DE2416210A1 - METHOD OF MANUFACTURING AN EXTRUDATE - Google Patents

Description

PATEWTANWALTSCÜRO TlEDTKE - - BüMLlNG - KlNNE 24 IbZ I

TEL. (089) 53 96 53-5S TELEX: 524 845 tipat CABLE ADDRESS: Germaniapatent Munich

8000 Munich 2

Bavariaring 4 April 3rd 1974

P.O. Box 202403

B 5923

Imperial Chemical Industries Limited London, UK

Process for making an extrudate

The invention relates to an extrusion process for extruding crystallizable synthetic polymers Materials.

In the journal "Polymer", January 1973, pages 16-20, is a technique for the production of crystallized oriented fibrils of a polymeric material described by extruding the polymer through opposing nozzles, wherein the polymer is subjected to a velocity gradient which the polymer molecules in the direction of extrusion aligns and induces crystallization of the aligned molecules. The fibrils created in this way have one high strength modulus.

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A modification of this technique has now been developed, which allows a single extrudate to be formed. The extrudate can be in the form of a film.

According to the invention a method for the production an extrudate of a crystallizable synthetic polymeric material which consists in separating Forms streams of a melt from the polymeric material, these converge or can flow together, whereby the polymer melt is subjected to a velocity gradient at the confluence of the currents, so that the molecules of the polymer melt relative to one another be aligned, wherein this polymer melt is extruded through a nozzle and wherein the temperature and pressure of the melt at the point at which it is subjected to the velocity gradient, is such that crystallization of the aligned Molecules is induced.

The invention is particularly applicable in the manufacture of films conventionally made from a Slot dies are extruded onto a casting drum, on which they are quenched before the subsequent orientation step, or which are extruded in a conventional manner from an annular slot nozzle, from where they are then inflated. The invention is also applicable to hot melt coating processes where film-forming polymers such as polyethylene (higher or lower Density), polypropylene, copolymers of propylene and ethylene with themselves or with other C ^ olefins and polyamides a support body made of, for example, a textile web, made of paper

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- 3 or another polymeric film is extruded.

Examples of other crystallizable film-forming polymeric materials are polyesters such as polyethylene terephthalate, Polyethylene oxybenzoate, polyethylene naphthalate and polyethylene 1: 2-diphenoxy-4: 4'-dicarboxylate.

Other components such as stabilizers, pigments, dyes, fillers and blowing agents can be incorporated into the mass from which the movie is created. Of particular interest is the production of foamed films using a Two component blowing agent system as described in British Patent 1,220,053.

The crystallized, aligned polymer molecules are generated by drawing the molten polymer material exposed to a velocity gradient so that the polymer molecules are aligned and crystallization initiated will. The crystallization takes place on the aligned molecules, as they are caused by the application of the velocity gradient of a Be subjected to tensile stress. The extrusion temperature should be above the crystalline melting point of the polymeric material so that not all of the extrudate crystallizes and solidifies and blocks the extruder nozzle.

The pressure applied also influences the start of crystallization. So it is possible to crystallize at temperatures induce above the crystalline melting point if

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the pressure is increased. The extrusion temperature and the pressure should therefore be chosen so that the mass of the
Polymers crystallize, only that part of the polymer melt that is put under tension.

Typical operating conditions for various polymeric materials are given in the table below.

Polymer Tempe
rature
( ⁰ C) pressure
(Atmospheres) Speed
gradient
(sec I) high density
Polyethylene
MFI O, 3 ¹
Polypropylene
MFI 0.5-1 ²
Polypropylene
MFI 4-5 ²
"Nylon" 66
Po Iy ä thy le n-
terephthalate 135-160
165-230
165-190
265
270 100-1000
100-1000
100-1000
1000
1000 Area preferred 10-250 50
10-250 50
100-2500 500
1000-25000 5000
1000-25000 5000

1. Melt flow index measured at a load of 2 kg and 190 C.

2. Melt flow index measured at a load of 2 kg and 23O ° C. The increase in temperature made it necessary to increase the pressure and / or the velocity gradient and vice versa.

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At the bottom of the specified in the table
Temperature range, a pressure and / or a speed gradient from the lower end of the specified range can therefore be used, while at higher temperatures pressures and / or speed gradients which are greater than the minimum specified in the table may be required.

