EP0310800A1 - Process for the preparation of polyvinyl alcohol yarns - Google Patents

Abstract

Process for the preparation of polyvinyl alcohol yarns having a viscosimetric average molecular weight Mv of between 10<5> and 4.10<5>. A solution of polyvinyl alcohol in an organic solvent (N-methylpyrrolidone, dimethyl sulphoxide, ethylene glycol, glycerol or 1,3-propanediol) is spun from a spinneret across an air gap or a gap containing an inert gas into a coagulation bath and then stretched. The invention is characterised in that the length of the spinneret channels is at least five times, preferably 5-50 times, as great as their diameter and the concentration C in % by weight of the polymer solution is chosen so that C is > 30 - 5.10<-><5> Mv. Spinnerets of carbon fibre-reinforced polyetheretherketone or polyphenylene sulphide are preferably used. <IMAGE>

Description

The invention relates to a method for producing polyvinyl alcohol yarns with a viscometric average molecular weight M _v between 10⁵ and 4.10⁵, in which a solution of polyvinyl alcohol in an organic solvent is spun from a spinneret through an air gap or a gap with an inert gas into a coagulation bath and then stretched. Such a procedure has already been proposed in European patent application 146 084.

Although strong yarns can be obtained according to the examples of this patent application, the applicant has not succeeded in producing yarns with comparable properties with the data given therein. In addition, the polyvinyl alcohol concentrations used in the examples are so low that the process loses attraction from an economic point of view.

The present invention now provides a method whereby yarns of polyvinyl alcohol with high tensile strength and other favorable physical properties can be obtained from polymer solutions with a much higher concentration of polyvinyl alcohol.

The invention consists in that, in a procedure of the known type mentioned at the outset, the length of the spinneret channels in the direction of the spinning solution flow is at least five times as large as their diameter and the concentration C in% by weight of the polymer solution is chosen such that C ≧ 30 - 5.10⁻⁵ M _v is.

The yarns produced using this method of operation not only show high tensile strength, but also high water resistance. The mechanical properties also largely correspond to the properties specified in the aforementioned European patent application, but are already obtained at lower stretching ratios than are mentioned therein.

To obtain filaments of sufficient tensile strength, it is necessary within the scope of the invention to use spinnerets in which the length of the spinneret channels is at least five times as large as their diameter. A preferred embodiment is that a spinneret is selected, the spinneret channels of which have a constant diameter over the entire length. Although in principle good results can always be obtained if the length / diameter ratio of the spinneret channels is chosen to be greater than 5, it is preferred for economic and technical reasons that the length / diameter ratio of the spinneret channels is between 5 and 50. Here the best results are obtained if the length / diameter ratio is chosen between 20 and 40.

Advantageously, the nozzle plates can consist of polyether ether ketone or polyphenylene sulfide, each of which contains e.g. 30 wt .-% carbon fibers are reinforced. In such nozzle plates, which are not attacked by N-methylpyrrolidone and other organic solvents at higher temperatures, nozzle capillaries with the claimed large length / diameter ratio can be drilled particularly easily. The gel is unable to adhere to the surface of such spinnerets, so that a particularly good spinning behavior can be observed.

In the context of the present invention, a method of operation is preferred in which, on the outlet side of the spinneret, the adjoining spinning mass flows leave the spinneret channels with respect to the intermediate surface of the spinneret plate at different levels. Such a mode of operation can only be realized through a special design of the spinneret.

Possible constructions include both an embodiment in which the spinneret channels protrude from the surface of the spinneret plate, i.e. form projections, and an embodiment in which the spinneret ends are at the same or almost the same level as the surface of the spinneret plate, with the proviso that around a recess is provided around the spinneret channel ends.

The spinneret channel ends are preferably frustoconical. This prevents the spinning mass flows from coming into contact with the surface of the spinneret plate after leaving the spinneret channels.

In the context of the present invention, various, preferably organic, solvents can be used to dissolve the polyvinyl alcohol. Good results are obtained if a polyhydric alcohol is used as the organic solvent. Examples of suitable polyhydric alcohols are ethylene glycol, glycerin and / or 1,3-propanediol.

Good results are also obtained if dimethyl sulfoxide (DMSO) is used as the organic solvent. However, the latter solvent is toxic and decomposes when exposed to temperatures above 140 ° C. It has been shown that optimal results can be obtained when using N-methylpyrrolidone as solvent. This solvent is not only much less toxic than dimethyl sulfoxide, but also leads to better yarn properties.

