EP0283097A2

EP0283097A2 - Process for producing a thread of polyamide-6

Info

Publication number: EP0283097A2
Application number: EP88200494A
Authority: EP
Inventors: Arturo Spani; Aldo Gentilucci
Original assignee: ENICHEM FIBRE SpA
Current assignee: ENICHEM FIBRE S.P.A.
Priority date: 1987-03-20
Filing date: 1988-03-17
Publication date: 1988-09-21
Also published as: IT1203844B; BR8801341A; EP0283097A3; IT8719775A0; AR242271A1

Abstract

Process for producing an interlaced and stretched thread of polyamide-6, which comprises the following steps, carried out in sequence:

(a) extrusion from molten polyamide-6 through the bores of a spinneret;
(b) cooling of the extruded filaments by means of an air stream;
(c) union of the cooled filaments to form a bundle of filaments (the thread) and simultaneous application of a finish liquid;
(d) interlacing of the thread treated with the finish liquid;
(e) stretching of the interlaced thread between a collection roll and a stretching roll, carried out in the absence of heating;
(f) relaxation of the interlaced and stretched thread by means of treatment with superheated steam;
(g) winding on a bobbin of the steamed thread.

Description

The present invention relates to a continuous process for the production of an interlaced and stretched thread of polyamide-6.
It is known in the art to produce stretched threads of polyamide-6, by means of processes which comprise the spinning from molten polyamide-6, and the stretching of the so-obtained filaments after being combined to form a bundle of filaments (the thread).
More particularly, according to the prior art, stretched threads of polyamide 6, provided with good characteristics, can be prepared by means of a process in which the spinning operations are distinct from the stretching operations, with said operations being carried out in two steps separate in space and in time, such as described, e.g., in Mark, Atlas, Cernia "Man Made Fibers; Science and Technology", 2nd Volume; 1968, page 255-foll.
According to the prior art, it is still possible to produce stretched threads of polyamide-6 by combining the operations of spinning with the stretching operations in a continuous process, such as disclosed, e.g., in U.K. patents Nos. 1,069,696; 1,256,376; and 1,275,873.
The continuous, single-step processes show, as compared to the double-step processes, some advantages, in particular as regards the cheapness and the high production rates.
However, in the single-step process problems exist, which heretofore did not find a completely satisfactory solution.
In particular, these problems derive from the thread shrinkage phenomena, after the stretching step, which originate a bad formation of the bobbins, and sometimes render useless the same bobbin. Other problems derive from the not complete stability of the thread under the various conditions of the process, what generates difficulties in operations, in particular at high speeds, and which causes low yields and a poor uniformity of the obtained product.
According to U.K. patent No. 1,471,395, a polyamide-6 thread is submitted to an interlacing treatment upstream a stretching step carried out over rolls heated at a moderately high temperature. This operating way does not anyway make it possible so high as desirable thread production speeds to be achieved.
According to Italian patent application No. 49,765 A/80, filed on Sept. 28th, 1980, a thread of polyamide-6 is submitted to a treatment of stabilization and/or interlacing downstream a stretching step carried out on not heated rolls. This operating way does not anyway allow a completely satisfactory stability of the thread to be achieved during all process steps.
The purpose of the present invention is overcoming the above-mentioned drawbacks.
More particularly, the purpose of the present invention is a simple and advantageous process which makes it possible stretched fibres of polyamide-6 to be continuously manufactured with good quality and uniform characteristics, by operating at a high speed, and under conditions of stability of the thread, and of the eventually obtained bobbins.
It was found, according to the present invention, that an interlaced thread of polyamide-6 can be stretched over not heated rolls, by operating at a high speed, and under conditions of perfect thread stablity. It was still found, according to the present invention, that it is possible to obtain a complete relaxation of the thread after the stretching, when said interlaced and stretched thread is submitted to a treatment with steam superheated at a relatively high temperature, by operating under conditions within which the structure of the same thread is not changed, or is not substantially changed.
In accordance therewith, the present invention is concerned with the production of an interlaced and stretched thread of polyamide-6, by means of a continuous process, which comprises the following steps, carried out in sequence:

(a) extrusion from molten polyamide-6 through the bores of a spinneret;
(b) cooling of the extruded filaments by means of an air stream;
(c) union of the cooled filaments to form a bundle of filaments (the thread) and simultaneous application of a finish liquid;
(d) interlacing of the thread treated with the finish liquid, with a number of interlacing points equal to at least 10 interlacing points per metre;
(e) stretching of the interlaced thread between a collection roll and a stretching roll, carried out in the absence of heating;
(f) relaxation of the interlaced and stretched thread by means of a treatment with steam superheated at a temperature of at least 115°C, carried out without varying, or without substantially varying, the structure of the thread;;
(g) winding on a bobbin of the steamed thread.

