Patent Publication Number: US-2016222550-A1

Title: Method for producing carbonized fabric

Description:
TECHNICAL FIELD 
     The present invention relates to a method for producing a carbonized fabric by heating a fabric containing cellulose in a furnace. 
     BACKGROUND ART 
     Charcoal obtained by carbonizing organic substances is used in various fields. For example, it is used as a heating element due to its imparted conductivity and also used as an adsorbent due to its wide surface area and its high porosity. Particularly, carbonized fabrics obtained by carbonizing fabric are preferred as a planar heating element of a floor heating apparatus, a snow-melting apparatus, or the like. 
     The carbonized fabric can be generally produced by heating a fabric under an inert atmosphere. However, there may be cases in which conductivity is not imparted if the carbonization is insufficient. 
     CITATION LIST 
     Patent Document 
     [Patent document 1] JP 2009429807 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     Therefore, an object of the present invention is to provide a method for producing a carbonized fabric which may be used as a highly efficient heating element generating heat instantaneously after power supply. 
     SOLUTION TO PROBLEM 
     As means for solving the problem, the following invention and the like are provided. Namely, there is provided a carbonized fabric production method for producing a carbonized fabric by heating a fabric containing cellulose in a furnace, the method comprising: a fabric arrangement step of arranging the fabric in the furnace; a first temperature-increasing step of increasing a temperature of at least a fabric-arrangement region in the furnace to a temperature that is closely below a carbonizing temperature of the fabric, while at least the fabric-arrangement region in the furnace being adjusted to be in an inert atmosphere; a second temperature-increasing step of, after the first temperature-increasing step, of increasing the temperature of at least the fabric-arrangement region in the furnace to a temperature in a range of from 1,200° C. to 1,400° C., while at least the fabric arrangement region in the furnace being adjusted to be in a reducing atmosphere relative to at least the inert atmosphere in the first temperature-increasing step; a maintenance step of maintaining, for a predetermined period of time, the temperature in the furnace which has reached a temperature in a range of from 1,200° C. to 1,400° C. in the second temperature-increasing step; a temperature-decreasing step of gradually decreasing the temperature in the furnace after a lapse of the predetermined period of time; and a furnace-opening step of opening the furnace after the temperature in the furnace has become about 100° C. or less in the temperature-decreasing step. 
     Furthermore, there is provided a carbonized fabric production method, wherein, in the above-described carbonized fabric production method, a raw material of the fabric is cotton. Furthermore, there is provided a carbonized fabric production method, wherein, in the above-described maintenance step, the predetermined period of time is about from 1 to 2 hours. Furthermore, there is provided a carbonized fabric production method, wherein a period of time to be spent for the above-described temperature-decreasing step is 20 hours or more. Furthermore, there is provided a carbonized fabric production method, wherein, in the above-described furnace-opening step, opening and shutting the furnace are performed intermittently so as to prevent a sudden decrease of the temperature in the furnace. 
     ADVANTAGEOUS EFFECT OF INVENTION 
     According to the present invention, it is possible to provide a method for producing a carbonized fabric which may be used as a highly efficient heating element generating heat instantaneously after power supply. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flow chart showing the flow of each step of a production method according to the present embodiment. 
         FIG. 2  is an FE-SEM photograph of a carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 3  is an FE-SEM photograph of the carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 4  is an FE-SEM photograph of the carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 5  is an FE-SEM photograph of the carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 6  is an FE-SEM photograph of the carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 7  is an FE-SEM photograph of the carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 8  shows Raman spectroscopy results of the carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 9  is a conceptual diagram showing an application example of carbonized fabric produced by the production method according to the present embodiment. 
         FIG. 10  is a conceptual diagram showing another application example of carbonized fabric produced by the production method according to the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments according to the present invention are described. The present invention is not to be limited to these embodiments at all and may be implemented in various modes without departing from the gist of the present invention. 
     &lt;Embodiment—Overview&gt; 
     In the method for producing carbonized fabric according to the present embodiment, the temperature in the furnace is increased to a temperature closely below a carbonizing temperature under an inert atmosphere, then the temperature in the furnace is further increased to a temperature in a range of from 1,200° C. to 1,400° C. while the atmosphere in the furnace is adjusted to be in a reducing atmosphere, and the resulting condition is maintained for a predetermined period of time. According to such a production method, it is possible to produce a carbonized fabric which may be used as a highly efficient heating element generating heat instantaneously after power supply. 
