CA1307889C - Roller-die extrusion of polymers - Google Patents

Abstract

PROCESS FOR OBTAINING ULTRA-HIGH MODULUS PRODUCTS
Abstract of the Disclosure A polymer is solid-state deformed under pressure through the rollers of an extrusion rolling die, at a temperature near but below its crystalline melting point, while controlling the extrusion rate and the rate of rotation of the rollers so that the rake of extrusion of the polymer is substantially the same as the rate of rotation of the rolling die surface.

Description

I 307~89 PROCESS FOR OBTAINING ULTRA-HIGH MODULUS PRODUCTS
SPECIFICATION
leld of Invention Thls lnvention relates to a solid-state deformation process and apparatus ~or achievlng the productlon of ultra-high modulus polymers of both simple and comple~ shapes, at rapld out-put rates and under moderate processlng condltions.
Back~round of the Invention The development of ultra-hi~h modulus polymers has been pursued in many academic and lndustrial laboratorles by the pre-paratlon of anlsotropic polymer morpholo~ies of highly oriented and extended molecular chains.
It has ~een known for a long tlme that the theoretlcal tensile modulus of a polymer should approach the modulus of steel (~208 GPa). However, untll a decade ago, the theoretlcal calcu-lations (for polyethylene ~240 GPa) were consldered unllkely to be ~chieved, because all known polymers had modull two orders of mag-nitude lower. The reason ~or such a low modulus was that the ; polymer assumed a random entangled and twlsted conflguratlon whlch had a low load bearlng capaclty. In recent years, lt was reallzed that the greatest modulus and strength would result from an aniso-tropic structure of hlghly oriented, extended, and densely packed ; chalns. Indeed, some polymers, ~or example polybenzamlde and I 3 () ~

1 polyethylene, have been processed into fibers that exhibit

2 moduli of 100 - 200 GPa, thereby indicating that the

3 earlier theoretical values can be approachedO

4 The development of ultra-high modulus products is S of paramount importance in view of their significantly 6 lower density; for example, steel is about eight times 7 more dense than polyethylene. The term "specific modulus~
8 refers to the quotient of modulus divided by density;
g therefor the specific modulus of polyethylene ultra-high 10 modulus fibers is significantly higher than the specific 11 modulus of steel.
12 Conventional flexible chain polymers, e.g., 13 polyethylene have been processed into high modulus ~ products by processes that may cause a permanent lS deformation of the internal structure, namely, the 16 conversion of an initially isotropic and spherulitic 17 structure to a fibrillar structure. The fibrils are made 18 of oriented and extended molecular chains which ensure 19 mechanical connection between crystals and load transfer.
Thus, it can be realized that, for maximum 21 mechanical performance, all polymer cha;ns should be 22 extended along the deformation direction. Thus macroscopic 23 deformation, which involves molecular deformation and is 24 accompanied by drastic dimensional changes in the case of flexible polymers, should not be confused with the shaping 26 processes which in general are also accompanied by ~7 dimensional changes but do not involve the transformations 28 f a spherulitic to a fibrillar morphology, which, in the 2g-case of high density polyethylene, takes place at a deformation ratio of approximately 4. Nor should 31 macroscopic deformation be confused with the conventional 32 melt extrusion process which may involve some molecular 33 orientation. Indeed, during any melt processing operation 34 some molecular orientation is bound t.o occur because of the viscoelastic nature of polymeric materials. ~owever, 6 the fraction of extended chains is exceedingly small, too 37 small to result in high modulus/strength performance.

I ~0/~89 _ 3 _ 1 Furthermore, the macroscopic deformation described 2 in this specification is not confined, as to deformation 3 limits, to the natural draw o~ a particular polymer, for 4 such limits can be overcome by the process of the present

5 invention.

6 Shaping processes such as calendering or rolling

7 are small deformation processes which do not result in

8 morphological transformation necessary for the ultra-high g modulus and strength performance and almost unequivocally 10 involve biaxial flow, i.e., deformation in both the 11 longitudinal ~machine) and the transverse direction.
12 Rolling combined with stretching may result in uniaxially 13 deformed polymer structures with significantly enhanced 14 tensile properties. However, this technology is confined to the processing of thin sheets and i5 limited by the 16 excessive loads involved to offset the counter-force and 17 the friction between the roll and the polymer surface.
~8 Anisotropic polymer morphologies with ultrahigh 19 modulus and strength have been obtained by processing 20 conventional flexible chain polymers by solid state ~1 deformation using the extrusion and drawing techniques, by ~2 extrusion of supercooled melts and by drawing from gels 23 and dilute flowing solutions.
24 Various semicrystalline polymers have been studied. High-density polyethylene has been studied the 26 most because of its simple composition and its high theoretical modulus (approximately 240 GPa). Similar 28 anisotropic morphologies have been obtained by the 29 chemical construction of polymers with rigid and semirigid backbone chains by introducing para-substituted aromatic 31 units and then processing with solution and melt . ~
32 processes. The para-benzamide polymers and the 33 copolyesters of poly(ethylene terephthalate) and p acetoxybenzoic acid are examples of riyid and semi-rigid poIymers sought to be processed into ultra-high modulus 36 products, i.e., products in which the molecules are not ; 37 only oriented but are also extended.
~ 38 3 ~ ~

1 Typically, the ultra-high modulus products from 2 the above processes have been in the form of fibers and 3 thin films, that is, structures which ~o not have bulk 4 mechanical properties. Two recent developments of 5 ultra-high modulus products with bulk structure have been 6 obtained by injection molding of high density polyethylene 7 and the copolyester of poly(ethyleneterephthalate) and 8 P 8cetoxybenzoic acid.

