JPH05163609A - Production of polyvinyl alcohol synthetic fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber excellent in the strength and water resistance and useful as a fiber for reinforcing cement products cured in autoclave by adding a prescribed amount of a dialdehyde to the fiber in a process up to a dry thermal drawing process, and further subjecting the treated fiber to the dry thermal drawing process, an acid treatment and a crosslinking reaction. CONSTITUTION:When a PVA spinning raw solution is subjected to a wet spinning process or to dry-wet spinning process and further to a drawing process to produce a highly strong fiber, a dialdehyde or acetal compound is added to the fiber in either of the processes up to a dry-thermal drawing process so that the dialdehyde or acetal compound is added in an amount of 0.3-10wt.% based on the fiber after the dry thermal drawing process or further after heat treatment. After dried, the fiber is subjected to the dry thermal drawing process of a high drawing ratio so as to give a fiber strength of >=10g/d, or further to the heat treatment. Subsequently, the drawn or further thermally treated fiber is treated with an acid to provide the objective fiber crosslinked therein.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a polyvinyl alcohol (hereinafter abbreviated as PVA) type synthetic material useful as a fiber for reinforcing (hereinafter abbreviated as FRC) industrial materials that require hot water resistance, particularly cement products for autoclave curing. The present invention relates to a fiber and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, health problems caused by asbestos have been clarified, and their use is being regulated. PVA-based synthetic fibers have the highest strength and elasticity among general-purpose fibers, and have good adhesiveness with cement and good alkali resistance, so that demand for them is rapidly growing as a substitute material for asbestos in the FRC field. However, since the PVA-based synthetic fiber originally has poor resistance to moist heat and dissolves under the condition of moist heat, autoclave curing is impossible and it has been used exclusively for room temperature curing. At present, carbon fibers are partially used as a substitute material for asbestos in autoclave curing, but in addition to poor adhesion to the cement matrix and poor reinforcing effect, they are extremely expensive as compared to asbestos and PVA-based synthetic fibers.

On the other hand, attempts have been made to improve the wet heat resistance of PVA synthetic fibers. For example, JP-A-2-
No. 133605 discloses a method of blending an acrylic acid-based polymer or crosslinking the fiber surface with an organic peroxide, an isocyanate-based compound, a blocked isocyanate-based compound, a urethane-based compound, an epoxy-based compound, or the like. It is disclosed. However, even if the acrylic acid-based polymer is blended, the acrylic acid-based polymer is eluted during the solvent extraction process of PVA and loses its effectiveness. Even if the eluate residue is cross-linked, the cross-linking is an ester bond, so that it is easily hydrolyzed by the alkali of the cement, and it cannot endure autoclave curing at all. Even if only the fiber surface is crosslinked, swelling and dissolution will occur from the center of the fiber during autoclave curing.

The concept of this surface cross-linking treatment is that if the cross-linking structure extends to the inside of the fiber, it becomes difficult to carry out high-strength drawing, and as a result, it becomes impossible to obtain high-strength fiber. It is to keep the cross-linked structure on the fiber surface in consideration of the improvement of the wet heat resistance. However, in the PVA fiber obtained by this treatment, the cross-linking structure formed is mainly unevenly distributed on the fiber surface. Therefore, when the fiber comes into contact with hot water as described above, it does not swell or swell from its central portion. It dissolves and the moist heat resistance becomes insufficient.

This phenomenon is particularly remarkable when the fiber is used for FRC. That is, the FRC fibers are generally mixed into the cement as cut fibers, and the cut surfaces are directly exposed to the steam containing the cement component and the alkali, and swelling or dissolution occurs from the central portion of the cross section where the crosslinked structure is not formed. It will be. Therefore, even if only the surface portion of the fiber is crosslinked, the wet heat resistance as the FRC fiber is not improved. In fact, this type of crosslinked fiber was found to lose its reinforcing effect upon autoclave curing at 140 ° C.