     &lt;Embodiment—Constitution&gt; 
       FIG. 1  is a flow chart showing the flow of each step of the method for producing carbonized fabric according to the present embodiment. The present embodiment is a carbonized fabric producing method for producing a carbonized fabric by heating a fabric containing cellulose in a furnace. The method includes a “fabric arrangement step” (S 0101 ), a “first temperature-increasing step” (S 0102 ); a “second temperature-increasing step” (S 0103 ); a “maintenance step” (S 0104 ); a “temperature-decreasing step” (S 0105 ); and a “furnace-opening step” (S 0106 ), as shown in the figure. 
     The fabric of the present embodiment contains cellulose. The fabric is, for example, made by knitting or weaving vegetable cellulosic fibers, such as cotton, linen, silk, bamboo, paper mulberry or wood pulp. Alternatively, the fabric may be fabric made of regenerated fibers which are manufactured by spinning natural fibers or polymers after dissolving them once. Examples of the fabric include, not only knit and woven fabric but also non-woven fabric. The fabric is not necessarily limited to be planar and may be string-shaped. 
     The “fabric arrangement step” (S 0101 ) is a step of arranging the fabric in the furnace. The furnace may be any one capable of controlling the temperature in the furnace, blocking outside air, and controlling the atmosphere in the furnace to be an inert atmosphere, a reducing atmosphere, or the like. 
     Examples of an embodiment of arranging the fabric in the furnace include arranging, in a stacking manner, the fabric which has been cut according to a size of an arrangement region, arranging the fabric which has been folded over and over without cutting, and arranging the fabric which is in a rolled state. 
     Although the region at which the fabric is to be arranged in the furnace is not particularly limited, the fabric is preferably arranged in a region where the temperature control and the furnace control as described above are favorably performed. In other words, at the stage of introducing inert gas into the furnace, if there may be a region where the inert gas hardly reaches, it is not preferable to arrange the fabric in such a region. 
     In a case in which, in order to make the furnace atmosphere into a reducing atmosphere, incomplete combustion is allowed to occur using a burner to generate carbon oxide, the fabric is preferably arranged so that combustion flame is not in contact with the fabric directly or so that the fabric is separated from the combustion flame with a refractory metal or the like. 
     The “first temperature-increasing step” (S 0102 ) is a step of increasing the temperature of at least the fabric arrangement region in the furnace to a temperature that is closely below a carbonizing temperature of the fabric, while at least the fabric arrangement region in the furnace being adjusted to be in an inert atmosphere. The carbonizing temperature of the fabric, which varies according to materials, composition, etc. of the fabric, is generally about from 300° C. to 500° C. The fabric arrangement region is maintained under the inert atmosphere until the temperature reaches a temperature at which the arranged fabric is carbonized. Examples of the inert gas used for producing the inert atmosphere include nitrogen gas, helium gas, argon gas, and neon gas. Increasing the temperature under the inert atmosphere promotes the carbonization without burning the fabric. The period of time to be spent for the first temperature-increasing step is according to various conditions such as material and quantity of the fabric, and volume of the furnace. The period of time to be spent for the first temperature-increasing step is, for example, about from 0.5 to 3 hours. In a case where the temperature is increased in an extremely short period of time, the fibers constituting the fabric may be broken or split due to rapid volume change thereof. 
     The “second temperature-increasing step” (S 0103 ) is a step of increasing the temperature of at least the fabric arrangement region in the furnace to a temperature in a range of from 1,200° C. to 1,400° C., while at least the fabric arrangement region in the furnace being adjusted to be in an inert atmosphere, after the first temperature-increasing step. 
     “Being adjusted to be in a reducing atmosphere relative to the inert atmosphere in the first temperature-increasing step” means that an atmosphere in the furnace is adjusted so as to contain a larger amount of the reducing atmosphere than the inert atmosphere. Adjusting the atmosphere in the furnace into the relative reducing atmosphere promotes the carbonization by a deoxygenation action to the fabric, and removes impurities to produce a carbonized fabric having a high carbon purity. 
