DE3916407A1 - Spinning stretching and injection of thermoplastic melt - has good properties in longitudinal direction achieved by spinning stretching and forming of extruded melt at two different stages - Google Patents

Abstract

A device and process for producing polymer extrudates used in conjunction with a conventional injection moulding machine are described Polymer melt is converted after extrusion into polymer strands by the use of a double spinning pump in two separate areas any by stretching and forming rollers. The strands can be reinforced with continuous fibres of glass, carbon or aramid and are subsequently cut into pellets by the rotating screw of an injection machine. The screw then plasticises, conveys and compresses the polymer melt in the final zone of the injection machine. With some changes the equipment can be applied to all injection machines. USE/ADVANTAGE - (P) produces polymer extrudates with chain alignment along the extrusion direction. High strengths are attained in this direction. Further processing retains the high longitudinal strength in the final product. (P) allows addition of reinforcing fibres.

Description

The invention relates to a method and a front direction for the production of polymer extrudates according to the The preambles of claims 1 and 8, respectively.

Polymer extrudates, e.g. Strands or foils are made Plastic raw material, preferably thermoplastics in Powder or granule form made from a Storage container fed to an extruder screw, there until heated to melt, provided with additives and closed Lich by means of a spinning pump through a spinneret is extruded. When the polymer melt passes through the spinneret can each set flow conditions through the many in the plastic extrudate of the polymer chains aligned along the direction of extrusion are. The extrudates produced in this way have one high tensile strength.

It is known that by aligning the macromolecules of the Polymers by stretching at a temperature close to that Melting point high strength can be achieved.

An overview of these and other manufacturing processes can be found in the essay by Eric Baer "Advanced Polymers ", Spectrum of Science, December 1986, Pages 150 to 160, especially page 152, right column, Figure 6 on page 155 and page 156, lower half of the middle column.

The specified procedures for aligning the macromolecules in polymers are used alternatively. You would namely the material produced by extrusion, such as Granules, staple fibers etc. again for a stretching pro heat zeß, so that would be achieved in the extrusion Alignment lost.  

In conventional injection molding of plastic parts the plastic, e.g. in the form of granules, possibly still with additives such as glass or carbon fibers in one length up to about two millimeters, heated to melting temperature and injected into a mold.

In addition to plastic extrudates from a thermoplastic outlet so-called composite materials are also produced in which at least two materials e.g. already combined and mixed in the extruder to certain that cannot be achieved by one material alone To achieve properties. Composite films of two or several polymer layers, coated polymer fibers or Matrix materials with particles embedded in the matrix, Short or long fibers are examples. The production such materials is complicated, but in today routine in many cases.

The invention has for its object a method and to develop a device with which to easily Way achieved a high alignment of the macromolecules , the method and the device so on can be developed in a subsequent Further processing of the extrudate the orientation mentioned is preserved and the opportunity is created Composite materials and plastic parts made of thermoplastics, also with fiber reinforcement.

This is the task for a method or a device according to the invention by the in the characterizing Tei len of claims 1 and 8 specified features ge solves.  

A basic idea of the invention is that by Flow through the spinneret obtained alignment of Macromolecules of the polymer and maintain improve by keeping the extruded polymer still in the state the melt is additionally stretched. The stretching takes place at extrusion temperature, which is in the range of the melting point of the plastic material used. Such a thing made plastic extrudates, e.g. in the form of fibers, Strands or foils have high tensile strengths and can be used in many ways, e.g. for the production of packaging films, of reinforcing materials for ver bundles or for the production of injection molded parts with high strength requirements.

Are preferred for a method according to the invention Thermoplastics used, such as polypropylene, polyethylene tere phthalate, polytetrafluoroethylene, polyvenylene sulfite, polyimi de and other thermoplastics.

Will the plastic extrusion manufactured according to the invention dat processed, e.g. for the production of injection molding sharing, it is essential during which the stretching subsequent steps within further processing the temperature of the plastic extrudate to be processed to keep essentially constant, i.e. on a value which is approximately that of the extrusion temperature or Injection temperature corresponds. So it is e.g. possible, extruded polymer strands according to the invention Cutting and conveying screw of an injection molding device feed in which the polymer strands either to a  Crushed granules with oriented fibers or directly then into the mold of the injection molding device be injected. This step remains the same Alignment of the polymer melt obtained so that the Strength of the plastic parts produced is higher than for a conventionally manufactured part and an elevation material savings of up to 30%.

