JPH06157117A - Carbon fiber reinforced gypsum forming mold and gypsum powder and production thereof - Google Patents

Abstract

PURPOSE:To produce a gypsum mold by enhancing the strength of the gypsum mold without degrading the functions of high measure accuracy, etc., and also uniformly dispersing numerous single fiber of carbon fiber in a gypsum slurry. CONSTITUTION:The carbon fiber reinforced gypsum forming mold is uniformly dispersed the carbon fiber with 5-100mm length into a gypsum structure of a base material of a molding gypsum forming mold in a dispersed state as a single fiber and at the 0.008-0.9wt.% ratio for the gypsum. Also the carbon fiber is cut by 5-100mm length and it is preliminarily dispersed to numerous single fiber, and then the gypsum powder and the above described carbon fiber dispersed to 0.01-5wt.% the single fiber for the gypsum powder are charged into circulating jet air stream and both are uniformly mixed and then recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carbon fiber-containing gypsum molding die for molding polymer processed products other than ceramic products, non-ferrous metal products, fine ceramic products or paperware products, and carbon fibers containing ceramics. The present invention relates to a raw gypsum powder for a reinforced gypsum molding die and a method for producing these. Conventionally, the strength of general molding gypsum molds (hereinafter simply referred to as gypsum molds) for molding polymer products, non-ferrous metal products, fine ceramic products or paperware products, etc. excluding ceramic products is increased. There are various methods for making it possible, for example, to mainly use β-type hemihydrate gypsum to mix α-type hemihydrate gypsum to reduce the amount of water mixed, or to mix cement or resin in gypsum. There is also a method to do so, and there is also a method to mix natural fibers such as hemp or glass fibers into the plaster. However, when the α-type hemihydrate gypsum is mixed with the β-type hemihydrate gypsum to reduce the amount of water mixed, the strength itself is slightly improved but the water absorption performance is deteriorated. Good water absorption performance of the gypsum mold is one of the most important factors for the plaster mold for casting such as pulp slurry. That is, when the water absorption performance of the gypsum mold is poor in the molding method utilizing the water absorption performance of the gypsum, the molding time per product becomes long, the molding efficiency decreases, and the finished shape of the product also deteriorates. Therefore, in the cast molding method involving dewatering operation such as fine ceramics and paper containers, the deterioration of the water absorption performance of the gypsum mold is a fatal defect in product manufacture. Molds for investment casting of gold, silver and copper alloys for dental materials and accessories, or molds for precision casting of non-ferrous metal products such as dies, machine parts in general, arts and crafts, etc. Permeability is one of the important factors to escape the gas generated at the interface between the cast metal and the cast metal. If adequate breathability is lacking, either pressure or vacuum casting must be utilized. Also, when cement or resin is mixed in gypsum, the strength itself is improved,
Similarly, it has the drawback that the water absorption performance is lowered and the physical properties of other gypsum are also changed. When natural fibers such as hemp are mixed in gypsum, the tensile strength of natural fibers is smaller than that of synthetic fibers, so the strength cannot be increased unless the amount of gypsum mixed is large. At the same time, an increase in the amount of natural fibers mixed inevitably leads to a decrease in the water absorption performance of the gypsum type. Moreover, since the natural fibers are thick monofilaments themselves, the ends of the fibers that have entered the surface layer of the gypsum type are The surface of the molded product is damaged by the exposed fiber ends, and the surface properties become inhomogeneous due to the lack of water absorption at the exposed fiber ends. . Furthermore, when glass fiber is mixed in gypsum, the strength of the gypsum mold is slightly improved, but since the glass fiber has rigidity, the end of the glass fiber that has entered the surface layer part is exposed on the molding surface and molded. It has the drawback of scratching the surface of the product. INDUSTRIAL APPLICABILITY The present invention has excellent strength characteristics, flexibility, light weight, low thermal expansion property, and further cuts carbon fibers having an extremely small diameter into a length of 5 to 100 mm, and then 0.008 to 0. By uniformly dispersing and mixing 9% by weight in the form of monofilament, water absorption performance, which is the main physical property of paperware molds, or dental materials, molds for investment casting of jewelry, or metalware The mechanical strength of the gypsum mold is increased without deteriorating the ventilation performance, which is an important physical property in the precision casting mold, and without changing other physical properties of the gypsum mold in the case of other general gypsum molds. The strength (durability) against a specific external force and the strength (durability) against an internal stress due to thermal strain are increased. A first object of the present invention is to increase the material mechanical strength of the gypsum mold without lowering the original functions of the gypsum mold, such as high dimensional accuracy, low cost, and ease of molding by casting, and strength against mechanical external force. When,
By simultaneously increasing both strength against internal stress due to thermal strain, damage to the gypsum mold due to external pressure or internal pressure during molding, and at the time of paper container molding, the drying time of the gypsum mold after each molding is completed. Shortening is to improve molding efficiency (productivity by plaster mold). A second object of the present invention is to produce a gypsum mold in which carbon fibers are mixed, in which a large number of monofilamentary carbon fibers are uniformly dispersed in the gypsum slurry, whereby the carbon fibers are uniformly dispersed in the gypsum matrix. It is to mix and disperse in. As the gypsum mold according to the present invention, a general cast molding gypsum mold, a precision metal casting gypsum mold, a press molding gypsum mold of powder or a plastic material, an extrusion molding gypsum mold, an injection molding gypsum mold, and the like. Fine materials such as press-molding plaster molds for so-called fine ceramics, injection-molding plaster molds, cast-molding plaster molds, etc. that do not contain clays in the raw material mixture of alumina, silicon carbide, silicon nitride, partially stabilized zirconia, sialon, etc. A gypsum mold for ceramic molding is included. Further, it includes a rocker molding die for fine ceramics, a casting molding die, and a casting molding die for producing a paper container from pulp slurry, which is carried out by utilizing the water absorption performance of gypsum itself. Further, the type of carbon fiber used in the present invention may be any of polyacrylonitrile-based, pitch-based, rayon-based or lignin-povar-based, but it has a high strength or a high strength because it increases the strength of the gypsum mold. An elastic carbon fiber is desirable, specifically, a tensile strength of 200 kgf / mm ² (Kg / mm ² ) or more and a tensile elastic modulus of 20.000 kgf / mm ² (Kg / mm ² ).
The above is desirable. In the present invention, it is a very important element to uniformly disperse and mix carbon fibers that tend to form nodules into a single-fiber state without producing nodules in the plaster mold of the base material (structure of the plaster mold). From this point of view, the length of carbon fiber to be mixed in the plaster mold as a reinforcing material,
And the weight ratio to gypsum is defined. The carbon fibers are dispersed into a large number of single fibers and mixed in the plaster mold of the base material. However, the length of the carbon fibers is 5 because of the reason described later.
To 100 mm, preferably 20 to 30 mm. Fig. 1 shows the ratio of 100 parts by weight of gypsum, 60 parts by weight of water, and 0.5 parts by weight of carbon fiber.
The graph of the test result showing the relationship between the length of the carbon fiber in the gypsum test piece of mm × 25 mm × 250 mm and the bending strength (bending strength) is shown, and as is clear from this, the length of the carbon fiber is It can be seen that the bending strength sharply decreases when the thickness is 15 mm or less. Here, the length of the carbon fiber to be dispersed and mixed in the plaster mold of the base material is 5 to 100.
When the length is less than 5 mm, it is not possible to sufficiently improve the strength of the gypsum mold due to the shortage of the total bonding area between the gypsum particles of the base material and the single fibers of the carbon fibers. 1