Further, JP-A-2-249705 discloses that a PVA fiber used as a reinforcing cord for a pneumatic tire is subjected to a crosslinking treatment for the purpose of improving fatigue resistance. Then, as a means for this, a cross-linking agent is post-treated with a cord of PVA-based fiber to form a cross-linked structure on the surface of the fiber. The idea of permeating and crosslinking even is disclosed. However, in the treatment in which the cross-linking agent is added to the spinning dope or the coagulation bath, in the former case, the cross-linking agent is eluted in the coagulation bath, and in the latter case, the coagulation bath is desolvated from the spinning dope exclusively to the center of the fiber. Since it does not diffuse, it does not lead to the formation of a crosslinked structure even in the central portion of the fiber, and neither has the effect of improving the moist heat resistance, which is the object of the present invention.

Further, in Japanese Patent Laid-Open No. 63-120107,
A method is described in which a PVA-based synthetic fiber stretched 15 times or more is formalized so that the degree of formalization is 5 to 15 mol%. However, at such a degree of formalization, only a very small part of the amorphous region is made hydrophobic, and it cannot withstand autoclave curing. As will be described in detail later, the gel elastic modulus of the fiber defined in the present invention is at most 1 to 2 × 10 ↑ -3 g / cm · d,
It is clearly distinguished from the fibers obtained according to the invention and this method does not disclose the method according to the invention for dialdehyde treatment.

The purpose of autoclave curing is the dimensional stabilization of cement products. The present inventors have examined various conditions and found that curing at 140 ° C. or higher significantly improves dimensional stability. However, this is a result of small test pieces of beaker scale, and in the products of industrially produced scales, especially long products, under such curing conditions, the effect is insufficient. all right. And I found that a more practical curing temperature was at least 160 ° C.

[0009]

Therefore, the present invention is based on PV
It is intended to provide a manufacturing method for obtaining a PVA-based synthetic fiber having a highly improved moist-heat resistance, which can withstand the 160 ° C autoclave curing, which was impossible to achieve by conventional techniques. Is.

As a result of intensive studies, the inventors of the present invention have found that the gel elastic modulus, which represents the degree of crosslinking, is extremely closely related to the autoclave resistance. That is, the present inventors examined various fibers having different gel elastic moduli, and the damage of the fibers after autoclave curing was smaller in the case of a larger gel elastic modulus,
In order to enable autoclave curing at ℃, the value must be 10.0 × 10 ↑ -3g / cm · d or more,
Moreover, it was found that when the elution rate is 40% or less, it has sufficient moist heat resistance.

Here, the gel elastic modulus is a numerical value of the degree of crosslinking, and the larger the value is, the more crosslinking is introduced. The method for measuring the gel elastic modulus will be described later, but it is roughly as follows. Since zinc chloride solution is a strong solvent for PVA,
The PVA synthetic fiber can be easily melted. However, when the PVA molecules are cross-linked, the PVA crystals are dissolved in the zinc chloride aqueous solution, but because of the cross-linking network, the fiber as a whole does not dissolve, but contracts into a gel state. The elongation behavior of this gel with respect to tensile stress complies with Hooke's law, and the gel elastic modulus is, so to speak, equivalent to its spring constant.

The elution rate, which will be described later in detail,
It is the weight reduction rate of the fiber when the fiber is cut into 6 mm and immersed in the artificial cement liquid at 160 ° C. If the numerical value is not less than 40%, the reinforcing effect cannot be obtained by autoclave curing at 160 ° C. or more. In other words, the cross-linkage is 40% or less only after the cross-linking is uniformly introduced into the fiber central portion. The gel elastic modulus described above indicates the degree of crosslinking, but does not necessarily reflect the uniformity of crosslinking in the fiber. Therefore, the gel elastic modulus is, so to speak, a necessary condition for withstanding autoclave curing at 160 ° C., while the elution ratio is a sufficient condition, and it is necessary to satisfy both conditions at the same time.

By the way, in the conventionally known cross-linking treatment, in order to achieve the gel elastic modulus as described above, the drug concentration and the stretching,
It is necessary to raise the heat treatment temperature extremely. However, at the same time, this significantly reduces the strength of the fiber, making it difficult to maintain the strength of 10 g / d required for the FRC fiber. That is, it does not contribute to the improvement of FRC characteristics.

