JP2002249927A - Polyimide fiber for short fiber nonwoven fabric and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyimide fiber having excellent heat, chemical and radiation resistances and flame retardance and a small fiber diameter and suitable for uses of short fiber nonwoven fabrics and to provide a method for producing the polyimide fiber by which the fiber can stably be produced for a long period. SOLUTION: This polyimide fiber for the short fiber nonwoven fabrics has <=30 μm fiber diameter and >=1.8 cN/dtex strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to heat resistance, flame retardancy,
The present invention relates to a polyimide fiber excellent in chemical resistance and radiation resistance, and relates to a polyimide fiber suitable for short fiber nonwoven fabric which can be used for industrial materials and a method for producing the same.

[0002]

2. Description of the Related Art Polyimide is called a super engineering plastic because of its excellent heat resistance, flame retardancy, chemical resistance, radiation resistance and the like. Polyimide, which is generally known, is a thermosetting resin and is used for varnishes and the like. However, among polyimides, there is a resin exhibiting thermoplasticity, and fiberization thereof is being studied. The fiber can be used in the field of industrial materials, and is not only used as a long fiber, but also as a short fiber non-woven fabric, mixed with other materials or other materials and heat-formed to produce a high-performance composite material. Have been.

[0003] As a method of forming a polyimide fiber, there is a method of spinning by dissolving or dispersing in a solvent or a plasticizer. However, this method requires cost for dissolving, removing the solvent and recovering the solvent, and is practically cost-effective from an industrial viewpoint. Was not the target.

[0004] In some cases, melt spinning using a thermoplastic polyimide as a raw material cannot be produced because of its high melting point, high melt viscosity, and easy occurrence of melt fracture. As a countermeasure, for example, JP-A-6-33316 discloses a method of performing stable spinning by limiting spinning conditions of thermoplastic polyimide. However,
The polymer melt viscosity range in which stable spinning is possible by this method is limited to 700 Pas or less, and it is difficult to produce a polyimide fiber made of a high molecular weight polyimide as a raw material, particularly a polyimide fiber having a fineness. there were.

Therefore, the present inventor has proposed a method for producing a polyimide fiber in Japanese Patent Application Laid-Open No. 2000-129535. Thereby, it has become possible to stably produce a high-strength polyimide fiber having excellent yarn properties. Also, Japanese Patent Application No. 11-3
No. 26957 proposes a polyimide fiber for a binder. Thereby, it became possible to obtain a polyimide fiber having a small fiber diameter. However, there has been a demand for a polyimide fiber having a small fiber diameter, which has improved yarn properties and quality and is suitable for short-fiber nonwoven fabrics, and a method for producing the same.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and has excellent heat resistance, flame retardancy, chemical resistance and radiation resistance, a small fiber diameter, high strength, An object of the present invention is to provide a polyimide fiber suitable for short fiber nonwoven fabric applications and a production method capable of producing this fiber stably for a long time.

[0007]

Means for Solving the Problems The present inventors have studied to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the present invention provides the following (1) and (2). (1) Polyimide fiber for short-fiber nonwoven fabric having a fiber diameter of 30 μm or less and a strength of 1.8 cN / dtex or more. (2) In producing the polyimide fiber described in (1), after drying the raw material polymer at 150 to 220 ° C, (Tg-180)
Preheat at ~ (Tg-60) ° C and 5 ~ 3 at 370 ~ 415 ° C
A method for producing a polyimide fiber, comprising melting for 0 minutes, extruding from a nozzle hole, and winding. Here, Tg is a glass transition temperature.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polyimide fiber of the present invention must have a fiber diameter of 30 μm or less.
It is preferable that it is not more than μm. When the fiber diameter is 30 μm or less, when used as a material for short-fiber nonwoven fabric, the number of constituent fibers per unit area can be increased,
The basis weight of the nonwoven fabric becomes uniform. By using a nonwoven fabric having a uniform basis weight, it is possible to sufficiently exhibit the performance of the polyimide fiber in applications to be used thereafter.

