh~n in dotted lines in Fi ~ e 1.
Suitable vacuum means or a combination of positive pressure vacuum and/or male die members are provided to cooperate with the mold cavities ~C to form predetermined shapes corresponding to those initially imparted to the .mold cavity in the web 14 and t]lese products 24 are schematically shown in cross-section leaving the uppermost 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 asse]nbly 18 may be set diffeTentially to impart a longitudinal stretch or a machine direction stretch to the web 14 and a similar differential rotational velocity between the l~eripheries of the output roller assembly 20 and the transverse ~tretcher blade assembly 18 may also be provided to impart additional machine direction stIetch or oricntation to the ~eb 14.
,.~, . ; , , .
I`lle trallsverse stretcher blade assembly 18 is best illustrated by joint reerence to Figures 1, SA and 5B in . which the transverse stretcher blade assembly 18 is illus-trated as including first and second circular saw blades 5 18A and 18B, respectively, ~hich 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 10 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 15 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 output side t 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 25 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 schematical.ly illustrated at 28 and 30 which post 28 is biased by suitable means 30 such that the output roller assembly 20 closely follows the peripheral contours of the polygon shaped mold wheel 22.
As a result, the oscillation of the vertical sul)port 28 P
about its center point 28C occurs as shown by the arcuate 35 arrow 28D in Figure 1. L
.
.. .. . .
- :
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~ O 2 'I`herefore, if the speed of the mold wheel 22 is increased to a point where production speeds of a highly desirable level are obtained, the inertial forces in the combined integrated input-tIansverse orientation-output roll S 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 and in some cases, an improper alignment on the mold wheel 22. This results, of course, in products which are inferior and which defy efforts to provide satisfactory quality -control. At sl'ower speeds, however, the continuity of the method and apparatus of Figure 1 provides a highly desirable process with high quality end products 24. t In the event that the extruder 10 emits material from the die 12 which is at a higher temperature than the optimum r 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 machine direction or longitudinal orientation to the extrudate web 14.
As illustrated in Figure 2, the extruder 10 and the die 12 feed an extrudate web 14 first into a bank of cooling rolls CR which are provided, as is well-known 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 temperature for orientation. r - , . . I
r - -' Tl~e i~ ut roller assembly 16 is illustratcd as including a first roller 16A and a second roller 16B which receives the web 14 in a serpentine path th~rebetween and which rolls 16A
and 16B are driven at differential rotational velocities to impart a longitudinal or machine direction oricntation 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 dri~ing 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 2Z 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-g- serrations, vacuum orifices or the like, schematically shown as upstanding teeth 22T on one of the flats of the mold wlleel 22 for piercing or otherwise securely engaging theweb to hold it against a relaxation of the imparted orientation therein during the molding process i~
- 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 towards the direction of the extTuder 10.
In this context, reference 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 shown in Figure 4.
i.
; - - 14 - I
11 ~ 5~2 1 While the severed products travel to a stack 24S, the selvage 14S travels to a selvage recycling means 34 whi~h cooperates with a source of new plastic granules or pellets 36 to place both reground selvage and the pellets 36 into a mi~er 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 more fully describedat a later ~
l~*S~ point here;n. FOT 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 common feature of all of the preferred embodiments of the present invention 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 no~
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 Ol 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, any other ratio of initial machine direction stretch and final machine direction stretch is also feasible. ~he degree of transverse or longitudinal orientation can be varied to suit a particular product which may have depth or shape requiring less initial orientation of the sheeting in one or another direction. Therefore, a system is provided which is very facile and variable with regard to unique and unusual m~lded shapes. .
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, ~
ii3~(~21 The ~l~lt of selvdge which falls outside of the transverse stretcher blades 18A and 18B is the same as that amount of selvage which falls outside of the llolding devices 22T about the periphery of 5 the mold wheel 22. These holding devices 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 view in Figure 6.