When it is more than 00 mm, it becomes difficult to handle it when it is dispersed into single fibers, when it is mixed with gypsum powder and water, or when it is poured into the case mold, and it is difficult to uniformly disperse it in the gypsum mold. This is because First, carbon fibers manufactured by a conventional method are cut into a length of 5 to 100 mm, and then separated into an infinite number of single fibers by a predetermined method. The following is an example of a method of dispersing the bundled carbon fibers into single fibers. First, the bundled carbon fibers are heated in an oxidizing atmosphere to oxidize and remove the sizing agent for handling and stabilizing applied on the surface, or the sizing agent is washed away with an acetone solvent to remove the sizing agent. The heating temperature for removing the sizing agent by heating is relatively determined by the relationship with the sizing agent applied to the surface, but is around 300 ° C, which is the general maximum safe use temperature of carbon fiber. It is desirable to do in. The carbon fibers from which the sizing agent has been removed by heating are easily dispersed in the countless (usually 1,000 to 24,000) single fibers having extremely small diameters (usually 5 to 10 μm) constituting the carbon fibers. Then remove the sizing agent and remove 5 to 1
When carbon fibers cut into a length of 00 mm were put into a water tank and gently rotated by a stirring blade while applying ultrasonic vibration, the sizing agent was removed by the previous heating and the carbon fibers were easily dispersed. Is dispersed in a myriad of single filaments having extremely small diameters without causing agglomeration due to the synergistic effect of ultrasonic vibration and gentle stirring. During stirring, the number of rotations should be 40 to 60 rpm in a water tank having a diameter of about 60 cm so that the carbon fibers are not damaged by the stirring blades. After the dispersion treatment, take out the innumerable dispersed single fibers from the water tank,
Dehydrate and dry. Further, as another method of separating the bundled carbon fibers into single fibers, there is a method of previously sizing the carbon fibers with a water-soluble sizing agent. That is, the bundle-like carbon fibers sized by the water-soluble sizing agent are cut into a length of 5 to 100 mm, and the carbon fibers suitable for one mixing ratio are weighed in advance, and the weighed carbon fibers are weighed. When the carbon fiber is put into a container 1 (see FIG. 4) containing water that is suitable for one mixing ratio and gently stirred by a stirring blade, the water-soluble sizing agent applied to the carbon fiber Is immediately dissolved in water and self-diffuses, and the bundle-like carbon fibers are uniformly dispersed in the countless single filaments having extremely small diameters in water without agglomeration by the stirring action of the stirring blades. Even in the case of this method, the rotation speed is 60 cm in diameter so that the carbon fibers are not damaged by the stirring blade during stirring.
It should be 40 to 60 rpm in a medium container. When the carbon fibers are dispersed into single fibers by this method, the gypsum powder suitable for the mixing amount once and the set retardation are set in the container 1 in which the carbon fibers are uniformly dispersed in water. Gypsum slurry is prepared by adding additives such as agents and stirring. Next, if a method of making a gypsum slurry in which carbon fibers dispersed in single fibers are mixed is described, the ratio of carbon fibers to gypsum powder is 0.01 to 1% by weight (of the hardened gypsum type) for the reason described below. Converted to the ratio of carbon fiber to gypsum of the base material, it is approximately 0.008 to 0.9% by weight), preferably 0.
It is necessary to make it 1 to 0.3% by weight. FIG. 2 shows 15 mm × 25 mm × 250 in which carbon fibers having a length of 20 mm are mixed in a required weight part (various weight parts) in a ratio of 100 parts by weight of gypsum powder and 60 parts by weight of water.
It is a graph of the test result which shows the relationship between the weight% of the mixed carbon fiber with respect to the gypsum powder in a gypsum test piece of mm, and bending strength. FIG. 5 is a graph of test results showing the relationship between the weight ratio of carbon fibers mixed in the gypsum powder and the water absorption rate, that is, the water absorption performance (weight% of water that can be absorbed by the test piece of hardened gypsum). As is clear from FIGS. 2 to 3, it is understood that as the weight ratio of the carbon fibers mixed in the gypsum powder increases, the flexural strength increases and the water absorption increases. Increasing the water absorption capacity of gypsum due to the incorporation of carbon fibers is that the particles of gypsum are needle-shaped, and the cross-sectional shape of the carbon fibers is circular or a shape similar to this, and the size of the particles of gypsum and carbon. It is considered that this is because the diameter of the fibers is not so different from each other, so that the mixing of the carbon fibers forms new voids between the carbon fibers and the gypsum particles. Here, the mixing ratio of the carbon fiber to the gypsum powder is set to 0.01 to 1% by weight, because the mixing ratio of the carbon fiber is less than 0.01% by weight, the ratio of the carbon fiber to the gypsum powder is too small and the gypsum mold is used. It is not possible to improve the strength sufficiently, and the mixing ratio of carbon fiber is 1
If it exceeds 10% by weight, the ratio of carbon fibers is too large when making the gypsum slurry, and the carbon fibers cannot be uniformly dispersed in the gypsum slurry in a single fiber state, and the agglomeration of carbon fibers easily occurs, Poor fluidity when pouring gypsum slurry into the mold makes casting work difficult, and water absorption or capillary (capillary porosity) of the gypsum mold to be molded
When the physical properties such as change the air permeability and water absorption, the condition as a molding material is no longer satisfied, and carbon fiber nodules easily form inside the molded gypsum mold, resulting in a non-homogeneous state. As a result, the function as a mold for precision products will no longer be satisfied. Then, in order to form a gypsum slurry in which carbon fibers are uniformly dispersed by using carbon fibers which have been separated into single fibers in advance by removing the sizing agent, in a container 1 as shown in FIG. Water and suitable additives such as a set retarder, a water reducing agent, etc., which are suitable for the mixing amount of water, have been put in advance, and then carbon fibers dispersed in a predetermined amount of single fibers preliminarily weighed in this container 1 , And finally, a predetermined amount of gypsum powder is charged and the container 1 is attached to a vacuum stirrer.
When the stirring blade is rotated at a low speed and mixed and stirred, a gypsum slurry in which monofilaments of carbon fibers are uniformly dispersed in the gypsum slurry is obtained without forming agglomerates. The reason why the carbon fibers are uniformly dispersed in the gypsum slurry without producing agglomerates is that the ratio of the carbon fibers to the gypsum powder is extremely small.
Next, in the case of manufacturing a plastic cast molding gypsum mold for molding a dish, the above-mentioned gypsum slurry in which carbon fibers are uniformly dispersed is used for upper mold molding as shown in Fig. 5 (a). Pour gently into the case mold 2 and leave it for a predetermined time, and after curing, apply a light impact to disperse the case mold 2 up and down to remove it, and after that, dry sufficiently at a predetermined temperature. The upper die 3 of a plastic molding gypsum mold for casting a plate as shown in FIG. Since carbon fiber has rich flexibility, it is understood that it deforms freely even after casting, and it easily enters between the particles of gypsum, and also mixes into the surface layer part of the cast gypsum mold. The end of the carbon fiber thus formed is hardly exposed on the molding surface, but even if it is exposed, the diameter of the single fiber of the carbon fiber is extremely small as described above, and it has rich flexibility. Therefore, the surface of the polymer molded product such as plastic or rubber is hardly scratched by the carbon fiber exposed on the molding surface. Similarly, the lower mold 4 of the plaster mold for plastic casting is molded using the case mold for molding the lower mold. The lower mold 4 is provided with a molten plastic injection hole 5. In the case of injecting at normal pressure, FIG. 5B is actually used in an inverted state. Thus, even if the ends of the carbon fibers are exposed to the molding surface, the surface of the molded product is hardly damaged, but especially the molded product is a high-grade product and the molding surface is extremely precise and smooth. When it is necessary to obtain the above, as shown in FIG. 6 (a), while rotating the case mold 2 at a low speed, a small amount of pure gypsum slurry is poured to form a thin film 6 having a thickness of 1 to 3 mm in advance. After that, the rotation of the case mold 2 is stopped and immediately the gypsum slurry in which the carbon fibers are uniformly dispersed is gently poured, and thereafter the same operation as described above is performed.
The upper mold 3'of the plaster mold for plastic molding is molded. When the lower mold 4'is molded in the same manner, as shown in Fig. 6 (b), the thin film 6 made of pure gypsum is formed on the outer peripheral surface which is the molding surface.
