Method and apparatus for circular extrusion involving rotation around the die axis

The present invention relates.to amethod of ״lujmfactur.i.ng <. sheet, board, tube or pipe, hereinafter referred to as shootlike structure, by extruding a material in a generally fluid state through a circular die or diepart rotating around its axis to form a structure with a direction of grain angularly arranged with respect to the forwarding direction.

A method and apparatus of this general type is known from U.S. Patent No. 3,2(31,8^7, in which two counterrotating exit parts form two circular helically twisted arrays of continuous fllaments, which join at their cross-points due to the shape of the orifices, by which a netstructuro la formed. Thia and close ly related methods are widely used tut have drawbacks or limitations, e.g in that the mesh has to be relatively wide and the. filaments relatively coarse.

Another family of methode and apparatus of the type in queetion ie diecloeod in U.S, Patents Noe. 3,505,102, 3,505,744 and 3,677,873. The basic idea of these patents is to join streams of different ma.terials to fluid sheet form in an internal chamber of the die and screw the streams, at the same time as they are strongly attenuated, by means of a rotating internal part. Thus the die may consist of! a fixed row of internal orifices which extrude the components in intersperse'! relationship, a first annular collecting chamber, a rotating circular row of partitions, and a second annular collecting chamber directly leading into an annular exit slot. The interspersed arrangement of different materials is hereby utilized to form a sheet with a fibrelike substructure of lamellar shape which can be applied to obtain, in combination with a layer of different grain, a high-strerigth film. Alternatively, the sub-, structure may be disrupted to obtain a non-woven fabric. Since the attenuation takes place in several steps, very thin lamella can be achieved, but due to a cutting of the lamellae into discontinuous lengths and a very irregular attenuation, both effects caused by the partions, the substructure is uneven with a negative effect on the strength properties. Another route disclosed in the same three patents consists in rotating the row of internal orifices, which extrude the components in interspersed relationship, and immediately join the streams in thecollecting chamber directly leading to the exit elot. There is hereby obtained continuous and very even lamellae, but much higher speed of rotation is required to achieve the same low thickness of the lamellae. However, the melt orientation created by such high rotation leads to high elastic tensions in the tube also after the exit from the die, which gives the/ tube a very pronounced tendency to shrink to a smaller diameter.

The control of the extrusion is therefore difficult.

A further method and apparatus of the abovementioned general type is known from U.S. Patent No. 3.632,711. The rotation is here a relative rotation between two concentrical dieparts forming two cylindrical walls in an annular passageway through which the material is extruded on its way to a cylindrical exit slot. Two or more components are passed side-by-side through said chamber, whereby the streams are smeared out to fine layers. These layers are subsequently combed by means of inwardly pointing teeth assembled on the two rotating walls, whereby the sheet acquiree a fibrous substructure with crisscrossing grain. The substructure is either utilized for production of high-strength film, or it is disrupted to a nonwoven fabric.

However, this method and apparatus have several drawbacks. One is that the fine teeth are difficult to maintain. Another that the attenuation (melt-drawing) takes place in a direction which is different from the combing, whereby the fibres of the substructure get notches or other irregularities.

The present invention has for its object to manufacture products of the abovementioned general type, which includes a great variety of products, without the abovementioned drawbacks.

The invention is characterized by the steps of, feeding the material to said circular die, said die having a rotating exit with a hollow center, and extruding the material through said die to the exit, discharging the material from said exit either in form of a circular array of free filaments of any shape including ribbons, or in continuous sheet form while stretching the discharged fluid material by said rotation, collecting the material on conveying means which at least in the zone of collection has a generally cylindrical shape concentric with the axis of rotation of the die and is for 3 49017/2 warded through the hollow center of the die, and while tho material is conveyed or immediately prior hereto, solidifying the material and, if necessary to achieve a self-supporting sheet structure, combining the material with one or more further materials.

Since the extruded material is directly wound on convoying means, the abovementioned drawbacks are eliminated. Thus the transverse elastic ί tension produced by the rotation now becomes an advantage, since it helps to transfer tho material precisely. Further, the location of conveying means close to the die exit enables a deeper draw-down, whereby very fine filaments and/or high melt-orientation is obtained. A further significant advantage of the invention is that it enables the production of sheet with higly fluid-drawn transverse structure made from such fluid extrudable materials which otherwise easily break during drawing, e.g. molten polymer of irrogular composition, molten or dissolved polymer or pre-polymer with high contents of solid staple fibres, and extrudable masses of fibres in swollen state, such as swollen collagen fibres and the like.

The use of conveying means through a hollow center of a circular extrusion die is known, but only in conjunction with a fixed circular die. In such known process the conveying can either take place without rotation of the means, by which there is not formed any biased direction of grain in the extruded pipe, or alternatively, the conveying means may rotate at the same time as they convey the pipe forward. The last possibility, however, is generally impractical since the pipe is then discharged from the machine in rotating state.

