JPH041087B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for making pitch fiber infusible. Pitch-based carbon fibers are produced by subjecting pitch fibers obtained by melt-spinning carbonaceous pitch to infusibility, carbonization, or further graphitization. The infusibility treatment of pitch fibers is usually carried out at temperatures below 400°C in the presence of oxidizing gases such as air, oxygen, ozone, nitrogen oxides, halogens, or sulfur dioxide gas. If pitch fibers coalesce with each other, albeit very slightly, and the mutually coalesced infusible fibers are carbonized or further graphitized, the splitting properties of the resulting carbon fibers will be reduced. An object of the present invention is to prevent coalescence between pitch fibers and improve splitting properties, thereby producing carbon fibers with excellent splitting properties. The object of the present invention is to provide a method for infusibility treatment of pitch fiber obtained by melt spinning carbonaceous pitch in an oxidizing gas atmosphere.
This is achieved by applying a non-emulsified dimethylpolysiloxane having a viscosity of 0.5 to 500 cSt and then making it infusible. It is known that after applying an oil agent to pitch fibers, they are treated to make them infusible. For example, a technique has been reported to bundle pitch fiber bundles using the water solubility of a water-soluble surfactant. No. 12740). However, when these water-soluble surfactants are used, although the cohesiveness of the fiber bundles is improved, when they are treated to make them infusible, the surfactants and pitch fibers interact with each other at high temperatures, and on the contrary, they become separated. Decreases fineness. On the other hand, there are reports that silicone oils are effective in thermally stabilizing polyacrylonitrile precursors (JP-A No. 54-131032,
No. 51-12739), and even if this is applied as is to pitch fibers, excellent effects cannot be obtained. The present inventors have found that a silicone compound with a limited structure and limited viscosity is extremely suitable for infusible fibers, and that the resulting infusible fibers have good splitting properties. This discovery led to the completion of the present invention. The present invention will be explained in detail below. The carbonaceous pitch used in the present invention includes various pitches such as coal-based pitch such as coal tar pitch and SRC, petroleum-based pitch such as ethylene tar pitch and decant oil pitch, or synthetic pitch, but petroleum-based pitch is particularly preferred. . The above pitch is modified, for example, treated with a hydrogen donor such as tetralin, 20-350 kg/
Various modified pitches such as those hydrogenated under hydrogen pressure of cm ² , modified by heat treatment, or modified by an appropriate combination of these methods are also considered carbonaceous pitches in the present invention. That is, the carbonaceous pitch of the present invention is used to collectively refer to precursor pitches capable of forming pitch fibers. The carbonaceous pitch of the present invention may be an optically isotropic pitch or an optically anisotropic pitch. When the pitch is optically isotropic, the reflectance is
Those exhibiting a value within the range of 9.0 to 11.0% are preferred.
Here, the reflectance is measured by embedding a pitch in a resin such as acrylic resin, polishing it, and measuring it in air using a reflectance measuring device. Optically anisotropic pitch is an optically anisotropic pitch obtained by heat-treating pitch, usually at 340 to 450°C while passing an inert gas such as nitrogen under normal pressure or reduced pressure. so-called mesophace)
A pitch containing 5 to 100% mesophace is particularly preferred. The carbonaceous pitch used in the present invention has a softening point of 240~
A temperature of 400°C is preferred, and a temperature of 260 to 300°C is particularly preferred. Pitch fibers can be obtained by melt spinning the carbonaceous pitch using a known method. for example,
Pitch fibers are obtained by melting carbonaceous pitch at a temperature 30 to 80°C higher than its softening point, and winding it at 100 to 200 m/min while extruding it through a nozzle with a diameter of 0.1 to 0.5 mm. For the pitch fiber thus obtained, 25
Apply dimethylpolysiloxane with a viscosity of 0.5 to 500 cSt at °C. The dimethylpolysiloxane mentioned here has the following structure, and preferably has a viscosity of 1.0 to 100 cSt at 25°C,
More preferably, it is 1.0 to 25 cSt. The viscosity of dimethylpolysiloxane is extremely important; if the viscosity is greater than the above range, it will hinder the infusibility reaction and reduce the infusibility rate.
On the other hand, if the viscosity is less than the above range, the splitting properties of the infusible fibers will decrease, and the effects of the present invention cannot be expected. Further, in the case of a mixture of two or more types of dimethylpolysiloxane, those whose viscosity as a mixture is within the above range can be used. Other known silicone-based materials include methylphenyl polysiloxane, methylhydrodiene polysiloxane, polyether-modified products (those with increased solubility in water), fluorine-modified products, and amino-modified products. However, it has become clear that all of these interact with pitch fibers during infusibility and reduce the splitting properties. Furthermore, even if dimethylpolysiloxane has a viscosity within the same range as the present invention, emulsified dimethylpolysiloxanes are not preferred and are excluded from the present invention because they result in a decrease in fiber splitting properties. The amount of dimethylpolysiloxane applied is 0.01 to 50% by weight based on the pitch fiber, preferably
It is 0.1-25% by weight. Further, the application method is not particularly limited, and known techniques such as oiling roller, coating, dipping, and spraying can be used. The pitch fibers coated with dimethylpolysiloxane are then treated to be infusible in an oxidizing gas atmosphere.
The infusibility treatment is usually carried out at a temperature of 400°C or lower, preferably 150 to 380°C, more preferably 200°C.
~350℃. If the treatment temperature is too low, the treatment time becomes long, and if the treatment temperature is too high, phenomena such as fusion or consumption of the pitch fibers occur, which is not preferable. As the oxidizing gas, one or more of oxidizing gases such as oxygen, ozone, air, nitrogen oxide, sulfur dioxide gas, or halogen are usually used. The infusible pitch fibers are then subjected to carbonization treatment or further graphitization treatment in an inert gas atmosphere to obtain carbon fibers. Carbonization usually involves temperature
Perform at 800-2000℃. Generally, the treatment time required for carbonization is 0.1 minute to 10 hours. When further graphitizing, the temperature is 2000 to 3500℃, usually 1 second to 1 hour.
Do time. Furthermore, during carbonization or graphitization, a slight load or tension may be applied to the object to be treated, if necessary, in order to prevent shrinkage, deformation, etc. EXAMPLES The present invention will be specifically explained below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 Contains 80wt% optically anisotropic phase and has a softening point of 280
Pitch fibers having an average diameter of 13 μm were obtained by melt-spinning petroleum precursor pitch at a temperature of 13°C. Dimethylpolysiloxane with a viscosity of 4.0cSt25℃ is added to this pitch fiber.
10wt% was applied and treated in oxygen at 250°C for 30 minutes to obtain infusible fibers. The obtained infusible fibers had extremely excellent splitting properties. Comparative Examples 1 to 6 10 wt% of various silicone oils shown in Table 1 were applied to the pitch fibers in Example 1, and the mixture was heated in oxygen.
Infusible fibers were obtained by treatment at 250°C for 30 minutes.

[Table] Siloxane

[Table] Monster

Claims (1)

[Claims] 1 In a method of infusibleizing pitch fiber obtained by melt spinning carbonaceous pitch in an oxidizing gas atmosphere, pitch fiber has a viscosity of 0.5 at 25°C.
A method for producing infusible fibers with excellent splitting properties from pitch fibers, which comprises applying a non-emulsified dimethylpolysiloxane having a weight of ~500 cSt and then infusifying the fibers.