The temperature at which the solution of polyvinyl alcohol can be spun is generally between 20 and 250 ° C and depends in part on the type of solvent used or the mixture of solvents. If a polyhydric alcohol is used as the solvent, the spinning temperature is generally chosen between 175 and 190 ° C or higher. When using dimethyl sulfoxide, the spinning temperature is usually not more than 80 ° C, although temperatures of 120 to 150 ° C can be used. The temperature of the coagulation bath will usually set to ambient temperature or lower.

After leaving the spinneret, the solution of polyvinyl alcohol passes through an air gap or a gap with an inert gas before it is coagulated in the coagulation bath. The distance between the outlet openings of the spinneret and the coagulation bath is generally chosen between 2 and 200 mm and preferably between 3 and 20 mm. With a shorter distance than 2 mm, the process control is extremely complicated, while with a larger distance than 200 mm, thread breaks can occur.

The coagulation bath usually contains a lower alcohol or an organic solvent such as acetone, benzene or toluene. Mixtures with a solvent for polyvinyl alcohol can also be used. It is also possible to use a saturated aqueous solution of an inorganic salt. However, acetone or a lower alcohol, such as ethanol, butanol and in particular methanol, are preferred. After coagulation, the filaments are wound up with e.g. Extracted methanol and dried.

In order to obtain a yarn with a high tensile strength, warm drawing should preferably be performed. The stretching process can be carried out in one or more process steps at a temperature between the glass transition temperature and the decomposition temperature and preferably between 190 and 250 ° C. In the context of the present invention, a procedure is preferred in which the stretching ratio is chosen between 10 and 35 and preferably between 15 and 30.

The invention is illustrated by the following examples. Of course, the invention is not limited to these exemplary embodiments.

• Fig. 1 zeigt in stark vergrößertem Maßstab eine Spinndüse in der Aufsicht.
• Fig. 2 zeigt in stark vergrößertem Maßstab die Spinndüse von Figur 1 in Vorderansicht.
• Fig. 3 zeigt in stark vergrößertem Maßstab die Spinndüse von Figur 1 von unten.

In carrying out the tests according to the invention, a spinneret was used, the construction of which is explained with reference to FIGS. 1-3.

• Fig. 1 shows a greatly enlarged scale of a spinneret in top view.
• FIG. 2 shows the spinneret of FIG. 1 in a front view on a greatly enlarged scale.
• Fig. 3 shows the spinneret of Figure 1 in a greatly enlarged scale from below.

The spinneret channels shown in FIG. 1 have a diameter of 250 μm. The spinneret channels indicated by broken lines in FIG. 2 are 9.5 mm long. The height of the truncated cone is 0.5 mm.

When producing a polyvinyl alcohol yarn on an industrial scale, the spinneret is provided with a large number, for example with 250 spinneret channels, instead of the six specified.

The mechanical properties of the yarns, the production of which is given in the examples below, are determined on an Instron universal testing machine at 20 ° C. and 65% relative humidity. The filament clamping length was 10 cm and the drawing speed was 100% per minute. Use was made of Instron 2712-001 Fiber clamps that were provided with copolyetherester clamping surfaces of 1X1 cm².

The tensile strength at break τ _b was determined from the end point of the tensile force-elongation curve and is given in cN / tex;
The maximum module E _max was determined numerically from the tensile force-length change curve and is given in N / tex;
The elongation at break values ε _b represent the percentages with which the original clamping length was increased by the filament draw.

To determine the molecular weight, intrinsic viscosity measurements were carried out in accordance with the standard method JIS 6726 (JAPAN INDUSTRIAL STANDARD: Testing methods for polyvinylalcohol). The viscometric average molecular weight M _v is then using the Mark-Houwink equation:

[η] _{30 ° C} = 4.53 · 10⁻⁴ M _v ^0.64

been calculated.

example 1

Average polyvinyl alcohol viscometric molecular weight M _{v of} the PVA ≈ 295,000, degree of saponification 99.9%) was dissolved at 140 ° C. for three hours under a nitrogen atmosphere in dried N-methylpyrrolidone (NMP) until a 20% by weight PVA solution was obtained. The solution thus obtained was introduced into a cylinder belonging to a mini-plunger spinning apparatus in the absence of air. This spinning apparatus contained the same spinneret as in Figures 1, 2 and 3 is shown (6 spinneret channels with a diameter d _p = 300 µm and a length of 1 cm). The length / diameter ratio of the spinneret channels was therefore approximately 33. The filaments were spun at a speed of 2.6 m / min and passed into a methanol coagulation bath via an air gap of approximately 2 cm. After the coagulation bath, the yarn was wound up at a speed of 2.85 m / min. The filaments were then extracted into methanol for 24 hours and then air dried for one hour. Hot stretching was then carried out in two process steps. During the first drawing, the filaments were passed over a hot plate at 205 ° C. with a feed speed of 14.5 cm / min and a winding speed of 231 cm / min, which corresponds to a draw ratio of 15.9. In the second process step immediately following this, the filaments were passed through a hot tube through which nitrogen flowed at 235 ° C. at a winding speed of 246 cm / min, which corresponds to a total draw ratio of 17.0.