Depending on the intended use and the material extruded, the stretching by rotation can bo carried out either in a free space between the exit orifice(s) and the generally cylindrical means or in a generally annular shear-chamber defined by the exit part of the rotating die and the generally cylindrical conveying means, whereby the rates of feed and convoying are adjusted to each other so as to maintain said chamber filled with material in a substantially pressurefree state. The. stretching in a shear-chamber between die and conveying means provides for the most efficient conveying of the mate- rial and therefore is generally preferable in the case of materials which are difficult to stretch, while the stretching in a free space has an advantage, e.g. for the construction of the apparatus since the friction between the fluid material and the apparatus parts (exit of the die and conveying means) is avoided.

4a

The invention is very suitable for producing continuous sheet- \ like structures (as opposed to open fabric structures) exhibiting a substructure composed of continuous or almost continuous filaments. This can be achieved by discharging an array of free filaments from the exit of the rotating die while adjusting the rates of feed and conveying of material, and speod of rotation, to one another so as to lay-up the filaments sufficiently densely on the conveying means.

Another embodiment which also primarily aims at the manufacture of a continuous sheet-like structure with a transverse, highly melt-stretched fibrous substructure, is characterized by extruding different materials interspersed with one another and merging the streams with one another, The filamentituous sub15 structure hereby becomes particularly distinct. Said merging can be carried out before the exit from the rotating die, and/or in a shear-chamber between the exit and the conveying means, and/or at the collection of free filaments on the conveying means. A comparison between the three possibilities is given in connection with the description of figs. 5 to 8.

The interspersed extrusion and merging of different materials can also with advantage be used for manufacture of structures other than continuous sheet-like structures, e*g. for nonwoven fabrics. No matter whether continuous sheet structures 25 . or other structures are taken up on the conveying means, the merging of streams of different materials can with advantage be carried out in a regular pattern which at the same time as it involves a side-by-side arrangement, also involves an embedment, at least in part, of a second na terial in a first ma30 terial. There is hereby generally achieved higher strength ih the manufactured product.

An example hereof is the procedure explained in connection with figs* 5 to 7 in which one of the lamella components also forms continuous surface layers so that the lamellae of 35 a different component are fully embedded. A more pronounced incorporation, very useful e.g. in connection with the manufacture of high-strength film, is characterized by extruding

- צ the first material, immediately prior to the merging, through a multitude of relatively long slots extending in the direction of the axis of the rotation and arranged in a circular array, and extruding the other component through smaller orifices collected in groups in the same array between said longer slots, said groups being preferably lineary groups extending generally axially.

The fibrous substructure of a continuous sheet structure manufactured according to the invention needs neither be based on a separate extrusion of filaments nor on a regular interspersing of different streams, but can also be a random subatructure, however, with a distinct direction of grain. Thus, an embodiment of the invention is characterized in that the discharged material is an inhomogenuous blend of fluid polymers and a continuous sheet structure is collected on the conveying means. Continuous sheet structures produced in this manner are very useful, e.g. as plies in laminated, oriented high-strength film, or in connection with a subsequent swelling (dissolving) of one component and fibrillation to a coherent splitfibre web, c.f. U.S. Patent No. 3,499.822. In both cases, the use of the present invention enables a particularly strong melt-drawing which is highly advantageous for the strength properties of the final product.

Another embodiment of the invention yielding a random substructure, is characterized in that the discharged material is a blend of fluid polymer material and solid staple fibres, and a continuous sheet structure is collected. Under the term staple fibres is also included pulp fibres. The incorporation of such fibres can be for filling and/or reinforcement purposes. The present invention provides for a very efficient transverse alignment of the solid fibres, and, due to the conveying, surprisingly high contents of fibres are allowable.

A further use of the invention in connection with the obtaining of a highly melt-drawn, random fibrous substructure, consists in discharging a molten polymer capable of segregating into different distinct fibrous polymer fractions when stretched

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in molten state and solidified, preferably a polymer with high contents of extraordinary high molecular weight substance, and collecting a continuous sheet structure. This embodiment is particularly suitable for manufacture of layers in lami5 nated high-strength film.

Alternatively, the discharged material can be a polymer with contents of a solvent or swelling agent, whereby a continuous sheet structure is discharged from the exit, and the solvent or swelling agent is caused to segregate in the polymer during 10 the conveying. This embodiment is particularly suitable for manufacture of film for fibrillation.

A similar embodiment of the invention is characterized in that the discharged material is a polymer which contains dispersed droplets or bubbles of liquid matter, and a continuous sheet 15 structure is collected.

An important aspect of the invention relates to the feeding of material into the rotating die and the extrusion towards the exit of the die, and has for its object to allow fast rotations in simple manner without the abrasion of sealings and 20 other problems connected with extrusion of very viscous material through revolving fittings of a big diameter. Accordingly, an embodiment of the invention is characterized by feeding in substantially pressurefree state at least one strand of the material in generally fluid state into a circular inlet ori25 fice or circular array of inlet orifices of the extrusion die, while distributing the material evenly over the circumference by the rotation of the die, setting-up an extrusion pressure at said inlet be shear action, and hereby extruding the mate- : rial to the exit of the die while maintaining it in form of a tubular stream or a circular array of streams.

