JP2001055620A - Acrylic fiber suitable for production of nonwoven fabric - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a acrylic fiber suitable for production of nonwoven fabrics, and also provide a method for producing the same. SOLUTION: This fiber is composed of an acrylonitrile-based copolymer containing acrylonitrile in 98 wt.% or more, having a tensile strength of 3 g/d or more, tensile elongation of 50% or more, and knot strength/tensile strength ratio of 0.9 or more. This acrylic fiber can be made into nonwoven fabrics which can go into various areas, e.g. wipers, filters, and construction and civil engineering materials for its excellent mechanical properties, in particular knot strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylic fiber suitable for nonwoven fabric processing and a method for producing the same, and more particularly, to a high acrylonitrile content and heat resistant acrylic fiber having physical properties suitable for nonwoven fabric processing and a method for producing the same. .

[0002]

2. Description of the Related Art Conventionally, fibers, whether natural or synthetic, have been generally used as spun yarns through a spinning process. However, with the development of nonwoven fabric technology and the widening gap between domestic and overseas spinning wages, the transition from spun yarn to nonwoven fabric as a fiber processing mode is increasing year by year. In particular, it is expected that the use of spun yarns will change dramatically from non-woven fabrics in the future in terms of cost, particularly for industrial material applications of any form as long as the required performance is satisfied.

[0003] On the other hand, acrylic fibers are used in large quantities for clothing, taking advantage of their excellent texture and dyeing properties, but are rarely used for industrial materials due to insufficient mechanical properties. At present, many attempts have been made to produce acrylic fibers having mechanical properties that can be used as fibers for industrial materials.

For example, Japanese Patent Application Laid-Open No. 57-51819 discloses that a fiber obtained by a wet or dry-wet spinning method is wet-drawn, dried under no tension, and subsequently contact-drawn on a heating plate to be effective. It has been proposed that the draw ratio be 9 to 25 times to obtain an acrylic fiber having a high elastic modulus. Japanese Patent Application Laid-Open No. 57-161117 discloses that the relative viscosity is 2.5 to
A method has been proposed in which an acrylonitrile-based polymer of 6.0 is dry- or wet-spun, wet-drawn during or after washing, dried on a heating roll under tension, and heat-treated under dry heat. However, although these known techniques can improve the tensile strength, it is difficult to provide the necessary properties when producing a nonwoven fabric.

In many cases, industrial materials are required to be a fiber having heat resistance in addition to the above-described high elastic modulus and high tensile strength. As described above, it is also necessary to provide the information. In order to meet such a demand for heat resistance in particular, for example, JP-A-1-104818 discloses a method in which an acrylonitrile-based polymer having a weight average molecular weight of 500,000 or more containing 95% by weight or more of acrylonitrile is dissolved in an organic solvent. The obtained spinning dope is dry-wet spinned in a coagulation bath, and the obtained coagulated yarn is drawn in warm water.
By performing dry heat stretching using a heating roller maintained at 0 ° C. or more, a tensile strength of 15 g / d or more and a knot strength of 4 g / d
It is described that acrylic fibers of d or more can be obtained.

[0006] However, the acrylic fiber has high tensile strength and high knot strength, and has a certain level of heat resistance, but is inferior in workability of a nonwoven fabric in that a single fiber is fibrillated. On the other hand, Japanese Unexamined Patent Publication No. Hei 5-279912 discloses that a spinning stock solution of an acrylonitrile polymer containing 95% by weight or more of acrylonitrile is dry-spun, and the obtained fiber is primarily drawn in a range of 1.5 to 4 times. Next, a drying and relaxation heat treatment is performed to give a shrinkage of 10 to 50%, and further, after a second stretching of 1.1 to 1.8 times under moist heat, 160 to 200 times.
Constant-length heat treatment at ℃, tensile strength 1-3g /
d, describes that an anti-pilling acrylic fiber having a product of knot strength (g / d) and knot elongation (%) of 50 or less can be obtained.

Although the acrylic fiber has a certain level of heat resistance, it has low tensile strength and low knot strength and is excellent in "anti-pilling property", but does not withstand nonwoven fabric processing. As can be understood from the above two examples, the heat resistance of the acrylic fiber is improved by increasing the acrylonitrile content of the polymer, but at present, there is no material that satisfies the heat resistance and the suitability for nonwoven fabric processing. . Nonwoven fabric processing suitability
Neither one with high mechanical properties (the former) nor one with low mechanical properties (the latter) are provided, indicating a high technical barrier to solve this.