As a result of 10 measurements, a tensile strength of 187 cN / text, a maximum modulus of 43.5 N / tex and an elongation at break of 7.0% were determined for the filaments produced in this way.

Examples 2 to 6

In these examples the effect of a number of solvents at different spinning temperatures is examined. The polyvinyl alcohol used had an average molecular weight viscometric M _v ≈ 200,000. The test conditions were identical to those of Example 1, with the proviso that the spinneret contained only a single spinneret channel with a diameter of 200 μm, which corresponds to a length / diameter ratio of 25 given the otherwise identical length of the spinneret channel.

The spinning temperature, the draw ratio λ and the properties measured on the filaments are given in Table 1. Table 1 example solvent Spinning temperature (° C) λ τ _b (cN / tex) E _max (N / tex) ε _b (%) 2nd Glycol 175 19th 125 44.5 3.7 3rd Glycerin 190 20th 143 44.5 4.0 4th 1,3-propanediol 190 18th 113 35.0 4.1 5 DMSO 80 25th 162 43.0 4.8 6 NMP 100 24th 144 35.0 4.9

Examples 7 to 10

The experiment of Example 5 was repeated with the proviso that the spinning concentration was varied from 12.5 to 20% by weight of PVA in DMSO. The spinning temperature varied from 25 to 55 ° C and the draw ratio from 19 to 29.

The spinning temperature, the draw ratio and the properties measured on the filaments are shown in Table 2. Table 2 example Spinning conc. % By weight T _spinning (° C) λ τ _b (cN / tex) E _max (N / tex) ε _b (%) 7 12.5 25th 21st 131 41.7 4.1 8th 15.0 25th 22 132 39.5 4.6 9 17.5 55 29 130 42.2 3.7 10th 20th 55 19th 133 39.0 4.3

Examples 11 to 15

The experiment from Example 1 was carried out using a polyvinyl alcohol M _v ≈ 200,000, DMSO as solvent, a spinning speed of approximately 1 to 2 m / min and a stretching temperature of approximately 225 ° C.

The spinning concentration, spinning temperature, the draw ratio and the properties measured on the filaments obtained are shown in Table 3. Table 3 example Spinning conc. % By weight T _spinning (° C) λ τ _b (cN / tex) E _max (N / tex) ε _b (%) 11 35 140 11.8 90 27.4 5.9 12 30th 140 16.2 142 35.7 6.3 13 25th 120 17th 114 35.2 5.3 14 25th 90 15.6 110 29.8 6.2 15 20th 50 15.0 105 30.7 5.9

Examples 16 to 19

The experiment from Example 1 was carried out using a polyvinyl alcohol M _v ≈ 200,000, a spinning speed of approximately 1 to 2 m / min and a stretching temperature of approximately 225 ° C. The spinning temperature was always 140 ° C and the solvent used was N-methylpyrrolidone (NMP).

The spinning concentration, the draw ratio and the properties measured on the filaments obtained are shown in Table 4. Table 4 example Spinning conc. % By weight λ τ _b (cN / tex) E _max (N / tex) ε _b (%) 16 25th 15.0 130 32.2 6.5 17th 25th 16.6 140 30.7 7.6 18th 25th 16.8 140 31.0 7.0 19th 23 18.2 152 43.9 4.9

Examples 20 to 25

The experiment from Example 1 was repeated with DMSO or NMP as the solvent, with polyvinyl alcohol of a different average molecular weight, with different spinning concentrations and stretching ratios. The molecular weight of the polyvinyl alcohol used, the degree of saponification of the polyvinyl alcohol, the solvent, the spinning concentration, the draw ratio, and the properties measured on the filaments are listed in Table 5. Table 5 example M _v x10⁻⁵ Degree of saponification solvent Spinning conc. % By weight λ τ _b (cN / tex) E _max (N / tex) ε _b (%) 20th 2.0 98-99 DMSO 25th 16 97 28.6 5.3 21st 1.15 99.9 DMSO 25th 17th 110 28.4 6.1 22 2.1 99.9 DMSO 25th 17th 107 30.0 5.5 23 2.1 99.9 NMP 25th 18.5 129 32.2 6, 24th 2.95 99.9 DMSO 20th 19th 171 41.6 6.1 25th 2.95 99.9 NMP 20th 17th 187 43.5 7.0 Comparative example 0.95 99.5 DMSO 25th 17th 82 25.6 6.1

From the results reported in the table above it is clear that one M _v <10⁵ (see comparative _example ) the properties behind the filaments made of a polyvinyl alcohol with a M _v > 10⁵ remain.

