JPS62149909A - Polyvinyl alcohol fiber - Google Patents

Abstract

PURPOSE:The titled fibers obtained by adding a specific amount, based on polyvinyl alcohol having a specific polymerization degree, of boric acid (salt) thereto and spinning and drawing the resultant solution and having a high strength and initial elastic modulus even at high temperatures and good heat resistance. CONSTITUTION:Polyvinyl alcohol fibers, obtained by adding a solution prepared by dissolving 200-8,000ppm, based on polyvinyl alcohol having >=3,000 polymerization degree, boric acid or borate in hot water to the polyvinyl alcohol to prepare a spinning solution, extruding the spinning solution through a spinneret, passing the extruded solution through an air layer, spinning the fibers into an aqueous solution containing sodium hydroxide and sodium sulfate at 50 deg.C to give undrawn fibers, drawing the undrawn fibers at 2 times draw ratio using rolls, neutralizing and washing the drawn fibers, wet hot-drawing at 2 times draw ratio, drying and winding the fibers and having at least 18g/denier strength and at least 35g/denier initial elastic modulus.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to polyvinyl alcohol (hereinafter abbreviated as PVA) fibers having high strength and high initial elastic modulus.
Furthermore, the present invention relates to PVA fibers that have high strength and initial elastic modulus even at high temperatures.

(Prior art) Recently, polyparaphenylene terephthalamide (hereinafter referred to as
It is abbreviated as PPTA. ) as exemplified by.

Using a polymer having a rigid molecular chain, the polymer is dissolved in a specific solvent such as sulfuric acid to a concentration such that the solution exhibits liquid crystallinity, and then spun. By performing so-called liquid crystal spinning, it has a strength of 20g/d or more and a strength of 500g/d.
It has become possible to obtain high-strength, high-modulus fibers with an initial elastic modulus of d or more, and PPT^ fibers have already entered the practical stage. however.

Such fibers are disadvantageous in terms of raw material costs and manufacturing costs, as they are extremely expensive compared to ordinary yarns.

On the other hand, a method for obtaining high-strength, high-modulus fibers from flexible high-molecular-weight polymers has also been developed and is attracting attention. This is the so-called gel spinning method. Polyethylene fibers produced using the gel spinning method have a strength that is approximately twice or more than that of PPTA fibers, and fibers with initial elastic modulus that are close to the ultimate limit have been obtained; however, due to their low melting point, It has the disadvantage of lacking heat resistance.

PVA fibers are superior to general purpose fibers in terms of strength and initial elastic modulus, and are also superior to polyethylene fibers in heat resistance. Therefore, if PVA fibers having strength and initial elastic modulus comparable to those of PPTA fibers could be obtained, it would be very advantageous in terms of cost performance and the range of uses could be expanded.

Conventionally, various methods for improving the strength and initial elastic modulus of pvΔ fibers have been studied2.For example, Japanese Patent Publication No. 48-3262
Publication No. 3, Special Publication No. 4B-32624, Special Publication No. 1973
Various proposals have been made in JP-A-9210, Japanese Patent Publication No. 53-1368, etc. However, these PVA fiber manufacturing methods have not been able to improve both strength and initial elastic modulus.

For example, in Japanese Patent Publication No. 48-32623, the degree of polymerization is 35.
It is described that a fiber with a strength of 17.2 g/d and a dynamic elastic modulus of 3.8 x 10" dyne/c+J at 20°C was obtained using PVA of 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001ss," The elastic modulus during high-speed deformation (cycle 7 seconds) was 250 g/d. 1. The present inventors carried out a follow-up test on the above invention, and 1. The initial elastic modulus was measured by a tensile test of the multifilament yarn described in the present invention. It wasn't too much.

Furthermore, an example of a proposal for incorporating boric acid or borate into PVA fibers is the above-mentioned Japanese Patent Publication No. 53-13.
No. 68, as well as Japanese Patent Publication Nos. 48-7887. However, although the fibers described in these documents have improved performance and water absorption at high temperatures, the degree of polymerization of the polymer used is low, and therefore the strength is only 14% at most.
g/d, and the initial elastic modulus is only 300 g/d, and no PVA fibers have been obtained that are comparable to PPTA fibers. Furthermore, in Japanese Patent Publication No. 53-1368, a PVA fiber with improved strength and initial elasticity at high temperatures (120) is proposed as 1.