The polyamide-6 useful for the purposes of the present invention has a value of the relative viscosity of from 2.55 to 2.65, when determined in sulphuric acid solvent at 95.7% by weight, with a polymer concentration of 1% by weight in the solution.
Such a polyamide-6 is molten, after drying (moisture content of the order of approximately 0.05% by weight), in a screw extruder, at a temperature of the order of 275°C, and is fed to the spinneret. Advantageously, the spinneret is provided with bores of a diameter of from 0.20 to 0.35 mm.
The filaments exiting the die are heated, inside a cooling chamber, by means of an air stream at room temperature (20-25°C) and with controlled moisture values, delivered perpendicularly, or approximaterly perpendicularly relatively to the filaments.
The cooled filaments are collected in a bundle of filaments (the thread), while to them a finish liquid is applied. From 3 to 18 filaments, and preferably 10 filaments, may be combined, to yield a bundle of filaments (thread). The finish liquid is constituted by an oil/water emulsion, and is selected from those in the art, and capable of giving the thread antistatic and lubricant characteristics. For these threatments, a thread-guide, finish-liquid-jet device can be used, which is equipped with a slot inside which the union of the filaments takes place, and with a bore through which the finish liquid is injected, by means of a metering pump.
The so-obtained finished thread is submitted to an interlacing treatment, so as to create at least 10, and up to 25 interlacing points per thread metre. That corresponds to values of from 10 to 4 cm between two adjacent interlacing points, as determined by APDC (Automatic Pin Drop Count). In the preferred form of practical embodiment, 15-18 interlacing points per thread metre are created. In order to carry out this interlacing operation, all those devices can be used, which are known from the prior art, by means of which one or more continuous air stream(s) are delivered perpendicularly, or approximately perpendicularly, to the thread, so as to cause the phenomenon of entanglement of the filaments which compose the same thread.
The so-obtained interlaced thread is collected on a collection roll, and is stretched between said collection roll and a stretching roll. The collection roll is a lapped chrome-coated roll, not heated, which revolves at a peripheral speed of, or higher than, 4,000 metres/minute, up to 5,000 metres/minute. For this purpose, a single collection roll with a single open winding of the thread can be used, or a collection roll coupled with an idle roll, which a single closed winding of the thread, can be used. In the preferred form of practical embodiment, for the stretching, a couple of lapped, chrome-plated, not heated, rolls can be used, with two or more thread windings. It was found that the number of thread windings on the stretching rollers is not critical, and that two windings are generally enough for the intended purpose. The peripheral speed of the stretching rollers is maintained at values of from 4,800 to 6,000 metres/minute, so as to create a stretch ratio of from 1.2 to 1.35.
According to the present invention, the so obtained interlaced and stretched thread is submitted to relaxation by treatment with superheated steam, carried out under conditions within which the structure of the same thread does not change, or does not substantially change.
In particular, for the intended purpose, steam superheated at a temperature of at least 115°C and up to 180°C, and preferably at temperatures of from 130°C to 170°C is used.
In the contact between the thread and the superheated steam, changes in thread structure, and, in particular, phenomena of further entangling of the filaments, and changes in the number of the interlacement points present in the same thread, should be prevented, or substantially prevented.
For such purpose, the contact between the thread and steam can be carried out inside a contact chamber, inside which the direct contact between the thread and the steam fed to the same chamber is carefully prevented.
A form of contact chamber, suitable for that purposes, is shown in Figures 1 and 2 of the hereto attached drawing table.
In particular, in Figure 1 a perspective view of a contact chamber is shown, wherein the contact chamber is composed by two half-chambers (1) and (2), shown spaced apart from each other for the sake of clearness. The two half-chambers (1) and (2) can be connected with each other, by means of screws, with the chamber being completely sealed in its rear portion, and with a port being formed which, peripherally, is of the order of 0.5 mm, and which extends through the area of passage of the thread (4), and to the front portion of the chamber. The chamber is furthermore provided on the upper with a thread guide of a ceramic material (3), in order to prevent the thread (4) from coming into contact with the metal walls of the contact chamber. A similar thread-guide, not shown in the Figure, is provided in the bottom portion of the contact chamber. In Figure 1, by the reference numeral (5), the inlet channel for superheated steam, and by the reference numeral (6) the outlet channel for the exhausted steam is indicated.
Figure 2 shows a vertical sectional view of the half-chamber (1) of Figure 1. In particular, in this Figure 2, by the reference numerals (5) and (6) the superheated steam inlet and the exhausted steam outlet are still respectively indicated. In this Figure, the outline of the inner wall of the half-chamber can be observed in particular, which is given a crown shape (8) in its upper portion. In this way, the steam entering the chamber through the duct (7) having a direction substantially from down upwards, impinges the crown-shaped inner wall of the half-chamber (1), generating a turbulent motion of steam, and preventing the thread (4) from coming into direct contact with the superheated steam entering the chamber.
The other half-chamber (2) does not require any particular shapes in its inner wall, which may be simply hollow, with its hollow being directed outwards.
In use, the contact chamber shall be suitably thermally insulated, by means of a suitable thermally insulating material.
The present Applicant found that, in order to obtain a complete relaxation of the stretched thread extremely short contact times are enough, which are as short as achievable inside a contact chamber having a height of a few cm, in general of from 4 to 6 cm.
The steamed thread is then wound at a speed which is approximately 8-10% lower than the peripheral speed of the stretching rollers. In practice, the winding is carried out at values comprised within the range of from 4,300 to 5,600 metres/minute, with a winding tension of the order of 0.10 to 0.15 g/denier.
By means of the process of the present invention, a stretched thread of polyamide-6 is obtained, which has a number of interlacements practically equal to that given during the step which precedes the stretching, on bobbins of extremely good appearance and quality, free from deformations, and with a practically quantitative yield. The characteristics of such a thread are uniform, and are typically comprised within the following ranges of values: count of from 22 to 78 dtex; tenacity higher than 40 cN/dtex; elongation at break lower than 45%; and residual shrink of, or lower than, 10%, in water at 100°C.
Such a yarn can be directly warped with optimum warping behaviours (0.01-0.03 faults per thread kg), and then transformed into a piece endowed with excellent dyeing evenness.

