JPH0491230A - Production of precursor - Google Patents

Abstract

PURPOSE:To obtain a precursor having dense fibril-aggregate structure giving high-tenacity carbon fiber by specifying total pore volumes and pore radius of coagulated yarn derived from spinning of a specific acrylonitrile-based polymer and drawn yarn derived from drawing of said coagulated yarn. CONSTITUTION:A spinning dope composed of acrylonitrile-based polymer containing >=93wt.% acrylonitrile and having 1.5-3 intrinsic viscosity eta is spun and the resultant coagulated yarn is drawn in wet heat at 1-6 times draw ratio and >=8 times total draw ratio by simultaneously making total pore volume VG and maximum value of pore radius RG of the coagulated yarn, and total pore volume of VW and maximum value of pore radius RW to satisfy formula VG/VW>1, formula RG/RW>1, VG<1.2cm<3>/g and RG<300Angstrom to afford the aimed precursor having <=1 d size of single fiber. Besides, the spinning method is preferably dry jet-wet spinning method.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to the production of acrylic precursor fiber bundles (precursors) having a slightly dense fibril aggregate structure with yarn defects, which are particularly suitable for producing high-strength carbon fibers. It is about the method.

(Prior art) Since it was known that acrylonitrile fibers are used as precursors to produce high-strength, high-elastic carbon fibers, improvements have been made in methods for producing precursors on an industrial scale, in firing methods, and in post-processing techniques. Many methods have been proposed. In particular, when carbon fiber is used as a reinforcing material for composite materials, a high degree of tensile strength is required, and in order to satisfy this requirement, the characteristics of the raw fibers used are even more important.
A number of techniques have been proposed to improve this.

The improved techniques to date can be roughly divided into ■ Selecting the fiber drawing conditions Appropriately setting the degree of orientation of the fibers ■ Minimizing defects caused by scratches from guides, etc. during the spinning process ■ Fiber surfaces Regulation of processing agents ■ Methods such as regulating polymer composition. However, the precursor is carbon*
In the firing process to convert into m bundles, the raw material fibers undergo a wide physical
Due to chemical changes, the firing conditions and associated
There are still many unresolved problems regarding the causal relationship with the conditions that should be met as a raw material fiber.

In view of the current situation, the present inventors investigated the variation of the fine structure during the initial structure formation process of the precursor from coagulation to drawing, and the relationship between the cormorant Il fin, especially the tensile strength, under such firing conditions. As a result of intensive study on the correlation, we discovered the four most important characteristics of a precursor and arrived at the present invention.

Furthermore, the maximum value of the pore radius specified by the present invention has been used to identify the microstructure of acrylic fibers, and research has been conducted in the past by Quinn et al. (R, G, Quinn ;
Ryes, J., 33.21 (1963)).

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for manufacturing a precursor that is suitable for manufacturing high-strength carbon steel pyramids.

(Means for Solving the Problem) The gist of the present invention is obtained by spinning a spinning dope made of an acrylonitrile polymer containing 93 or more parts by weight of acrylonitrile and having an intrinsic viscosity [η] of t5 to 3.0. When producing a precursor for producing carbon fibers with a fiber density of 1 d or less by stretching a coagulated thread under moist heat 1 to 6 times at a total stretching ratio of 8 times or more, the total pore volume (VG) and pores of the coagulated thread are determined. There is a method for manufacturing a precursor in which the maximum value of the radius (Ra), the total pore volume (vv) of the drawn yarn, and the maximum value of the pore radius (XW) satisfy the following formula.

vG (1.2m"/f, RG<30OA) The carbon fiber obtained by firing the precursor which satisfies the characteristics specified by the present invention has seven fiber physical properties, especially strand strength, such as china clay. As a result, it becomes possible to industrially widely supply reinforcing fibers for composite materials suitable for aviation and space applications.

In the present invention, first, under moist heat and stretching conditions of 1 to 6 times, any range of stretching conditions is required. Also, VG/TV≦1゜RG/RW≦
If a relationship of 1 is established, it is inferred that microstructural changes, that is, reorganization of the fiber microstructure including cutting and integration of microfibrils, occur on a large scale during the drawing process.

Therefore, this may result in the inclusion of minute defects that later inhibit strength development. When viewed at a macro level, the above-mentioned defects usually disappear by increasing the drawing ratio to a high degree, and although on the surface it appears that there are no problems to be worried about, this defect point still remains latently. For example, when we closely observe fractured portions of carbon fiber using a scanning electron microscope, it is clear that many fractures occur in areas that cannot be detected at the macro level. be.

In the present invention, the density of the coagulated thread must not be extremely low. That is, the ve of the coagulated thread is 12 cm.
”/ is above, and if the RG force is 300 m or above, how is vo/vv) 1 and ljG/ljW >
Even if stretching is performed to satisfy the relational expression 1, the densification as a precursor is incomplete, and the carbon edge obtained by firing and carbonizing it contains many structural defects.The object of the present invention is therefore is not achieved.

