EP1543184A1

EP1543184A1 - Method for producing highly stable polypropylene fibres

Info

Publication number: EP1543184A1
Application number: EP03757872A
Authority: EP
Inventors: Hendrik Tiemeier; Horst Kropat
Original assignee: Saurer GmbH and Co KG
Current assignee: Oerlikon Textile GmbH and Co KG
Priority date: 2002-09-26
Filing date: 2003-09-19
Publication date: 2005-06-22
Anticipated expiration: 2023-09-19
Also published as: AU2003273907A1; BR0314746A; CN1328423C; KR20050061480A; DE50312095D1; RU2005112708A; CN1685092A; RU2318085C2; EP1543184B1; WO2004031459A1

Abstract

The invention relates to a method for producing highly stable polypropylene fibres with a strength in excess of 6 cN/dtex. and an elongation of less than 40 %. To obtain the highest possible fineness of fibre, the fibre strands are first spun at a low melting temperature of less than 250 °C and a relatively low drawing speed of less than 100 m/min, whilst being cooled by a gaseous medium. The fibre strands are then stretched in at least three stretching stages with an overall stretching ratio in excess of 4:1, whereby said fibre strands are partially stretched in the first stretching stage to at least 70 % of their overall stretched state. After the stretching process, the fibre strands are cut to form the polypropylene fibres.

Description

Process for the production of high-strength polypropylene fibers

The invention relates to a process for producing high-strength polypropylene fibers with high strength and low elongation by continuous shrink spinning, drawing off, stretching and cutting fiber strands to form the polypropylene fibers.

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

In the known method, the fiber strands are passed directly into a water bath after spinning for the purpose of cooling and then drawn in a drawing zone with a high drawing ratio of up to 10: 1. The relatively rapid cooling of the fiber strands in the water bath results in a relatively high degree of preorientation in the edge region of the individual fibers, with the result that they are difficult to stretch. The known method is also only suitable for relatively coarse fibers with a single titer in the range of greater than 3 dtex. manufacture. The higher friction effect on the individual filaments caused by the water bath alone does not allow the spinning of fibers with finer titers.

However, especially when using such fibers to reinforce concrete, there is a desire for very high-strength and fine fibers. From DE 198 60 335 AI a polypropylene fiber is known in which the disadvantage of rapid quenching in a liquid has been replaced by air cooling. Although fiber strands with lower individual titers could be produced with this, but with the disadvantage that the fibers showed 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 reinforcement fibers should correspond approximately to those of the base material to be reinforced, so that the loads can be absorbed by the fibers as early as possible and the base body remains unaffected. Fibers with relatively high elongation values are therefore of very limited use.

A polypropylene fiber is known from EP 0 535 373 A1, which shows a necessary fineness with high strength, but can only be produced in a complex two-stage process. The fiber is temporarily stored after spinning and drawing, with additional treatment by impregnation. The fiber strands are then taken up again in a second stage, dried and cut.

It is an object of the invention to provide a process for producing high-strength polypropylene fibers of the type mentioned at the outset, by means of which particularly fine fibers with an individual titer of below 2 dtex. are producible.

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

This object is achieved according to the invention by a method with the features according to claim 1 and by a device with the features according to claim 12.

Advantageous developments of the invention are given by the features and the combinations of features 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 take-off speed favors a partial molecular orientation of the undrawn fibers and therefore a higher strength of the fiber is established. Due to the slow withdrawal speeds, significantly lower internal tensions between the polymer chains in the filaments occur during the Cooling process after spinning. The subsequent drawing in three successive drawing stages, taking into account that 70% of the total drawing is already introduced into the fiber in the first drawing step, enables a steady slow polymer crystallization to be produced in the fibers, so that in addition to the high strength, a low residual elongation and a corresponding one Fineness in the fibers.

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

In order to obtain the most pronounced possible partial drawing in the first drawing zone after spinning, the fiber strands are drawn off after the melt spinning by a first drawing device with several drawing rollers, the jacket surfaces of which are cooled. The fiber strands are then passed 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 transition in the drawing stages that is as continuous as possible, the fiber strands are continuously heated to a temperature of> 100.degree. C. after passing through the first drawing stage until they enter the third drawing stage by guiding them over several heated drawing rollers. For this purpose, the drafting rollers of the drafting units forming the second drafting stage are preferably heated.

In addition, a further heat treatment of the fiber strands can be carried out through a further hot stretching channel within the second stretching stage. The fiber strands can be heated both by hot air or by superheated steam within the hot stretching channels. It has been found to be particularly advantageous that the fiber strands in the first Stretching zone with hot air and in the second stretching zone with a superheated steam.

After drawing, the fiber strands are preferably cooled by guiding them over several cooled drawing rolls on a fourth drawing device at the end of the third drawing step.

