Polyvinyl alcohol fibre having excellent properties at high temperature and radial-ply tyre comprised of the same

<td>POLAND</td><td>PATENT DESCRIPTION</td><td colspan="2"> 88890</td>

<td>RZECZPOSPOLIIA</td><td></td><td></td><td></td>

<td>CHINA</td><td></td><td></td><td></td>

<td></td><td>Additional patent to patent no.</td><td colspan="2">MKP DOlf 7/02</td>

<td>ei</td><td>Reported: 24.11.70 (P. 144605)</td><td></td><td></td>

<td></td><td>Priority: 25/11/69 Japan</td><td colspan="2">Int.Cl.i D01F 6/14</td>

<td>OFFICE PATENT</td><td>The application was announced: 14.04.73</td><td></td><td>READING ROOM</td>

<td>PRL</td><td rowspan="2">Patent description published · 30.07.1977</td><td></td><td>In the Patent⁰riliiai HaamaaiaN *!</td>

<td></td><td></td><td></td>

Inventor: Patent holder: Kuraray Oo., Ltd Sakazu (Japan)

Method for producing fibers from polyvinyl alcohol and

The present invention relates to a process for producing polyvinyl alcohol fibers containing orthoboric acid or its borate salt by wet spinning.

Polyvinyl alcohol (PAW) fibers outperform other synthetic fibers in terms of tear strength and modulus of elasticity and have recently found wide application in many fields, for example in fiber reinforced plastics. I know well₁₀The fact is that PAW fibers, which stretch to the stretch limit and in which shrinkage is minimized, have very good tear strength and modulus of elasticity. However, as with other synthetic fibers, the properties of PAW fibers at high temperatures deteriorate in proportion to the increase in temperature.

The object of the invention is to develop a method for producing polyvinyl alcohol fiber ₂of the above-mentioned disadvantages, and in particular having 'better tensile strength and better modulus of elasticity and creep than known PAW fibers.

The object of the invention is achieved by the fact that the prepared aqueous PAW solution, which contains orthoboric acid or its borate salt (spinning solution), is subjected to spinning in a coagulating bath containing water, sodium or potassium hydroxide and sodium sulfate, in a predetermined amount, ₃stretches the formed fibers between the rollers, acid neutralizes bases adhering to the fibers, stretches wet the fibers, washed with water to adjust the content of orthoboric acid remaining in the fibers to the specified range, dehydrates and dries and dry stretches the fibers. .

The stretch of synthetic fibers increases in proportion to the increase in temperature, while they decrease in strength and modulus of elasticity. It is easy to see that this phenomenon occurs due to the initiation of the fiber molecular chain shift in regions with low particle density after heating the fibers. This shift moves to areas of the fibers where the molecular orientation is concentrated. Therefore, to improve the properties of synthetic fibers at high temperatures, it is important to inhibit the movement of molecular chains as much as possible. This can be achieved in two ways, either by intensifying the orientation of the molecular chains to such an extent as to counteract this shift, or by adding a material to the polymer that counteracts the movement of the molecular chains. However, these two methods, when used separately, do not allow fibers with good physico-mechanical properties to be obtained.

It has been found that the essential factor that fulfills the stated purpose of the invention is structure

890

890 fibers in which the molecular orientation of the chains is concentrated, but which also contains a substance that counteracts the extension of the molecular chains, where this orientation is relatively loose. That is, part or all of orthoboric acid or. its ram salt contained in the fibers can combine with the PAW in a relatively loose orientation, counteracting the displacement of molecular chains caused by heating. When the amount of orthoboric acid or taranic salt is less than 0.2 · / · by weight relative to PAW, it is insufficient to limit chain displacement. When the content of orthotaric acid or taranic salt exceeds 0.8 · / ·, it prevents the formation of molecular chains of high orientation, thereby reducing the strength of the yarn.

