EP1543184B1 - Method for producing highly stable polypropylene fibres - Google Patents

Description

The invention relates to a process for producing high strength polypropylene fibers having high strength and low elongation by continuous melt spinning, stripping, drawing and cutting fiber strands into the polypropylene fibers.

Such a one-step process for the production of high-strength polypropylene fibers is known from DE 35 39 185 known.

In the known method, the fiber strands are passed directly after spinning for the purpose of cooling in a water bath and then stretched in a draw zone with a high draw ratio of up to 10: 1. The relatively rapid cooling of the fiber strands in the water bath leads to a relatively high preorientation in the edge region of the individual fibers, with the consequence of poor stretchability. The known method is also only suitable for relatively coarse fibers with a single titer in the range of greater than 3 dtex. manufacture. However, the higher friction effect on the individual filaments caused by the water bath does not allow the spinning of fibers with finer titer.

However, especially when using such fibers to reinforce concrete, there is a desire for very high strength and fine fibers. From the DE 198 60 335 A1 For example, a polypropylene fiber is known in which the disadvantage of rapid quenching in a liquid has been replaced by air cooling. Although it was possible to produce fiber strands with smaller individual titers, this had the disadvantage that the fibers exhibited a high elongation of more than 60%. However, it has been found in the reinforcement of concrete base bodies that the elongation values of the reinforcing fibers should approximate those of the base material to be reinforced so that the loads As soon as possible can be absorbed by the fibers and the body is spared. Thus, fibers with relatively high elongation values are very limited.

From the EP 0 535 373 A1 is a polypropylene fiber is known, which indeed shows a necessary fineness with high strength, but can only be produced in a complicated two-stage process. The fiber is stored after spinning and stretching, with additional treatment by impregnation. Subsequently, the fiber strands are taken up again in a second stage, dried and cut.

From the WO 2004/007817 A1 a device for the production of staple fibers is known, which operates at high production speeds. In this device several Galettenduos are used as drafting systems, around which the fibers are each looped several times. The device is designed for specific parameter ranges and is in particular not suitable for the production of fibers with very large fiber titers.

From the US 5,846,654 is a drawing device with two draw stages known, which is not combined with a spinning device.

It is an object of the invention to provide a process for producing high-strength polypropylene fibers of the type mentioned, by which particularly fine fibers with a single titer of below 2 dtex. can be produced.

Another object of the invention is to provide an apparatus for carrying out the method.

This object is achieved by a method with the features of claim 1 and by a device having the features of claim 12.

Advantageous developments of the invention are given by the features and the feature combinations of the respective subclaims.

The invention is characterized in that on the one hand the low melt temperature during spinning in conjunction with a slow draw speed favors a partial molecular orientation of the undrawn fibers and therefore sets a higher strength of the fiber. Due to the slow withdrawal speeds, significantly lower internal stresses occur between the polymer chains in the filaments during the

Cooling process after spinning on. By the subsequent drawing in three successive stretching stages, taking into account that 70% of the total drawing in the fiber is already introduced in the first drawing stage, a continuous slow polymer crystallization in the fibers can be produced, so that in addition to the high strength, a low residual elongation and a corresponding Fineness in the fibers sets.

In order to increase the favorable properties of the fiber, the partial extension of the fiber strands in the second drawing stage is carried out higher than in the subsequent third drawing stage. Thus, the total drawing in the draw stages takes place with decreasing draw ratio.

In order to obtain as pronounced partial drawing in the first draw zone after spinning, the fiber strands are withdrawn after melt spinning by a first drafting system with several drafting rollers, the shell surfaces are cooled. Subsequently, the fiber strands are guided through a hot stretching channel within the first plug-in stage and heated to a temperature of above 100 ° C. for stretching.

In order to obtain a continuous transition as possible in the drawing stages, the fiber strands are continuously heated to a temperature of> 100 ° C after passing through the first drawing stage to run into the third drawing stage by guiding over several heated draw rolls. For this purpose, preferably the draw rolls of the draw frames forming the second draw step are designed to be heated.

In addition, within the second drawing stage, a further heat treatment of the fiber strands can be carried out by means of a further hot stretching channel. Within the hot stretch channels, the fiber strands can be heated both by a hot air or by a superheated steam. Be particularly advantageous has been found that the fiber strands in the first Stretching zone are heated with a hot air and in the second draw zone with a superheated steam.