Example

A polyamide-6 having a relative viscosity of 2.60 when measured in sulphuric acid at 95.7% by weight, and with a concentration of polymer in the solution of 1% by weight, is used.
Polyamide-6 granules, dried down to a moisture content of approximately 0.05% by weight, are molten inside a screw extruder of 38 mm of diameter, and having a length/diameter ratio of 24/1. The molten material, at a temperature of 275°C, is fed through a 4-delivery metering pump, to 4 spinnerets, each having 45 mm of diameter, and each equipped with 10 bores. Each bore has a diameter of 0.25 mm, and the height to diameter ratio of the bore is of 2.
The extruded filaments are cooled inside a cooling chamber provided under the spinnerets, by means of an air stream fed with an inlet temperature of 22°C, a relative humidity of 60%, and a constant outlet rate of 0.5 metres/second.
At a distance of approximately 140 cm from the spinnerets 4 filament bundles (threads) are formed, each of which is obtained by combining 10 filaments. For that purpose, the ceramic device manufactured by BETTINI, Model BX914A, of the slotted type, is used, which is provided, at slot bottom, with a channel through which by means of a metering pump an oil/water emulsion having antistatic and lubricant characteristics, is fed.
The four threads, provided with the finish coating, run then, in air, through an approximately 6-metre long spinning tube, and, at tube outlet, each of them runs through an interlacement device manufactured by BARMAG, Ceramic Tangle Jet Type, Model 465664/9, provided with two bores of 1.1 mm each.
Inside the bores of the device, compressed air is fed at a pressure of 5 kg/cm², and at room temperature, with vorticity being generated in the area through which the thread runs. In this way, on each thread approximately 16 points of interlacement per metre (approximately 6 cm between two adjacent interlacement points according to APDC - Automatic Pin Drop Counts) are generated.
Each of the four interlaced threads is collected on a not heated roll/idle roll couple, with a single closed winding of the thread, which revolves at a peripheral speed of 4,500 metres/minute. The stretching of the four threads takes place between said roll/idle roll couple, and a couple of not heated rolls, with 2.5 thread turns, which revolve at a peripheral speed of 5,400 metres/minute.
The four stretched threads subsequently run each through a contact chamber of the type disclosed in the present disclosure, and shown in the hereto attached drawing table. The contact chamber has a height of 52 mm, and to the chamber superheated steam is fed at a temperature of 150°C.
Each of the four steamed threads is finally wound on a winding machine, which operates at a collection speed of 4,900 metres/minute, with a winding tension of 0.10-0.15 grams/denier. Packages of 10 kg of thread, free from faults, and from any phenomena of instability of bobbin, are formed.
The so-obtained threads of polyamide-6 have a number of interlacements practically equal to that given during the step preceding the stretching. The characteristics of the threads are:
- Count :44 dtex
- Tenacity :42-44 cN/tex
- Elongation at Break : 42 %
- Residual Shrink in water at 100°C : 10 %
In warping and weaving, these threads make it possible a yield practically equal to 100%, evaluated on the whole bobbin, to be achieved.
By repeating the above example, without or with treatment of interlacement being carried out after the stretching step, bobbins were obtained, which showed a certain instability.
Furthermore, a loss in yield due to filament breakage phenomena was observed.

