JP2009108432A - Polyvinyl alcohol-based fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a PVA-based fiber having improved modulus at a high temperature and excellent fatigue resistance. <P>SOLUTION: The PVA-based fiber comprises an atactic polyvinyl alcohol-based polymer having 1,000-2,000 viscosity-average polymerization degree, and contains 1,000-12,000 ppm boric acid or borate expressed in terms of a boron atom based on the polyvinyl alcohol. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a polyvinyl alcohol (hereinafter abbreviated as PVA) fiber having excellent fatigue resistance and improved elastic modulus at high temperature, and a method for producing the same.

  Conventionally, PVA fibers are superior to polyamide, polyester, and polyacrylonitrile fibers in terms of strength, elastic modulus, weather resistance, chemical resistance, adhesiveness, etc. Has pioneered. Recently, it has been attracting attention as a suitable material for fields such as cement reinforcing fibers (substitution for asbestos) and alkaline battery separators that utilize the characteristics of alkali resistance. In addition to these features, if a PVA fiber having higher strength, higher elastic modulus, and better fatigue resistance is developed, it can be used as a reinforcing material for rubber and plastic. In particular, in rubber reinforcement applications, safety and dimensional stability are required in addition to fatigue resistance, and a fiber having a high elastic modulus and low shrinkage at high temperatures has been demanded as a rubber reinforcement.

  As a method of cross-linking PVA fibers for the purpose of improving fatigue resistance at high temperature and heat-and-moisture resistance, acetalization treatment is known (for example, see Patent Document 1). However, this method has improved wet heat resistance, but has a problem that the elastic modulus is lowered.

  Further, a method of crosslinking with boric acid or borate is disclosed as one that does not cause a decrease in strength and elastic modulus during crosslinking (see, for example, Patent Document 2). However, it was found that the stretchability was hindered by the boric acid crosslinking, and the performance was lowered.

  Furthermore, it is disclosed that a high syndiotactic PVA blended with atactic PVA and boric acid or borate added to the drying step exhibits a high elastic modulus at a high temperature (see, for example, Patent Document 3). ). However, since PVA or syndiotactic PVA with a high degree of polymerization is used, there is a problem that an organic solvent must be used as a solvent for the PVA polymer, and there is a means that can be produced in an aqueous system from the viewpoint of safety and environment It was requested.

JP 63-120107 A JP 62-149909 A JP 7-243122 A

  An object of the present invention is to provide a PVA fiber excellent in fatigue resistance and having improved elastic modulus at high temperature.

  In order to achieve the above object, the present inventors have conducted intensive studies. As a result, after the polymer composed of an atactic PVA polymer is made into a fiber using water as a solvent, the resulting PVA fiber is resistant to cross-linking by containing a predetermined concentration of boric acid or borate to the fiber. The present inventors have found that it is excellent in fatigue property and can improve the elastic modulus at high temperature, and has completed the present invention.

That is, the present invention is a PVA fiber comprising an atactic PVA polymer having a viscosity average degree of polymerization of 1000 to 2000, and further containing boric acid or borate in an amount of 1000 to 12000 ppm in terms of boron atom. Preferably, the PVA fiber is characterized in that all of the following conditions (1) to (3) are satisfied.
(1) The strength at 80 ° C. is 4 cN / dtex or more,
(2) The elastic modulus at an atmospheric temperature of 80 ° C. is 120 cN / dtex or more,
(3) The hot water shrinkage at 100 ° C. is 7% or less,

  And, the present invention is a method for producing a PVA fiber by discharging a solution of an atactic PVA polymer from a nozzle to form a yarn, then removing the solvent from the yarn and drying, followed by dry heat drawing. Use of water as a solvent for the PVA polymer, and addition of boric acid or a borate after the dry heat drawing step, causing the presence of 1000 to 12000 ppm in terms of boron atom, production of the above PVA fiber Is the method.