Therefore, the problem to be solved by the present invention is to satisfy the gel elastic modulus and elution rate as described above and to have a fiber strength of 10 or less.
The present invention relates to a method for rationally producing PVA-based fibers having a g / d or more.

[0015]

DISCLOSURE OF THE INVENTION The inventors of the present invention have considered that the gel elastic modulus indicates the degree of cross-linking between PVA molecules, and have paid attention to a dialdehyde or an acetalized product thereof which easily causes inter-molecular cross-linking. As a result of examination, the present invention has been achieved. That is, in the present invention, in the process for producing a PVA-based synthetic fiber, in any step up to dry heat drawing, the dialdehyde or its acetalized product is added in an amount of 0.3 to 10% by weight based on the fiber after dry heat drawing or heat treatment. % Of the dialdehyde is dried and then subjected to high-magnification drawing in an uncrosslinked state of the dialdehyde, and the fiber after dry heat drawing or the fiber after subsequent heat treatment is subjected to acid treatment to obtain fibers. The method is characterized in that crosslinking is generated therein.

Conventionally, formaldehyde, which has been most often used for acetalization of PVA, hardly causes intermolecular cross-linking and has a gel elastic modulus of 10.0 × 10 ↑ -3 g / cm ·
In order to raise it above d, it is necessary to extremely raise the concentration of formaldehyde, and the productivity is poor in terms of environment and cost. On the other hand, if a dialdehyde compound is used, it is possible to easily introduce intermolecular cross-linking with a lower concentration than formaldehyde.

However, in the past, examination of crosslinking of PVA-based synthetic fibers with a dialdehyde compound was conducted in Japanese Examined Patent Publication No. 29-6.
As disclosed in Japanese Patent Publication No. 145 and Japanese Patent Publication No. 32-5819, post-treatment is carried out in a mixed bath of a dialdehyde compound and an acid which is a reaction catalyst. It is difficult to apply it for the purpose of obtaining a fiber having strength. That is, the PVA-based synthetic fiber having low strength for clothing, which has been used in the past, has a loose fiber structure and a low crystallinity, so that the dialdehyde compound easily penetrates into the fiber central portion. When the highly stretched fiber having a strength of 10 g / d or more required in the present invention is treated, dialdehyde permeates almost the center of the fiber because the molecule of the fiber is highly oriented and crystallized. It is difficult to form crosslinks only on the surface portion, and even if the gel elastic modulus is satisfied, the elution rate is large and the target fiber cannot be obtained.

In the process of producing a PVA-based synthetic fiber, it is possible to surely permeate the dialdehyde or its acetalized product into the center of the fiber by adding the dialdehyde or its acetalized product in any step up to the dry heat drawing. One feature of the method. The orientation and crystallization of PVA molecules are
Mainly, it is a step of dry heat drawing, and it can penetrate relatively easily before that. Furthermore, the acid treatment is another feature after the dry heat drawing or the subsequent heat treatment. That is, if the dialdehyde or its acetalized product and the acid which is the reaction catalyst are used together before being applied to the fiber before dry heat drawing, cross-linking is generated prior to the drawing, which makes the drawing impossible at all. In this method, since the dialdehyde compound in the first stage is a process of allowing the dialdehyde compound to permeate into the fiber without adding an acid as a reaction catalyst, it is possible to perform high-strength drawing because the dialdehyde compound is in an uncrosslinked state. Therefore, it becomes possible to manufacture high strength fibers,
After the production of this high-strength fiber, the fiber can be subjected to a post-stage acid treatment to cause crosslinking throughout the fiber.

Therefore, the method of the present invention applies a dialdehyde or an acetalized product thereof to a fiber before dry drawing,
Ensures that it penetrates to the center, contains a cross-linking agent, but has not undergone substantial cross-linking yet, is sufficiently dry-heat stretched to promote the orientation and crystallization of the molecules that make up the fiber, and to improve strength and elasticity. After increasing mechanical properties such as rate, acid treatment is carried out to cause a cross-linking reaction and improve wet heat resistance. Further, generally, it is a big problem that dialdehyde or an acetalized product thereof is polymerized and colored immediately when coexisting with an acid and deactivated as a cross-linking agent. The above method does not have such a problem, and also in this respect, the present invention can be said to be an extremely preferable method for carrying out the production process of the high-strength fiber.