The next important thing is the intrinsic viscosity [η] of the polymer. In general, in order to obtain high-performance carbon fibers, especially high-strength type carbon fibers, it is necessary to make the precursor finer in order to minimize the number of defects per single yarn denier, or to obtain such precursor f. In order to achieve the fineness of -, a polymer with a molecular weight of 150,000 or more is required, which can be stretched at a high magnification of 8 to 10 times or more. Therefore, the preferred denier of the high-strength carbon fiber precursor intended by the present invention is aSa~1(1, more preferably (17(1) or less, and the intrinsic viscosity of the polymer is t5 More preferably, it should be set to 2 to 3.

Note that when a high molecular weight polymer with an intrinsic viscosity [η] of more than 3 is used, the viscosity of the spinning dope increases OI! Although it is necessary to lower the solid content concentration just in case, this is undesirable as it results in a porous coagulated thread with poor density with a VG of 1.2 cm/ or more. Unless the carbon fiber is subjected to advanced stretching treatment to increase its molecular weight, no improvement in the performance of the resulting carbon fiber can be expected.

An example of a manufacturing method for obtaining the state of solidification and stretched structure of the precursor, which is the focus of the present invention as described above, will be described below.

It is preferable to use a polymer containing acrylonitrile in an amount of 93% by weight or more, preferably 95% by weight or more. Copolymerization components other than acrylonitrile include acrylic acid,
Examples include methacrylic acid, itaconic acid and their salts and esters, allylsulfonic acid, methallylsulfonic acid and their salts, and mixtures of two or more Fi.

These polymers are produced by conventionally known polymerization methods such as aqueous suspension polymerization and solution polymerization in dimethylformamide using, for example, ammonium persulfate/ammonium bisulfite redox.

The spinning dope is determined by the molecular weight of the polymer, but one with a polymer concentration of less than 26 mw on an 18 mw plate is used. The spinning method can be either wet or dry-wet, but
It is desirable to employ the dry-wet spinning method because it can increase the density of the surface layer (skin layer) of the coagulated yarn.

The composition of the coagulation bath may be a mixture of water and an organic solvent such as dimethylformamide or dimethylacetamide, or an aqueous solution such as rhodan salt or nitrate, and the coagulation bath temperature is preferably kept at a low temperature, particularly below 15°C.

It is also important to note how fine coagulated filaments can be obtained using the above method, and the subsequent drawing process causes large changes in the fibril aggregation structure (disordering, cutting of microfibrils, and the size of the pore radius distribution curve due to integration). The performance of carbon fiber can be expected to improve if it is stretched in such a way that a change in In order to suppress such changes as much as possible, it is desirable to provide two or more stages of stretching under moist heat, and to perform stretching approximately 4 to 6 times in multiple stages.

Furthermore, in order to improve the orientation of the raw yarn, after such stretching under moist heat, it is further stretched under dry heat or in a pressure steamer.
The present invention will be specifically explained with reference to Examples, in which stretching is carried out by about 5 to 2 times, and the total stretching ratio is at least 8 times or more.

Physical property values were measured by the following method.

B. Intrinsic viscosity of polymer [η] Polymer 11 was dissolved in 100 mK of methylformamide containing α1N rhodan soda and measured at 25°C.

mouth, carbon fiber strand strength, elastic modulus J engineering 8 R-
7601: Determined from strands impregnated with epoxy resin. This is the average value measured using 10 samples of Test 200-1.

C. Maximum value of total pore volume and pore radius After washing the l/hFi drawn yarn with coagulated yarn with water at room temperature to sufficiently replace the solvent with water, it is immersed in liquid nitrogen and frozen. After that, the frozen thread was placed under reduced pressure (approximately 10"" Tor
The waste was dried for 72 hours while being cooled in a dry ice-methanol bath at -5°C to -10°C.
15F was used as each sample. The maximum value of the pore radius determined from the pore volume differential curve is (1! Measured by mercury intrusion method using a porosimeter 200 manufactured by ARLORRB).
This indicates the maximum value of the pore radius distribution curve of cylindrical pores.

In the mercury intrusion method, mercury, which has relatively poor wettability, is subjected to a predetermined pressure (
The amount of mercury permeated into the Km cone is measured at each pressure.The relationship between each pressure and the pore radius measured at that time is It is briefly defined by the following formula.

Mercury pressure λ method rr”P=-2treIcos# #: Surface tension of mercury (480dyne/a*) r: Pore radius #: Contact angle (140°) r = 7.5 X 1
0' /p (mu) From the upper hole to the external pressure P, the pore radius (
r) was determined, the pore volume was determined from the amount of mercury intrusion under each pressure, and the total pore volume was determined as the cumulative value.

Example 1 An acrylic polymer prepared by an aqueous suspension polymerization method, having 9498 parts by weight of acryloethyl alcohol, 2 parts by weight of methacrylic acid, and an intrinsic viscosity [η] of 2.2, was dissolved in dimethylformamide.
A concentrated stock solution was prepared.

This undiluted solution was once discharged into the air using a spinning nozzle with a pore diameter of α15 mm and a number of holes of 1,500, and after passing through approximately 5 intestine spaces, it was placed in a coagulation bath consisting of an aqueous solution of 774 dimethylformamide adjusted to 5°C. Guided and coagulated. This coagulated thread was stretched 3 times t in the air, followed by 2 times stretching in 60° C. warm water, and further 2 times stretching while submerged.

