JPH0791458B2 - Fine powder-containing aramid extrusion composition and method for producing the same - Google Patents

Description

The present invention relates to a fine powder-containing aramid composition and a method for producing the same.

(Prior Art) Polymetaphenylene isophthalamide aromatic polyamide (hereinafter abbreviated as PMIA) has a glass transition temperature of about 280 ° C., a melting point of about 430 ° C., and a limiting oxygen index of about 30. It is widely used as various molded products such as fibers, films, compression molded products, etc. because of its low heat resistance and excellent heat resistance and flame retardancy. By the way, in the production of these molded products, since the melting point of PMIA and the thermal decomposition point are extremely close to each other, it is generally impossible to carry out melt molding, and conventional solution molding or compression molding method below melting point has been adopted. . However, in the solution molding method, since it is necessary to remove the solvent, only fibers having a thickness of several tens of denier and films having a thickness of approximately 100 microns can be molded. On the contrary, it is practically impossible to produce a fiber or film-like material by the compression molding method.
On the other hand, the present inventors have conducted various studies to form PMIA bristles, and as a result, succeeded in instant thermoplastic molding and disclosed in JP-A-57-192436,5.
8-109618,58-109619,59-144607,61-245305
Enables bristle molding of PMIA.

After that, the present inventors have conducted various studies to develop new applications for PMIA bristles, one of which is a heat-resistant abrasive brush, and develops bristles mixed with inorganic fine particles such as alumina and carborundum. However, it was proposed in JP-A-58-136829.

The bristles proposed by this proposal have been found to be extremely useful as a heat-resistant polishing brush because they have a polishing effect in addition to heat resistance.However, since the inorganic fine particles are uniformly dispersed in the PMIA bristles, the bristle strength is increased. It had a defect that its elongation was low and it was easily broken.

Therefore, the inventors of the present invention invented a flat PMIA bristles in which an abrasive grain mixed layer and a non-mixed layer are arranged side by side in a cross section, and proposed this in JP-A-63-21920.
The brush made of this bristles was hard to break and had excellent abrasiveness, and was sufficiently satisfying the intended purpose.

However, this proposal remained difficult to answer the following needs.

(1) Bristles with a circular cross section are required for brush production or usage.

(2) Bristles with fine powder exposed not only on the tip but also on the entire side surface are required for soft brush and abrasive non-woven fabric applications.

(Means for Solving Problems) Therefore, the inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, contain fine powder having an extremely remarkable advantage.
The inventors have found a method for obtaining PMIA bristles and have further expanded this method to reach the present invention.

That is, the present invention is a fine powder-containing aramid extrusion composition characterized by comprising a fibrillar tetrafluoroethylene resin (PTFE) and an inorganic fine powder dispersed in an aromatic polyamide resin, and a method for producing the same.

The aromatic polyamide (PMIA) in the present invention is a homopolyamide or copolyamide in which 85 mol% or more of all repeating units are metaphenylene isophthalamide units.
This PMIA is obtained by polycondensing metaphenylenediamine as an amine component or another aromatic diamine with it, and isophthalic acid or another aromatic dibasic acid or its derivative as an acid component.

As a specific method for producing PMIA, the interfacial polymerization method described in JP-B-47-10863 is preferable. This is because this method yields a PMIA powder that is extremely suitable as one of the raw materials for the extruded aramid composition of the present invention. That is, the powder obtained by this method has fine and uniform primary particles with a diameter of about 1 μm, and the primary particles are aggregated.
It is a porous powder with a size of 30-100μ.

As the fine powder in the present invention, well-known inorganic fine powder may be used. Specifically, for example, it is a powder of several tens of meshes to about 10,000 meshes made of silicon carbide, alumina, diamond and the like.