It is known that the knot strength of a fiber is improved by forming the fiber into a modified cross section such as a cocoon shape or a triangular shape. However, even if the knot strength is improved by such a method, the tensile elongation is not improved at all,
Such fibers are still fragile and cannot be said to have mechanical properties suitable for making into a nonwoven fabric. That is, the improvement in the knot strength of the fiber itself is merely an apparent one based on the cross-sectional shape of the fiber.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an acrylic fiber having excellent mechanical properties and heat resistance required for forming a nonwoven fabric, and a method for producing the same.

[0010]

Means for Solving the Problems The present inventor has intensively studied acrylic fibers in order to impart heat resistance to nonwoven fabric while maintaining heat resistance. As a result, if the acrylonitrile content of the polymer is increased in order to impart heat resistance to the acrylic fiber, the crystallization of the fiber proceeds and becomes rigid if the production method is ordinary. The present invention was found out that some fibers must be unsuitable and must have a certain strength-elongation balance, and that even fibers with a high acrylonitrile content can be given the strength-elongation balance by selecting manufacturing conditions as shown on the left. did.

The present invention comprises an acrylonitrile-based polymer containing at least 98% by weight of acrylonitrile, and has a tensile strength of more than 3 g / d, a tensile elongation of 50% or more, and a knot strength / tensile strength ratio of 0.9 or more. This fiber is obtained by spinning an acrylonitrile-based polymer containing at least 98% by weight or more of acrylonitrile by a wet or dry-wet spinning method, washing with water, and stretching, and then, at 110 to 130 ° C. , A relaxation heat treatment in a humid atmosphere, followed by a relaxation drying treatment to give a total shrinkage of 25 to 40%.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The acrylonitrile-based polymer which is a raw material of the acrylic fiber employed in the present invention is an acrylonitrile homopolymer or a copolymer of 98% by weight or more of acrylonitrile and 2% by weight or less of a vinyl monomer copolymerizable with acrylonitrile, An appropriate polymerization degree obtained by polymerization using a well-known polymerization initiator and a chain transfer agent for adjusting the degree of polymerization is used. Examples of vinyl monomers copolymerizable with acrylonitrile include, for example, C1 to C4 alkyl acrylates and alkyl methacrylates, acrylic acid, methacrylic acid, methacrylonitrile, acrylamide, vinyl bromide, vinyl fluoride, vinyl acetate, vinylidene bromide, Examples thereof include styrene, ethylene, and propylene, but are not particularly limited as long as they can be copolymerized with acrylonitrile, and two or more vinyl monomers can be used in combination. Acrylonitrile is 98
If the amount is less than 10% by weight, the heat resistance required for industrial material use cannot be imparted to the acrylic fiber, and the invention cannot be achieved.

The acrylonitrile-based polymer is dissolved in a solvent for the acrylonitrile-based polymer to prepare a spinning dope.
Such solvents are not particularly limited, for example, dimethyl sulfoxide, dimethylformamide, organic solvents such as dimethylacetamide, nitric acid, rhodan salt,
Inorganic solvents such as zinc chloride can be used. However, in order to achieve a higher degree of suitability for nonwoven fabric processing as the acrylic fiber of the present invention, it is preferable that the cross-sectional shape of the fiber is a circular shape that is less likely to be excessively fibrillated and pulverized when the nonwoven fabric is formed. In terms of making the cross-sectional shape of the acrylic fiber circular, an inorganic solvent is excellent as such a solvent, and among them, a rhodan salt is preferable.

The spinning solution is spun into a coagulation bath by a wet or dry-wet spinning method, and then washed and stretched to obtain a gel yarn. Needless to say, wet spinning is a method in which a spinneret is immersed in a coagulation bath to discharge the yarn.
Dry-wet spinning refers to a spinning method in which a yarn discharged from a spinneret is once introduced into a coagulation bath through a non-coagulating medium, generally an inert gas. The gel yarn thus obtained is an intermediate raw material for the fiber of the present invention, and is a wet swelled body composed of a polymer and a coagulable non-solvent, and possibly a small amount of a residual solvent. The details of the method for producing such a gel yarn are not particularly limited as long as the method is a generally known wet or dry-wet spinning method for producing an acrylic fiber, and the spinning, washing and drawing processes are performed. No, for example, JP-A-60-139809,
JP-A-60-139810, JP-A-61-16701
No. 3, JP-A-62-57910 and the like.