9 The solid-state extrusion process has also been investigated for i~s potential use for ~he production of 11 ultra-high modulus products with bulk structure, but it 12 has been severely restricted by low processing rates (a 13 few centimeters per minute), for it is a solid-state 14 deformation process throuyh a convergent geometry. It has also required very high extrusion pressures, especially 16 for the preparation of products with complex or large 17 cross-sectional areas. An analysis of the extrusion 18 process shows that a high extrusion pressure is required 19 a~ to shear and elongate the polymer and b) to overcome 20 the die polymer friction. Equation (1) shows the pressure 21 balance in the solid-state extrusion process through a 22 Conical die:

24 PE * e (Bo )PO = e (Bo ) [orEoa()d + ~ (o ) 4 S (o ,a) ] (1 ~6 where PE is the pressure of extrusion, 27 Po is the pressure at the die exit, 28 B is ~cot [a], 29 ~ ~ is the friction coefficient, a ls the die half angle, 31 is the strain, ~ ~ . .
32 ~o is the strain at the exit of the die, 33 ~) iS the true stress at strain , 34 S is the work of shear and shear yield at strain o and die angle a.

I ~(J1~3~9 1 Equation (1) indicates that the friction 2 coefficient term B is significant and that extrusion 3 pressure increases with increasing Eriction.

5 Summary of the Invention 6 The invention comprises a method for producing 7 high modulus products and includes solid-state deforming a 8 polymer morphQlogy under pressure through the convergent 9 geometry of the rollers of an extrusion rolling die in

10 which the polymer is confined over the entire perimeter by

11 the moving surface of the die during the deformation

12 process. This is done, at a temperature near but below its

13 crystalline melting point, while controlling the ex~rusion

14 rate and the rate of rotation of the rollers so that the

15 rate of extrusion of the polymer is substantially the same

16 as the rate o rotation of the rolling die surface. This

17 is not a two-stage process with an extrusion and then a

18 rolling. The extrusion-rolling die used in this invention

19 is a one piece apparatus in which the polymer is extruded,

20 not rolled, through the simple or complex conduit 2~ ~eometry The process is to be contrasted with ~2 conventional calendering or rolling, in which lateral 23 deformation perpendicular to ~he machine direotion may ~4 occur. In the present invention no lateral deformation is 2S permitted.
26 The invention also includes an extrusion rolling 27 die for producing high modulus polymer products. This 28 apparatus comprises a pair of rotatable rollers which are g-kept at a temperature near but below the crystalline 30 melting point of the polymer to be processed. There are 31 foxce-applying means for applying extrusion pressure to 2 the feed zone of the rollers and control mea~s for 33 controlling the rate of rotation of the rollers so that the rate of extrusion of the polymer is substantially the same as the rate of rotation of the rolling die surface.

:

1 307~3~9 ~a 61968-725 According to one aspect of the present invention therP
is provided a method for producing high-modulus semic.rystalline polymer products comprisiny:
solid-state e2truding a polymer having an initial polymer morphology by ~eeing under pressure through an extrusion-rota~ion die having a static entry position and a succeeding friction-reducing moving portion, said succeeding friction-reducing moving portion of said die comprising a pair of opposi~ely rota~ing members, each having integral shaped wall surfaces strictly confining, engaglng and compressing the entire perimeter of the polymer durin~ extrusion and providing the geometry of a die exit and a profile for extrudate which has practically the same cross-sectional area and lateral dimensions as the cross-sectional area and lateral dimensions of the die exit said static and succeeding friction~reducing moving portions of the die having a ; polymer-containlny zone with convergent yeometry through which the polymer is compressed orlented and extruded under conditions of minimal friction between the polymer and the die surface for reducing the extrusion pressure, said minimal frictlon being obtained by substantially synchronous movement of the rotating members of the die - and the polymer, said extrusion being at a temperature near but below the crystalline melting point of said polymer, to obtain an extruded polymer product having a markeflly transformed morphology as compared with ~aid initial polymer morphology comprised of oriented and , _:

1 ~07~9 5b 61968-725 extended molecular chains and markedly enhanced tenslle propertles, the values of which are for the Young's modulus wlthln the range of 2 to 220 GPa and for the tensile strength wlthln the range of .015-4 GPa, and whlch depend upon the extent of the cross-sectlonal area reduction durln~ extruslon.
Accordlng to a further aspect of the present ln~ention there is provide~, an extrusion rolllng dle ~or carrylng out the above method and ha~lng a periphery for produclng hlyh modulus products having a crystalllne meltlng point, comprlslng: a pair of rotatable rollers providlng a rage of rotatlon having an input side and an output s1de and die-provldlng exterior shapes forming the convergent geometry of the dle and confinln~ the entlre perimeter of material extruded therethrough at a rate or e~truslon of the material and reducing the material overall cross-ssctlonal area, means for keeplng said rollers at a temperature near ~ut below the crystalline melting polnt of the materlal to be processed, force-applying compresslon me ns for extruding the pol~mer through sald rollers, and gear control means driven by the appllcatlon of e~ternal force fQr controlling the rate of rotatlon of the rollers so that the rate o~ extruslon of the material is substantlally the same as the rate o~ rotation of the rolllng ~1e ~ur~ace.
;

~ ,.