A coagulating bath that is used. in the known spinning method - wet PAW fibers that do not contain ortolar acid or borate are almost saturated with sodium sulfate when used as a dehydrating salt in the bath. This is due to the fact that the fibers stick together due to insufficient coagulation when the concentration of the dehydrating salt in the bath is less than 100 g / 1.

Sodium or potassium hydroxide in a predetermined amount was also used in the coagulation bath used in the process of the invention, thereby facilitating the spinning of a spinning solution containing orthoboric acid or borate. The properties of the PAW fibers produced in this way depend very little on the temperature. It is often observed that when the sodium sulfate content of the coagulation bath is high, there is a tendency to increase the extensibility.

Compared to known PAW fibers that do not contain orthotaric acid, the synthetic fibers produced by the method of the invention have better extensibility and their properties are less dependent on temperature.

Radial tires, which uses PAW fibers produced according to the invention in the interlayer layer, show excellent results in impact tests, high speed tests, torsional forces tests, tread wear tests and durability tests.

It has been found that an aqueous spinning solution - containing orthoboric acid or its ram salt can coagulate to form synthetic PAW fibers showing tensile strength, modulus of elasticity and creep not much dependent. temperature.

The fiber produced by the process of the invention is spun from an aqueous PAW solution containing orthoboric acid or its basal salt in a coagulating bath which is highly alkaline (thanks to the addition of 10 to 100 g / 1 sodium hydroxide or potassium hydroxide and 100 to 330 g / 1 sodium sulfate The formed fiber is subjected to further processing such as stretching on rolls, neutralizing with alkali, washing with water. for determining the content of residual orthobaric acid on * fibers - in the range from 0.2 to 0.9 · / · by weight in relation. for PAW content, dehydration and drying ornzr * dry stretching.

It is preferable to add ortobaric acid or its tx&gt; ronium salt to the spinning solution in an amount of 1 to 5 · · · by weight relative to the PAW content.

According to the present invention, * orthoboric acid or any water-soluble taranic salt thereof may be used. Any basal salt - soluble - in the aqueous spinning solution can be used, for example, alkali metal rams such as sodium ram, potassium ram etc. The weak acid solution is preferably kept, preferably in the pH range from 3 to 5. The pH can be used. adjust if necessary by adding acid to the solution. Acids that can be added to the solution are, for example, inorganic acids such as sulfuric acid, nitric acid and hydrochloric acid, organic acids such as acetic acid, tartaric acid, etc., or combinations of organic acid and organic acid salts, e.g. citric acid and sodium citrate , acetic acid and sodium acetate, tartaric acid and potassium tartrate, tartaric acid and sodium tartrate etc.

When the spinning solution has a pH value below 3, then the coagulation speed in the coagulation bath decreases and the equipment corrodes due to the high acidity. On the other hand, when the pH value is higher than 5, then the solution is unstable causing the viscosity to increase and the spinning conditions to be seriously affected.

The concentration of PAW in the spinning solution is preferably from 10 to 30 · w / w, Areckii the degree of PAW polymerization is from 1209 to 3500, preferably - from 1300 to 3000. The spinning solution is subjected to spinning by introducing it into a strongly alkaline coagulating bath, containing_ water and sodium hydroxide or potassium hydroxide in an amount of - 10 to 100 g / 1 and · sodium sulfate in an amount of 100 to 330 gZL

If the content - sodium hydroxide - or 'potassium hydroxide' of less than 10 g / 1, there are unfavorable phenomena such as lowering - coagulation velocity and reduction of fiber stretch during spinning. It is disadvantageous to exceed the content of sodium hydroxide - or - potassium hydroxide over 100 g / 1, because - gelation becomes due to the presence of a base so active that the spinability of the spinning solution is reduced, resulting in deterioration of properties such as tensile strength, elasticity modulus and crawl. When the sodium sulfate content is less than 100 gd, then gelation dominates over dehydration and coogulovion due to the action of sodium sulfate. This causes the fibers to swell during coagulation, which worsens the quality of the product. On the other hand, sodium sulphate contents exceeding 330 g / 1 cause deformation of the fiber cross-section to a substantially elliptical shape, since dehydration and coagulation dominate - over other phenomena. Cross-sectional deformation of ββββ fibers. is the reason for reducing stretch.

