JPH0284577A - Surface-treated carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber, excellent in preservation stability and impregnating properties, etc., into thermoplastic resins and capable of providing composite materials with various synthetic resins excellent in mechanical properties by treating the surface of carbon fiber with a modified polyamide compound soluble in water and alcohols and a hydrophobic compound. CONSTITUTION:The objective carbon fiber obtained by, e.g., applying a modified polyamide compound, such as N-substituted alkoxymethylated polyamide (preferably 10-50mol% N-substituted alkoxymethylation degree and 5000-100000 molecular weight) in an amount of about 0.1-10wt.% (expressed in terms of solid based on the weight of carbon fiber) soluble in water and alcohols, to the carbon fiber preferably subjected to surface treatment with an acid by a roller method, etc., drying the fiber at 80-150 deg.C and then applying about 0.1-1wt.% combination of a hydrophobic compound, such as epoxy resin, with a low-boiling organic solvent, such as methanol or acetone, converted into the form of an emulsion thereto by the roller method, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to surface-treated carbon fibers suitable for producing carbon fiber-reinforced resin composite materials.

[Conventional technology]

Composite materials of carbon fiber and matrices such as various synthetic resins, metals, or ceramics have excellent mechanical properties such as specific strength and specific modulus, so they are used in aircraft parts, space equipment, precision machinery, tennis rackets, and golf shafts. It is used in a wide range of fields such as sports equipment.

By the way, various studies have been conducted on methods to improve carbon fiber reinforced composite materials to have higher strength and higher elasticity, but in general, in order to fully utilize the excellent properties of carbon fiber, carbon It is important to improve the affinity and adhesion between fibers and matrix, and from this point of view, many proposals have been made regarding surface treatment methods or treatment agents (i.e., sizing agents) for activating the surface of carbon fibers. .

[Problem to be solved by the invention]

Examples of such sizing agents include those using thermosetting resins such as epoxy resins, and those using thermoplastic resins such as polyester, polyamide, and polysulfone. It has the following drawbacks.

In other words, although sizing agents based on epoxy resins have excellent affinity and impregnating properties with thermosetting resins, they are poorly compatible with thermoplastic resins, so when a thermoplastic resin is used as the matrix resin, , the carbon fibers cannot be sufficiently impregnated into the matrix resin, and therefore the adhesion between the carbon fibers and the matrix resin in the composite material is poor.
The problem is that sufficient strength is not developed.

On the other hand, sizing agents for polyamides, copolymerized polyamides, etc. require the use of acidic organic solvents such as sulfuric acid as solvents, so it is difficult to remove the solvent after the sizing process, and if the organic solvent remains in the composite material. However, it has the disadvantage that the adhesion and impregnation properties between the carbon fibers and the matrix resin are insufficient.

Also, water and/or alcohol soluble modified polyamides, such as N-methoxymethylated nylon 6, α-(
N,N-dimethylamino)-ε-caprolactam (co)
It has also been proposed to use a polymer as a sizing agent, and the modified polyamide has good impregnating properties with thermoplastic resin, and when a thermoplastic resin is used as the matrix resin, it is difficult to bond between carbon fiber and matrix resin. However, these modified polyamides have high hygroscopicity and poor storage stability.

A drying process is required before molding the composite material, and if the drying conditions are strict, there are drawbacks such as fusion of the sizing agent and decreased fibrillation of the yarn.

The object of the present invention is to provide a surface-treated material that has excellent impregnation and adhesion with matrix resins, particularly thermoplastic matrix resins, has excellent storage stability, and can exhibit sufficient interfacial effects as a composite material. Our objective is to provide carbon fibers with improved carbon fiber properties.

[Means to solve the problem]

According to the present invention, carbon fibers are provided that are surface-treated with a water- and/or alcohol-soluble modified polyamide compound and a hydrophobic compound.

The present inventors have discovered that the water- and/or alcohol-soluble modified polyamide sizing agent described above has excellent sizing performance for carbon fibers, and particularly excellent impregnating properties for thermoplastic matrix resins.