3 ~ 9 1 In accordance with the present invention, a high 2 modulus product such as a high density polyethylene i5 3 produced by a solid-state deformation technique at rapid 4 output rates and in shapes of different complexity. Such a 5 high modulus is produced by deforming the polymer 6 preferably near to, bu~ below i~s crystalline melting 7 point through an extrusion rolling die.
8 The extrusion rolling die ic a key feature in 9 this invention and is composed of a feed zone reservoir 10 adjacent to a set of master rollers on which cylindrical 11 sleeYes of different diameters and~or shapes can be 12 mounted to result in converging geometries of different 13 configurations with moving wall elements. This type of die 14 design is distinctly different from the dies used in solid 15 state extrusion and the die-or-zone-drawing processes 16 which are static and use converging conical or tapered 17 slit dies with no moving wall elements.
18 The extrusion rolling die of this invention has 19 an exponential profile or trumpet shape and therefore has 20 the advantage of trumpet-shape dies for extrusion at lower

21 strains, and consequently it results in lower extrusion

22 pressures since the pressure increases with the strain and

23 the strain drops rapidly with die-half angle. According to 2~ this invention the motion of the roller elements of the ~5 extrusion rolling die and the polymer between them is 26 substantially synchronous a~d thus may result in a process 27 in which the friction between the polymer and the die 28 8urface is minimiæed and consequently the extrusion 29 pressure is reduced. The kind of synchronous motion of the ~n rollers and the polymer under ex~rusion conditions may be 31 considered analogous to a substrate drawing process. This 32 can be demonstrated in a co-extrusion experiment wherein tbe material to be deformed is sandwiched between two substrate layers, and the entire structure is then co-extruded through a convergent die geometry. In this 36 configuration, the material between the two substrates (e.g., a polyethylene film between two polyethylene 3~

.
.

1 3()7~9 1 substrates) is deformed under compression and without 2 friction on the surrounding substra~es, as lony as the 3 extrusion rates of the substrates and the material in the 4 middle are the same. An additional advantage of the 5 reduction of friction between the polymer die surfaces by 6 the synchronous motion of the rollers and the polymer, is 7 that the polymer is deformed under elongational flow 8 conditions in comparison to the shear flow conditions g which prevail in conventional solid state extrusion. I~
10 has been suggested ~hat elongation flow is beneficial for 11 the achievement of ~ltra-high modulus products.
12 Also, the extrusion rolling process is different 13 from the calendering process which is typically a shaping 14 process between parallel rollers and is accompanied by 15 dimensional changes in two directions. The designing of 16 convergin~ geometries between the roller elements of the 17 extrusion rolling die in this invention imposes lateral 18 constraints during extrusion and results in uniaxially 19 drawn products.
The invention applies to the manufacture of 21 various shapes, including tubes.
22 The method applies to semicrystalline polymers and 23 thermotropic aromatic copolyesters.

24 Suitable semicrystalline polymers include

25 polyethylene, polypropylene, polyamides, polyoxymethylene,

26 poly(ethylene terephthalate), poly(vinylidene fluoride)

27 and polymethylpentene. Suitable thermotropic aromatic

28 copolyesters include 32 t o ~ ~ C ~ -C ~ R

34 where 7~89 4 R i s --O~C--, --o~ , or 9 --0~0--ll (2) ~C~C~O~Il~O ~ R--0 16 where 9 F< is ~ ~ ~, or ~1 ~3 (3) ~5 0 01 26 ~C ~c--CH2CH2~C~O~

29 :: (4) ~ ~:

`` I 307~8~

1 Brief Description of the Drawings 2 Fig~ l is a simplified and somewhat diagrammatic 3 isometric view in section of an extrusion rolling die 4 with a preceding feed zone reservoir, for use in an S embodiment of the invention.

7 Fig. 2 is a similar view of a modifie~ form of die 8 and feed zone reservoir.

Fig. 3 is a fragmentary isometric vie~ of an 11 extrusion rolling die, showing one shape usable in 12 practicing the invention.

14 Fig. 4 is a fragmentary end view in perspective of 15 the shape of the polymer extruded from the die of Fig. 3.

17 Fig. 5 is a view like Fig. 3 showing a die of a 18 different shape.

Fig. 6 is a view like Fig. 4 showing the shape of ~1 the polymer extruded from the die of Fig. 5.

23 Fig. 7 is a diagrammatic isometric view of still 2~ another extrusion rolling die usable in the present invention producing a differently shaped polymer 26 extrusion.

~8 Fig. 8 is a diagrammatic view ;n side elevation 29 and in more detail of the die of FigO 7 and associated apparatus, illustrating the use of botb extrusion pressure 31 on the input side o the die and a pulling load on the 32 output side of the die.

Fig. 9 is a view in elevation of ~he back plate thereof.

1 307~q 1 Fig. 10 is a view in side elevation of the back 2 plate portion of the die.

4 Fig. 11 is a more complete isometric view of a S rolling die like that of Fig. B incorporated into a 6 thermally insulated housing and provided with heaters.

8 Fig. 12 is a view in elevation and in section of a g modified form of rolling die also embodying the principles 10 f this invention, which can be used in the apparatus of 11 Fig. 11 to replace the rolling die of Fig. 8.

13 Fig. 13 is a fragmentary view in sec~ion taken 14 along the line 13-13 in Fig. 12.

16 Fig. 14 is a view in elevation at right angles to 17 Fig. 12, showing one master roller and one cylindrical 18 s1eeVe thereon.

