JPH1025627A - Acrylic carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acrylic carbon fiber, used for aircraft, capable of manifesting composite characteristics excellent in impact resistance characteristics and having controlled surface characteristics. SOLUTION: This acrylic high-performance carbon fiber has >=1580kg/mm<2> strand strength and 30-40 tons/mm<2> elastic modulus measured according to JIS R-7601, further 12-20ÅLc and 30-40ÅLa measured according to a wide angle X-ray analytical method, 0.10-0.25μA/cm<2> surface characteristic parameter ipa measured according to the potential scanning method and >=30kg/mm<2> value of CAI measured according to the NASA Reference Publication (NASA RP) 1092.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-performance acrylic carbon fibers having controlled surface properties.

[0002]

^2. Description of the Related Art The demand for higher performance of carbon fiber has been increasing year by year, and particularly, in the direction of higher strength and higher elasticity of carbon fiber for aircraft, an elastic modulus of about 30 ton / mm ² has been recently used. Medium-elastic carbon fibers having the following are being pursued as the mainstream of development.

[0003] A composite used for the primary structural material of an aircraft must have high impact resistance, and particularly high residual compressive strength after impact (hereinafter abbreviated as CAI) with emphasis on damage tolerance. Has been demanded.

[0004] In order to improve the CAI of the composite, many attempts have been made in general to improve the toughness of the matrix resin and the elongation of the carbon fiber.

Although it has been widely recognized that the surface properties of carbon fibers are extremely important factors influencing the properties of composites, no attempt has been made to improve CAI by controlling the surface properties. ,
Therefore, carbon fibers exhibiting a sufficient CAI value have not yet been developed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an acrylic carbon fiber having a controlled surface property and capable of exhibiting composite properties excellent in impact resistance mainly used for aircraft. .

[0007]

The gist of the present invention is that the strand strength and the elastic modulus measured by JIS R-7601 are respectively 580 kg / mm ² or more and 30 to
40 ton / mm ² , and L by wide-angle X-ray analysis
c and La are 12 to 20 and 30 to 40 °, respectively, and the surface characteristic parameter ipa measured by the potential scanning method is 0.10.
Acrylic high-performance carbon fibers having a CAI value of ０．２0.25 μA / cm ² and a NASA RP1092 of 30 kg / mm ² or more.

The strand elastic modulus is 30 to 40 ton / m
Medium-high elasticity acrylic carbon fiber of m ²
Although the crystal structure is much more developed than that of the ton / mm ² type, the present inventors have found that in developing a carbon fiber having a good CAI of the composite, the size of the crystal is measured by a wide angle X-ray diffraction method. However, the magnitudes of Lc and La are one of the very important factors in determining CAI, and each of them is 12Å ≦ Lc ≦ 20Å, preferably 12Å ≦
It has been found that controlling in the range of Lc ≦ 15 ° and 30 ° ≦ La ≦ 40 ° improves CAI.

If the parameters Lc and La of the crystal structure are larger than the above ranges, the inactive graphite surface will be greatly expanded even in the surface layer of the carbon fiber, and not only will the surface oxidation in the post-treatment process be difficult to occur, but also Even if the surface is oxidized to a certain level, the oxidized part is localized only on the periphery of the wide graphite surface,
The graphite surface having a poor interaction with the matrix resin covers a large amount of the surface, and the effect of the post-treatment surface oxidation is hardly exhibited, and the CAI does not improve.

It is well known that the CAI of the composite increases as the strand elongation at break of the carbon fiber increases, but in general, the acrylic carbon fiber plays a major role in improving the strength due to the fibril structure derived from the precursor. Since the fibril structure is destroyed when Lc and La increase, the strength decreases when the carbonization temperature is increased and Lc and La are increased.

[0011] By controlling Lc and La within the range of the present invention, the strand strength, that is, the elongation at break is increased, which is advantageous in improving CAI. The elongation at break of the strand is desirably 1.6% or more.

Therefore, it is extremely important to control Lc and La within the above range in order to improve the CAI of the composite. Conventionally, a relatively high temperature, at least 1500 ° C., is required for obtaining a 30-40 ton / mm ² middle-high elastic yarn.
Although it was common to fire at the above temperature, the present inventors focused on the fact that the elastic modulus is more dominantly determined by the crystal orientation rather than the crystal size, By firing at a temperature of 1400 ° C. or lower at a lower temperature than before, a desired elastic modulus is secured by increasing the orientation without increasing the crystal size, and a high strength and good CAI of the composite are obtained. A carbon fiber can be obtained.

