JPH03113075A - Surface coating method for carbon fiber and surface-coated carbon fiber - Google Patents

Abstract

PURPOSE:To improve the coherence and the adhesivity to matrix resin of carbon fiber by attaching a polyamide resin to the surface formed by coating an oxidation-treated carbon fiber surface with a specific compound followed by heat-treatment to effect chemical bond formation. CONSTITUTION:A bis-(2-oxazoline) compound is attached to an oxidationtreated carbon fiber surface followed by heat treatment to effect chemical bond formation between said compound and the acidic polar group present on said fiber surface, thus forming the first layer. Thence, 0.5-10wt.%, based on the carbon fiber, of a polyamide resin is attached to the surface of the first layer to effect chemical bond formation between the residual unreacted ring of said compound and the functional group of said polyamide resin, thus giving the objective surface-coated carbon fiber. Thereby, the coherence and the adhesivity to matrix resin (esp. polyamide resin) of the carbon fiber can be improved, and when such carbon fiber is used as a reinforcing material, the properties of the resulting composite material can be markedly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for surface coating carbon fibers and surface-coated carbon fibers.

Due to its excellent mechanical properties such as specific strength and specific modulus, carbon fibers are used as materials for aviation and space, fishing rods, tennis rackets,
It is widely used as a reinforcing material for composite materials that are molded materials for golf shafts, machine parts, etc.

However, carbon fiber itself is rigid and brittle, and has poor bending and abrasion resistance, so it is prone to thread breakage and fluffing during its manufacturing and processing processes, and it also has poor adhesion to the matrix resin that makes up the composite material. It goes without saying that the use of carbon fibers that have broken or fluffed fibers, or that have poor adhesion to matrix resins in composite materials as reinforcing materials will have a serious negative effect on the physical properties of the composite materials. Nor.

Therefore, there is a need to improve the physical properties of composite materials by imparting cohesiveness and adhesiveness to matrix resins to carbon fibers and using such carbon fibers as reinforcing materials.

The present invention relates to a method for surface coating carbon fibers and surface-coated carbon fibers that meet such demands.

<Prior art and its problems> Conventionally, when carbon fibers are surface oxidized by a wet method or an electrolytic method, the surface of the carbon fibers is oxidized with yoC-0-, ::C-
CPr, which is known to generate acidic polar groups such as 02-COOH and chemically bond with epoxy resin.
ocess, Uses Carbon Fiber
Re1nf.

Plast, 1981. pp. 45-64), a sizing agent for carbon fibers that has been proposed to improve bending resistance and abrasion resistance by imparting cohesiveness to carbon fibers, as well as improve adhesion to matrix resins. Among them, there are many that take into consideration the reactivity with acidic polar groups as mentioned above (USP-4409288, USP-442051
7, USP-4167538).

However, methods for treating carbon fibers with these sizing agents containing epoxy resins are effective when the matrix resin is epoxy resin or unsaturated polyester resin, but are not effective when the matrix resin is polyamide resin. However, there is a problem in that the adhesion of the carbon H&male to the polyamide resin which is the matrix resin is poor. Means for applying N-methoxymethylated nylon 6 dissolved in a methanol solution to the surface of carbon fibers (JP-A-62
-7225) and means for applying water-soluble polyamide resin (
JP-A-6O-36510) has also been proposed, but these agents are difficult to chemically bond to the surface of carbon fibers under normal drying conditions, and are merely physically adsorbed to the surface of carbon fibers. Therefore, there is a problem that the carbon fiber does not effectively adhere to the polyamide resin that is the matrix resin. Resin compositions in which nylon 46 resin is blended with bisoxazoline compounds, pigments, and fibrous materials such as carbon fibers have also been proposed (Japanese Unexamined Patent Publication No. 1983
-243160), this was originally an attempt to extend the chain with a bisoxazoline compound in order to suppress the decrease in viscosity due to polymer depolymerization during thermoforming of nylon 46 resin, and the bonding of carbon fibers to matrix resin. It's not about improving your sexuality.