The spinning method of the PVA synthetic fiber is not particularly limited as long as it can secure the required strength, and known wet spinning or dry wet spinning (including gel spinning) can be adopted. For example, (1) a method in which boric acid or a salt thereof is added to an aqueous solution of PVA as a spinning stock solution and spun into an alkaline coagulation bath at a relatively high temperature, or (2) PVA is added to an organic solvent such as dimethyl sulfoxide or glycerin. A known solution such as a method of spinning the solution in a methanol coagulation bath using the dissolved solution as a spinning stock solution can be adopted. In addition, (3) one or two or more surfactants are added to the spinning dope for 1 to PVA.
Addition of 20% by weight is preferable because penetration of the cross-linking agent and aldehydes is promoted and stretchability is also enhanced.

The degree of polymerization of PVA to be used is not particularly limited, but as the reinforcing fiber is used, the higher the strength is, of course, the more preferable, and the gel elastic modulus is affected by the degree of polymerization to some extent, and is preferably 1,500 or more. Is more than 2000,
More preferably, it is 3000 or more. Saponification degree is 98
Mol%, preferably 99.5 mol% or higher, and higher values are advantageous.

In the case of the above method (1) in which water is used as the solvent for PVA, the spinning process is carried out by a conventional method, followed by stretching, neutralization, wet heat stretching, washing with water, drying and dry heat stretching, and further, if necessary. Accordingly, heat treatment can be performed to obtain a PVA-based fiber having excellent strength. In the case of the above method (2) in which an organic solvent is used as the solvent for PVA, the spinning stock solution discharged from the nozzle is coagulated or gelled in a coagulation bath or a cooling gelation bath according to a conventional method, and then wet drawing, the stock solution. Extraction of the solvent, drying of the second solvent used in the extraction step,
PVA-based fibers having excellent strength can be obtained by performing dry heat drawing and further performing heat treatment as necessary. Furthermore, in the case of the method (3) of adding a surfactant to the stock solution,
A PVA-based fiber having excellent strength can be obtained by the same process as in (1). In any of the above production methods, as a method for producing a fiber that simultaneously satisfies the strength, gel elastic modulus, and elution rate specified in the present invention, a dialdehyde may be formed on the thread after spinning in any step before dry heat drawing. Alternatively, the acetalized product is applied, and after drying, dry heat drawing or dry heat drawing and heat treatment is performed, and then acid treatment is performed.

Examples of the dialdehyde compound which can be used in the present invention include linear compounds such as glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, and hexane-1,6 dial, or orthophthalaldehyde, isophthalaldehyde and terephthalate. There are aromatic compounds such as aldehyde and phenylmalondialdehyde, and one or more of them may be mixed. Further, among these malondialdehyde, a compound which is polymerized with high reactivity even when it does not coexist with an acid can be acetalized with alcohol and used as an acetal compound. A typical example is tetramethoxypropane, which is acetalized malondialdehyde with methanol, and is stable if an acid does not coexist.
It becomes possible to react with A.

In the method of the present invention, the fibers are dried and drawn while containing the dialdehyde or the acetalized product thereof, and therefore it is preferable that these compounds have a boiling point as high as possible. Glyoxal has a boiling point of 60 ° C
It is very low and easily evaporates during drying and stretching, eg 1%
Even if added, only 0.4% remains after stretching, resulting in a loss. Even in such a case, loss can be reduced by acetalizing with methanol or ethanol to increase the molecular weight and raise the boiling point.

Preferred compounds are those having high reactivity with PVA, easy to penetrate into fibers, that is, the molecules are not so large, and conversely, they are large molecules having a high boiling point. With the above requirements, tetramethoxypropane, succinaldehyde and glutaraldehyde are preferable.

The method of applying these compounds to the fiber is not particularly limited as long as it can be applied uniformly. For example, a method of making an aqueous solution, dipping the fiber before drying in this and appropriately squeezing the solution is preferable. It can be said to be an aspect.

