Method and device for producing a continuous thread

The present invention relates to a device and a method for producing a continuous thread from a synthetic polymer melt.

In the production of continuous threads from polymer melts a plurality of filament strands are extruded in a spinning apparatus and are cooled thereafter. Said cooling will in most cases be performed with the aid of air within a so-called quench box, the filament strands being cooled to a temperature below 50°C. The filament strands will be combined into a yarn and be drafted in a drafting zone. Then, the yarn will be wound onto a reel. The manner in which the drafting occurs depends on the polymer melt and on the final properties of the final product to be achieved.

From the state of the art, also further methods for the production of threads with high strength are known. One such further method is disclosed e.g. in WO 2009/061161. According to this method, a further increase of the strength of the polyester threads is achieved by use of a polymer melt with high intrinsic viscosity. The polymer melt is kept under a nitrogen atmosphere for avoiding contact with the ambient air. Immediately behind the spinnerets, the filament strands spun from the polymer melt will be passed through a re-heater which will further improve the drawability of the filament strands.

In each of the methods for the production of high-strength threads that are known from the state of the art, the starting product is a polymer of high quality. Thus, it is an object of the invention to provide a device and a method which make it possible to produce a high-strength thread starting from an inexpensive low-value polyester. The above object is achieved by a device and a method comprising the features defined in the independent claims.

The device for producing a continuous thread from a synthetic polymer melt comprises a spinning apparatus for extruding and cooling a plurality of filament strands, a device for applying a spinning preparation, a winding device and a drafting zone for drawing the filament strands that is provided between the spinning apparatus and the winding device.

The drafting zone is formed by a feed roller pair, arranged behind the spinning apparatus, and four to six, preferably five successive drafting roller pairs. The first drafting roller pairs are provided with a heating apparatus, and the last drafting roller pair is provided with a cooling apparatus. At least one of the two rollers of each drafting roller pair is provided with a heating or cooling apparatus. By the active cooling of the thread by the last drafting roller pair, an influence on the molecular chain in the polymer is achieved which will lead to an increased strength. In the process, the crystallinity and the orientation of the molecules will be influenced and the molecular structure will be fixed by the cooling.

The feed roller pair as well as the drafting roller pairs can be formed as so-called duos comprising two driven rollers, or as so-called monos comprising one driven roller and one associated auxiliary roller. According to a preferred embodiment, use is made of one feed roller and five drafting roller pairs, with said feed roller being formed as a mono and the drafting roller pairs as duos. The respective roller pairs will have the thread wound around them a plurality of times.

In order to achieve the effect that is obtained by cooling the filament strands or the thread, respectively, the surface temperature of the roller - equipped with the cooling apparatus - of the last drafting roller pair is provided to be less than 100°C. Preferably, the surface temperature is below 60°C. The cooling effect exerted on the thread which is wound around the drafting roller pair a plurality of times, can additionally by increased by providing both rollers of the last drafting roller pair with a cooling apparatus. Best suited as a cooling apparatus is a liquid cooling apparatus. Via the surface of the roller, heat is withdrawn from the thread. The heat will be discharged via cooling liquid circulating in the roller. The temperature of the cooling liquid is controlled in such a manner that the surface temperature of the roller will not exceed the predefined temperature of 100°, preferably 60°.

The drafting zone is formed by the feed roller pair and the subsequent drafting roller pairs. Preferably, the feed roller pair is followed by five drafting roller pairs. Along the whole drafting zone, the total drafting of the thread arriving from the spinning apparatus is provided to be three to eight times the original thread length. Preferably, the total drafting will be five to seven times as big. In this regard, the individual extents of the drafting are 1.02 to 1.1 between the feed roller pair and the first drafting roller pair, 4 to 6 between the first drafting roller pair and the second drafting roller pair, 1.2 to 2.0 between the second drafting roller pair and the third drafting roller pair, 0.7 to 1.2 between the third drafting roller pair and the fourth drafting roller pair, and 0.7 to 1.2 between the fourth drafting roller pair and the fifth drafting roller pair. According to a particularly preferred embodiment, the total drafting is 6.2 times as big. In this regard, the individual extents of the drafting are 1.04 between the feed roller pair and the first drafting roller pair, 4.6 between the first drafting roller pair and the second drafting roller pair, 1.3 between the second drafting roller pair and the third drafting roller pair, 1.01 between the third drafting roller pair and the fourth drafting roller pair, and 1.0 between the fourth drafting roller pair and the fifth drafting roller pair. The actual drafting is each time performed between the drafting roller pairs. The two rolls of a drafting roller pair are operated substantially at the same rotational speed.