2~ Fig. 15 is a view like Fig. 12 of another modified 21 form of rolling die.

23 Fig. 16 is a fragmentary view in section taken 24 along the line 16-16 in Fig. 15.

26 Fig. 17 is a view like Fig. 14 of a portion of 27 Fig. 15.

29 Fig. 18 is a diagra~matic view showing two rolling 3~ dies of the invention in series.

32 Fig. 19 is a view in longitudinal section of a device for converting thick-walled~ small-diameter tubes of polymer to thinner-walled, larger-diameter tubes.

., 1 .~ 0 1~8q 1 Fig. 20 is a view in cross section taken along the 2 line 20-20 in Fig. 19.

4 Fig. 21 is a view in cross section taken along the 5 line 21-21 in Fig. 19.
7 Fig. 22 is a diagrammatic view showing how the 8 tube resulting from Figs. 19 - 21 can ~e used to make a 9 polymer sheet~

11 Description of Some Preferred Embodiments of the Invention 12 As shown "in Fig. 1, an extrusion rolling die 20 13 may include a pair of master rollers 21 and 22 which 14 receive the polymer under pressure on their input side 15 from a feed zone 23 having parallel side walls 24 and 25, 16 a rear wall 26, and a front wall (not shown due to the 17 section).
18 Fig, 2 shows an alternative type of die 30 having 19 master rollers 31 and 32 receiving polymer under pressure 20 from a feed zone 33 having converging side walls 34 and 21 35, as well as a front wall (not shown) and a rear wall 22 36.
23 The master rollers may be shaped (or mounted with 24 cylindrical sleeves of different diameters) to give products of any desired degree of complexity. For exa~ple, 26 the rollers 21 and 22 are shown in Fig. 3 as provided with 27 extrusion channels 27 and 28 that produce an extrud~te 29 ~8 that is square in cross section, as shown in Fig. 4.
~9 On the other hand, the rollers 31 and 32 are shown in Fig. 5 to have channels 37 and 38 that produce an 3.1 extrudate 39 (Fig. 6) which has a tee shape in cross 32 section.
Further, Fig. 7 shows a pair of master rollers 41 34 and 42 having extrusion channels 43 and 44 shaped to produce an extrudate 45 that has the cross-sectional shape 36 f an H.

I 307~9 -- ]2 -1 Thus the roller (or cylindrical sleeves on them as 2 in FigO 11 et seq) can form converging dies of different 3 geometries through which a polymer can be deformed in 4 different shapes and in dif~erent sizes. The rollers of 5 each of these extrusion dies act to confine the material 6 within them, no movement widthwise is permitted. The 7 rollers may be viewed as the convergent landing surfaces 8 of the die, even through these landings surface can move g synchronously with the solid polymer and do so in order to 10 minimize friction.
lL As shown in Figs. 10 and 11 and described below, 12 the rollers 41 and 42 can be heated over a wide range of 13 temperature conditions so that the polymer can be deformed 1~ at a temperature preferably near to but below its melting 15 point.
16 The extent of deformation is determined by the 17 deformation ratio, which is defined as the ratio of the 18 cro6s-sectional area of the entrance of ~he feed zone to 19 the sross-sectional area of the product extrudate. To 20 achieve the transformation from a spherulitic to a ~1 fibrillar morphology, a deformation ratio of at least 4 is 22 required for polyethylene.
23 The polymer can be deformed by ~his process either 24 under extrusion pressure alone ~Figs. 1-6), or a combined 25 extrusion pressure and a pulling load on the emerging 26 extrudate, as shown in Figs. 7-10. In Fig. 8, the rollers 27 41 and 42 are preceeded by a feeding zone 46 filled with 28 polymer 47, against which a hydraulic piston 48 acts to 29 provide extrusion pre~sure Simultaneously the extrudate 45 is attached to a clamping block 50 to which a pulling 31 load is ~tt^ached by a pulley wheel 51 and a wire or cable 32 52, which winds around the wheel 51. A continuous chain 53 33 links the wheel 51 and its pulling cable 52 to a pulley 34 portion 54 on the roller 41, so that the angular velocity of the rollers 41 and 42 and the speeds of pulling and 36 extrusion are coordinated. The rollers 41 and 42 are supported by a frame 55. ~hus, the deformation process can .