[0015] First, the gel yarn thus obtained is subjected to 110-110.
A relaxation and moisture heat treatment is performed in a humidity and heat atmosphere of 130 ° C., and then a relaxation and drying treatment is performed, so that a total of 25 to 4 is obtained.
Give 0% shrinkage to obtain the inventive acrylic fiber. Here, the total shrinkage of 25 to 40% is the sum of the shrinkage due to the relaxation wet heat treatment and the shrinkage due to the relaxation drying treatment. The length of the gel thread before the relaxation wet heat treatment is X cm, and the fiber after the relaxation drying treatment is When the length is Ycm, (XY) / X × 1
It is a value given by 00.

The method of relaxing heat treatment according to the present invention includes, for example, a method of relaxing the gel yarn of the present invention in a moist heat atmosphere using a carrier or an autoclave. Examples of the medium in a wet heat atmosphere include saturated steam and superheated steam, but are not particularly limited. If the moist heat atmosphere temperature is less than 110 ° C,
Since the gel yarn cannot be given sufficient shrinkage, the acrylic fiber of the present invention is characterized by a knot strength / tensile strength ratio,
And tensile elongation could not be imparted to the fiber.
If the temperature exceeds 0 ° C., the fibers shrink extremely, so that the tensile strength characteristic of the acrylic fibers of the present invention cannot be imparted to the fibers, or partial fusion between the gel yarns occurs. Or In addition, the residence time of the gel yarn in a moist heat atmosphere is preferably 3 to 30 minutes. When the residence time is less than 3 minutes, the contraction between the gel yarns becomes uneven, so that the mechanical properties of the obtained acrylic fiber become non-uniform. Since the contraction of the strip is completely completed, the wet heat environment is wasted and the productivity of the acrylic fiber is reduced.

The relaxation drying treatment method described in the present invention is, for example, a high-temperature, low-humidity atmosphere having a humidity of 40% or less and a temperature of 110 to 160 ° C. in a state where the fibers are relaxed using a tunnel dryer or a drum dryer. A method of performing a drying treatment in a medium may be used, but the method is not particularly limited as long as the total shrinkage of the above-described relaxation and moisture treatment and the contraction in the relaxation and drying treatment is 25 to 40%.

The acrylic fiber obtained as described above has a tensile strength of more than 3 g / d, a tensile elongation of 50% or more, a knot strength / tensile strength ratio of 0.9 or more, that is, sufficient for the production of a nonwoven fabric. Has mechanical properties. Needless to say, the acrylic fiber of the present invention can be mechanically crimped and cut into staples, if necessary, in order to be suitably used for the production of nonwoven fabrics.

The acrylic fiber used in the present invention is 3 g / d
, Tensile elongation of 50% or more, and knot strength / tensile strength ratio of 0.9 or more. 3g tensile strength
If the ratio is not more than / d, the fiber shows brittleness even though the knot strength / tensile strength ratio is high. For this reason, when producing such a nonwoven fabric, the strong shearing force applied to entangle the fibers makes it easy to pulverize the fiber, resulting in a low strength of the nonwoven fabric. It is hard to say that it is. Further, a fiber having a tensile elongation of less than 50% or a knot strength / tensile strength ratio of less than 0.9 has a strong orientation in a fiber axis direction, so that the fiber has a rigid property. Also in this case, when the nonwoven fabric is produced, the fibers are excessively fibrillated by a strong shearing force applied to entangle the fibers to form a felt, which is not suitable for the production of the nonwoven fabric.

[0020]

The following examples are provided to facilitate understanding of the present invention, but are merely illustrative, and the gist of the present invention is not limited thereto.

Example 1 Acrylonitrile was polymerized by an aqueous continuous polymerization method using a redox-based polymerization initiator consisting of ammonium persulfite / sodium pyrosulfite to obtain an acrylonitrile homopolymer having a weight average molecular weight of 150,000. The acrylonitrile homopolymer was dissolved in a 53% by weight aqueous sodium thiocyanate solution to prepare a spinning dope having a pore size of 0.125 mm.
Then, the mixture is coagulated in a coagulation bath composed of a 15% by weight aqueous solution of sodium thiocyanate adjusted to -5 ° C. through a spinneret having a circular hole shape, and then subjected to water washing and 12-fold stretching. Thus, a gel thread comprising the acrylonitrile homopolymer was obtained. The gel yarn was placed in an autoclave and placed in a moist heat atmosphere of saturated steam at 110 ° C. for 15 minutes.
After a relaxing heat treatment for 1 minute, use a tunnel drier for 1 minute.
By performing a relaxation drying treatment in a heating atmosphere at 25 ° C. and a relative humidity of 40% for 15 minutes, a total of 27.5%
Acrylic fiber with shrinkage was obtained. Conditions adopted,
Table 1 shows the evaluation results of the obtained acrylic fibers.
The acrylic fiber of Example 1 has a tensile strength of 3.88 g / d,
The tensile elongation was 51.3%, and the knot strength / tensile strength ratio was 0.93, indicating mechanical properties suitable for forming into a nonwoven fabric.