     Examples of the reducing gas used for producing the reducing atmosphere include carbon monoxide gas, hydrogen sulfide gas, sulfur dioxide gas, hydrogen gas, and formaldehyde gas. With respect to the introducing of the reducing gas into the furnace, the gas may be introduced directly. Alternatively, for example, a burner for combusting fuel gas such as propane or butane may be provided in the furnace, and carbon monoxide gas may be produced by incomplete combustion. Alternatively, reducing metal particles may be exposed in the furnace by sputtering, vapor deposition, or the like, so that the furnace atmosphere is made into the reducing atmosphere by reactions of these metal particles. Examples of the metal which may be used include lithium, cesium, rubidium, potassium, barium, strontium, calcium, sodium, magnesium, thorium, beryllium, aluminum, titanium, zirconium, manganese, tantalum, zinc, chromium, iron, cadmium, cobalt, nickel, tin, and zinc. The above-mentioned each process of producing the reducing atmosphere may be performed simultaneously or may be performed step-by-step. Furthermore, the fuel gas of the burner, which is not limited to gas containing the above-mentioned propane and methane with a purity of 100%, may be town gas in which an odorant such as thiol is added. 
     With regard to the carbonization of the fabric, crystallization of carbon proceeds better as the carbonizing temperature is higher. Although the crystallization occurs partially, the conductivity improves thereby. On the other hand, embrittlement proceeds more intensely as the carbonizing temperature is higher, so that a shape as the fabric may be lost. Therefore, the temperature to reach in the second temperature-increasing step is determined as described above. Namely, in a case where the reached temperature is below 1,200° C., it may be difficult to obtain the desired conductivity. Moreover, if the reached temperature is above 1,400° C., the embrittlement may proceed excessively. 
     The period of time to be spent until the temperature in the furnace reaches the temperature to reach in the second temperature-increasing step may appropriately be determined according to the material and the quantity of the fabric to be carbonized, the volume of the furnace, and the like. For example, it is preferably about from 1 to 5 hours. If the temperature is increased in an extremely short period of time, the fibers constituting the fabric may be broken or split due to rapid volume change thereof. Conversely, even if increasing the temperature is performed over an extremely long period of time, it is not much effective, so that it may be a waste of time and energy. 
     The “maintenance step” (S 0104 ) is a step of maintaining the temperature in the furnace which has reached a temperature in range of from 1,200° C. to 1,400° C. in the above-mentioned second temperature-increasing step for a predetermined period of time. The carbonization is completed in the maintenance step. The period of time to be spent for the maintenance step is according to various conditions such as the material and the quantity of the fabric, and volume of the furnace. For example, it is preferably about from 1 to 2 hours. If the period of time is shorter than 1 hour, the carbonization may be insufficient, so that there may be cases in which the desired conductivity cannot be obtained. Conversely, if the period of time is longer than 2 hours, the embrittlement may proceed. 
     The atmosphere in the furnace in the maintenance step may be the inert atmosphere or the reducing atmosphere. For example, the maintenance step may be performed under the reducing atmosphere continuously in so far as the reducing gas introduced into the furnace in the second temperature-increasing step exists, or may be performed while the atmosphere in the furnace is made into the relative reducing atmosphere in the same way as in the second temperature-increasing step. As described above, from the viewpoint of enhancing the carbon purity and removing the impurities, it is preferable that the reducing atmosphere is maintained. 
     The “temperature-decreasing step” (S 0105 ) is a step of gradually decreasing the temperature in the furnace after a lapse of the above-mentioned predetermined period of time. A sudden decrease in the temperature in the furnace causes internal stress of the carbonized fabric, so that heterogeneity of structure and properties may be introduced to the carbonized fabric and the fibers constituting the fabric may be broken or split. This step is a step for preventing such adverse effects. The temperature-decreasing step is performed under the inert atmosphere or the reducing atmosphere, similarly to the above-mentioned maintenance step. Preferably, the temperature-decreasing step is performed under the above-mentioned relative reducing atmosphere. 
     The period of time to be spent for the temperature-decreasing step is according to various conditions such as the material and the quantity of the fabric, and volume of the furnace. For example, it is preferably 20 hours or more. By gradually decreasing the temperature in the furnace over such a period of time, the above-mentioned adverse effects caused by the sudden decrease can be prevented. 
