JP2002121295A - Carbon fiber-reinforced plastic and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To find a surface modification method capable of improving affinity between carbon fiber and a resin and provide a carbon fiber-reinforced plastic improved in adhesiveness by utilizing the above method. SOLUTION: The carbon fiber-reinforced plastic is characterized by using a carbon fiber having amino group on the surface as a filler. The method for producing the carbon fiber-reinforced plastic is characterized by bonding carbon fibers each having amino group on the surface with a curable plastic and curing the plastic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon fiber reinforced plastic and a method for producing the same, and more particularly, to a carbon fiber reinforced plastic using a carbon fiber having an amino group on its surface as a filler and a method for producing the same.

[0002]

2. Description of the Related Art With the rapid development of recent advanced technology fields, various materials are required to have higher functionality and higher added value. As a result, a single material is often unable to exhibit the required physical properties,
From such a viewpoint, a composite material obtained by combining two or more types of materials having different physical and chemical properties has attracted attention.

[0003] Fiber reinforced plastics occupy an important position as a composite material having both the high strength and high elastic modulus of fiber and the excellent properties of matrix resin such as light weight and toughness. ing. Above all, carbon fiber reinforced plastic (CFRP) using carbon fiber as a filler has been put to practical use in a wide range of industrial fields such as airplanes, building materials, tennis rackets and the like.
Hull, Translated by Hiroo Miyairi, Introduction to Composite Materials, (1984) Baifukan; Kensuke Okuda, Carbon Fiber and Composite Materials, (1984) Kyoritsu Shuppan).

In the case of a fiber-reinforced plastic in which different materials are combined, an interface always exists between the fiber and the matrix, and the characteristics of the interface may greatly affect the macroscopic characteristics of the material itself. For example, in the case of CFRP, there is a problem that the interface elasticity between the carbon fiber and the resin is low and peeling is likely to occur.

[0005] The adhesion between carbon fiber and plastic is
Surface condition of carbon fiber, such as surface functional groups (VJ Mimeau
lt, Fiber Sci. 4, (1971) 273; NL Weinberg, H. J
ager, J. Appl. Electorochem., 3, (1973); P. Ehrbu
rger, JB Donnet, Phil. Tras. R. Soc. Lon. 294,
(1980) 495; E. Fitzer, R. Weiss, Carbon 25, (1987)
455; Y. Sawada, Y. Nakanishi, T. Fukuda, Composite
s, 24, (1993) 19: F. Nakao, H. Asai, Sen-I Gakkaish
i, 49 (1993) 19)
33, (1976) 367), and attempts have been made to modify the carbon fiber surface by various methods in order to improve the adhesiveness. For example,
As a method for modifying the surface of carbon fiber, oxidation of the carbon fiber surface by electrolytic treatment (edited by the Society of Carbon Materials Science, New
An introduction to carbon materials, (1976) 367), coating and the like are known.

[0006] However, the surface modification of carbon fiber by the above-described method has not been able to clearly increase the adhesiveness between carbon fiber and plastic.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to find a surface modification method capable of improving the affinity between a carbon fiber and a resin, and to utilize the surface modification method to improve the adhesiveness of the carbon fiber. Is to provide plastic.

[0008]

SUMMARY OF THE INVENTION The present inventors have improved the adhesion between carbon fibers and plastics, and have improved the strength of C.
Intensive study was conducted to obtain FRP. In the course of the study, they came to realize that amino-based curing agents were used as epoxy resin curing agents, which are frequently used as CFRP matrices. The affinity between epoxy resins increases,
The idea was to improve the adhesion.

Then, when an amino group was actually introduced into carbon fiber and its strength and the strength when this was bonded to an epoxy resin were examined, it was found that both were excellent, and the present invention was found. completed.

That is, the present invention provides a carbon fiber reinforced plastic characterized in that carbon fiber having an amino group on its surface is used as a filler.

The present invention also provides a method for producing a carbon fiber reinforced plastic, which comprises bonding and curing a carbon fiber having an amino group on its surface with a curable plastic.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A carbon fiber having an amino group on its surface (hereinafter referred to as "amino-modified carbon fiber") used in the present invention is obtained by introducing an amino group into the surface of a general carbon fiber. Although the preparation of the amino-modified carbon fiber is not particularly limited, for example, JP-A-11-335
No. 617. That is, it is obtained by first causing concentrated nitric acid to act on carbon fibers to introduce a nitro group, and then reducing the nitro group to an amino group.