After stretching, the fiber strands are preferably cooled by guiding over a plurality of cooled draw rolls at a fourth drafting device at the end of the third draw step.

Another variant of the method is given by the fact that the fiber strands are crimped after stretching and before cutting.

In order to achieve the highest possible daily capacities of more than 10 t, preferably the fiber strands are extruded through an annular or rectangular spinneret with a plurality of approximately 60,000 to 120,000 nozzle bores.

The device according to the invention for carrying out the method according to the invention according to claim 12 is characterized by the formation and distribution of the drawing stages, so that polypropylene fibers with high strength of more than 6 cN / dtex. can be produced at a low elongation of below 40%, preferably below 20% with appropriate fineness in the individual titers. The draw rolls of the middle draw frames are preferably designed to be heatable in order to obtain a uniform and continuous temperature control of the fiber strands during drawing. The drafting units at the inlet and at the outlet of the overall drawing zone are preferably formed with cooled draw rolls.

The method according to the invention will be described in more detail below with reference to an embodiment of a device according to the invention with reference to the accompanying drawings.

Fig. 1

schematisch ein erstes Ausführungsbeispiel einer erfindungsgemäßen Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens

Fig. 2

schematisch ein weiteres Ausführungsbeispiel der erfindungsgemäßen Vorrichtung

They show:

Fig. 1

schematically a first embodiment of a device according to the invention for carrying out the method according to the invention

Fig. 2

schematically a further embodiment of the device according to the invention

In Fig. 1 a first embodiment of a device according to the invention for the single-stage production of polypropylene fibers is shown schematically. Such devices are generally known in the art as compact spinning machines for the production of staple fibers, preferably of polypropylene. The compact systems are available with spinning speeds in the range of max. 250 m / min. operated. This means that very high production capacities of up to 50 t per day can be achieved.

The device according to the invention corresponds to such compact systems and has for this purpose a spinning device 1 with a plurality of juxtaposed spinning stations 2.1, 2.2 and 2.3. The number of spinning stations of in Fig. 1 shown embodiment is exemplary. Each of the spinning stations 2.1 to 2.3 is constructed identically, so that it is explained in more detail with reference to the spinning station 2.1.

For extruding a plurality of fiber strands a preferably annular spinneret 3 is provided which has a plurality of nozzle bores on its underside. Thus, for example, up to 120,000 nozzle bores can be arranged in an annular or rectangular arrangement in the spinneret 3. The spinneret 3 is connected to a melt source (not shown here), which supplies the spinneret 3 with a melt stream under pressure. In principle, extruders, pumps or combinations of both are suitable as melt sources in order to supply a melt stream to the spinneret 3. The spinnerets 3 of the spinning stations 2.1, 2.2 and 2.3 are arranged in a heated spinning beam 15. Below the spinneret 15 is in the spinning station 2.1 substantially centrally to the spinneret 3 a Cooling device 4 is arranged. The cooling device 4 is formed as an Anblasung in which a cooling air flow is generated from an annular blowing nozzle, so that the cooling air penetrates the annular veil formed by the fiber strands from the inside out and leads to cooling of the fiber strands. In the illustrated embodiment, the cooling air of the cooling device 4 is supplied from above through the spinning beam 15. However, it is also possible to place the cooling air supply laterally next to the exiting fiber strands.

For the guidance and treatment of the fiber strands, which in the embodiment according to Fig. 1 are characterized by the reference numeral 5, the spinning device 1 are arranged downstream of several treatment facilities. First, the spinning device 1 is immediately associated with a trigger device 6. The take-off device 6 contains per spinning station devices for preparing and guiding the fiber strands 5. Thus, for example, during preparation, a spin finish can be applied to the fiber strands by rolling. The withdrawal device 6 is arranged below the spinning device 1. By the deduction device 6, the fiber strands 5 of the spinning units 2.1, 2.2 and 2.3 are deflected out of a vertical guide and brought together. The plurality of fiber strands 5, which are also referred to as tow or tow, are deducted by a first drafting system 7.1. The drafting system 7.1 is arranged directly next to the withdrawal device 6.