Claims

1. Continuous process for the production of an interlaced and stretched thread of polyamide-6, comprising the following steps, carried out in sequence:

(a) extrusion from molten polyamide-6 through the bores of a spinneret;

(b) cooling of the extruded filaments by means of an air stream;

(c) union of the cooled filaments to form a bundle of filaments (the thread) and simultaneous application of a finish liquid;

(d) interlacing of the thread treated with the finish liquid, with a number of interlacing points equal to at least 10 per metre;

(e) stretching of the interlaced thread between a collection roll and a stretching roll, carried out in the absence of heating;

(f) relaxation of the interlaced thread by means of the treatment with superheated steam at a temperature of at least 115°C, carried out without varying, or without substantially varying, the structure of the thread;;

(g) winding on a bobbin of the steamed thread.

2. Process according to claim 1, characterized in that in the (a) step a polyamide-6 having a relative viscosity of from 2.55 to 2.65 (determined in a solution at 1% by weight in sulphuric acid at 95.7% by weight) is molten at a temperature of approximately 275°C and is extruded through a spinneret equipped with bores of a diameter comprised within the range of from 0.20 to 0.35 mm.

3. Process according to claim 1, characterized in that in the (b) step an air stream at room temperature is fed perpendicularly, or approximately perpendicularly, to the filaments.

4. Process according to claim 1, characterized in that the (c) step from 3 to 18 filaments are collected in a filament bundle (thread).

5. Process according to claim 4, characterized in that each filament bundle (thread) contains 10 filaments.

6. Process according to claim 1, characterized in that in the (d) step from 10 to 25 interlacement points are created per each thread metre.

7. Process according to claim 6, characterized in that said interlacement points are 15-18 per thread metre.

8. Process according to claim 1, characterized in that in the (e) step, the thread is collected over a collection roll having a peripheral speed comprised within the range of from 4,00 to 5,000 metres/minute, and is then stretched between said collection roll and a stretching roll revolving at a peripheral speed comprised within the range of from 4,800 to 6,000 metres/minute, with a stretch ratio comprised within the range of from 1.20 to 1.35

9. Process according to claim 8, characterized in that one single collection roll, with one single open winding of the thread is used.

10. Process according to claim 8, characterized in that a collection roll coupled with an idle roll, with one single closed winding of the thread is used.

11. Process according to claim 8, characterized in that a couple of stretching rollers with two or more thread windings are used.

12. Process according to claim 1, characterized in that in the (f) step steam superheated at a temperature comprised within the range of from 115 to 180°C is used.

13. Process according to claim 12, characterized in that said temperature of the superheated steam is comprised within the range of from 130 to 170°C.

14. Process according to claim 1, characterized in that the (f) step is carried out inside a contact chamber inside which the direct contact between the thread and superheated steam, fed to the same chamber, is prevented.

15. Process according to claim 14, characterized in that said contact chamber has a height comprised within the range of from 4 to 6 cm, and has at least one of its inner surfaces with a crown shape, and superheated steam is fed to the chamber, with a direction substantially from down upwards, so as to impinge the portion of the inner wall of the chamber which is given said crown shape.

16. Process according to claim 1, characterized in that in the (g) step the thread is collected at a winding speed comprised within the range of from 4,300 to 5,600 metres/minute (8-10% lower than the stretching speed), with the winding tension being of the order of 0.10-0.15 g/denier.