A gypsum mold for plastic pressure casting coated with is obtained,
It is possible to reliably prevent the carbon fibers from being exposed on the molding surface. It is also possible to mold plastic injection molding dies made of beryllium copper alloy, aluminum alloy, zinc alloy or mold non-ferrous alloy articles with a plaster mold whose molding surface is covered with a thin film of pure gypsum. In this case, the molding surface of the molding die or the surface of the container is not damaged by the end of the carbon fiber. Further, in the case of manufacturing a large number of plaster molds for plastic-molding a plate-shaped body having an engraved pattern, it is carried out as follows. 7th
In the figure, gypsum prototypes or prototypes (first mold) 11 to original molds in which carbon fibers are uniformly dispersed and mixed, or only the inside uses carbon fiber-containing gypsum and pure gypsum is used for the surface layer part (Prototype female mold) {second mold} 12a, 12b is duplicated and manufactured. In the case of precision casting of metal, the original molds 12a and 12b are called master molds. The entire plaster female die of this original die is divided into upper and lower halves, and a female die (not shown) corresponding to the upper male die portion 12b and a male die 1 corresponding to the lower female die 12a.
A female mold 16 including 3a is manufactured. The lower female mold 14 has a gypsum slurry injection port 15. This mold 16 is a so-called case mold (third mold) in ceramic molding. In the following, metal or plastic other than ceramic and paper container molding are also referred to as case type. The above-mentioned gypsum slurry in which carbon fibers are uniformly dispersed is injected into the case mold 16 through the gypsum slurry injection port 15. When injecting gypsum slurry under normal pressure (atmospheric pressure), the case mold 16 shown in Fig. 7 (c) is used.
Must be done upside down. After being left for a predetermined time and cured, the upper mold 13 and the lower mold 14 are separated, and the lower mold 17 of the molding mold (fourth mold) is taken out. Similarly, a case mold is molded from the upper part 12b of the original mold, and gypsum slurry in which carbon fibers are uniformly dispersed is injected into the case mold to mold the upper mold 18 of the mold. A combination of the upper mold 18 and the lower mold 17 of this mold is a so-called "use mold" in ceramic molding. The gypsum mold reinforced with the carbon fiber according to the present invention has a small volume expansion coefficient in the curing process, and further, the thermal expansion coefficient of the cured gypsum mold is small. If gypsum that is uniformly dispersed and mixed is used, it is possible to duplicate a highly accurate mold from the original mold to the molding mold with little dimensional change. In the case of a gypsum mold for molding a molding die such as a beryllium copper alloy, aluminum alloy or zinc alloy plastic injection molding mold, as compared with the case of direct molding with a gypsum mold,
Since the shape duplication process is more and more complicated, the volume expansion coefficient in the hardening process of the gypsum mold and the small thermal expansion coefficient of the hardened gypsum mold are more important characteristics in high precision duplication. In addition, when the gypsum slurry in which the carbon fibers are uniformly dispersed is produced by the above-mentioned method, a small amount of carbon fibers must be accurately measured every time the gypsum slurry is produced, which is troublesome. Therefore, a jet air flow that circulates carbon fibers, which is lightweight and rich in buoyancy, and is difficult to handle, or by using oscillating rotation, is mixed and dispersed in the gypsum powder evenly in the single fiber state in advance. You may use it as a powder. As a result, it is possible to eliminate the troublesome operation of measuring only a small amount of carbon fiber suitable for one mixing amount each time gypsum slurry is produced. More specifically, a mixing method using a circulating jet air flow will be described. A mixing device for mixing gypsum powder and carbon fibers dispersed in single fibers at a ratio of 0.01 to 5% by weight of carbon fiber to gypsum powder. When it is put into the air flow, the gypsum powder and the carbon fibers dispersed in the single fibers are appropriately mixed while being circulated many times in a state of being scattered by the jet air flow, and then the cyclone or the back filter causes the air flow to flow into the air flow. When separated and recovered from the above, a gypsum powder containing carbon fibers is obtained in which the gypsum powder and the carbon fibers dispersed in the single fibers are uniformly mixed. Here, the pressure of the jet air flow is 1 to 2 kgf / cm ² (Kg / c
m ² ), it is necessary to have a low pressure of m ² ). When the air pressure is increased, the collision force between the gypsum particles or the gypsum particles and the carbon fiber becomes large at the time of mixing, so that the gypsum particles and the carbon fiber are separated from each other. All of them are crushed to change the physical properties as a plaster mold material, which is not preferable. Further, as another method for uniformly mixing the carbon fiber with the gypsum powder, there is a mixing method using oscillating rotation. As shown in FIG. 8, the gypsum powder and the carbon fibers dispersed in the carbon fibers dispersed in the monofilament are placed in the flexible bag body 21 as compared with the gypsum powder. When the oscillating plate 22 attached to the bottom of the bag body 21 is oscillated by the oscillating shaft 24 eccentrically attached to the rotating shaft 25, the bag body 21 The mixture in the inside is accelerated, and the magnitude and direction of the velocity thereof are changed arbitrarily, so that the gypsum powder and the carbon fiber in the bag body 21 are uniformly mixed. When carbon fibers are mixed in the gypsum powder, it is possible to simultaneously mix necessary additives such as a set retarder and a water reducing agent. In addition, the above-mentioned gypsum powder is one in which carbon fibers dispersed in innumerable single fiber state are uniformly mixed and dispersed in the gypsum powder. In the case of sizing-treated carbon fiber, it is not necessary to disperse it into preliminarily monofilament, and since the water-soluble sizing agent has the property of elution into water and self-diffusion when making gypsum slurry, the gypsum in the bag body It can be put in the powder as a bundle and mixed. Furthermore, when using the raw gypsum powder mixed and dispersed in the gypsum powder in a proportion higher than the weight ratio when the carbon fiber is used, the gypsum powder is mixed again during use, and the gypsum powder and the carbon fiber are mixed with gypsum. Although the carbon fiber must be diluted to a ratio of 0.01 to 1% by weight with respect to the powder, this method can reduce the transportation cost of the gypsum powder mixed with the carbon fiber. If the ratio of carbon fiber to gypsum powder is 0.01 to 5% by weight, it is difficult to mix it in a single fiber state if it exceeds 5% by weight, and if it is less than 0.01% by weight, the molding is continued. This is because it cannot be used for molding. When it is used as it is without dilution, the mixing ratio of carbon fiber to the gypsum powder is 0.01 to 1% by weight. In addition, when plaster mixed with carbon fiber is used as a mold material for a general molding die or a molding die, a ceramic molding die is manufactured from the gypsum mold to perform polymer processing or metal precision molding. When performing casting or casting of ceramics other than ceramics, that is, glass, fine ceramics, or blow molding of high-grade glassware, the expansion coefficient during hydration hardening of gypsum mixed with carbon fiber, Also, since the expansion rate during cooling demolding and the subsequent drying shrinkage rate / expansion rate are both small, the accuracy of the replicated product when casting it repeatedly into the mother mold (female mold) and replicating the mold is good, and an accurate replicated product. You can In addition, since the coefficient of thermal expansion of the mold itself is small, expansion and contraction due to temperature change is small, which enables highly accurate replication and improves the accuracy of the molding mold itself. Therefore, even if the repetitive duplication is repeated several times, the duplication error between the first die (prototype) and the final die (molding die) is small.
This point is the most important as a mold material for molding a metal mold or a ceramic mold in precision casting. When the gypsum mold according to the present invention is used as a press mold, the state of the molding raw material such as metal, plastic, or ceramics may be in the form of dry powder, or may be in the form of paste such as china clay. Further, it may have a sheet shape. Further, although the present invention has a direct purpose of strengthening the molding die itself with carbon fibers, a member constituting the molding die such as a ceramic core (core) in an investment mold, or holding the molding die. The jig-like member for positioning or positioning may be made of gypsum reinforced with carbon fiber.
Next, examples of the present invention and comparative examples will be given.