1 3 ) 7 ~ 8 9 1 occur under conditions of minimum friction. This is 2 another key feature of this invention and can be achieved 3 by adjusting the angular velocity of the rollers 41 and 4 42, the throughput rate, and/or the pulling rate on the 5 emerging extrudate 45, so that the polymer and the rolling 6 die surface move at the same velocity.
7 As shown in Figs. 9 and 10, the two rollers 41 and 8 42 are ~eared together near a back plate 56 of the frame 9 55 The back plate 56 supports the rollers 41 and 42, on 10 which ~ears ~7 and 58 are mounted coaxially with the 11 rollers 41 and 42. Two other gears 60 and 61 are meshed 12 together, the gear 60 being in mesh with the gears 57 and 13 61 and the gear 61 being in mesh with the gear 58, so that 14 the two rollers 41 and 42 rotate at exactly the same 15 an9Ular velocity~
16 Figs. 9 and 10 also show rotary conduits 66 and 67 17 in the rollers 41 and 42 are joined by conduits 71 and 72 18 and rotary unions 68 and 69 (see Fig. 11) to a 19 temperature-controlled oil bath 70 having a heater ~not 20 shown). Thus, as shown in Figs. 10 the processing 21 temperature may be attained by circulating hot oil through 22 the master rollers 41 and 42 from a hot silicone oil bath 23 70, thermostated at the desired temperature.
24 Fig. 11 shows a slightly different configuration.
25 The rollers 41 and 42 are again provided with conduits 66 ~6 and 67 leading to rotary unions 68 and 59, which are 27 connected to a hot oil bath 70 by conduits 71 and 72.
28 Here, the rollers 41 and 42 are also shown inside a 29 chamber 73 comprising thermal insulation 74 on all side~
and provided at the bottom with hot air blowers 75 and 76 31 to supplement the hot oil bath by air convection in the 32 thermally insulated chamber 73 surrounding the rolling die 33 40, and supply additional heat~ although either heat source could be used alone. Also the heating may be partly obtained by preheating the polymer stock in a reservoir 77 1 307~89 1 with electrical band heaters 78 mounted around the 2 reservoir 77 and at the entrance of the 2xtrusion rolling 3 die 40.
4 The solid state deformation through extrusion S rolling dies can be used with various semicrystalline 6 polymers such as polypropylene and polyamides to obtain 7 also products with enhanced bulk properties, --not ]ust 8 thir. films as have ~een produced by rolling combined with 9 stretching, or fibers, which are obtained by 1~ fiber-spinning operations. This has been demonstratea by 11 the preparation of high~density polyethylene extrudates 12 with circular and square cross sections at different 13 deformation ratios~
14 ~igs. 12-14 show an alternative structure of a 15 rolling die 80. ~ere, there are master rollers 81 and 82, 16 whiCh are cylindrical and preferably hollow for 17 circulation of heated liquid within them. Instead of being 18 directly machined, the master rollers 81 and 82 are 19 splined to respective cylindrical sleeves 83 and 84, each 20 having a semicircular outer periphery 85 as seen in cross-21 section ~Fig. 14). The sleeves 83 and 84 may be replaced, 2~ as shown in Figs. 15-17 with otherwise shaped sleeves, ~3 such as sleeves 86 and 87 having a rectangular 24 CrOSS-8eCtional shape.
The feeding apparatus in Figs. 1~ and 13 comprises 26 a cylindrical tube 90 with an inner circular cylindrical 27 passage 91 and an exterior circular flange 92. A fitting 28 93 is cylindrical with a bottom, inwardly extendlng ~lange 94 and an interior thread 95 (Fig. 12), into which is threaded the exterior thread 96 of a conduit 97.
1 The feeding apparatus of Figs. 15 and 16 is 32 similar except that it has a tube 100 with an exterior 33 flange 101 and an interior passage having a lower square portion 102 and an upper conical portion 103.
In a typical experiment, an extrusion rolling die 6 generally like that shown in Figs. 7~10 incorporated a series of juxtaposed cylindrical sleeves of different ` :

1 3078~9 diameters and widths, as shown in Figs. 12-17, to result 2 in both circular and square cavities between the rollers 3 of progressively smaller cross sectional areas. These 4 circular and square cavities between the rollers part of 5 the ex~rusion die are in sharp contrast to the open-ended slit be~ween conventional rollers. It is important to note 7 that in the present invention the polymer is completely 8 confined widthwise. The slee-~es on the master rollers were ~ heated to 125-130C. by convection in a thermally 10 insulated chamber. Preformed samples having circular or 11 square cross-section, according to which cavities they 12 were to be fed, were placed into the die, and after 13 thermal equilibration, each sample was pulled through the 14 die by a pulling load. Minimum friction requirements were 15 met by synchronizing the rate o~ the pulling load and the 16 rotation of the rollers using the pulley system and gears 17 in Figures 8 to 10. To commence the extrusion through the 18 extrusion rolling die, the end of the initial stock was 19 trimmed to an area slightly smaller than the 20 cross sectional area between the rollers so that it could 21 be fed through the rollers section of the die and gripped 22 by the clamping block 50 as in Fig. 8.
23 Transparent extrudates of deformation ratio 12 24 were obtained by applying a pulling load of 25 MPa.
Additional compaction and drawing can be obtained 26 by use of a plurality or series of rolling dies, as shown 27 in Fig. 18, where rolling dies 110 and 111 are in series 28 and the polymer 112 is first subjected to the die 110 and 29 its extrudate 113 is then subjected to the die 111 to produce an extrudate 114.

31 In another set of experiments, polyethylene was 2 extruded under the combined effects of an extrusion 33 pressure and a pulling load. The polyethylene was 34 crystallized in a reservoir, and, a~ter reaching thermal equilibration at 130C. was extruded initially through a 6 straight conical die (a-20) of deformation ratio 2 and 37 under an extrusion pressure of less than 50 Mæa. The 1 30788~