<Problems to be Solved by the Invention, Means for Solving the Problems> The present invention provides a method for surface coating carbon fibers and a surface-coated carbon am, which solves the conventional problems as described above and meets the above-mentioned demands. It is something to do.

However, as a result of intensive research from the above perspective, the present inventor found that
A first layer in which a bis-(2-oxazoline) compound was chemically bonded was formed on the surface of the surface-oxidized carbon fiber, and then a polyamide resin was chemically bonded to the surface of the first layer. By forming a second layer, the thus surface-coated carbon fibers have significantly improved adhesion to matrix resins, especially polyamide resins, and also improve the mechanical strength of moldings obtained from composite materials using such carbon fibers as reinforcement. They discovered that physical properties were significantly improved, and completed the present invention.

That is, the present invention involves attaching a bis-(2-oxazoline) compound to the surface of carbon fibers subjected to surface oxidation treatment, thereby connecting the acidic polar groups present on the surface of the carbon fibers with the bis-(2-oxazoline) compound. Form a first layer by chemically bonding,
Next, a second layer is formed by attaching a polyamide resin to the surface of the first layer and chemically bonding the unreacted 2-oxazoline ring remaining in the first layer with the functional group of the polyamide resin. The present invention relates to a method for surface coating carbon fibers, which is characterized in that the carbon fibers are coated with carbon fibers.

Carbon mm surface oxidized by wet method, electrolytic method, etc.
As mentioned above, acidic polar groups such as carboxyl groups and phenolic hydroxyl groups are generated on the surface of the compound, but the 2-oxazoline ring present in the bis-(2-oxazoline) compound is highly reactive with such acidic polar groups. The present invention utilizes the characteristics of such bis-(2-oxazoline) compounds.

In the present invention, first, a bis-(2-oxazoline) compound is attached to the surface of a carbon ta fiber that has been subjected to a surface oxidation treatment, and the acidic polar groups present on the surface of the carbon fiber are combined with the bis-(2-oxazoline) compound. The first layer is formed by chemically bonding the two.

In this case, the bis-(2-oxazoline) compound should be added in an amount of 2 to 10 times the total equivalent of the acidic polar group in order to fully chemically bond the two. It is preferable to attach 4 to 8 times the equivalent of bis-(2
It is more preferable to attach a compound (-oxazoline).

In the present invention, next, a polyamide resin is attached to the surface of the first layer to chemically bond the unreacted 2-oxazoline ring remaining in the first layer to the functional group of the polyamide resin. to form a second layer. In this case, it is preferable to attach a polyamide resin of 0.5 to 10% by weight to the carbon fibers, in order to sufficiently chemically bond the two, while also considering cohesiveness, yarn handling properties, etc. .0~
More preferably, 5.0% by weight of polyamide resin is deposited.

Specifically, the attachment of the bis-(2-oxazoline) compound and polyamide resin is achieved by preparing each treatment liquid, applying the prepared treatment liquid by spraying, squeezing with a roller, and preferably further heating at 90 to 120°C. This can be done by drying to a certain degree. In this case, each treatment liquid is prepared as a solution using an organic solvent or as an aqueous dispersion using a surfactant. Examples of organic solvents used here include acetone, methyl ethyl ketone, ethyl acetate, dichloromethane, and methanol. In addition, surfactants include polyoxyethylene (hereinafter abbreviated as POE) alkyl ether, POE alkyl phenyl ether, POE polybenzylated phenyl ether, etc., depending on the purpose of use of the resulting surface-coated carbon fiber. In addition to POE ether type nonionic surfactants, there are POE alkyl ester type nonionic surfactants.

