EP0213772B1

EP0213772B1 - Method for the production of acrylic fibers with high physical properties

Info

Publication number: EP0213772B1
Application number: EP19860305986
Authority: EP
Inventors: Akiyoshi Uchida
Original assignee: Japan Exlan Co Ltd
Current assignee: Japan Exlan Co Ltd
Priority date: 1985-08-05
Filing date: 1986-08-04
Publication date: 1990-04-11
Anticipated expiration: 2006-08-04
Also published as: JPS6233817A; EP0213772A3; EP0213772A2; DE3670312D1

Description

This invention relates to a method for the industrial production of acrylic fibres with high physical properties. The fibres are suitable for use as a material for cement reinforcement.
Fibres having high strength and high modulus of elasticity are required for a wide range of uses, one of the most important of which is as a reinforcement material. In recent years, various attempts have been mode to improve the physical properties of acrylic fibres. One such attempt is described in Japanese Patent Kokai (Laid-open) No. 134 124/79, wherein fibres produced in the usual way are restretched in pressurized steam, thereby attaining high stretching times and finally producing fibres with high physical properties.
Another approach, as represented by Japanese Patent Kokai (Laid-open) No. 199 809/84, is to attain high physical properties by using a super-high molecular weight polymer as the fibre-forming starting material; arranging polymer molecular chains in parallel in the steps of preparing the spinning solution, and spinning the solution into fibres, etc. by various contrivances, thereby bringing the whole molecular chains near to the so-called "stretched-to-full-length" state in the direction of the fibre axis.
In the afore-mentioned re-stretching method in pressurized steam, there are problems in the apparatus (such as sealing) and operation, resulting from the use of pressurized steam. This method makes it possible to attain high stretching times by lowering the cohesive force of nitrile groups by the so-called plasticizing effect of water, but on the other hand, it is difficult for this method to exert the original stretching effect of bringing the whole molecular chains near to the "stretched-to-full-length" state, because molecular slipping may occur. For this reason, extremely high stretching times, preferably 35 to 100 times, are necessary as described in the above-mentioned Japanese Patent Kokai (Laid-Open) No. 199 809/84. Moreover, such a stretching method in steam is liable to produce microvoids in the fibre structure, and these microvoids obstruct the attainment of high physical properties.
Furthermore, in the method using a super-high molecular weight polymer, it is necessary to prepare a special polymer which is different from polymers of general use, and with the increase of the degree of polymerization, the viscosity of the polymer solution (spinning solution) increases remarkably, so that the handling, defoaming, spinning, etc. of the solution become difficult. When the polymer concentration of the solution is reduced to lower the viscosity, the productivity and the physical properties of the fibres obtained are also lowered.
EP-A 0 044 534, EP-A 0 061 117 and GB-A 2 018 188 also relate to polyacrylonitrile fibres and filaments, and processes for the production thereof. However, the conditions employed are distinct from those used in the method of the present invention.
The object of this invention is to provide a method for producing acrylic fibres with high physical properties, suitable as a material for cement reinforcement, and which avoids the above-mentioned problems.
The present invention provides a method of producing acrylic fibres with high physical properties and composed of more than 80 weight % acrylonitrile, said method being characterised by comprising the steps of spinning an acrylonitrile polymer spinning solution while maintaining the linear velocity ratio of extrusion (as herein defined) at a value of above 4; water-washing and stretching the thus obtained gel fibres; regulating the internal water content of the gel fibres to within the range of from 2 to 20% by weight; subjecting the stretched fibres to dry-heat treatment under tension or dry-heat stretching at a temperature within the range ± 30°C of the temperature at which maximum stretching is possible; and thereafter cooling the fibres under tension so that the effective total stretching times will be more than 15 times, the linear velocity ratio of extrusion being defined as:
wherein V_o represents the linear velocity of extrusion (m/min) of the spinning solution, and V represents the winding speed (m/min) of the extruded gel fibres.
The resulting acrylic fibres are composed of a polymer containing more than 80 weight % acrylonitrile (hereinafter referred to as AN) and have strength-elongation characteristic determined by the following formulae:

(I) 70 cN/tex s TS (8 g/d s TS);
(II) 1230 cN/tex E (140 g/d s E);
(III) TE s 15%; and
(IV) 15800 ≤ E x TE (1800 ≤ E x TE), wherein TS represents tensile strength, E represents Young's modulus and TE represents elongation.