The aramid extruded composition of the present invention may take any form such as fiber, film, rod, pipe, plate, etc. In any case, the fibril type PTFE resin and fine powder are added to the PMIA resin. Are dispersed. The dispersed state of the fibrils is extremely fine and uniform, so it is difficult to distinguish them by direct observation of the composition itself.
The composition was mixed with PMIA solvent (concentrated sulfuric acid, N-methylpyrrolidone, N, N
Dimethylformamide, N, N dimethylacetamide) etc. to dissolve and remove PMIA, collect the insoluble matter in the solvent, place it on the preparation, drop the solvent on it, and place the slide glass on 50 ~ The disperse state can be clearly identified by observing with a 100 × microscope.

That is, the dispersion state of the fibrillar PTFE resin is extremely fine mesh-like, and the inorganic fine powder is firmly entangled in the mesh, so that the composition of the present invention can be immersed in the solvent of PMIA to form the inorganic fine powder. Does not leave the mesh.

The dispersed state of fibrillar PTFE observed by such means has the appearance of a capillary tube in a living body. FIG. 1 is a micrograph showing an example thereof. This is a monofilament-shaped aramid extruded composition of the present invention (1% mixture of PTFE) is dipped in N-methylpyrrolidone to dissolve PMIA, and then a white thread-like insoluble matter is gently taken out. It is a photograph (200 times).

The aramid extrusion composition of the present invention may have a multi-phase structure of a dispersed phase in which fibrillar PTFE and inorganic fine powder are dispersed in PMIA and a single phase of PMIA only.

The content of fibrillar PTFE in the aramid composition of the present invention is preferably in the range of 0.01 to 10% by weight. If it is less than 0.01% by weight, the effect of the present invention is not exhibited, and if it exceeds 10% by weight, the mechanical properties are rather deteriorated. The preferred content of PTFE in the fibrillar PTFE dispersed phase is 0.1-5% by weight,
More preferably, it is 1 to 3% by weight.

Fibril-like PTFE in the aramid extrusion composition of the present invention
The dispersion amount may be changed stepwise from the surface layer to the inner layer of the composition (dispersion density). Such a sparse and dense structure can be utilized when the difference in physical properties between the surface layer and the inner layer of the composition is remarkably exhibited.

The content of fine powder in the aramid extruded composition of the present invention can be appropriately determined depending on the purpose of use of the composition, but in many cases, it is about 3 to 50% by weight.

The fibrillarly dispersed PTFE of the present invention is highly oriented and crystallized. This contributes to the excellent mechanical properties of the composition of the present invention. The oriented crystallization of PTFE in the composition can be clearly identified by wide-angle x-ray photography. FIG. 2 is a wide-angle X-ray photograph of the monofilament composition, and the two spots on the equator are reflections on the (1,0,0) plane of the PTFE crystal. Also, the ring of dots is a reflection of silicon carbide (# 1500) dispersed in PMIA.

The aramid extrusion composition of the present invention is a PTFE resin-coated mixed powder obtained by mixing an aqueous suspension of PTFE, an inorganic fine powder and a PMIA powder, and then drying the mixture (hereinafter referred to as PTFE-coated mixed powder). Aromatic polyamide powder (PMIA powder) containing is heat-compressed and then extruded from a thermoforming die.

The aqueous suspension of PTFE used in the method of the present invention may be an aqueous colloidal suspension generally commercially available. For example, first, a commercially available aqueous suspension having a resin content of 60% by weight is diluted with water to prepare a desired aqueous suspension for mixing, and this, inorganic fine powder and PMIA powder are mixed with a mixer, and then dried. Machine dry to produce PTFE coated mixed powder. The mixing ratio of the mixed powder of the inorganic fine powder and the PMIA powder to the aqueous suspension for mixing is preferably 1: 4 to 2: 1. If the former is too small, the mixing will be non-uniform, and if too large, not only will the drying take longer, but the uniformity of the mixing will be lost. The preferred concentration of PTFE in the mixed aqueous suspension of PTFE is in the range of 0.1 to 20%, more preferably 0.5 to
It is in the range of 10%.