The drafting system 7.1 is followed by a total of three further drafting systems 7.2, 7.3 and 7.4. Between the drafting systems 7.1, 7.2, 7.3 and 7.4 each drawstring is formed. Thus, a first drafting stage 9.1 between the first drafting system 7.1 and the second drafting system 7.2 is formed. A second drafting stage 9.2 is formed between the drafting units 7.2 and 7.3 and the third drafting stage 9.3 between the drafting units 7.3 and 7.4. Each of the drafting systems 7.1 to 7.4 has in each case a plurality of drafting rollers 8, which guide the fiber strands 5 with simple looping. The drafting rollers 8 of the drafting systems 7.1 to 7.4 are driven, wherein the drafting rollers 8 of the drafting systems 7.1 to 7.4 in Depending on the desired draw ratio can be operated at different peripheral speeds. For simultaneous thermal treatment of the fiber strands, the drafting rollers 8 of the drafting systems 7.1 to 7.4 can have a cooled roll shell or a heated roll shell, as required. Furthermore, a hot stretching channel 10 is provided for the thermal treatment of the fiber strands between the first drafting system 7.1 and the second drafting system 7.2 in the first drafting stage 9.1. Within the hot stretch channel 10, the fiber strands 5 can be tempered to a predetermined temperature by means of hot air or by means of a superheated steam. In the second drawing stage 9.2, another hot stretching channel 10 is likewise arranged between the drafting arrangements 7.2 and 7.3.

At the end of the fiber line formed by the drafting systems 7.1 to 7.4 arranged one behind the other, an adjusting device 11 and a cutting device 12 are provided in order to cut the fiber strands continuously into staple fibers having a predetermined fiber length.

For carrying out the method according to the invention is in the in Fig. 1 The device initially shown a polymer melt of polypropylene in the spinning device 1 via the spinnerets 3 of the spinning units 2.1 to 2.3 extruded under pressure to a plurality of fiber strands. The fiber strands 5 emerging from the spinnerets 2 are conveyed via the draw-off device 6 through the drafting device 7.1 from the spinnerets 3 at a take-off speed below 100 m / min. preferably at a withdrawal speed below 50 m / min. deducted. In this case, the fiber strands 5 are cooled by means of the cooling device 4 by a foggy or gaseous cooling medium stream, preferably from air, then prepared and brought together on leaving the discharge device 6 to a tow contained all fiber strands. The drafting rollers 8 of the first drafting system 7.1 are driven at the take-off speed, wherein at the same time further cooling of the fiber strands takes place at the circumference of the drafting rollers 8 of the first drafting system 7.1. These are the drafting rollers 8 of the first drafting system 7.1 formed with cooled jacket surfaces.

Das.Verstrecken the fiber strands 5 takes place in a total of three draw levels 9.1, 9.2 and 9.3, each with different draw ratios. The total draw ratio is above 4: 1. The stretching of the fiber strands in the steps is carried out with different intensity. In order to obtain a high-strength, particularly fine fiber, the fiber strands are stretched in the first draw stage 9.1 with a partial stretch, which accounts for at least 70% of the total drawing. For stretching in the first drawing stage 9.1, the fiber strands 5 are preferably heated in the hot drawing channel 10 by hot air to a temperature of> 100 ° C and then passed over the likewise heated to a temperature of about 100 ° C drafting rollers 8 of the second drafting system 7.2. The second Teilverstreckung the fiber strands 5 takes place in the second draw stage 9.2, wherein also a treatment in a hot stretching channel 10 is provided. The fiber strands are further partially drawn by the third drafting system 7.2, wherein the partial drawing in the second drawing stage 9.2 is higher than the last partial drawing in the third drawing stage 9.3. The rollers 8 of the third drafting system 7.3 are also heated to a surface temperature of> 100 ° C to obtain a uniform continuous drawing. After the third partial drawing, the fiber strands 5 are cooled by the cooled drafting rollers 8, the fourth drafting system 7.4 and then cut uniformly into fibers in the predetermined fiber length.

Using a commercially available polypropylene polymer, it was possible to produce fibers with a fiber length of 6.6 mm, alternatively 13 mm, in several test series, which have a single titer in the range from 0.9 to 1.6 dtex, a strength in the range from 8 to 9 cN / dtex. and exhibited an elongation in the range of 18 to 21%. Here, the melt temperature during spinning of the fiber strands was set to a value <250 ° C. The nozzle plate had a annular arrangement of the nozzle bores with a number of several 10,000 nozzle holes.