In order to obtain the fiber of the present invention, it is necessary that the dialdehyde or its acetalized product is present in an amount of 0.3% by weight or more based on the fiber after dry heat drawing or heat treatment. Therefore, the conditions for defining the applied amount such as the concentration may be appropriately adjusted in consideration of the conditions of the subsequent dry heat drawing and heat treatment. If the applied amount after dry heat drawing or heat treatment is less than 0.3% by weight, the target gel elastic modulus and elution rate cannot be obtained. On the other hand, when the content exceeds 10% by weight, the strength is largely decreased, which is not preferable.
It is more preferably 0.5 to 8% by weight, and even more preferably 1 to 5% by weight.

After that, drying, dry heat stretching, and heat treatment as necessary may be carried out by a conventional method, but it is necessary to increase the stretching ratio as much as possible from the viewpoint of strength, preferably 15 times.
It is more preferably 17 times or more.

Subsequently, acid treatment is performed. As the acid, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, or organic acids such as carboxylic acid and sulfonic acid can be used, but sulfuric acid is most commonly used. As the acid treatment condition, the concentration is required to be 0.05 normal or higher, preferably 0.1 normal or higher. The temperature is 60 to 100 ° C, preferably 70 to 95 ° C
Is. Glauber's salt may be appropriately added to suppress excessive swelling of fibers.

[0030]

EXAMPLES The present invention will be described below with reference to examples. still,
In the examples, strength, gel elastic modulus, elution rate, bending strength of slate, and dialdehyde or acetalized product thereof in fibers shall be measured by the following methods.

(1) Strength: Multifilament yarn 8
Measured with an Instron tensile tester in compliance with JISL-1017 using 0T / m twisted yarn as a sample.

(2) Gel elastic modulus; 1000-2000 denier multifilament yarn is fixed to the upper end so as to have a length of 20 cm and suspended, and a load of 1 gram is applied to the lower end. When this is immersed in an aqueous solution of zinc chloride at 50 ° C. and 50% by weight, the fibers shrink. The sample length when the contraction is completely stopped is measured, and this is defined as Acm. Next, the load is changed from 1 gram to 30 grams, and the sample length is similarly measured in the zinc chloride aqueous solution, which is defined as Bcm. Gel elasticity = 29 / (B−A) · D g / cm · d. However, D is the denier of the sample before being immersed in the zinc chloride aqueous solution.

(3) Elution rate: Fiber was cut into 6 mm,
About 0.5 g thereof is weighed (denoted as Ag), put into a stainless steel autoclave having a thickness of 4.5 mm together with 100 cc of artificial cement liquid, and immersed in an oil bath at 160 ° C. for 2 hours. After that, the fiber is pulled up from the oil bath and cooled, the fiber is taken out, dried and then weighed (Bg). Elution rate = (A−B) / A × 100 (%). The artificial cement liquid is 3.5 g of potassium hydroxide /
1, sodium hydroxide 0.9 g / l, calcium hydroxide 0.4 g / l.

(4) Bending strength of slate: PVA synthetic fiber was cut into a length of 6 mm, wet-machined by a checkex machine with a mixture of 2 parts of the fiber, 4 parts of pulp and 94 parts of Portland cement, and at 50 ° C. 16 hours after primary curing for 12 hours
Autoclave curing was carried out at 0 ° C. for 10 hours to obtain a slate plate, and bending strength was measured according to JIS K6911. A bending strength of 240 kg / cm 2 or more is judged to have a reinforcing effect.

(5) Dialdehyde in fiber or acetalized product thereof; fiber before acid treatment is cut into 1 mm length and 1
After drying at 05 ° C. for 4 hours, it is weighed (Ag). This is soxhlet-extracted with methanol, and methanol is completely evaporated from the extract to weigh (Bg). The dialdehyde or its acetalized product in the fiber is expressed as B / A × 100 (% by weight).