A KM/recon type oil agent was applied to the obtained bath-drawn yarn so that the coating amount was α3 to α7 based on the dry yarn weight, and then 1
After drying and densification treatment was carried out using a heating roller at 50° C., the film was further stretched 169 times using a heating roller 2 at 180° C., so that the total stretching ratio was 10 times. The pore volume distribution curves of the coagulated yarn and drawn yarn obtained at this time are shown in FIG.

The obtained fiber had a single yarn denier (17 (1, strength 7, O
f/a and elongation of 94. This precursor is 220
After flame-retardant treatment in the range of ~260°C for 40 minutes, carbonization treatment was performed by applying a temperature increasing gradient from 500 to 1400°C in N to obtain carbon fibers.

Table 1 shows the pore volume distribution analysis results and Km fiber physical properties of the precursor obtained at this time. V G /V11 and RG/RW I showing changes in precursor microstructure.
d), it can be seen that good stretching was performed without any major change in the fibril aggregation structure.

In addition, the carbon fiber physical properties showed high values such as strand strength of 600 y/cm2 or more and strand elastic modulus of 352 t/cm2.

Comparative Example 1 A precursor was produced in the same manner as in Example 1, except that the air stretching t was 3 times higher than that in 60°C hot water, the heating roll t was 44 times, and the total stretching ratio was 75 times, followed by carbonization treatment. Made of carbon fiber. The results are shown in Table 1, and V G / V W and RG are indicators of changes in the fine structure of the precursor.
/RW values were all the same as in Example 1, but when the total stretching ratio was as low as 75 times, the physical properties of the carbon fiber were generally inferior.

Comparative Example 2 A precursor was produced in the same manner as in Example 1, except that the concentration of the stock solution was changed to 16% by weight, followed by carbonization treatment to obtain carbon fibers. The results are shown in Table 1.

As the concentration of the stock solution decreases, the total pore volume becomes t41tx”/
It was observed that the strands had poor density and a decrease in strand strength.

Comparative Example 3 Same as Example 1, except that the intrinsic viscosity of the polymer [η]
was set as t8, and in order to optimize the optimum viscosity during spinning, the concentration of the stock solution was changed by 23 weight IK to produce a precursor, which was then carbonized to obtain carbon fiber. The results are shown in Table 1. VG, which is an indicator of the density of coagulated thread, is (L 86 em”/
It shows a low value of t, but V G / Y W line KRG /
RW values of 1 and 1 kb cause a large change in the fibril aggregation structure during stretching, resulting in a decrease in strand strength. The pore volume distribution curve obtained at this time was
As shown in the figure, compared to the case of Example 1, the maximum value of the differential curve of the drawn yarn is largely shifted to the right, that is, toward the larger pore radius.
7, and the cumulative value is 4t compared to the case of Example 1.
, 02 ex”/f.

Comparative Example 4 Same as Example 1, except that the limiting viscosity of Dalimer was
In order to optimize the optimum viscosity during spinning by changing 50 FC, the spinning stock solution was adjusted to a stock solution concentration of 12% by weight, and a precursor was manufactured. did.

The results are shown in Table 1.VG, which is an index of the density of the coagulated thread, shows a high value of t5Sam''/t, and no matter how much the subsequent drawing process Kk is performed, VW and RW show low values. It can be seen that the low density remains potentially, resulting in a decrease in strand strength.

Comparative Example 5 A precursor was produced in the same manner as in Example 1, except that the stretching conditions were changed to 5 times t in air, 2 times in hot water at 60°C, 588 times in boiling water, and a total stretching ratio of 10 times. When the stretching under moist heat exceeded 6 times, the fluffy yarn broke significantly during winding and sewing, resulting in poor spinnability. The results are shown in Table 1.

[Brief explanation of drawings]

Figure 1 is an analysis diagram of the pore radius and pore volume distribution of the precursor obtained in Example 1, and Figure 2 is an analysis of the pore radius and pore volume distribution of the breaker No. 0 obtained in Comparative Example 3. Each figure is shown below.

Claims (1)

[Scope of Claims] 1. A coagulated yarn obtained by spinning a spinning dope made of an acrylonitrile polymer containing 93% by weight or more of acrylonitrile and having an intrinsic viscosity [η] of 1.5 to 3.0 is processed under moist heat. 1
When producing carbon fiber precursors with a single fiber fineness of 1 d or less by stretching up to 6 times and a total stretching ratio of 8 times or more, the maximum value of the total pore volume (VG) and pore radius (RG) of the coagulated yarn
, the total pore volume (VW) and the maximum value of the pore radius (R
A method for manufacturing a precursor, characterized in that W) satisfies the following formula (VG)/(VW)>1, (RG)/(RW)>1VG
<102cm^2/g, RG<300Å2, and the manufacturing method according to claim 1, wherein the polymer concentration of the spinning dope is 18% by weight or more and less than 26% by weight.