The table above also shows that the best results are obtained when the polyvinyl alcohol has the highest possible degree of saponification (see Example 20 with Example 22) and when NMP is used as a solvent (see Example 22 with Example 23; example) 24 with example 25).

Example 26 (comparative example)

The experiment from Example 1 was carried out using a polyvinyl alcohol M _v ≈ 200,000, DMSO as solvent, repeated with spinning concentrations between 15 and 30 wt .-% and spinning temperatures between 25 and 150 ° C, with the proviso that now a wet spinneret with 30 spinneret channels was used, which has a length / diameter ratio of 1 with a diameter of 70 microns.

In no case could a stable spinning situation be created. Drop formation continuously occurred at one or more outlet openings.

Example 27

A piston spinning machine with a 6 hole spinneret was used. The nozzle plate consisted of 30 wt .-% carbon fiber reinforced polyphenylene sulfide. The 6 outlet openings had a diameter d _p = 220 μm and a length of 3.5 mm. A 25% by weight solution of polyvinyl alcohol in N-methylpyrrolidone was used for spinning. The polyvinyl alcohol had a molecular weight of 210,000.

The solution was pressed through the piston nozzle through the nozzle plate and passed through an air gap (= 1 cm) into a coagulation bath made of methanol. The filaments were spun at a speed of 3.0 m / min. After the coagulation bath, the yarn is wound up at a speed of 3.6 m / min. The bobbin was then extracted with the yarn in methanol for 24 hours. After air drying the filaments were over three hot plates, each having a temperature of 90 ° C, 230 ° C and 245 ° C, at a feed rate of 1 mm / sec. stretched with an aspect ratio of 16. The drawn filaments had the following properties:
Tensile strength: 135.3 cN / tex
Elongation at break: 6.3%
E _max : 35.1 N / tex

Example 28

A 23% by weight solution of polyvinyl alcohol in N-methylpyrrolidone with a molecular weight of 210,000 was pressed through an extruder and spinning pump through a die plate made of 30% by weight carbon fiber reinforced polyphenylene sulfide. The 35 outlet openings had a diameter d _p = 270 µm and a length of 6.5 mm. The spinning solution passed through an air gap (= 1 cm) into a coagulation bath made of methanol. The filaments were spun at a speed of 4 m / min and wound up at a speed of 8 m / min. The bobbin was then extracted with the yarn in methanol for 24 hours. After air drying, the filaments were drawn over two hot plates, each at 100 ° C and 230 ° C, at a feed rate of 32 cm / min. The draw ratio over the first plate was 7.3 and that over the second was 1.8. The total stretch ratio was 13.5. The drawn filaments had the following properties:
Tensile strength: 127.4 cN / tex
Elongation at break: 6.2%
E _max : 33.1 N / tex

Claims (12)

1. Process for the production of polyvinyl alcohol yarns with a viscometric average molecular weight M _v between 10⁵ and 4.10⁵, in which a solution of polyvinyl alcohol in an organic solvent is spun from a spinneret through an air gap or a gap with an inert gas into a coagulation bath and then stretched, characterized in that the length of the spinneret channels in the direction of the Spinning solution flow is at least five times as large as its diameter and the concentration C in wt .-% of the polymer solution is chosen so that C ≧ 30 - 5.10⁻⁵ M _v is. 2. The method according to claim 1, characterized in that the spinneret channels have a constant diameter over the entire length. 3. The method according to claim 1, characterized in that the length / diameter ratio of the spinneret channels is chosen between 5 and 50. 4. The method according to claim 1, characterized in that the length / diameter ratio of the spinneret channels is chosen between 20 and 40. 5. The method according to claim 1, characterized in that spinnerets made of carbon fiber reinforced polyether ether ketone or polyphenylene sulfide are used. 6. The method according to claim 1, characterized in that on the outlet side of the spinneret, the adjacent spinning mass flows leave the spinneret channels with respect to the intermediate surface of the spinneret plate at different levels. 7. The method according to claim 1, characterized in that a polyhydric alcohol is used as the organic solvent. 8. The method according to claim 7, characterized in that ethylene glycol, glycerol and / or 1,3-propanediol is used as the polyhydric alcohol. 9. The method according to claim 1, characterized in that dimethyl sulfoxide is used as the organic solvent. 10. The method according to claim 1, characterized in that N-methylpyrrolidone is used as the organic solvent. 11. The method according to claim 1, characterized in that the stretching ratio is chosen between 10 and 35. 12. The method according to claim 11, characterized in that the stretching ratio is chosen between 15 and 30.

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