The strength and initial elastic modulus at 120°C are each at most 10
g/c! , about 140 g/d.

On the other hand, methods for improving both the strength and initial elastic modulus of PVA fibers are disclosed in JP-A-59-130314 and JP-A-6.
It has been proposed in Publication No. 0-12631.2. In these publications, water is used as a solvent for the spinning stock solution, and specific examples include the use of aqueous solutions containing inorganic salts such as calcium chloride, zinc chloride, aluminum chloride, or rhodan soda. There is no mention of including a specific inorganic salt in the drawn yarn of the PVA fiber obtained in No. 1, or that the drawability is improved by including the inorganic salt.

(Problems to be Solved by the Invention) Therefore, the object of the present invention is to create a fiber that has strength and initial elastic modulus comparable to those of PPTA fibers, has superior high-temperature properties at 120°C than conventional PVA fibers, and is better than polyethylene fibers. The object of the present invention is to provide PVA fibers having high heat resistance, and to be able to manufacture the fibers at low cost.

(Means for Solving the Problems) In view of the current situation, the present inventors made PVA with appropriate heat resistance, which has higher strength and initial elastic modulus than conventional products, and which can be used even at high temperatures. As a result of intensive studies aimed at obtaining PVA fibers of a high standard, the present invention was arrived at.

That is, in the present invention, 200 to 800
Contains 0 ppm of boric acid or borate and has a degree of polymerization of 30
00 or higher and at least 18 g/d
and an initial modulus of at least 350 g/d.

The present invention will be explained in more detail below.

To produce the high-strength/high-initial-modulus PVA fiber of the present invention, boric acid is added to an aqueous solution of PVA having a degree of polymerization of 3000 or more, or a boric acid salt and a small amount of acid are added to prepare a spinning stock solution. After dry/wet spinning the spinning solution using a neutral or alkaline aqueous solution containing dehydrating salts as a coagulation bath,
It may be stretched until the desired strength and initial elastic modulus are achieved, and the embodiment thereof will be described in more detail.

Boric acid or a boric acid salt in an amount of 0.1 to 5 weight based on PVA is added to an aqueous solution with a pv^ of a polymerization degree of 3000 or more.

The spinning stock solution is prepared by adjusting the pH to a range of 3.5 to 5 with an acid such as hydrochloric acid or sulfuric acid. PVA concentration of spinning stock solution is 5-50
% by weight is preferred. Further, it is important to use an acidic aqueous solution as the spinning stock solution in order to prevent PVA from crosslinking with poric acid or borate to form a gel. Suitable examples of borates include sodium borate, potassium borate, ammonium borate, lithium borate, and the like.

Next, the spinning dope prepared in duplicate is extruded from the spinning nozzle, passed through a layer of inert gas such as air or nitrogen, and then 30-400 g/l of dehydrating salts and alkali hydroxide O- 300g#! The yarn is spun into an aqueous solution containing PVA and coagulated to form a gel-like undrawn yarn crosslinked with PVA and boric acid or borate. Next.

Neutralization treatment, heat treatment, and washing treatment of gel-like undrawn yarn.

Apply treatment such as oil treatment and drying, and during this time 3 to 8
The yarn is spun and stretched twice as much, and then wound up once as an undrawn yarn, or it is continuously drawn with dry heat or with a hot solvent.

The temperature during such stretching is preferably 220°C or higher, more preferably 245°C or higher, and multi-stage stretching of two or more stages is preferred.

In order to obtain a PVA fiber having a dual strength of at least 18 g/d and an initial elastic modulus of at least 350 g/d as in the present invention, in the above embodiment, the total draw ratio including spinning/drawing is 18 times or more, preferably 25 times. What is necessary is just to extend so that it may be more preferably 30 times or more.