The rollers of the first drafting system 7.1 were at a take-off speed in the range of 25 to 40 m / min., The drafting rollers of the second drafting system 7.2 at a speed in the range of 80 to 115 m / min., The drafting rollers of the third drafting system 7.3 at a speed in the range of 100 to 140 m / min. and the drafting rollers of the fourth drafting system 7.4 at a speed of 110 to 160 m / min. driven. The surface temperatures of the drafting rollers 8 were at the first drafting system 7.1 about 30 ° C, at the second drafting 7.2> 100 ° C, at the third drafting system 7.3 also> 100 ° C and at the fourth drafting 7.4 about 30 ° C. The temperature control of the fiber strands was carried out in the first drawing stage through the hot drawing channel 10 with a hot air having a temperature of above 100 ° C. In the second draw stage 9.1, the fiber strands were treated with a superheated steam at a temperature <100 ° C. The partial stretches achieved thereby for the production of the designated fibers were in the range of 2.8 to 3.2: 1 in the first draw stage 9.1, in the range of 1.05 to 1.5: 1 in the second draw stage 9.2 and in the area 1, 05 to 1.3: 1 in the third draw step 9.3. In particular, the high draw ratio in the first draw stage 9.1 and the subsequent draw in the second draw stage 9.2 at high temperature or at low temperatures in the third draw stage 9.3, in combination with the relatively low take-off speed, the preferred slow and steady polymer crystallization in the fiber strands , This slow and steady crystallization has the consequence that a high strength is achieved at low residual strain. Due to the multi-stage stretching can be a particularly fine fiber with Einzeltitern below 2 dtex. produce.

In Fig. 2 is a further embodiment of a device according to the invention for carrying out the method according to the invention shown schematically. At the in Fig. 2 illustrated embodiment is the Spinning device 1 and the discharge device 6 is not shown. These are identical to the previous embodiment, so that reference is made to the preceding description.

The treatment of the fiber strands successively arranged treatment facilities are in the in Fig. 2 illustrated embodiment by the drafting systems 7.1, 7.2, 7.3 and 7.4 and a crimping device 13, a drying device 14, and the pulling device 11 and the cutter 12 is formed. The drafting systems 7.1 to 7.4 are designed substantially identical to the previous embodiment, only the number of drafting rollers 8 used per drafting device is different. To treat the fiber strands, a hot stretching channel 10 is provided in each of the stretching stages 9.1, 9.2 and 9.3. The treatment of the fiber section in the hot stretching channels 10 in the first drawing stage 9.1 and in the second drawing stage 9.2 is preferably carried out by a hot air and in the third drawing stage 9.3 with a steam. However, it is also possible to provide, in each of the drawing stages 9.1 to 9.3, the treatment of the fibers by a combination of a hot air treatment and a steam treatment.

With the in Fig. 2 In the embodiment shown, it is possible to produce a crimped polypropylene fiber having a strength of greater than 6 cN / dtex, an elongation of <40%, preferably <30% and a fineness with a single denier of <2dtex. having. For this purpose, the fiber strands 5 are curled after stretching by the crimping device 13. The crimping device 13 is usually designed as Stauchkammerkräuseleinrichtung, in which the fiber strands are pressed by a conveyor into a stuffer box. After crimping, the fiber strands are fed to the drying device 14 and then fed by the tensioning device 11 with a defined tension of the cutting device 12. Usually, the crimping device is preceded by a cable connection and a damping channel (both not shown).

The structure of the embodiments according to Fig. 1 and 2 for the device according to the invention are exemplary in the number and choice of treatment facilities. In principle, it is possible to introduce additional treatments and treatment stages, for example by cable combination to set a suitable for the crimp fiber occupancy. Likewise, more than three draw steps can be formed one behind the other. Essential for the inventive method and apparatus according to the invention is a spinning with low melt temperatures at low take-off speeds in conjunction with a stretching of the fiber strands in at least three draw levels, taking into account a high Teilverstreckung in the first draw stage. Essential for the success of the method according to the invention is first a slight pre-oriented molecular structure of the fiber section after spinning and cooling, in order then to obtain a uniform and continuous crystallization. In principle, however, it is also possible to process other polymers such as polyester or polyamide with the device according to the invention.

