Abstract:
A method for adjusting the softening point of a pitch material includes heating the pitch material to form molten pitch material, and rising the softening point of the pitch material by moving a plurality of movable members so that the movable members repetitively move at least some of the molten pitch material out of a liquid level of the molten pitch material and back to the molten pitch material.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and an apparatus for adjusting the softening point of a pitch (hereinafter referred to as the “pitch material”) such as coal tar pitch or petroleum pitch. 
     When spinning carbon fibers from a pitch material, it is desirable that the pitch material have a high softening point to improve the spinning properties and smoothen post-spinning processing, such as when processing the spun pitch material to be infusible. 
     Japanese Laid-Open Patent Publication No. 9-143475 discloses an example of a method for adjusting the softening point of a pitch material. In this method, 500 g of a pitch material having a softening point of 125° C. is placed in a one-liter autoclave. Then, an oxidizing gas such as air is blown into the autoclave at a rate of five liters per minute while agitating and heating the pitch material at a temperature of 350° C. for two hours. This produces a pitch material having a softening point of 296.3° C. 
     However, the method described in the above publication requires an autoclave, which is a relatively costly apparatus, and a troublesome process of blowing oxidizing gas into the pitch material. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is a method for adjusting the softening point of a pitch material. The method includes heating the pitch material to form molten pitch material, and rising the softening point of the pitch material by moving a plurality of movable members so that the movable members repetitively move at least some of the molten pitch material out of a liquid level of the molten pitch material and back to the molten pitch material. 
     A further aspect of the present invention is an apparatus for adjusting the softening point of a pitch material. The apparatus is provided with a pitch tank including a heating member. The pitch tank contains molten pitch material. A plurality of movable members are arranged on an upper portion of the pitch tank. The movable members are configured to be moved so that the movable members repetitively move at least some of the molten pitch material out of a liquid level of the molten pitch material and back to the molten pitch material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view showing a first embodiment of an apparatus for adjusting the softening point of a pitch material; 
         FIG. 2  is a cross-sectional view taken along line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a plan view showing a second embodiment of an apparatus for adjusting the softening point of a pitch material; and 
         FIG. 4  is a cross-sectional view of the apparatus shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     A first embodiment of a method and an apparatus for adjusting the softening point of a pitch material will now be described with reference to  FIGS. 1 and 2 . 
     As shown in  FIGS. 1 and 2 , the apparatus includes a pitch tank  10 . The pitch tank  10  includes an outer tank  11  and an inner tank  14 . The outer tank  11  includes a recess  111 , which has a substantially semicircular cross-section and is open at the upper side. The inner tank  14  is semi-cylindrical and received in the recess  111  of the outer tank  11 . The inner tank  14  is separable from the outer tank  11 . Further, the inner tank  14  has a hollow wall that accommodates a heater  12 , which serves as a heating member. The inner tank  14  contains a pitch material  15  that is heated and molten by the heater  12 . 
     Two bearings  16  are respectively arranged on the two ends of the upper surface of the outer tank  11 . Each bearing  16  includes a U-shaped or V-shaped groove  161 . A movable unit  17  is supported by the grooves  161  of the two bearings  16 . The movable unit  17 , which is rotatable and separable from the grooves  161 , includes a shaft  18  and plate-like movable members fixed to the shaft  18 . For example, the movable members may be disks  19 . The disks  19  are parallel to one another and arranged at equal intervals on the shaft  18 . The shaft  18  extends through the center of each disk  19 . The shaft  18  is supported by the grooves  161  of the two bearings  16  so that the shaft  18  is located proximate to and extends parallel to the liquid level  151  of the pitch material  15  in the inner tank  14 . The inner tank  14  has an arcuate inner surface that is proximate to and concentric with the circumferential surface of each disk  19  when the movable unit  17  is mounted on the pitch tank  10 . Rotation of the movable unit  17  about the shaft  18  rotates each disk  19  between the upper side (atmosphere) and the lower side of the liquid level  151  of the pitch material  15  in the inner tank  14 . Each disk  19  rotates in a direction intersecting the thickness direction of the disk  19 . The inner tank  14 , the shaft  18 , and the disks  19  may be formed from stainless steel. 