After attaching the bis-(2-oxazoline) compound, the bis-(2-oxazoline) compound and the acidic polar groups present on the surface of the carbon fiber are sufficiently chemically bonded to form a strong first layer. In addition, after the polyamide resin is attached, the polyamide resin and the unreacted 2-oxazoline ring remaining in the first layer are sufficiently chemically bonded to form a strong second layer. It is preferable to perform a heat treatment, for example, a heat treatment for 150 to 15 minutes, after each of these is deposited.

In the present invention, the bis-(2-oxazoline) compound includes 1,3-phenylene-bis-(2-oxazoline), 1,4-phenylene-bis-(2-oxazoline), 2,2'-bis- (2-oxazoline), 1.4-
In addition to butylene-bis-(2-oxazoline), etc., 1,
3-phenylene-bis-(4-methyl-2-oxazoline), 1,4-phenylene-bis-(4-methyl-2-
Oxazoline) etc. can be used. Among these, 1
．． 3-phenylene-bis=(2-oxazoline), 1.
4-phenylene-bis-(2-oxazoline) or 2,
The synthesis of these bis-(2-oxazoline) compounds, preferably 2°-bis-(2-oxazoline), is described in "Kobunshi Kako J, 1975 (1), pp. 5-11.

In the present invention, the polyamide resin includes an aliphatic polyamide obtained by polycondensation of an aliphatic dibasic acid having 4 to 12 carbon atoms and an aliphatic diamine having 4 to 12 carbon atoms, and an ε having 4 to 6 carbon atoms. -Aliphatic lactam or α-amino substituted-(-Aliphatic polyamide obtained by ring-opening polymerization of aliphatic lactam, copolymer having both the polyamide obtained by the above polycondensation and the polyamide obtained by ring-opening polymerization as polymer blocks) In addition to the polyamide, part or all of the above aliphatic dibasic acids or aliphatic diamines may be substituted with α, ω-polyethylene glycol dicarboxylic acid or α,
Polyether polyamides obtained by replacing with ω-polyethylene glycol diamine, etc. can be used. Among these, poly ε-caprolatam, polyhexamethylene adipamide, polyhexamethylene sebacamide, and poly α-(N,N-dimethylamino)-ε-caprolatam are composed of two or more types of polymer blocks. Copolyamides are preferred (ELVAM from DuPont
IDE, AQ nylon A-90 manufactured by Toshisha, etc.), especially those whose melting point is 180'O or less and whose glass transition temperature is 3
0°C or less, and the number average molecular weight is 5ooo to 20
000 is preferred.

According to the surface coating method of the present invention, when a bis-(2-oxazoline) compound is attached to the surface of carbon fibers subjected to surface oxidation treatment and both are reacted, the acidic polar groups present on the surface of carbon M&fibers are Bis-(2-oxazoline)
The compound undergoes ring-opening addition to form a first layer in which the carbon fibers and the bis-(2-oxazoline) compound are chemically bonded. Then, when a polyamide resin is attached to the surface of the first layer and both are reacted, the 2-oxazoline ring remaining in the first layer and the carboxyl group or amino group existing as an end group of the polyamide resin are combined. A chemically bonded second layer is formed. Thus, the outermost second polyamide resin coating layer and the central carbon fiber are chemically bonded through the middle layer, the first bis-(2-oxazoline) compound coating layer. . Therefore, the surface-coated carbon fiber obtained by the present invention exhibits good adhesion to matrix resins, especially matrix resins mainly composed of 6-nylon and 6.6-nylon, and has good coherence and thread handling properties. This also results in better sex.

Examples will be given below to make the structure and effects of the present invention more concrete, but the present invention is not limited to these Examples.

