JP2003064540A - Composite yarn for forming composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a yarn for producing a base cloth suitable for a reinforcing material of a composite material-forming material or utilizable as the reinforcing fiber by itself in the composite material-forming material. SOLUTION: This composite yarn for forming the composite material is constituted by a polybenzazole fiber having <=20 nm mean square coarseness of the fiber surface and <=0.6% equilibrium water content, and a matrix fiber consisting of a thermoplastic polymer having 200-600 deg.C melting point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite yarn suitable for forming a composite material molded body. More specifically, a yarn for manufacturing a fabric used as a reinforcing material for structural parts of various machines, a pressure vessel, a tubular structure, or the like, or the yarn itself is used for reinforcement in a molded composite material or the like. The present invention relates to a composite yarn that can be used as a fiber.

[0002]

2. Description of the Related Art A molded composite material is expected to have a wide range of uses because of its excellent properties such as high strength, high initial elastic modulus, high fatigue resistance and low specific gravity, and has been attracting attention as an important industrial material. In this composite material molded body, reinforcing fibers as a reinforcing material are bonded and integrated with a thermosetting resin having good fluidity at room temperature as a thermoplastic matrix. However, one of the problems of this molding method is that the working efficiency or productivity is low because the time required for molding, mainly the thermosetting of the matrix resin, takes a long time. On the other hand, in order to improve this drawback, development of a composite material molded body in which reinforcing fibers are bonded and integrated with a matrix made of a thermoplastic polymer is underway. For example, JP-A-60-56545 discloses that a reinforcing fiber and a matrix fiber made of a thermoplastic polymer are combined, and the yarn is used as a warp and a weft, and the resulting fabric is heat treated to form a composite material. The body technology is disclosed. Since the composite yarn according to the same publication is not in a mixed fiber state, there is no guarantee that the thermoplastic matrix fibers uniformly permeate the reinforcing fiber gaps when the fabric is heated and melted. Japanese Patent Laid-Open No. 60-20903
Japanese Unexamined Patent Publication No. 3 proposes a method of mixing the thermoplastic matrix fiber and the reinforcing fiber at the single fiber level so that the melted thermoplastic matrix fiber uniformly penetrates into the gap between the reinforcing fibers. However, in general, in order to improve the handleability of the composite material molded body in the processing step, it is first knitted and woven into a cloth form. However, in this case, the composite yarn is likely to be damaged in the rewinding process and the weaving / knitting process, and when the composite yarn is used for the weft yarn and the warp yarn, the amount of the thermoplastic matrix fiber in the fabric is increased, etc. The mechanical properties of the green compact tend to deteriorate. Conventionally, the strength of the high-strength fiber used as a reinforcing fiber has been about 3.0 GPa, but an ultra-high-strength polyethylene fiber has been developed and is disclosed in JP-A-1111034.
The publication proposes a composite yarn formation suitable for forming a composite molded body by using the ultrahigh-strength polyethylene fiber as a reinforcing fiber and combining this with a thermoplastic fiber having a melting point lower than that of the polyethylene fiber by 10 ° C. or more. There is. However, ultra-high-strength polyethylene fibers have low heat resistance, and strict temperature control is required at the time of melt molding in order to prevent thermal deterioration of low-melting-point reinforcing fibers. Further, since these fibers generally have low adhesiveness, they are inevitable. However, there are various manufacturing problems such as a narrow selection range of the types of thermoplastic matrix fibers. Further, JP-A-1-306679 proposes a polybenzazole- and / or polybenzothiazole-coated fiber coated with a thermoplastic resin. However, again, JP-A-1-306679
The publication proposes polybenzazole and / or polybenzothiazole coated fibers coated with a thermoplastic resin.
The coated fiber proposed in the same publication is a polybenzazole and / or polybenzothiazole fiber to which a thermoplastic resin or a molten thermoplastic resin dissolved in a solvent is applied. The method of applying the thermoplastic resin with a solution requires a solvent evaporation step, and the method of applying the molten thermoplastic resin, when the fiber form is multifilament, obtains fibers in which each filament is uniformly coated. It is difficult to do so.

[0003]

DISCLOSURE OF THE INVENTION According to the present invention, when a fabric made of a composite yarn is formed by heating, the permeability of the thermoplastic matrix fiber into the gap between the reinforcing fibers is good, and the obtained composite molded product is a conventional product. In comparison, the composite yarn exhibits high heat resistance and mechanical properties, and it is an object of the present invention to provide a composite yarn that can be used as a reinforcing fiber of a composite molded body.