A further process variant is given in that the fiber strands are crimped after stretching and before cutting.

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

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

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

They represent: Fig. 1 shows schematically a first embodiment of an apparatus according to the invention for performing the method according to the invention

Fig. 2 schematically shows another embodiment of the device according to the invention

In Fig. 1, a first exemplary embodiment of a device according to the invention for the one-step production of polypropylene fibers is shown schematically. Such devices are generally known in the art as compact spinning systems for the production of staple fibers, preferably made of polypropylene. The compact systems are spinning speeds in the range of max. 250 m min. operated. This means that very high production capacities of up to 501 per day can be achieved.

The device according to the invention corresponds to such compact systems and for this purpose has a spinning device 1 with a plurality of spinning stations 2.1, 2.2 and 2.3 arranged next to one another. The number of spinning positions of the exemplary embodiment shown in FIG. 1 is exemplary. Each of the spinning stations 2.1 to 2.3 is constructed identically, so that this is explained in more detail using the spinning station 2.1.

To extrude a large number of fiber strands, a preferably ring-shaped spinneret 3 is provided, which has a large number of nozzle bores on its underside. 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 spinning beam 15 is in the spinning station 2.1 essentially centrally to the spinneret 3 Cooling device 4 arranged. The cooling device 4 is designed as a blower 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 to the outside and leads to cooling of the fiber strands. In the exemplary embodiment shown, the cooling air is fed to the cooling device 4 from above through the spinning beam 15. However, it is also possible to place the cooling air supply to the side of the emerging fiber strands.

For the guidance and treatment of the fiber strands, which are identified by the reference symbol 5 in the exemplary embodiment according to FIG. 1, the treatment device 1 is followed by a plurality of treatment devices. First of all, a take-off device 6 is assigned directly to the spinning device 1. The take-off device 6 contains devices for preparing and guiding the fiber strands 5 per spinning station. For example, during the preparation, a preparation agent can be applied to the fiber strands by rolling. The take-off device 6 is arranged below the spinning device 1. Through the Ab2_ιgseinrichtung 6, the fiber strands 5 of the spinning stations 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 spinning bucket, are drawn off by a first drafting system 7.1. The drafting system 7.1 is arranged directly next to the trigger device 6.

The drafting system 7.1 is followed by a total of three further drafting systems 7.2, 7.3 and 7.4. A drafting stage is formed between the drafting systems 7.1, 7.2, 7.3 and 7.4. A first drafting stage 9.1 is thus formed between the first drafting system 7.1 and the second drafting system 7.2. A second drafting stage 9.2 is formed between the drafting systems 7.2 and 7.3 and the third drafting stage 9.3 between the drafting systems 7.3 and 7.4. Each of the drafting systems 7.1 to 7.4 each has a plurality of drafting rollers 8 which guide the fiber strands 5 with a single loop. The drafting rollers 8 of the drafting systems 7.1 to 7.4 are driven, the drafting rollers 8 of the drafting systems 7.1 to 7.4 in Depending on the desired stretching ratio can be operated at different peripheral speeds. For the simultaneous thermal treatment of the fiber strands, the drawing rollers 8 of the drafting devices 7.1 to 7.4 can have a cooled roller jacket or a heated roller jacket, depending on the requirements. Furthermore, a hot drawing duct 10 is provided for the thermal treatment of the fiber strands between the first drafting device 7.1 and the second drawing device 7.2 in the first drawing stage 9.1. Within the hot stretching 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 drafting stage 9.2, a further hot stretching duct 10 is likewise arranged between the drafting units 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, a tension control device 11 and a cutting device 12 are provided in order to continuously cut the fiber strands into staple fibers with a predetermined fiber length.

To carry out the method according to the invention, in the device shown in FIG. 1, a polymer melt made of polypropylene is first extruded in the spinning device 1 via the spinnerets 3 of the spinning stations 2.1 to 2.3 under pressure to form a large number of fiber strands. The fiber strands 5 emerging from the spinnerets 2 are pulled by the spinnerets 3 via the draw-off device 6 through the drafting system 7.1 at a take-off speed of less than 100 m / min. preferably with a take-off speed below 50 m / min. deducted. In this case, the fiber strands 5 are cooled by means of the cooling device 4 by means of a foggy or gaseous cooling medium stream, preferably made of air, then prepared and brought together to form a tow containing all the fiber strands when they leave the extraction device 6. The drafting rollers 8 of the first drafting system 7.1 are driven at the take-off speed, with a further cooling of the fiber strands taking place at the circumference of the drafting rollers 8 of the first drafting system 7.1. For this are the drafting rollers 8 of the first drafting system 7.1 are formed with cooled jacket surfaces.