  According to the present invention, a PVA fiber having excellent fatigue resistance and high elastic modulus, and particularly improved elastic modulus at high temperature can be obtained. Such a fiber of the present invention is suitable for reinforcing materials such as rubber, plastic and cement or general industrial materials such as ropes, fishing nets, tents and civil engineering sheets, and particularly excellent for rubber reinforcing materials such as tires, hoses and belts. PVA fiber.

Hereinafter, the present invention will be specifically described.
First, the PVA polymer constituting the PVA fiber of the present invention will be described. The atactic PVA polymer used in the present invention is a syndiotacticity S = 52-54% obtained by dyad display obtained from NMR, which will be described later, and is a straight chain having a viscosity average polymerization degree of 1000-2000. belongs to. If the syndiotacticity S is less than 52%, it may be inferior in terms of strength, resistance to moist heat and the like.
On the other hand, it is preferable to use a high syndiotacticity because it is excellent in terms of strength, moist heat resistance and the like, but syndiotacticity S is 54% or less from the viewpoint of polymer production cost and fiberization cost. preferable. Also, with respect to the viscosity average degree of polymerization, it is preferable to use those having a high degree of polymerization because they are excellent in terms of strength, moist heat resistance, etc., but those having an average degree of polymerization of 1200 to 1900 from the viewpoint of polymer production costs and fiberization costs Are preferred, and those of 1400-1800 are more preferred. The degree of saponification is not particularly limited, but is preferably 98 mol% or more, more preferably 99 mol% or more, particularly preferably 99.7 mol% or more in terms of crystallinity and orientation of the obtained fiber. is there.
In addition, syndiotacticity as used in the field of this invention is syndiotacticity (T. Moritani et al.) By the triad display calculated | required by the proton NMR measurement value of the PVA-type polymer melt | dissolved in deuterated dimethylsulfoxide (d6-DMSO). , Macromolecules, 5, 577 (1972)) and calculated from the following equation from syndiotacticity (S), heterotacticity (H), and isotacticity (I).
s = S + H / 2 (Syndiotacticity with dyad display)
i = I + H / 2 (isotacticity by dyad display)

  The atactic PVA polymer constituting the fiber of the present invention is not particularly limited as long as it has a vinyl alcohol unit as a main component, and has other structural units as long as the effects of the present invention are not impaired. It doesn't matter. Examples of such a structural unit include olefins such as ethylene, propylene, and butylene, acrylic acid and salts thereof and acrylic esters such as methyl acrylate, methacrylic acid and salts thereof, and methacrylate esters such as methyl methacrylate. Acrylamide derivatives such as acrylamide, N-methylacrylamide, methacrylamide derivatives such as methacrylamide, N-methylol methacrylamide, N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, polyalkylene oxide Allyl ethers having a side chain, vinyl ethers such as methyl vinyl ether, nitriles such as acrylonitrile, vinyl halides such as vinyl chloride, maleic acid and salts thereof or anhydrides thereof and the like And the like unsaturated dicarboxylic acids such as ester. Such a modified unit may be introduced by copolymerization or post-reaction.

  The atactic PVA fiber of the present invention is produced by solution spinning, specifically, wet spinning, dry wet spinning, and dry spinning, of a spinning stock solution containing a PVA polymer. As the solvent used for the spinning dope, water is preferable from the viewpoints of availability and influence on the environmental load. The polymer concentration in the spinning dope varies depending on the composition and degree of polymerization of the PVA polymer, but is generally in the range of 6 to 60% by mass. As long as the effects of the present invention are not impaired, the spinning dope includes an antioxidant, an antifreezing agent, a pH adjusting agent, a concealing agent, a coloring agent, an oil agent, etc., in addition to the PVA polymer, depending on the purpose. Additives and the like may be included.

  Such a spinning dope may be discharged from the die and spun by, for example, a wet spinning method, a dry spinning method, a dry wet spinning method, or the like. When the wet spinning method or the dry and wet spinning method is adopted, a desired yarn can be obtained by discharging the spinning stock solution to a solidification bath having a solidification ability and appropriately applying wet heat drawing, drying and the like. For example, when a PVA-based aqueous solution is used as a spinning solution, wet spinning may be performed using a saturated salt solution as a solidification solution.