     A bracket  21  is coupled to one side of the outer tank  11  to support a motor  20  that rotates the movable unit  17 . A coupling  22  is located between an end of a motor shaft  201  and an end of the shaft  18  of the movable unit  17 . The coupling  22  includes a driving connector  221 , which is fixed to the motor shaft  201 , and a driven connector  222 , which is fixed to the shaft  18  of the movable unit  17 . Removable pins  223  join the two connectors  221  and  222  to couple the motor shaft  201  and the shaft  18  of the movable unit  17  in a separable manner. 
     A method for adjusting the softening point of the pitch material with the apparatus described above will now be described. 
     The pitch material  15  is placed in the inner tank  14  and heated and molten by the heater  12 . The temperature of the pitch material  15  in the inner tank  14  is approximately 250° C. to approximately 300° C. Under this condition, when the motor  20  rotates the movable unit  17 , the disks  19  continuously rotate between the upper side and the lower side of the liquid level  151  of the pitch material  15  in the inner tank  14 . This agitates the pitch material  15 . In this case, the rotation speed of the movable unit  17  is approximately 10 to 30 rotations per minute. Some of the molten pitch material  15  adheres to the portion of each disk  19  located in the molten pitch material  15 . When such portion of the disk  19  is moved out of the molten pitch material  15  and into the atmosphere by the rotation of the movable unit  17 , the pitch material  15  adhered to the surface of the disk  19  cools and solidifies while reacting with the oxygen in the atmosphere. Further rotation of the movable unit  17  returns this portion of the disk  19  to the molten pitch material  15 . Thus, the pitch material  15  on the disk  19  melts again. The repetition of such motion gradually draws oxygen from the atmosphere into the pitch material  15  and raises the softening point of the pitch material  15 . When the softening point of the pitch material rises, the pitch material becomes solid and gradually accumulates on the surface of each disk  19 . 
     The adjustment of the softening point of the pitch material  15  is completed when most of the pitch material  15  in the inner tank  14  becomes adhered to the disks  19 . Then, the pins  223  are manually unfastened from the coupling  22  to separate the shaft  18  of the movable unit  17  and the motor shaft  201 . 
     The movable unit  17  is then separated from the upper portion of the outer tank  11 . The pitch material  15  of which the softening point has been adjusted is removed and collected from the surface of each disk  19 . Further, the inner tank  14  is separated from the recess  111  of the outer tank  11 , and the residual pitch material  15 , of which softening point has been adjusted, is removed and collected from the inner surface of the inner tank  14 . 
     In one example, a pitch material  15  having a softening point of 110° C. was placed in the inner tank  14 . The pitch material  15  was heated by the heater  12  and kept molten at a temperature between 270° C. and 280° C. Under this situation, the motor  20  rotated the movable unit  17  for two hours. This obtained the pitch material  15  of which the softening point had been adjusted to 200° C. or higher. The high softening point pitch material  15  thus obtained is crushed, reheated, and used for spinning. 
     The above embodiment has the following advantages. 
     (1) The disks  19 , which serve as movable members, partially move the pitch material  15  between the upper and lower sides of the liquid level  151  of the molten pitch material  15 . That is, the disks  19  move the pitch material  15  that is adhered to each disk  19  out of and into the molten pitch material  15 . This motion gradually draws oxygen from the atmosphere into the pitch material  15  and raises the softening point of the pitch material  15 . In this manner, the present embodiment differs from the prior art in that there is no need to perform a burdensome process such as agitating a pitch material in a costly instrument such as an autoclave while blowing oxidizing gas into the pitch material. Further, in the prior art, it is difficult to uniformly blowing oxidizing gas into the pitch material and uniformly agitate the pitch material. When such uniformity cannot be achieved, it becomes difficult to obtain a pitch material having a high softening point. In contrast, the present embodiment uniformly and effectively raises the softening point of the pitch material  15  without the need to perform a burdensome process such as blowing oxidizing gas into the pitch material while using a costly instrument like an autoclave. 