By dry and wet spinning as described above, conventional PV
Even if PVA with a polymerization degree higher than that of A is used,
It is now possible to obtain undrawn yarn with extremely high drawability,
The undrawn yarn is heat-stretched to a high magnification or warm-stretched to obtain the P of the present invention having high strength and high initial elastic modulus.
It can be a VA fiber.

The PVA constituting the PVA fiber of the present invention has a polymerization degree of 30.
00 or more, preferably 4000 or more.

The degree of saponification of pvΔ used in the production of the PVA fiber of the present invention is preferably 99% or more, but when performing dry/wet spinning,
By making the coagulation bath alkaline.

Since it can be resaponified, it is also possible to use PVA with a saponification degree of less than 99%. If the degree of polymerization of PVA is less than 3000, the high strength/high initial modulus fiber of the present invention cannot be obtained.

Also, the PVA fiber of the present invention must contain boric acid or borate. This is explained above as <, PV
It became possible to obtain an undrawn yarn with extremely high drawability by dry/wet spinning a spinning stock solution of /l, but this was achieved by dry/mixing yarn, using PVA with a high degree of polymerization, This can only be achieved by incorporating boric acid or a boric acid salt into the undrawn yarn. The reason is that the stock solution, which is an aqueous solution of PVA, contains boric acid.

When spun into an alkaline coagulation bath, the viscosity increases significantly due to the change in p, resulting in gel fibers. Other than boric acid or boric acid salts, there are no known substances that have such a mechanism of action other than those that exhibit significant coloration.

Since the PVA fiber of the present invention is obtained only by drawing such boric acid-containing gel undrawn yarn at a high magnification, the drawn yarn contains boric acid or a boric acid salt. Although it is possible to elute boric acid or borate from the drawn yarn with a suitable solvent such as water.

Since the drawn yarn is composed of highly oriented PVA, it may be difficult for the solvent to enter the fiber, so it takes a considerable amount of time for it to elute, and in that case it may damage the fiber surface. This is undesirable because it causes a decrease in fiber performance. Furthermore.

Boric acid or borate content from PVA fiber is 200%
If it is removed to less than ppm, the high temperature properties will deteriorate, which is not preferable.

It is important that the content of boric acid or borate in the PVA fibers is in the range of 200 to 8000 ppm based on PVA. If the content is less than 200 ppm, the fibers swell during washing with water and become sagging, causing instability in the process such as winding around a roller, and the stretching properties are also lowered due to insufficient quantity.

Furthermore, as mentioned above, the strength and initial elastic modulus at high temperatures also decrease. On the other hand, if the content exceeds 8,000 ppm, the drawability is rather reduced, and the strength and initial elastic modulus values are reduced.

The content of boric acid or borate in the present invention is
All of the boric acid and boric acid salts in the PVA fibers were converted into boric acid (therefore, hereinafter referred to as boric acid content), and the quantitative determination was performed by the method shown below.

That is, approximately 2 g of pvAiQ fiber was accurately weighed in a crucible and -1
0 = After adding 0.1N sodium hydroxide aqueous solution to the extent that the sample does not come out from the liquid level, heat it at about 105°C to distill off the moisture, and then heat it in an electric furnace at 400 to 500°C. Bake at high temperature for about 1 hour. Put this together with the crucible in a beaker, add ion-exchanged water, and let it sit for a while, then add the indicator phenolphthalein dropwise, add 0.1 N hydrochloric acid dropwise until the aqueous solution changes color, and boil for about 1 hour. do. After cooling, neutralize to p117 with sodium hydroxide or hydrochloric acid, add mannitol, and boil until pi becomes 7 again.
．． Titration was performed with a 1N aqueous sodium hydroxide solution to determine the required amount (in cc). The weight of pvΔ in the sample is Wg, 0
．． Titer and titration of 1N aqueous sodium hydroxide solution (
The required amount) are respectively f and Vcc.

The boric acid content B relative to PVA is given by the following formula.