1 straight conical die was in close proximity to the 2 extrusion rollers, to serve as the feed zone 46 of the 3 extrusiOn rolling die shown in Fig. 8. The emerging 4 extrudate 45 from the straight conical die was pulled 5 through the extrusion rollers by adjusting the rate of 6 pulling and the rotation of the rollers 41 and 42 to 7 meet the minimum friction requirements as described 8 previously.
9 In an independent experiment, when an attempt was 10 made to pull a polyethylene sample between two freely 11 rotating rolls to a draw ratio of >10, the polymer slipped 12 on the rolls and deformed by a necking process similar to 13 a drawing process or to what is encountered in a simple 14 tensile test. The situation can be aggravated when the 15 cross-sectional area of the initial stock polymer is 16 large.
17 The extrudates under both conditions of 18 experimentation were transparent. Transparency of such 19 extruded samples arises from an increase in crystal size 20 and concentration and, most importantly, from the 21 crystalline orientation and the dense packing of ~he 22 polymer chains which are produced by extruding through a 23 contained geo~etry under the compression conditions in the 24 extrusion rolling die. When the pulling rate on the 25 emerging extrudate is higher than the rate of extrusion ~6 rollers, post necking may occur beyond the exit of the die 27 and result in translucent extrudates. Such loss of 28 transparency is associated with the formation of voids 29 during the drawing process and beyond the die exit; these

30 are known to occur in conventional solid-state drawing of

31 high-density polyethylene. The variation of output speed

32 with the pulling load and an extrusion pressure of 5-10

33 MPa is summarized in Table 1. The deformation ratios, the

34 Young's modulus and the tensile strength of the extrudates

35 are included also.
3~

1 307~89 TA~L~ I

Pulling Load Output Speed Defol^matlon Young's Tenslle Ratios Modulus Strength (MPa)_Im/min) _ _ (GPa) (MPa) 4.4 2 5 2.5 1~0 10.6 2 8 5 260 Yet, in another experiment, a melt crystalllzed mor-pholoqy of ultra-high molecular welght polyethylene, i.e., a poly-ethylene with molecular weight of ~ 2 - 8x106, has been e~trudo-rolled into ribbon and rod products of DR 5-8 wlth a Young's modu-lus o~,10 GPa and tenslle strength of 0.25 GPa. UHMWPE ln con-trast to the conventlonal hlgh density polyethylenes havlng mole-cular welghts of up to 400, 000 ls lntrac~able. The polymer is supplied as flne powder and ls processed lnto varlous pro~lles uslng compresslon moldln~ and ram extruslon, whlch are known to be slow processes. Furthermore, when the ram extruslon process was used, solid state to extrude the UHMWPE and obtain a product of DR~J5, an extrusion pressure as hlgh as 300 MPa was required, and it resulted in unstable extruslon.
Thls lnventlon lncludes within its scope the processing of melt-crystallized powder and gel morphologies of semi-crystalllne polymers; also the processing of thermotroplc aromatlc copolyesters. Polymer powders may be loaded lnto the feed reser-~ voir and pre~compacted or compacted durlng the deformation process ;; under the combined effects o~ extruslon pressure and a pulling load through the extrusion rolllng die as shown in Fig. 8. The I 307~c~9 ].7a 61968-725 polymer powder ls never used by thermal treatment above the melt-ing polnt of the polymer. The powder is compacted ~elow thls meltlng polnt Tm and ls also solid-state deformed below Tm, ln contrast to efforts to fuse the ' 1 307~9 polymer powder. If, for example, a single crystal 2 morphology of polyethylene powder were to be heated to the 3 melting point of the polymer, it would transform to a 4 non-single crystal morphology. In the present invention~
5 one must stay always below the melting point of the 6 p1ymer.
7 Polymer powder morphologies exhibit high 8 deformability in comp2rison to melt-crystallized ~ morphologies. This has been shown to be associated with 10 the lack of molecular network between the powder particles 11 and the type of the powder morphology. Thus, ultra-high 12 molecular wei~ht polyethylene powders have been compacted 13 and extruaed to a 3-5 times higher draw ratio in 14 comparison to the maximum draw ratio achieved by extruding a melt-crystallized morphology. For example, a 16 solution-grown ultra-high-molecular-weight polyethylene 17 has been deformed by this invention to a draw ratio of 1~ about 50 it then had a Youngls modulus of 40 GPa and a 19 tensile strength of 0.6 GPaO Yet the single crystal 20 morphologies O~ the ultra-high molecular weight 21 polyethylene have been compacted and drawn to an even 30 22 times higher draw ratio by a multistep extrusion-drawing 23 process. Such morphologies can be deformed to a draw of 24 ~ 150 and have a Young's modulus of ~00 GPa and a tensile strength of 3~5 - ~ GPa. These values are one order of 26 magnitude higher than the values of polyethylenes drawn to ~7 the "natural" draw ratio. Similarly, polymer morphologies 28 prepared ~rom gels may be loaded into the feed reservoir 29; and deformed through the extrusion rolling die. Polymer morphologies prepared from gels have high deformability 31 because o~ the reduced physical entanglements in their 32 molecular network and can be drawn to a lO times higher 33 dra~ ratio in comparison to the melt-crystallized morphologies, and they have a Young's modulus value of lO0 GPa and a tensile strength of 3 GPa.