A nucleating agent can be added to the polymer to prevent the crystallization of the aligned polymer molecules to support.

Also, since polymer melts have some heat memory, it may be desirable to use a polymer in the process that has been previously crystallized and not at a temperature above that for such a period of time
crystalline melting point was kept that memory
is lost to the previous crystallization.

• The velocity gradient is obtained by combining
two converging streams of a melt generated. The polymer at the interface of the converging streams is accelerated and thereby subjected to a velocity gradient.

The separate streams are expediently generated by dividing a single stream; of course, im If necessary, currents from separate sources can also be used.

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In a preferred embodiment of the invention three streams of polymer melt are allowed to flow together: two fast moving streams that are on either side of one Converge current traveling at a slower rate in the direction of extrusion. This is preferably achieved by divides a single stream into three streams. The central current is carried out between a pair of protruding links that extend on in this way form a narrowed flow path, while the other flows into channels with a larger cross-section than the narrowed one Durchlußweg are passed. The polymer melt can thus move faster through the channels than between the preceding ones Divide so that the currents emerging from the channels move faster at the point of confluence as the central stream passing through between the foregoing members.

The invention is illustrated in the following with the aid of a schematic Drawings of several exemplary embodiments explained in more detail.

Fig. 1 is a cross-sectional view of a nozzle having two converging polymer streams;

Figure 2 is a view corresponding to Figure 1 showing a nozzle having three converging polymer streams shows;

Fig. 3 is an illustration corresponding to Figs. 1 and 2 showing a nozzle with a series of convergent 409843/0810

- Figure 7 shows yawing currents;

Fig. 4 is a cross-sectional view of a nozzle assembly for generating tubular film;

Fig. 5 is a view corresponding to Fig. 4 showing an alternative nozzle arrangement;

Figure 6 is a cross-sectional view of a nozzle assembly for removing and recycling a portion of the unoriented polymer melt;

Figure 7 is a cross-sectional view of a nozzle assembly for axial orientation of a tubular Extrudate.

Fig. 1 shows a slot nozzle which is formed by upper and lower nozzle parts 1 and 2, respectively. These parts limit one slot-shaped extrusion opening 3. Between the parts 1 and 2 hangs with the help of spokes 4 a torpedo body 5. Polymeres can can be fed to the nozzle via the inlet channel 6. The torpedo 5 divides the polymer in channel 6 into two streams which are deflected into channels 7 and 8 on either side of torpedo 5. At the downstream end of the torpedo 5, the currents of the channels 7 and 8 flow together, whereby the channels 7 ■ and 8 polymers located near the torpedo 5 subjected to a velocity gradient as the streams recombine

409843/08 1 day

The velocity gradient directs the polymer molecules in the direction of extrusion, the temperature and the melt pressure being selected so that the speed gradient Induced crystallization. The aligned polymer molecules are crystallized in this way, the out of the opening 3 exiting molten extrudate has a core of crystallized Has material that is oriented in the direction of extrusion and sandwiched between two unaligned layers of the Polymers is located. The core of the crystallized, aligned polymer gives strength to the otherwise melted extrudate.

In Fig. 2, a preferred embodiment of the nozzle is shown. Here the torpedo 5 of Fig. 1 is through a pair replaced by spaced members 9, 10, which together form a third, central channel 11. This channel offers preferred the flow of material has a greater flow resistance than the channels 7 and 8 by having a smaller cross-section obtained or by, in the event that a part of the channels 7, 8 has the same cross-section as the channel 11, the bank length of this Partly selects smaller than the length of the channel 11. It therefore flows the polymer more quickly through the channels 7, 8 than through the channel 11. Thus, the channels 11 and 'the channels 7 and 8 converge on downstream of the end of the nozzle, the polymer emerging from the channel 11 is accelerated and thus accelerated in the longitudinal direction subject to acting speed gradients, so that aligned or aligned polymer molecules obtained will.

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Preferably, the melting temperature is by a suitable cooling device - not shown - set in the torpedo 5 (Fig. 1) or in the links 9 and 10 (Fig. 2).