[0009] The polyimide fiber of the present invention has a strength of 1.8 cN / dtex or more, and more preferably 2.0 cN / dtex or more. By making it 1.8 cN / dtex or more, when the polyimide fiber is cut or dispersed, the workability is improved and the handleability is improved and the non-woven fabric suitable for industrial materials is obtained. Can be.

The polyimide (raw material) in the present invention may contain a copolymer, a blend, or an inorganic additive, but is required to be a polyimide exhibiting thermoplasticity. By showing thermoplasticity, melt spinning becomes possible,
There are industrial advantages in terms of cost.

It is preferable that the polyimide is crystalline. For example, a polyimide formed from a tetracarboxylic acid or a derivative thereof and a diamine or a derivative thereof may be mentioned. Among them, a polyimide having a repeating unit represented by the following general formula (1) is preferable.

[0012]

Embedded image

Further, a polyimide represented by the general formula (1) having a Tg of 230 ° C. or higher and a melting point of 400 ° C. or lower is more preferable. Examples of the polyimide represented by the general formula (1) include those marketed by Mitsui Chemicals, Inc. under the trademark “AURUM”. This polymer has a melting point
Since the temperature is 400 ° C. or lower, melt spinning is possible, and since the polymer is crystalline, its mechanical properties are excellent. Further, since the Tg is high, the dimensional stability at a high temperature is excellent, so that it is a suitable material for short fiber nonwoven fabric fibers used as an industrial material.

Next, the method for producing the polyimide fiber of the present invention will be described. First, it is necessary to dry the raw material polymer at 150 to 220 ° C. The raw material polymer may be in the form of a chip or a powder. The main purpose of drying is to reduce the amount of water and unreacted substances contained in the polymer, and it is preferable that the moisture content is reduced to 50 ppm or less by drying.

Water, unreacted substances and the like contained in the polymer have an adverse effect on the polymer during the spinning process, such as deterioration of the polymer and generation of voids in the fiber. In particular, since the spinning temperature is extremely high in the melt spinning of polyimide, the influence of a very small amount of water and the presence of unreacted substances becomes remarkable. Therefore, drying at 150 ° C. to 220 ° C. is required, and if the temperature is lower than 150 ° C., the effect is not exhibited, and the spinning property is deteriorated due to foaming and generation of voids during melt spinning. Even if the drying time is long,
If the temperature is lower than 0 ° C., the effect is not exhibited. Meanwhile, 220 ° C
Exceeding the limit causes problems such as polymer deterioration and fusion between polymer solids in the drying step.

Further, even if the temperature is lower than 220 ° C., the treatment at a temperature higher than Tg may cause problems such as polymer deterioration and fusion between polymer solids, so that (Tg−15) ° C.
Preferably, the temperature is as follows.

Although the drying method is not particularly limited,
A tumbler type, a shelf type type, a hopper dryer type under a nitrogen flow, or a vacuum drying method performed under reduced pressure may be used. The drying time is preferably 4 to 24 hours. If the time is less than 4 hours, the inside of the chip will be insufficiently dried. If the time exceeds 24 hours, no improvement in the effect will be recognized, and at the same time, the cost will increase, which is not preferable.

The raw material polymer after drying is then (Tg-
(180) ~ (Tg-60) Pre-heating at ℃. The purpose of preheating the raw material polymer in this temperature range is that since polyimide has a high melting point, it is difficult to rapidly heat and melt it from a low temperature, and even if it can be formed, it induces melting spots at the time of melting. If the polymer is further melted at a high temperature for the purpose of suppressing the melting spots, the polymer is deteriorated, which causes problems such as deterioration of the spinning property. Therefore, (Tg-180) to (Tg
When preheating is performed in the temperature range of −60) ° C., the heating is sufficiently performed to the inside of the polymer solid, so that it is possible to reduce problems such as poor biting at the time of melting and mixing of bubbles into the molten polymer, It is possible to obtain a high-quality fiber with good spinnability.

