JP3048481B2 - Bundled carbon fiber, method for producing the same, and carbon fiber reinforced thermoplastic resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reinforcing material for a thermoplastic resin.
Carbon fiber useful as a material, a method for producing the same, and
The present invention relates to a carbon fiber reinforced thermoplastic resin .

[0002]

2. Description of the Related Art In recent years, a fiber-reinforced molding material obtained by mixing and dispersing carbon fibers in various matrices has been known to have excellent properties of carbon fibers, such as high strength, high rigidity, low specific gravity, high electric conductivity, and low thermal expansion. Due to its high modulus and high wear resistance, it is expected to be used in a wide range of applications, and is attracting attention as an industrially important material.

[0003] Usually, carbon fibers are bundles composed of hundreds to millions of extremely fine fibers. When the carbon fibers are mixed and dispersed in various matrices to obtain a fiber-reinforced molding material, the carbon fibers are required to be made of carbon fibers. In order to facilitate the handling of the carbon fiber and to enhance the workability in the mixing and dispersing processes, a short carbon fiber obtained by bundling a large number of fine carbon fibers with a sizing agent in advance and then cutting them is used.

[0004] In such a case, if the short carbon fibers bundled by the sizing agent are not sufficiently bundled, various problems occur in the process of mixing and dispersing in the matrix resin. Fiber pills are formed, and the fibers tend to open and become cotton-like due to friction with the resin. As a result, clogging occurs in the supply process, making it impossible to supply quantitatively and making it impossible to disperse fibers uniformly in the matrix. In other words, there are problems such as difficulty in obtaining a resin composition constantly and a decrease in productivity. Therefore, in order to obtain a carbon fiber reinforced molding material of high quality efficiently, short carbon fibers sized with a resin having high convergence must be used.

In addition, the sizing agent has the function of enhancing the convergence of the fibers, and at the same time, increasing the interfacial bonding force between the carbon fibers and the matrix, increasing the breaking strength of the fiber-reinforced resin composite material, and improving the reinforcing effect. It is also required to work to enhance it. Therefore, the sizing agent for short carbon fibers must be excellent in sizing properties and physical properties of molded articles, and must be capable of obtaining slivered carbon short fibers.

[0006]

Conventionally, in a polycarbonate resin reinforced with short carbon fibers, a thermoplastic polyurethane resin, an epoxy resin, a nylon resin or the like has been used as a sizing agent for the short carbon fibers. Polycarbonate resin has high heat resistance, so when extruding during kneading and mixing of reinforcing fiber materials, the temperature of the extruder is high, the sizing agent for short carbon fibers causes thermal decomposition, and the decomposition products are extruded. There are problems such as clogging the vent.

Also, in the molding process, the sizing agent of the short carbon fiber is thermally decomposed due to the similarly high injection molding temperature, and these decomposed products accumulate in the mold and time is required for cleaning. In addition, the productivity is reduced, and the decomposed product adheres to the surface layer of the molded product, resulting in poor appearance and increased occurrence of defective products. Furthermore, the low-decomposition products in which the sizing agent is decomposed lower the molecular weight of the polycarbonate resin and change the molding conditions, so that molding cannot be performed stably, resulting in problems such as reduced productivity.

[0008] Short carbon fibers sized with a polyurethane resin are made of a urethane resin having flexibility and elasticity, which is difficult to obtain with other resins, because it forms a strong film, so that it has a strong convergence and excellent extrudability. Becomes Furthermore, since the urethane strong coating covers the surface layer of carbon fiber,
Even during kneading in an extruder, the urethane coating protects the carbon fibers and prevents breakage of the fibers, so that the length of the carbon fibers in the molded product is kept long, and as a result, the physical properties of the molded product are significantly improved.

It is generally considered that the mechanical properties of a molded article are improved by increasing the wettability and interfacial bonding strength between the carbon fiber and the matrix. On the other hand, another purpose of using carbon fibers is to improve the conductivity of a molded article.
However, contrary to the mechanical properties, the conductivity increases as the wettability between the carbon fiber and the matrix decreases. This is because when the wetting becomes better, the wet resin covers the surface layer of the carbon fiber, which forms an insulating coating layer and lowers the conductivity. In other words, reducing the wettability and bringing the carbon fibers into bare contact with each other as much as possible will improve the conductivity.