The dry powder formed in this way also contains inorganic fine powder
The surface of each of the IA powders is covered with a thin film of PTFE. In particular, the PMIA powder obtained by the interfacial polymerization method described in JP-B-47-10863 is an agglomerated particle of primary particles having a diameter of about 1 μm, and it is easy for the aqueous PTFE suspension to penetrate.

Furthermore, it should be noted that PMIA particles adhere to the surface of each inorganic fine powder to form a stable mixture.

Generally, since the inorganic fine powder and PMIA have different specific gravities, a simple powder mixture is easily separated during the operation such as when the powder is put into a molding machine, and the uniform mixing property of the molded product is often lost. In the case of the present invention, since PTFE plays a role like an adhesive, the positional relationship between the particles is stably maintained.

The aramid extrusion-molded product of the present invention is obtained by thermally compressing the PTFE-coated mixed powder obtained as described above and then extruding it from a heat-molding die. Here, the PTFE-coated mixed powder (coated powder) is a mixed powder in which the coated powder and the uncoated original fine powder or / and PMIA powder (original powder) are substantially uniformly mixed by a mixer or the like, Alternatively, it means a composite powder in which the coating powder and the original fine powder are mixed in a respective phase, or 100% of the coating powder, or a powder obtained by combining these three.

In the method of the present invention, after thermally compressing the PMIA powder containing the coating powder as described above, the aramid molded article of the present invention is extruded from the heat-molding die, and the heat-pressing operation and the extruding operation from the heating die, It may be discontinuous or continuous.

For example, in the case of discontinuity, the means described in JP-A-61-293818 is used to form a molded product having a certain shape, for example, a plate shape, and then the means described in JP-A-61-245305 is used. Then, the aramid composition of the present invention can be extruded. On the other hand, in the case of continuous operation, a plunger type extrusion device in which a heat compression zone and a heat extrusion zone are separated is used.
Whatever means is used to produce the aramid composition of the invention, the process of the invention has enormous manufacturing advantages. That is, since the PMIA powder used in the present invention contains the PTFE-coated powder, the PMIA does not easily stick to the inner wall of the molding machine at the time of thermal compression and at the time of extrusion molding from the heating die, and the molding is smooth. Not only
Enables continuous production for a long time.

Next, the method of the present invention will be described in more detail with an example using the apparatus shown in FIG.

FIG. 3 is a schematic diagram showing a plunger type extrusion device for forming a rod-shaped aramid molded product by using the method of the present invention. In order to mold the rod-shaped aramid composition of the present invention with this apparatus, first, a PTFE-coated mixed powder is prepared by the above-mentioned method, and a powder obtained by mixing the PTFE-coated mixed powder with the original powder at a constant ratio, or preferably only the coated powder is used as a raw material. As No. 1, it is put into the thermal compression zone in the extruder. The thermal compression zone is divided into a cylindrical part 2 and a conical part 3 as shown in the figure. The cylindrical part 2 is set to a temperature (about 260 ° C) slightly lower than the glass transition temperature of PMIA (about 280 ° C), and the conical part 3 is made of glass. Set a temperature 30 to 70 ° C higher than the transition temperature. Further, the extrusion zone 4 constituted by a thermoforming die having a thermoforming nozzle having a nozzle having a conical portion and a cylindrical portion is set to a temperature 20 to 80 ° C. lower than the melting point (about 430 ° C.). Thus, when the plunger 5 directly connected to the hydraulic cylinder is lowered and pressurized, the powder in the cylindrical portion of the thermal compression zone is heated and compressed while transmitting the pressure while maintaining the porous state. On the other hand, the powder in the conical portion is heated to the above temperature, so that it is softened and compressed while pushing out the air inside, and finally the filling rate reaches 100%. In this case, what is important is that the pressure loss of the plunger is transmitted to the lower side, and for that purpose, it is necessary to reduce the friction coefficient between the powder and the inner wall of the molding machine as much as possible. In the method of the present invention, the friction coefficient is extremely low because a mixed powder of PTFE-coated fine powder and PMIA is used.