Example 1 Polyacrylonitrile-based fibers were heat treated at about 300 ° C. and then further heat-treated at about 1300 ° C. in a nitrogen gas atmosphere to be graphitized, and about 6000 single fibers each having a diameter of 7 μm were bundled into a carbon fiber. I was there. The physical properties of this carbon fiber are as follows: tensile strength 300 kgf / mm ² (Kg / mm ² ), tensile elastic modulus 23,000 kgf / mm ² (Kg / mm ² ), density 1.75 g / cm ³ , linear expansion coefficient −0. .1 × 10 ⁻⁶
/ ° C, thermal conductivity 15 Kcal / m. hr ・ ° C (17.4
5 W / mK, specific heat 0.17 cal / g ° C (0.7
It was 1 kJ / kg · K). This carbon fiber is about 20m
It was cut into a length of m and dispersed into innumerable single fibers by a synergistic effect of ultrasonic vibration and stirring in water. 100 parts by weight of β-gypsum powder, 60 parts by weight of water, 0.1 parts by weight of carbon fiber, and 0.2 parts by weight of borax (setting retarder) were mixed and stirred to uniformly disperse the carbon fibers. A plaster mold for casting was prepared by making a plaster slurry and pouring the plaster slurry into a case mold to cast a plastic elliptical dish. In this cast molding gypsum mold, single fibers of carbon fibers were uniformly dispersed over the entire cut cross section, and this dispersion state was visible to the naked eye.