FIG. 3 shows a further nozzle which corresponds to a series arrangement of two of the nozzles in FIG. Downstream of the links 9 and 10 is a second pair of spaced apart links 12, 13 which are held by means of spokes 14 are. The members 12, 13 define a central channel 15 and with parts 1 and 2 extensions 16, 17 of channels 7 and 8.

In the present case, not all of the Channels 7,8 located melt through the channels 18 and 19 located between the members 9 and 12 and 10 and 13 with the out The material exiting the channel 11 is combined, but some material is deflected into the channels 16 and 17, with this Material meets the polymer stream exiting channel 15. The flow of channel 15 comes from the polymer union formed from the channels 18 and 19 and the polymer stream from channel 11. The polymer emerging from the channel 15 is thus through the polymer emerging from the channels 16 and 17 subjected to further velocity gradients so that more polymer is aligned and crystallized.

4 shows the application of the invention in tubular film production. Here the nozzle has a radial design and is formed by the lips 20, 21 of the nozzle bodies 22, 23. The body 22 is supported with respect to the nozzle body by a tube 24. That

■ 4 0 9 8 h 3/0 8 1 h

Tube 24 has holes 25 at each end so that the nozzle body 23 via the supply channel 26 supplied polymers both along the annular channel 27 between the pipe 24 and the nozzle body 23 as also upward in the tube 24, through the holes 25 located at the end of the tube 24 remote from the supply channel 26 and the ring 28 can flow along between the tube 24 and the nozzle body 22. Thus opposing streams of polymer material meet at the beginning of the radial nozzle lips on top of each other, with the polymer at the interface or intermediate surface of the flows is subjected to a speed gradient in the radial direction. The polymer molecules are thereby aligned in the radial direction. Further, since the polymer is extruded radially, when it moves radially, its circumference is increased so that it also subjected to a speed gradient in the circumferential direction is, whereby the polymer molecules also in the circumferential direction be aligned. A planar alignment is obtained in this way of the polymer molecules. As before, temperature and pressure are chosen so that the crystallization of the molecules through the velocity gradient is induced. The resulting film can be axially pulled away from the nozzle body 23 and has a core of planar aligned and crystallized molecules, causing the melted film in all directions of the Film level receives an improved modulus of strength.

5 shows an alternative to radial extrusion. Here the nozzle body 22 is supported with the aid of a plunger 29 relative to the nozzle body 23, the pipe 24 not so far enough that it touches the nozzle body 22. The polymer is the

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Feed channel 26 conveyed along and flows down the annular channel 27 between the tube 24 and the nozzle body 23 along. Furthermore, polymer flows through the holes 25 at the end of the pipe attached to the nozzle body 23 and further through the annular channel 30 between the tube 24 and the punch 29. The two polymer streams converge at the open end 31 of the tube 24 and are passed through the Radial nozzle pressed radially outwards. As in the previous case, the polymer becomes one in the radial direction and in the circumferential direction acting speed gradients subject. The relative cross-sections and lengths of channels 27 and 30 are preferred selected so that the material located in channel 30 moves much more slowly than that in channel 27.

In the invention, only a relatively thin layer of material is subjected to the aligned crystallized state, this layer being sandwiched between two layers of molten material. In some cases, some of the melted Materials are removed to produce thinner products with a higher proportion of aligned crystallized material to obtain.

An example of a suitable device is shown in FIG. The nozzle shown in FIG. 2 is used here first however, a modification has been made to the effect that 3 cutting bodies 32 are provided at the outlet. This cutting body can be moved with the help of means not shown, whereby in the retracted position their inner edges 33 a Supply continuation of the walls forming the outlet 3. In pre

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In the retracted position according to FIG. 6, the edges 33 delimit one narrower outlet, the knife edges 34 dividing the polymer stream passing through outlet 3 and some of the molten one Material which forms the outer layers of the laminated body is diverted into return channels 35. This diverted material will returned to a section of lower pressure in the material feed or is taken under with the help of a suitable melt pump Pressure is set before it is fed to the feed channel 6 again.

In use, at the beginning of the extrusion process, the knife bodies are withdrawn and then advanced, to recycle some of the misaligned molten material.

