JPH05140337A - Polyimide fiber for matrix resin for molding - Google Patents

Abstract

PURPOSE:To provide the subject fiber containing a specific amount of a specific recurring unit, having a specific shape, exhibiting excellent wettability to reinforcing fiber in melt molding and giving a composite material having excellent mechanical properties, heat-resistance, etc. CONSTITUTION:The objective fiber contains >=85mol% of the recurring unit of formula and has a melt viscosity(MV) of <=7,000 poise at 400 deg.C and a shearing rate of 100 sec<-1>, a shearing elongation (EL) of 50-120% and a crystallinity (Xp) of <=20%. The fiber can be produced by reacting a diamine with a tetracarboxylic acid dianhydride and dehydrating and cyclizing the obtained polyamic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyimide fiber for a molded base material resin, which is suitable for producing a composite in which reinforcing fibers are embedded in a base material resin.

[0002]

2. Description of the Related Art Polyether ether ketone (PEE)
K), polyetherimide (PEI), polyphenylene sulfide (PPS), or other heat-resistant thermoplastic resin is used as the matrix resin of the fiber-reinforced composite.
Compared to those that use a thermosetting resin such as epoxy resin for the matrix, it has excellent heat resistance, moisture resistance and flame retardancy, at the same time can shorten the molding cycle, and has excellent long-term storage stability of the base material resin. It has features. However, on the other hand, the melt viscosity is large and the wettability to the reinforcing fiber and the fiber impregnation property are poor, and the tackiness and the drape property of the prepreg impregnated with the resin are also poor,
There is a problem that the molding temperature and the molding pressure must be increased.

In order to solve such problems, in particular, in order to improve the fiber impregnation property, a method has been proposed in which the above-mentioned thermoplastic resin is made into a fiber and mixed with a reinforcing fiber to be used. For example, a method of wrapping the reinforcing fiber tow with a thermoplastic fiber, a method of aligning or alternately weaving the reinforcing fiber and the thermoplastic fiber, and the like have been proposed, but both are impregnated with the thermoplastic resin at the time of molding (wetness). Sex) is still insufficient. In order to further improve this point, a method of mixing and weaving thermoplastic fibers and reinforcing fibers with a fluid or the like (for example, combed yarn) has been proposed (JP-A-60-209033, JP-A-60-209034).
(See the official gazette). The molded product obtained by such a method is excellent in impregnation property and uniform dispersibility of the base material resin, so that the reinforcing effect of the reinforcing fiber is improved. In recent years, in order to further improve the reinforcing effect of the reinforcing fibers, a technique of mixing the thermoplastic fibers and the reinforcing fibers in a non-twisted or non-glued state, or a technique of mixing the reinforcing fibers without causing crimps has been proposed. There is. In addition, as a method for inexpensively obtaining a composite, a method has been proposed in which a cloth made of thermoplastic fibers and a cloth made of reinforcing fibers are alternately laminated and thermoformed.

Conventionally, PEEK, PEI and PP have been used as the thermoplastic fibers used for the base resin of the molded product.
Fibers made of S or the like have been proposed, but in recent years, particularly in the fields of aviation, space, etc., there has been a demand for fibers for base material resins that have even higher heat resistance. In order to answer such requests, in recent years,
Various methods of using polyimide, which is said to have the highest heat resistance among organic polymers, as the fiber for the base resin have been studied, but conventional polyimide fibers are difficult to melt-spin or are substantially infusible. Therefore, there is a problem in that a good complex cannot be obtained because of its excellent properties.

On the other hand, a melt-moldable polyimide resin has been recently proposed, and a fiber obtained by melt-spinning and stretching such a resin is
It has been disclosed that it has a high strength and a high elastic modulus (Japanese Patent Laid-Open No. 63-213319 and Japanese Patent Laid-Open No. 23491/1991).
No. 1, JP-A-3-10344). However, since these fibers have characteristics such as high strength and high elastic modulus, when they are used as fibers for molded product base material resin, the resulting molded product is apt to warp or distort, and at the time of molding process. Even if the polyimide fiber was melted, it was difficult to penetrate between the reinforcing fibers, and therefore sufficient adhesion between the reinforcing fiber and the matrix fiber could not be obtained, and there was a problem that a composite having a good reinforcing effect could not be obtained. ..

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the above-mentioned prior art, allows the amount of deformation at the time of producing a molded product to be arbitrarily changed, and provides a reinforcing fiber at the time of melt molding. It is an object of the present invention to provide a novel polyimide fiber for a base material resin for a molded product, which is capable of obtaining a composite having good wettability, excellent mechanical properties, and good heat resistance.