Example 2 A gypsum slurry in which monofilaments of carbon fibers were uniformly dispersed was prepared by the same conditions and method as in Example 1, and pure gypsum slurry without carbon fibers was poured in advance while rotating the case mold at a low speed. Plaster for casting to form a thin plastic film with a thickness of 1 to 3 mm, then stop the rotation of the case mold and pour the plaster slurry mixed with carbon fibers to cast a plastic elliptical dish. Got the mold. The molding surface of this cast molding gypsum mold was covered with a thin film of pure gypsum, and carbon fibers were not exposed at all on the molding surface.

Example 3 Polyacrylonitrile-based fiber was heat treated at about 300 ° C., and then special heat treatment was further performed at about 2500 ° C. in a nitrogen gas atmosphere for graphitization, and a single fiber having a diameter of about 7 μm was sized with polyvinylpyrrolidone to about 6000. A bundle of carbon fibers was used. The physical properties of this carbon fiber are
Tensile strength 250 kgf / mm ² (Kg / mm ² ), tensile elastic modulus 35,000 kgf / mm ² (Kg / m
m ² ), density 1.77 g / cm ³ , linear expansion coefficient −0.1
× 10 ⁻⁶ / ° C, thermal conductivity 100 Kcal / m · hr ·
℃ (116W / m ・ K), specific heat 0.17cal / g ・ ℃
(0.71 kJ / kg · K). This bundle of carbon fibers is cut into a length of 25 mm, and the carbon fibers are weighed in advance so that the ratio of the carbon fibers to 100 parts by weight of β-gypsum powder is 0.3 parts by weight. When put into a container of water weighed in advance and agitated supplementarily, the bundled carbon fibers self-diffuse and are dispersed into innumerable single fibers, and are evenly distributed in water by the agitating action. Dispersed. Thereafter, gypsum powder, borax (hardening retarder) and Melment F-20 (water reducing agent) manufactured by Showa Denko KK were added and mixed and stirred to give 100 parts by weight of gypsum powder, 60 parts by weight of water, carbon fiber. A homogeneous gypsum slurry was made up in the proportions of 0.3 parts by weight, 0.2 parts by weight of retarder and 0.2 parts by weight of water reducing agent. First, as shown in FIG. 9, from the prototype 31 of the cup, the original mold (second
The lower mold of the intermediate mold) 32 is manufactured, and the lower mold of the case mold (third intermediate mold) 35 is manufactured by using the master mold 32 with the plaster slurry. In order to form a silver alloy cup by pouring pure gypsum slurry while rotating the case mold 33 combined with the upper case 34 at a low speed of 100 rpm to form a thin film 35 having a thickness of 1 mm in advance and then casting the gypsum slurry. The lower mold 36 of the plaster mold 38 for cast molding was obtained. The state of dispersion of the carbon fibers mixed in the lower mold 36 of the cast molding gypsum mold was substantially uniform as in Example 1. Similarly, the upper mold 37 was manufactured, and the upper mold 37 and the lower mold 36 were combined to integrally cast a silver alloy cup. The delicate pattern on the outer surface was reproduced precisely to obtain a magnificent silver alloy cup.