If the preheating temperature is lower than (Tg-180) ° C., the effect becomes insufficient, while if it exceeds (Tg-60) ° C., handling becomes difficult. Examples of the preheating method include a method of heating using a drier or the like in a vacuum under a nitrogen atmosphere under the influence of moisture and oxygen under a nitrogen atmosphere, a method of heating in a hopper of a spinning machine, and the like. The heating time is not particularly limited, and may be a time in which the inside is uniformly heated in any of the methods.

Next, the raw material polymer is heated at a temperature of 370 to 415 ° C.
Perform melting for 5-30 minutes. In other words, to melt the polyimide and extrude it from the spinneret,
Melt at 370-415 ° C. If the melting temperature is lower than 370 ° C., the melt viscosity of the molten polymer is high, the polymer is insufficiently melted, the distribution of the molten polymer stream in the spinneret becomes extremely poor, and stable spinning becomes extremely difficult. On the other hand, if the melting temperature exceeds 415 ° C., decomposition of the polymer and the low-molecular-weight substances contained therein will occur, voids will be generated in the filament, and stable spinning will be difficult.

The melting time of the polymer is 5 to 30 minutes, more preferably 10 to 20 minutes. If the residence time is less than 5 minutes, the heat treatment time is insufficient and the temperature of the polymer is hard to be uniform, and the melt viscosity is uneven, so that it is difficult to stably produce fine fibers. On the other hand, when the time exceeds 30 minutes, thermal degradation of the polymer is caused, and stable spinning becomes difficult.

The polymer melted as described above is extruded from a spinneret and spun. The spun yarn is cooled and solidified and then bundled. At this time, it is preferable to apply an oil agent to the polyimide fiber when the yarn is cooled and solidified. After that, it is taken up and wound up.

At this time, the polyimide fiber discharged from the spinneret is preferably wound at a speed of 100 to 2000 m / min, more preferably 200 to 1500 m / min. Winding speed is 100
If it is less than m / min, not only the productivity is low, but also the fiber diameter of the yarn may be non-uniform. On the other hand, the winding speed is 20
If it exceeds 00 m / min, the morphological change of the filament at the time of take-up becomes large, and yarn breakage is easily induced.

The polyimide fiber of the present invention has a fiber diameter of 30 μm.
Hereinafter, in order to make the strength 1.8 cN / dtex or more, it is preferable to perform a 1.2- to 5.0-fold stretching treatment on the drawn yarn. The stretching treatment may be performed in a separate step for the yarn once wound, or may be performed immediately after winding without directly winding the yarn.

If the draw ratio is less than 1.2 times, uneven drawing may occur, and it is difficult to obtain a filament having a uniform fiber diameter. It tends to cause breakage, making it impossible to obtain the desired polyimide fiber.

The stretching is preferably performed by hot stretching, preferably by using a non-contact heat treatment heater (slit heater or hot air heater) at a temperature of 180 to 350 ° C.

The polyimide fiber for short-fiber nonwoven fabric of the present invention has properties such as flame retardancy, heat resistance, and chemical resistance inherent in the polyimide fiber, and has a fineness and high strength. The nonwoven fabric can be suitably used for industrial materials, particularly as a substrate for printed circuit boards and the like.

[0028]

Next, the present invention will be described in detail with reference to examples. In addition, evaluation and evaluation of each physical property in an Example are performed by the following methods. a) Strength Using a Shimadzu Autograph DSS-500, sample length 3
The measurement was performed under the conditions of 0 cm, a grip interval of 5 cm, and a tensile speed of 30 cm / min. b) Yarn-making performance Continuous spinning is performed for 24 hours, during which the following two stages are evaluated according to the conditions such as yarn breakage and single yarn winding on a roller. The case where cutting or the like occurred and the yarn-forming property was poor was indicated by x. c) Evaluation of adaptability as a fiber for short-fiber nonwoven fabric The filament was cut into a length of 5 mm, dispersed in water, and then subjected to papermaking to obtain a sheet. At this time, the basis weight of the sheet was 55 g / m ² . This sheet was press-formed at a temperature of 300 ° C. The surface of the obtained sample was observed with a microscope, the state of dispersion of the fibers was visually judged, and those that were uniformly dispersed were indicated by と し て as good dispersibility, and those that were non-uniform were rated X. d) Handling properties When the obtained fiber is rolled up, cut and processed, it causes filament breakage or thread breakage, etc.で indicates.