Therefore, it has been extremely difficult to find a sizing agent which simultaneously satisfies both the opposite properties of mechanical properties and conductivity. However, polyurethane resin is a very excellent sizing agent as a sizing agent for short carbon fibers, because by preserving the fiber length in a molded article for a long time, it is possible to improve both mechanical properties and conductivity, which are contradictory properties. .

However, since the polyurethane resin has a lower thermal decomposition temperature than a sizing agent such as epoxy, it has been difficult to use it with a polycarbonate resin. Therefore, in order to make use of the excellent properties of polyurethane resin, it is desirable to reduce the total amount of thermal decomposition by improving the heat resistance and increasing the convergence to reduce the sizing amount. It is rare.

On the other hand, the epoxy resin has good wettability with carbon fibers, improves the adhesiveness between the carbon fibers and the matrix, and improves the physical properties of molded articles, particularly mechanical strength. However, the epoxy resin has too good wettability, and conversely lowers the conductivity of the molded product, and is inferior in the sizing agent's focusing ability as compared with the urethane resin. In order to maintain the convergence of short carbon fibers, a large amount of sizing is required, which causes a problem that the amount of thermal decomposition increases in proportion to the sizing amount.

[0013]

SUMMARY OF THE INVENTION The present invention has solved the above-mentioned problems. That is, the present invention provides the following (1) to
It is as (3). (1) Polyurethane resin and epoxy resin become carbon fiber
0.2 to 3% by weight of the
Bunched charcoal with polyurethane resin crosslinked by hardener
Raw fiber. (2) The mixing ratio of the polyurethane resin and the epoxy resin is 2
After contacting or dipping the carbon fiber in an aqueous emulsion of / 8 to 7/3, the mixture is heated and the polyurethane resin is bridged with a curing agent.
A method for producing bundled and bundled carbon fibers. (3) Polyurethane resin and epoxy resin become carbon fiber
0.2 to 3% by weight of the
Bunched charcoal with polyurethane resin crosslinked by hardener
5-50% by weight of short carbon fiber obtained by cutting raw fiber and heatable
Carbon fiber reinforced thermoplastic containing 95 to 5% by weight of plastic resin
Resin.

The sizing agent in the present invention is a sizing agent obtained by mixing a thermosetting polyurethane resin and an epoxy resin. The polyurethane resin is cured with a curing agent to improve heat resistance, suppress the occurrence of thermal decomposition of urethane during extrusion and molding, and the cured polyurethane resin also improves the convergence of fibers. Thus, bundled carbon short fibers can be obtained with a small sizing amount, and the amount of thermal decomposition can be reduced in proportion to the reduced sizing amount.

Further, by mixing the thermosetting polyurethane resin and the epoxy resin, the convergence of the short carbon fibers is improved as compared with the case where each is used alone, so that the sizing amount can be further reduced, and the extrusion and molding can be performed. The amount of thermal decomposition during processing can be significantly reduced.
Hereinafter, the present invention will be described in detail.

The polyurethane resin used in the present invention is not particularly limited, and is at least one of isocyanates having two or more isocyanate groups in the molecule and at least one of polyols having two or more hydroxyl groups in the molecule.
Known ones obtained by reacting the species can be used. As isocyanates, 1,6-hexane diisocyanate, 4,4'-diphenylmethane diisocyanate,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, 4,
4'-dicyclohexylmethane diisocyanate, 4,
4'-hydroxylated diisocyanate, isophorone diisocyanate, 1,5-naphthalenediisocyanate, 4,
4'-diphenyl diisocyanate, phenylene 1,4
-Diisocyanate, phenylene 2,6-diisocyanate, 1,3,6-hexamethylene triisocyanate and the like.

The polyols include ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, 1,4-butanediol, 1,6-
Glycols having two alcoholic hydroxyl groups, such as hexanediol, diethylene glycol, dipropylene glycol, polycarbonate diol, neopentyl glycol, alkylene oxide adducts of bisphenols and alkylene oxide adducts of hydrogenated bisphenols, polyethylene glycol, and polypropylene glycol Polyether diols such as polyoxytetramethylene glycol, polyethylene adipate, polypropylene adipate, polybutylene adipate, polytetramethylene adipate, polypentamethylene adipate, polyhexamethylene adipate, polyester diols such as polycaprolactone diol, and trimethylolethane , Trimethylolpropane, glycerin, pentaerythri Polyhydric alcohols having an alcoholic hydroxyl group, such Lumpur 3 or more can be mentioned.

Among them, preferred polyols are polyether diols and polyester diols. As a curing agent for the polyurethane resin of the present invention, an isocyanate, preferably a blocked isocyanate can be used. As the blocked isocyanate, the isocyanates exemplified above can be used.