Example 4 A gypsum mold for producing synthetic rubber balls by casting a gypsum slurry in which monofilaments of carbon fibers are uniformly dispersed according to the same conditions and methods as in Example 3 is cast into a mother mold. It was

Example 5 Under the same conditions and methods as in Example 3, gypsum slurry in which monofilaments of carbon fibers were uniformly dispersed was prepared, and this was poured into a mother die to form a ceramic ball in an isostatic press (isostatic press). A gypsum mold for casting a polyurethane / rubber mold for molding was obtained.

Example 6 A gypsum slurry in which monofilaments of carbon fibers were uniformly dispersed was prepared by the same conditions and methods as in Example 3, and the gypsum slurry was poured into a mother mold to cast a sialon crystal glass blow mold. A plaster mold was obtained.

Comparative Example 1 100 parts by weight of β-gypsum powder, 60 parts by weight of water, and 0.2 parts by weight of borax were mixed and stirred to prepare a pure gypsum slurry containing no carbon fiber, and the gypsum slurry was placed in a case mold. An injection-molding plaster mold for pouring and injection-molding a plastic oval dish was obtained.

Example 7 Polyacrylonitrile-based fibers were heat treated at about 300 ° C., and then further heat-treated at about 1300 ° C. in a nitrogen gas atmosphere to be graphitized, and about 6000 single fibers each having a diameter of about 7 μm were bundled into a carbon fiber. I was there. The physical properties of this carbon fiber are as follows: tensile strength 300 kgf / mm ² (Kg / mm ² ), tensile elastic modulus 23,000 kgf / mm ² (Kg / mm ² ), density 1.75 g / cm ³ , linear expansion coefficient −0. .1 × 10 ⁻⁶
/ ° C, thermal conductivity 15 Kcal / m · hr · ° C (17.4
5 W / mK, specific heat 0.17 cal / g ° C (0.7
It was 1 kJ / kg · K). This carbon fiber is about 20m
It was cut into a length of m and dispersed into innumerable single fibers by a synergistic effect of ultrasonic vibration and stirring in water. 100 parts by weight of β-gypsum powder, 60 parts by weight of water, 0.1 part by weight of carbon fiber, and 0.2 part by weight of borax (setting retarder) were mixed and stirred to uniformly disperse the monofilament of carbon fiber. Made plaster slurry. Then, as shown in FIG. 10, the prototype 41 is embedded in the clay or gypsum up to the division surface, and the plaster slurry is poured as it is to mold the upper half surface of the prototype 41, and then the prototype 41 is inverted. Then, the same operation is performed to mold the lower half surface of the master 41 to produce the master 42. The lower molds 43 and 44 are manufactured by pouring the gypsum slurry into the original mold 42, and the upper molds 45 and 46, which are separately manufactured, are combined to form the case mold 4.
7,48. In the case molds 47 and 48, carbon fiber monofilaments are uniformly dispersed over the entire surface including the cross section,
The dispersed state was visible to the naked eye.
The case molds 47 and 48 were used as casting molds while rotating at low speed, and a molten liquid of aluminum was cast to manufacture a plastic casting mold 49. The pattern on the surface of the master 41 was accurately transferred to the mold 49 as it was.

Comparative Example 2 100 parts by weight of β-gypsum powder, 60 parts by weight of water, and 0.2 parts by weight of borax were mixed and stirred to prepare a pure gypsum slurry containing no carbon fiber, and this gypsum slurry was used as Example 7. Pour into the same original mold to make a case lower mold and a case upper mold, combine them with a separately manufactured upper case to obtain a case mold, and cast an aluminum alloy melt into this case mold to make a plastic. A casting mold was manufactured. The rate of change in length and the replication accuracy at each temperature during dry release of the gypsum case molds of Example 7 and Comparative Example 2 were as follows. Regarding the rate of change in length, at the maximum heat generation of the case type (53.2 ° C), the conventional product not mixed with carbon fiber expanded 0.076% (0.38 mm against 500 mm) (when cured) The product of the present invention has expanded 0.066% (0.33 mm with respect to 500 mm) and has a room temperature (23.5%).
After cooling to 0 ° C.), the conventional product has a density of 0.
It expanded by 025% (0.125 mm for 500 mm), while the product of the present invention expanded 0.018% (500 mm).
0.09 mm) had been expanded. After that, 50
When dried in a hot air dryer at ℃ for about 10 days, the accuracy of replication is 0.06mm compared to 500mm for conventional products.
The product of the present invention was dried and shrunk and expanded by 0.065 mm with respect to the master mold, whereas the product of the present invention was shrunk by 0.04 mm and expanded by 0.05 mm with respect to the master mold. As is clear from this, it is understood that the product of the present invention has a small expansion during hydration hardening and has a good replication accuracy. The physical properties of the gypsum molds of Examples 1 to 6 and Comparative Example 1 such as transverse rupture strength, water absorption capacity, breaking temperature difference in the atmosphere, bulk specific gravity and expansion coefficient upon curing were as shown in the table below. .