36

37

38 1 30788q Table II below summarlzes the mechanlcal propertles of solid state deforme~ ultra-high molecular welght polyethylene (UHMWPE) from different morphologles.
TABL~ II
Young's Tensile Modulus Strength UHMWPE Draw Ratio (GPa) (GPa~
Melt cry~tallized 5 - 8 10 - 15 0.15 - O. 25 Compound powder of single crystal at 90C. 200 - 300 200 - 220 3.5 - 4 Crystall lne morphology from gel precursor 40 - 50 100 - 120 2 - 4 A modiflcation of the extruslon dle descrlbed above can be u~ed for obtaining tubular products biaxlally or unlaxlally de-form~d ln the hoop dlrectlon. Figures 19 - 21 show a schematic representatlon of such a die modlf lcat ion which ls comprlsed of Q
cyllndrical mandrel 120 with dlameter dl whlch is connected to a cyllndrlcal mandrel 121 of l~rger dlameter d2, vla an inverted conlcal re~ion 122, and extrusion rollers 123 and 124, which pro-vide a con~ined clrcular passage around the mandrel 120 to obtaln ; the clesired tubular proflles. Wh~n a polymer tubular stock 125 is fed on the mandrel 121, lt is drlven by rollers 123 on the invert-ed conlcal mandrel section 122. An e~panded tube 126 i9 obtalned~
: the tube 126 is deformed in the clrcumferential (hoop) direction.
The extent of deformation, the deformatlon ratlo, can be calcu-lated from the ratlo of the diameters of the mandrels 120 and 121 at the exit and the entrance of the dle d-dl 1 ~()188q 1 If ten5ion is applied on the so expanded tubel a biaxially 2 deformed product may result. The tension can be applied by 3 a pulling load of the rollers 123 and 124 or an additional 4 set of ~pulling" rollers 127 and 128 may be used to 5 provide a confining circular passage around the larger 6 diameter mandrel 121, their rotational speed being higher 7 than that o~ the rollers 123 and 124.
~ In a typical experiment with ultra high ~olecular g wei~ht polyethylene (UHMWPE), (Mw ~ 2 x 106), a preformed 1~ tubular stock with internal diameter 0.95 cm heated at 11 180C. was placed on the mandrel 120 having diameter 12 dl = 0.95 cm preheated to 180C. (While this may seem to 13 be a high temperature for polyethylene, U~MWPE does not 14 melt-flow at this temperature.) It was driven on the 15 expanding section of the mandrel 120 by the rollers 123 16 and 124 to the larger diameter (d2 = 2O54 cm) mandrel 121, 17 where it was cooled to below 120C. and retrieved. The 18 expanded UHMWPE tubular product 126 was thus stretched in 19 the hoop direction by ~2.7x. When such a laterally stretched tube 126 was reheated to 160C. it shrank to 21 practically its original dirnensions, thus exhibiting 22 remarkable elasticity. With this particular polymer, 23 UHMWPE, higher temperatures than 180C. can be used for 24 its deformation using this methodology that extend well beyond 200C. as descr;bed in U.S. Patent No~ 4,587,163.
26 Like the uniaxially drawn UHMWPE rods which can be 27 obtained using the extrusion-rolling die device in Figure 28 1 or 2, the laterally drawn UHMWPE tubes 126 obtained 2g using the modified device in Figures 19 - 21 exhibit enhanced tensile properties in the lateral direction. For 31 example, the Figs 19 - 21 drawn UHMWPE tubes 126 exhibit 3~ in ~he hoop direction a Youn~'s modulus of ~2.0 GPa and a 33 tensile strength~150 MPa, in comparison to the Young's 34 modulus of 0.6-1 GPa and tensile strength of ~40 MPa for the isotropic UHMWPE.

1 301~3~9 1 A tubular product 126 drawn only in the lateral 2 direction using this processing methodology can be split 3 along a line 130 in the machine direction into a flat 4 sheet 131 which in a subsequent process can be stretched 5 uniaxially by pulling or rolling to a biaxially drawn 6 sheet. This is of advantage in comparison with the 7 conventional rolling process in which a biaxially ~ stretched film or sheet must be rolled first in one g direction, then turned by gO and rolled again.
This invention includes within its scope the 11 processing of semicrystalline polymers such as 12 polypropylene, nylons (polyamides)l polyoxymethylene, 13 poly(ethylene terephthalate), poly(vinylidene fluoride) 14 and polymethylpentene, which are known to be deformable in the solid state and which give products of high stiffness.
16 In the case of the rigid or semirigid polymers, polymers 17 within the scope of this invention are the thermotropic 18 aromatic copolyesters which may be processed at a 19 temperature above the glass transition of the polymer and within a range near and preferably below the 21 solid-to-mesophase transition temperatuxe of the polymer.
22 The device is also useful Eor processing metal 23 powder particles into thin metal profiles. Such metals as 24 aluminum, titanium, and alloys and fiber-reinforced aluminum composite materials can be treated in this way.
26 In this case, the straight or conical part of the 27 extrusion-rolling die serves as the feed zone of the die 28 device, and the rolling part serves for the compaction and 29 deformation of the metal powder particles.
Outstanding points of the processing in this 31 invention are 32 1. It operates under moderate conditions at rapid output rates.
34 2~ It operates under conditions of minimum friction.
36 3. It produces high modulus polymers of both 37 simple and complex geometrical configurations.

