JPH0116925B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing fine short fibers that have excellent heat resistance and mechanical properties and are suitable for resin reinforcing materials, friction materials, paper-like materials, reinforcing short fibers, and the like. More specifically, it is characterized by imparting appropriate molecular orientation to a molded product such as a sheet, film, or fiber containing a specific aromatic copolyamide as a main component, and then crushing the molded product into fibrils using shear force. The present invention relates to a method for producing fine short fibers. Conventional technology Polymers such as aromatic polyamide, polyamide hydrazide, and polyhydrazide have been used as pulp particles, fibrids, fibers, films, sheet materials, resins, and laminates with excellent heat resistance, mechanical properties, and electrical properties. Known to be useful. Among the polymers, para-oriented poly(paraphnylene terephthalamide) is used as a film.
A method has been proposed for producing fibrillated fine short fibers by molding the molded product into fibers and crushing the molded product by applying mechanical shearing force (Japanese Unexamined Patent Application Publication No. 1973-1992).
No. 82028). However, the fibrillation ability of poly(paraphenylene terephthalamide) is not necessarily sufficient, and producing fine short fibers from molded products not only requires a long processing time, but also requires a long processing time. The state of development is also not completely satisfactory. OBJECTS OF THE INVENTION It is an object of the present invention to provide a method that allows for easier fibrillation and obtains fine short fibers with better performance than the above-mentioned conventional techniques. Structure of the Invention As a result of various studies on the above-mentioned method, the present inventors discovered that a method consisting of a specific aromatic copolyamide,
The inventors have discovered that a molded product having a specific molecular orientation can be broken into fibrils very easily by shearing force, and that the resulting fine short fibers are extremely useful, leading to the present invention. That is, the present invention provides a specific aromatic copolyamide, specifically, (a) the following general formula (-A) In the formula, Y ₁ is -O-, -S-, -SO ₂ -

[Formula] -NH-, -CH ₂ - or

A diamine repeating unit represented by at least one group selected from the group consisting of [Formula] and the following general formula (-B) -NH-Ar ₁ -NH-(-B) [In the formula, Ar: , a phenylene group, a naphthylene group, or a biphenylene group in which the bonding chains extend in the same or parallel axes, or the following formula:

[Formula] (In the formula, Y ₂ may be the same as or different from Y ₁ ,
It is the basis of the same definition as Y ₁ . )] A diamine repeating unit represented by (b) the following general formula () (In the formula, Ar ₂ may be the same as or different from Ar ₁ and has the same definition as Ar _1. ) The number of moles of -A) and (-B) is substantially equal to the number of moles of the dicarboxylic acid repeating unit (), and the diamine repeating unit (-A) accounts for 7.5 to 50 mol% of the total repeating units. A molded article containing the aromatic copolyamide as a main component is subjected to specific conditions, namely,
at or above the second order transition temperature of the aromatic copolyamide,
Moreover, the method for producing fine short fibers is characterized in that after drawing at a temperature below the flow transition temperature, shearing force is applied to crush the fibers into fibrils. In the aromatic copolyamide used in the present invention, in the formula (-A), Y ₁ is -O-, -S-, -
SO ₂ − or

It is preferable to have the formula [Formula], and most preferably, it is particularly preferable that Y ₁ is -O-. Also, Ar ₁ in the above formulas (-B) and ()
and Ar ₂ may be the same or different, and they represent the same group of definition, but Ar 1 and Ar ₂ may be the same or different.
It is preferred that Ar ₂ is a phenylene, naphthylene or biphenylene group in which the bonding chains extend both coaxially or in parallel axes. Ar ₁ and/or
1,4-phenylene group is especially suitable as a group in which Ar ₂ bond chains extend in the coaxial direction, and as a group in which the bond chains extend in parallel axes directions, 1,4-phenylene group is particularly suitable.
1.5 naphthylene group and 2.6 naphthylene group are preferred, and 2.6-naphthylene group is particularly preferred. Ar ₁ and
The most suitable Ar ₂ is 1.4−
This is the case with a phenylene group. In addition, in the above formula (-B), Ar ₁ and/or Ar ₂ are of the following formula Y ₂ has the same definition as above, and as with Y ₁ above, -O-, -S-, -SO ₂ - or