The heat-compressed aramid that has passed through the heat-compression zone reaches the extrusion zone 4 composed of a heat-molding die, where it is further heat-thinned and extruded as a rod-shaped resin having a constant diameter
The aramid composition 7 of the present invention is introduced into the cooling bath 6.

In the above steps, focusing on the behavior of PTFE coating the inorganic fine powder and the aromatic polyamide powder, it becomes more apparent that the aramid extrusion composition of the present invention is formed by the method of the present invention. In the present invention, the inorganic fine powder and PMIA
Since the PTFE coating with the powder is made from an aqueous suspension as described above, it is not a continuous film but an aggregate of fine particles and is unstable enough to be dispersed again in water without any treatment. Is. When the mixed powder coated with such a resin is heat-compressed at the above temperature (310 to 350 ° C), the fine particles having a melting point of about 330 ° C are softened, and the fine particles adjacent to each other adhere to each other to form a mesh. It will be continuous. The mesh-like PTFE formed in this manner is further heated and stretched into a fibril shape in the next heat extrusion step.

In this way, in order to further improve the mechanical properties of the extruded rod-shaped aramid composition, it is desirable to stretch it near the glass transition temperature of the aromatic polyamide. This stretching operation not only causes the molecules of the aromatic polyamide itself to be oriented, but also causes the fibrillar PTFE to be oriented and crystallized.

Further, focusing on the inorganic fine powder coated with PTFE, it is presumed that the PTFE on the surface thereof undergoes a large shearing force during the molding process and is oriented and crystallized into fibrils.

(Effects of the Invention) The aramid extrusion composition of the present invention has the following effects.

(1) Bending fatigue is improved. Therefore, it was possible to sufficiently meet the desired goals of the round cross-section bristles for brushes and the needs for full-face exposure type bristles of inorganic fine powder. This effect is presumed to be due to the mesh-like dispersion of fibrillar PTFE.

(2) Wear resistance is improved. This is the PMIA of the composition
It is presumed that the part is covered with PTFE and the friction coefficient is lowered, and that the inorganic fine powder is entangled in the mesh PTFE fibrils and is firmly fixed inside the composition, so that it is difficult to separate.

(3) Static electricity is hard to generate. This is because the charge series of the aromatic polyamide and the charge series of the PTFE are almost opposite to each other, and the fibrillar PTFE neutralizes the static electricity due to the structure dispersed in the aromatic polyamide. It is presumed that.

(4) Chemical resistance is improved.

(5) Since the surface is non-adhesive, foreign matter is unlikely to adhere and stains are hard to occur.

The method for producing an aramid extrusion composition of the present invention has the following effects.

(1) A mixture of inorganic fine powder and PMIA powder is stable and easy to handle during molding.

(2) It does not easily stick to the die during molding and can be operated for a long time.

(3) Since the surface of the inorganic fine powder is coated with PTFE, the surface of the die is not damaged by the fine powder.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples.

Example 1 A rod-shaped aramid extrusion composition was molded by the following method.

(1) Preparation of PTFE-coated mixed powder 30 parts by weight of silicon carbide (SiC) having a viscosity of 240 mesh (80μ) and meta-type aromatic polyamide (PMIA) powder obtained by the interfacial polymerization method described in JP-B-47-10863. 70 parts by weight (secondary particle average diameter: 70 microns) and 100 parts by weight of a 2% by weight aqueous PTFE resin suspension were prepared. First, silicon carbide and PMIA were mixed for 30 minutes with a V-type mixer. Thereafter, an aqueous suspension of PTFE was added, and the mixture was further mixed for 30 minutes and then dried by a drier to substantially remove water, thereby preparing a PTFE-coated mixed powder (coated powder).

