JPS62238828A - Carbon fiber for composite material - Google Patents

Abstract

PURPOSE:To obtain the titled fiber having excellent mechanical properties, especially compressive strength after impact (CAI), by specifying the content of oxygen-containing functional group on the surface, a water-extractable coefficient and an expansion coefficient of the tow. CONSTITUTION:A carbon fiber having an oxygen-containing functional group content (O1S/C1S) of 0.05-0.3 on the surface measured by X-ray photoelectron spectrometry, a water-extractable coefficient of <=2.0 and an expansion coefficient of two of >=1X10<-3>. The fiber can be produced e.g. by charging 1g of a fiber with electrical charge of 60-600 coulomb, oxidizing the fiber surface with an aqueous solution of nitric acid or heat-treatment at 100-200 deg.C for 1-5min in air containing 1-5vol% O3, washing the surface-oxidized fiber with water of e.g. 4-12 pH and, if necessary, applying a sizing agent (e.g. bisphenol A diglycidyl ether) preferably in an amount of <=0.01wt%.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to carbon IN which is effective for carbon-41 fiber composite materials having excellent mechanical properties, particularly compressive strength properties after impact. Composite materials using fibers are widely used in aircraft, Japan, and general industrial applications.

[Conventional technology]

When using a polyacrylonitrile precursor as a starting fiber, carbon Il fibers used in conventional carbon fiber composite materials are first treated with odor resistance at 200 to 300°C in an oxidizing atmosphere, then carbonized in an inert atmosphere, and then generally is oxidized in gas phase or liquid phase to improve IIW properties with the matrix, and then treated with an appropriate sizing agent in order to suppress thread breakage and fluffing in post-processing.

However, composite materials using these carbon fibers still do not have sufficient adhesion between the yarn and the matrix, and in particular, the compressive strength after impact (CA I) is
No. 81 Publication Table■ As seen in Example 35, after an impact of 68.1 to 9/crtr (= 15001b in/in), 193.2xlO3kPa (=19.7 to 9
/rtm2') level is common, and this Example 3
It is extremely difficult to improve CAI using a highly heat-resistant matrix as shown in No. 5.

Also, CA [Yo O Tsuba Public Patent 133280 to improve
In Example 6.7.8 of the publication, the average value is 45.3k.
The performance of si (=31.ENKF/rMA2) is 1
However, this composite material has a highly tough layer called interleaf in the prepreg, and because of the presence of this layer, the miscellaneous volume content does not increase, and the prepreg The surface had a certain directionality, making it difficult to handle.

On the other hand, in the aircraft industry, CAI is used for the purpose of reducing the weight of aircraft, etc.
There is a demand for 27 kg/cm2 or more, and in order to satisfy this demand, it is desired to develop a composite material that does not include a special layer.

[Problem that the invention seeks to solve]

In view of the above-mentioned problems, the inventors of the present invention have made extensive studies and found that by using carbon fibers that have been oxidized and satisfies the specific conditions described below, even though the same matrix resin is used, the impact The present invention was completed by discovering a scale that significantly improves the subsequent compressive strength.

(Means for Solving the Problems) The gist of the present invention is that the amount of oxygen-containing functional groups (O1S/C15) on the surface measured by X-ray photoelectron spectroscopy is 0.5 mg as carbon for composite materials. 05 to 0.30, and the water extractable coefficient is 2.0 or less, preferably 0.5
By using carbon v&fiber with a tow spreading coefficient of 1X10' or more and preferably 0.1wt% or less of 11i with a sizing agent, even though the same matrix resin is used, The object is to significantly improve the compressive strength after impact.

The water-oil extrusion coefficient referred to in the present invention is calculated by placing carbon fibers 1 to 59 in a beaker with an inner diameter of 8 to 16α, and adding distilled water to the carbon fibers 11 to 59.
(weight ratio) and put it into an ultrasonic cleaning tank (oscillation frequency 43 to 1
1z, high frequency power 90-) for 10 minutes, then the supernatant was collected and a 1 crrr cell length quartz cell was washed for 10 minutes.
Put it in the FJtJV cell, add distilled water as a control solution and apply UV light.
Scan from 187 to 400 rv with a spectrophotometer, and
The absorbance in nm is determined, and this absorbance is referred to herein as the water extract coefficient.