  When it is preferable that the fiber is in the form of a filament as in the case of a brake hose reinforcement, it is preferable to perform spinning by a dry spinning method in which a spinning solution is discharged into a gas. Air is generally used as the gas, and the temperature of the gas is generally 60 to 140 ° C. The discharged yarn may then be heated, and is generally dried by running the yarn using a hot plate, hot roller, heated air zone, or the like.

  In the present invention, it is preferable to perform at least dry heat drawing from the viewpoint of enhancing the mechanical performance and hot water resistance of the fiber. The method of hot drawing is appropriately selected, such as a method in which an undrawn yarn is brought into contact with a heating body such as a hot roller or a heat plate, a method in a hot solvent, a method in a hot air heating apparatus, a method of performing a dielectric heating method, etc. do it. The stretching temperature is preferably 100 ° C. or more and less than 250 ° C., particularly 200 to 240 ° C. from the viewpoint of suppressing the decomposition of the polymer and efficiently stretching. Further, from the viewpoint of the mechanical performance of the fiber, it is preferable that the total stretching ratio is 7 times or more, particularly 8 times or more, and more preferably 10 times or more. At this time, from the viewpoint of increasing the fatigue resistance of the fiber, a field in which a heat shrink treatment is performed after dry heat drawing is preferable. The heat shrinking treatment is preferably performed at 230 ° C. or higher, and is preferably performed at a temperature 3 ° C. or higher, particularly 5 ° C. higher than the dry heat stretching temperature. Furthermore, the relaxation rate is preferably 1% or more, and is preferably 20% or less, particularly preferably 15% or less from the viewpoint of not substantially impairing the mechanical performance of the fiber. Further, the higher the relaxation rate, the higher the elongation of the fiber and the better the fatigue resistance. Therefore, the elongation of the fiber is preferably 3% or more, and more preferably 5% or more.

  In the present invention, it is necessary to add boric acid or a borate to the PVA fiber after the stretching step so that the PVA polymer contains boric acid or borate in an amount of 1000 to 12000 ppm in terms of boron atom. When boric acid or a borate is added before the stretching step, the stretchability is hindered by the boric acid crosslinking, and the performance is lowered. The present invention contains boric acid or a borate, causes cross-linking, and has an effect of suppressing a decrease in elastic modulus at a high temperature of dry heat by suppressing molecular chain mobility at a high temperature of dry heat. If the content of boric acid or borate in the PVA polymer is less than 1000 ppm, the effect of the present invention is not sufficiently exerted because the crosslinking point is small and the effect of suppressing the movement of the molecular chain is insufficient. Is significantly reduced. Therefore, the boric acid content is preferably 1000 to 12000 ppm, preferably 2000 to 10000 ppm, and more preferably 3000 to 8000 ppm.

  The PVA fiber of the present invention can be subjected to acetalization treatment and other crosslinking treatments generally performed for PVA fibers for the purpose of improving hot water resistance depending on applications and purposes. That is, the fiber can be hydrophobized by treating the PVA fiber in an aqueous solution containing a crosslinking agent such as formaldehyde that reacts with the hydroxyl group of the PVA polymer to block the hydroxyl group. The treatment may be performed before or after the boric acid crosslinking treatment, and the order of the treatment is not particularly limited, but it is preferable to perform the treatment after the boric acid crosslinking treatment.

When the PVA-based fiber of the present invention is used for applications that particularly require mechanical properties, heat resistance, moist heat resistance, etc., the strength at 80 ° C. is 4 cN / dtex or more, and the elastic modulus at 80 ° C. is 120 cN / dtex or more. It is preferable that
When the strength at 80 ° C. is smaller than 4 cN / dtex, the function as a reinforcing fiber may not be sufficiently achieved. More preferably, it is 5 cN / dtex, More preferably, it is 7 cN / dtex or more and 20 cN / dtex or less. Further, when the elastic modulus at 80 ° C. is less than 120 cN / dtex, the function as the reinforcing fiber may not be sufficiently achieved. More preferably, it is 150 cN / dtex or more, More preferably, it is 160 cN / dex or more and 400 cN / dtex or less. In addition, the intensity | strength and elastic modulus in 80 degreeC are measured by the method mentioned later.