[0004]

That is, the present invention has the following constitution. 1. A composite yarn for molding a composite material, comprising a polybenzazole fiber having a mean square roughness of 20 nm or less on the fiber surface and a matrix fiber made of a thermoplastic polymer having a melting point of 200 to 600 ° C. 2. 2. The composite yarn for molding a composite material according to 1, wherein the crystal orientation angle of the fiber surface of the polybenzazole fiber is 1.3 degrees or less. 3. 2. The composite yarn for forming a composite material according to 1, wherein the equilibrium water content of the polybenzazole fiber is 0.6% or less. 4. The cycle until breakage in the abrasion test of the polybenzazole fiber is 5200 times or more. 1
A composite yarn for molding a composite material as described. 5. The composite yarn for molding a composite material according to 1, wherein the void diameter of the polybenzazole fiber is 25.5Å or more.

Hereinafter, the present invention will be described in detail from a method for producing a fiber to a method for producing a composite yarn for forming a composite material. Rigid polymers such as so-called ladder polymers have been considered as a means of achieving the ultimate physical properties of fibers, but such rigid polymers are not flexible and are required to have flexibility and workability as organic fibers. It is an important condition to be a linear polymer.

SG Wierschke et al.
iety Symposium Proceedings Vol.134, p.313 (1989)
As shown in Fig. 3, the linear polymer having the highest theoretical elastic modulus is cis-type polyparaphenylene benzobisoxazole. This result was also confirmed by Tashiro et al. (Macromolecules vol. 24, p. 3706 (1991)), and among polybenzazoles, cis-type polyparaphenylenebenzobisoxazole has a crystal elastic modulus of 475 GPa (P . Galen et al. Material Research Society Symposium P
roceedings Vol. 134, p.329 (1989)), considered to have the ultimate primary structure. Therefore, in order to obtain the ultimate elastic modulus, the theoretical conclusion is to use polyparaphenylene benzobisoxazole as the polymer material.

Fiberization of the polymer is described in US Pat. No. 5,2961,
No. 85, US Pat. No. 5,385,702, and the heat treatment method is the method proposed in US Pat. No. 5,296,185. The equilibrium moisture content of the yarn obtained by such a method is 0.6%. That is all. Therefore, as a result of keenly aware of the need for research on improvements of these methods, as a result of intensive research, the desired physical properties can be easily achieved industrially by the following methods even if the void diameter in the fiber is 25.5 Å or more. I found a thing.

A dope composed of polyparaphenylene benzobisoxazole (PBO) and polyphosphoric acid is spun from a spinneret. Thereafter, it is manufactured through coagulation, neutralization, washing with water, drying, and heat treatment under tension. As a means for suppressing the equilibrium moisture content to a low level, there is a method of densifying and highly orienting the crystal structure of the surface portion of the polymer constituting the fiber. In the present invention, for this purpose, a polybenzazole fiber was successfully industrially obtained in which the crystal structure of the surface of the polybenzazole fiber was finely changed and the water absorption was suppressed to an extremely low level.

The surface crystal structure of the fiber is characterized in that the mean square roughness of the fiber surface is 20 nm or less, and more preferably, the crystal orientation angle of the fiber surface is 1.3 degrees or less. The fiber is characterized by having an equilibrium moisture content of 0.6% or less, or a polybenzazole fiber characterized by having a cycle to break of 5200 or more in an abrasion test. Therefore, the present invention provides a polyparaphenylene benzobisoxazole fiber having an equilibrium moisture content as close to zero as possible by overcoming the technical difficulties so far and realizing a unique crystal orientation by such a technical background. It enables industrial production.

In order to bring out the above structural characteristics, the points of the present invention can be realized by the following method. That is, a spun yarn obtained by extruding a polymer dope composed of polyparaphenylene benzobisoxazole into a non-coagulating gas from a spinneret was introduced into a coagulating bath to extract phosphoric acid contained in the dope yarn. After that, neutralization, washing with water, drying,
It was found that polybenzazole having a densified fiber surface was obtained by heat-treating the fiber at a constant tension of 500 ° C. or higher.

The present invention will be described in more detail below. The polybenzazole fiber in the present invention means PBO homopolymer,
And a random, sequential or block copolymer with polybenzazole (PBZ) containing substantially 85% or more of PBO components. Here, the polybenzazole (PBZ) polymer is, for example, “Liquid
Crystalline Polymer Compositions, Process and Pro
ducts "U.S. Pat. No. 4,703,103 (October 27, 1987)
Sun), “Liquid Crystalline Polymer Compositions, P
rocess and Products "U.S. Pat. No. 4,533,692 (1985)
, August 6,) "Liquid Crystalline Poly (2,6-Benzot
hiazole) Compositions, Process and Products "US Patent No. 4533724 (August 6, 1985)," Liquid Cr
ystalline Polymer Compositions, Process and Produc
ts "US Pat. No. 4533693 (August 6, 1985), Eve
rs 「Thermooxidative-ly Stable Articulated p-Benz
obisoxazole and p-Benzobisoxazole Polymers "US Patent No. 4539567 (November 16, 1982), Tsai et al.," Method for making Heterocyclic Block Copolymer ".
U.S. Pat. No. 4,578,432 (March 25, 1986), and the like.

