JPS648091B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a novel method for producing a carbon fiber molded sheet. Furthermore, the present invention relates to a manufacturing method for obtaining a bulky molded sheet with excellent chemical resistance, electrical conductivity, and strength by directly firing an organic fiber sheet obtained by a papermaking method after press molding. (Prior Art) Conventionally, no good method for obtaining a carbon fiber molded sheet, particularly a carbon fiber molded sheet having irregularities on the order of millimeters, has been known. A conventionally known method involves re-sintering a sheet made of carbon fibers together with pulp and a binder to obtain a carbon fiber sheet, and then cutting the sheet to obtain a molded sheet. However, such a method requires time-consuming cutting and therefore has the disadvantage of poor yield efficiency. In addition, it is difficult to control the bulk density and pore size to suit various uses such as fuel cells, and it also requires two firing steps, making it extremely expensive. Development of a manufacturing method was desired. (Objective of the Invention) The object of the present invention is to improve the above-mentioned drawbacks and to provide an inexpensive method for manufacturing a carbon fiber molded sheet. (Structure of the Invention) The present invention provides a method for making paper by mixing 70 to 95 parts by weight of at least one organic fiber selected from regenerated cellulose fibers and polyacrylonitrile fibers, 3 to 25 parts by weight of pulp, and 2 to 15 parts by weight of a papermaking binder. The resulting sheet is impregnated with a solution of an organic polymer substance, dried, precured, molded using a press, and if necessary, subjected to infusibility treatment, and then dried in an inert atmosphere. This is a method for producing a carbon fiber molded sheet, which comprises heating and carbonizing the sheet at a temperature of 800° C. or higher, preferably under press pressure of 2 to 50 g/cm ² . Components of the present invention will be explained in detail below. The organic fibers used in the present invention include rayon,
Organic fibers commonly used in the production of carbon fibers, such as polyacrylonitrile fibers, are suitable, with a length of 0.5 to 15 denier and a length of 2 to 15 mm, preferably 0.5 to 8 denier and a length of 2 to 15 mm from the viewpoint of paper-making properties, etc. 3～
A 10 mm diameter one is selected depending on the purpose and used alone or in combination of two or more. From the viewpoint of ease of molding and obtaining a good molded product, it is preferable to blend thermoplastic fibers such as acrylic fibers as organic fibers at 40 parts by weight or more, preferably at least 60 parts by weight based on the total solid content. . In addition to cellulose pulp, various synthetic pulps are suitable as the pulp used in this invention, and these pulps act as a binder for organic fibers during paper making. As the binder for paper making, for example, fibers that do not dissolve in cold water but dissolve in hot water, such as polyvinyl alcohol fibers, various synthetic pulps, and rayon for paper making, which are generally commercially available as binders for paper making can be used. . Synthetic resin emulsions can also be used as papermaking binders. Binders for organic fibers, pulp and papermaking are
70-95 parts by weight, 3-25 parts by weight and 2-95 parts by weight, respectively.
They are mixed in a proportion of 15 parts by weight (as solid content) and made into paper by a conventional method. If the amount of organic fiber is less than 70 parts by weight, it becomes difficult to control the pore size, porosity, etc., and the strength also decreases, making it impossible to obtain a good sheet. It's difficult. Furthermore, in order to maintain wet strength, it is preferable to mix the pulp and papermaking binder in a total amount of 5 parts by weight or more. Examples of organic polymer substances used for impregnation include phenolic resins, epoxy resins: unsaturated polyester resins, thermosetting resins such as polydivinylbenzene, vinyl chloride resins, vinylidene chloride resins, vinyl fluoride resins, vinylidene fluoride resins, Thermoplastic resins such as acrylonitrile resins, as well as lignin, pitch or tar, are also used. The desirable properties of these polymer compounds are that they are soluble in some kind of solvent or melt at high temperatures during heat treatment, and that they have a carbon content of 30% by weight or more and can be used as a carbonaceous binder to bond within carbon fibers after carbonization. It's useful. (Impregnation Treatment) The mixed paper is impregnated with a solution or dispersion of the organic polymer substance described above. If the amount of impregnation adhering to the mixed paper is too small, the binder effect and carbonization yield during carbonization will be poor, and if it is too excessive, it will be difficult to adjust the porosity due to clogging, and it will become brittle. The preferred amount of impregnation is the weight of the mixed paper.
It is 20 to 200%, more preferably 30 to 120%. When using regenerated cellulose, such as rayon, as the organic fiber, in addition to the impregnation treatment with the organic polymer liquid described above, impregnation treatment with a heat resistance improver can be used in combination to bring about more effects in terms of carbonization yield, strength, etc. . As the heat resistance improver, any of those commonly used in producing rayon carbon fibers can be used. For example, phosphate metal salts include monobasic magnesium phosphate, monobasic calcium phosphate, monobasic sodium phosphate, monobasic potassium phosphate, etc., and ammonium salts of various acids include ammonium chloride, ammonium sulfate, ammonium hydrogen sulfate, and ammonium phosphate. , ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium salt of polyphosphoric acid, ammonium borate, etc. can be suitably used. (Precuring Treatment) If a mixed paper impregnated with an organic polymeric substance is press-molded as is, the organic polymeric substance will be unevenly distributed within the sheet, making it impossible to obtain a uniform sheet. Therefore, after the impregnation treatment and drying, it is necessary to further perform a preliminary curing treatment. The degree of precuring must be such that the impregnated polymeric material does not become fluid during subsequent press molding and maintains thermoplasticity to the extent that press molding can be easily performed. Suitable treatment conditions are 140° C. to 180° C. and about 5 minutes to 30 minutes. (Press molding process) The impregnated sheet subjected to the above pre-curing process is