When Lc and La are smaller than the above ranges,
Even if the crystal orientation is improved, the elastic modulus, which is a basic property, is 30 to
It is difficult to set it to 40 ton / mm ² .

It is important to control the crystal size for the expression of CAI of the composite, and to control ipa, which is a parameter of the surface characteristics detected by the potential scanning method, within the range of 0.10 ≦ ipa ≦ 0.25. It is essential at the same time.

Ipa is considered to be a parameter that changes depending on the concentration of functional groups on the surface of the carbon fiber that can be reversibly oxidized and reduced, such as hydroxyl group and carboxyl group, and the state of the electric double layer between the carbon fiber electrode where the functional groups are present and the measuring solution. Although it is generally determined by the maximum carbonization temperature in the firing process, it can be controlled to an arbitrary size by surface oxidation treatment after firing. When ipa is less than 0.10, it becomes inactive to the matrix resin and the interaction is poor and the CAI is low. On the other hand, when ipa exceeds 0.25, not only the rate of increase of the functional group is reduced but also the surface layer is reduced. More fragile portions are formed, and the CAI is rather reduced.

Controlling ipa within the above range maximizes the CAI of the composite.

O _iS / C _{iS and the} like are usually measured by X-ray photoelectron spectroscopy as surface characteristic values of carbon fibers, but these values are merely indicators of the chemical functional group concentration, and the CAI of composite In order to improve _OiS /
It became clear that controlling C _{iS and the} like was not effective. That is, even if the surface oxidation level is increased, O _iS / C _iS
Shows a tendency of saturation and plateau, so that for CAIs that decrease with increasing processing level, O _iS / C
_iS control has no effect.

That is, CAI can be improved for the first time by controlling ipa.

A further feature of the present invention is a carbon fiber wherein the water extract has an absorbance at 250 nm by UV of 0.2 or less. Tar and mist components sintering and adhering during the firing process and their oxides oxidized during the surface treatment adhere to the surface of the carbon fiber, or deposit on microvoids between crystals, forming a fragile layer or portion This weakened portion is generally weakly bonded to the fiber substrate and is in a state of being easily peeled.

In order to improve the CAI of the composite, it is important to minimize the exfoliation inside the composite caused by the impact. For this purpose, it is necessary to oxidize the carbon fiber surface layer and simultaneously remove the fragile portion. Based on the recognition that it is indispensable, among these surface stains, carbon fibers from which water-soluble components have been removed are particularly C
It is important for improving AI, particularly for obtaining carbon fibers with small variation in CAI value.

The tar and mist components generated in the calcination process are remarkably oxidized and converted into water-soluble components in the subsequent surface treatment process, but the remaining amount is greatly affected by the surface treatment method. When the wet treatment is performed, it is washed and removed to some extent together with the electrolyte in the subsequent water washing process.However, when the dry treatment such as air oxidation is performed, most of the dirt components are not washed and removed. A large amount remains attached to the fiber surface layer. Therefore, in any of the surface treatment methods, a subsequent cleaning step is required.

The control of Lc and La, the control of ipa, and preferably the removal of surface dirt are JIS R-76 of the present invention.
The strand strength and elastic modulus measured at 01 were 58
0 kg / mm ² or more, 30-40 ton / mm ² ,
CAI value measured by NASA RP1092 is 30kg
/ Mm ² is important for obtaining high-performance acrylic carbon fibers, and is an indispensable condition for improving the CAI of composites and reducing dispersion. It can achieve its intended purpose.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon fiber of the present invention can be produced as follows. In order to keep Lc and La within the above-mentioned ranges, the maximum carbonization temperature in the firing process is set to 1
In order to obtain a desired elastic modulus, a spinning solution obtained by filtering impurities of 3 μ or more is spun.
It is necessary to use a precursor having a range of 9d and a surface roughness of 1.0 to 3.0 when observed with an electron microscope. This is because a material having a smaller surface roughening degree absorbs impact energy at the interface between the fiber and the resin at the time of impact and does not damage the fiber itself.