The water absorption capacity is measured by immersing the test piece under normal temperature and pressure.
It is the weight percentage of absorbed water. The rupture temperature difference represents the minimum temperature difference that results in rupture when a test piece heated in a high temperature atmosphere is quickly taken out into a room and left in a room temperature atmosphere.
The expansion coefficient at the time of hardening is the ratio of the length of the master mold to the length measured when the gypsum slurry was cast into the master mold, hardened and then demolded, and immediately before drying. As is clear from the above table, the gypsum mold mixed with carbon fiber has greatly improved the transverse rupture strength and the difference in fracture temperature in the atmosphere as compared with the gypsum mold not mixed with carbon fiber, and also in other physical properties. It turned out to be excellent. FIG. 11 is a photograph of a thin piece manufactured from the cut surface of the gypsum hardened body of Example 1 taken at a magnification of 2000 with a scanning electron microscope. A slender straight cylinder extending from the upper left corner to the center is a mixed carbon single fiber, and the shard-like crystals are β-type dihydrate gypsum. FIG. 12 is the same as that of Example 1, that is, FIG. 11 except that α-type gypsum powder is used, and is a scanning electron micrograph of 2000 times. In addition, FIG. 13 shows a gypsum test piece of 15 mm × 25 mm × 250 mm formed by casting gypsum slurry mixed with 100 parts by weight of gypsum, 60 parts by weight of water, and a predetermined weight part of pitch-based carbon fiber having a length of 25 mm. The relationship between the elapsed time when a bending test is performed by a test apparatus and the transverse rupture strength is shown, and is the test result when the weight ratio of the mixed carbon fibers is used as a parameter. As is clear from the graph of FIG. 13, the greater the ratio of the mixed carbon fibers, the greater the transverse rupture strength, and the fragility of simple fracture due to the maximum transverse rupture force is eliminated and so-called tenacity as a material occurs. I understand. The suban for this test is 200m
In m, the load is applied to the center and the displacement speed at the load point is 1 m
It was m / min. FIG. 14 shows a curve showing the rate of change in length at each temperature between a pure gypsum test piece and a gypsum test piece reinforced with carbon fiber. The length of the gypsum test piece mixed with carbon fiber is shown. It can be seen that the rate of change (expansion) of the thickness is slightly smaller in both positive and negative cases than the rate of change (expansion) of the length of the gypsum test piece in which carbon fiber is not mixed. It is understood that this is because carbon fibers having a coefficient of thermal expansion almost equal to zero enter between the particles of the gypsum, and the carbon fibers suppress expansion or contraction of the gypsum. Therefore, the gypsum mold mixed with the carbon fiber has little expansion or contraction due to temperature, and the dimensional accuracy of the molded product is improved. Here, when the gypsum mold is used as a metal forming or polymer processing forming mold or a paper container forming mold, the material mechanical strength of the stone-growing mold is increased due to a great improvement in bending strength and bending strength. By increasing the mechanical strength of the part that was conventionally damaged by external pressure or internal pressure during molding, damage to the gypsum mold can be prevented, and high (fast) cycle molding becomes possible and molding efficiency ( Productivity) and the life of the plaster mold is extended. In addition, damage to the molding machine such as pressure casting, centrifugal casting, vacuum casting, and injection molding due to breakage of the plaster mold during molding can be prevented from being interrupted by production, and damage to the molding machine can be prevented. It is possible to save the trouble of replacing the parts and readjusting them. Furthermore,
By significantly improving the mechanical strength, it is possible to reduce the thickness of the gypsum mold, which in turn reduces the amount of gypsum used. In addition, the difference in the destruction temperature in the atmosphere due to the incorporation of carbon fibers is that the gypsum itself expands by a predetermined amount due to the temperature increase, but the carbon fibers themselves do not expand at all, so the carbon fibers inside the gypsum mold are Along with a tensile force applied in the length direction, a compressive force is applied to the gypsum, which causes an internal stress in the length direction of the carbon fiber, which is a state where prestress is introduced just like PS concrete. It is understood that it is because of it. A large increase in the fracture temperature difference in the atmosphere means that the gypsum mold can withstand a large temperature difference, and in the case of molding fine ceramics or paper containers, increase the drying temperature of the gypsum mold after molding. It becomes possible. Therefore, the drying time of the gypsum mold for each molding can be shortened, the number of molding dies to be held in the drying device can be reduced, and the molding efficiency (productivity) can be improved. Therefore, it is possible to reduce the number of operating gypsum molds with respect to the number of molded products such as fine ceramics and paper containers, which is suitable for molding a large number of small-volume products, and at the same time, it is possible to reduce the product cost. In addition, the reduction in bulk specific gravity reduces the weight of the gypsum mold, and the transport or handling of the gypsum mold is improved. Further, due to the slight decrease in expansion during hardening, the pressure applied to the case mold during molding of the gypsum mold is reduced, which facilitates demolding, and at the same time prevents damage to the case mold. The same effect can be obtained in the case of manufacturing other molds for non-ferrous metal casting. Summarizing the above, the present invention has the following effects.

(1) The material mechanical strength of the gypsum mold is greatly increased to prevent damage to the gypsum mold due to external pressure or internal pressure during molding, and at the same time, strength (durability) against internal stress due to temperature difference. Greatly increased, and in the molding that utilizes the water absorption performance of the gypsum mold, such as cast molding of fine ceramics and paper containers, it is possible to raise the drying temperature of the gypsum mold for each molding and shorten the drying time. At the same time, complete drying is possible, and the molding efficiency can be remarkably improved.

(2) As a gypsum-type reinforcing material, since carbon fiber having an extremely small diameter, a large strength and a high flexibility is used, even if the mixing ratio of the reinforcing material to the gypsum is small, the mechanical characteristics of the gypsum-type are large. Since the strength against external force and thermal inhomogeneity can be increased, and the mixing ratio of the reinforcing material is small,
Water absorption performance, which is the basic performance of a plaster mold for molding that utilizes water absorption such as cast molding of fine ceramics and paper containers due to the incorporation of carbon fibers, or air permeability in the case of molding non-ferrous metal products It never drops.