In this. the spun fibers are subjected to the following known operations such as stretching on rolls, neutralizing alkali with acid, stretching. wet and flushing in water to adjust the amount of orthoboric acid remaining on the fibers from AM to. OM * / · by weight PAW.

The amount of residual orthoboric acid after _fThe rinsing with water should be more than 0.2 /// PAW weight, because with a smaller amount, fiber swelling can occur during rinsing. Swelling of the fibers causes them to hang, which in turn can then cause them to get caught by the rolls, resulting in process instability, which also worsens the properties of the yarn, such as tensile strength, modulus of elasticity and creep.

These defects, however, are not observed in the process according to the invention, because orthoboric acid residues present in the fibers or react with PAW to form outside and outside molecular. cross-links hanging on PAW chains or remain unregistered. This is one of the characteristic features of the invention. When the amount of orthoboric acid exceeds 0.9 /// by weight, then the stretchability of the fibers decreases thus reducing the absolute values ​​of the tensile strength and elastic modulus of the yarn.

Thus, by choosing optimal coagulation conditions, the production of highly stretchable fibers can be stabilized. In addition, by determining the conditions of flushing with water to maintain orthoboric acid residues in an amount of 0.2 to 0.9 / w / w, preferably in the range from 0.2 to 0.7 / w / w, products with properties are obtained slightly dependent on temperature without reducing dry stretch.

In the method of the invention, after rinsing with water, dehydration and drying, dry stretching of PAW fibers should be carried out to achieve a total stretch ratio of 1300 ///.

If the total stretch ratio is less than 1300 ///, then it is difficult to produce PAW fibers with the properties described above. According to the invention, PAW 'fibers can be stretched to a total stretch of 1800 /.

The properties of the yarn obtained from PAW fibers are as follows: tensile strength at 120 ° C - co. the cheapest 7.5 G / den, modulus of elasticity at 120 ° C - at least 100 G / den, creep at 135 ° C - below 2 /// (elongation degree. under a load of 1 G / den within 60 min.). The fibers contain 0.2 to 0.9 /// orthoboric acid or borate salt. The fibers of the invention have better high temperature properties than known PAW fibers that do not contain orthoboric acid or iborane. .

The amount of orthoboric acid remaining in the synthetic fibers is measured as follows:

About 2 g of fibers are converted into pure PAW and placed in a crucible to which they are added

0.1 molA of aqueous sodium hydroxide solution covering the fibers. After the next crucible holding in the dryer at 105^QC during one night the fibers are roasted in an electric pice within 60 min. at a temperature of 400 to fi00 ° C. Then the fibers from the crucible are put into a beaker, to which an aqueous ion exchanger is added and kept for 60 min. Pour a few drops of phonolphthalein into the beaker, then add 0.1. mole / 1 and hydrochloric acid until the solution changes color from red to yellow. After boiling for 30 to 60 min. the solution is cooled and neutralized to pH = 7 by adding sodium hydroxide or hydrochloric acid as needed. Mannite beakers are added and the solution is neutralized again to pH "7 by titration with 0.1 mol / 1 sodium hydroxide. Titrated. volume V is measured in cm /. The amount of orthoboric acid remaining in the fibers is calculated from the following formula

0.62 - f · V

In

where W is the mass of PAW in grams in the sample measured according to the method described above, afi V are the tensile strength and the titrated volume of '0.1 molar aqueous sodium hydroxide solution, respectively

The tear or dry tensile strength of the dried sample is determined according to JISL 1070 . Thus, the fiber sample is twisted eight times over a length of 10 cm. dried at 105 ° C for 3 hours. and immediately measures the tearing strength for a 20 cm sample at a tensile speed of 10 cm / m using a tensile strength meter measuring constant elongation speed in which the surfaces of the jaws are covered with a layer of polyurethane.