(Function) As described above, in the present invention, it is essential to use an acidic aqueous spinning stock solution to which boric acid or a borate salt is added. This allows a crosslinked structure to be formed within the undrawn yarn when the spinning dope is spun into the coagulation bath. Therefore, in the present invention, even if medium-highly polymerized PVA with a polymerization degree of 3,000 to 6,000 is used, it is possible to obtain a drawn yarn with high drawability, 350 g/d 1'J,...lr.

can be drawn into a fiber with an initial modulus of . JP-A-59-13031, JP-A-60-12631
Publication No. 2 describes water and various salts dissolved in water as solvents for spinning stock solutions, such as lithium chloride, calcium chloride,
Solutions of aluminum chloride, zinc chloride, rhodan soda, and other substances capable of increasing the solubility of PVA by breaking hydrogen bonds have been described. There is no suggestion of using an acidic aqueous solution containing . In the former case, this point is
In the latter case, as in the comparative example of Example 1 of the same publication, in the case of an aqueous solvent, the drawing ratio does not increase and this is probably the reason why high strength and high modulus fibers cannot be obtained.

(Examples) Hereinafter, the present invention will be explained in more detail by giving examples.

In addition, the strength and initial elastic modulus in one example are JIS L 101
7, and the strength and initial elastic modulus at high temperatures were also measured at an atmospheric temperature of 12
The above method was followed at 0°C.

The degree of polymerization of PVA is calculated by rounding off the 10th place according to the method specified in JIS K 6726.

Example 1. Comparative Examples 1 and 2 Polymerization degree 3200 (7) PVA and PVA double T
A spinning dope having a PVA concentration of 12% by weight was prepared by dissolving i,o% by weight of boric acid in hot water. 70% of this spinning stock solution
It was extruded from a spinning nozzle at 10°C, passed through a 4 mm air layer, and then spun into an aqueous solution at 50°C containing 100g/12 sodium hydroxide and 100g/12 sodium sulfate.

After forming a PVA gel-like undrawn yarn, it was stretched with a roller at a draw ratio of 3 times, neutralized and washed, then warm-stretched at a draw ratio of 2 times, dried, and then wound up.

The thus obtained undrawn yarn was further hot-stretched at a temperature of 245° C. so that the total stretching ratio including spinning and stretching was 20 times.

For comparison, drawn yarns were obtained in the same manner as in Example 1, except that PVA with a polymerization degree of 2300 or Pv^ with a polymerization degree of 1700 was used instead of I'VA with a polymerization degree of 3200. However, in the case of PVA with a 5 degree of polymerization of 1700, it was not possible to stretch the film until the total stretching ratio reached 20 times, so the total stretching ratio was set to 15.2 times, which allows smooth stretching without yarn breakage.

Table 1 shows the properties of the drawn yarn obtained.

=14- Table 1 Example 2 Degree of polymerization 3200 (7) PVA, 1 for PVA
．． A spinning stock solution having a PVA concentration of 12% by weight and a pH of 4 was prepared by dissolving 5% by weight of sodium borate and sulfuric acid in hot water. This spinning stock solution is extruded from a spinning nozzle at 75°C,
After passing through a 5 mm air layer, add 1 ml of sodium hydroxide.
After spinning in a 50 ° C. aqueous solution containing 20 g/z and 150 g of sodium sulfate to obtain a PVA gel-like undrawn yarn, spinning and drawing was performed at a draw ratio of 5 times, followed by neutralization, wet heat treatment, washing, and drying. Subsequently, the first hot stretching was carried out in a hot air circulating oven at 230°C so that the total stretching ratio was 21.3 times, and after further immersion in a mineral oil-based water emulsion with a depth of 6%, the second drawing was carried out at 245°C with a stretching ratio of 1.3 times. Perform hot stretching to 1ooOd1
A drawn yarn of 500 f was obtained. The total stretching ratio including spinning and drawing was 2744 times. The strength of the obtained drawn yarn was 22.5 g/d, the initial elastic modulus was 441 g/d, and the elongation was 3.6%. Contains L
1 was 3000 ppm.

Example 3 A spinning dope having a PVA concentration of 10% by weight was prepared by dissolving PVA with a polymerization degree of 4500 and 0.5% by weight of boric acid based on PVA in hot water. This spinning dope was extruded from a spinning nozzle at 80°C and passed through a 7 mm air layer, followed by 50 g/β of sodium hydroxide and 100 g/100 g of sodium sulfate.
Spun into a 40°C aqueous solution containing ff.