Next, pressure and molding is performed using a mold with an uneven surface. In this case, it is preferable to use heat treatment in combination to prevent deformation in subsequent steps and to facilitate molding. Press molding conditions are appropriately selected depending on the raw materials used and the required physical properties of the final sheet. (Infusibility treatment) The above-mentioned mixed paper that has been subjected to molding treatment is made infusible if necessary and then fired to form carbon fiber paper. This method is particularly effective when a thermosetting resin such as a phenol resin is used as the molecular substance, and has a remarkable effect on improving carbonization yield and sheet strength. The processing conditions for infusibility are not particularly specified, but for example, the mixed paper to which the organic polymer substance is attached is heated at 150 to 350°C for several tens of minutes to several tens of hours in air or an inert gas atmosphere. This makes it infusible. (Heat carbonization treatment) The above-mentioned mixed paper to which the organic polymer substance solution has been attached is made infusible as necessary, and then heat treated and fired at a temperature of 800°C or higher in an inert atmosphere.
A carbon fiber paper containing a carbonaceous binder is formed.
By changing the heat treatment temperature, it is possible to control the electrical resistance value of the final product carbon fiber paper. Further, when the above heat treatment and firing is performed while pressurizing at a pressure of 2 to 50 g/cm ² , a carbon fiber sheet having extremely high strength and uniform thickness can be obtained. (Effect of the invention) The present invention obtains a sheet by a papermaking method from fibers such as regenerated cellulose fibers and polyacrylonitrile fibers, which are normally used as raw materials for manufacturing carbon fibers, and after press molding, carbon fibers are produced by a general carbonization process. This is a method for obtaining sheets, and compared to the conventional method of cutting carbon fiber sheets, the manufacturing process is easier and it is now possible to obtain sheets at a very low cost. In addition, by using press pressure during the carbonization process, a sheet with significantly improved mechanical strength and thickness accuracy can be obtained compared to conventional methods, and the carbon fibers do not fall off the sheet at all and are uniform. It has become easy to obtain sheets with Furthermore, by appropriately selecting the thickness and length of the raw organic fibers, and by blending the pulp and papermaking binder, it is possible to reduce the pore size and porosity of the sheet, which is a particular problem when used as an electrode base material for fuel cells. It has also become possible to control freely and easily. In addition, since the present invention obtains a sheet from organic fibers by a papermaking method, it is easier to form a sheet than a carbon fiber papermaking method, a uniform sheet can be obtained, and the sheet basis weight (g/
cm ² ) also has the advantage of being able to obtain any desired value. (Examples) Examples are shown below to make it easier to understand the present invention, but the following examples do not limit the present invention. In addition, in the examples, parts and % are parts by weight and % by weight, respectively. Examples 1 to 4 Acrylic fibers with a thickness of 8 denier and 3 denier, 7 denier short rayon fibers, Canadian Freeness 500ml pulp (LUKP), polyvinyl alcohol fiber (manufactured by Kuraray, VPB105-2×3)
Water was added to the slurry at the proportions shown in Table 1 to obtain a slurry, and a mixed paper having a basis weight of 700 g/m ² was made using a conventional method using a circular wire paper machine. This mixed paper was impregnated with a 20% aqueous solution of phenolic resin (PR-51404 manufactured by Sumitomo Durez) (phenol resin adhesion amount: 60%/mixed paper), dried at a temperature of 120°C, and then heated at 180°C for 15 minutes. Summer. The sheet thus obtained was then
Insert between the male mold 1 and female mold 3 of the mold shown in the figure,
Pressure molding was performed at 180℃ for 10 minutes at 13Kg/ ^cm2 , and 220
After oxidation treatment at 1100° C. for 5 hours, heating and firing was performed in a nitrogen gas atmosphere furnace at 1100° C. for 30 minutes under a press pressure of 10 g/cm ² to obtain a carbon fiber sheet. The physical properties of this sheet are shown in Table 1. According to the method of the present invention, in which a paper sheet is directly fired after molding, a carbon fiber molded sheet with excellent electrical resistance and strength can be obtained, and by changing the composition of raw material fibers, the pore size and porosity can be adjusted freely. It can be seen from Table 1 that this can be controlled. 【table】

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a molding die. The symbols in the figure represent the following, respectively. 1...Male type, 2...Male type protrusion, 3...Female type, 4...Female type groove.

Claims (1)

[Claims] 1. At least one organic fiber selected from regenerated cellulose fibers and polyacrylonitrile fibers.
A sheet obtained by mixing 70 to 95 parts by weight of pulp, 3 to 25 parts by weight of pulp, and 2 to 15 parts by weight of papermaking binder is impregnated with a solution of an organic polymer substance, and after drying, a preliminary curing treatment is performed. A method for producing a carbon fiber molded sheet, which comprises performing press molding, performing an infusibility treatment if necessary, and then heating and carbonizing the sheet at a temperature of 800°C or higher in an inert atmosphere. 2. A method for producing a carbon fiber sheet according to claim 1, characterized in that heating carbonization is performed under press pressure of 2 to 50 g/cm ² .