The structural unit contained in the PBZ polymer is preferably selected from lyotropic liquid crystal polymers. The monomer units consist of the monomer units described in structural formulas (a) to (h), and more preferably essentially consist of monomer units selected from structural formulas (a) to (d).

[0013]

[Chemical 1]

[0014]

[Chemical 2]

Suitable solvents for forming the dope of the polymer consisting essentially of PBO include cresol and non-oxidizing acids capable of dissolving the polymer. Examples of suitable acid solvents are polyphosphoric acid, methanesulphonic acid and concentrated sulfuric acid or mixtures thereof. Further suitable solvents are polyphosphoric acid and methanesulfonic acid. The most suitable solvent is polyphosphoric acid.

The concentration of polymer in the solvent is preferably at least about 7% by weight, more preferably at least 10%.
% By weight, most preferably 14% by weight. The maximum concentration is
Limited by practical handling properties such as polymer solubility and dope viscosity. Due to these limiting factors, the polymer concentration does not exceed 20% by weight.

Suitable polymers, copolymers or dopes are synthesized by known methods. For example, Wolfe et al., U.S. Pat. No. 4533693 (August 6, 1985), Sybert et al., U.S. Pat. No. 4,772,678 (September 20, 1988), Har.
synthesized by the method described in US Pat. No. 4,847,350 of ris (July 11, 1989). Polymers consisting essentially of PBO are described by Gregory et al., US Pat. No. 5,089,591 (1992).
(February 18, 2012), it is possible to achieve a high molecular weight at a high reaction rate in a dehydrating acid solvent under relatively high temperature and high shear conditions.

The dope polymerized in this manner is supplied to the spinning section and is usually discharged from the spinneret at a temperature of 100 ° C. or higher. A plurality of die holes are usually arranged in a circumferential shape or a lattice shape, but other arrangements may be used. The number of spinneret pores is not particularly limited, but the array of spinneret pores on the spinneret surface must be maintained at a pore density that does not cause fusion between the discharge yarns.

The spun yarn requires a sufficient draw zone length, as described in US Pat. No. 5,296,185, in order to obtain a sufficient draw ratio (SDR), and at a relatively high temperature (dope It is desirable to uniformly cool with a rectified cooling air having a solidification temperature or higher and a spinning temperature or lower). The length (L) of the draw zone needs to be the length at which solidification is completed in the non-solidifying gas, and is roughly determined by the single hole discharge amount (Q). In order to obtain good fiber properties, the draw-out stress in the draw zone needs to be 2 g / d or more in terms of polymer (assuming stress is applied only to the polymer).

The yarn drawn in the draw zone is then introduced into the extraction (coagulation) bath. Since the spinning tension is high, it is not necessary to consider disturbance of the extraction bath and any type of extraction bath may be used. For example, a funnel type, an aquarium type, an aspirator type or a waterfall type can be used. The extract is preferably phosphoric acid aqueous solution or water. Finally, in the extraction bath, the phosphoric acid contained in the yarn is extracted by 99.0% or more, preferably 99.5% or more.
The liquid used as the extraction medium in the present invention is not particularly limited, but preferably water, methanol, ethanol, acetone, ethylene glycol or the like which is substantially incompatible with polybenzazole. Also extraction (coagulation)
It is also possible to separate the bath in multiple stages, dilute the concentration of the phosphoric acid aqueous solution sequentially, and finally wash with water. Further, it is desirable to neutralize the fiber bundle with an aqueous solution of sodium hydroxide and wash it with water.

A method of finely changing the fiber surface structure, which is particularly important in the present invention, will be described. In order to prevent moisture absorption, realization of high crystal orientation on the fiber surface is an important factor.
For this reason, it is important to slow the coagulation rate of the fiber dope in the extraction step to change the structure in the inner and outer layers of the fiber. As a method of slowing the coagulation rate, it is effective to increase the concentration of the phosphoric acid aqueous solution in the coagulation liquid, lower the bath temperature, or select a non-aqueous coagulant. The optimum phosphoric acid aqueous solution concentration is 50% or more and less than 80%, preferably 55% or more and less than 70%, and most preferably 60% or more and less than 65%. The higher the concentration, the greater the effect, but if the concentration is higher than necessary, the fiber strength will decrease, which is not preferable. The coagulation bath temperature may be any number as long as it is approximately 5 ° C. or lower, but even if the temperature is lowered too much, dew is generated around the bath, which is not preferable in operating the manufacturing machine. The temperature range is preferably 4 ° C to -30 ° C, more preferably 0 ° C to -15 ° C. When a non-aqueous coagulant is selected, an organic solvent having an affinity for water, such as alcohols such as ethanol and methanol, ketones such as acetone, glycols such as ethylene glycol, is preferable. Of course, a plurality of the above non-aqueous coagulants and water may be mixed and used.