Further, in the flame-proofing step, the heating rate is set to 0.3 to 0.8 ° C./min, the elongation is set to 15% or more, and the fiber density is set to 1.25 to 1.4 g / cm ^3. Flame resistant.

Then, after giving elongation of 3% or more at a temperature of 300 to 800 ° C. in an inert atmosphere, the elongation is further increased to 1150 to 14
Heat treatment is performed under tension at a temperature of 00 ° C. to obtain carbon fibers.

Although it is possible to increase the elastic modulus by lengthening the calcination time in the carbonization step, since the elastic modulus tends to saturate with time, the treatment time of 1 to 3 minutes according to the present invention is reduced. Is important in achieving the purpose of
Carbonization times in excess of minutes are industrially disadvantageous.

As a surface treatment method for controlling ipa within the range of the present invention, there are known methods, that is, oxidation treatments such as electrolytic oxidation, chemical oxidation, and air oxidation, which are widely practiced industrially. In electrolytic oxidation, the simplest way to control ipa within the above-mentioned range is to change the amount of electricity. In this case, even when the amount of electricity is the same, ipa varies greatly depending on the electrolyte used and the concentration thereof.
The oxidation treatment is preferably performed by passing a quantity of electricity of coulomb / g. Then, ipa is reduced to 0.10 by the oxidation treatment.
０．２0.25 μA / cm ² .

In air oxidation, ipa can be controlled by changing the heating temperature.
At this time, by using air containing 1 to 2 vol% of ozone as the atmospheric gas, the oxidation treatment can be performed at a temperature of 140 to 230 ° C. for 0.5 minutes or more, which makes it possible to control ipa with high accuracy, which is industrially more preferable.

The higher the carbonization temperature in the firing process, the lower the ipa of the obtained carbon fiber, and the subsequent surface treatment must be performed under strong conditions within the above range.

In order to reduce the absorbance of the water extract of the carbon fiber after the surface treatment to 0.2 or less, the surface-treated carbon fiber is washed with water,
Alternatively, it is easily achieved by immersion cleaning treatment in an alkaline aqueous solution, but in order to more completely achieve the object of the present invention, water washing or water washing after performing an electrolytic oxidation treatment in an alkaline aqueous solution as the surface treatment method described above. It is desirable to carry out the washing treatment in an alkaline aqueous solution.

The fragile portion of the carbon fiber surface layer is not removed at all as long as the electrolytic oxidation is carried out in an acidic aqueous solution. Thereby, the fragile portion having increased polarity can be easily eluted into the alkaline aqueous solution.

When the electrolytic oxidation is performed in an alkaline aqueous solution,
As can be seen from the fact that the electrolyte solution is significantly colored,
Simultaneously with the oxidation, it is possible to remove the fragile portion of the carbon fiber that adversely affects the CAI. By combining subsequent washing with water or sufficient washing and removal in an alkaline aqueous solution, the carbon fiber substrate and the resin are firmly bonded. By bonding, the peel strength against impact can be greatly improved.

After the electrolytic oxidation treatment, the higher the treatment temperature is, the more effective it is at the time of washing with water.
It is preferable to carry out a washing treatment at a temperature of at least ° C, more preferably at least one minute using boiling water. When the temperature is lower than 40 ° C., the cleaning effect is reduced, and the cleaning time becomes longer, which is industrially disadvantageous.

Further, depending on the processing conditions in the electrolytic oxidation, the pH may vary.
The cleaning can be more effectively performed by using an alkaline aqueous solution having a value of 7 or more. Washing in an alkaline aqueous solution is more effective when the electrolytic density is increased by increasing the current density or when the elution of solubles is suppressed by lowering the alkali concentration of the electrolytic solution. In this case, the alkaline aqueous solution for washing does not need to be the same as the alkaline aqueous solution for electrolysis, and it is acceptable to adopt a completely different alkaline species, concentration and pH, but it is advantageous to use the same solution industrially. That is natural.