By utilizing adhesive properties and suppressing hygroscopicity, storage stability has been improved. Moreover, as a result of intensive studies on obtaining surface-treated carbon fibers that exhibit excellent composite physical properties when made into composite materials, these requirements were met by two-stage surface treatment including treatment with the modified polyamide sizing agent. The present inventors found that the present invention was satisfied and completed the present invention.

In the present invention, the carbon fibers to be surface treated include various types of fibers such as pitch-based, acrylic-based, and cellulose-based fibers as precursors, which are first treated to make them infusible or flameproof using known methods. 800~ in active gas atmosphere
When fired at 3000° C., 1'I carbonized type and graphitized type are included, but it is particularly desirable to use one whose surface has been oxidized.

In the present invention, carbon fibers are first surface-treated with a water- and/or alcohol-soluble modified polyamide compound. The modified polyamide compound used in this primary surface treatment maintains the cohesiveness of the carbon fibers, has good impregnating properties and adhesive properties between the carbon fibers and the thermoplastic matrix resin, and exhibits sufficient interfacial effects as a composite material. This is the resin obtained.

Such water and/or alcohol soluble modified polyamide compounds include, for example, N-substituted alkoxymethylated polyamides and l modified with unsaturated carboxylic acids.
N- such as 1l-fi substituted alkoxymethylated polyamide
Modified polyamides having a 17-substituted alkoxymethyl group and dialkylamino groups such as α-(N,N-dimethylamino)-E-prolactam polymers and copolymers of the same with cyclic amides such as E-caprolactam Examples include modified polyamides.

Modified polyamides having an N-substituted alkoxymethyl group represented by N-methoxymethylated nylon 6 are homopolymers such as nylon 6, nylon 66, nylon 610, nylon 12, or nylon 6/66, nylon 66/ 610, nylon 6/11, nylon 66
/610/6 by treating a copolymer such as /610/6 with a mixture of formalin and alcohol in the presence of an acid.

In this case, the degree of N-[substituted alkoxymethylation is 10 to 50
M) Lt%, especially D25-35 mol%, molecular weight s, oo
o~ioo, ooo, especially 10,000~70,000
is preferably used.

If the degree of N-substituted alkoxymethylation is less than 10 mol 2, the solubility in alcohol will be significantly reduced, and if it exceeds 50 mol %, physical properties such as heat resistance and rigidity will be reduced, and water absorption will be reduced. This is undesirable because the polymer surface becomes sticky in the air. Also, the molecular location is s, ooo
If it is less than 100,000, the carbon fibers will have poor convergence and opening properties after surface treatment, and if it is more than 100,000, the viscosity of the treatment liquid will increase, making it difficult to handle.

Also preferably used is a modified N-substituted alkoxymethylated polyamide obtained by modifying this N-substituted alkoxymethylated polyamide with an unsaturated carbon-11 derivative such as an acrylic acid derivative. This modified N-substituted alkoxymethylated polyamide is usually obtained by graft polymerizing an unsaturated carbon v derivative onto an N-substituted alkoxymethylated polyamide, preferably in the presence of a radical reaction initiator. Examples of unsaturated carboxylic V derivatives in this case include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, chloronic anhydride, hymic acid, hymic anhydride, acrylamide, and methacrylamide. In addition, hydrophilic vinyl compounds such as hydroxyethyl methacrylate can be used. Acrylic acid derivatives, from the point of view of only one reactivity,
Especially acrylic acid.

Preferably, methacrylic acid, acrylamide, methacrylamide, etc. are used.

Modification with this unsaturated carboxylic acid derivative increases the solubility of the modified polyamide compound in water and alcohol. The content of the unsaturated carboxylic acid derivative in the modified polyamide compound is usually preferably 5 mol% or more. When the content of the unsaturated carboxylic acid derivative is less than 5 mol 2 , the effect on solvent solubility is very small.

Note that it is also possible to use a compound obtained by further treating the monosubstituted alkoxymethylated polyamide modified with an unsaturated carboxylic acid derivative with aqueous ammonia to form an ammonium salt.