After that, the fiber is dried and further heat-treated. The drying temperature is a temperature at which the fiber strength is not lowered, and specifically 150 ° C. or higher and 400 ° C. or lower, preferably 200 ° C. or higher and 300 ° C. or lower, more preferably 220 ° C. or higher and 270 ° C. or lower. The heat treatment temperature is 400
℃ or more and 700 ℃ or less, preferably 500 ℃ or more and 680 ℃
The temperature is more preferably 550 ° C. or higher and 630 ° C. or lower.

The fiber according to the present invention has a mean square roughness of the fiber surface of 20 nm or less, preferably 16 nm or less, more preferably 10 nm or less, and a crystal orientation angle of the fiber surface of 1.3 ° or less, preferably 1.1 ° or less, further Preferably 0.9 degrees or less, the equilibrium moisture content is 0.6% or less, preferably 0.55% or less, more preferably
0.5% or less, 5200 cycles to break in wear test
15 times or more, preferably 5600 times or more, more preferably 6000 times or more, void diameter is 25.5 Å or more, preferably 30 Å or more 15
It is less than 0 Å, more preferably 35 Å or more and less than 90 Å. The indexing of the diffraction points used in this patent is Frat.
ini et al. (Material Research Society Symposium Proceedi
ngs Vol. 134, p. 431 (1989)).

The mean square roughness Rms of the fiber surface is evaluated using an atomic force microscope (AFM). AFM is Seik
o Instruments (SII) SPI3800N
-Use SPA300. The probe has a spring constant of 2 N / m and a length of 450 μm.
A Si rectangular type cantilever SII (Si-DF3) having a width of 60 μm and a thickness of 4 μm was used. The scanner is a 100 μm scanner and the observation mode is DFM mode. Scan speed 0.5 Hz
The scanning direction is parallel to the fiber axis, and the measurement is performed under the conditions of 20 degrees Celsius and 65% relative humidity in the atmosphere. The fibers used for measurement are
It was used after being washed with a mixed solution of ethanol and n-hexane and dried. The observation field of view is a square area of 5 μm square on each side, and after observation, 3D tilt correction of the attached software is applied to perform planarization processing. In order to take into account the distortion caused when the image is flattened due to the presence of the fiber curvature, the mean square roughness Rms of only the central square area of 3 μm square is calculated after correction using the attached software. The observation was performed at random at 10 or more points, the Rms of each was calculated, and the average value was calculated. Note that Rms can be expressed using Equation 1.

Rms = [(1 / N) Σ (Z i −Z 0) ² ] ^0.5 Equation 1 Here, Z i is the height at each measurement point, Z 0 is the average height over the entire measurement point, and N is Indicates the number of measurement points.

The crystal orientation angle of the fiber surface is analyzed and evaluated by observing a thin piece peeled from the fiber surface with a high resolution using an electron microscope (eg Phillips TEM-430, JEOL JEM-2010). First, a collodion solution diluted with isoamyl acetate is thinly spread and spread on a glass plate, and several fiber single yarns are arranged. Wait for the collodion solvent to evaporate and solidify before peeling the fiber off the glass plate. At this time, it can be confirmed by a stereomicroscope that the flakes peeled off from the fibers adhere to the traces (on the film of collodion) peeled off at this time. This part is cut out together with the collodion film using a razor about 3 mm square, and the surface with the polybenzazole fiber surface flakes on the micro grid made by Nisshin EM Co. for electron microscope observation or the holey carbon film made by Agar Scientific. Place them face down. Transfer to a Petri dish with a lid and leave in the presence of isoamyl acetate vapor for several hours to allow the fiber flakes to adhere well to the microgrid.

After that, isoamyl acetate is added until the microgrid is immersed, and the mixture is left for one day and night, and the collodion film is poured off and then dried. For high-resolution observation, an electron microscope was used after correcting astigmatism at 200,000 times or more. The exposure time required for one-view photography is 5 to minimize damage from the electron beam received by the sample fiber flakes.
Within a second, the total irradiation time including correction of astigmatism should be kept within 35% of the life of the fiber when it receives an electron beam (duration where an electron beam diffraction pattern with sufficient resolution can be observed). It was For recording high-resolution electron microscope (lattice) images, use Kodak SO-163 negative film with Kodak D-
19 Develop with undiluted developer or use an imaging plate system (eg, JEOL Pixsys TEM). The photographed lattice image is printed on photographic paper.
It is observed that the (200) lattice runs almost in the equilibrium direction with the fiber axis. Two crystals next to each other have (200)
The angle φ formed by the lattice axis is defined as the crystal orientation angle. A set of 100 or more crystals is observed and averaged to evaluate the crystal orientation angle.