     The “furnace-opening step” (S 0106 ) is a step of opening the furnace after the temperature in the furnace has become about 100° C. or less in the temperature-decreasing step. In a case in which the furnace is opened in a state in which the temperature in the furnace is high, the carbonized fabric may burn by contact with air. Therefore, to prevent occurrence of such a case, the furnace is opened after the temperature in the furnace has become about 100° C. or less. 
     In the above-mentioned furnace-opening step, it is preferable that opening and shutting of the furnace are performed intermittently to lower the rate of decrease in the temperature in furnace, rather opening the furnace firstly and then maintaining the opened state. For example, when the furnace is first opened, the furnace is once shut immediately after the first opening, and then the furnace is opened again. It is preferable to intermittently repeat such opening and shutting of the furnace. As described above, influence of the internal stress and the like is preferably suppressed by performing the furnace-opening step so as to slowly lower the temperature in the furnace. 
       FIG. 2  is a photograph of a carbonized fabric produced by the carbonized fabric production method according to the present embodiment, which was taken at a magnification of 30 times by FE-SEM (Field Emission Scanning Electron Microscope). The fabric used for producing the carbonized fabric is a fabric made by knitting natural cotton.  FIG. 3  is a photograph of the above-mentioned carbonized fabric, which was taken at a magnification of 100 times.  FIG. 4  is a photograph of the above-mentioned carbonized fabric, which was taken at a magnification of 1000 times.  FIGS. 5 to 7  are photographs of the above-mentioned carbonized fabric, which were taken at a magnification of 10000 times. 
       FIG. 8  is Raman spectroscopy results of the above-mentioned carbonized fabric. Using “NRS-3100 (JASCO Corporation)” as a spectrophotometer, the measurement was performed five times (N=1 to 5) at difference places, under conditions of a laser wavelength 532 nm, a laser beam intensity of 10 mW, an exposure time of 30 sec, and cumulative number of 2 times, to measure the “G band intensity (1,590 cm −1 )”, the “D band intensity (1,350 cm −1 )”, and the “Raman intensity ratio (D/G)”. According to the measurement result, although the D band intensity is higher, the G band intensity derived from graphite structure exists to a certain extent. Accordingly, it is thought that partial graphitization occurs. 
     The carbonized fabric produced by the production method according to the present embodiment may be applied as a heating element in various modes.  FIG. 9  is a conceptual diagram showing a carbonized fabric which is applied as a planar heating element. As shown in the figure, on the edges facing each other of the carbonized fabric ( 0901 ) according to the present embodiment, a positive long electrode and a negative long electrode ( 0902 ,  0903 ) are attached respectively. By connecting a power source ( 0904 ) to the positive electrode and the negative electrode and applying voltage, the carbonized fabric generates heat instantaneously. Such an embodiment is suitable for realizing a floor heating apparatus, a snow-melting apparatus, or the like. 
     For example, on the two edge portions in a longitudinal direction of a carbonized fabric having a width of 150 mm and a length of 1,000 mm, a positive long electrode and a negative long electrode are provided respectively. As a result of applying voltage adjusted to about 30 V with a transformer to the fabric, the current become about 3 A, and a temperature near a surface of the carbonized fabric reaches 80° C. in 2 to 3 seconds after the voltage application. Furthermore, this heat generation occurs in the whole carbonized fabric without unevenness. As such, because of reaching the high temperature instantaneously after the power supply, at an electric power of less than 100 W, it can be understood that the carbonized fabric is a highly efficient heating element. 
       FIG. 10  is a heating element made by encapsulating a fibrous carbonized fabric ( 1001 ) in a quartz glass tube ( 1002 ) under vacuum. The carbonized fabric having a string shape is provided with an electrode at each edge thereof, to which a power source ( 1003 ) is connected. This carbonized fabric having a string shape generates heat as a result of application of voltage. Such an embodiment is suitable for realizing in a heating apparatus, a heating cooking apparatus, a lighting apparatus, or the like. 
     &lt;Embodiment—Effect&gt; 
     According to the carbonized fabric producing method of the present embodiment, it is possible to produce a carbonized fabric which may be used as a highly efficient heating element generating heat instantaneously after power supply. 
     REFERENCE SIGNS LIST 
     
         
         S 0101  fabric arrangement step 
         S 0102  first temperature-increasing step 
         S 0103  second temperature-increasing 
         S 0104  maintenance step 
         S 0105  temperature-decreasing step 
         S 0106  furnace-opening step