As the AN polymer used in this invention, any polymer insofar a it contains more than 80 weight % of AN, preferably more than 90 weight % of AN, can be used without limitation as to its molecular weight. As the other components, there may be mentioned known monomers that can be copolymerized with AN, for example such as methyl, ethyl, butyl, octyl, methoxyethyl, phenyl and cyclohexyl, esters of (meth)acrylic acid; vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; (meth)acrylamide and derivatives thereof; unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid and itaconic acid, and salts thereof; unsaturated sulfonic acid such as vinylsulfonic acid, (meth)allylsulfonic acid, p-styrenesulfonic acid and acrylamide propanesulfonic acid, and salts thereof; vinyl halides and vinylidene halides such as vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride and vinylidene fluoride; vinyl compounds such as styrene, ethyl vinyl ketone, methyl vinyl ether, (meth)allylalcohol, vinyl pyridine, dimethyl aminoethyl methacrylate, vinylidene cyanide, methacrylonitrile and glycidyl (meth)acrylate.
As the solvents for dissolving such a polymer to produce a spinning solution, there may be mentioned organic solvents such as dimethylformamide, dimethylacetamide and dimethyl sulfoxide; and aqueous solutions of inorganic solvents including thiocyanates such as sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate, and nitric acid and zinc chloride. The use of an aqueous solution of an inorganic solvent, especially a thiocyanate, is preferred.
There is no limit on the polymer concentration but, from the industrial viewpoint, it is desirable for it to be generally at 5-30 weight %, preferably at 7-15 weight %.
In this invention, it is important to conduct spinning while maintaining the linear velocity ratio of extrusion of the spinning solution at above 4, desirably between 5 and 20, and more desirably between 6 and 12. When the ratio is below the lower limit of this range, the stretchability is reduced, and if the fibres are not subjected to a special stretching operation, such as multi-stage stretching in a high boiling point medium above 100_°C, it is impossible for the fibres to attain the necessary effective total stretching times and the finally obtained fibres show only inferior physical properties. When the ratio goes above the upper limit of the range, there occur problems such that the use of a deep coagulation bath is necessary, or the physical properties become uneven. Insofar as the fibres are extruded through a spinnerette while satisfying the above-mentioned conditions and are wound (drawn) out of the coagulation bath, not only the usual wet-spinning but also the so-called "dry-wet-spinning" may be employed, wherein the fibres are once extruded into an inert atmosphere such as air and subsequently introduced into the coagulation bath.
The extruded gel fibres drawn out of the coagulation bath are then washed with water and stretched.
In the water-washing and stretching steps, the fibres may be cold-stretched and heat-stretched during water-washing (solvent removal) in the usual way or after water washing. Each of the cold and heat stretchings may be conducted in multi-stage steps.
The water content of the gel fibres immediately after such stretching steps is desirably within the range of from 50 to 150%, preferably from 55 to 130%. Means for controlling the water content include regulation of the polymer concentration in the spinning solution, the temperatures of the coagulation bath, water-washing and stretching. However, by setting the stretching times in the above-mentioned cold and heat-stretching steps at more than 10 times, preferably from 12 to 20 times, while taking into account the above-mentioned linear velocity ratio of extrusion, the water content can be controlled advantageously and finally the fibres with high physical properties can be provided in an industrially advantageous manner. Further, by apportioning the cold stretching times and heat stretching times as follows, more desirable results can be obtained:
wherein A represents cold stretching times and B heat stretching times.
The fibres thus obtained by spinning, water-washing and stretching could be sent to the succeeding step while maintaining the above-mentioned water content. However, it is necessary from the viewpoint of efficient operation to regulate the internal water content of the gel fibres just after stretching to within the range of from 2 to 20%, preferably from 5 to 15%, and thereafter to subject the fibres to dry-heat treatment under tension or to dry-heat stretching.
Among the various possible means for regulating the internal water content, the following may be mentioned for use in an industrial scale operation. The gel fibres, after the heat stretching, are dried on heated rolls under tension (with limited shrinkage, preferably in a definite length) successively or under a certain degree of stretching (less than about 1.2 times) so as to regulate the internal water content of the gel fibres to within the prescribed range. The temperature of the heated rolls is desirably set at below about 140_°C, preferably within the range of from 60 to 120_°C, and most preferably from 70 to 100_°C.
When the internal water content is outside of the aforementioned range, problems in operation are liable to occur such as fibre breakage and/or lowering of stretchability, especially in the succeeding steps (among others, in the dry-heat stretching step).