1 3()7~9 - 2~ ~

1 4. It is a continuous process.
2 5~ It is adaptable to commercially available 3 polymer processesO
4 To those skilled in the art to which this invention relates, many changes in construction and widely 6 differing embodiments and applications oE the invention 7 will suggest themselves without depart;ng from the spirit 8 and scope of the inventionO The disclosures and the g descriptions herein are purely illustrative and are not intended to be in any sense limiting.
11 What is claimed ;s:

Claims (32)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for producing high-modulus semicrystalline polymer products comprising, solid-state extruding a polymer having an initial polymer morphology by feeding under pressure through an extrusion-rotation die having a static entry position and a succeeding friction-reducing moving portion, said succeeding friction-reducing moving portion or said die comprising a pair of oppositely rotating members, each having integral shaped wall surfaces strictly confining, engaging and compressing the entire perimeter of the polymer during extrusion and providing the geometry of a die exit and a profile for extradate which has practically the same cross-sectional area and lateral dimensions as the cross-sectional area and lateral dimensions of the die exit said static and succeeding friction-reducing moving portions of the die having a polymer-containing zone with convergent geometry through which the polymer is compressed oriented and extruded under conditions of minimal friction between the polymer and the die surface for reducing the extrusion pressure, said minimal friction being obtained by substantially synchronous movement of the rotating members of the die and the polymer, said extrusion being at a temperature near but below the crystalline melting point of said polymer, to obtain an extruded polymer product having a 23a 61968-725 markedly transformed morphology as compared with said initial polymer morphology comprised of oriented and extended molecular chains and markedly enhanced tensile properties, the values of which are for the Young's modulus within the range of 2 to 220 GPa and for the tensile strength within the range of .015-4 GPa, and which depend upon the extent of the cross-sectional area reduction during extrusion.

2. The method of claim 1 in which the polymer is chosen from the group consisting of polyethylene polypropylene, polyamides polyoxymethylene, poly(ethylene terephthalate), and poly(vinylidene fluoride).

3. The method of claim 1 in which the polymer is a thermotropic aromatic copolyester which is processed at a temperature above its glass transition temperature and slightly below its solid-to-mesophase transition.

4. The method of claim 3 wherein the polymer is chosen from the group consisting of (1) where R is , or (2) where R is ,or (3) (4)

5 . The method of claim 1 in which said polymer is in the form of a continuous solid.

6 . The method of claim 1 in which said polymer is in the form of a powder and the method includes the step of compacting said powder before introducing it to said die.

7 . The method of claim 1 in which said polymer is in the form of a gel.

8 . The method of claim 1 including supplying said polymer as a solid hollow tube and enlarging the diameter of said tube while thinning the thickness of the walls of tube.

9 . The method of claim 8 including slitting the enlarged-diameter tube longitudinally to produce a sheet.

. The method of claim 1 wherein said material is a powdered metal.

11 . The method of claim 10 wherein said metal is chosen from the group consisting of aluminum, titanium, aluminum alloys, titanium alloys and fiber-reinforced aluminum and titanium.

12 . The method of claim 1 wherein said temperature is attained by circulating heated oil through said rollers.

13. The method of claim 12 also including air-convection heating means for preheating the material stock just prior to entry between said rollers

14. The method of claim 1 comprising a plurality of said extrusion rolling dies and the extrudate is sent from one said die to a succeeding said die.

15. The method of claim 1 wherein said method is continuous.

16. The method of claim 1 comprising performing said solid state deforming at a deformation ratio of at least 4.

17. An extrusion rolling die for carrying out the method of claim 1 and having a periphery for producing high modulus products having a crystalline melting point, comprising: a pair of rota-table rollers providing a rage of rotation having an input side and an output side and die-providing exterior shapes forming the convergent geometry of the die and confining the entire perimeter of material extruded therethrough at a rate or extrusion of the material and reducing the material overall cross-sectional area, means for keeping said rollers at a temperature near but below the crystalline melting point of the material to be processed, force-applying compression means for extruding the polymer through said rollers, and gear control means driven by the application of external force for controlling the rate of rotation of the rollers so that the rate of extrusion of the material is substantially the same as the rate of rotation of the rolling die surface.

18. The die of claim 17 having a supporting frame with a distal end and wherein said control means comprises:
a chain-engaging pulley wheel rotatably mounted on said distal end of said frame, one said roller having a chain-engaging wheel rigidly mounted thereon, a gear train means for keeping the two said rollers at identical rotational speeds, a chain looped around said two wheels and cable means attached at one end to said pulley wheel adapted for attachment of its other end to the extrudate from said die.

19. The die of claim 18 wherein said cable means is attached to said extrudate by a clamping block attached to said cable means.

20. The die of claim 17 having material feed means at the input side of said rollers.

21. The die of claim 17 having a circular periphery and a mandrel going centrally between said rollers said mandrel having a conical portion with an enlarged circular cross-sectional area on the output side of the die for feeding a tube and enlarging its diameter and simultaneously thinning the tube walls.

22. The die of claim 21, having a second pair of rotatable rollers around the enlarged-diameter portion of said mandrel, said control means being connected there to maintain said rates of extrusion and rotation at equal speeds.

23. The die of claim 20 having air heating means with a heated-air outlet adjacent to said material feed means for preheating said material before extrusion.

24. The die of claims 20, wherein said material feed means comprises a hydraulic piston.

25. The die of claim 20 wherein said material feed means has parallel side walls.

26. The die of claim 20 wherein said material feed means has converging parallel side walls.

27. The die of claim 17 wherein the contained convergent geometry of the input side of the die has an exponentially shaped profile.

28. The die of claim 17 having liquid heating means, circulation means in said rollers for circulating heated liquid through said rollers, and means connecting said heating means to said circulation means.

29. The die of claim 28 also having air heating means with air outlet for heated air adjacent said rollers.

30. The die claim 17 having powder compacting means on the input side of said die.

31. The die of claim 17 wherein the rollers are provided with their exterior shape by separate sleeves mounted on the rollers and having the desired exterior shapes.

32. The die of claim 17 wherein said force applying means comprises means to apply force sufficient to achieve a deformation ratio of at least 4.