The modulus of elasticity is obtained according to JISL 1073 from the stress-elongation curve and determined when determining the dry tear strength: To determine the module at room temperature, test. performed at 20 ° C, while to determine the module at high temperature the upper and lower jaws of the strength tester are kept in the atmosphere of an electric furnace at 120 ° C, and the measurement is carried out until the sample breaks.

The following examples further describe, determine and compare polyvinyl alcohol fibers according to the invention and methods for their preparation. Percentages are in percent by weight, unless otherwise indicated.

Example 1. 10 kg of an aqueous spinning solution containing '1.7 kg of PAW with a polymerization degree of 1750 and a saponification number of 99.5 · mol / i, 34 g of orthobpric acid and nitric acid in an amount sufficient to adjust pH = 4.3 was prepared. Solution. the spinning coil was passed through spinnerets containing 600 holes with a diameter of 0 ^ (00 mm for a coagulation bath, containing 30 g / 1 sodium hydroxide and 230 g / 1 sodium sulfate).

890 '7

In this way, fibers spun from was taken from the bath at a speed of 10 m / min. and · followed by operations such as stretching by 10 (0% on rolls, neutralizing in a bath containing 70 g / 1 sulfuric acid and 300 g / 1₈ sodium sulfate, wet stretching by 15%, flushing with water to determine the amount of orthoboric acid 0.45%, dehydration, drying and dry stretching by 220 *%. The final product is stretched to a total stretch of 1₀1500%.

The product thus obtained has a tensile strength at 120 ° C - 9.3 G / den, a modulus of elasticity at 120 ° C - 135 G / den and creep at 135 ° C - 1.4%.

Table I presents comparable examples that illustrate the impact of changes in process conditions and orthoboric acid concentration on yarn properties. Also for comparison are the conditions used in example przedstawiono and the resulting yarn properties.

Table I

<td></td><td></td><td>Example AND</td><td>comparative Nawcz a sample 1</td><td>comparative Nawcz a sample 2</td><td>comparative Nawcz a sample 3</td><td>comparative Nawcz a sample 4</td><td>comparative Nawcz a sample 5</td><td>comparative Nawcz a sample 6</td><td>comparative Nawcz a sample 7</td>

<td></td><td></td><td> 1</td><td> 2</td><td> 3'</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td>

<td></td><td>Material:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>Degree of polymerization, PAW The number of saponification</td><td> 1750</td><td> 1750</td><td> 1750</td><td> 1750</td><td> 1750</td><td> 1750</td><td> 1750</td><td> 1750</td>

<td></td><td>PAW mol% Spinning solution whether:</td><td> 99,5</td><td> 99,5</td><td> 99,5</td><td> 99,5</td><td> 99,5</td><td> 99,5</td><td> 99,5</td><td> 99,5</td>

<td></td><td>PAW content% amount added orthoboric acid</td><td> 17</td><td> 17</td><td> 17</td><td> 17</td><td> 17</td><td> 18</td><td> 18</td><td> 17</td>

<td></td><td>go%</td><td> 2,0</td><td> 2,2</td><td> 2,2</td><td> 2,2</td><td> 2,2</td><td> 2,6</td><td> 2,6</td><td> 2,0</td>

<td>• F</td><td>pH</td><td> 4,3'</td><td> 4,1</td><td> 4,1</td><td> 4,1</td><td> 4,1</td><td> 4,0(1)</td><td> 4,0(1)</td><td> 4,3(2)</td>

<td>ABOUT *about ABOUT</td><td>Coagulating bath:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>and 03</td><td>NaOH (g / 1)</td><td> 30</td><td> 8</td><td> 110</td><td> 80</td><td> 15</td><td> 40</td><td> 40</td><td> 30</td>

<td rowspan="2">C r * rl Ϊ</td><td>On "SO4 (g / 1)</td><td> 230</td><td> 260</td><td> 150</td><td> 90</td><td> 360</td><td> 220</td><td> 220</td><td> 230</td>