More specifically, preferably, nitro groups are introduced onto the surface of the carbon fiber by dropping fuming nitric acid over about 3 to 8 hours onto the carbon fiber suspended in a solvent such as acetic anhydride. can do. Since this reaction is an exothermic reaction, it is preferable to keep the temperature at 5 ° C. or lower during the reaction by water cooling or the like. After the end of the exothermic reaction, the treated carbon fiber is washed and dried to obtain a nitro group-introduced carbon fiber.

Next, the nitro group introduced on the surface of the carbon fiber is reduced to an amino group. This reaction is
It is preferably carried out by reacting a reducing agent containing a hydrosulfate such as sodium hydrosulfite in the presence of a solvent such as aqueous ammonia. The reduction is preferably performed at about room temperature with stirring for about 12 to 24 hours. After performing this reduction reaction, the target amino-modified carbon fiber is obtained by washing and drying.

In producing the amino-modified carbon fiber,
Examples of the carbon fiber used as a raw material include polyacrylonitrile-based carbon fiber, rayon-based carbon fiber, pitch-based carbon fiber, and the like, and the use of polyacrylonitrile-based carbon fiber is preferred. Further, the shape of the carbon fiber is more preferably a strand shape.

On the other hand, in the present invention, the curable plastic forming the matrix resin includes, for example, unsaturated polyester, epoxy resin and the like, and among them, the use of epoxy resin is preferable. Further, among the epoxy resins, a bisphenol A type liquid epoxy resin is particularly preferable.

In order to produce a carbon fiber reinforced resin using the amino-modified carbon fiber as a filler and a curable plastic as a matrix resin, a method known in the art can be employed. That is, it can be produced, for example, by stretching amino-modified carbon fibers in the form of a piece in a river shape, a mesh shape, or the like, injecting a curable plastic to which a curing agent is added, and causing a curing reaction.

As a curing agent for curing the curable plastic, polyamines such as triethyltetramine and aromatic polyether ketones such as polyether ether ketone are used. Epoxy resin is used as the curable plastic. In some cases, polyamines,
For example, the use of triethyltetramine is preferred.

In the production of the carbon fiber reinforced resin, the mixing ratio of the curable plastic and the curing agent is about 1 to 50 parts by weight, preferably about 5 to 20 parts by weight, per 100 parts by weight of the curable plastic. Is the ratio of

The curing reaction is carried out at 30 to 200
C., preferably at 40 to 150.degree. C. for 20 minutes to 3 hours, preferably about 2 hours. The heating reaction is also preferably performed stepwise, for example, 40 to 60 ° C.
After heating for 40 to 80 minutes, the temperature can be raised to about 100 ° C. and heating can be further continued for about 60 to 100 minutes to promote curing.

After the above-mentioned curing reaction is completed, the product is dried and taken out from a piece according to a conventional method to obtain a carbon fiber reinforced resin product.

[0022]

Next, the present invention will be described with reference to examples, but the present invention is not limited by these examples.

Example 1 Preparation of Amino-Modified Carbon Fiber: (1) Introduction of Nitro Group into Carbon Fiber A PAN-based strand-like carbon fiber (manufactured by Toho Rayon, diameter 7 mm) was used as the activated carbon fiber. Thus, a nitro group was introduced. That is, the activated carbon fiber
400 ml of acetic anhydride was added to 10.0 g, and the reaction solution was cooled with ice while stirring. While maintaining the temperature at 5 ° C. or lower, 100 ml of fuming nitric acid was added dropwise from the dropping funnel over 5 hours. Next, the temperature of the reaction solution was gradually raised to room temperature, and the reaction was allowed to proceed for 19 hours. After the reaction, the reaction solution was gently poured into 2 liters of ice water, and after heat generation was completed, washing by suction filtration was performed until the conductivity of the filtrate became 10 × 10 ⁻⁶ S / cm or less. Further, it was dried in vacuum at 110 ° C. for 24 hours, and activated carbon fibers (NO ₂ -C
F) was obtained.

(2) Reduction reaction of nitro group 28 to 30 g of 6.0 g of NO ₂ -CF obtained in the above (1)
% Ammonia water 24ml and ion exchange water 100m
and 150 ml of a 10% aqueous sodium hydrosulfite solution. After reacting while stirring at room temperature for 24 hours, washing by suction filtration was performed until the conductivity of the filtrate became 10 × 10 ⁻⁶ S / cm or less.
Furthermore, it was vacuum-dried at 110 ° C. for 24 hours to obtain activated carbon fibers (NH ₂ —CF) into which amino groups were introduced.