Examples of the blocking agent include alcohols, phenols, ε-caprolactam, oximes, active methylenes, mercaptans, amines, imides, acid amides, imidazoles, ureas, carbamates and imines. , Sulfites and the like are used. The amount of the blocked isocyanate is preferably such that the NCO group of the polyurethane resin is equivalent to the urethane group of the blocked isocyanate. Therefore, the polyurethane resin crosslinked with the blocked isocyanate is a so-called thermosetting polyurethane resin having NCO / OH> 1. It is.

In addition, by using a blocked isocyanate as a crosslinking agent for a polyurethane resin, a sizing agent for an aqueous emulsion can also be used, and there is no need to recover a solvent as compared with a solvent-based one, which is economical and has no danger. There are advantages such as no pollution for environmental problems. Further, in order to accelerate the crosslinking reaction, it is also preferable to use a catalyst, for example, triethylamine, triethylenediamine, tin octylate, dibutyltin dilaurate, 1,3-diacetoxytetrabutylstannoxane and the like are added to the emulsion solution. Is also good.

The epoxy resin used in the present invention is bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak type epoxy resin, resol type epoxy resin, brominated epoxy resin, glycidylamine type epoxy resin and the like. In particular, in order to effectively exert the present invention, it is preferable to use a mixture of two or more epoxy resins having different molecular weights.

The preferred molecular weight of the epoxy resin used in the present invention is in the range of 800 to 5000, more preferably in the range of 900 to 4000. When the molecular weight is less than 800, it is difficult to obtain the effect of improving the convergence of short carbon fibers by mixing with the thermosetting polyurethane resin, and when it exceeds 5,000, the physical properties of the obtained short carbon fiber reinforced molding material may be reduced. .

In order to coat the carbon fiber of the present invention with a sizing agent, for example, roving of the carbon fiber is carried out in a solution obtained by mixing an aqueous emulsion of a polyurethane resin, an aqueous emulsion of a blocked isocyanate, and an aqueous emulsion of an epoxy resin. Contact or soak,
Conventionally known methods, for example, hot air drying, infrared drying, microwave drying, etc., heat-treated, the polyurethane resin coated on the surface of the carbon fiber is cross-linked with blocked isocyanate, thermosetting polyurethane resin and epoxy resin To obtain a coated carbon fiber.

The mixing ratio of the thermosetting polyurethane resin and the epoxy resin as the sizing agent for short carbon fibers used in the present invention is preferably such that the thermosetting polyurethane resin is 20 to 70% by weight. If the thermosetting polyurethane resin is less than 20% by weight, the amount of the thermosetting polyurethane resin having excellent convergence may decrease. On the other hand, when the amount of the thermosetting polyurethane resin exceeds 70% by weight, the amount of thermal decomposition generated during injection molding increases, which may cause a decrease in the molecular weight of the matrix resin.

A more preferable mixing ratio of the thermosetting polyurethane resin and the epoxy resin is 30 to 65% by weight of the thermosetting polyurethane resin. The coating amount of the sizing agent of the present invention needs to be in the range of 0.2 to 3% by weight based on the weight of the carbon fiber. If this amount is less than 0.2% by weight, the short carbon fiber convergence is insufficient and the workability during extrusion is poor. If the sizing amount exceeds 3% by weight, the amount of thermal decomposition at the time of extrusion and molding is increased, and the productivity is reduced, and the molecular weight and mechanical properties of the obtained molded product are reduced, and the effect of the present invention is sufficiently improved. Not demonstrated.

Particularly preferred coating amounts are in the range from 0.3 to 2.5% by weight. In the present invention, the carbon short fiber used as a material is not particularly limited, and various known carbon fibers, for example, carbonaceous fiber or graphite produced using rayon, polyacrylonitrile, pitch, lignin, hydrocarbon gas and the like are used. And metal-coated carbon fibers obtained by coating them with a metal. Preferably, carbon fibers or graphitic fibers obtained from polyacrylonitrile are used.

It is an object of the present invention to provide a bundle of short carbon fibers in this way, but other fillers used in fiber-reinforced molding materials, such as glass fibers, aramid fibers, silicon carbide fibers, The present invention can be applied to metal fibers, boron fibers, and the like. In order to produce a fiber-reinforced molding material using the bundled short carbon fibers of the present invention, a known method for producing a glass fiber-reinforced molding material can be applied.