According to the invention it is also possible to stretch the Plastic extrudate, e.g. stretched polymer strands, again while maintaining the extrusion temperature with a further, preferably the same plastic extrudate coat, after which a stretching process takes place again.

Furthermore, the extruded, with a spinning pump via a Extruded and stretched material with a spinneret Reinforcing material, e.g. directional reinforcing fibers made of glass, carbon or aramid. This Reinforced material can then, as mentioned above, additional with a second spinneret gene plastic extrudate, preferably a polymer melt ze from the same starting material and given if stretched. This results in materials with directional fibers and high strength.

Strands produced in this way can e.g. for injection molding of plastic parts can be used. The strands will in sections of e.g. Cut 6 to 7 mm in length and ordered with the help of e.g. a screw conveyor in the Injection mold introduced. The temperature of the melt will maintained until the spraying process so that the alignment tion of the polymer chains within the composite preserved. In conventional processes e.g. Glass or plastic fibers in short sections with 1 to Cut 2 mm in length and added to the polymer melt.  

Aside from the fact that these short cut fibers are the Parts of the screw and the extruder housing as well Cutting and conveying device due to friction and scratching those who serve as reinforcements will attack significantly Fibers are only created in a disordered manner in the injection molding.

Further refinements of the invention can be found in the sub claims.

The invention is in exemplary embodiments based on the Drawing explained in more detail. Show it:

Figure 1 shows a cross section through a spinning and a stretching part of a spinning-stretching device for producing plastic films by a method according to the invention.

Fig. 2 is a schematic view of the machine in Fig. 1 between the spinneret and two stretching rollers;

Figure 3 is a sectional front view of a spin-stretch injection molding machine according to the invention with a first spinning area, a first stretching area, a first molding area, a second Spinnbe rich, a second stretching area, a second molding area, and the actual Spritzgießvor direction.

Fig. 4 is a sectional side view of the injection molding machine in Fig. 3;

5 shows a longitudinal section through the first spinning area and the first stretch and shape the area of the injection molding machine with a feed device for the reinforcing fibers.

Fig. 6 is a schematic view of the parts important for stretching and forming strands;

Fig. 7 is a longitudinal section through the second spinning area and the second stretching and the second mold section of the machine of FIG. 3;

. Fig. 8 is a schematic view of the important for the function of parts of the machine shown in Figure 7 members;

Fig. 9 shows a cross section through part of an injection molding machine in a further embodiment for the production of several injection molded parts.

In Fig. 1 is provided with the A spinning area shown with B of the stretching region of a spin-draw apparatus 1. Molten thermoplastic material is fed via a line 2 from a spinning pump, not shown here, into a distribution chamber 3 , which is closed with a spinneret 4 . A film 6 then emerges through the spinning slot of the spinneret 4 and is fed to a pair of stretching rollers 7 in a stretching channel 6 . The two stretching rollers 7 rotate so quickly that their peripheral speed is higher than the spinning speed, so that the extruded film is stretched. The film exiting between the pairs of rolls is guided out of area B via a discharge channel 8 . Along the housing of the spray-stretching device 1 and also on important functional parts, heating bands 9 are provided, only heating bands in the region of the spinneret and in the region of the pair of stretching rollers being shown here. These heating tapes are intended to ensure that the temperature is maintained at substantially the same, so that the stretching of the plastic film 5 takes place at about melting temperature immediately after spinning. In order to prevent gas inclusions in the film and thereby bubble formation during spinning, a degassing channel 10 is provided, through which the stretching channel 6 can be evacuated.