[0007]

Means for Solving the Problems As a result of intensive investigations by the present inventors in order to achieve the above-mentioned object, PEEK, which has been variously studied in recent years as having excellent heat resistance, and polyether having a melting point higher than that of PEEK have been investigated. Aromatic polyethers represented by ketones (PEK) can be stably formed into fibers without thermal decomposition even at a high temperature of 350 ° C. or higher, but their glass transition points are 145 ° C. and 165 ° C., and the heat-resistant temperature is 220 ° C.
While it cannot be used in the aerospace field where the above requirements are required, a specific polyimide resin can be stably spun even at a high temperature of about 410 ° C, and the obtained fiber has good wettability with the reinforcing fiber, and The inventors have found that the glass transition point is 240 ° C. or higher and the heat resistance is extremely excellent, and that the polyimide fiber is also easy to handle, and thus arrived at the present invention.

That is, according to the present invention, 85 mol% or more of the repeating units are the following units,

[0009]

[Chemical 2] Melt viscosity at a temperature of 400 ° C and a shear rate of 100 sec ^-1 (M
V) a fiber made of a thermoplastic polyimide having a poise of 7,000 poise or less, and an elongation at break (EL) of 50 to 120.
%, And the crystallinity (Xρ) is 20% or less, a polyimide fiber for molded product base material resin is provided.

Each requirement and its function and effect constituting the present invention will be described in detail below. The polyimide referred to in the present invention is obtained by further subjecting a polyamic acid obtained by reacting a diamine and a tetracarboxylic acid dianhydride to a cyclodehydration and containing 85 mol% or more of the following repeating units. However,

[0011]

[Chemical 3]

Even a polyimide obtained by copolymerizing a third component within the range not impairing the object of the present invention, is a compound in which the polymer terminal is blocked with a dicarboxylic acid anhydride for the purpose of improving thermal stability. Good.

The polyimide may contain additives such as a stabilizer, a plasticizer, a matting agent, a lubricant and a flame retardant within the range not impairing the object of the present invention.

Next, the polyimide has a temperature of 400.
Melt viscosity (MV) at a shear rate of 100 sec ^-1 at 7 ℃
It must be 000 poise or less. When the melt viscosity is more than 7,000 poises, not only the spinning property in obtaining the fiber of the present invention is lowered, but also the productivity is poor, and it becomes difficult to obtain a fiber having a small single fiber fineness, and moreover, it is combined with the reinforcing fiber. The wettability (with the reinforcing fiber) at that time is also lowered, and a composite having good mechanical properties cannot be obtained, which is not preferable.

Further, the polyimide fiber of the present invention has a breaking elongation (EL) of 50 to 120% and a crystallinity (Xρ) of 20.
It is important to be less than%. If the EL is less than 50%, the polyimide molecular chains are highly oriented in the fiber axis direction, so the fiber strength increases and the handleability improves, but heat melting to form the base resin of the molded product. During the treatment, the fibers shrink, resulting in voids between the reinforcing fibers, and warping or distortion of the molded product, which is not preferable. On the other hand, when EL exceeds 120%, the degree of orientation is small and shrinkage during processing into a molded product is small, but
The detailed reason is unknown, but when carbon fiber or ceramic fiber is used as the reinforcing fiber, the orientation of the base material resin on the surface of the reinforcing fiber is when the orientation in the fiber state partially remains. The crystal easily grows with the surface of the reinforced fiber as a nucleus, whereas when EL exceeds 120%, the crystal growth becomes small and the adhesive strength becomes small, which is not preferable.

Even if EL is within the above range, the crystallinity Xρ must be 20% or less. If it exceeds 20%, the flowability and wettability at the time of composite heating and melting with the reinforcing fibers to produce a composite are deteriorated and voids are generated between the reinforcing fibers, which is not preferable.

To produce the above-described polyimide fiber of the present invention, for example, the melt spinning / drawing method described below may be employed. That is, the above-mentioned thermoplastic polyimide is melted at a melting temperature of 400 to 430 ° C. and extruded from the spinneret. If the melting temperature is less than 400 ° C, melting is insufficient and stable spinning becomes difficult, while if it exceeds 430 ° C, gelation of the polymer tends to occur, which is not desirable.

Next, it is desirable to set the temperature of the spinneret in the range of 395 to 425 ° C. If the temperature is lower than 395 ° C., the discharged polymer is not sufficiently thinned and stretched frequently, resulting in frequent yarn breakage. On the other hand, when the temperature exceeds 425 ° C., foreign matter adheres to the surface of the spinneret and gel is easily generated in the polymer, and stable spinning cannot be performed for a long time. The spinneret temperature can be easily controlled by controlling the temperature around the spin pack and the ambient temperature immediately below the spinneret.