(11) Modified polyamide having dialkylamino group Examples of modified polyamide having dialkylamino group include α-(N,N-dimethylamino)-E-caprolactam polymer and copolymerization thereof with cyclic polyamide such as ε-caprolactam. Examples include merging. This modified polyamide can be obtained by anionically polymerizing the α-substituted-ε-caprolactam alone or together with a comonomer.

In this case, the content of α-(N,N-dimethylamino)-ε-caprolactam is preferably 30 to 100 mol%. If the content of α-(N,N-dimethylamino)-ε-caprolactam is less than 30 mol%, the solvent solubility will be poor and the carbon fibers will become rough and hard after surface treatment. Further, the relative viscosity of the modified polyamide is preferably 1.5 or more and 3 or less.

If the relative viscosity is less than 1.5, the convergence and opening properties of the carbon fibers after surface treatment will be poor, and if the relative viscosity exceeds 3, the viscosity of the surface treatment liquid will increase, making handling difficult.

Note that the primary surface treatment in the present invention sufficiently achieves its purpose by using the modified polyamide, but the quaternized polyamide can also be used to improve solvent solubility,
In particular, since the water solubility is improved, it can be suitably used as a surface treatment agent. The quaternization reaction method includes a method in which the modified polyamide is dissolved in a suitable solvent or melted and then a quaternizing agent is added thereto, or a method in which the modified polyamide is present in the gas phase of the quaternizing agent. There are many ways to react.

As the quaternizing agent, usual ones such as protonic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, phthalic acid, and acrylic acid, and alkyl halogen compounds such as methyl iodide and methyl bromide can be used.

The above-mentioned modified polyamide compound is added to an aqueous solution such as water or alcohol in an amount of, for example, 0.1 to 30% by weight.

It is preferably dissolved at a concentration of 0.5 to 10% by weight and applied to the surface of carbon fibers in the form of an aqueous solution. Of course, there is no problem in including auxiliary agents and the like that are normally added to this surface treatment agent.

The method for attaching the modified polyamide compound to the carbon fiber surface is not particularly limited, and may include the usual dip method,
A spray method, a roller method, etc. can be adopted.

The amount of this modified polyamide compound attached to the carbon fibers is about 0.1 to about 10% by weight in terms of solid content per weight of carbon fibers.
Preferably it is 0.5 to 5% by weight. This amount of adhesion is approximately 0
．． If it is less than 1% by weight, the handling of the carbon fiber is insufficient, which may cause fuzz or yarn breakage during compounding.On the other hand, if it exceeds about 10% by weight, the carbon fiber will become coarse and hard. Therefore, it lacks flexibility.

Next, the carbon fibers coated with the modified polyamide compound are dried, but if the drying temperature exceeds 200°C, thermal deterioration of the modified polyamide compound tends to occur, so drying is usually carried out at 80-150°C. Good.

In this way, the carbon fibers to which the water- and/or alcohol-soluble modified polyamide compound has been applied are first wound up onto a bobbin, but of course the surface treatment causes the carbon fibers to exhibit excellent cohesiveness and to prevent fluff and threads. Demonstrates excellent effectiveness against cuts, etc.

The carbon fibers that have undergone the above primary surface treatment are then subjected to a secondary surface treatment using a hydrophobic compound, preferably in a separate step. Hydrophobic compounds used in this secondary surface treatment include epoxy resin, unsaturated polyester, vinyl ester, urethane acrylate, silicone oil,
Higher fatty acids and their metal salts, higher fatty acid esters, and various waxes are used.

Here, the epoxy resins include various known epoxy resins,
For example, (i) glycidyl ether type epoxy resin (bisphenol A, F, S type epoxy resin, novolac type epoxy resin, brominated bisphenol A type epoxy resin), (ii) cycloaliphatic epoxy resin, (m) glycidyl ester type Examples include epoxy resins, (iv) glycidylamine-based epoxy resins, (v) heterocyclic epoxy resins, and various other epoxy resins.