In practice, the holding devices or ~ripping devices 10 2~T about the periphery of the mold wheel can be made r effective on tlle 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 r stripping or molded product removal side or stations of 15 the mold wheel polygon 22 such that the stripping 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 20 transverse stretching zone TS which is preceeded on the upstream side by a machine stretch zone MSl and on the down-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 stretch has been 25 effectuated in the zone MS2 as indicated by the wider spacing between the edge adjacent dots 14I which are uti-lized to designate equal increments of unbiased web 14 in F
the initial spacing shown in the zone MSl of Figure 3B
which is a totally unoriented configuration and spacing.
30 Thi~ spacing is incremental in both the longitudinal and transverse directions of the web, i.e., the dots 14I
define biaxial lncre-ents of th- web 14 , - .:
' ~
il 3~0 ~
Referrin~ next to Figure 3C, it can be seen that the rotational velocity of the transverse stretcher blades 18A
is such that the web travels faster in the transverse stretching zone TS and therefore has imparted to it both S transverse and longitudinal stretch and has no additional longitudinal stretch imparted to it in the doh~nstream 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 r 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 transverse stretching is achieved within the i 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 impart machine direction stretch to the web 14 in the upstream zone MSl.
Referring furtller 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 roll 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. .
.. . .
~ 02 1 The surface speed of the second roll 16B is usually faster than the surface speed of the first roll 16A so as to achieve longitudinal stretch in the upstream area MSl and preferably, the surface speed of the roller 16B as compared to that of the roller 16A is such that 50% of the longitudinal or machine direction orientation OCCUTS in the transfer of material from the roller 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 ofthe second roller 16B and t:he 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-trate the edge of the web OT strip 14 50 as to hold thematerial 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 SA and 5B.
The third or initial output roller 20A is also posi-20 tioned very close to the teeth 18T of the blades 18A and 18Bso 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 25 the perimeter speed of the transverse stretching blades 18A and 18B and the fourth roller 20B is maintained close to the third roller 20A in order to minimize shrinl;back during the transfer from one roller to another. Usually, the fourth roll 20B is run faster than the third roller 20A with the~preferred speed being such as to accomplish the Temain-ing 50% of the longitudinal or machine direction orientation in the web 14. The web 14, as it leaves the lourth or interfacing Toller 20B onto the mold w]leel 22, is thus fully biaxially oriented.
_ _ _, _ _ _ _ _ , - . .
- , ~ ' As cliscloscd with reference to Fi~ures 1 and 2~ the entire orientation device 16-18-20 in thc 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 ;n Fgiure 1 or a pneumatic cylinder schematically shown in Figure 2 is provided to bias the final output or interfacing roller 20B against the peri- -pheral shoulders of the mold wheel 22 such tllat the teeth 22T on the mold wheel will avoid contact with the rolleT
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 ~C therein.
All of the longitudinal stretching rollers 16A, 16B,, , 20A a,nd 20B,are,preferably coated with fluorocarbon e-g- ~hat known by the Trade Mark TEFLON to avoid sticking of the web 14 the~eto. 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 149 the ro.lls reach about the .same temperature as that of the web itself.
A low inertia orientation ap~tus 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 outl~ut roller set 120 which is comprised of three rollers 120A, 170B and 120C mounted on a common frame 120D which is biased by suitable means 120E toward the mold wlleel 22 SUC]I tlnat the fi~al output or interfacing roller 120C is engaged with ' the mold wheel 22 in a manner similar to that of the final roller 20B in the previous embodiments.
The biasing means 120E can be any suitable device such as a compression spring or a pneumatic spring or cylinder such as already described in re~erence to the embodiments of Figure 1 and Figure 2, respectively.
` 19 -113~i021 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 input 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 t~o rollers. The gap between the three rollers 120A - 120C is kept very small to avoid shrinXback of the now biaxially oriented web traversing these rolls. Because the inertia of this particular output stretch and interface roll means has 'oeen minimized, 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 which engages drive pulleys or sprockets Sl and S2 mounted on the shafts of the rollers 120A and 16B, respectively.