Example 2 Test for confirming introduction of amino group on carbon fiber surface: Example 1
Carbon fibers (NO) introduced with nitro groups on the surface by (1)
_2- CF) and carbon fibers (amino-modified carbon fibers / NH ₂ -CF) having amino groups introduced on the surface according to (2).
To confirm the introduction of each unit, check with XPS (Shimadzu Corporation AX
IS-HS). A1K as excitation X-ray source
α ray (1486.6 eV) was used. The results are shown in FIGS.

As is apparent from FIGS. 1 and 2, NO
_{In 2} -CF, a peak attributed to a C—N—O bond was observed at about 405 eV. Further, in NH ₂ —CF,
The peak (405 eV) attributed to the C—N—O bond decreased, and the intensity of the peak (400 eV) attributed to the C—N—C and C—N—H bonds increased.

Table 1 below shows the results of determining the intensity ratio of each peak to the peak attributed to the Cls orbital.

[0028]

[Table 1]

From these results, it was confirmed that a nitro group was introduced into the carbon fiber surface by the reaction with fuming nitric acid and an amino group was introduced by a reduction treatment using sodium dithionite. Further, as can be seen from the intensity ratio of the peak intensity attributed to Ols to the Cls peak, the oxygen content is increased by the nitration treatment, and the oxygen content is decreased by the amination treatment. This is because oxygen was oxidized by the nitric acid used at the time of nitration, and an oxygen-containing group was introduced into the carbon fiber surface.

Example 3 Single Fiber Tensile Strength Test: The tensile strength test of a single fiber was conducted according to JIS.
Performed according to R 7601. That is, a single fiber was carefully sampled from a carbon fiber strand so as not to damage the single fiber, and this was stuck to a paper frame. Furthermore, 10N
Attached load cell, gauge length 10mm, 20m
The test was performed 100 times for each of three conditions of m and 40 mm.

The tensile strength of the fiber is generally considered to follow the Weibull distribution. Conversely, if the result of the tensile test follows the Weibull distribution, it can be determined that the test method is appropriate. The probability cumulative distribution function F (σ) (probability that the breaking strength is smaller than σ) of the activated carbon fiber of length L breaking under the stress of σ is
When the tensile strength follows the Weibull distribution, it is expressed by equation (1) (W. Weibull, J. Appl. Mech., 9, (1951) 293).

[0032]

(Equation 1)

Where α and β are Weibull parameters,
L0 is a reference length, which is 1 m here.
By transforming equation (1), equation (2) is obtained.

[0034]

(Equation 2)

Therefore, the second term of the above equation is represented by the vertical axis (Y),
If a linear relationship is obtained when 1nσ is plotted on the horizontal axis (X), it can be determined that the tensile strength distribution follows the Weibull distribution, and the Weibull parameters α and β can be obtained from the slope and intercept of the straight line.

Unmodified carbon fiber (CF), NO ₂ -CF
FIGS. 3 to 5 show Weibull plots of single fiber tensile strengths for NH ₂ and NH ₂ -CF. The plot is 10, 2
The measurement was performed for each sample length of 0 and 40 mm. As is clear from the figure, the plot for each sample is almost a straight line, and it can be seen that the Weibull distribution is established.

The Weibull parameters α, β of each activated carbon fiber calculated from the slope and intercept obtained in FIGS.
Are shown in Table 2 below. The values of α and β slightly differ depending on the gauge length, but this is considered to be caused by the existence of multiple causes of fracture.

[0038]

[Table 2]

Since it was confirmed that the tensile strength of each carbon fiber followed the Weibull distribution, the relationship between the test length and the average tensile strength was plotted (FIG. 6). In each case, the tensile strength decreased as the fiber length increased. However, when the tensile strength was compared with the same sample length, it was found that there was almost no change before and after the surface modification. That is, it was found that the surface modification can be performed without reducing the tensile strength of the carbon fiber by applying the modification method of the present study.

Example 4 Production of Carbon Fiber Reinforced Plastic: (1) Preparation of Matrix Resin: In a plastic beaker, bisphenol-A type liquid epoxy resin and triethylenetetramine were mixed at a weight ratio of 100: 11.
Then, the matrix resin was obtained by leaving still in a vacuum device for 12 minutes while keeping the temperature at about 50 ° C. to remove bubbles.