The crystal orientation ratio between the center of the fiber and the surface is obtained by measuring a selected area electron diffraction image of an ultrathin section made by slicing the fiber. A product embedded with Spurr epoxy resin in which a single fiber and a curing agent are mixed is left overnight in an oven at 70 ° C. to be solidified and fixed. Next, this resin block is attached to an ultramicrotome manufactured by Reichert, and polished using a glass knife until the embedded fibers appear near the block surface. Next, an ultrathin section is prepared using a diamond knife manufactured by Diatome Co., and then collected on a 300-mesh copper grid and subjected to thin carbon vapor deposition. An ultrathin section is placed in an electron microscope, a section having both the center and the surface of the fiber is sought, and a selected area electron diffraction image is taken of both the surface and the center. FIG. 3 shows a bright-field image of an ultrathin section, a portion (diameter 0.3 μm) where electron beam diffraction was measured, and a measurement example of the measured electron beam diffraction pattern. Images are recorded using electron microscopy film (eg Agfa Scientia EM 23D56, or Kodak SO-163 negative film) or an imaging plate system. The method of RJ Young et al. (J. M.
At. Sci., 24, p5431 (1990)), the half width 2θ of the peak profile is calculated from the spread of the diffraction intensity profile in the meridional direction of the (010) and (−210) diffraction points, and then the equation 2 is calculated. The half-value width 2θ of the fiber center is divided by the half-value width 2θ of the fiber surface to obtain the crystal orientation ratio between the fiber surface and the center. An optical negative film blackness reading device (for example, Joyce-Loebl Chromoscan 3) is used to quantify the diffraction intensity profile from the electron microscope film.

[0029]  Crystal orientation ratio = 2θ (fiber center) / 2θ (fiber surface) Formula 2

The moisture content of the fiber is determined by allowing the fiber to stand in an environment of 20 ° C. and a relative humidity of 65% until no change in weight is observed, and then weighing it. That is, the weight of the fiber is weighed using an analytical balance, and the fiber is left for 30 minutes in an electric oven adjusted to 230 ° C. to remove water in the fiber and then weighed again. Equilibrium moisture content is evaluated using the formula shown in Formula 3.

Equilibrium moisture content = 100 × (fiber weight when reaching equilibrium-fiber weight after drying) / fiber weight after drying [%]

The wear resistance was evaluated in accordance with JIS L1095-7.10.2 by counting the cycles until breakage.
At this time, a tension of 1.0 g / d was applied to the fiber.

<Measurement Method of Small Angle X-Ray Scattering> The evaluation of the void diameter was performed by the following method using the small angle X-ray scattering method. The X-rays used for measurement are rotor flex RU manufactured by Rigaku Corporation.
It was generated using -300. A copper anticathode was used as a target, and the operation was performed at a fine focus of 30 kV x 30 mA. The optical system was a point-focusing camera manufactured by Rigaku Corporation, and the X-rays were monochromatic using a nickel filter. The detector is
Imaging plate (FDL U manufactured by Fuji Photo Film Co., Ltd.)
RV) was used. Distance between sample and detector is 200mm to 350m
Any suitable distance between m is acceptable.

Helium gas was filled between the sample and the detector in order to suppress disturbing background scattering from air and the like. The exposure time was 2 hours to 24 hours. Digital micrography (FDL5000) manufactured by Fuji Photo Film Co., Ltd. was used to read the scattering intensity signal recorded on the imaging plate. The data obtained are the Guineer plots for the scatter intensity I in the equatorial direction after background correction (the natural logarithm ln (I) of the scatter intensity after background correction is calculated for the square k ² of the scatter vector). Created). Where the scattering vector k is k = (4π /
λ) sin θ, λ is the X-ray wavelength 1.5418Å, θ is the scattering angle 2θ
Is half of.

The reinforcing fibers constituting the composite yarn of the present invention are the above-mentioned polybenzazole fibers. Considering that a composite material molded body composed of a fabric obtained by knitting and weaving the composite yarn as warp and / or weft is used for various machine parts and the like requiring high strength, at least 4. It preferably has a tensile strength of 0 GPa or more. The same applies when the composite yarn is used as a reinforcing material as it is. There is no particular limitation on the physical properties required for the thermoplastic matrix fiber, and it is sufficient if the fiber has mechanical properties sufficient to exhibit stable process passability in the rewinding process, the fiber opening process, and the weaving and weaving process. .