In Fig. 7 a nozzle arrangement is shown which allows a tubular, from an annular slot nozzle to give the extrudate exiting a biaxial orientation. The nozzle consists of a body 36 and a rotatable outer one Nozzle lip 37. The inner nozzle lip is formed by a body 38 which can be rotated in the opposite direction to the nozzle lip 37. Nozzle bodies 39 and 40 of the type shown in FIG. 2, but in the form of a ring, are provided upstream of the body 38. That from the nozzle bodies Polymers exiting 39 and 40 are thus aligned and crystallized in the extrusion direction acting in the longitudinal direction. If the inner and outer layers of the extruded tube meet the rotating nozzle bodies 37 and 38, they will exposed in the circumferential direction running speed gradients and thus aligned in the circumferential direction and crystalline

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sated. The resulting tube has a layer of crystallized and circumferential on the inside and outside oriented material, while another section in the thickness of the extrudate crystallizes and is longitudinally oriented is.

example

High density polyethylene from MFI (19O ° C / 2 kg) 0.008

was with a melt temperature of 148 ° C in air at 20 ° C

-9 3

extruded, with a volume flow rate of 8 10 m / s was chosen. The nozzle had a slot with a width of 1 mm, a width of 10 mm and a bank length of 5 mm. Direct a pair of spaced links as shown in FIG. 2 were inserted upstream of the slot. Finally it was the stream divided into three separate streams which converged just before the slot. When the currents converged, it was the melt subjected to a velocity gradient that accelerated the flow and the molecules in the direction of extrusion aligned while crystallizing. The extrusion pressure was 40 atmospheres with a withdrawal tension of 5 kg. Here received a tape 8 mm wide and 1.3 mm thick; this is about the same cross-sectional area as that of the slot. (Without the stripping required an extrusion pressure of 270 atmospheres, and even under these circumstances the extrudate tended to plug).

This experiment was carried out using the same 409843/0810

Polymers with a melting temperature of 160 ° C repeated.

At this temperature the aligned molecules crystallized

not.

Extrusion conditions and belt properties for both experiments are given in the table below,

Air temperature melt temperature melt pressure Peel tension volume flow rate belt speed module

tensile strenght

("Modulus" means stress divided by elongation at 0.2% elongation, as it would be at a constant elongation rate of 5% per minute).

The data given above clearly show the through the melt orientation obtained increase in modulus and tensile strength. Same module and same tensile strength can be obtained by making a (not oriented) tape extruded and stretching the extruded tape in a solid state. Such a material drawn or stretched in the solid state is shown however, there is a strong tendency towards fibrillation. A ribbon oriented in the melt according to the invention does not readily lead to

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20 ° C 20 ° C 148 ° C 160 ° C 40 atm. 25 atmospheres. 5 kg 0.05 kg 8 χ 1O ~ ⁹ m ³ / s 8 χ 1O ~ ⁹ m ³ / s 0.8 mm / s 0.8 mm / s 3.3 GN / m ² 0.120 GN / m ² 120 MN / M ² 20 MN / m ²

Formation of fibrils.

The invention thus provides a method of allowing streams of polymer melt to converge can preferably converge on a slower moving stream, so that a portion of the polymer melt has a velocity gradient is subjected to thereby align or orient the polymer molecules. The temperature conditions and the pressure conditions are chosen so that the crystallization of the aligned polymer molecules is induced / the melt is then extruded.

4098 ^ 3/0810

Claims (5)

Claims [1.jProcess for the production of an extrudate from
a crystallizable synthetic polymeric material,
characterized in that separate streams are formed from a melt of the polymeric material, these streams converging
leaves, with the polymer melt at the point of confluence
the streams is subjected to a velocity gradient in order to align the molecules of the polymer melt and that the
Polymer melt extruded through a nozzle, the temperature and the pressure of the melt at the point at which it is subjected to the velocity gradient being selected so that the
Crystallization of the aligned molecules is induced. 2. The method according to claim 1, characterized in that the separate streams by dividing a single stream
can be obtained. 3. The method according to claim 1 or 2, characterized in that three separate streams are formed. 4. The method according to claim 3, characterized in that a single original stream in two faster moving Streams and a central, slower moving stream are split and the three streams are reunited, whereby the central stream accelerates and thereby the velocity gradient is subjected. 4098 ^ 3/081 ti 5. The method according to one or more of the preceding Claims, characterized in that the polymeric material is a Is a polyolefin, a polyamide or a polyester. 40 9 8 A3 / 08 1