In particular, when used for rubber reinforcement, the PVA fiber preferably has a hot water shrinkage rate at 100 ° C. of 7% or less, and fatigue resistance in rubber at 100 ° C. is 70% or more in terms of strength retention. If the hot water shrinkage is greater than 7%, the fibers may melt during the rubber vulcanization process.
Further, when the fatigue resistance of the PVA fiber in 100 ° C. rubber is less than 70%, the function as the reinforcing fiber may not be sufficiently achieved.
The hot water shrinkage at 100 ° C. and the fatigue resistance in rubber at 100 ° C. are measured by the methods described later.

  The fiber of the present invention can be used in any fiber form such as staple fiber, shortcut fiber, filament yarn, spun yarn and the like. The cross-sectional shape of the fiber at that time is also not particularly limited, and may be circular, hollow, or a different cross section such as a star shape. Furthermore, you may mix and use the fiber of this invention with another fiber. In this case, the fiber that can be used in combination is not particularly limited, and examples thereof include PVA fibers that are not subjected to boric acid crosslinking treatment, polyester fibers, polyamide fibers, and cellulose fibers.

  The fiber of the present invention can be suitably used for various uses such as industrial materials, clothing, and medical use. For example, various filters, heat insulating materials, high heat retaining clothing, house wrapping paper, cleaning mop materials, and reinforcing (cement , Rubber, resin, etc.). In particular, it is suitable as a reinforcing fiber for cement, rubber, resin, etc. because of its excellent mechanical properties, heat resistance, and moist heat resistance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples. In the following examples, each physical property value is measured by the following method.

[Viscosity average polymerization degree of atactic PVA]
According to the JIS K-6726 test method, the viscosity average polymerization degree was determined from the measured value of the intrinsic viscosity [η] of an aqueous solution at 30 ° C. according to the following formula.
Pa = ([η] × 10 ⁴ /8.29) ^1.63

[Boron content ppm]
The PVA fiber was dissolved in 140 ° C. water under hermetic conditions, mannitol (manufactured by Kanto Chemical Co., Ltd.) that easily reacts with boron was added, and calculation was performed by titration with NaOH.

[Tensile strength and elastic modulus of PVA fiber cN / dtex]
In accordance with the JIS L-1013 test method, a pre-dried yarn was measured under the conditions of a test length of 20 cm, an initial load of 0.25 g / d, and a tensile speed of 50% / min. Adopted. Fiber physical properties at room temperature were measured in air at 20 ° C. Further, the fiber physical properties at high temperature were determined by attaching a high-temperature air tank to a tensile tester and measuring the strength and elastic modulus at 80 ° C. The fiber thickness (dtex) was determined by a mass method.

[Hot water shrinkage%]
A 2 mg weight per decitex is attached to one end, the other end is fixed on the scale plate, and the fiber length _A0 is measured. This was immersed vertically in 100 ° C. hot water, allowed to stand for 30 minutes, and then the fiber length B ₀ in the hot water was read from the scale, and the shrinkage was calculated from the following equation. .
Hot water shrinkage (%) = (A ₀ −B ₀ ) / A ₀ × 100