<td>Neutralizing bath:</td><td></td><td></td><td></td><td>not suitable</td><td></td><td></td><td></td><td></td>

<td>ct * s</td><td>HSSO₄ (G / 1)</td><td> 70</td><td> 70</td><td> 70</td><td>spinning</td><td> 70</td><td> 80</td><td> 80</td><td> 70</td>

<td>What N S</td><td>On₂SO4 (g / 1)</td><td> 300</td><td> 300</td><td> 300</td><td> —</td><td> 300</td><td> 320</td><td> 320</td><td> 300</td>

<td>C £</td><td>Stretching:</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>43 b</td><td>degree of total</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td> £</td><td>stretch,%</td><td> 1500</td><td> 1100(3)</td><td> 1200(4)</td><td> —</td><td> 1000(3)</td><td> 1500</td><td> 1200</td><td> 1100</td>

<td rowspan="2">s e . a c3 ' £</td><td>stretching on rolls,%</td><td> 100</td><td> 100</td><td> 100</td><td> _</td><td> 100</td><td> 100</td><td> 100</td><td> 100</td>

<td>wet stretching,%</td><td> 150</td><td> 150</td><td> 140</td><td></td><td> 150</td><td> 150</td><td> 140</td><td> 150</td>

<td></td><td>stretching on</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>cho,%</td><td> 220</td><td> 140</td><td> 192</td><td> —</td><td> 120</td><td> 220</td><td> 192</td><td> 140</td>

<td></td><td>The amount of residual · orthoboric acid, %</td><td> 0,45</td><td> 0,51</td><td> 0,52</td><td></td><td> 0,49</td><td> 0,15</td><td> 1,00</td><td> 0,46</td>

<td></td><td>Tensile strength at 120 ° C,</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>G / den</td><td> 9,3</td><td> 6,2</td><td> 7,0</td><td> —</td><td> 5,4</td><td rowspan="2"> 7,3</td><td> 7,0</td><td> 6,5</td>

<td></td><td>Flexibility module</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td>at 120 ° C, G / den Passage at 135 ° C,</td><td> 135</td><td> 72</td><td> 82</td><td> —</td><td> 63</td><td> 91</td><td> 82</td><td> 96</td>

<td></td><td> %</td><td> 1,4</td><td> 2,5</td><td> 2,2</td><td> —</td><td> 3,1</td><td> 2,3</td><td> 2,4</td><td> 2,3</td>

(2) - acetic acid and sodium acetate were used to determine the pH (3) - the sample exhibits insufficient extensibility «(4) - the sample exhibits insufficient spinning capacity.

Notes to Table I:

In Example I, comparative sample 1 uses nitric acid to adjust the pH.

(1) - tartaric acid was used to adjust the pH

890

Example II In the same way eo in Example 1, PAW fibers containing sodium borate are produced and stretched to a total stretch ratio of 1500 · / · except that 1.5 · / · sodium borate is used relative to the amount of PAW instead of acid orthoboric and tartaric acid instead of nitric acid was used to adjust the pH. The yarn obtained had the following properties: tensile strength at 120 ° C - 9.1 G / den, elastic modulus at 120 ° C - 127 G / deh and creep at 135 ° C - 1.5 · / ·.

Example III. An aqueous PAW solution with a PAW concentration of 15% by weight and containing 150 g of PAW with a degree of polymerization of 2,350 and a saponification number of 99.5 · mol · mixed with 30 g of orthoboric acid (2% by weight relative to the PAW content) and a small amount of acetic acid for the preparation of a spinning solution with a pH = 4.5. This solution was subjected to spinning in a strongly alkaline coagulating bath, mainly in an aqueous solution containing 40 g / 1 sodium hydroxide and 250 g / 1 sodium sulfate. After receiving the yarn from the bath at a speed of 10 m / min, it was subjected to 100% stretching on rolls, neutralizing, wet stretching by 150%, washing with water to determine the residual content of orthoboric acid in the amount of 0.4% by weight in relation to the PAW content, dehydration, drying and dry stretching to 200%. The yarn thickness of 1200 den per 600 fibers obtained in this way had a stretch ratio of 1400%. It had the following properties: tensile strength at 120 ° C - 9.2 G / den, modulus of elasticity at 120 ° C - 131 G / den, and creep at 135 ° C - 1.9%, with the final product having better properties at higher temperatures.