(2) Production of carbon fiber reinforced plastic:
Create a Teflon specimens type shape shown in FIG. 7, this amino surface modified carbon fibers (NH ₂ -C
F) was stretched without slack, and both ends were temporarily fixed with an adhesive. Next, the mixed matrix resin was poured into a test piece mold, and both sides of the test piece mold were sandwiched between glass plates. This is a programmable precision temperature tester (Applied Giken Sangyo,
MT-311P) at 50 ° C for 60 minutes and at 100 ° C for 8 minutes.
The mixture was cured and dried for 0 minutes, taken out of the test piece mold, and a carbon fiber reinforced plastic (test piece) of the present invention was obtained. At the same time, carbon fibers (NO ₂ -C
With F) and unmodified carbon fiber (CF), the other is NH ₂
A carbon fiber reinforced plastic (test piece) was obtained in the same manner as in -CF.

Example 5 Tensile Test of Carbon Fiber Reinforced Plastic The tensile test of carbon fiber reinforced plastic was performed using a tensile tester attached to an optical microscope as shown in FIG. For observation of fiber breakage, use an optical microscope (Olympus, B
HT-113MD). Maximum 200kgf
A tensile load was applied to the test piece using a tension-compression dual-purpose small load cell (manufactured by Kyowa Dengyo Co., Ltd., DMP-600) capable of measuring up to and measuring the number of fiber breaks at each strain of 0.1%.
The strain is measured at a position where it does not hinder the internal observation of the test piece (KFG-2-120-, manufactured by Kyowa Dengyo).
Cl-11L1M2R).

(Results) Interfacial shear strength (τ) FIG. 4 is a diagram showing a matrix material and a single fiber embedded along its center line. Consider a case where a tensile load is applied in the fiber axis direction of the test piece shown in FIG. The tensile load is transmitted to the fiber through the fiber-matrix interface by the shear stress (σ) generated in the fiber axis direction. When the load reaches the tensile strength of a single fiber, the fiber breaks. Since the breaking strain of the matrix resin is much larger than that of the fiber, the breaking is repeated until the fiber length reaches the critical breaking length (Ιc). The shear stress at this time becomes the maximum shear stress (σf). Assuming that the shear stress at the interface is constant along the fiber length direction, the interface shear strength (τ), which is an index of the adhesive strength between the fiber and the matrix resin, is expressed by equation (3). . Kelly, WR Tyso
n, J. Mech. Phys. Solids. 13, (1965) 329).

[0044]

(Equation 3) Here, d is the diameter of the fiber, and Δav is the average breaking length.

Using the apparatus shown in FIG. 8, the breaking density of the fiber under a tensile load of the carbon fiber reinforced plastic was observed under a microscope and plotted against the magnitude of the strain. As an example, the results for NO ₂ -CF are shown in FIG. Rupture began to be observed when the strain exceeded about 1.3%, and the number of fractures did not increase any more when the strain exceeded 4%. Therefore, the average distance between the rupture points when a strain of 5% was applied was defined as the average rupture length (lav).

Unmodified C obtained by the single fiber buried test method
F, NO₂-CF and NH₂-Critical breaking length of CF
3 is shown. Critical breaking length, unmodified CF> NO₂-CF>
NH ₂−CF. Carbon fiber and matri
Critical breaking length becomes shorter as adhesive strength between resin
Therefore, the adhesive strength is unmodified CF> NO₂-CF> NH
₂-CF order, strong adhesion to aminated resin
You can see that it is getting worse.

Further, the interfacial shear strength of each sample was calculated by determining the tensile strength of the single fiber at the critical breaking length by extrapolating the straight line shown in FIG. 6 and substituting it into equation (3) (Table 3).

[0048]

[Table 3]

As a result, the interface shear strength was NH ₂ --CF
It was 33.6 MPa for the unmodified CF and 27.3 MPa for the unmodified CF, and it was found that the increase was about 1.3 times due to the introduction of the amino group. _Further, NO 2 -CF any interfacial shear force 3
It became 5.1 MPa, and showed a high value almost equivalent to NH ₂ —CF. From these results, it was found that functional groups were introduced into the carbon fiber surface by the surface modification, and the interaction between these functional groups and the epoxy resin improved the interfacial shear strength.

Relationship of Ols / Cls Ratio In general, it is said that as the oxygen content on the carbon fiber surface increases, the interfacial shear strength with the matrix resin increases. This is because it is considered that the adhesion at the interface between the carbon fiber and the epoxy resin contributes to the adhesion by the acidic functional group present on the carbon fiber surface reacting with the epoxy resin. Thus, FIG. 10 shows the relationship between the interfacial shear strength of each sample and the Ols / Cls ratio obtained from the XPS measurement. N
The improvement of the interfacial shear force in O ₂ —CF is considered to be due to the effect of the oxygen-containing group, since the oxygen content is much higher than that of the unmodified CF. However, a high oxygen content may cause oxidative degradation after a long period of time, even if the adhesion is improved immediately after sample preparation.