In addition, examples of higher fatty acids include stearic acid, palmitic acid, myristic acid, lauric acid, undecanoic acid, capric acid, pelargonic acid, caprylic acid, enanthic acid, caproic acid, butyric acid, and higher fatty acid metals. Examples of the salt include zinc stearate and calcium stearate.

Furthermore, examples of higher fatty acid esters include common waxes such as carnauba wax.

Candelilla wax, whale wax, shellac wax, rice bran wax, origin wax, beeswax, montan wax, cotton wax.

Wool wax is common. In addition, examples of pure products include various esters of the above-mentioned higher fatty acids and lower and higher alcohols. In addition, various glycerides which are esters with glycerin, natural oils and fats such as various vegetable oils and animal oils, and artificial oils and fats are also effective in the present invention. In addition to the various waxes mentioned above, examples of the wax include polyethylene wax, paraffin wax, and the like. Among these, liquid hydrophobic compounds are particularly preferred because they have a low water absorption rate even in small amounts and have little effect on the physical properties of the composite material.

These hydrophobic compounds include alcohols such as methanol and ethanol, acetone, and methyl ethyl! It is applied in the form of an emulsion to the surface of the carbon fibers which have been subjected to the primary surface treatment, in combination with a low boiling point organic solvent such as ketones such as -N or a suitable emulsifier. In this secondary surface treatment, it is necessary to minimize the adhesion μ of the hydrophobic compound to the carbon fiber in order not to impair the sizing performance of the modified polyamide compound obtained by the primary surface treatment. , particularly preferably about 0 per ton of carbon fiber weight
．． 1 to about 1 percent.

Further, the method of this surface treatment is not particularly limited, and ordinary dip methods, spray methods, roller methods, etc. can be employed.

In addition, when using an epoxy resin compound that is relatively compatible with the above-mentioned modified polyamide, it is also possible to mix it with the modified polyamide compound and carry out simultaneous treatment.

By applying the hydrophobic compound to the carbon fiber in this way, the hygroscopicity of the surface of the carbon fiber is sufficiently suppressed and storage stability is improved without impairing the original sizing performance of the modified polyamide compound. Therefore, when carbon fiber is used as a composite material, there is no need to dry it before molding.

The carbon fibers that have been surface-treated as described above are once wound up onto a bobbin, or are continuously sent as they are to a composite forming process.

The surface-treated carbon fiber of the present invention has excellent impregnability with various 71 helix resins, and has a remarkable effect of improving impregnability particularly with polyamide resins and polyimide resins.

As such polyamide resin, ordinary nylon-
6, Nylon-66, Nylon-610, Nylon-1
2. Nylon 4-6, etc., but there are also fully aromatic polyamides and polyimide resins with excellent heat resistance made from aromatic diamines and aromatic carboxylic acids or aromatic acid chlorides, such as polyamideimide, Examples include thermoplastic resins such as polyetherimide, thermosetting polyimides, and bismaleimides.

As mentioned above, the surface-treated carbon fibers of the present invention have excellent impregnating properties and adhesive properties with polyamide-based and polyimide-based 71-Lix resins.

Of course, it also exhibits excellent performance with other thermoplastic matrix resins, such as polyphenylene sulfide, polysulfone, polyethersulfone, polyetherketone, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, etc., and also with epoxy resins, The effect is also expressed on thermosetting resin matrix resins such as unsaturated polyester resins and polyphenol resins.

Methods for forming composite materials from such matrix resins and carbon fibers include Hunt lay-up method, filament winding method, pultrusion method, continuous fiber composite materials such as prepreg method, press autoclave molding method, sheet molding method ( Commonly employed methods include chopped short fiber composite materials such as SMC) method/press molding method and injection molding θ;. For example, injection molding.

The surface-treated carbon fiber bundle of the present invention is cut into 1 to 2 pieces with a cutter.
It is cut into 0 mm lengths, mixed with nylon powder 4f and pellets in a blender, kneaded in an extruder, and then injected into a mold and molded to obtain the desired molded product.