In the dry-heat treatment step under tension or in the dry-heat stretching step, the temperature condition is particularly important. It is necessary to set such temperature within the range ± 30°C, preferably ± 20°C, of the temperature at which maximum stretching is possible. This means the temperature at which the maximum stretching times can be obtained without causing fibre breakage in the dry-heat stretching step. Only by satisfying such a temperature condition, will the fibre manifest the high physical properties which have been imparted to it in the previous steps. When the temperature is outside of this range, it is impossible to produce the fibres of this invention. For the attainment of the object of this invention, it is desirable to dry-heat stretch the fibres more than 1.05 times, preferably from 1.1 to 2.5 times, and most preferably from 1.2 to 2.3 times.
In this invention, it is important to subsequently cool the fibres under tension. As for the tension condition, it is desirable to stretch more than 1.02 times, preferably 1.05 times, so that the fibres after the dry-heat treatment under tension or dry-heat stretching are not relaxed and lowered in physical properties while they are cooled to room temperature, or are not wound around the rollers. If the fibres are heat-set after dry-heat stretching and before cooling under tension, the physical properties can be further improved. The recommended heat-set condition is dry heat between 180_° and 250_°C, preferably under a definite length.
For the acrylic fibres produced in the above-mentioned steps under the afore-mentioned conditions, it is necessary to determine a stretching condition so that the effective total stetching times should be finally above 15 times, preferably above 18 times, and most preferably above 20 times. By satisfying these requirements, acrylic fibres with high physical properties can be finally produced without any problems in operation and on an industrial scale.
The temperature making possible the maximum stretching varies greatly depending on, for example, the polymer composition, polymer molecular weight and spinning condition, so that it is impossible to specify precisely. However, in the case of a polymer with a practical polymer composition and molecular weight, for example AN s 85 weight % and weight average molecular weight of from 70,000 to 250,000, the temperature generally varies within the range of from 140° to 180°C. The precise value of such a temperature may be determined as follows. For example, the dry-heat stretching temperature for the sample fibres is gradually changed and the stretching times for each temperature at which the fibres are broken are obtained. Thus, the dry-heat stretching temperature giving the maximum stretching times can be obtained.
In this way, it is possible to provide industrially advantageous acrylic fibres having strength-elongation characteristics of a tensile strength (TS) generally above 70 cN/tex (8 g/d), preferably above 88 cN/tex (10 g/d), a Young's modulus (E) above 1230 cN/tex (140 g/d), preferably above 1320 cN/tex (150 g/d), an elongation (TE) less than 15%, preferably less than 12%, and a product of Young's modulus and elongation (E x TE) above 15800 (1800).
We do not fully understand why acrylic fibres with such high physical properties can be provided on an industrial scale by employing the above process requirements in combination. However, a possible explanation is as follows. The solvent removal and coagulation speed, due to the spinning under the conditions of the linear velocity ratio of extrusion recommended in this invention, bring the polymer molecular structure in the extruded gel fibres to a state in which excellent stretching and orientation can be obtained in the following stretching step. Further, the succeeding water-washing and stretching, and the subsequent dry-heat treatment under tension or dry-heat stretching under a particular temperature condition, as well as the cooling which comes next, aid in bringing the molecular chains of the finally formed fibres into parallel arrangement near the "stretched-to-the-full-length" chains, without forming voids in the fibre structure. Thus, the high physical properties are manifested.
It is an effect worthy of special mention of this invention that an industrially advantageous method of producing acrylic fibres with high physical properties has been provided, without any problems in operation, without preparing a special polymer as the fibre-forming starting material, and without using as an essential means a stretching step in pressurized steam which has problems with the apparatus, its operation and in the physical properties achieved.
It is also a characteristic advantage of this invention that, since there is no need to use a spinning solution of high viscosity, there is no difficulty in the handling of the solution or in the operations of defoaming and spinning, and that the invention has therefore provided a means which does not necessitate lowering of the polymer concentration (which may lower the productivity and fibre physical properties) to avoid such difficulties.
Furthermore, the acrylic fibres of this invention retain a moderate elongation contrary to common knowledge, and have a high strength and modulus of elasticity. Therefore, when the fibres are used, for example, as a cement reinforcement material, they can withstand stresses such as shear and bend upon dispersion, moulding or shrinkage of the cement. Also, the fibres can minimize the cracks generated during the use of cement reinforced with the fibres, thus improving its tenacity. Moreover, the fibres of the invention have the advantage of elevating the impact strength of the reinforced cement.
The acrylic fibres of this invention can thus be widely used in the industrial field, including as reinforcement materials for resin and cement, tyre cords, precursors for carbon fibres and ropes. The fibres of this invention are therefore very useful.
For a better understanding of the invention, some Examples of the invention in practice are given below. Percentages in the Examples are by weight unless otherwise indicated.