(2) Molding of Rod-Shaped Aramid Extrusion Composition Using the above-mentioned coated powder as a raw material, a rod-shaped aramid composition having a diameter of 5 mm was molded using the apparatus shown in FIG. 4 under the following conditions.

Thermal compression zone Cylindrical part: Diameter 50mm, temperature 260 ℃ Cone: Bottom diameter 20mm, temperature 340 ℃ Extrusion zone Cylindrical part: Diameter 5mm, temperature 370 ° C Finishing at the point where the lowest point is reached, the next molding is a discontinuous molding method in which the plunger is raised and the powder is charged, and the same operation is repeated, but in this example, no matter how many times the molding is repeated, A good molded product was obtained without foreign matter adhering to the inside of the molding machine.

When a part of the obtained molded product was dipped in dimethylacetamide, PMIA was dissolved and removed, and microscopic observation was performed by the above-mentioned method. As a result, a PTFE fibril-like substance having the appearance of water algae and SiC entangled therein were observed.

Comparative Example 1 The same mixture of SiC and PMIA powder as in Example 1 was used as a raw material as it was, and an attempt was made to mold a molded product of the same shape by using the same apparatus and molding method.

As a result, PMIA adhered to the conical portion of the heat compression zone and the inner wall of the extrusion zone, making molding impossible.

Comparative Example 2 Same as Example 1, 30 parts by weight of SiC, 70 parts by weight of PMIA powder, and PTFE
6 parts by weight of fine powder (polyfluorocarbon molding powder manufactured by Daikin Industries, M-12, average particle size 25μ) are mixed with a V-type mixer for 30 minutes to prepare a mixed powder, which is the same as in Example 1. A rod-shaped molded product was molded by the method. As a result, the amount of adhesion inside the molding machine was slightly reduced as compared with Comparative Example 1, and the first molding was possible, but at the second time, the adhesion to the wall surface was also severe and molding was impossible.

Regarding the obtained molded product, when the dispersion state of the PTFE resin contained in the molded product was examined, it was a non-uniform collection of short fibrous substances, scale-shaped substances and other complicated shaped substances, and SiC was almost entangled. No, it separated and settled at the bottom of the container.
It was confirmed by infrared analysis that these insolubles were tetrafluoroethylene resin.

Example 2 Five types of fibrous aramid compositions were molded by the following method.

(1) Preparation of PTFE-coated mixed powder Five kinds of 50 parts by weight of aqueous suspension containing 1,2,6,10,20% by weight of PTFE respectively, 10 parts by weight of SiC having a particle size of 500 mesh and PMIA of Example 1 90 parts by weight of powder are prepared, and the aqueous suspension and Si
Mix the ratio of C and PMIA to 50: 1: 90, then dry,
Five types of coated mixed powders were prepared.

(2) Molding of fibrous aramid composition In order to produce a fibrous aramid molded product from the above-mentioned mixed coating powder as a raw material, first, the above-mentioned mixed coating powder is heated to 320 ° C. using an apparatus described in JP-A-61-293818. It was heat-compressed at 50 Kgf / cm ² to form a plate-shaped molded product having a thickness of 8 mm. At this time, surprisingly, it was possible to form a plate-like material having a filling rate of 100% at a low pressure without containing a small amount of water in the powder. This is PTF
It is presumed that this is due to the fact that the E resin mixed the powder to lower the internal friction and filled the spaces between the particles.

Next, using this plate-shaped molded product as a raw material, the method disclosed in JP-A-61-245305 was used.
The fibrous aramid composition of the present invention was molded in the following manner by utilizing the method described in the publication, and using the apparatus shown in Fig. 3 of the publication. That is, the plate-shaped molded product is pushed into a box-shaped preheating zone to be preheated to 255 ° C., and then it is softened by heating to 350 ° C. by a heating molding die (die) forming a softening zone and extruded from a round cross section nozzle, and further 340 ° C. In a box-shaped heat retention zone heated to
This was further stretched 2.5 times on a stretch plate at 280 ° C.
A 600 denier fibrous aramid composition was molded. still,
For comparison, a plate-shaped molded product made of SiC and PMIA powder not coated with PTFE resin was molded and subjected to 600
A denier (round cross section) fibrous aramid composition was molded.