The alkali compound may be any compound which is normally dissolved in water at 0.02%, preferably 0.05% or more, and has a pH of more than 7 and 14 or less. Potassium, water softeners such as barium hydroxide, ammonia, disodium phosphate, tripotassium phosphate, sodium carbonate, sodium hydrogencarbonate, ammonium carbonate, ammonium hydrogencarbonate, inorganic salts such as sodium nitrate, sodium acetate, potassium acetate, Organic salts such as sodium benzoate and ammonium benzoate can be used alone or as a mixture of two or more. In order to avoid the alkali metal and alkaline earth metal remaining in the carbon fiber, it is preferable to use ammonium salts such as diammonium phosphate, ammonium benzoate, and ammonium carbonate. Further, ammonium carbonate, ammonium hydrogen carbonate, and carbamine Ammonium acid and the like are more preferable because they can be removed by thermal decomposition.

When washing with an alkaline aqueous solution, heating at 30 to 80 ° C. is more effective and desirable. However, for compounds that are easily decomposed by heating, such as ammonium carbonate and ammonium hydrogen carbonate, it is appropriate to treat at room temperature.

The washing time is not particularly limited, but for the purpose of the present invention, washing is preferably carried out until the UV absorbance at 250 nm of the carbon fiber distilled water with distilled water becomes 0.2 or less.

The washing step may be a method of washing continuously after electrolytic oxidation treatment, or a method of winding the carbon fiber once and then washing it again continuously or in batches to further improve the washing effect. For this purpose, it is possible to forcibly flow hot water, perform bubbling using an inert gas, or apply vibration by ultrasonic waves.

[0039]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. (B) "Strand modulus and strength" is JIS R-7
601 was measured.

(B) "Size Lc, La of microcrystals measured by wide-angle X-ray diffraction method" is described in Japan Society for the Promotion of Science, 117
The committee issued the magazine “Carbon”, No. 36, pp. 25-34
The measurement was performed in accordance with the method described in “Method for measuring lattice constant and crystallite size of artificial graphite” posted on page (1963).

(C) "ipa" is a standard scanning speed of 2 mV
The measurement was performed by the method described in JP-A-60-252718, from page 10, lower left column, line 10 to page 3, upper left column, bottom, line 12, except that the rate was changed to / sec.

(D) "Absorbance" was measured by placing 1 to 5 g of carbon fibers in a flask equipped with a cooler, adding distilled water 10 times the weight of carbon fibers by weight, and adding an ultrasonic cleaner (water temperature in the tank ± 2 ° C.). Extraction was carried out for 10 minutes in an oscillation frequency of 43 KHz and high-frequency output of 90 W). Then, the supernatant was recovered and placed in a quartz UV cell having a cell length of 1 cm, and distilled water was used as a control solution.
V is the absorbance at a wavelength of 230 nm measured by a spectrophotometer.

(E) "Residual compressive strength after impact (CAI) is NASA Reference Publication"
n 1092 (1983) "Standard Te
stsfor Toughened Resin Co
compositions "Revised Edition. 50 parts of bis (4-maleimidophenyl) methane was pre-reacted with 450 parts of 2,2-bis (4-cyanatophenyl) propane at 120 ° C. for 20 minutes to obtain a pre-reacted product. Co., Ltd., epoxy equivalent 250) and 4,4-diaminodiphenyl sulfone and amino group / epoxy group = 1/4
At 160 ° C. for 4 hours at an equivalent ratio of
Preliminary reaction (2,000 parts) diluted to 80% with No. 7 (manufactured by Yuka Shell Co., epoxy equivalent: 170) was added, and the mixture was uniformly mixed at 70 ° C. for 30 minutes.
Epoxy resin obtained by adding 100 parts of -N ', N'-dimethylurea, 1 part of dicumyl peroxide and 25 parts of silicon oxide fine powder Aerosil 380 (manufactured by Nippon Aerosil Co., Ltd.) and uniformly mixing at 70 ° C for 1 hour. A unidirectional prepreg is prepared from carbon fiber and carbon fiber and laminated in a pseudo-isotropy of [+ 45/0 / -45 / 90] _4S , and cured at 180 ° C. for 2 hours to obtain a size 4
A test piece of × 6 × 0.25 inch is prepared.

After fixing the test piece on a steel table having a hole of 3 × 5 inches, a 4.9 kg weight having a nose of 0.5 inch R was dropped at the center thereof, and a plate thickness of 1
After applying an impact of 1500 Lb-in per inch, the plate was subjected to a compression test to determine the CAI.