The fiber strands 5 are stretched in a total of three stretching stages 9.1, 9.2 and 9.3, each with different stretching ratios. The total draw ratio is above 4: 1. This involves stretching the fiber strands. executed in the stages with different intensities. In order to obtain a high-strength, particularly fine fiber, the fiber strands are stretched in the first stretching stage 9.1 with a partial stretching, which makes up at least 70% of the total stretching. For drawing in the first drawing stage 9.1, the fiber strands 5 in the hot drawing duct 10 are preferably heated to a temperature of> 100 ° C. by hot air and then passed over the drawing rollers 8 of the second drawing device 7.2, which are also heated to a temperature of over 100 ° C. The second partial drawing of the fiber strands 5 takes place in the second drawing stage 9.2, whereby treatment in a hot drawing duct 10 is also provided. The fiber strands are further partially drawn by the third drafting system 7.2, the partial drawing in the second drawing stage 9.2 being higher than the last partial drawing in the third drawing stage 9.3. The rollers 8 of the third drafting device 7.3 are also heated to a surface temperature of> 100 ° C. in order to obtain a uniform, continuous drawing. After the third partial drawing, the fiber strands 5 are cooled by the cooled drawing rolls 8, the fourth drawing device 7.4 and then cut evenly into fibers of the specified fiber length.

When using a commercially available polypropylene polymer, fibers with a fiber length of 6.6 mm, alternatively 13 mm, could be produced in several test series, which had 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 showed an elongation in the range of 18 to 21%. The melt temperature during the spinning of the fiber strands was set to a value <250 ° C. The nozzle plate had one circular arrangement of the nozzle bores with a number of several 10,000 nozzle bores.

The rollers of the first drafting system 7.1 were at a take-off speed in the range from 25 to 40 / 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 Range from 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 approximately 30 ° C. for the first drafting system 7.1,> 100 ° C. for the second drafting system 7.2, also> 100 ° C. for the third drafting system 7.3 and approximately 30 ° C. for the fourth drafting system 7.4. The temperature of the fiber strands was carried out in the first stretching stage through the hot stretching duct 10 using hot air which has a temperature of above 100 ° C. In the second stretching stage 9.1, the fiber strands were treated with superheated steam at a temperature <100 ° C. The partial stretchings achieved in this way for the production of the fibers mentioned were in the range from 2.8 to 3.2: 1 in the first stretching stage 9.1, in the range from 1.05 to 1.5: 1 in the second stretching stage 9.2 and in the range 1, 05 to 1.3: 1 in the third stretch 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, bring about the preferred slow and steady polymer crystallization in the fiber strands , This slow and steady crystallization has the consequence that a high strength with low residual elongation is achieved. The multi-stage stretching enables a particularly fine fiber with individual titers below 2 dtex. produce.

A further exemplary embodiment of a device according to the invention for carrying out the method according to the invention is shown schematically in FIG. In the exemplary embodiment shown in FIG. 2, the Spinning device 1 and the Ab∑πigseinrichtung 6 not shown. These are identical to the previous exemplary embodiment, so that reference is made to the preceding description.

Arranged one after the other for the treatment of the fiber strands

Treatment devices are shown in FIG

Exemplary embodiment by the drafting systems 7.1, 7.2, 7.3 and 7.4 as well as a

Crimping device 13, a drying device 14, and the tension control device

11 and the cutting device 12 are formed. The drafting systems 7.1 to 7.4 are essentially identical to the previous exemplary embodiment, only the number of drafting rollers 8 used per drafting system is different. To treat the fiber strands in each of the stretching stages 9.1,

9.2 and 9.3 each have a hot stretching channel 10 provided. The

Treatment of the fiber draw in the hot drawing channels 10 in the first drawing stage 9.1 and in the second drawing stage 9.2 preferably by

Hot air and made in the third stretching stage 9.3 with a steam. However, it is also possible to treat the in each of the stretching stages 9.1 to 9.3

Fibers by a combination between a hot air treatment and a

To provide steam treatment.