<Examples, etc.> Preparation of fist treatment liquid A-1 1.3-phenylene-bis-(2-oxazoline)1.
5 kg, boriogyshiethylene (30 mol) as a dispersant
Tribenzylated phenyl ether 100g and water 3.7g
Wet-type crusher (manufactured by Igarashi Kikai Seizo Co., Ltd. (7) ULTRA
-VI SCO-MI LL) and subjected to wet pulverization using glass beads as rigid media to obtain 28.3% by weight of l,3-phenylene-bis=(2-oxazoline).
A stable aqueous suspension was prepared containing: The average particle size of suspended particles in this aqueous suspension was 0.35 gm. This aqueous suspension was diluted with water and 1,3-phenylene-bis-(
The treatment liquid A-1 was prepared by reducing the content of 2-oxazoline to 6% by weight, and was used in the following treatment.

Preparation of dispute resolution solution B-1 Polycaprolactam/polyhexamethylene adipamide/
A ternary block copolyamide consisting of polyhexamethylene sebacamide (ELVAMIIDE8 manufactured by DuPont)
063, melting point 157°C) in methanol/water = 8
It was dissolved in 96 parts by weight of 5/15 (weight ratio) and used as treatment liquid B-1 in the following treatment.

・Example 1 Surface oxidized carbon fiber (3000 filament,
Acid value 3.2) 30g was immersed in treatment liquid A600, and wet pick up amount (wet pi
ck-up amount) is 50% by weight (the target solid content adhesion amount as a bis-(2-oxazoline) compound is 3% by weight)
(calculated from the increase in dry weight), and the number of adhesion equivalents calculated from the surface acid value of the carbon fiber was 5 times equivalent). Then, the carbon fibers treated with treatment solution A were heated at 90°C
The carbon fibers were dried with hot air for 0 minutes and further heat-treated at 160° C. for 10 minutes, and the surface acid value of the carbon fibers at this stage was measured by the method described below.

Next, the carbon fibers after heat treatment were treated with treatment liquid B600IIfL.
The wet pick-up amount is 40% by weight based on the original carbon w1 fiber (the target solid content adhesion amount as a polyamide resin is 1.6% by weight (calculated from the increase in dry weight)). It was attached like this. The carbon fibers treated with treatment solution B were then dried with hot air at 1O5°C for 5 minutes.

The thus surface-coated carbon fiber strand was cut into 6 ml fiber lengths using a guillotine cutter to obtain chopped strands, which were subjected to the evaluation described below. The treatment details and evaluation results are shown in Table 1.

・Examples 2 to 5, Comparative Examples 1 to 2 Carbon fibers subjected to surface oxidation treatment were treated in the same manner as in Example 1 using treatment liquid A-1 and treatment liquid B-1 with the contents listed in Table 1. A surface-coated carbon fiber strand was obtained, further made into a chopped strand, and subjected to the evaluation described below. The treatment details and evaluation results are shown in Table 1.

...Method for measuring surface oxidation of carbon fibers Disperse 0.5 g of carbon fibers in neutral ethanol water (95% by volume), titrate with N150 aqueous potassium hydroxide solution using phenolphthalene as an indicator, and add acid according to the usual method. The value was calculated.

Evaluation method: Chopped strand bundled state The carbon fiber strand was cut into a length of 6 cm with a guillotine cutter, and the bundled state was evaluated on the following three levels.

3: No splitting even after cutting 2: Split into 2-3 pieces 1: Split into pieces...Fiber pole formation rate (weight %) Chopped strand 20 parts by weight and 6.6-nylon pellets 80 parts by weight were charged into a V-type blender and mixed at 45 rpm for 10 minutes, and the amount of flocculent carbon fibers (% by weight) was expressed relative to the amount of chopped strands charged. When many fiber poles occur, processability deteriorates and the physical properties of the composite deteriorate.

...Measurement of tensile strength and bending strength 120 parts by weight of chopped trough and 80 parts by weight of 6,6-nylon resin were tri-blended in a V-type blender,
The obtained blend was cross-extruded using an extruder to produce pellets. The pellets were then injection molded using an injection molding machine to obtain a molded product, and the tensile strength and bending strength of this molded product were measured.