[Formula] is preferred, and -O- is particularly preferred. The aromatic copolyamide used in the present invention is prepared by dissolving 5 g of the polyamide in 100 ml of 98% concentrated sulfuric acid.
Intrinsic viscosity (ηinh) is 0.5 based on measurements at 30°C
-7 Especially preferred are those between 0.8 and 4.0. By stretching a molded product containing such an aromatic copolyamide as a main component at a specific temperature range and then applying a shearing force, the molded product can be easily fibrillated.
Fine short fibers with excellent electrical insulation, heat resistance, flame retardancy, and paper-making properties can be obtained. The aromatic copolyamide used in the present invention is substantially composed of diamine repeating units of the formulas (-A) and (-B) and dicarboxylic acid repeating units of the formula (). However, Ar ₁ and/or Ar ₂ in formula (-B) and formula () are, for example, halogen atoms such as chlorine and bromine, lower alkyl groups such as methyl group and ethyl group, lower alkyl groups such as methoxy group and ethoxy group, etc. It may have a substituent such as an alkoxy group, a cyano group, an acetyl group, or a nitro group. Furthermore, in addition to the repeating units of formulas (-A), (-B), and (), the aromatic copolyamide used in the present invention may contain the above-mentioned repeating units if the amount does not exceed 5 mol% of the total repeating units. Any other repeating unit copolymerizable with the polymer may be contained as a modifying component. When producing the aromatic copolyamide used in the present invention, polymerization methods normally used for producing polyamides, such as melt polymerization method, solid phase polymerization method,
Interfacial polymerization method and solution polymerization method can be used.
Among them, interfacial polymerization method and solution polymerization method are preferred.
More preferred is a solution polymerization method. In the solution polymerization method, the above-mentioned at least two types of diamines and at least one type of dicarboxylic acid are reacted using substantially equal moles of the diamine and dicarboxylic acid to form the highly polymerized aromatic polyamide. Preparing the aromatic copolyamides used in the invention by carrying out the process in an at least partially soluble organic solvent, optionally in the presence of an acid acceptor, at a temperature ranging from -20°C to 100°C. Can be done. In this case, it is preferable to carry out the above reaction in the presence of a halide of a metal of Group 1 or Group 1 of the Mendelev Periodic Table or a hydrogen halide. These metal halides and hydrogen halides are used as solubilization aids for the resulting aromatic copolyamide. An amide solvent is suitable as the above-mentioned organic solvent, and preferable examples of such an amide solvent include, for example, tetramethylurea, hexamethylphosphoramide, N,N-dimethylacetamide,
N,N'-dimethylformamide, N-methylpyrrolidone-2, N-methylpiperidone-2, N,
N-dimethylethyleneurea, N,N,N',N'-
Tetramethylmalonic acid amide, N-methyl caplactam, N-acetylpyrrolidine, N,N'-diethylacetamide, N-ethylpyrrolidone-2.
N,N-dimethylpropionic acid amide, N,N-
Examples include dimethylisobutyramide, N-methylformamide, N,N'-dimethylpropylene urea, and mixtures thereof. Among these, N-methylpyrrolidone-2.hexamethylphosphoramide, N,N-dimethylacetamide, N,N
-dimethylformamide and mixed systems thereof are preferred. The aromatic copolyamide solution (polymerization solution) obtained by the solution polymerization method described above has fluidity, stretchability, and threadability characteristics suitable for solution molding, so it can be directly used in the present invention. It can be used for manufacturing molded products. The above-mentioned aromatic copolyamide is a polymer that provides fine short fibers with excellent solubility, electrical insulation, heat resistance, and flame retardancy. Conventionally, it has been known that polyamide polymers obtained only by the above formula (-b) and the compound represented by formula () provide fibers with excellent mechanical properties. Polymers do not have sufficient solubility in organic solvents, so it is difficult to obtain a highly concentrated solution suitable for molding, and it is difficult to obtain a highly concentrated solution suitable for molding. Must-have. However, in the method of the present invention, the aromatic copolyamide may be obtained by directly using a polymerization solution obtained by a solution polymerization method, or by using not only the solution polymerization method but also a conventionally known melt polymerization method, solid phase polymerization method, oricomer polymerization method. A copolyamide formed by a polymerization method, an interfacial polymerization method, or a combination thereof may be once separated and recovered from the polymerization reaction mixture, and the copolyamide may be redissolved in an appropriate solvent and used. The aromatic copolyamide used for the function of the molded product used in the present invention includes:
Those with an intrinsic viscosity (ηinh) of 0.5 to 7 as mentioned above,
Particularly suitable is one between 0.8 and 4.0. By using an aromatic copolyamide having such an intrinsic viscosity, the molded product can be fibrillated to a volume by stretching it at a specific temperature range, and therefore, it is possible to easily produce fine short fibers with excellent impregnating properties and paper-making properties. can be manufactured. In the present invention, in order to bring the molded product of the aromatic copolyamide into an oriented state that allows easy fibrillation, the polymer solution of the aromatic copolyamide is passed through a nozzle, a slit, etc. into a thread-like, string-like,
It is extruded into a film or sheet, and a precipitant, i.e. water,