[0022]

[Table 1]

Example 2 Example 1 was conducted except that a relaxing wet heat treatment was performed for 15 minutes in a moist heat atmosphere of saturated steam at 130 ° C. using an autoclave.
Was carried out in the same manner as in Example 1 to obtain an acrylic fiber having a total shrinkage of 39.5%. Table 1 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. Example 2
Acrylic fiber has a tensile strength of 3.17 g / d, a tensile elongation of 60.5%, and a knot strength / tensile strength ratio of 0.99.
It showed mechanical properties suitable for making into a nonwoven fabric.

Example 3 A weight-average molecular weight obtained by polymerizing 98% by weight of acrylonitrile and 2% by weight of methyl acrylate by a water-based continuous polymerization method using a redox-based polymerization initiator composed of ammonium persulfite / sodium pyrosulfite. Except that 150,000 acrylonitrile-based polymers were used, the same procedure as in Example 1 was carried out to obtain an acrylic fiber having a total shrinkage of 28.0%. Table 1 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. The acrylic fiber of Example 3 has a tensile strength of 3.72 g / d and a tensile elongation of 52.7.
%, And a knot strength / tensile strength ratio of 0.96, indicating mechanical properties suitable for forming a nonwoven fabric.

Example 4 Example 3 was conducted except that a relaxing wet heat treatment was performed for 15 minutes in a moist heat atmosphere of saturated steam at 130 ° C. using an autoclave.
Was carried out in the same manner as in Example 1 to obtain an acrylic fiber having a total shrinkage of 40.0%. Table 1 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. Example 4
Acrylic fiber has a tensile strength of 3.14 g / d, a tensile elongation of 61.5%, and a knot strength / tensile strength ratio of 0.99.
It showed mechanical properties suitable for making into a nonwoven fabric.

Example 5 The same procedure as in Example 2 was carried out except that a spinneret having a hole area of 0.032 mm ² and a hole shape of a bow tie was used as the spinneret. A total shrinkage of 39.0% was obtained. The applied acrylic fiber was obtained. Table 1 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. The acrylic fiber of Example 5 has a tensile strength of 3.10 g / d and a tensile elongation of 6
Although the knot strength / tensile strength ratio was 0.0%, which was a sufficiently acceptable level, the cross-sectional shape was cocoon-shaped, and the fibers became slightly fibrillated when converted into a nonwoven fabric as compared with the acrylic fiber of Example 2. The tendency was easy to see.

COMPARATIVE EXAMPLE 1 Example 1 was conducted except that a relaxing wet heat treatment was performed for 15 minutes in a moist heat atmosphere consisting of saturated steam at 105 ° C. using an autoclave.
Was carried out in the same manner as described above to obtain an acrylic fiber having a total shrinkage of 24.5%. Table 2 shows the adopted conditions and the evaluation results of the obtained acrylic fibers. Although the acrylic fiber of Comparative Example 1 exhibited a tensile strength of 4.03 g / d, the tensile elongation was 34.9% and the knot strength / tensile strength ratio was 0.79, so that the acrylic fiber was excessively excessive when forming into a nonwoven fabric. The result was unsatisfactory because it was easily fibrillated.

[0028]

[Table 2]

COMPARATIVE EXAMPLE 2 Example 1 was repeated except that a relaxing heat treatment was performed for 15 minutes in a moist heat atmosphere of saturated steam at 135 ° C. using an autoclave.
Acrylic fibers with a total shrinkage of 41.0% were obtained. Table 2 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. Comparative Example 2
Acrylic fiber has a tensile elongation of 63.0% and a knot strength / tensile strength ratio of 1.00, but has a tensile strength of 2.92 g / d. The result was not possible.