[Fatigue resistance%]
The yarn was twisted in the z direction at 365 t / m to form a lower twisted yarn, and three lower twisted yarns were twisted 300 t / m in the S direction to prepare a cord. An RFL resin, which is a rubber adhesion improver, was attached to this cord at a solid content of 5% by mass, dried at 110 ° C., and heat treated at 160 ° C. to obtain a dip cord. Using this dip cord and rubber having a composition of natural rubber / styrene butadiene rubber = 1/1, using a disk fatigue test apparatus described in JIS L-1017 chemical fiber tire cord test method, compression 3%, elongation 3%, Fatigue was carried out at a temperature of 100 ° C. and 300,000 times, and the strength retention (%) was calculated from the dip cord strength after the test. The RFL resin having the following composition was used.
<RFL liquid composition>
A liquid
Water 67 parts by weight Resorcin 2.8 parts by weight Formaldehyde (37%) 6.1 parts by weight Sodium hydroxide aqueous solution (10%) 2.0 parts by weight The above solution A was aged at 25 ° C. for 6 hours.
B liquid
SBR latex 50 parts by weight Vinylpyridine-modified SBR latex 21.5 parts by weight Water 76.3 parts by weight The above B liquid was mixed with the aged A liquid and then aged at 25 ° C. for 16 hours. A chlorophenol-based auxiliary was added as an agent to prepare an RFL solution having a concentration of 8 wt%. The measurement was made in accordance with the single tongue method of the JIS L1906 test method.

[Example 1]
(1) A PVA polymer having an average degree of polymerization of 1700, a degree of saponification of 99.9 mol%, and a syndiotacticity S = 53.4% was added to water so that the PVA concentration would be 41.0% by mass, and 95 ° C. And dissolved by heating. The obtained spinning dope was spun through a round nozzle having a hole diameter of 0.10 mm and a hole number of 40 at a stock solution discharge rate of 100 cc / min and a take-up speed of 155 m / min, and then stretched 10 times at 240 ° C.
(2) The PVA fiber obtained in (1) above is immersed in a bath of an aqueous solution of boric acid 80 g / L and sodium hydroxide 20 g / L at 80 ° C. for 60 minutes at a bath ratio of 50: 1, and then fully After washing with water and air drying for 24 hours, PVA fibers with a boron content of 5700 ppm were obtained.
The fiber thus obtained was excellent in elastic modulus and durability at 80 ° C. The results are shown in Table 1.

[Example 2]
A PVA fiber obtained in exactly the same manner as in Example 1 was placed in a bath of an aqueous solution of boric acid 80 g / L and sodium hydroxide 20 g / L at a temperature lower than that of Example 1 (60 ° C.) for 60 minutes and a bath ratio of 50. After being soaked in water and thoroughly washed with water, it was air-dried for 24 hours to obtain a PVA fiber having a boron content of 1700 ppm.
The fiber thus obtained was excellent in elastic modulus and durability at 80 ° C. The results are shown in Table 1.

[Example 3]
The PVA fiber obtained in exactly the same manner as in Example 1 was placed in a bath of an aqueous solution of boric acid 80 g / L and sodium hydroxide 20 g / L at a temperature higher than that of Example 1 and a longer processing time (at 85 ° C. 80 minutes), and then immersed in a bath ratio of 50: 1, and then sufficiently washed with water and air-dried for 24 hours to obtain a PVA fiber having a boric acid content of 8400 ppm.
The fiber thus obtained was excellent in elastic modulus and durability at 80 ° C. The results are shown in Table 1.

[Example 4]
(1) A PVA polymer having a viscosity average polymerization degree of 1400, a saponification degree of 99.9 mol%, and a syndiotechnity S = 53.4% was added to water so that the PVA concentration was 41.0% by mass. Dissolved by heating at ℃. The obtained spinning dope was spun at a stock solution discharge rate of 100 cc / min and a take-up speed of 155 m / min through a round nozzle having a hole diameter of 0.10 mm and a hole number of 40, and then stretched 10 times at 240 ° C. Fiber was obtained.
(2) The obtained PVA fiber was immersed in an aqueous solution of boric acid 80 g / L and sodium hydroxide 20 g / L at a bath ratio of 50: 1 at 80 ° C. for 60 minutes, and then thoroughly washed with water and washed. PVA fibers having a boric acid content of 5700 ppm were obtained by air drying for a period of time.
The fiber thus obtained was excellent in elastic modulus and durability at 80 ° C. The results are shown in Table 1.

[Example 5]
The PVA fiber obtained in exactly the same manner as in Example 1 was placed in a bath of an aqueous solution of boric acid 80 g / L and sodium hydroxide 20 g / L at the same temperature as Example 3 and under a long treatment time (at 85 ° C. 120 minutes) and then immersed in a bath ratio of 50: 1, then washed thoroughly with water and air-dried for 24 hours to obtain a PVA fiber having a boric acid content of 11500 ppm.
The fiber thus obtained was excellent in elastic modulus and durability at 80 ° C. The results are shown in Table 1.