The spreading coefficient of the present invention is determined by applying a tension of 75 Iq per denier to the untwisted tow as shown in Fig. 1 with a 50φ bar (
Surface treatment Hard chrome plating #200 (matte finish) was passed through at an entry angle of 30° and an exit angle of 45° at a linear speed of ITrL/win, and the width on the perspective was measured (#III+) and divided by the toe denier. It is determined as a value. Also, the distance between bar 1.2 is 30 cm, and the distance between bar 2.3 is 50 cI11.

The targeted carbon fibers may be obtained from either a polyacrylonitrile precursor or a pitch precursor, and their tensile modulus is 1tOn/mm.
l#+2 or more, tensile strength t, t 25 OK! j/M
2 or more, and the tensile elongation is 1.5% or more.

The carbon am of the present invention has an oxygen-containing functional group amount (01, /C1,
) is required to be 0.05 to 0.30.

If it is less than 0.05, the adhesion between the matrix resin and carbon fibers will be insufficient, and if it exceeds 0.30, the fiber strength will decrease, which is not desirable. In order to obtain carbon fibers having an oxygen-containing functional group content of 0.05 to 0.30, in the case of liquid phase treatment, carbon tdAH 6 per gram of carbon fiber between a platinum shield plate placed in the treatment solution and a +IjJ voltage applied to the
In the case of a method of loading electricity m of 0 to 600 coulombs, or in the case of gas phase treatment, for example, ozone 1 of 100 to 200 °C
Examples include a method of processing for 1 to 5 minutes in an air atmosphere containing 1 to 5 vol%.

These surface-treated carbon fibers are generally immediately treated with a sizing agent, but the spreading coefficient is 1 x 1
The type of sizing agent is not particularly specified as long as the relationship between the sizing agent and the amount is satisfied such that it is above 0-3. In any case, it is desirable that the material has high compatibility with the matrix. When the spreading coefficient is less than 1×10 −3 , the fibers within the tow are not sufficiently opened, which impairs the adhesion with the matrix resin, which is not preferable.

With sizing agent that satisfies the above conditions @Yang is Q, 1w
It is less than t%, preferably less than 0.01'llt%.

Sizing agent adhesion amount is JIS R760168, 2V
Measure using the acid washing method.

If the amount of sizing agent attached exceeds 0.1 wt%, the spreadability of the tow deteriorates and fibers locally adhere to each other, which tends to inhibit the penetration of the matrix resin into those areas. The tow is defibrated once with hot air, defibrated through a bar, or defibrated by hitting the fibers under tension, either singly or in combination, to achieve a spreading coefficient of 1 x 10-3. 0 if it can be raised to the level of
．． There is no problem even if more than 1 wt% of the sizing agent is attached. The sizing agent used here is bisphenol A diglycidyl ether or its reaction product with bisphenol 8, or the following general formula in which the glycidyl group is reacted with a polyether alcohol obtained from ethylene oxide, because it is easily compatible with the matrix resin. Such compounds are desirable.

Upper C Tomoe-δ Yo-Ikkimi When the water extractable coefficient of the present invention is greater than 2.0,
A layer of relatively weak bonding force is formed on the surface of the carbon fiber, and the matrix resin is bonded through this layer, so it is thought that the layer of weak bonding force is destroyed especially by impact force.

Therefore, it is preferable to further reduce this layer, and its level needs to be 2.0 or less as a water extractable coefficient.

In order to reduce the water extractable coefficient of carbon mmi, it is effective to perform a surface oxidation treatment on the carbon fiber after manufacturing it, and then wash it with water or a water wet solution having a pH of 4 to 12, for example. During this cleaning, it is effective to use ultrasonic cleaning in combination or to further heat it, and it is also effective to use dielectric h11 heat.

[Example of real curtain]

The present invention will be specifically described below with reference to Examples.

The post-impact compressive strength was measured by the following method.