Further, the roller 16B includes a passive output gearing Gl whic~ is engaged with compatible gearing ~of a predetermined ratio) G2 mounted on the shaft of the initial input roller 16A such that the differential speed between the rollers 16A and 16B can be effectuated from the same common drive means DC that drives both the rollers 16B
and 12OA.
., _ 20 -O~l Tl~us,the ratio of the gears Gl and G2 can be changed to vary the amount of longitudinal stretch achieved between the initial input rollers 16A and 16B.
The last two rolls 120B an(~ 120C on the downstream side of the transverse stret~heT blades 18 are not driven from the stretcher apparatus. Tl~e 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 pro~ide the proper longitudinal orientation when measured against the fixed speed of the initial output roll 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 12~A and 120C of the set 12~.
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 center 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 d'irection 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 of the latter.
- Suitable stop means or bosses are provided on the saw blade adj~stment brackets to interact with the mounting of t]le various input rollers 16A and 16B to preclude engagement of the rolls with the saw blade but maintaining the desired immediate' proximity thereof.
The mat:Cl`ial tellS iOIl Or thc wcb 14 proceedin~ bcncath the roller lGA l-ack over tlle roller 16B and thcrlce bcncath the saw blades 18A ancl 18B is sufficient, since tl~e web 14 initially approaches the roll 16A from above, to cause the roll 16A to track the movements of the roll 16B ~nd thereby maintain the desired minimum spacing by l~ay of the material tension in the web 14.
Suitable means are also provided ~ithin the mounting bracket 120D of the output roll set 120 to provide for moving the t}-ree rollers 120A, 120B and 120C apart and back 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-of ordinary sXill 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 orientation of the l~eb 14, by way of an exemplary process parameter. In this case, the die opening would be on the order f 0 090 inches of ~.eb 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 roo]s CR before enteTing the initial rollers 16A and 16B of the stretcher apparatus of ~n aspect of the prese,nt invention.
At an output rate of approximately 600 pounds of wcb material per hour, the speed of the extrudate ~.~ould be 90 feet per minute before entering the initial rolls 16 of the stretcher assembly and ~ 270 feet per mintlte leaving the last or interfacing roller 120C of the stretch~r assembly. This 270 foot per minute speed ~.ould m~tch the speed of the mold surface OT mold polygon 22.
.
, Zl Fifty percent of the longitudinal orientation in the web 14 would probably be accomplished between the rollers 16A and 16B, all of the transverse orientation between the transverse stretcher blades 18A and lBB 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. ~he plate 24 would weight 10 grams and 324 plates per minute would be produced at a mold wheel speed of 21rpm.
In acllieving 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 n~ethod with a relatively high speed of production and high quality control with a low~inertia apparatus is readily effectuated by the embodiments of ~igures 4, 5A, 5B and 6.
,
Claims (3)
1. Means for interfacing a web of continuously formed thermo-plastic material with a continuously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in said web and con-form a surface of said web with said peripheral surface, said web being in continuous longitudinal motion, said means comprising:
elongated bracket means extending longitudinally of said web and pivotally mounted on a transverse axis at its upstream end for rotation toward and away from said peripheral surface;
a plurality of parallel roller means mounted for rotation in said bracket means transversely of said web and mutually parallel with said peripheral surface;
said web being threaded in a serpentine manner through said roller means;
downstream roller means in said plurality of roller means constrained by said bracket means to follow said peripheral surface throughout its undulations and driven by the latter at a like peripheral speed, transferring said web directly onto said peripheral surface; and upstream roller means in said plurality of roller means initially receiving said web on its peripheral surface and having an axis of rotation substantially coincident with the said transverse pivotal axis of said bracket means.