[Comparative Example 1]
When the PVA fiber obtained in Example 1 was not treated with boric acid, the obtained fiber had a low elastic modulus at 80 ° C. of 86 cN / dtex.

[Comparative Example 2]
The PVA fiber obtained in exactly the same manner as in Example 1 was immersed in a bath of boric acid 150 g / L in an aqueous solution of 150 g / L at 80 ° C. for 60 minutes at a bath ratio of 50: 1, then washed thoroughly with water and then air-dried for 24 hours. As a result, a PVA fiber having a boric acid content of 15500 ppm was obtained, but the strength was inferior because the boric acid content was too high, and the PVA fiber targeted by the present invention was not obtained. The results are shown in Table 1.

[Comparative Example 3]
A PVA fiber was obtained in exactly the same manner as in Example 1 except that an atactic PVA polymer having a viscosity average polymerization degree of 600 was used. The PVA fiber thus obtained was inferior in fatigue resistance because the polymerization degree of the PVA polymer was too low.

[Comparative Example 4]
Except for using an atactic PVA polymer having a degree of polymerization of 5000, an attempt was made to obtain PVA fibers in exactly the same manner as in Example 1, but hot water was sufficient because the degree of polymerization of the PVA polymer was too high. The fiber was not able to be obtained by spinning.

[Comparative Example 5]
The PVA fiber obtained in exactly the same manner as in Example 1 was placed in a bath of an aqueous solution of boric acid 80 g / L and sodium hydroxide 20 g / L at a temperature lower than that of Example 1 and a short processing time (60 ° C. For 5 minutes) and then thoroughly washed with water and air-dried for 24 hours to obtain PVA fibers having a boric acid content of 500 ppm. The PVA fiber thus obtained had a low elastic modulus at 80 ° C. of 95 cN / dtex, and the PVA fiber targeted by the present invention was not obtained. The results are shown in Table 1.

[Comparative Example 6]
Except for using a high syndiotactic PVA polymer having a polymerization degree of 1600, a saponification degree of 99.9 mol%, and a syndiotacticity S = 61.5%, fiberization was performed under exactly the same conditions as in Example 1. Attempts were made to dissolve the PVA polymer in water at 95 ° C. by heating, but the PVA polymer was not sufficiently dissolved, and the fiber could not be obtained by spinning.

  The fiber of the present invention can be suitably used for various uses such as industrial materials, clothing, and medical use. For example, various filters, heat insulating materials, high heat retaining clothing, house wrapping paper, cleaning mop materials, and reinforcing (cement , Rubber, resin, etc.). In particular, it is suitable as a reinforcing fiber for cement, rubber, resin, etc. because of its excellent mechanical properties, heat resistance, and moist heat resistance.

Claims (3)

  A polyvinyl alcohol fiber comprising an atactic polyvinyl alcohol polymer having a viscosity average polymerization degree of 1000 to 2000, and further containing boric acid or borate in an amount of 1000 to 12000 ppm in terms of boron atom. The polyvinyl alcohol fiber according to claim 1, wherein all of the following conditions (1) to (3) are satisfied.
(1) The strength at 80 ° C. is 4 cN / dtex or more,
(2) The elastic modulus at 80 ° C. is 120 cN / dtex or more,
(3) The hot water shrinkage at 100 ° C. is 7% or less,   In the method of producing a polyvinyl alcohol fiber by discharging a solution of an atactic polyvinyl alcohol polymer from a nozzle to form a yarn, then removing the solvent from the yarn and drying, followed by dry heat drawing. 3. The polyvinyl according to claim 1, wherein water is used as a solvent for the alcohol-based polymer, and boric acid or borate is further added after the dry heat stretching step so that 1000 to 12000 ppm in terms of boron atom is present. A method for producing alcohol-based fibers.