The temperatures of the heated drafting rollers are to be provided in accordance with the polymer melt that is used. Each time, at least one of the two rollers of the drafting roller pair is heated. Preferably, both rollers of a drafting roller pair are heated to the same temperature. The surface temperatures are in the range from 40 to 90° for the first drafting roller pair, from 80 to 170° for the second drafting roller pair, from 120 to 280° for the third drafting roller pair and from 120 to 250° for the fourth drafting roller pair. According to a preferred embodiment, the surface temperatures are 85°C for the first drafting roller pair, 110°C for the second drafting roller pair, 245°C for the third drafting roller pair and 225°C for the fourth drafting roller pair.

The fifth drafting roller pair, due to its cooled surface, has the effect that the molecule orientation within the individual filaments will be influenced and be fixed, thus resulting in a higher strength. This makes it possible to produce threads which have a strength of more than 80 cN/tex while undergoing an elongation of less than 12%. Preferably, the threads have a strength of more than 85 cN/tex while undergoing an elongation of less than 11%. The threads produced according to the invention preferably have a strength of more than 50 cN/tex while undergoing an elongation of less than 5% which is also referred to as TASE (Tenacity At Specific Elongation).

With the device of the present invention, a high-strength thread can be produced from various polymer melts. With polyester, this is possible already with polymer melts having an intrinsic viscosity of less than 1.2 dl/gr, preferably of less than 1.03 dl/gr. With polyamide, polymer melts can be used that have a relative viscosity of less than 3.6, preferably of less than 3.5. With polypropylene, polymer melts can be used that have a melt flow index larger than 2, preferably larger than 4.

The invention will be explained in greater detail hereunder by way of an exemplary embodiment with reference to the Figures.

Figure 1 schematically shows an embodiment,

Figure 2 is a graphic illustration of the strength development F as a function of the elongation D, using polyester as an example.

Figure 1 schematically shows an embodiment of a device for producing an endless thread from a synthetic polymer melt. By means of a spinning apparatus 1, a plurality of filament strands 3 is extruded at a temperature which is by 40°C to 50°C above the melting temperature of the polymer which is used. In a quench box 2 following the spinning apparatus 1, the filament strands 3 will be cooled to a temperature below 50°C, preferably to 20°C. Said cooling within the quench box 2 may be effected by cooling air. Then, the filament strands 3 will be combined into a thread 5 and provided with a spinning preparation 4. After application of the spinning preparation, the thread 5 will reach a feed roller pair 7 via a pre-swirling device 6. It is possible to omit the pre-swirling device 6. The presence of a pre-swirling device 6 facilitates the further guiding of the filament strands 3 or of the thread 5, respectively. Following the feed roller pair 7, the thread 5 is guided around five drafting roller pairs 8, 9, 10, 11, 12. The thread 5 is preferably wrapped several times around the feed roller pair 7 and the drafting roller pairs 8, 9, 10, 11, 12. The two rollers of a drafting roller pair 8, 9, 10, 11, 12 are driven at the same circumferential speed. The respective successive drafting roller pairs 9, 10, 11, 12 are driven at a circumferential speed different from that of the preceding drafting roller pair 8, 9, 10, 11. Thereby, the thread 5 is exposed to a tension between the drafting roller pairs 8, 9, 10, 11, 12, with the circumferential speed increasing, and the thread is correspondingly drafted.

When the circumferential speed decreases, the tension on the thread 5 is relieved and the thread experiences relaxation.

The first drafting roller pairs 8, 9, 10, 11 are provided with a heating apparatus (not shown). The last drafting roller pair 12, by contrast, is provided with a cooling apparatus 14. At least one roller of drafting roller pair 12 is connected to the cooling apparatus 14 via coolant connections 13. The heat which is introduced via the thread 5 into the drafting rollers 12 via their surfaces will be discharged with the aid of a coolant via the coolant connections 13 to the cooling apparatus 14 and the thread 5 itself is cooled thereby. The cooling connections 13 may be pipe lines or hoses. For improving the efficiency, it can also be provided that both rollers of the drafting roller pair 12 are connected to the cooling apparatus 14.

Downstream of the last drafting roller pair 12, the thread 5 will be supplied via a swirling apparatus 15 to a winding device 16.

Figure 2 is a graphic illustration of the strength development F as a function of the elongation D, using polyester as an example. A dotted line represents the force-elongation curve of a conventional yarn of the prior art. In a tensile test a yarn is elongated with an increasing load. In the process, the development of the strength F is recorded as a function of the elongation D. when the elongation D is increased, i.e. when a stretching of the yarn occurs that is caused by an increase in load, the yarn will break at a certain elongation D. The curve illustrates as a solid line 21 shows the strength development of a yarn produced with a device according to the invention. Other than in the yarn of the prior art, a high strength (TASE) of 85 cN/tex is reached already at an elongation D of 12% at most, preferably 11%, and a strength (TASE) of 60 cN/tex is reached already at an elongation of 5%. When a conventional yarn was loaded with 60 cN/tex, an elongation of more than 9% was obtained. Owing to the improvement achieved, it is possible to use significantly cheaper yarns also in technically challenging fields of application, e.g. heavy duty ropes or cables.