〔Effect of the invention〕

Since the surface-treated carbon fibers of the present invention are surface-treated with a water- and/or alcohol-soluble modified polyamide compound and a hydrophobic compound, the modified polyamide compound has excellent impregnating properties with thermoplastic resins. In addition to exhibiting sufficient adhesion, hygroscopicity is sufficiently suppressed and storage stability is excellent. Therefore, the resin composite material containing the surface-treated carbon fibers of the present invention is an extremely excellent mechanical material. , and does not require drying before molding.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Carbon fiber (Torayca T-3006; manufactured by Toshisha Co., Ltd.) was fired at 800°C for 5 hours in a nitrogen atmosphere and then subjected to continuous electrolytic oxidation treatment, followed by a single layer of N-methoxymethylated nylon-6. M
% methanol solution and passed through a drying oven at 100°C to perform a primary surface treatment.

Next, the fibers are treated with epoxy resin (
Epicoat 828; manufactured by Shell Chemical Co., Ltd.) 0.5% acetone? Immersion treatment using 8 liquids and drying were performed continuously.

Next, the surface-treated carbon fibers were placed in parallel in one direction, 1f
nylon-6 (A-103011R)
(Made by Unitika) were stacked in a sandwich shape, preheated in a hot press at 260°C for 5 minutes, and pressurized for 5 minutes to form a sheet approximately 1 m thick, containing carbon fiber, 1 lIt5
A composite material of 0 volume M% was obtained.

For curved surface treated carbon fibers: 23°C, humidity 65%
After being left in a constant temperature room for 24 hours, the surface treatment agent was dissolved in acetone and methanol, and the water content of the solution was determined by Karl Fischer method. In addition, regarding the obtained composite material, void ratio al and ASTM
A bending test was conducted on D-790.

The results are shown in Table-1.

Example 2 One surface was treated in the same manner as in Example 1, except that acrylic acid-modified N-methoxymethylated nylon-6 was used instead of N-methoxymethylated nylon-6 as the treatment agent for the first surface treatment. Obtaining the treated carbon fiber 5 and producing a composite material,
Furthermore, the water content of the surface-treated carbon fibers was measured, and the void ratio a+IJ of the composite material was determined and a bending test was conducted. The results are shown in Table-1.

Examples 3 to 13 As a secondary surface treatment agent, instead of epoxy resin, silicone oil was mixed with F-50, To"54 (hereinafter "manufactured by Nishinetsu Chemical Co., Ltd.); stearic acid, which is a higher fatty acid, and undecane mini. Stearic acid substituent, which is a higher fatty acid metal salt; carnauba wax, which is a waxing material ([]Ko Fine Products Co., Ltd.'
I! 2), Mold with 33PA (manufactured by Axel)
, Copper [EF5070 (manufactured by Kinube Shoji Co., Ltd.); The same procedure as in Example 1 was used except that one of the waxes Hoechstwax OP, Hoechstwax E (hereinafter referred to as Hoechst fp5), and 1IYPAc907 (manufactured by Bareco Co., Ltd.) was used. What about surface-treated carbon fiber? ! ) + and prepare a composite material, and further increase the water content M8111 of the surface-treated carbon fiber and the voids L of the composite material. Il'l constant and bending tests were performed. The results are shown in Table-1.

Examples 14 to 16 The surface-treated carbon fiber obtained in Example 1 was cut into short fibers with a length of 3 mm using a roving cutter manufactured by Sansui Giken Kogyo Co., Ltd. to obtain chopped fibers. Japan Steel Works Tεx
Using a twin-screw extruder (45mφD), 6-nylon (A-
1030BI (manufactured by Unitika Co., Ltd.) was introduced from a first-stage feeder and chopped fibers were introduced from a second-stage feeder to obtain carbon fiber/nylon compound pellets. When the compound 12 was produced, the chopped fibers penetrated well from the feeder, and no foaming such as air bubbles was observed in the pellets obtained, and a good compound was obtained.