Alternatively, it is necessary to coagulate it in an aqueous solution containing an organic polar solvent, dry it, and then stretch it in one step in a specific temperature range, that is, in a temperature range above the secondary transition temperature and below the flow temperature, to achieve proper orientation. It is. In the present invention, as the organic polar solvent in the coagulation bath, any of the organic solvents mentioned above as suitable for preparing the solution can be used. In particular, when preparing the solution, the same organic solvent as the organic solvent can be used. is preferred. The temperature of the precipitant may be any temperature between 0°C and the boiling point of the coagulation bath (under atmospheric pressure), and the concentration of the organic polar solvent in the precipitant can be adjusted to obtain a molded product of the aromatic copolyamide composition. You can set an appropriate range. Depending on the composition of the aromatic polyamide, or if the solution contains the metal halide and/or hydrogen halide, depending on the type and content thereof, water or the polar organic solvent may be added. , in water, lithium chloride, sodium chloride, calcium chloride, magnesium chloride, zinc chloride, strontium chloride, aluminum chloride,
stannic chloride, nickel chloride, calcium bromide,
At least one inorganic salt selected from the group consisting of calcium nitrate, zinc nitrate and aluminum nitrate
Preference is given to using precipitants comprising seeds. The aqueous solution containing an organic solvent as a precipitant is an aqueous solution of an organic solvent selected from N-methylpyrrolidone, N,N dimethylacetamide, hexamethylphosphoramide, tetramethylurea, N-methylformamide, and a mixture thereof. An aqueous solution containing 5 to 70% by weight of an organic solvent is preferred. More preferably, it is 10 to 50% by weight. In the present invention, the above-mentioned aromatic copolymer is discharged into the above-mentioned precipitant through a nozzle slit or the like, and after drying the substantially non-oriented molded product obtained by coagulation, the secondary transition point of the polymer is In order to facilitate fibrillation by stretching at a temperature above and between the flow transition temperature, it is preferable to stretch in the longitudinal direction at a stretching ratio of 30% or more of the cutting stretching ratio at the stretching temperature. The second-order transition temperature and flow transition temperature of the aromatic copolyamide used in the present invention are determined as follows. That is, when a substantially non-oriented molded product obtained by coagulation and drying from a polymerization solution of the copolyamide is heated from room temperature and the cutting stretch ratio at that temperature is measured, first, the temperature As the temperature rises, the cutting/stretching ratio increases monotonically, and when it reaches a certain temperature (Tg),
The temperature dependence of the cutting/stretching ratio begins to become extremely small, and as the temperature is further increased, the cutting/stretching ratio suddenly increases again from a certain temperature (Tf). (Tg) is the second-order transition temperature, the latter specific temperature (Tf)
can be determined as the flow transition temperature. FIG. 1 is a diagram showing the relationship between the stretching temperature, the cutting draw ratio, and the strength of the drawn yarn in the Examples described below, and the subscript number in the figure is the ratio of the draw ratio to the cutting draw ratio. In the case of Figure 1, Tg is approximately 300℃,
Tf is approximately 400°C, and stretching is performed in a temperature range of 300 to 400°C. In the present invention, as described above, by stretching the non-oriented molded product of aromatic copolyamide under specific conditions to obtain a molded product in a so-called incompletely stretched state,
The reason why it can be easily fibrillated is still not clear. However, when a molded product of the aromatic copolymer is stretched at low temperature, the stretching ratio cannot be high, and the molded product has insufficient orientation, low crystallinity, and many amorphous parts, resulting in a microstructure of the molded product. As a result, the phase separation between the crystalline phase and the amorphous phase becomes unclear, and fibrillation is difficult to be achieved by simple means.Also, when the molded product is stretched at high temperature, the molecular chains that make up the molded product move. It is presumed that this makes it easier for molecular chains to become entangled with each other, making the separation between the crystalline phase and the amorphous phase unclear, or that the binding force between the crystalline phases becomes stronger, making it difficult to form fibrillations by simple means. Ru. Therefore, in order to make the molded product easy to fibrillate, it is stretched at a temperature that allows crystallization orientation due to stretching stress to increase the proportion of the crystalline phase and to orient it, and