In addition, regarding the composition in which the PTFE resin is mixed, N, N '
The PMIA component was dissolved and removed with a dimethylformamide solution, and then the residue was observed under a microscope. As a result, as shown in Fig. 1, it was confirmed that the fibrillar PTFE was entangled with SiC and dispersed in a mesh shape. Also, when I took a wide-angle x-ray,
As shown in FIG. 2, a pattern in which the PTFE resin component was highly oriented and crystallized was obtained.

When a test brush was prepared from the obtained fibrous aramid composition and the moldability and the brush performance were evaluated, the results shown in Table 1 were obtained, and it was found that the content of PTFE is preferably 1 to 3%.

Formability (rank), number of broken brushes, abrasiveness (rank), antifouling property (rank), electrostatic potential (KV) evaluation method and judgment criteria were based on the following methods and criteria.

(1) Moldability (rank) Qualitative judgment based on the frequency of yarn breakage of fibrous molded products after continuous operation for 24 hours.

(2) Number of broken brushes (number) The number of broken pieces when the test brush was set on the rotary shaft and rotated by contact with the ceramic plate for 30 hours (1200 rpm).

(3) Abrasiveness (rank) Set the test brush on the rotating shaft and place it on the iron plate (SS-41).
Qualitative judgment by grinding elongation when minute contact rotation (1200 rpm).

(4) Antifouling property (rank) Comparative qualitative judgment was made on the brush contact properties of the brush used for brush breakage characteristics and abrasiveness evaluation.

(5) Electrostatic potential (KV) Set the test brush on the rotating shaft, rotate the iron plate (SS-41) in contact (1800 rpm), and measure the potential with a current collector.

Example 3 40 parts of the 2.9 wt% PTFE-coated mixed powder used in Example 2 was placed in the middle layer part, and 30 parts of the original PMIA powder was placed in the upper layer part and the lower layer part. The article was molded.

This is extruded from the same device as in Example 2 in which the mouthpiece part is replaced with a slit nozzle of 1 mm (same temperature condition), thickness 0.3 m
A film-like composition of m was formed. Next, this film was stretched 1.5 times in the width direction.

When this film was dipped in dimethylacetamide, the white paper-like insoluble matter was taken out and observed under a microscope.
Fibrils resembling a non-woven structure interspersed with were observed.

When this film-shaped aramid composition was used as a polishing sheet, it not only has heat resistance compared to conventional sandpaper, but also has very little SiC detachment and high abrasion resistance, and has about 10 times durability. It has been found.

[Brief description of drawings]

FIG. 1 is a 200 × micrograph showing the shape of a fiber made of fibrillar PTFE containing inorganic fine powder dispersed in the aramid extruded product of the present invention, and FIG. 2 is a wide-angle x-ray photograph of the aramid extruded composition. , FIG. 3 is a schematic view of an aramid molded article molding apparatus.

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Claims (4)

[Claims] 1. A fine powder-containing aramid extruded composition comprising a fibrillar tetrafluoroethylene resin and an inorganic fine powder dispersed in an aromatic polyamide resin. 2. A fine powder-containing aramid extrusion composition according to claim 1, wherein the extrusion composition is fibrous. 3. The fine powder-containing aramid extrusion composition according to claim 1, wherein the extrusion composition is in the form of a film. 4. An aromatic polyamide containing a tetrafluoroethylene resin-coated mixed powder obtained by mixing an aqueous suspension of an tetrafluoroethylene resin, an inorganic fine powder and an aromatic polyamide powder, and drying the mixture. A method for producing a fine powder-containing aramid extrusion composition, which comprises extruding a powder from a hot-molding die after the powder is hot-pressed.