Example IV 4.17% aqueous PAW solution containing 100 kg of PAW with a degree of polymerization of 1750 and a saponification number of 99.9 mol% was mixed with 2 kg of orthoboric acid (2% by weight relative to the PAW content) and 0.3 kg of acetic acid (0.005 g means equivalent to 100 g PAW) for the preparation of the spinning solution. The pH value was set to 4.5. The spinning solution was passed through nozzles having 1000 holes with a diameter of 0.15 mm into a coagulating bath containing 50 g / 1 sodium hydroxide and 200 g / 1 sodium sulfate. Then the fibers were collected from the bath at a speed of 10 m / min.

Spinning conditions in this case were very stable, since during the two-week spinning no difficulties such as clogging of the nozzles were observed. In this way, the spun fibers were subjected to the same operations as in Example 3, i.e. stretching on rolls, ne:₅ stabilized, wet drawing, washing with water to determine the residual content of orthoboric acid in an amount of 0.5% by weight relative to the PAW content, dehydration, drying and dry drawing. Received in this_L0 yarn method, with a thickness of 1800 den to 1000 fibers was stretched by 1406 · / ·. It had the following properties: tensile strength at 120 ° C - 9.3 G / den, modulus of elasticity at 120 ° - 134 G / den and creep at 135 ° C - 1.8%.

Example V. 1 kg of an aqueous spinning solution of 170 g PAW was prepared with a degree of polymerization of 1750 and a saponification number of 99; 5 mol%, 5.95 g orthoboric acid (3.5% by weight relative to the PAW content) and sufficient sulfuric acid to adjust the pH = 4. The spinning solution was passed through nozzles for a coagulation bath containing 15 g / 1 sodium hydroxide, and 230 g / 1 sodium sulfate. The obtained fiber was subjected to the same subsequent treatment as in Example 1 to produce PAW fibers containing 0.5% by weight of orthoboric acid. The final product produced in this way showed excellent properties at 120 ° C.

° Example VI. An aqueous spinning solution containing 17% by weight of PAW with a degree of polymerization of 1700 and a saponification number of 99.5 mol%, 3% by weight of orthoboric acid relative to PAW and 0.2% by weight of nitric acid relative to PAW was prepared to adjust the pH = 4. The spinning solution was passed through known nozzles containing 600 holes for a coagulating bath at 40 ° C containing 20 g / 1 sodium hydroxide and 250 g / 1 sodium sulfate. The fibers produced in this way were stretched on rollers and further subjected to operations such as acid neutralization of the sodium hydroxide contained in the fibers, hot stretching, washing with water of the fibers to determine the remaining amount of orthoboric acid in the fibers, drying and dry stretching to a total degree of stretching 1300— 1500%. Table II shows the properties of PAW fibers made of different amounts of ortorboric acid.

Table II

<td>The content of orthoboric acid in fibers,% in relation to PAW</td><td> 0</td><td> 0,21</td><td> 0,36</td><td> 0,50</td><td> 0,67</td><td> 0,85</td><td> 0,95 .</td><td> , 1,05</td>

<td>Total stretch,%</td><td> 1200</td><td> 1500</td><td> 1500</td><td> 1500</td><td> 1500</td><td> 14(0</td><td> 1200</td><td> 1140;</td>

<td>denier / number</td><td> 1200/</td><td> 1200/</td><td> 1200/</td><td> 1200/</td><td> 1200/</td><td> 1280/</td><td> 1480/</td><td> 1550/</td>