     (2) The disks  19  are rotated about the shaft  18 . In other words, each disk  19  is rotated in a direction intersecting the thickness direction of the disk  19 . This moves the pitch material  15  that adheres to the disks  19  into and out of the molten pitch material  15 , that is, between the upper and lower sides of the liquid level  151  of the pitch material  15 , to raise the softening point of the pitch material  15 . Thus, the pitch material  15  is not excessively agitated, and subtle bubbles enter the pitch material  15 . This limits the degradation of the pitch material  15 . 
     (3) To raise the softening point of the pitch material  15 , each disk  19  is simply rotated at a relatively slow speed in a direction intersecting the thickness direction of the disk  19  between the upper and lower sides of the liquid level  151  of the molten pitch material  15 . Thus, there is no need for the motor to output high power when rotating the disks  19 . This allows for a reduction in the running cost used to adjust the softening point of the pitch material  15 . 
     (4) The main elements of the apparatus are only the pitch tank  10 , which is provided with the motor  20 , and the movable unit  17 . Thus, the apparatus includes few components and has a simple structure. 
     (5) The inner surface of the inner tank  14  of the pitch tank  10  is proximate to and concentric with the circumferential surface of each disk  19 . Thus, the process for raising the softening point can be efficiently performed on the entire pitch material  15  in the inner tank  14 . 
     (6) The disks  19  are arranged parallel to and spaced apart from one another on the shaft  18 . This increases the entire surface area of the disks  19 , which is the sum of the surface area of each disk  19 . Thus, the rotation of the disks  19  allows for the pitch material  15  to be efficiently adjusted to a high softening point within a short period of time. 
     Second Embodiment 
     A second embodiment of a method and an apparatus for adjusting the softening point of a pitch material will now be described focusing on differences from the first embodiment. 
     In the second embodiment, as shown in  FIGS. 3 and 4 , a plurality of (two in this embodiment) movable units  17  are arranged next to each other on the outer tank  11 . Each movable unit  17  is supported by two bearings  16  and includes a shaft  18  and disks  19 . The disks  19  of one of the movable units  17  and the disks  19  of the other one of the movable units  17  are alternately arranged. A coupling  22  couples the shaft  18  of one of the movable units  17  to a motor shaft  201  of a motor  20  in a separable manner. A driving sprocket  25  is fixed to the motor shaft  201 . 
     A further coupling  22  couples the shaft  18  of the other movable unit  17  to a cooperative shaft  26  in a separable manner. The cooperative shaft  26  is rotatably supported by a bearing  27  on the bracket  21 , which supports the motor  20 . A driven sprocket  28  is fixed to the cooperative shaft  26 . A chain  29  runs around the driving sprocket  25  and the driven sprocket  28 . The sprockets  25  and  28  may be gears, and the chain  29  may be a belt. The motor  20  generates rotation that integrally rotates the two movable units  17  with the chain  29  to adjust the softening point of the pitch material  15 . The two shafts  18  may be coupled to different motors  20  to separately control the rotation of the shafts  18 . 
     In addition to advantages (1) to (6) of the first embodiment, the second embodiment has the advantage described below. 
     (7) The use of the plurality of movable units  17  allows for a large amount of the pitch material  15  to be adjusted to a high softening point within a short period. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
     The movable members may be rods or polygonal plates. In such cases, the movable members may be linearly moved between the upper and lower sides of the liquid level  151  of the pitch material  15 . 
     The disks  19  may be corrugated to increase the surface area. 
     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.