The obtained compound was processed using an injection molding machine J7 manufactured by Japan Steel Works.
A test piece for physical property testing was prepared by injection molding using 5SA. For the obtained test piece, ASTM D
A bending test was conducted in accordance with -790.

The results are shown in Table-2.

Examples 17 to 19 Except for using the surface-treated carbon fiber obtained in Example 2,
In the same manner as in Examples 14 to 16, carbon fiber/nylon compound pellets 1- were mixed with 7:? A test piece was prepared and a bending test was conducted. The results are shown in Table-2.

Examples 20 to 22 Except for using the surface-treated carbon fiber obtained in Example 5,
Carbon fiber/nylon compound pellets were obtained in the same manner as in Examples 14 to 16, and test pieces thereof were prepared and subjected to ill lobe tests. The results are shown in Table-2.

Example 23 Bismaleimide (BT Resin IIT2562F; manufactured by Mitsubishi Gas Chemical Co., Ltd.) was impregnated into the surface-treated carbon fiber obtained in Example 1, and press molded at 180°C for 3 hours and 24 hours.
It was cured at 0° C. for 3 hours to obtain a unidirectional laminate. The physical property d1 determination result for the obtained laminate is Vf=58.5%
.

Void rate 0.1%, bending strength 178kg#++m,
III's elastic modulus was 13.8 ton/mm''.

Example 24 A compound with chopped fiber was obtained in the same manner as in Example 14, except that polyetherimide (Urethem 2100; manufactured by GE) was used instead of 6-nylon.

Thereafter, a test piece was prepared in the same manner as in Example 14,
When its physical properties were determined, vf=;30%.

Bending strength: 38, 0 kg/mm, bending modulus: 2
, 140 kg/rttn 2.

Comparative Example 1 Surface-treated carbon fibers were prepared in the same manner as in Example 1, except that the secondary surface treatment in Example 1 was not performed.
, and a composite material was produced, and the water content of the surface-treated carbon fiber was measured, and the composite material was subjected to void RS g+++ constant and bending tests. The results are shown in Table-1.

Comparative Example 2 Surface-treated carbon fibers were obtained and a composite material was produced in the same manner as in Example 2, except that the secondary surface treatment in Example 2 was not performed, and the water content of the surface-treated carbon fibers was 811 constant and void ratio of composite material 41 constant and bending tests were conducted. The results are shown in Table-1.

Comparative Example 3 Secondary surface treatment was performed using 0.5% F2O in silicone oil.
Surface-treated carbon fibers were obtained and a composite material was produced in the same manner as in Example 3, except that a 5.5% acetone solution of KF50 was used instead of the acetone solution. Furthermore, the water content of the surface-treated carbon fibers, the void ratio of the composite materials, and a bending test were conducted. The results are shown in Table-1.

Comparative Example 4 Surface-treated carbon fibers were obtained in the same manner as in Example 1, except that the secondary surface treatment in Example 1 was not performed. Next, using the surface-treated carbon fibers, carbon fiber/nylon compound pellets were obtained in the same manner as in Example 15, and test pieces thereof were prepared and subjected to a 111-degree test.

The results are shown in Table-2.

Comparative Example 5 A surface-treated carbon fiber was obtained in the same manner as in Example 2, except that the secondary surface treatment in Example 2 was not performed. Next, using the surface-treated carbon fiber, carbon fiber/nylon compound pellets 1- were obtained in the same manner as in Example 18,
A test piece was prepared and subjected to a bending test. The results are shown in Table-2.

From the results in Tables 1 and 2, it was found that the surface-treated carbon fibers of the present invention have sufficiently suppressed hygroscopicity and have excellent storage stability, and the resin composite material containing the carbon fibers has excellent storage stability. It can be seen that it has mechanical properties.

Patent applicant: Toa Fuel Industries Co., Ltd.

Claims (1)

[Claims] (1) A carbon fiber characterized by being surface-treated with a water- and/or alcohol-soluble modified polyamide compound and a hydrophobic compound.