<td>the fiber</td><td> 500</td><td> 000</td><td> 000</td><td> 000</td><td> 000</td><td> 600</td><td> 000</td><td> 000</td>

38&amp;80

cd tabett II

<td rowspan="2">J.0 DEGC</td><td>dry tear strength G / den</td><td> 0,7</td><td> 11,2</td><td> 11,6</td><td> 11,7</td><td> 11,8</td><td> 10,1</td><td> 9,8</td><td></td>

<td>modulus of elasticity, G / den</td><td> 230</td><td> 240</td><td> 245</td><td> 230</td><td> 247</td><td> 230</td><td> 210</td><td> 284</td>

<td rowspan="2">, M0 ° C</td><td>tear resistance to. dry G / den</td><td> 7,0</td><td> 8,0</td><td> 8,5</td><td> 8,7</td><td> 8,6</td><td> 8,5</td><td> 74</td><td>7.3 and</td>

<td>modulus of elasticity, Gjlden</td><td> 70</td><td> 101</td><td> 115</td><td> 120</td><td> 127</td><td> 122</td><td> 96</td><td> 96</td>

Pm yk Ł ·· ad. VII. . An aqueous spinning solution containing 17 * / · PAW was prepared₁₅with a degree of polymerization of 1750 and a saponification number MJW · molar, 2.8 · · · by weight. orthoboric acid calculated as pure PAW and 0.24 * / · by weight of tartaric acid calculated as pure PAW for 'pH = 4. The spinning solution was then passed through the same nozzles as in Example 1 into a coagulation bath at 45 ° C containing 30 g / 1. sodium hydroxide and 22β g / 1 sodium sulfate. The fibers produced in this way were subjected to the next one₂₅operations such as stretching on rolls, acid neutralization of sodium hydroxide contained in the fibers, wet stretching, rinsing the fibers with water to determine the content of ortdboric acid in the amount of about 0.5 · · ·, drying and dry stretching to a total degree of stretching of 1200—— 1600 * / ·. Properties of Włtiden produced in this way are shown in Table III.

These hoses are used in hydraulic equipment and oil revenues, because the expansion of the hose under the action of internal pressure is very small, due to the high value of the fiber modulus. At high temperature.

The excellent properties of synthetic fibers * PAW at 'high temperature' enable it to be used in full radial and cross tire tires.

Although specific materials and process conditions are given in the above-described exemplary methods for making polyvinyl alcohol fibers, they are intended to illustrate the invention only.

Also various other polyvinyl alcohols, water-soluble borates and process conditions can be introduced, with similar results, in place of the example shown.

Table III ±

<td colspan="2">The content of · orthoboric acid in fibers (* · relative to PAW)</td><td> 0,46 *</td><td> 0,52</td><td> 0,48</td><td> 0,50</td>

<td colspan="2">Total stretch, · / ·</td><td> 1200</td><td> 1350</td><td> 1400</td><td> 1500</td>

<td colspan="2">fiber</td><td> 1204/600</td><td>120 (V600</td><td> 1204/600</td><td>I2W «00</td>

<td rowspan="2">20 ° C</td><td>dry tensile strength, G / den</td><td> | 9,7</td><td> 10,4</td><td> 11,0</td><td> 11,5</td>

<td>initial modulus of elasticity G / den</td><td> ' 232</td><td> 230</td><td> 245</td><td> 260</td>

<td rowspan="2">! 20 ° C</td><td>dry tensile strength, G / den</td><td> 7,0</td><td> 8,0</td><td> 8,2</td><td> 8,6</td>

<td>initial modulus of elasticity G / den</td><td> 76</td><td> 102</td><td> 100</td><td> 127</td>

Synthetic polyvinyl alcohol fibers produced by the process of the invention which have the above-described high temperature properties are widely used, e.g. The high tensile strength at break and low creep of these fibers at high temperature allow the production of V-belts with high dimensional stability in harsh operating conditions. Using the PAW fibers produced by the method of the invention, considerably. the quality of high-pressure bends is improved