Depending e.g. on the flow-properties of the extruded material, different measured can be preferable to create the extrusion pressure e.g.:

'יי a) a rolling or scraping action against the inlet orifice or !

. . ' ' | orifices, c.f. figs. 1 and 6, fa \

b) forming at least a circular inlet orifice of the conduit system from two parte which are rotated relative to each other (at the same time as there is produced an overall rotation of the material in one direction) and corrugating the surface of at least one of said rotating parts in engagement with the material in an oblique direction with respect to the tangency, 80 as to help the pumping towards the exit - cf. fig. 2,

'.׳. ..׳׳ י. ' . q). similar to point b), but with use of the Weissenberger ef/feet which means that a visco-elastic material under rotational shear between discs drags towards the axis of the discs ;;'due to the elastic forces created by the shear. In this case, it is not necessary to make any surface corrugated, but it is a must that the passageway leads generally inwardly in the zone under shear and that the material used is visco*. elastic - cf. fig. 4,

d) by a fixed insert (e.g. ringformed) in a circular inlet ori20 fice relative to which one or both surfaces of the inlet orifice rotate, cf. fig. 3. The insert and/or orifice surface(s) can be corrugated in analogy with point b) above, or there can be made use of the Weissenberger effect described in point c) above.

When extruding tubular items and using relative rotations as described under points b) and c), it is generally preferable to form the whole die of two parts moving relative to each 0ther from inlet to exit of the conduit. In this embodiment the construction of the die is particularly simple.

It is of course necessary to adjust to each other, on one hand the velocity by which the material is fed to the die (normally from a conventional extruder) and on the other hand the velo— city of the rotation or rotations which cause the pumping of material through the die. Within limits, however, there is a selfcontrolling effect in the means described above under a) to d). Thus - to take b) as an example - the more the inlet orifice is filled with material, the greater will be the p.ortion of the corrugated surface which is covered with material and which therefore participates in the pumping action.

As already mentioned, the grain formed in the sheetlike material according to the invention can in many cases with, advantage be a grain based on random blending. In order to carry out such blending in expedient manner, an embodiment of the 10 above described rotating extrusion with substantially pressurefree feed is characterized in that different materials are fed at different locations to one and the same inlet orifice and are blended during the passage to the exit. One of said < different materials can be a mass of solid staple fibres from 15 & substance which does not melt or decompose at the temperatures of the extrusion. The material fed simultaneously with the solid fibres can be molten or dissolved polymer, or a pre-polymer. Due to the distribution by the rotation of the die around its axis, and to a blending immediately prior to the extrusion, 20 blends with surprisingly high contents of solid fibres can be extruded in satisfactory eveness.

The advantages of interspersed extrusion of separate streams have also been mentioned above. In conventional circular coextrusion, there are constructional complications in obtai25 ning an even circumferential distribution of several components. In this connection, the pressurefree feed allows a significant simplification, and accordingly a preferred embodiment is characterized in that different extrudable materials are fed into different circular inlet orifices or different 30 circular arrays of inlet orifices, whereafter the materials are brought into interspersed relationship with one another, and are extruded in such relationship. (Reference to figs. 5,6, and 7).

Depending on the special circumstances, the collecting and con35 ' veying of discharged material can be carried out in different manner. A particularly precise collecting is chaieved when the material is collected on endless moving means, from which the material ie finally removed. A very practical way of estab- 9 lishing such cylindrical continuous conveying is by one orseveral continuously moving belts, which in the zone of collecting are helically wound on a support with the edges immediately adjacent so. as to form an essentially cylindrical body in said zone, said helically wound belts being subsequently unwound from said support, while cutting-up the collected material at the location where two adjacent edges are separated from each other.

Alternatively, the conveying means can consist of or comprise 10 a rotating generally toroid shaped mandrel. This can be made a particularly solid construction able to take up high torsional forces.

However, simplest and in many cases fully satisfactory is to use as conveying means a continuously forwarded flexible sheet 15 supported by a fixed mandrel. .

The material as collected on the conveying means can be very fragile due to the fibrous generally unidirectional substructure, and may even consist in a transverse array of unconnected filaments.

Therefore, in order to bring the material into self-supporting state, it is often necessary to combine the material with one or more further materials. Such combination can comprise lamination with a reinforcing substance while the material is conveyed by the conveying means. As an example hereof, the rein25 forcing substance is fed between the conveying means and the extruded material. As another example hereof, the sheet used as conveying means is maintained as a layer in the final sheetlike structure. This is a particularly simple and practical manner, when the sheet is a flexible sheet supported by a fixed mandrel as mentioned above. (Reference to fig. 4).

Alternatively, or additionally, the rotating extrusion accor t ' ' ' .

ding to the invention can be carried out from several rotating dies working in line with use of one and the same collecting means, and with the rotations so adapted that the different dies produce a different direction of grain to obtain a crosslaminate. (Reference to figs. 1 and 10).