Table 1 Note: In Table 1, House 1: Wet kick-up amount Paddy: Solid content adhesion amount 3: Bis=(2-oxazoline) compound adhesion amount Bundle 4:
The adhesion equivalent of the bis(2-oxazoline) compound is 1 to 3 and the fiber pole formation rate is % by weight, and the tensile strength and bending strength are kg/cm2.

These are the same in Table 2.

・Preparation of treatment liquid A-2 1. Same as treatment liquid A-1 except that 1,4-phenylene-bis-(2-oxazoline) was used instead of 3-phenylene-bis-(2-oxazoline). A treatment liquid A-2 was obtained. Furthermore, it is water-based! The average particle size of the suspended particles in the IA suspension was 0.43 gm. - Preparation of treatment solution B-2 A block copolymer consisting of α-(N,N-dimethylamidium/)-(-caprolactam/ε-caprolactam) polyamide(
AQ nylon A-90 manufactured by Toshisha, Tg 15° C1 Softening point 100-110° C.) 4.9 Polyoxyethylene (6 mol) nonylphenyl ether as a heavy part and wetting agent 0
．． 1 m by weight was dissolved in 95 parts by weight of water, and this was added to treatment liquid B.
-2.

・Examples 6 to 9, Comparative Examples 3 to 4 Carbon fibers subjected to surface oxidation treatment were treated in the same manner as in Example 1 using treatment liquid A-2 and treatment liquid B-2 with the contents listed in Table 2. A surface-coated carbon fiber strand was obtained, further made into a chopped strand, and subjected to the above-mentioned evaluation. The treatment details and evaluation results are shown in Table 2.

Table 2 Note) In Table 2, Book 5: Adhesive amount of polyamide resin (wt%) <Effects of the invention> As explained above, the present invention has the following characteristics: In addition to improving the adhesion to matrix resins, particularly when used as a reinforcing material for composite materials using polyamide resin as the matrix resin, significantly improving the physical properties of molded products obtained from the composite materials. It has the effect of being able to.

Claims (1)

[Claims] 1. Bis-(2-
A first layer is formed by attaching a bis-(2-oxazoline) compound and chemically bonding the acidic polar group present on the surface of the carbon fiber with the bis-(2-oxazoline) compound. A second layer is formed by attaching a polyamide resin to the surface and chemically bonding the unreacted 2-oxazoline ring remaining in the first layer to the functional group of the polyamide resin. Carbon fiber surface coating method. 2. The method for surface coating carbon fibers according to claim 1, wherein the carbon fibers are chemically bonded by heat treatment. 3. The method for coating the surface of carbon fibers according to claim 1 or 2, wherein a bis-(2-oxazoline) compound is attached to the surface of the carbon fiber in an amount of 2 to 10 times the equivalent of the total amount of acidic polar groups present on the surface. . 4. 0.5 to 10% by weight of carbon fiber on the surface of the first layer
4. The method for coating the surface of carbon fibers according to claim 1, 2 or 3, wherein the polyamide resin is attached. 5. The bis-(2-oxazoline) compound is 1,3-phenylene-bis-(2-oxazoline), 1,4-phenylene-bis-(2-oxazoline) or 2,2'-bis-(2-oxazoline). 5. The method for surface coating carbon fibers according to claim 1, 2, 3 or 4. 6. The polyamide resin is poly ε-caprolactam, polyhexamethylene adipamide, polyhexamethylene sebacamide, and poly α-(N,N-dimethylamino).
Claims 1, 2 and 3 which are copolyamides consisting of two or more polymer blocks selected from -ε-caprolactam.
The method for surface coating carbon fibers according to , 4 or 5. 7. Carbon fiber whose surface is coated by the surface coating method according to claim 1, 2, 3, 4, 5 or 6. 8. The carbon fiber according to claim 7, which is a reinforcing carbon fiber for a matrix resin containing 6-nylon or 6,6-nylon as a main component.