In FIGS. 3 to 8, a part of a spin-draw injection molding machine 20 is shown comprising an extruder 21 and a dual spin pump 22, followed by a spinning area A, a stretching region B, a forming area C, a second spinning area D, connect a second stretching area E , a second molding area F and a casting and injection area G. Via a first drain pipe 23 of the double spinning pump 22 , the plastic melt is supplied to a spinning nozzle 25 at a high pressure, a distribution chamber 24 , from which, as indicated schematically in FIGS . 5 and 6, a large number of threads 26 emerge as a plastic melt are fed within a stretching channel 27 two stretching rollers 28 , the peripheral speed is set by means of a drive 29 only indicated in Fig. 4 to a value which is higher than the spinning speed. The threads in which the macromolecules of the polymer are already aligned by spinning are stretched in the stretching roller pair 28 , so that an almost complete alignment takes place. The threads 26 are stretched at a temperature which corresponds to the extrusion temperature (ie approximately the melting temperature of the polymer used. In order to maintain the temperature during the entire machining process, only indicated heating devices 30 are provided in the figures. In addition, the drawing rollers 28 can be heated.

The stretched spun threads are fed to a pair of shaping rollers 32 and are formed there into four plastic strands 33 . A drive 34 schematically indicated in FIG. 4 is provided for the pair of forming rolls 32 . The stretching channel 27 is degassed via a degassing line 31 in order to prevent air inclusions in the melted threads and in the strands.

Via feed channels 35 the reinforcing fibers 36 , for example glass fibers, are supplied from the outside to the molding rolls 32 with matrix, with which the plastic strands 33 are reinforced ver. These reinforcing fibers are pressed into the plastic strands 33 by the shaping rollers 32 , so that longitudinally reinforced plastic strands 37 result, as is indicated in FIG. 7. These reinforced strands 37 are fed to the second spinning area D. In this spinning area D leads a second drain pipe 39 of the double spinning pump 22 , through which plastic melt is supplied into a distribution chamber 39 for a second spinneret 40 , through the central recess of which the reinforced strands 37 are guided. A large number of threads emerge from the spinneret 40 and surround the reinforced strands 37 , as is indicated schematically in FIGS. 7 and 8. These threads are introduced in a stretching channel 42 , which can be degassed via a degassing line 43 to prevent gas inclusions in the polymer, by means of a second pair of shaping rollers 44 to the four reinforced strands 37 , as is shown schematically in FIG. 8, so that these to be covered with a plastic jacket 45 . There are four composite strands 46 with directional reinforcing fibers, as shown in cross section below in FIG. 7.

The peripheral speed of the drive with a drive 47 schematically indicated in Fig. 4 Formwal zen 44 may be greater than the speed of the strands 37 , so that the composite strands in these form rollers are additionally, if slightly stretched. The degree of stretching is of course dependent on the elasticity of the reinforcing fiber and is usually in the range of a few percent. The alignment of the macromolecules in the longitudinal direction of the threads 41 is therefore essentially carried out by the spinning process. In the second spinning process and the second molding process, too, the temperature of the threads and strands is kept constant at the extrusion temperature, again with the aid of heating devices 30, etc., the second pair of molding rolls 44 again being able to be heated if necessary.

The composite strands 46 are fed in the casting and injection region G to a cutting and conveying screw 50 , with which the strands are cut into small melt sections 51, schematically indicated in FIG. 8, while maintaining the injection temperature substantially corresponding to the extrusion temperature. The cutting process also takes place at injection temperature, so that the strangab sections consist of stretched and reinforced polymer strands with orderly reinforcing fibers. These Strangab sections 51 are conveyed into a chamber 53 by rotating the screw conveyor 50 with the aid of a drive 52 . The cutting and conveying screw 50 is also connected to a piston rod 54 and to a piston 55 of a differential cylinder 56 . The piston can, for example, be moved pneumatically, in which case the screw conveyor 50 in Fig. 3 is shifted to the left and thereby the melted Strangab sections 51 collected in the chamber 53 are pressed into an injection mold 57 .

This produces a plastic part 58, which is only indicated.

The injection temperature is also maintained in the casting area G , so that the stretching of the polymer fibers in the strand sections is not lost. The cutting and conveying screw 50 keep the strand sections in plastic form at least a certain orientation within the casting area, which is at least partially maintained in the injection mold 57 . The cooled injection molded part is thus composed of stretched and reinforced composite polymer and shows a high strength, which is partly and depending on the thermoplastic, such as nylon 6, polyamide, polyester, polypropylene, etc. up to 30% higher than with unfilled polymer.