The yarn in which the reinforcing fiber and the thermoplastic matrix fiber are composited is used alone as a reinforcing material in a composite molding material, or after the composite yarn is knitted into a fabric as warp and / or weft, Used as a reinforcing material in composite molding materials. In either case, the thermoplastic matrix fibers are melted by thermoforming. Naturally, it is advantageous to use a thermoplastic matrix fiber having a low melting point from the viewpoint of workability at the time of heat molding, but inevitably only a composite molding material having low heat resistance can be obtained. In order to effectively utilize the excellent heat resistance of polybenzazole fibers, it is essential to combine thermoplastic matrix fibers with high heat resistance. For this purpose, the thermal decomposition of polybenzazole fibers at a melting point of at least 200 ° C or higher is required. It is necessary to select the thermoplastic matrix fibers from the thermoplastic polymer fibers that are below the initiation temperature. Examples of the thermoplastic synthetic fiber having a melting point of 200 ° C. or higher include polyester-based thermoplastic polymers such as polyethylene terephthalate and polybutylene terephthalate, and polyamide-based thermoplastic polymers such as nylon 6, nylon 66 and nylon 46. Fibers that have been used. Among the above-mentioned thermoplastic synthetic fibers, polyethylene terephthalate fibers are most preferable in consideration of price, thermal stability, and adhesiveness with the thermoplastic matrix fiber after forming the composite material molded body. In addition, the decomposition initiation temperature of polybenzazole fiber is 600 ° C, which has extremely high heat resistance among organic synthetic polymers. It depends on the type of thermoplastic matrix fiber to be combined, but it is a thermoplastic matrix fiber with a relatively high melting point. Even if there is, it is possible to perform heat molding to a high temperature range. Therefore, if it is a thermoplastic matrix fiber with a relatively high thermal decomposition temperature, the melt viscosity is lowered by hot molding at high temperature to increase the permeability of the matrix and the composite material molding with excellent physical properties and appearance with a low void generation rate. The body is obtained. When a thermoplastic matrix fiber having a melting point of less than 200 ° C. is used, the heat resistance of the composite molding material in which the knitted fabric is molded is naturally lowered, and a composite material molded body utilizing the excellent heat resistance of the polybenzazole fiber is obtained. Can't get On the other hand, the melting point of the thermoplastic matrix fiber must be 600 ° C. or lower in view of the heat resistance of the polybenzazole fiber.

The composite yarn itself or the composite yarn is knitted or woven to form a fabric, and is further heat-molded. As described above, the permeability of the molten thermoplastic matrix fiber at the time of melting is composite-molded. It affects the material, and also the physical properties, morphology and appearance of the product. For that purpose, it is important to preliminarily make a uniform mixed state of the composite yarn composed of the reinforcing fiber and the thermoplastic matrix fiber constituting the composite material. In general, the mixed state is a composite in a non-mixed fiber state, that is, a side-by-side or covering type by covering in which the reinforcing fiber yarn and the thermoplastic matrix fiber yarn are simply aligned. When a fabric composed of composite yarns mixed in such a form is melt-molded, the permeability of the thermoplastic matrix fiber into the reinforcing fiber is low, which is not preferable. The mixed state of the present invention means that the matrix fiber single fibers and the reinforcing fiber single fibers made of a thermoplastic polymer are arranged or arranged substantially randomly with respect to each other in any cross section of the composite yarn. That is, in order to keep the occurrence rate of cavities low by increasing the permeability of the matrix fiber melted at the time of heat molding into the reinforcing fiber gap and keep the strength of the final composite material molded body good, Let A be the number of filaments of the polybenzazole fiber in contact with the single filaments of the matrix fiber made of the thermoplastic polymer in the cross section, and B be the total number of filaments of the polybenzazole fiber, (A / B) × 10
The dispersity of single fibers calculated at 0% is preferably 46% or more and less than 74%. When the degree of dispersion of the filaments of the reinforcing fiber in the composite yarn is less than 46%, when a fabric composed of the composite yarn as a single component or only the composite yarn is heat-molded, the matrix is dispersed in the reinforcing fiber gap. Permeability tends to be non-uniform and voids are likely to occur. On the other hand, a higher dispersity is preferable in terms of quality and quality of the composite material molded body, but it is not easy to obtain a dispersity of 74% or more in a stable state at the current level of mixed fiber technology, and 74% or more. Even if the degree of dispersion of 1 is obtained, the degree of contribution (quality / cost) to the quality / quality improvement of the composite material molded body cannot be expected, so the degree of dispersion may be less than 74%.

The mixing ratio of the reinforcing fiber (polybenzazole fiber) and the fiber made of a thermoplastic polymer (matrix fiber) is important from the viewpoint of the reinforcing effect of the composite material molded body. This is an extremely important factor when used as a composite material without knitting or weaving. From this viewpoint, the content of the reinforcing fibers and the thermoplastic matrix fibers is preferably 30 to 85% by weight / 70 to 15% by weight, and more preferably 40 to 70% by weight / 60 to 30% by weight. is there. When the content of the reinforcing fiber in the composite yarn is less than 30% by weight, the reinforcing effect of the composite material molded body is relatively low, and when the content of the reinforcing fiber exceeds 99% by weight, the dispersity of the composite yarn is high. Even when the above conditions are satisfied, the melting and penetrating properties of the thermoplastic matrix fiber become low, and the void ratio V% of the final composite material molded product becomes large.