After making PVA gel-like undrawn yarn, it is neutralized and heated.

After washing, oil treatment, drying, first hot stretching at 230°C, immersion in mineral oil water emulsion, second hot stretching at 240°C, further immersion in mineral oil water emulsion, Third hot stretching is performed at 250°C,
A drawn yarn of 750d1500f was obtained. The total stretching ratio at this time was 34.5 times.

The obtained drawn yarn had a strength of 25.9 g/d, an initial elastic modulus of 498 g/d, and an elongation of 3.2%.
The boric acid content was 700 ppm.

Comparative Example 3 The same operation as in Example 3 was performed except that boric acid was not added to the spinning dope. After spinning, the fibers tended to wrap around the rollers, resulting in poor spinning properties.

A drawn yarn was obtained. However, both the first hot stretching and the second hot stretching are 23
The third hot stretching was not performed at 0°C.

Since the film could not be stretched to 34.5 times, the total stretching ratio was set to 17.2 times, which allowed smooth stretching without yarn breakage.

The obtained drawn yarn had a strength of 12.8 g/d, an initial elastic modulus of 267 g/d, and an elongation of 5.6%.

Comparative Example 4 In Example 3, when the spinning nozzle was immersed in a coagulation bath to perform wet spinning, the drawability was extremely low and yarn breakage occurred frequently.

Comparative Example 5 In the cleaning process, in Comparative Example 5, the boric acid content was 110
In Comparative Example 6, the boric acid content was 11 so that it was 0pp.
The same procedure as in Example 2 was carried out except that washing was carried out to obtain a concentration of 0,000 pp.

In Comparative Example 5, winding around the rollers occurred, resulting in a decrease in spinning properties and also in drawability, and in Comparative Example 6, due to excessive boric acid content, drawability was reduced.

High strength/high elastic modulus fibers could not be obtained.

Example 4. Comparative Example 7 PVA with average polymerization degree of 3500 and 1.5 for PVA
A spinning stock solution having a PVA concentration of 11% by weight was prepared by dissolving % by weight of boric acid in hot water. This spinning dope was spun using the following two methods.

(1) The spinning stock solution was passed through a 5 mm air layer from a spinning nozzle, and then spun into an aqueous solution containing 10 g/A of sodium hydroxide and 400 g/L of sodium sulfate (Example 4).

(2) Sodium hydroxide log/7! Comparative Example 7 in which the spinning solution was immersed in an aqueous solution containing 400 g/R of sodium sulfate and the spinning stock solution was directly spun into this aqueous solution.
).

After that, Example 4. Comparative Example 7 Both were subjected to 5 times spinning and stretching, and then 300 g/IV of sodium sulfate and 3 sulfuric acid were added.
0g/I! Heat treated in a 90°C bath containing , and washed with water.

It was dried. The dry fibers were dried at 230°C by 3.0 times the first
After hot stretching, the fibers were immersed in a stretchable oil emulsion mainly composed of mineral oil and pressed to add 30% moisture to the fibers at 240°C.
After performing a second hot stretching of 1.3 times at
A drawn yarn of d1500f was obtained.

The properties of the obtained drawn yarn are as shown in Table 2 (Effects of the Invention) The PVA fiber of the present invention has extremely high strength and initial elastic modulus compared to PVA fiber obtained by conventional wet spinning. Its value is comparable to that of r'PTA fiber. Also,
It has higher heat resistance than high-strength, high-modulus polyethylene fibers, and is particularly suitable for use in reinforcing materials such as sea 1 and industrial fabrics such as canvas tents, tires, and asbestos substitute concrete. can.

Claims (1)

[Claims] (1) 200-8000 for polyvinyl alcohol
Contains ppm of boric acid or borate, and has a degree of polymerization of 3000
A polyvinyl alcohol fiber comprising the above polyvinyl alcohol and having a strength of at least 18 g/d and an initial elastic modulus of at least 350 g/d.