As mentioned before, the invention enables a processing of צ fluid materials which are otherwise difficult to extrude. This opens a simple way to extrusion of substructured very valuable sheets from dissolved or swollen polymer substances, from blends of such substances with solid fibres, and from blends of solid fibres and pre-polymers. In such cases, a rather prolongated i solidification process can be involved, and it is in this con״ nection a great advantage that the material is conveyed.

Thus an embodiment of the invention comprises extrusion of a dissolved or swollen polymer, or a blend of dissolved polymer and solid fibres, and a solidification of the material by co״ !5 agulation and/or drying.

f.' . .

In similar way, a further embodiment comprises extrusion of a blend of solid staple fibres and a .pre-polymer, and solidification of the material by after-polymerization on the conveying means.

The invention further relates to an apparatus for carrying out the method, comprising a rotatable circular extrusion die with a hollow, open core zone, and provided at the inner circum״ ferential wall, or an end wall, or at a boundary between such walls, with a circular exit slot or a circular array of exit

2צ slots, the apparatus further comprising means for feeding fluid extrudable material into said die and means for extruding the material through the die to the exit, and means for continue ously passing generally cylindrical conveying and collecting means through the core.

Different embodiments of this apparatus appear from the above discription of the method.

. 1 . .

The invention will now be described in more detail with reference to the drawings of which;

Fig. 1 is a schematical perspective view illustrating a preferred embodiment of the method and apparatus according to the invention, showing a pressurefree feed to a rotating die, external rollers as means to set up the extrusion pressure, the 5 use of two counter-rotating independently extruding dies around the same mandrel to produce criss-crossing directions of grain, and a set of conveyor belts on the mandrel as forwarding takeup means, fig. 2 is a schematical perspective view with partial sections illustrating another preferred embodiment of the method and apparatus according to .the invention, showing as means to setup the extrusion pressure two disc-formed dieparts moving with different velocities and supplied with internal guide vanes, further showing a toroidal mandrel as conveyor, and illustra15 ting a consolidation by chemical treatment while the extruded product is conveyed on the mandrel, fig. כ is a perspective view with partial sections of an embodiment of the rotating extrusion device in connection with the invention, in which the extrusion pressure is set-up by means of an inserted fixed plate, the drawing futher serving to show a suitable arrangement of drive and bearings, i ' ~ 'Γ ; . 'r fig. 4 is a schematical perspective view with partial section of still another preferred embodiment of the method and apparatus according to the invention, showing a separate feed of solid staple fibres to the rotating die to be blended with the polymer by the relative rotations, and further showing the use of a fixed mandrel, and as conveying means a sheet which is folded over the mandrel and is laminated with the material collected from the rotating die and which forms a layer In the final product, figs. 51 6, and 7 are three different sections which show in principal manner -a.pref erred embodiment of the method and^zapparatus in which two sets of streams of different composition are merged with each other generally side-by-side in the rotating die and are subsequently attenuated to a fine structure in the space between the die exit and the mandrel, the drawings further showing the use of ecrabers at the two inlet grooves to the rotating die as means to set-up the extrusion pressure, fig. 8 is a section through the exit part of the rotating die and the mandrel which illustrates, also in principal manner, a modification of the embodiment shown in figs. 5, 6 and 7, by which the two sets of streams are brought in interspersed relationship within the rotating die, but are extruded and attenuated separately and are merged into a sheet at the collection on the mandrel, fig. 9 is a detail shown in perspective of fig. 8 with special orifice shapes adapted to produce continuous filaments of one component wholly embedded in another component, fig. 10 is' a schematical perspective view, of a further, preferred embodiment of the meithod and apparatus according to the invention, illustrating the use of a helically moved conveyor belt in the hollow center of the die.

The apparatus of fig. 1 comprises a fixed mandrel (1) provided with three endless conveyor belts (2) that mainly cover the surface of the mandrel. After the cooling of the film, it is cut up and rolled on bobbins (4) and (5).

The apparatus shown also comprises a composite die (3) with two counter-rotating single dies (6) and (7) each part fed pressurefree from two extruders of which ohly two (8) and (9) are shown, while the streams emerging from the two other extruders are indicated by (10) and (11). The rollers (12) which press the polymer(s) into circular inlet grooves (13) can conveniently be heated by hot air, e.g. from the inside. They may be substituted by scrapers heated e.g. by a cycloterm.

The extrusion die (3) may be heated from at least one location / as the rotation of the die will distribute the heat. Induction heating may be used, and the temperature ma־y be controlled by pyrometers.

Each inlet groove (13) is connected with one or several exit orifices (not shown). The composite extrusion die can be fed from fewer or more extruders and the die could consist of one, two or more rotating or counter-rotating single dies, if convenient with fixed extrusion dies in-between.

' A pronounced advantage by the combination of several single dies around one mandrel is the fact that the layers of a composite sheet may be extruded successively over each other, but under relatively independent circumstances, so that each layer may be treated individually, e.g. as to heat. Generally, 15 the extrusion can take place out of a circular exit slot or slots or out of one or more orifices or׳ out of a circular row of orifices. The exit orifice(s) or slot(s) can be situated on the inside surface of the extruder die, which is convenient by fast rotation, at the end surface of the die, e.g. by slow 20 or no rotation but most practically at the boundary between these two mentioned surfaces, as the conditions for simultaneously controlling and cooling the polymer stream at this point are optimal.