Comparative Example 3 The gel yarn comprising the acrylonitrile polymer obtained in Example 3 was first heated at 125 ° C. using a tunnel dryer.
After performing a relaxation drying treatment in a heating atmosphere of 40% relative humidity for 15 minutes, and performing a relaxation moisture heat treatment for 15 minutes in a humid atmosphere consisting of saturated steam at 130 ° C. using an autoclave, a total of 24.0% is obtained. A contracted acrylic fiber was obtained. Table 2 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. Although the tensile strength of the acrylic fiber of Comparative Example 3 was 4.77 g / d, the tensile elongation was 31.2% and the ratio of the knot strength / tensile strength was 0.42, so that the acrylic fiber was excessively changed into a nonwoven fabric. The result was unsatisfactory because it was easily fibrillated. Example 1
In comparison with Comparative Example No. 4, it is easily understood how the method for producing acrylic fiber proposed by the present invention gives acrylic fibers having mechanical properties suitable for forming into a nonwoven fabric together with Comparative Examples 4 and 6 described below. .

Comparative Example 4 The gel yarn made of the acrylonitrile homopolymer obtained in Example 1 was subjected to a relaxation drying treatment for 15 minutes in a heating atmosphere at 125 ° C. and a relative humidity of 40% using a tunnel dryer. Thereafter, an acrylic fiber having a shrinkage of 23.5% in total was obtained by performing a relaxation and moisture heat treatment for 15 minutes in a moist heat atmosphere of saturated steam at 130 ° C. using an autoclave. Table 2 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. Although the acrylic fiber of Comparative Example 4 exhibited a tensile strength of 4.85 g / d, the tensile elongation was 30.2% and the ratio of the knot strength / tensile strength was 0.39, so that the acrylic fiber was excessively excessive when forming into a nonwoven fabric. The result was unsatisfactory because it was easily fibrillated.

Comparative Example 5 A weight-average molecular weight obtained by polymerizing 95% by weight of acrylonitrile and 5% by weight of methyl acrylate by a water-based continuous polymerization method using a redox-based polymerization initiator composed of ammonium persulfite / sodium pyrosulfite. Except that 150,000 acrylonitrile-based polymers were used, the same procedure as in Example 3 was carried out to obtain acrylic fibers having a total shrinkage of 33.0%. Table 2 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. The acrylic fiber of Comparative Example 5 uses an acrylonitrile-based polymer having an acrylonitrile content of 95% by weight, so that the heat resistance is not sufficient, and the fibers are partially fused to each other during the relaxation heat treatment. It was not a fiber that could be used for forming a nonwoven fabric.

Comparative Example 6 The gel yarn obtained in Example 5 was subjected to a relaxation drying treatment in a heating atmosphere at 125 ° C. and a relative humidity of 40% for 15 minutes using a tunnel drier, and then to an autoclave for 13 minutes.
An acrylic fiber having a total shrinkage of 24.0% was obtained by performing a relaxation and moisture heat treatment for 15 minutes in a moist heat atmosphere of saturated steam of 0 ° C. Table 2 also shows the adopted conditions and the evaluation results of the obtained acrylic fibers. The acrylic fiber of Comparative Example 6 has a tensile strength of 3.72 g.
/ D and the cross-sectional shape is cocoon-shaped, the knot strength / tensile strength ratio was 0.92, but the tensile elongation was 30.8.
%, Resulting in unsatisfactory results due to excessive fibrillation during the formation of a nonwoven fabric.

[0034]

As described above, the present invention comprises an acrylonitrile-based polymer containing at least 98% by weight of acrylonitrile, and has mechanical properties suitable for forming a nonwoven fabric, that is, a tensile strength exceeding 3 g / d and a 50% strength. The fact that the acrylic fiber having the above tensile elongation and the knot strength / tensile strength ratio of 0.9 or more, and the method for producing the same are a remarkable effect, and have great industrial significance.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4L031 AA17 AB01 AB34 CA07 CA08 DA17 4L035 BB02 BB04 BB66 CC05 CC07 EE08 EE20 FF05 MB00 4L036 MA04 MA24 MA33 PA01 PA03 PA10 PA19 RA03 UA21 4L047 AA17 AB02 AB10 BA05 CC05 CB01

Claims (2)

[Claims] 1. An acrylonitrile comprising at least 98% by weight
Consisting of the acrylonitrile-based polymer contained above, 3 g
/ D, tensile elongation of 50% or more, 0.9
An acrylic fiber having the above knot strength / tensile strength ratio. 2. At least 98% by weight of acrylonitrile
The acrylonitrile polymer containing above is spun by a wet or dry-wet spinning method, washed with water, and subjected to a stretching treatment.
2. The method for producing acrylic fiber according to claim 1, wherein a relaxation heat treatment is first performed in a moist heat atmosphere at 110 to 130 [deg.] C., and then a relaxation drying treatment is performed to give a total shrinkage of 25 to 40%.