For example, a carbon fiber reinforced molding material can be manufactured by melt-kneading the cut bundled carbon short fibers with a matrix resin using an extruder. In the molding material, as a filler, other than the short carbon fiber bundle, for example, glass, calcium carbonate, metal oxide,
If necessary, a powdery or flake-like additive such as carbon black may be contained.

The matrix resin used for the carbon fiber reinforced molding material is generally commercially available polycarbonate, polyamide, polyphenylene ether, polyoxymethylene, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyolefin, ABS resin. , Polyether, polyether ketone, polyimide, polysulfone,
Known matrices such as polymers such as polyethersulfone, polyurethane, phenolic resin, and epoxy resin, and copolymers thereof can be given.

Particularly, a polycarbonate resin, a thermoplastic polyester resin, a polyoxymethylene resin, and a polyamide resin are preferable because they significantly improve the mechanical properties and conductivity of a molded product. Furthermore, the sizing agent used in the present invention has the advantages of suppressing a decrease in the molecular weight of the polycarbonate resin at the time of molding the polycarbonate resin, stably producing a molded product, and eliminating the decrease in physical properties of the molded product.

The polycarbonate resin is prepared by a method similar to the conventional method for producing a polycarbonate resin, that is, by reacting an aromatic dihydroxy compound with phosgene or a carbonic acid diester. In this case, as the aromatic dihydroxy compound, 2,2-bis (4-hydroxyphenyl)
Propane (generic name bisphenol A), tetramethylphenol A, tetraethyl bisphenol A, tetrabromobisphenol A, bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl)
Ethane, 1,1-bis (4-hydroxyphenyl) propane 1,1-bis (4-hydroxyphenyl) butane,
1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 2,2-bis (3,5-dibromo-4-
(Hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfide, bis (4-hydroxyphenyl) sulfone and the like.

Particularly preferred polycarbonate resins are
2,2-bis (4-hydroxyphenyl) alkane-based,
Particularly, it is a polycarbonate containing bisphenol A as a main component. Average molecular weight 15,000-100,000
Are preferred.

[0033]

The present invention will be described below in detail with reference to examples. The measuring method in the examples is as follows. (1) Mechanical properties of fiber-reinforced molding material Measured according to JIS K6810. (2) Conductivity of fiber-reinforced molding material An injection-molded product is cut into 50 mm × 90 mm × 2.5 mm, and the conductive paste is cut into a square parallel 2 piece having a side of 50 mm.
The coating was applied on the sides, and the electrical resistance value between them was defined as the surface resistivity (Ω). (3) Molecular weight of polycarbonate resin Gel permeation chromatography (TOSOH HLC802
0), column (Tosoka TSK-GEL (G4000Hx
L, one G5000HxL each)), column temperature 40 ° C,
The molecular weight was measured with a solvent, THF, and the weight average value was calculated from the polystyrene equivalent value.

[0034]

Example 1 Solid weight of an aqueous emulsion of polyurethane resin (KP-2807 manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) was 44 g.
And an aqueous emulsion of blocked isocyanate (CAT-11 manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) with a solid content of 6 g, an aqueous emulsion of bisphenol A type epoxy resin having a molecular weight of about 1000 into an emulsion having a thermosetting polyurethane resin of 50 g. 50 g of solid content of
The weight ratio of thermosetting polyurethane resin to epoxy resin is 1
A one-to-one solution was prepared.

A polyacrylonitrile-based carbon fiber (manufactured by Shin-Asahi Kasei Carbon Fiber Co., Ltd., 12,000 high-carbon 12Kf-based single fibers) is immersed in the sizing solution, and a sizing agent of 1.5% by weight is attached to the carbon fiber. And dried with hot air at 180 ° C. for 5 minutes to crosslink and dry the polyurethane compound. The bundled carbon fibers thus obtained were cut to a length of 6 mm to produce bundled carbon short fibers, and further subjected to a heat treatment at 160 ° C. for 2 hours to crosslink unreacted polyurethane.

To 30% of the obtained bundle of short carbon fibers, 70% of a bisphenol A type polycarbonate resin was added and dry blended with a V-type blender. This dry blend was kneaded and extruded with a twin-screw extruder equipped with a screw feeder. However, even after continuous 10 hours of operation, the strand did not break and the extrusion rate (15 kg / hr) was constant. The obtained strand was pelletized to obtain a fiber-reinforced molding material. Then, a test piece for evaluation was obtained using a Toshiba IS75E injection molding machine, and the bending strength, the bending elastic modulus, and the surface resistance were measured. A part of the molded product was dissolved in methylene chloride to remove short carbon fibers, and the molecular weight of the polycarbonate resin was measured. Table 1 shows the results.