In accordance with NASA RP 1092, a board with panel dimensions of 4" x 6" x 0.25" was fixed on a steel stand with a 3" x 5" hole, and a 1/2" R nose was placed in the center. A weight of 4.9 kg attached was dropped, and the thickness of the plate was 1.
After applying an impact of 15,001 bins per inch, the panel is subjected to a compression test to determine the post-impact compressive strength.

Example 1 Acrylonitrile 98wt%, methyl acrylate 1wt
%, specific viscosity with a composition of methacrylic M 1 wt% [
ηSt)]=0.20 was wet-spun using dimethylformamide as a solvent, then stretched 5 times on a hot water bath, washed with water, dried, and further stretched 1.3 times with dry heat at 170°C. Acrylic fibers having a fineness of 1.2 denier and having 6000 filaments were obtained.

The orientation degree of taIi determined by X-ray diffraction is 90.3
%Met.

This acrylic fiber was heated at 220℃-240℃-260℃
During the flame-retardant treatment by passing through a hot-air circulating type flame-retardant furnace with a temperature-controlled O file for 600 minutes, the fibers elongate by 15% due to the speed difference of the rotating rolls until the fiber reaches a density of 1.22 g/cm3. was applied, and then the speed of the rotating roll in contact with the fibers was fixed at a constant speed, thereby suppressing local shrinkage of the fibers and completing the flame-retardant treatment.

The flame-retardant fibers are then passed through a first carbonization furnace at 600°C in a pure N2 stream for 3 minutes, elongated by 10%, and then subjected to a second carbonization process in the same atmosphere with a maximum i0i temperature of 1200°C. Heat treated in a furnace under a tension of 400 parts g/denier, resulting in a tensile strength of 503 Kff/mar.
, elastic modulus 24 ton/mm2, density 1.7
A carbon fiber (I-a>) having physical properties of 9 (1/cc, 0.4 g/TrL) was obtained.

The carbon fibers obtained above were then heated to 1.8% by volume at 200°C.
After being allowed to stay in the tow state for 3 minutes in air containing 03,
iooom in a stainless steel perforated paper tube with an outer diameter of 70 mm.
After winding, it was left in clean water at a bath ratio of 1/20, and the water extract image @2.5.0.8.0.7.0.5 was obtained by changing the standing time.
1 n of each Leherno carbon 11 fiber (I-b) was prepared. Surface oxygen-containing functional walk of carbon fiber at this time (015/C1
,) was 0.15 to 0.20. Next, this carbon fiber was passed through a solution of Epicoat 834 (bisphenol A type epoxy resin manufactured by Yuka Shell Co., Ltd.) dissolved in methyl ethyl ketone to reduce the chance of sizing agent adhesion.
．． 07.0.2.0.5 each W (% carbon fiber (I-c)
I got it.

The obtained various carbon materials shown in Table 1 were
To 100 parts of the matrix resin methyl ethyl ketone solution (epoxy resin (III) (Epicote 828, manufactured by Shell Chemical Co., Ltd.) described in Example 1 of Publication No. 289, 9 parts of 4.4'diaminodiphenyl sulfone was added, and the mixture was heated with a shank. The mixture was placed in a container and polymerized for 4 hours with stirring at an internal temperature of 150°C. After polymerization, the mixture was discharged onto a thin film onto a water-cooled panel to stop the polymerization.
N-(3.
Add 3 parts of 4-dichlorophenyl)-N'-N'-dimethylurea and stir and mix at 50°C to make 1q of paste.
, 60 parts of this paste-like material was mixed with 40 parts of methyl ethyl ketone to form a homogeneous solution) and wound around a drum, dried, and then cut open.
A unidirectional prepreg (thickness: 145 s/m 2 , resin content: 33 wt%) was obtained.

This prepreg was laminated in an annular orientation of [+4510/-45/90] 4s and cured for 2vF at 180°C to obtain a composite panel.

The fiber volume content of the composite was as shown in Table 1. Thereafter, the compressive strength after impact was determined. The results are also shown in Table 1. From these results, it is clear that carbon fibers with a low water extractable coefficient, a large spreading coefficient, and a low amount of sizing agent attached provide high compressive strength after impact.