While it is expected that the rolling or scraping action de25 scribed in connection with fig. 1 is especially efficient in connection with material of particularly low fluidity, e.g. very high molecular weight polymers, the extrusion die of fig. 2 is preferred in many other cases due to its simplicity. The die - which is fed with a pressurefree stream (stcand) from an 30 extruder outlet (14) - consists of two unconnected parts (15) and (16) which define a conduit consisting of the inlet orifice (17) and in immediate connection herewith the exit orifice (18) .(There may however, conveniently be a longer passageway between the inlet and exit comprising one or several widened chambers for further improvement of the distribution). j A

The two parts (15) and (16) are held in position and in the proper distance from each other through external bearings and are driven at different velocities through gear wheels (for details regarding the arrangement of bearings and gear wheels, see fig3 ״). The different velocities are indicated by the two arrows of different lengths. In order to achieve an efficient pumping action, the walls of the inlet orifice can be supplied with suitable vanes (19) which here are only shown on one of the parts* However, a sufficient pumping action can often be obtained without such vanes or corrugations due to the known tendency in visco-elastic material to drag inwardly when &pplied between discs which counter-rotate (the Weissenberger effect).

At the same time as the two parts (15) and (16) move relative to each other, it is essential that the material fed into the die is rotated on the whole in order to become properly distributed. The arrows indicate that they rotate at different velocities in the same direction. It is also allowable to let one stand still, or eveix to rotate the two parts in opposite directions, however, with different numercial velocities 80 that the material on the average Is always rotated in one direction.

Also in this embodiment the heating of the die can be by induetion, but due to the simplicity and compactness of the construetion, it is even possible to use open flames.

The exit orifice can be a plain circular slot extruding a tubular film - as indicated at (18) - or alternatively it can be supplied with corrugations - as indicated at (20) - adapted to extrude a circular array of filaments. When the distance from the die exit to the collecting mandrel (21) is short, the risk of breaking such fibres is greatly reduced, and a layer of fine fibres can be produced even from a rather unevenly corrugated exit slot.

The collecting and forwarding mandrel (21) is of toroidal shape and supported and continuously driven in the direction of the arrow (22) by means cf a series of driven wheels of which one >

'-י-(23) is shown .

In order to facilitate the support and drive, the inner part of the toroidal mandrel is supplied with a deep narrow groove 3 (24) with which the wheels fit. The wheels (23) may convent— ently be gear-wheels fitting with a gearing in the groove of the mandrel.

The invention is very suitable for materials which require a relatively complicated or prolongated treatment, e.g. coagu10 lation of dissolved polymer, or other chemical treatment. Such treatment is Indicated by the circular airless spray (25) from which e.g. a solution for coagulation can be sprayed onto the material. Similarly, there can be special heating and/ or cooling means and/or irradiation means in conjunction with 15 the mandrel.

Before being stripped off from the mandrel, the material !_scut, conveniently at the place of the groove (24), as shown by the rotating knife (26). There can further be scrapers or the like (not shown) to remove extruded material from the 20 groove.

Due to the lack of sealings, the rotating die can without much complication be manufactured with relatively big diameter, ©.g. 1 to 2 m. The toroidal mandrel can conveniently have a main diameter 5 to 20 times that of the inner diameter of the d*®» ^aud should in practice be assembled from several preferably hollow sections.

In fig. 2 the die lips at the exit rotate relative to each other. The shear at the exit can,introduce tensions which under certain rheological conditions can introduce instabilities during the draw-down.

ו The embodiment shown in fig. 3 takes care of this difficulty since it allows the two parts (15) and (16) to rotate at the same velocity (and in the same direction).

If the device is constructed for extrusion of an array of fi.^ laments, they can even be connected through an orifice-block at the exit (not shown).

The extrusion pressure is achieved by means of a ringformed insert (27) fixed through several supports of which one (28) is shown. There is hereby established a driving shear between the insert (27) and each of the parts (15) and (16). The insert is shown supplied with vanes (29).

There can also, or alternatively, be vanes on the inlet orifice surfaces of (15) and (16) or all vanes (corrugations) can be omitted. There is preferably fed one or several strands of ma, terial on each side of the insert (27).

This drawing further shows the bearings (30) and (31) for each 15 of the die parts (15) and (16).

In fig. 4 there is fed, simultaneously with the pressurefree feed of polymer from the extruder outlet (14), a web (32) of staple fibres which have melting point higher than the proceasing temperature of the die. This can e.g. be inorganic fibres such as glass, asbestos or rockwool. The feed is shown taking.place by means of a conveyor belt, but could also be by any other means. The die is shown without any internal vanes or corrugations, i.e. the extrusion pressure is set-up entirely by the Weissenberger effect. In fact, a slight corrugation is generally preferable, while strong shear forces may cause excessive breaking of the fibres. It should be noted that a direct feed of fibres into the die is highly preferable compared with a prior admixture of the fibres to the polymer and common feeding through (14).