Legend
1 spinning apparatus
2 quench box
3 filament strands
4 spinning preparation
5 thread
6 pre-swirling device
7 feed roller pair
8 first drafting roller pair
9 second drafting roller pair
10 third drafting roller pair
11 fourth drafting roller pair
12 fifth drafting roller pair
13 coolant connection
14 cooling apparatus
15 swirling apparatus
16 winding device
20 force/elongation curve of conventional yarn
21 force/elongation curve of a yarn produced according to the invention
F strength in cN/tex
D elongation in %

Claims

1. A device for producing a continuous thread (5) from a synthetic polymer melt, comprising a spinning apparatus (1) for extruding and cooling a plu¬rality of filament strands (3), a device for applying a spinning preparation (4), a winding apparatus (16) and a drafting zone for drawing the filament strands (3) that is provided between the spinning apparatus (1) and the winding apparatus (16), characterized in that the drafting zone is formed by a feed roller pair (7) and four to six successive drafting roller pairs (8, 9, 10, 11, 12) and the first drafting roller pairs (8, 9, 10, 11) are provided with a heating apparatus and the last drafting roller pair (12) is provided with a cooling apparatus (13, 14), wherein at least one of the two rollers of each drafting roller pair (8, 9, 10, 11, 12) is provided with the heating or cooling apparatus (13, 14).

2. The device of claim 1, characterized in that the drafting zone is formed by five successive drafting roller pairs (8, 9, 10, 11, 12).

3. The device of claim 1 or 2 characterized in that a surface temperature of the roller of the last drafting roller pair (12), which is provided with the cooling apparatus (13, 14), is provided to be less than 100°C.

4. The device of claim 1 or 2, characterized in that a surface temperature of the roller of the last drafting roller pair (12), which is provided with the cooling apparatus (13, 14), is provided to be less than 60°C.

5. The device of one of the preceding claims, characterized in that both rollers of the last drafting roller pair (12) are provided with a cooling apparatus (13, 14).

6. The device of one of the preceding claims, characterized in that the cooling apparatus (13, 14) is a liquid cooling.

7. The device of one of claims 2 to 6, characterized in that a heating is provided by means of the heating devices of the first four drafting roller pairs (8, 9, 10, 11) such that the surface temperature is from 40 to 90°C for the rollers of the first drafting roller pair (8), from 80 to 170°C for the rollers of the second drafting roller pair (9), from 120 to 280°C for the rollers of the third drafting roller pair (10) and from 120 to 250°C for the rollers of the fourth drafting roller pair (11).

8. The device of one of the preceding claims, characterized in that a total drafting of 3 to 8 times is provided in the drafting zone.

9. The device of one of claims 1-7, characterized in that a total drafting of 5 to 7 times is provided in the drafting zone.

10. The device of one of claims 2 to 9, characterized in that the extents of the drafting are 1.02 to 1.1 between the feed roller pair (7) and the first drafting roller pair (8), 4 to 6 between the first drafting roller pair (8) and the second drafting roller pair (9), 1.2 to 2.0 between the second drafting roller pair (9) and the third drafting roller pair (10), 0.7 to 1.2 between the third drafting roller pair (10) and the fourth drafting roller pair (11), and 0.7 to 1.2 between the fourth drafting roller pair (11) and the fifth drafting roller pair (12).

11. A method for producing a continuous thread (5) from a synthetic polymer melt, characterized by the following method steps:

a) extruding filament strands (3) from a polymer melt,

b) cooling and combining the filament strands (3) into a thread (5),

c) applying a spinning preparation (4) onto the thread,

d) drafting the thread (5) with a total drafting of the yarn of 3 to 8 with the aid of a feed roller (7) and four to six successive drafting roller pairs (8, 9, 10, 11, 12), the first drafting roller pairs (8, 9, 10, 11) being heated and the last drafting roller pair (12) being cooled,

e) winding up the thread (5).

12. A thread (5) produced from a synthetic polymer melt with a device as defined in one of claims 1 to 10, characterized in that the thread (5) has a strength of more than 85 cN/tex at an elongation of less than 12%.

13. The thread (5) of claim 12, characterized in that the synthetic polymer melt is a polyamide with a relative viscosity less than 3.6.

14. The thread (5) of claim 12, characterized in that the synthetic polymer melt is a polyester with an intrinsic viscosity less than 1.2 dl/gr.

15. The thread (5) of claim 12, characterized in that the synthetic polymer melt is a polypropylene with a melt flow index higher than 2.