FIGS. 2 and 3 show electronic mirror photographs (each magnified at 900 times) of the fracture surfaces of the test pieces of the II post-compression test of Example 1 and Comparative Example 1. It is clear from this photograph that the BW properties (of the yarn and the matrix) vary greatly depending on the water-HBB extraction coefficient, and that those with a high water-extractable coefficient have low adhesion.

Examples 5 to 8, Comparative Examples 5 to 8 In Example 1, 2% lil was used as the carbon fiber.
'By passing 200 coulombs of electricity per gram of thread in a 1M aqueous solution, it is anodized and then washed with hot water to reduce the surface oxygen-containing functional group ffl (01,/C1,) from 0.18 to 0.
．． The results shown in Table 2 were obtained in the same manner as in Example 1, except that the composition of Example 4 of JP-A-59-215314 was used as the matrix resin.

Examples 9 to 12, Comparative Examples 9 to 12 The results shown in Table 3 were obtained in the same manner as in Example 1, except that the composition of Example 2 of European Patent Publication No. 133281 was used as the matrix resin.

Comparative Example 13 The carbon fiber (I-a) obtained in Example 1 was heated to 1.8
The tow was oxidized by being left in air containing 1% 03 by volume for 0.5 and 8 minutes, and then treated with clean water as in Example 1 to give a water extractable coefficient of 0.5. At this time, the amount of surface oxygen-containing functional groups (0, , / C1s) is 0, respectively.
．． It was 03.0.4. Next, after obtaining carbon fibers to which 0.01 wt% of the sizing agent of Example 1 was attached,
A composite was prepared in the same manner as in Example 1, and the compressive strength after impact wJ was determined.
(VF61%), 25 to 9/a+” (Vf60%
) T: Yes, and it is clear that sufficient performance cannot be obtained when the amount of surface oxygen-containing functional groups is low. It can also be seen that performance deteriorates when the temperature is too high.

Examples 13 to 16, Comparative Examples 14 to 17 In obtaining the carbon fiber (I-a) in Example 1, the tensile strength was 458 kg by setting the firing conditions to a maximum temperature of 1800°C in the atmosphere of the second carbonization furnace. /rItIR2,
Elastic modulus 30.2 ton/m2, density 1.7709/c
A carbon fiber having physical properties of 0.39 s/m and a basis weight of 0.39 s/m was obtained. This was mixed in an aqueous solution of 5% ammonium bicarbonate at 2 ml per gram of yarn.
After being anodized by flowing 50 coulombs of electricity, the surface after washing with hot water has a HM-containing functional base material 013/CIs of 0.
2-0.21 was obtained. The results shown in Table 4 were obtained in the same manner as in Example 1, except that the composition of Example 2 of JP-A-60-58424 was used as the matrix resin.

Example 17, Comparative Example 18 The same procedure as Example 1 and Comparative Example 1 was carried out except that the carbon fiber used in Example 1 and Comparative Example 1 was impregnated with the matrix resin of Example 8 of European Patent Publication No. 133281. A composite was prepared and a compression test was conducted after impact. The results are shown in Table 5.

[Brief explanation of drawings]

FIG. 1 shows the method of measuring the spread coefficient. Arrows indicate the direction of tow movement. 1: weight 2.3, 4: 50Φ roll 5: carbon fiber tow Figures 2 and 6 are electron micrographs of the particle structure of the fractured surface of the test pieces obtained in Example 1 and Comparative Example 1, respectively. (900 times each). The white portion at the lower left corner of each drawing indicates a length of 10μ.

Claims (3)

[Claims] (1) The amount of oxygen-containing functional groups on the surface (O_1_S/C_1_S) measured by X-ray photoelectron spectroscopy is 0.05 to
0.3, a water extractable coefficient of 2.0 or less, and a tow spreading coefficient of 1×10^-^3 or more. Carbon fiber for composite materials having excellent impact resistance. (2) The carbon fiber according to claim 1, wherein the amount of sizing agent deposited is 0.1 wt% or less. (3) Tensile strength is 250 kg/mm^2 or more, tensile modulus is 19 ton/mm^2 or more, and tensile elongation is 1.
The carbon fiber according to claim 1, characterized in that the carbon fiber content is 5% or more.