Hereby a more even feed is secured with much less occurance of fibre breakage, whereby also much higher contents of fibres can be used.

The mixing of fibres and fluid polymer takes place partly at the feed, partly by the shear exerted during the passage to- 17 ~ wards the circular exit slot (18). The conveying and supporting take-up system consists of a mandrel (34) that is fixed by means not shown, and a flat sheet (35)» folded to a tubular shape around the mandrel (34). The sheet (35) may be produced e.g. from a flat die in line with the rotating extrusion or may be produced beforehand.

For the sake of clarity a space is shown between the mandrel (34) and the folded sheet (35)» but of course the sheet is lying towards the mandrel. The sheet (35) is pulled through the extru-, sion die over the mandrel as indicated by the arrow (36). When the polymer film in molten state leaves the rotating exit slot (18), it is strongly melt-stretched (attenuated) by which the fibres allign in the direction of attenuation, and is caught by the folded sheet (35) because of the elastic retention in the attenuated polymer. Thus it is wound around said folded sheet and forwarded along with it, obtaining a helical running direction of grain indicated by the arrows (37).

The forwarding of the sheet (35) is established by conveyor belts (38). The mandrel is preferably supplied with cooling means (not shown). The contraction of the extruded material can conveniently be matched by a gradual reduction of the diameter of the mandrel.

The conveyor sheet is produced from generally the same polymer as that wound unto it in molten state - or an adhesive can be applied - so that conveying sheet will be laminated with the other material to form a layer in the final product.

The product so manufactured is a tube or pipe with transverse reinforcement, suitable for improvement of the cushion strength. Further improvements of the strength characteristics can be obtained by two stations of rotating extrusion (cf. fig. 1) and/or by inclusion of longitudinally arranged fibres in the conveyor sheet. Further, if a relatively thick inner layer is desirable, the rotating extrusion can be carried out around such layer in generally tubular shape without any fixed mandrel located in the hollow of the die.

§ I ' ־. V ,

The feature of laminating the conveying means with the rota״.

tingly extruded material is neither restricted to the appllca-־ tion in conjunction with a feed of higher melting fibres to the rotating die, nor to the production of reinforced pipes or tubes, but has many other applications in connection with consolidation or reinforcement of rotatingly extruded material,

. . . . .. ׳

The die shown in different sections in figs. 5, 6, and 7 consists of three parts, viz. an inlet and manifold part (3?) and two separate exit half-parts (40) and (41). The three parts 10 are rotated around the axis (42) by drives (43),1(44), and (45), respectively, all in the same direction and all three with relatively high velocity. The two exit half-parts (40) and (41) move at the same velocity, and the relative velocity between these parts and the first part (39) is low compared to their 15 absolute velocities.

The die is- fed from two extruder outlets ,(46) and (47) into circumferential grooves (48) and (49), respectively, and the two different polymer materials (50) and (51) are brought under pressure by rows of scrapers (52), and are through two 20 rows of passageways (53) and (54) brought side-by-side in one array, and extruded through a circular row of alternating orifices (55) and (56) into a short annular collecting chamber .(57)» formed between the two parts (40) and (41), and ending in a circular exit slot (58) .

From the exit slot (58) the two sets of Juxtaposed streams are extruded in form of a composite tubular sheet (59) onto the cylindrical conveying means, here shown ae a toroid (60).

י

In the collecting chamber (57) and the exit slot (58), the interspersed (juxtaposed) streams still form a relatively coarse 30 configuration, limited in structure fineness by the pitch of the row of orifices (55) and (56), but when the composite still fluid sheet is attenuated between the relatively fast rotating circular exit slot (58) and the mandrel (60), each part-stream is strongly attenuated and is converted to a thin ribbon. By sufficiently high velocities the ribbons can be attenuated to a few microns thickness, or less.

The sheet has a lamellar structure, i.e« a sheet sub-structure constituated of thin elements which form an angle to the sur.^, face of the sheet. ,

Other methods of producing a lamellar structure are disclosed

e.g. in U.S. Patents Nob. 3,505.162, 3,565.744, and 3,677,873, where e.g. the applicatibns of this sub-structure is explained.

However, the method described above allows much stronger and regular attenuation and hence a formation of a finer regular substructure.

As it appears from fig. 7, the slots (55) are longer than the slots (56) and extend beyond both ends of these shorter slots. By the movement of the collecting chamber (57) relative to the orifices, the na terial extruded through the longer orifices will hereby normally by smearing-out form continuous layers on both surfaces. This feature as such is known from the abovementioned U.S. Patent No. 3,565,744 where it is further explained If such effects are not desired, there is no need to move the exit of the die in relation to the passageways (53) and (54). This is e.g. the case if it is desirable to produce a lamel20 lar substructure with all lamellae traversing from one sheet surface to the other. The orifices (55) ^and (56) can then preferably be of equal length and fully in array.

It is obvious that this embodiment of the invention can be carried out also with three or more components coextruded 25 and interspersed with one another.