As a specifically preferable mixing method, for example, a so-called Taslan method for forming a loop or entanglement by supplying a plurality of multifilament yarns to a fluid turbulent zone of an air jet in a relaxed state, or a multifilament yarn A so-called electric fiber opening method in which fibers are electrically opened, short fibers are superposed on the front roller, twisted and wound, and further, two or more eddy turbulent flow zones are arranged substantially parallel to the yarn axis. And a so-called interlace method in which a yarn is guided into the zone to form a non-bulky and tight yarn under a tension that does not cause a loop or crimp.
When the reinforcing fiber and the thermoplastic matrix fiber are mixed and depending on the opening means, for example, when the electric opening method is adopted, the opened state is extremely stable in the range of 100 denier to 1500 denier, A composite yarn with high dispersibility can be obtained. Further, the single yarn fineness of the reinforcing fibers and the thermoplastic matrix fibers has a considerable influence on the uniformity of the mixed state of the fibers, and the fineness range of 0.5 to 3.0 denier is preferable for both the reinforcing fibers and the thermoplastic matrix fibers. However, the fineness of the single fiber is not particularly limited to this range and may be appropriately selected according to the opening / mixing means to be used. The polybenzazole fiber used in the present invention is characterized in that the surface structure is particularly dense as compared with the conventional product. For this reason, it was newly revealed that not only the hygroscopicity was low, but also the workability in the post-processing step and the process passability were improved. In other words, when a composite yarn is created using conventional polybenzazole fibers, scum (filament of fibrillar fibers) accumulates on guides, winders, etc. in the yarn path of the manufacturing process, and product quality is degraded or generated. There was a manufacturing loss such as stopping the manufacturing process to clean the scum. In the present invention, obstacles in process passability due to this type of scum could be significantly improved.

The composite yarn of the present invention is made into a sheet of a composite molded article by itself or through a fabric knitted and woven in combination with a thermoplastic matrix fiber yarn, and is formed into a sheet of a predetermined size for further secondary processing. And a predetermined number of sheets are superposed on each other, placed in a mold preheated to a temperature higher than the melting point of the thermoplastic matrix fiber yarn, and the mold is pressed to form a sheet of the composite molded article. It is molded into a desired shape. The cloth knitted and woven here includes knits, woven fabrics, and non-woven fabrics, and the knitted and woven structure thereof is not particularly limited.

<Tensile Strength / Elongation of Fiber and Initial Tensile Elastic Modulus> According to JIS L 1013, a tensilon manufactured by Orientec Co., Ltd. was used to measure a gripping interval of 20 cm, a pulling speed of 100% / min, and n = 10. Then, the arithmetic mean value was calculated from the measured values.

<Fiber dispersity%> (a) A cross-section (a plane perpendicular to the yarn axis) is cut at an arbitrary number of points in the composite yarn with a sharp blade, and the entire cut surface is photographed. . (B) From the photograph, the number of filaments of the polybenzazole fiber which would come into contact with the filaments of the matrix fiber made of a thermoplastic polymer or which would come into contact if the filaments of the matrix fiber were displaced by 10% of the diameter was measured. , This is A (book).
(C) The total number of filaments of the polybenzazole fiber existing in the entire cross section of the composite yarn taken in the photograph is measured, and this is designated as B (book). (D) Measured A and B
The polydispersity% of the polybenzazole fiber is calculated from the following formula. Dispersion (%) = (A / B) × 100

<Reinforcing Fiber Content FK%> Weight DK (g) of reinforcing fiber measured after dissolving and removing the test piece of the composite material molded body using a solvent that selectively dissolves only the thermoplastic matrix fiber. The content FK% of the reinforcing fiber was calculated from the following formula and the weight DT (g) of the test piece of the composite material molded body before the dissolution treatment. FK (%) = DKx100 / DT

<Tensile Strength, Elongation and Initial Tensile Elastic Modulus of Molded Composite Material> Tensile properties were measured according to JIS K-7054 with the axial direction of the reinforcing fiber as the tensile direction of the test piece.

<Porosity V%> (a) The specific gravity SGT of the test piece of the composite material molded product and the specific gravity SG of the reinforcing fiber by the A method specified in JIS K7112.
K, the specific gravity SGM of the thermoplastic matrix fiber is determined.
(B) After the test piece of the composite material molded body is dissolved and removed using a solvent that selectively dissolves only the thermoplastic matrix fiber, the weight of the reinforcing fiber is measured, and the test of the composite material molded body before the dissolution treatment is performed. The weight of the matrix fiber was determined from the weight difference from the weight of the piece. From these weight data, the reinforcing fiber mass content FK% and the matrix fiber mass content FM% were determined, and the void ratio V% of the sample was determined according to JIS K 7053-1998.
It was calculated by the following formula described in 7. V = 100-SGT [(FK / SGK + FM / SG
M)]

<Measurement Method of Moisture Absorption Rate> The moisture absorption rate of the composite molded article was evaluated by measuring the weight increase rate after immersion in water at 23 ° C. for 24 hours.