With the exemplary embodiment shown in FIG. 2, there is the possibility of producing a crimped polypropylene fiber which has a strength of greater than 6 cN / dtex., An elongation of <40%, preferably <30% and a fineness with an individual titer of <2dtex. having. For this purpose, the fiber strands 5 are crimped after being stretched by the crimping device 13. The crimping device 13 is usually designed as a stowage chamber crimping device in which the fiber strands are pressed into a stuffer box by a conveying means. After the crimping, the fiber strands of the drying device 14 are guided and then fed in by the tension adjusting device 11 with a defined tension of the cutting device 12. A cable junction and a damping channel (both not shown) are usually connected upstream of the crimping device. The structure of the exemplary embodiments according to FIGS. 1 and 2 for the device according to the invention are exemplary in the number and the choice of treatment devices. In principle, there is the possibility of introducing additional treatments and treatment stages, for example by means of a cable junction to set a fiber assignment that is suitable for the crimp. Likewise, more than three stretching stages can be formed one after the other. It is essential for the method and the device according to the invention that spinning with low melt temperatures and at the same time low take-off speeds in conjunction with drawing of the fiber strands in at least three drawing stages, taking into account a high partial drawing in the first drawing step. Essential for the success of the method according to the invention is first a light, pre-oriented molecular structure of the fiber stretch after spinning and cooling, in order to then obtain a uniform and steady crystallization. In principle, however, there is also the possibility of processing other polymers such as polyester or polyamide with the device according to the invention.

LIST OF REFERENCE NUMBERS

1 Spiimeinrichtung

2.1, 2.2, 2.3 spinning station

3 spinneret

4 cooling device

5 fiber strands

6 trigger device

7.1, 7.2, 7.3, 7.4 drafting systems

8 stretching rollers

9.1, 9.2, 9.3 draft level

10 hot stretching channel

11 train control device

12 cutting device

13 crimping device

14 drying device

15 spinning beams

Claims

claims

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

1.1 Melt spinning a large number of fiber strands from one

Polypropylene melt with a melt temperature <250 ° C; 1.2 pulling off the fiber strands at a withdrawal speed of <100 m min while cooling the fiber strands with a gaseous cooling medium;

1.3 drawing of the fiber strands in at least three drawing stages with a total drawing ratio of more than 4: 1, the fiber strands receiving a partial drawing of at least 70% of the total drawing in the first drawing stage, and

1.4 Cutting the fiber strands into the polypropylene fibers with the specified fiber length.

2. The method according to claim 1, characterized in that the partial drawing of the fiber strands in the second drawing stage is higher than the partial drawing of the fiber strands in the third drawing stage.

3. The method according to claim 1 or 2, characterized in that the fiber strands are drawn off after the melt spinning by a first drafting device with a plurality of drawing rollers, which drawing rollers each have a cooled jacket surface.

4. The method according to any one of claims 1 to 3, characterized in that the fiber strands within the first stretching stage by one

The hot stretching duct is guided and heated to a temperature> 100 ° C.

5. The method according to any one of claims 1 to 3, characterized in that the fiber strands are tempered to a temperature> 100 ° C after the first stretching stage and up to the entry into the third stretching stage by guiding over several heated stretching rollers.

6. The method according to claim 4, characterized in that the drafting rollers of the drafting units forming the second drafting stage have heated surfaces with temperatures> 100 ° C.

7. The method according to any one of the preceding claims, characterized in that the fiber strands are guided and heated within the second stretching stage through a hot stretching channel.

8. The method according to claim 3 or 7, characterized in that the fiber strands during the passage through the hot stretching channel through a

Hot air and / or a superheated steam are heated.

9. The method according to any one of claims 1 to 8, characterized in that the fiber strands are cooled after stretching, the fiber strands being guided for temperature control over a plurality of cooled drafting rollers of a fourth drafting unit at the end of the third drafting stage.

10. The method according to any one of claims 1 to 9, characterized in that the fiber strands after stretching and before cutting _. be curled.

11. The method according to any one of the preceding claims, characterized in that the fiber strands are extruded through an annular spinneret with a plurality of 60,000 to 120,000 nozzle bores.

12. Device for performing the method according to one of claims 1 to 11, with a spinning device (1) for melt spinning the Fiber strands (5), with a plurality of treatment devices (6, 7, 10, 11) for guiding and treating the fiber strands (5) and with a cutting device (12) for cutting the fiber strands (5), the treatment devices (6, 7, 10 , 11) a plurality of drafting systems (7.1, 7.2, 7.3), each with a number of drafting rollers (8) for stretching the fiber strands

(5), characterized in that the drafting systems (7.1-7.4) are arranged in a total of three drafting stages (9.1, 9.2, 9.3) and in that the drafting rollers (8) of the drafting systems (7.1-7.4) can be driven relative to one another such that at least one speed difference between the drafting units (7.1, 7.2) forming the first drafting stage (9.1)

70% of the total drawing.

13. The apparatus according to claim 9, characterized in that the stretching rollers (8) of the drafting units (7.2, 7.3), which form the second stretching stage (9.2), are heatable.

14. The apparatus of claim 12 or 13, characterized in that the stretching rollers (8) of a first drafting unit (7.1) are cooled before the first stretching stage (9.1).

15. Device according to one of claims 12 to 13, characterized in that the stretching rollers (8) of a last drafting unit (7.4) are designed to be cooled at the end of the third stretching stage (9.3).