LIST OF REFERENCE NUMBERS

1

spinner

2.1, 2.2, 2.3

spinning unit

3

spinneret

4

cooler

5

fiber strands

6

off device

7.1, 7.2, 7.3, 7.4

drafting

8th

stretching rolls

9.1, 9.2, 9.3

drawing stage

10

Hot stretch channel

11

Zugstelleinrichtung

12

cutter

13

crimping

14

drying device

15 -

spinning beam

Claims (15)

1. Method for producing polypropylene fibers of high-strength, having a strength above 6 cN/dtex and an elongation below 40 %, in the following steps:

   1.1 melt spinning a multiplicity of fiber strands from a polypropylene melt with a melting point ≤ 250°C;

   1.2 withdrawing the fiber strands at a withdrawal speed < 100 m/min, while simultaneously cooling the fiber strands with a gaseous cooling medium;

   1.3 drawing the fiber strands in at least three draw stages, which are formed by four draw systems, with a total draw ratio greater than 4 : 1 wherein the fiber strands undergo in the first draw stage a partial drawing of at least 70% of the total drawing, and

   1.4 cutting the fiber strands to the polypropylene fibers of a predetermined fiber length.
2. Method according to claim 1, characterized in that the partial drawing of the fiber strands is higher in the second draw stage than the partial drawing of the fiber strands in the third draw stage.
3. Method according to claim 1 or 2, characterized in that after melt spinning the fiber strands are withdrawn by a first draw system with a plurality of draw rolls, which have each a cooled envelope surface.
4. Method according to one of claims 1 to 3, characterized in that the fiber strands are advanced within the first draw stage through a heated draw channel and heated to a temperature > 100°C.
5. Method according to one of claims 1 to 3, characterized in that the fiber strands are tempered to a temperature > 100°C after the first draw stage until they enter the third draw stage and by advancing over a plurality of heated draw rolls.
6. Method according to claim 4, characterized in that the draw rolls of the draw systems forming the second draw stage, have surfaces that are heated to temperatures > 100°C.
7. Method according to one of the preceding claims, characterized in that within the second draw stage the fiber strands advance through a heated draw channel and are heated therein.
8. Method according to claim 4 or 7, characterized in that the fiber strands are heated by a hot air and/or a hot vapor while advancing through the heated draw channel.
9. Method according to one of claims 1 to 8, characterized in that after having been drawn, the fiber strands are cooled, wherein for tempering the fiber strands advance over a plurality of cooled draw rolls of a fourth draw system at the end of the third draw stage.
10. Method according to one of claims 1 to 9, characterized in that the fiber strands are crimped after having been drawn and before being cut.
11. Method according to one of the preceding claims, characterized in that the fiber strands are extruded through an annular spinneret with a multiplicity of 60.000 to 120.000 spin holes.
12. Apparatus for carrying out the method of one of claims 1 to 11 for producing fiber strands (5) from fibers with filament titers from under 2 dtex., with a spinning device (1) for melt spinning the fiber strands (5), with a plurality of treatment devices (6, 7, 10, 11) for advancing and treating the fiber strands (5) and with a cutting device (12) for cutting the fiber strands (5) wherein the treatment devices (6, 7, 10, 11) comprise a plurality of draw systems (7.1, 7.2, 7.3, 7.4) with each draw system having a plurality of draw rolls (8) for drawing the fiber strands (5), characterized in that four drawing systems (7.1 - 7.4) are arranged to form a total of three draw stages (9.1, 9.2, 9.3) and that the draw rolls (8) of the drawing systems (7.1 - 7.4) being single enlaced can be driven relative to one another such that a speed difference, which is adjusted between the draw systems (7.1, 7.2), forming the first draw stage (9.1) results in at least 70 % of the total drawing with the draw ratio greater than 4:1.
13. Apparatus according to claim 12, characterized in that the draw rolls (8) of the draw systems (7.2, 7.3), which form the second draw stage (9.2), are made heatable.
14. Apparatus according to claim 12 or 13, characterized in that the draw rolls (8) of a first draw system (7.1) are made to be cooled upstream of the first draw stage (9.1).
15. Apparatus according to one of claims 12 to 13, characterized in that the draw rolls (8) of a last draw system (7.4) are made to be cooled at the end of the third draw stage (9.3).

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