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EXAMPLES (Examples 1 and 2, Comparative Examples 1 and 2) US Patent No.
Polyparaphenylene benzobisoxazole having an intrinsic viscosity of 24.4 dL / g, measured by a methanesulfonic acid solution at 30 ° C., obtained by the method shown in No. 4533693 (14.0% by weight) and phosphorus pentaoxide content of 83.17% A spinning dope consisting of phosphoric acid was used for spinning. The dope was passed through a metal mesh filter material, then kneaded and defoamed with a biaxial kneading device, and then the pressure was raised to maintain the polymer solution temperature at 170 ° C and from a spinneret having 166 holes. After spinning at 170 ° C and cooling the discharged yarn using cooling air at a temperature of 60 ° C, and further cooling the discharged yarn to 40 ° C by natural cooling,
It was introduced into the coagulation bath. Fibers were prepared using ethanol at a temperature of -10 ° C as a coagulating liquid. Next, the fiber was wound around a gozette roll, the yarn was washed with ion-exchanged water in a second extraction bath at a constant speed, and then the fiber was immersed in a 0.1 N sodium hydroxide solution for neutralization. After further washing with water in a washing bath, it was wound up, dried in a drying oven at 80 ° C., and allowed to stand until the moisture content in the fiber became 2% or less. Further, heat treatment was performed for 2.4 seconds under the condition of tension of 5.0 g / d and temperature of 600 ° C. The fiber thus obtained was used as a raw yarn for producing a composite yarn. The crystal orientation angle of this fiber was 0.77 degrees, and the mean square roughness was 14.2 nm. Next, the polybenzoxazole fiber prepared as described above is used as a reinforcing fiber and has a melting point of 2
A composite yarn was made using an interlacer device in which two pairs of opposed roller fluid conduits were opened using polyethylene terephthalate fibers at 60 ° C. as matrix fibers.
Processing conditions are fluid pressure of 3.5 kg / cm ² and yarn speed of about 50.
It was set to 0 m / min. The fineness of the composite yarn after mixing is 8
At 50 denier, the polybenzazole fiber content and the single fiber fineness of the polybenzazole fiber and the polyethylene terephthalate fiber were then changed. Next, using this composite yarn as a warp and using only polyethylene terephthalate fiber as a weft, a plain weave was woven with a warp density of 50 yarns / inch and a weft yarn density of 50 yarns / inch. 20cmx20 for the obtained cloth
After being cut into a size of cm, the cloth is vacuum dried at 80 ° C. for 16 hours under the condition of 0.1 mmHg or less, and then three cloths are laminated so that the reinforcing fibers are aligned in the same direction. The body was formed into a body, put in a mold, and subjected to a heat treatment for 5 minutes at a temperature of 290 ° C. and a pressure of 17.0 Kg / cm ² . After that, the mold was removed, and air-cooling was performed until the surface temperature was lowered to 80 ° C. to obtain a unidirectionally oriented reinforced laminate. Table 1 shows the tensile properties of the laminate.

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[Table 1]

Comparative Example 3 Except that aramid fiber (Kevlar 29) was used instead of polybenzazole fiber,
A reinforced laminate was prepared in the same manner as in Example 1. Table 1 shows the physical properties of the laminate.

Comparative Example 4 Fiber surface mean square roughness is 24
A reinforced laminate was obtained under the same conditions as in Example 1, using polybenzazole fibers having a fiber orientation of 1.5 degrees on the fiber surface. The results are shown in Table 1.

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The composite yarn of the present invention can be melt-impregnated at high temperature, has good permeability, can reduce voids, and has good workability. The laminated body can provide a yarn that enables production of a base fabric suitable for a composite molded body having excellent tensile strength properties. In the composite yarn manufacturing process, improvement of processability was recognized. Further, it was also shown that a composite molded body having low hygroscopicity can be prepared. Therefore, the composite material molded body obtained by further using the base fabric made of this yarn for the composite material molded body is required to have mechanical properties, heat resistance, and thermal conductivity as automobile parts, aerospace members, and computer-related members. It is important to contribute in the fields where

Claims (5)

[Claims] 1. A composite material molding comprising a polybenzazole fiber having a mean square roughness of 20 nm or less on the fiber surface and a matrix fiber made of a thermoplastic polymer having a melting point of 200 to 600 ° C. For composite yarn. 2. The composite yarn for molding a composite material according to claim 1, wherein the crystal orientation angle of the fiber surface of the polybenzazole fiber is 1.3 degrees or less. 3. The equilibrium water content of the polybenzazole fiber is 0.
It is 6% or less, The composite yarn for composite material molding of Claim 1 characterized by the above-mentioned. 4. The composite yarn for molding a composite material according to claim 1, wherein the cycle until breakage in the abrasion test of the polybenzazole fiber is 5200 times or more. 5. The void diameter of the polybenzazole fiber is 25.
The composite yarn for molding a composite material according to claim 1, which has a length of 5 Å or more.