Reference Example 1

An AN copolymer composed of 90% AN and 10% methyl acrylate (MA) and having an intrinsic viscosity [η] in dimethylformamide at 30_°C of 1.4, was dissolved in an aqueous 50% sodium cyanate solution, to prepare a spinning solution of a polymer concentration of 10% (the viscosity at 30_°C: 5.5 Pa.s/55 poises).
The spinning solution at 80°C was extruded into an aqueous 15% sodium cyanate solution at -3°C through a spinnerette (50 orifices, diameter of each orifice: 0.05 mm), and the resulting fibres were wound at various linear velocity ratios of extrusion (as shown in Table 1). The fibres were then cold-stretched 3.0 times and thereafter heat-stretched in boiling water, thereby to obtain the maximum heat-stretching times.
The results are shown in Table 1.
It is seen from the above Table that, by increasing the linear velocity ratio of extrusion, the total stretching times (maximum stretching times allowing stretching (cold x heat) without causing fibre breakage) can be remarkably increased.

Reference Example 2

Water-swollen gel fibres (internal water content: 73%) were produced in the same way as in Reference Example 1 No. 5, except that the heat-stretching times were 5.3 times.
Then, sample fibres were dried under a definite length on heated rolls at 80°C so that the internal water content became 10%, and the fibres were then heat-stretched at various temperatures of the heated rolls (as shown in Table 2). Thus, the maximum stretching times (dry-heat stretching time at breakage) at each temperature was obtained.
The results are shown in Table 2.
It is seen from the above Table that the temperature allowing the maximum stretching times is 150°C.

Example 1

The sample fibres described in Reference Example 2 (except that the heat-stretching times were 4.0 times) were dry-heat stretched under the conditions described in Table 3, and 6 kinds of fibres (A-F) were produced.
The physical properties of these fibres were measured and the results are shown in Table 3.
All these fibres showed good operability, without causing fibre breakage upon dry-heat stretching. But when undried sample fibres (internal water content: 73%) and sample fibres dried to an internal water content of 1%, were dry-heat stretched in the same way as Fibre D, there was remarkable fibre breakage and it was impossible to continue operation.
From the above Table, it is clearly seen that the fibres of this invention have excellent physical properties, and that when the dry-heat stretching temperature goes outside of the range of this invention (Fibre F, and Fibre E cooled without tension), it was impossible to obtain fibres with high modulus of elasticity and high elongation.

Example 2

In the same way as with Example 1 Fibre C, except that the linear velocity ratio of extrusion was varied as shown in Table 4, three kinds of fibres (G, H and I) were produced. The internal water content and physical properties were measured. The results are shown in Table 4.
From the above Table, it is clearly seen that the fibres of this invention have excellent properties, and that when the linear velocity ratio of extrusion goes outside of the range of this invention (Fibre G), fibres with high physical properties could not be obtained owing to inferior stretchability.

Example 3

Fibres J and K were produced in the same way as Example 1 Fibre D, except that the molecular weight of the AN copolymer was changed to [η]1.8, or the composition was changed to 97% AN and 3% MA, and that, as the dry-heat stretching temperature, temperatures allowing the maximum stretching shown in Table 5 were employed.
From Table 5, it is clearly seen that the fibres of this invention have excellent physical properties.

Claims

1. A method of producing acrylic fibres with high physical properties and composed of more than 80 weight % acrylonitrile, said method being characterised by comprising the steps of spinning an acrylonitrile polymer spinning solution while maintaining the linear velocity ratio of extrusion (as herein defined) at a value of above 4; water-washing and stretching the thus obtained gel fibres; regulating the internal water content of the gel fibres to within the range of from 2 to 20% by weight; subjecting the stretched fibres to dry-heat treatment under tension or dry-heat stretching at a temperature within the range ± 30_°C of the temperature at which maximum stretching is possible; and thereafter cooling the fibres under tension so that the effective total stretching times will be more than 15 times, the linear velocity ratio of extrusion being defined as:

wherein V_o represents the linear velocity of extrusion (m/min) of the spinning solution, and V represents the winding speed (m/min) of the extruded gel fibres.

2. The method as claimed in claim 1, wherein an aqueous solution of an inorganic solvent is used as the solvent for producing the spinning solution.

3. The method as claimed in claim 1 oder claim 2, wherein the spinning is conducted while the linear velocity ratio of extrusion is maintained at 5-20.

4. The method as claimed in any of the preceding claims, wherein the internal water content of the gel fibres immediately after the heat stretching step is within the range of from 50 to 150% based on the dry weight of the fibre-forming polymer.

5. The method as claimed in any of the preceding claims, wherein the stretching times of cold stretching and heat stretching are set at more than 10 times.

6. The method as claimed in any of the preceding claims, wherein the apportionment of the cold stretching and heat stretching is regulated as the following formula:

wherein A represents cold stretching times and B represents heat stretching times.

7. The method as claimed in any of the preceding claims, wherein the fibres are dry-heat stretched within the range of from 1.1 to 2.5 times.

8. The method as claimed in any of the preceding claims, wherein the fibres are cooled under the stretching condition of more than 1.02 times.

9. The method as claimed in any of the preceding claims, wherein the fibres are dry-heat stretched, heat-set and cooled under tension.