Examples 1 to 3, Comparative Examples 1 and 2: Degree of polymerization 3
000 of completely saponified PVA was dissolved in water at a concentration of 11%, boric acid was added at 2% by weight to PVA, and nonylphenol ether ethylene oxide 40 mol adduct was added at 3% by weight to PVA. A spinning dope was prepared. 25 g / l of sodium hydroxide and 3 parts of Glauber's salt
Wet spinning was performed in a coagulation bath of 20 g / l at 65 ° C., followed by roller stretching, neutralization, wet heat stretching, and water washing according to a conventional method, followed by immersion in tetramethoxypropane aqueous solution having different concentrations, followed by drying, and then 235 ° C. Was dry-heat stretched so that the total stretching ratio was 25 times. The thus-obtained fibers were each acid-treated in a sulfuric acid bath at 85 ° C. and 1 N. The physical properties and the like of the obtained fiber are shown in Table 1.

[0037]

[Table 1]

In the above example, the present method can be carried out at a high total draw ratio to obtain high-strength fibers, and as shown in Table 1, TMP is applied to the fibers within the range specified by the present method and treated. By doing so, the target fiber was obtained in terms of strength, gel elastic modulus and elution rate.
It is shown that the bending strength of the slate plate in the case of 0 ° C. autoclave curing is also excellent.

Comparative Example 3: When tetramethoxypropane was applied in Example 2 and 1N sulfuric acid was applied at the same time, crosslinking was formed during drying, and dry heat drawing could not be performed at all.

Example 4 A completely saponified PV having a polymerization degree of 2400 was dissolved in dimethyl sulfoxide at a concentration of 14%,
Dry-wet spinning was performed in a methanol coagulation bath. After that, the solvent was extracted, wet-stretched, and dried according to a conventional method, and then a concentration of 15 g / l was applied to 4
It was immersed in a 0 ° C. glutaraldehyde aqueous solution, dried, and then dry heat stretched at 230 ° C. so that the total stretching ratio was 20 times. The fiber contained 1.5% by weight of glutaraldehyde. The fiber was subsequently treated with 2N 80 ° C sulfuric acid. The fiber thus obtained has a strength of 14.8 g / d, a gel elastic modulus of 14.3 × 10 ↑ -3 g / cm · d, and an elution rate of 34.
%, The bending strength of the slate was as excellent as 310 kg / cm ↑ 2.

Comparative Example 4: For the fiber stretched dry without immersing in glutaraldehyde in Example 4,
Glutaraldehyde / sulfuric acid = 15/98 g / l (sulfuric acid 2
(Normal) bath at 80 ° C. The fiber thus obtained has a strength of 13.1 g / d and a gel elastic modulus of 16.3 × 10 ↑.
Although it was -3 g / cm · d, the dissolution rate had large unevenness of 36 to 63%, indicating that glutaraldehyde may not sufficiently penetrate into the center of the fiber. In addition, the treatment bath was less than 30 minutes, and glutaraldehyde was polymerized with each other, resulting in intense coloring.

[0042]

INDUSTRIAL APPLICABILITY The fiber obtained by the method of the present invention is suitable not only as a fiber for FRC for autoclave curing but also because of its excellent strength and water resistance, the conventional water resistance is insufficient. The steam vulcanization that was previously possible is now possible, and it can be easily applied to rubber materials such as hoses, and it is also useful as a general industrial material such as ropes, FRP, and marine products. Further, the production method of the present invention is extremely effective in obtaining such excellent fibers.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location D06M 13/137 15/39 // D06M 101: 24

Claims (1)

[Claims] 1. A method for producing a high-strength fiber by wet- or dry-wet spinning of a polyvinyl alcohol-based spinning dope and stretching to produce a high-strength fiber, at any step until dry heat stretching,
The amount of the dialdehyde or acetal compound is 0.3 to 0.3 with respect to the fiber after dry drawing or further heat treatment.
It is applied so that it exists in an amount of 10% by weight, and after drying, high-strength dry heat drawing with a fiber strength of 10 g / d or more is performed.
Alternatively, the method for producing a polyvinyl alcohol-based synthetic fiber is characterized in that heat treatment is further performed, and then the fiber after the drawing or heat treatment is subjected to an acid treatment to cause crosslinking in the fiber.