elongated bracket means extending longitudinally of said web and pivotally mounted on a transverse axis at its upstream end for rotation toward and away from said peripheral surface;
a plurality of parallel roller means mounted for rotation in said bracket means transversely of said web and mutually parallel with said peripheral surface;
said web being threaded in a serpentine manner through said roller means;
downstream roller means in said plurality of roller means constrained by said bracket means to follow said peripheral surface throughout its undulations and driven by the latter at a like peripheral speed, transferring said web directly onto said peripheral surface; and upstream roller means in said plurality of roller means initially receiving said web on its peripheral surface and having an axis of rotation substantially coincident with the said transverse pivotal axis of said bracket means.
2. Means for interfacing a web of continuously formed thermo-plastic material with a continuously undulating and rotating peripheral surface to minimize resulting longitudinal stresses in said web and con-form a surface of said web with said peripheral surface, said web being in continuous longitudinal motion, said means comprising:
elongated bracket means extending longitudinally of said web and pivotally mounted on a transverse axis its upstream for rotation toward and away from said peripheral surface;
a plurality of parallel roller means mounted for rotation in said bracket means transversely of said web and mutually parallel with said peripheral surface;
said web being threaded in a serpentine manner through said roller means;
downstream roller means in said plurality of roller means, constrained by said bracket means to follow said peripheral surface throughout its undulations and driven by the latter at a like peripheral speed, transferring said web directly onto said peripheral surface; and upstream roller means in said plurality of roller means initially receiving said web on its peripheral surface and having an axis of rotation substantially coincident with the said transverse pivotal axis of said bracket means; and an odd number of intermediate roller means between said upstream and downstream roller means.
elongated bracket means extending longitudinally of said web and pivotally mounted on a transverse axis its upstream for rotation toward and away from said peripheral surface;
a plurality of parallel roller means mounted for rotation in said bracket means transversely of said web and mutually parallel with said peripheral surface;
said web being threaded in a serpentine manner through said roller means;
downstream roller means in said plurality of roller means, constrained by said bracket means to follow said peripheral surface throughout its undulations and driven by the latter at a like peripheral speed, transferring said web directly onto said peripheral surface; and upstream roller means in said plurality of roller means initially receiving said web on its peripheral surface and having an axis of rotation substantially coincident with the said transverse pivotal axis of said bracket means; and an odd number of intermediate roller means between said upstream and downstream roller means.
3. The means of claim 2 wherein said upstream roller means includes drive means maintaining a differential peripheral speed between said upstream and downstream roller means to impart longitudinal orienta-tion to said web in said interfacing means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000386352A CA1135021A (en) | 1978-03-13 | 1981-09-21 | Means for interfacing web with rotating surface |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US886,160 | 1978-03-13 | ||
| US05/886,160 US4250129A (en) | 1978-03-13 | 1978-03-13 | Method for the continuous formation of biaxially oriented thermoplastic materials and forming articles therefrom in a continuous process |
| CA323,052A CA1127364A (en) | 1978-03-13 | 1979-03-09 | Method and apparatus for the continuous formation of biaxially oriented thermoplastic materials and forming articles therefrom in a continuous process |
| CA000386352A CA1135021A (en) | 1978-03-13 | 1981-09-21 | Means for interfacing web with rotating surface |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1135021A true CA1135021A (en) | 1982-11-09 |
Family
ID=27166128
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000386352A Expired CA1135021A (en) | 1978-03-13 | 1981-09-21 | Means for interfacing web with rotating surface |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1135021A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6136396A (en) * | 1996-08-12 | 2000-10-24 | Tenneco Packaging Inc. | Polymeric articles having antistatic properties and methods for their manufacture |
-
1981
- 1981-09-21 CA CA000386352A patent/CA1135021A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6136396A (en) * | 1996-08-12 | 2000-10-24 | Tenneco Packaging Inc. | Polymeric articles having antistatic properties and methods for their manufacture |
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