Example 1 Thermoplastic polyimide (AURUM450 Tg = 250 manufactured by Mitsui Chemicals, Inc.)
° C) as a raw material. At this time, the raw material polymer was in the form of chips and was first subjected to a drying step. A vacuum drying method was employed, and the drying time was 6 hours. next,
The polymer was preheated at 80 ° C. for 1 hour in a heater under a nitrogen atmosphere. The preheated polymer is melted at a melting temperature of 395 ° C. for 10 minutes using an extruder-type spinning machine, and the molten polymer is extruded quantitatively from a spinneret having 96 nozzle holes having a diameter of 0.3 mm, at a speed of 500 m / min. speed)
Rolled up. When the filament has cooled and solidified,
An oil agent was applied. Thereafter, the yarn was passed through a slit heater heated to 300 ° C. and subjected to a 2.5-fold heat drawing treatment to obtain a multifilament.

Examples 2 to 5, Comparative Examples 1 to 5 Except that the drying temperature, preheating temperature, melting temperature, and melting time were changed to the values shown in Table 1 (Example 5, Comparative Examples 1, 6 Was changed in the same manner as in Example 1 to obtain a multifilament.

Example 6 A multifilament was obtained in the same manner as in Example 1, except that the take-up speed was changed to 1000 m / min.

Comparative Example 6 A multifilament was obtained in the same manner as in Example 1 except that the stretching ratio was changed to 1.2 times.

Table 1 shows the thread properties and various evaluation results of the multifilaments obtained in Examples 1 to 6 and Comparative Examples 1 to 6.
Shown in

[0034]

[Table 1]

As is evident from Table 1, the fibers obtained in Examples 1 to 6 were fine and high-strength, had excellent yarn-making properties, and were suitable for short-fiber nonwoven fabrics. .
On the other hand, Comparative Example 1 was unsuitable as a short-fiber nonwoven fabric because the fibers had a large discharge amount and a large fiber diameter. In Comparative Example 2, the drying temperature was too low, in Comparative Example 3, the preheating temperature was too low, in Comparative Example 4, the melting temperature was too high, and in Comparative Example 5, the melting time was too long. Bad, no fiber could be obtained. In Comparative Example 6, since the draw ratio was low, the fiber had low strength, the handling property was poor, and a nonwoven fabric could not be obtained.

[0036]

The fiber of the present invention is excellent in heat resistance, flame retardancy, chemical resistance and radiation resistance, and has a small fiber diameter and high strength. It can be suitably used as a substrate for a fiber-reinforced composite such as for a printed circuit board. Further, according to the production method of the present invention, the fiber of the present invention can be stably produced for a long time.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Terumi Murata 23 Uji Kozakura, Uji-city, Kyoto Unitika, Central Research Laboratory, F-term (reference) 4J043 PA02 QB31 RA35 SA06 TA14 UA151 UB131 VA021 YA28 ZA12 ZA13 ZA14 ZA17 ZB04 4L035 AA02 BB32 BB76 BB91 DD19 EE01 FF01 FF05 MD02 4L047 AA24 AB02 AB08 AB10 CB05 CB10

Claims (3)

[Claims] 1. The fiber diameter is 30 μm or less, and the strength is 1.8 cN /
Polyimide fiber for short fiber non-woven fabric which is dtex or more. 2. The polyimide fiber for short-fiber nonwoven fabric according to claim 1, which is a polyimide having a repeating unit represented by the following general formula (1). Embedded image 3. In producing the polyimide fiber according to claim 1 or 2, the raw material polymer is dried at 150 to 220 ° C., and is preheated at (Tg−180) to (Tg−60) ° C.
A method for producing a polyimide fiber, comprising melting at a temperature of 5 ° C. for 5 to 30 minutes, extruding from a nozzle hole, and winding.