On the other hand, NH ₂ —CF is NO ₂ —
Although the oxygen content is much lower than CF (less than unmodified CF), the interfacial shear strength is improved. This is considered to be because the introduced amino group interacts with triethylenetetramine used as a curing agent for the epoxy resin, and the introduction of the amino group makes it easier for the epoxy resin to wet the carbon fiber surface. . From these results, it was found that the amino group introduced on the surface of the carbon fiber had an effect of improving the adhesiveness to the epoxy resin, similarly to the surface acidic functional group.

[0052]

As is apparent from the above results, a carbon fiber reinforced plastic having improved adhesion between a carbon fiber and a resin was obtained by introducing an amino group into the surface of the carbon fiber.

The carbon fiber reinforced plastic having the improved adhesive strength is less likely to peel off when a force is applied, and has higher strength than the conventional carbon fiber reinforced plastic, and is used for building materials, small boats, sports equipment and the like. It can be advantageously used as various materials.

[Brief description of the drawings]

FIG. 1 is a diagram showing confirmation of introduction of a nitro group into carbon fibers.

FIG. 2 is a diagram showing confirmation of introduction of an amino group into carbon fibers.

FIG. 3 is a view showing a Weibull plot of a single fiber tensile strength of an unmodified carbon fiber (CF).

FIG. 4 shows nitro group-introduced carbon fibers (NO ₂ -C
It is a figure which shows the Weibull plot of the single fiber tensile strength regarding F).

FIG. 5 shows carbon fibers (NH ₂ -C
It is a figure which shows the Weibull plot of the single fiber tensile strength regarding F).

FIG. 6 is a diagram plotting a relationship between a test length and an average tensile strength of each carbon fiber.

FIG. 7 is a view showing a test piece.

FIG. 8 is a diagram showing a tensile tester for carbon fiber reinforced plastic.

FIG. 9 shows carbon fibers (NO ₂ —CF) into which nitro groups have been introduced.
FIG. 4 is a diagram in which the breaking density of a fiber in a state where a tensile load is applied to a carbon fiber reinforced plastic using as a filler and the magnitude of strain are plotted.

FIG. 10 is a diagram showing the relationship between the interfacial shear strength of each sample and the Ols / Cls ratio determined from XPS measurement. that's all

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) D06M 11/64 D06M 101: 40 // C08L 63:00 7/00 A D06M 101: 40 (72) Inventor Hideki Sakai Kanagawa (72) Inventor Keiko Kawashima 1143-27, Hyuga-cho, Tatebayashi-shi, Gunma (72) Inventor Katsuhiro Nishiyama 2090-49, Fune, Tone-cho, Kitasoma-gun, Ibaraki Prefecture 3-6-18-610 Komone, Itabashi-ku, Tokyo F-term (reference) 4F072 AA01 AA02 AA06 AA07 AB10 AC15 AD23 AD28 AD38 AL02 AL04 AL17 4J002 CD001 CF211 FA046 FB076 FD016 4L031 AA27 AB01 BA15 BA17 CA02 CA03 DA21 4L037 AT02 CS03 FA01

Claims (10)

[Claims] 1. A carbon fiber reinforced plastic characterized by using a carbon fiber having an amino group on its surface as a filler. 2. The carbon fiber reinforced plastic according to claim 1, wherein the carbon fiber having an amino group on the surface is derived from polyacrylonitrile-based carbon fiber. 3. The carbon fiber reinforced plastic according to claim 1, wherein the carbon fibers having amino groups on the surface are in the form of strands. 4. The carbon fiber having an amino group on its surface obtained by treating a carbon fiber with concentrated nitric acid to introduce a nitro group and then reducing the nitro group. 3. The carbon fiber reinforced plastic according to claim 2. 5. The carbon fiber reinforced plastic according to claim 1, wherein the matrix resin is an epoxy resin. 6. A method for producing a carbon fiber reinforced plastic, comprising bonding and curing a carbon fiber having an amino group on its surface with a curable plastic. 7. The method for producing a carbon fiber reinforced plastic according to claim 6, wherein the curable plastic is an epoxy resin. 8. A method for producing a carbon fiber having an amino group on its surface, comprising treating a polyacrylonitrile-based carbon fiber with concentrated nitric acid to introduce a nitro group, and reducing the nitro group. 9. The method according to claim 8, wherein the concentrated nitric acid is fuming nitric acid. 10. The method for producing carbon fibers having amino groups on the surface according to claim 8, wherein the reduction is carried out with a hydrosulfate.