In fig. 8 the juxtaposed extrusion system explained above is modified by omitting the independent two exit half-parts (40) and (41)_v and bringing the two sets of passageways (53) and (54) - in fig. 8 numbered (53 ^a) and (54 a) - all way through 30 to the exit of the die, from where the two components are extruded directly into the space between the rotating die and the mandrel (61) through a circular array of protruding exit orifices (62) and (63). The fibres of different materials, (64) and (65) respectively, are attenuated generally tangen35 tially with respect to the mandrel and are collected and forwarded on the latter in interspersed relationship.

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The protruding asymmetrical design of the orifices (62) and (63) secures the release of the material from the die.

If the exit orifices (62) and (63) are slots with a relative high elongation generally in the axial direction of the die, they will extrude ribbon-filaments which will be collected on the mandrel in overlapping manner, generally as a lamellar¹structure. A much more irregular, but more truely fibrous interspersed sheet substructure is usually achieved if the oriflees are relatively short in the axial direction.

^v In fig. 8 the exit orifices (62) for one component are very elongated slots while each of the orifices (63) for the other component is a row of small part-orifices (66). The ribbons extruded through (62) will be collected in overlapping arrangewent like shingles, while each of the filaments extruded through a part-orifice (66) will be embedded between a pair of the ribbons. The merged ribbons will hereby form matrix for the filaments of the other material. The diameter of the fibres so produced can e.g. be 1 to 20 denier, many times smaller than the thickness of the sheet, and thay can be arranged so densely that they occupy e.g. 5θ to 9θ% of the entire sheet.

Although several methods are known for coextrusion of continuous filaments in a sheet matrix, none of these enables the obtaining of similar fibre fineness simultaneously with a similar fibre density.

The sheet so produced is very suitable e.g. as a layer in high-strength film. For this purpose, the. filaments should pre;ferably consist of highly crystalline polymer (e.g. poiypropylene) and the matrix of a much softer and less crystalline polymer (e.g. low density polyethylene}.

Comparing the embodiment shown in figs. 5, 6, and 7 with the modification hereof shown in fig. 8 ( and 9), the merging of streams to sheet-form prior to the discharge through the exit slot generally allows higher throughputs and a higher degree of attenuation between die and mandrel without breakage, but optimal results are only obtained in this case if the meltviscosities of the different materials match relatively well.

When, on the other hand, the part streams are attenuated pres5 surefree and the Joining takes place on the mandrel (’of. fig.

8) there is no need to match the melt viscosities. A kind of compromise between the two systems can also be used, viz. to extrude the streams separately to the inside circumference of the rotating die, and adapt the velocity of the mandrel to the 10 total throughput of the two components so that the space be- tween die and mandrel is filled-up with polymer without ereation of an excess of pressure in this space. In other words, the space between die and mandrel serves as a collecting chamber in which the interspersed streams are smeared out by 15 the rotation. In this case, a protruding of the exit orifices ^; should preferably be avoided.

A further suitable way to utilize the Juxtaposed arrangement formed by the passageways (53) and (54) of fig. 5 is ^to Join the two (or more) different materials to an array of conjugent 20 filaments (which may also be ribbons) which are extruded 8eparately and collected and bonded together on the mandrel. Each conjugent filament may either have ordinary side-by-side or sheaf/core or any other convenient conjugent structure.

Instead of converting such conjugent filaments into a continuous sheet at the take-up on the mandrel, the throughputs, die rotation and mandrel velocities can be adapted to form an open set of spiral-laid filaments, which can subsequently be combined with similar conjugent filaments, laid-up by a die rotating in the opposite direction, cf. fig. 1. The two sets of filaments can conveniently be fused together, while still on the mandrel, at a temperature at which one component is molten and the other one solid.

In fig. 10, an endless continuously moved conveyor'belt (67)

18 wound helically around a fixed mandrel (68) in such a way that its left edge (69) fits with its right edge (70). Thus it acts, in the hollow center of a die (?1) as were it an endless cylinder continuously screwed forward. At the point where the belt is unwound, a knife (72) cuts the collected material u

in order to release the belt from the mandrel« If the die rotates very fast compared to the movement of the belt, the direction of grain will be almost ¼5° as shown by arrows (73). With the same belt, but over another mandrel (74) with axis perpendicular to (68), a similar lay-up is carried out, from another rotating die (75)» whereby another layer of material is formed with direction of grain (76) almost perpendicular to (73).

The driving means are not shown. The mandrels (68) and (74) can conveniently be supplied with special bearings to facilitate the movement of the conveyor belt (67). The procedure can be carried out without any use of a mandrel to support the belt (67) provided the latter has a convenient stiffness and is supported by suitable bearings.

The above description of the drawings has dealt with different aspects of the invention: different ways of setting-up an extrusion pressure in a pressurefree fed rotating die, the feed of solid fibres to the rotating die, the interspersing of different streams prior to the take-up on conveying means, different conveying means in connection with the take-up, and different ways of consolidating the sheet. The different aspects described can of course be combined in many ways other than those expressly mentioned.