[0037]

Comparative Example 1 Of the mixed sizing agents in Example 1,
Except that only 1.5% by weight of carbon fiber was adhered to the carbon fiber using only the thermosetting polyurethane resin excluding the epoxy resin.
In the same manner as in Example 1, a short carbon fiber was obtained, a molded product was prepared, and its physical properties were measured. A part of the molded product was dissolved in methylene chloride, and the molecular weight of the polycarbonate resin was measured. As a result, the molecular weight was significantly reduced. Table 1 shows the results.

[0038]

Comparative Example 2 A bundled short carbon fiber was obtained in the same manner as in Example 1, except that 2.5% by weight of carbon fiber was adhered using only the epoxy resin. In the extrusion process, clogging of short carbon fibers in the screw feeder and poor biting in the extruder hopper occurred, strand breaks occurred frequently, and a carbon short fiber reinforced molding material could not be obtained.

[0039]

Comparative Example 3 A bundled short carbon fiber was obtained in the same manner as in Example 1, except that 5.5% by weight of carbon fiber was adhered to the carbon fiber using only the epoxy resin. In the extrusion process, the strand was not broken even after continuous operation for 5 hours, and the extrusion was stable, but a low-decomposition product of the sizing agent was clogged in the vent port, and the degree of depressurization of the vent was reduced.

The obtained pellets were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

[0041]

Example 2 Among the mixed sizing agents in Example 1,
Except for attaching 0.3% by weight to the carbon fiber, a bundled short carbon fiber was obtained in the same manner as in Example 1. Table 1 shows the results.

[0042]

Example 3 Among the mixed sizing agents in Example 1,
Except for attaching 2.5% by weight to the carbon fiber, a bundled short carbon fiber was obtained in the same manner as in Example 1. Table 1 shows the results.

[0043]

Comparative Example 4 Of the mixed sizing agents in Example 1,
Except for attaching 0.1% by weight to the carbon fiber, a bundled short carbon fiber was obtained in the same manner as in Example 1. In the extrusion process, clogging of short carbon fibers in the screw feeder and poor biting in the extruder hopper occurred, strand breaks occurred frequently, and a carbon short fiber reinforced molding material could not be obtained.

[0044]

Comparative Example 5 Of the mixed sizing agents in Example 1,
Except for attaching 3.2% by weight to the carbon fiber, a bundled short carbon fiber was obtained in the same manner as in Example 1. Table 1 shows the results.

[0045]

[Table 1]

[0046]

The sizing agent of the present invention improves the heat resistance and, with a small amount of sizing, enhances the convergence of short carbon fibers, improves the extruding operation, and reduces the amount of thermal decomposition of the sizing agent during extrusion and molding. , The productivity of the short carbon fiber reinforced molding material and the molded article is stabilized, and furthermore, the decrease in the molecular weight of the matrix of the molded article due to the thermal decomposition product of the sizing agent can be suppressed. In addition, it is possible to simultaneously satisfy both physical properties and electrical properties which are opposite to each other in conductivity of a molded article.

Claims (6)

(57) [Claims] The polyurethane resin and the epoxy resin are made of carbon.
0.2 to 3% by weight of the raw fiber
And carbon fibers in which the polyurethane resin is cross-linked by a curing agent . 2. The bundled carbon fiber according to claim 1 , wherein the curing agent is a blocked isocyanate . 3. A method in which a carbon fiber is contacted or immersed in an aqueous emulsion having a mixing ratio of a polyurethane resin and an epoxy resin of 2/8 to 7/3, and then heated to cure the polyurethane resin.
A method for producing bundled carbon fibers , which is crosslinked by a method. 4. The method for producing bundled carbon fibers according to claim 3 , wherein the curing agent is a blocked isocyanate . 5. The method according to claim 1, wherein the polyurethane resin and the epoxy resin are charcoal.
0.2 to 3% by weight of the raw fiber
And the polyurethane resin is cross-linked by a curing agent.
A carbon fiber-reinforced thermoplastic resin comprising 5 to 50% by weight of short carbon fibers obtained by cutting a bundle of carbon fibers and 95 to 5% by weight of a thermoplastic resin. 6. The carbon fiber reinforced thermoplastic resin according to claim 5 , wherein the curing agent is a blocked isocyanate .