It is thought that the aromatic copolyamide used in the present invention has a fine morphology that can be easily fibrillated only by stretching at a temperature that does not cause entanglement of molecular chains. is considered to be extremely suitable for satisfying this condition. In the present invention, after the molded product made of the aromatic copolyamide is stretched in a specific temperature range, it is necessary to apply an appropriate shearing force such as crushing, grinding, extrusion, or impact in order to loosen it into a fibril shape. It is. Various types of grinders, mills, pulverizers, etc. can be used to apply the shearing force. Furthermore, since this process has considerable similarities with preparation in paper manufacturing, various heaters, heat exchangers, refiners, etc. can be applied. Furthermore, a part of the wood crusher grinder used in pulp production can also be used in the present invention. Furthermore, it is also possible to mix the molded product as it is into a resin or the like and crush it into threads by the shearing force applied during kneading. Effects of the Invention The present invention improves the problem of molding methods for films, threads, etc. that are oriented in the longitudinal direction, tend to tear in the longitudinal direction, or easily form fibrillations, which has been considered a drawback in the past, and provides useful fine particles. This provides a new method for producing short fibers. Not only does the aromatic copolyamide used in the present invention become easily broken into fibrils only after it is stretched and oriented to a relatively high degree, but the fibrous material made of the backbone polymer according to the present invention is inherently rigid; Since they are fibrillated after being stretched and oriented, they have even higher rigidity, and the obtained fine short fibers are mechanically extremely strong compared to pulp particles obtained by introducing a polymer into a precipitant while stirring. It will be excellent. The fine short fibers obtained in the present invention can be formed into sheet-like materials such as heat-resistant insulating paper by taking advantage of their excellent heat resistance. It also has high mechanical properties, especially high modulus and strength, as well as glass fibers.
Since it has a lower specific gravity than carbon fibers, metal fibers, etc., it is industrially useful as resin reinforcing materials, friction materials, etc. Furthermore, excellent synthetic paper can be produced by mixing the fine short fibers obtained by the present invention with pulp particles containing the aromatic copolyamide as a main component used in the present invention. Examples The present invention will be described below with reference to Examples. In the examples, the logarithmic viscosity (ηinh) was calculated using concentrated sulfuric acid as a solvent.
This is a value measured at 30°C at a concentration of 0.5g/100. Example 1 3.484 g of 3.4'-diaminodiphenyl ether
(0.0174 mol) and paraphenylenediamine 1.882 g
(0.0174 mol) and N-methylpyrrolidone-2.150
Dissolve terephthalic acid dichloride powder in g under a stream of dry nitrogen gas and stir vigorously at room temperature.
7.068 g (0.0348 mol) was quickly added and the polymerization reaction was carried out at 60° C. for about 3 hours. Thereafter, 1.95 g of calcium oxide was added to neutralize the by-product hydrochloric acid, and stirring was continued at 70° C. for about 3 hours. The resulting polymerization solution had a polymer weight concentration of approximately 6.5%.
The ηinh of the polymer was 2.25. This polymerization solution was extruded at 100℃ from a nozzle with a diameter of 0.2mm and 50 holes at a discharge rate of 22g/min, and after traveling about 10mm in the air, N-methylpyrrolidone-2/water (30% 70% by weight) in a precipitation solution, taken at a speed of 30 m/min, and then heated at 50°C.
It was washed in a water washing bath and dried with hot air at 150°C. This dry thread was brought into contact with a hot plate with an effective length of 500 mm for 50
FIG. 1 shows the relationship between the stretching temperature and the strength of yarns drawn at a cutting draw ratio and 0.3, 0.5, and 0.8 times the cutting draw ratio by varying the drawing temperature during drawing at a speed of m/min. In FIG. 1, Tg means the second-order transition temperature and Tf means the flow transition temperature. The thread drawn with Tg or Tf is in a state where it can be easily fibrillated by grinding it with fingers, and after cutting it into lengths of 1 to 10 cm, it is stirred with water in a homomixer to form fine fibrillar short lengths. Fibers were obtained. Yarn drawn at a temperature lower than Tg and yarn drawn at a temperature higher than Tf cannot be ground with fingers, cannot be fibrillated even with a homomixer, and furthermore, when ground in a mortar, the thread becomes flat. Or, even if it was torn apart, it only showed a lump-like form.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between stretching temperature, cutting stretching ratio, and strength of drawn yarn according to an example of the present invention. The appended numbers in the figure are the ratio of the stretching ratio to the cutting stretching ratio.

Claims (1)

[Claims] 1 The following general formula (-A) [In the formula, Y ₁ is -O-, -S-, -SO ₂ -,
At least one group selected from the group consisting of [Formula], [Formula] -CH ₂ -, or [Formula]. ] A diamine repeating unit represented by the following general formula ( _-B ) -NH-Ar ₁ -NH-(-B) A phenylene group, a naphthylene group, a _biphenylene group _, or _a diamine represented by the following formula: The system repeating unit and the following general formula -CO-Ar ₂ -CO- () [In the formula, Ar ₂ may be the same or different from Ar ₁ and is a group with the same definition as Ar ₁ . ], and the total number of moles of the diamine repeating units (-A) and (-B) is the number of moles of the dicarboxylic acid repeating units (). A molded article containing an aromatic copolyamide as a main component which is substantially equal to , and in which the diamine-based repeating unit (-A) is contained in an amount of 7.5 to 50 mol% of the total repeating units, is prepared as a secondary product of the copolyamide A method for producing fine short fibers, which comprises stretching the fibers at a temperature above the transition temperature and below the flow transition temperature to obtain fibers with a fiber strength of 12 g/denier or below, and then crushing the fibers into fibrils by applying shearing force.