Next, the discharged yarn is provided at a position just below the surface of the spinneret and has a length of 10 cm or more and an ambient temperature of 250 to 4
After passing through a heating spinning tube adjusted to 00 ° C, it is cooled and wound up. If the yarn is not passed through the heating spinning cylinder, the discharged yarn is cooled and solidified too quickly to wind up a sufficiently thin yarn at a high speed. Therefore, it becomes difficult to obtain a fine monofilament fineness that is preferably used for a molded product matrix resin, which is not preferable.

The shape of the heating cylinder is preferably cylindrical in order to keep the atmospheric temperature in the cylinder as uniform as possible, and the length is 10 cm or more, preferably 20 to 100 cm. If the length is less than 10 cm, the discharged yarn is cooled rapidly and the yarn is easily broken, while if it exceeds 100 cm, it is disadvantageous in terms of handleability and workability in spinning and has an effect. It is not preferable because it is almost saturated.

Even if a heating cylinder is provided, if the atmosphere temperature under the spinneret near the spinneret in the cylinder is less than 250 ° C., the spinneret temperature will be less than 395 ° C. If the polyimide fiber is cooled rapidly, the number of yarn breakages increases, making it impossible to stably collect the polyimide fiber. On the other hand, when the ambient temperature exceeds 400 ° C, the spinneret temperature exceeds 425 ° C, the discharged yarn is not cooled appropriately, and the temperature rises in the middle, so that the temperature is stable for a long time. As a result, the polyimide fiber cannot be collected.

Next, it is drawn at a speed of 100 to 2000 m / min, preferably 500 to 1500 / min, and further stretched if necessary. A generally known method can be applied to the stretching, for example, a hot roller, a plate heater, a hot water bath,
A heating means such as a steam chamber can be used. The stretching ratio is preferably 2 times or less, and the stretching temperature is also preferably 300 ° C. or less, so that the breaking elongation is 50 to 1
A polyimide fiber having a crystallinity of 20% or less and 20% or less can be easily obtained. The stretching temperature is usually the glass transition point (T
g) higher temperature, that is, it is generally carried out at 250 ° C. or higher in the thermoplastic polyimide targeted by the present invention, and may be selected from the range of 250 to 300 ° C.,
In the present invention, sufficient stretching is possible even in hot water at 90 to 98 ° C or in steam.

In the spinning process and the drawing process, it is preferable not to use an oil agent other than water, a sizing agent, etc. in the yarn. Oils and sizing agents not only prevent the fibers from melting and entering between the reinforcing fibers, hinder the adhesion between the base resin and the reinforcing fibers, and reduce the performance of the base resin, but also molding It is likely to be thermally decomposed at a temperature to generate a gas, which causes a void or a defect in the molded product and causes a dent on the surface.
The thermoplastic polyimide fiber of the present invention has a molding temperature of 400
Since the temperature is up to 400 ° C., an oil agent or a sizing agent that does not cause thermal decomposition at such a temperature and does not hinder the adhesion is not actually required. However, when a fabric such as a woven or knitted fabric is made of polyimide fibers alone, an oil agent or a sizing agent may be used for the purpose of improving handleability, and the fabric may be removed in the scouring step. In that case, it is necessary to select a material that can be easily removed. Usually, in a spinning process or a drawing process, a small amount of anion activator such as potassium oleyl phosphate as an antistatic agent is added to a polyether-based oil agent having a molecular weight of about 1000 to 2000, which is a copolymer of propylene oxide and ethylene oxide. Is used as an oiling agent, and if such an oiling agent is washed with an ordinary solvent or detergent, then the solvent or detergent is removed with warm water, and then dehydration and drying are sufficiently performed by a scouring step. It can be removed. Also, if the sizing agent is one that is usually used, it can be removed in the scouring step as well.

The polyimide fiber of the present invention obtained by spinning or further drawing as described above has a single fiber denier of 1 to 4 when used as a multifilament.
The total yarn denier may be appropriately set to the total yarn denier of the reinforcing fiber by setting it to 0 de, preferably 1 to 5 de. If the single fiber denier is less than 1 de,
In the spinning drawing or the subsequent steps, fluff and single fiber breakage are likely to occur, and air bubbles may be lost during molding and melting. If it exceeds 40 de, the drape property of a fabric is deteriorated, it is difficult to obtain a uniform mixed yarn when a mixed yarn of reinforcing fibers is obtained, and the base material resin penetrates between the reinforcing fibers during molding and melting. It becomes difficult to do.
Regarding the total yarn denier, the volume fraction of the reinforcing fibers in the molded product, that is, the ratio of the volume of the reinforcing fibers (value of weight divided by density) to the volume of the molded product (value of weight divided by density) is 40 to Since the range of 70% is preferable, it may be appropriately set according to the total denier of yarns of the reinforcing fibers used together so that this volume fraction can be easily obtained.

[0025]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In addition, each physical property in an Example is measured by the following method.