Example 1.

Thia example illustrates the use of the invention for production of a/porous paper to textile like sheet with a fibrous ־ substructure, by extrusion of a polymer in dissolved state and segregation of the solvent within the sheet during the solidification.

For this purpose, the following procedure will be convenient«

A 50 0/0 solution of high density polyethylene can be used (density of the solid polymer« 0,96 , melt index« 0.2 according to the ASTM melt index specification, condition L). The apparatus shown in fig.

will be suitable, however without feed of fibres, and preferably provided with vanes in order to increase the pumping effect. Inner diameter of the die JOO mm, and temperature of extrusion 120°C. Two such dies should be used, in adjacent arrangement around the same mandrel; and rotating in opposite directions to obtain criss-crossing fibre grain.

The conveying sheet, forewarded over a fixed mandrel of diameter 280 mm, can conveniently be a nylon or polyethyleneterephthalate film taken from one bobbin, wound around the mandrel, brought back to flat shape after use, and finally collected on another bobbin for re-use.

The mandrel should be cooled from the inside. The polyethylene collected will hereby precipitate as a J-dimensional net-like substructure consisting of micro-fibres. A part of. the polyethylene will bleed-out, while most of the rest remains between the fibres as a distinct phase.

One extrusion die lays-up the polymer in a left-handed helical grain, and the other in a right-handed helical grain. Angles of about.70° with the mandrel axis are suitable.

After stripping-off from the conveyor film, the fibrous sheet should be stretched longitudinally, e.g. until the two directions of grain become essentially perpendicular to each other, taken as an average (the fibres will become partly randomized by the stretching). The sheet is hereby made more porous and flexible. The remaining xylene is finally removed by vacuum-drying.

Example 2.

This example illustrates a special use of the preesure-freely fed rotating.extrusion die, and the combined conveying and lamination, with the object to form a novel corrugated drainage pipe without 5 . corrugation of the inner surface. For this purpose, the following procedure will be convenient:

The die of fig. J should be used, however ending in e.g. 2 exit orifices (one would also be sufficient) of about 5 ™n diameter.

“ Polyethylene of density Ο.96 and melt index 0,2 (ASTM condition L as above), can.conveniently be used for this extrusion which is a melt-extrusion carried out e.g. at 200°C.

As conveying״and support means should be used a fixed mandrel and a pre-formed film, generally as shown in fig. 4. However, when the pre-formed film (ribbon) is folded around the mandrel, a gab of about 15 1 mm should be maintained between the edges instead of bringing the latter to overlap. The purpose of this gab is to make the final pipe permeable. This conveyor film, which is intended to form the inner surface of the pipe, conveniently consists of the same material as the polymer fed to the rotatable die.

The rotations should be adjusted to wind the two coarse filaments around the conveyor film in form of a double spiral (thread.) with a few millimeters pitch. A suitable temperature of the mandrel at the zone of collection will be about 100°C so as to allow the extruded double thread to fuse together with the conveyor film. A suitable thickness of the latter will be about 0,5 mm. Direct water-cooling should be applied on the pipe immediately after the collection.

The structure can of course be modified by arranging two or more ribbons instead of only one ribbon around the mandrel with a small gab between each pair of adjacent edges.

Example 3»

With the object of producing an impermeable corrugated pipe, the procedure of example J can be modified by placing a fixed circular die in front of the mandrel and extruding the conveyor film directly in tubular shape over this mandrel. In order to secure a smooth drawing of this tube over the mandrel, slot of the fixed die should be a few centimeters bigger than the diameter of the mandrel. Strong cooling should be applied where the still molten conveyor film meets the mandrel and is calibrated by the latter.

Example 4«

This example illustrates the use of the invention for production of a novel sheet-like meat-substitute with a bi-component lamellar structure, in which lamellae of protein are interspersed with lamellae of a polymeric softening agent. For this purpose, ths following procedue 'will be convenient 1

The apparatus of figs. 5» 6 and 7 should be used, however simplified by a) avoiding the relative . rotation between the inlet and exit parts, b) making ths internal extrusion Blots of even length, and c) substituting the toroid-shaped mandrel by a fixed cylindrical mandrel surrounded by a conveyor film of oriented polyethyleneterephthalate film, which is taken from a bobbin and is maintained as a support when the final food product is packed. The conveying through the hollow in the center of the rotating die should be carried our vertically downwards.

A suitable first component is a solution of soyabeen protein in 10 $ NaOH solution, the concentration of the protein being adjusted to give :a viscosity about 100.000 cp at room temperature. A suitable second component (the softening component) is a solution of carboxymethyl-cellulose with addition of caramel (for sweetening and aroma). The concentration of the CMC should be adjusted to give the same viscosity as that of the first component.

A coagulating agent is rinsed over the extjuded material immediately־׳ after the collection on the film. This can conveniently he a solution of 20 NaCl and 10 $ lactic acid. Only the protein is coagulated.

On leaving the mandrel, the conveying film with collected foodstuff sheet should be unwound to flat form, whereafter the collected material should be partly dried in an oven. .