(F) "Surface roughening degree" is disclosed in
The surface roughness was measured in accordance with the method for measuring the degree of surface roughening described in the third line from the lower right column of the upper right column on page 2, page 3 of JP-A-130320.

Example 1 98% by weight of acrylonitrile, 1% by weight of methyl acrylate, 1% by weight of methacrylic acid
A polymer having the following composition was dissolved in dimethylformamide to a solid concentration of 26% by weight to form a dope.
After performing 0μ filtration and 3μ filtration, wet spinning is performed, and subsequently, it is stretched 5 times in a hot water bath, washed with water and dried, and further dried with hot heat 170 ° C.
The film was stretched 1.5 times at ℃ to obtain an acrylic fiber precursor having 0.8 denier, 2.3 degree of surface roughening and 9000 filaments.

The precursor was passed through a hot-air circulation type flame stabilizing furnace at 220 to 260 ° C. for 60 minutes, and a 15% elongation operation was performed when the flame stabilization treatment was performed.

Next, 3 oxidized fibers were placed in a pure N ₂ gas stream for 30 minutes.
When passing through a first carbonization furnace having a temperature gradient of 0 to 600 ° C., an elongation of 8% was added, and 13%
40 in a second carbonization furnace with a maximum temperature of 00 ° C.
Heat treatment was performed for 2 minutes under a tension of 0 mg / d to obtain carbon fibers.

Subsequently, 10% by weight of ammonium carbonate was added.
After running in an aqueous solution, the carbon fiber was used as an anode, and a current was passed through the counter electrode so that the amount of electricity became 100 coulombs per gram of the carbon fiber to be treated. After washing and drying, a carbon fiber was obtained. This carbon fiber exhibited the properties shown in Table 1.

Example 2 The same conditions as in Example 1 except that the precursor having a precursor fineness of 0.4 denier and a surface roughness of 2.4 were treated at a maximum temperature of 1400 ° C. in the second carbonization furnace. The precursor was spun, flame-resistant and carbonized.

Further, the same surface treatment and cleaning treatment as in Example 1 were carried out, except that the treatment was carried out at an electric quantity of 200 coulombs / g during electrolytic oxidation. The obtained carbon fiber exhibited characteristics as shown in Table 1.

Example 3 Precursor Fineness is 0.6
Example 1 except that the denier and the surface roughness were 2.5.
Under the same conditions as for the precursor spinning, flame resistance, carbonization,
Surface treatment and cleaning treatment were performed. Table 1 shows the obtained carbon fibers.
The characteristics shown in FIG.

(Comparative Example 1) Carbon fiber obtained by spinning, oxidizing, and carbonizing in the same manner as in Example 1 was treated with 5% phosphoric acid.
Perform electrolytic oxidation at 20 coulomb / g in aqueous solution, and then
A cleaning treatment was performed in the same manner as in Example 1. This carbon fiber exhibited the properties shown in Table 1.

(Comparative Example 2) 1.2 denier, degree of surface roughening 1
The flame resistance, carbonization, surface treatment, and cleaning treatment were performed in the same manner as in Example 1 except that the treatment was performed at the maximum temperature of the second carbonization furnace of 1500 ° C. using a precursor of 0.5. The obtained carbon fiber exhibited characteristics as shown in Table 1.

Comparative Example 3 Spinning, flame resistance, surface treatment, and washing were performed under the same conditions as in Example 1 except that carbonization was performed at a maximum temperature of 2000 ° C. under a tension of 400 mg / denier. The obtained carbon fiber exhibited characteristics as shown in Table 1.

[0056]

[Table 1]

[0057]

Industrial Applicability The carbon fiber of the present invention is an acrylic carbon fiber having a controlled surface property which can exhibit composite properties excellent in impact resistance mainly used for aircraft.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiaki Maruyama 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory

Claims (1)

[Claims] 1. The strand strength and elastic modulus measured according to JIS R-7601 are each 580 kg / mm ² or more.
30 to 40 ton / mm ² , Lc and La by wide-angle X-ray analysis are 12 to 20 and 30 to 40 °, respectively, and the surface characteristic parameter ipa measured by the potential scanning method is 0.
An acrylic high-performance carbon fiber having a 10 to 0.25 μA / cm ² and a CAI value measured by NASARP 1092 of 30 kg / mm ² or more.