1. Melt Viscosity (MV) Using a high-performance flow tester manufactured by Shimadzu Corporation, sample 5 g,
Nozzle size 0.5mmφ × 4mm, drum rotation speed 1rp
m, a load of 10 to 100 kg, and a temperature of 400 ° C. were measured, and the melt viscosity (MV) was calculated. Then, using a logarithmic log graph, the relationship between the viscosity (MV) and the shear rate was graphed, and the melt viscosity at a shear rate of 100 sec ⁻¹ was read.

2. Tensile test "Tensilon" RTM-100 manufactured by Orientec Co., Ltd.
Using a die tensile tester, test length 20 at room temperature 25 ° C and humidity 60%
cm, and the pulling speed was 200 mm / min.

3. Crystallinity (Xρ) The density of the fiber at 25 ° C was measured with a density gradient tube prepared by using n-heptane as the light liquid and carbon tetrachloride as the heavy liquid, and calculated by the following formula.

Xρ = (ρ−ρa) ρc / {ρc−ρ) · ρ} ρ: Density of sample ρc: Density of crystalline part (1.420 g / cm ³ ) ρa: Density of amorphous part (1.330 g) / Cm ³ )

4. Bending strength It was measured by a method according to JIS K6911.

Polyimide (NEW manufactured by Mitsui Toatsu Chemicals, Inc.)
-TPI) chips were dried in a hot air dryer at 250 ° C for 15 hours. Using this chip, it was melted at 420 ° C. and the pore size was 0.1
22 from a spinneret with a discharge hole of 4 holes at 4 mm
It was extruded at a discharge rate of g / min and wound at a speed of 1000 m / min to obtain a multifilament of 200 de / 24 fil. However, in Examples 8 and 9 and Comparative Examples 8 and 9, the denier after stretching was 200 because the stretching was further performed.
Spinning was carried out by changing the discharge amount so that it became de / 24 fil. Table 1 shows the melt viscosity (MV) of the polymer, the spinneret temperature, the length of the heating cylinder and the ambient temperature and the spinning condition at that time, the drawing conditions, the breaking elongation of the obtained fiber, the crystallinity, and the fiber. The three-point bending strength of a molded product using as a base material resin is shown.

Molding is carried out by weaving a polyimide fiber obtained by spinning or further drawing into a plain woven fabric, alternately laminating 10 sheets of this woven fabric and 9 sheets of Toray carbon fiber trading card T-300 plain woven fabric, and then compressing. 25kg / cm2 by heat molding machine
After pressing for 15 minutes at room temperature from the room temperature to 430 ° C. and holding at the temperature of 430 ° C. for 20 minutes,
Cooled to 150 ° C. in 20 minutes. During this time, the pressure is 25k
It was kept at g / cm ² . The obtained flat plate shaped product is JIS
Three-point bending strength was determined by the measuring method of K6911.

The spinning condition was 0 when the number of yarn breakages was 0 during continuous operation for 2 hours, Δ was 1 to 2 times, and 3 was more than 3 times.

As is clear from Table 1, in Examples 1 to 10 in which the thermoplastic polyimide fiber according to the present invention was used as the matrix resin, high flexural strength was exhibited, while high elongation at break and high degree of orientation were observed. In Comparative Example 7 which is low, only low bending strength is obtained, and conversely, Comparative Example 8 in which the elongation at break is low and
It can be seen that in Comparative Example 9 having a high degree of crystallinity, the resin does not sufficiently penetrate between the carbon fibers, voids are observed, and only a resin having a low bending strength is obtained.

[0035]

[Table 1]

[0036]

EFFECT OF THE INVENTION The thermoplastic polyimide fiber of the present invention can be mixed with carbon fiber or ceramic fiber used as a reinforcing fiber, or can be used alone as a woven or knitted fabric, or can be woven with a reinforcing fiber to form a woven fabric, Molded product that is suitable for use as a thermoplastic fiber for molded product matrix resin, has excellent strength and good heat resistance (composite product) ) Can be obtained. In addition, compared with conventional molded products that are combined with thermosetting resins, the properties of thermoplastic polyimide have been utilized to make them flame-retardant, low moisture absorption, mechanical properties (bending strength, compression strength) and fatigue resistance. It also has the feature of being excellent.

Therefore, it can be used as a primary structural material in the fields of space and aviation by taking advantage of these characteristics, and can also be suitably used as an interior material for aircraft etc. by taking advantage of the characteristics of flameproofness and flame retardancy. ..

Claims (1)

[Claims] 1. The following units account for 85 mol% or more of repeating units: Melt viscosity at a temperature of 400 ° C and a shear rate of 100 sec ^-1 (M
V) a fiber made of a thermoplastic polyimide having a poise of 7,000 poise or less, and an elongation at break (EL) of 50 to 120.
%, And the crystallinity (Xρ) is 20% or less, a polyimide fiber for molded product base material resin.