In Fig. 9, a modified molding area G 'of an injection molding machine is shown. The chamber 53 is followed by a distributor block 60 with a central valve 61 , through which the material flow from the chamber can be guided in succession into three different injection molds 57-1, 57-2 and 57-3 . The injection molding process can be carried out quasi continuously in this way, and injection molds of different shapes and with different weights can be produced in the individual injection molds. The valve 61 can be controlled automatically, for example, with the aid of only indicated sensors 62 .

Claims (17)

1. A process for producing polymer extrudates, in which a polymer, preferably a thermoplastic in powder or granular form, is extruded and spun into a film, fibers or strands and this extrudate is additionally stretched, characterized in that the polymer immediately after the spinning is still stretched in the melt state to orient the rod-shaped molecules of the polymer chains of the polymer in one or two directions. 2. The method according to claim 1, characterized in that the polymer is stretched at the extrusion temperature. 3. The method according to claim 1 or 2, characterized net that the polymer formed into strands after the Stretching kept in the melted state, crushed and in an injection mold for the production of an injection molded part is injected. 4. The method according to any one of claims 1 to 3, characterized characterized in that after stretching the polymer still kept in the melt state and with a further, preferably the same polymer melt is occupied.   5. The method according to claim 4, characterized in that the stretched polymer before loading the other Polymer with a reinforcing material, preferably Glass or carbon fibers. 6. The method according to claim 4 or 5, characterized in net that the occupied polymer continues to be in the melt state is held and stretched again. 7. The method according to any one of the preceding claims characterized in that the polymer melt in all Processing steps is degassed at the same time. 8. Device for producing polymer extrudates according to one of the preceding claims with an extruder, a spinning pump and a spinneret, characterized in that immediately after the spinneret ( 4 , 25 ) a stretching channel ( 6 , 27 ) with stretching rollers ( 7 , 28 ) is provided for stretching the polymer melt, and that heating devices ( 30 ) for maintaining the temperature in the device are provided essentially at the extrusion temperature. 9. The device according to claim 8, characterized in that the device following the stretching rollers ( 28 ) has forming rollers ( 32 ) for molding the polymer melt ( 33 ), and that heating devices ( 30 ) are provided to the temperature during molding in to keep essentially at the extrusion temperature. 10. The device according to claim 8 or 9, characterized in that a further stretching channel ( 42 ) with stretching and forming rollers ( 44 ) is provided that at the input of the white stretching channel ( 42 ) a second spinneret ( 40 ) for supplying Polymer melt is provided, which surrounds the shaped and stretched polymer melt ( 33 ), and that means ( 30 ) are provided to keep the temperature during loading, shaping and optionally stretching of the composite material substantially at the extrusion temperature. 11. The device according to claim 9 or 10, characterized in that a feed device ( 35 ) for feeding reinforcing material ( 36 ), preferably glass or plastic fibers, is provided, with which the extruded and stretched polymer melt is coated. 12. Device according to one of claims 8 to 11, characterized in that a cutting and Fördereinrich device ( 50 ) for the strands ( 46 ) shaped and stretched polymer extrudate ( 33 , 46 ) is provided, and that with the cutting and Conveying device ( 50 ) an injection mold ( 57 ) of an injection molding machine ( 20 ) is connected. 13. The apparatus according to claim 12, characterized in that in the region of the cutting and conveying device ( 50 ) heating devices ( 30 ) are provided for maintaining the temperature substantially at the extrusion temperature. 14. The apparatus according to claim 12 or 13, characterized in that a screw conveyor ( 50 ) for cutting the stretched and optionally reinforced by fibers th strands ( 46 ) in strand sections ( 51 ) is provided, and that the screw conveyor with a cylinder-Kol ben unit ( 56 ) for conveying the strand sections ( 51 ) into a chamber ( 53 ) of the subsequent injection mold ( 57 ) is connected. 15. Device according to one of claims 12 to 14, characterized in that the cutting and conveying device ( 50 ) is connected to a distributor ( 60 ) which has a valve ( 61 ) for connecting the cutting and conveying device ( 50 ) has several injection molds ( 57-1, 57-2, 57-3 ). 16. The apparatus according to claim 15, characterized in that the injection molds ( 57-1, 57-2, 57-3 ) are created for injection molded parts of different shapes and / or under different weights. 17. The apparatus of claim 15 or 16, characterized in that the valve ( 61 ) by sensors ( 62 ) is controllable.