(3) When the surface layer, which is the molding surface of the gypsum mold, is covered with a thin film of pure gypsum, it is possible to reliably prevent the ends of the carbon fibers from being exposed on the molding surface, and to smooth the surface of the molded product. Can be

(4) Since the carbon fiber having a high temperature heating and burning property is mixed as a reinforcing material, the gypsum mold which is damaged during use or cannot be used is crushed for a long time. By gently performing the high temperature heat treatment, only the carbon fibers mixed in the inside can be easily burned and removed, and the cured gypsum can be reused. In this regard, if a material that does not burn by heating, such as glass fiber, is mixed in as a reinforcing material,
It is extremely difficult or impossible to recycle or reuse the gypsum mold by removing only the entrained reinforcements.

(5) The carbon fiber is cut into a length of 5 to 100 mm, the sizing agent is removed by heating, and the mixture is stirred in water while applying ultrasonic vibration. -Shaped carbon fibers can be easily dispersed into innumerable monofilaments, which allows even dispersion of innumerable monofilaments of carbon fibers in gypsum slurry, which in turn allows the carbon fibers to be uniformly mixed in the plaster mold. it can.

(6) In the case of using carbon fiber sized with a water-soluble sizing agent, the carbon fiber should be 5 to 100
After cutting to a length of mm, it is put into water to dissolve the water-soluble sizing agent in water to disperse bundle-like carbon fibers into innumerable single fibers, and then gypsum powder is added and mixed and stirred. As a result, a gypsum slurry in which carbon fibers are uniformly mixed and dispersed can be produced, and thus pretreatment only for dispersing bundled carbon fibers into innumerable single fibers becomes unnecessary.

(7), carbon fiber is cut into a length of 5 to 100 mm and preliminarily dispersed into innumerable monofilaments, and gypsum powder,
The carbon fibers dispersed in monofilaments in a predetermined weight ratio with respect to the gypsum powder are put into a circulating jet air flow to uniformly mix the both, and then recovered, and then put into the gypsum powder. By uniformly mixing and dispersing the dispersed carbon fibers in the single fibers, it is possible to eliminate the need to measure only a small amount of carbon fibers suitable for one mixing amount each time gypsum slurry is prepared.

(8) Conventionally, in order to cast gypsum slurry into a mother mold, the gypsum slurry is poured into the mother mold to form a first layer having a thickness of 5 to 10 mm to be a surface layer portion, and then a second layer is similarly formed. Then, the reinforcing material obtained by cutting fibers such as hemp and the like is sprinkled on the second layer, and the reinforcing material is mixed in the gypsum slurry by pushing it with a finger, and then the third layer and the fourth layer are similarly formed. The gypsum layers containing the reinforcing material and the reinforcing material were sequentially laminated to form a desired thickness. On the other hand, in the present invention, since carbon fiber as a reinforcing material is mixed in advance in the gypsum slurry, the stirring slurry is poured to form a relatively thick first layer, and then the stirring slurry is simply poured. The second layer may be laminated and molded to a required thickness. Therefore, according to the present invention, a large amount of sludge can be poured into the mother die at a time, and the working time can be shortened.

(9) Since the plaster containing the carbon fiber of the present invention dispersed and mixed therein has a small expansion coefficient during hydration hardening, there is little error when replicating from the original mold to the original mold, the case mold, and the molding mold, and accurate molding is possible. The mold can be manufactured. The same can be said for other synthetic rubber molding dies used in precision pressure casting of metals, pulp slurry casting, plastic injection molding, synthetic rubber casting, isostatic molding of fine ceramics and the like.

(10) When manufacturing a metal casting mold such as precision metal casting, a master mold that duplicates a model (corresponding to the original mold of ceramics) and a mold that molds the master mold for molding (ceramic mold) If the carbon fiber reinforced gypsum mold according to the present invention is used in place of the metal mold as the molding mold and the molding mold, these molds can be manufactured very easily and accurately, and the product can be easily manufactured similarly. Moreover, it can be manufactured accurately. Therefore, a prototype of a cast product, that is, a prototype of a product can be extremely easily prototyped in a short period of time, and further, a subsequent design change can be promptly and economically dealt with. Moreover, it is possible to make a trial with higher accuracy than either sand molds or metal molds, and it is possible to produce small lots, and it is particularly suitable for the non-ferrous metal plaster molding method for high-mix low-volume production.

(11) If there is a complicated pattern such as deep undercut engraving, the part corresponding to the pattern part of the original mold, which is the intermediate mold of the used mold manufacturing, such as the case mold, is a mold surface using silicon rubber or the like. However, if the carbon fiber reinforced gypsum mold according to the present invention is used for the molding die, the pattern of the original mold can be reproduced on the molding die much easier and more accurately than the molding die made of pure gypsum. can do.

(12) In the case of molding a non-ferrous metal mold, particularly high precision is required, so that the plaster molding mold according to the present invention has a small volume expansion during curing, a small drying shrinkage, and a small thermal expansion coefficient. It is possible to manufacture high precision molds.

(13) Compared to the case of using a sand mold or a metal mold, the surface is extremely smooth, and even fine wood grain or fingerprint patterns can be accurately cast, and the draft angle is 2 ° or less, depending on the case. Molding and demolding are possible even when there is no.

(14) Since the cooling rate of the casting is slower than that of the sand mold,
Casting distortion is small, and the structure and mechanical properties are uniform,
It is possible to manufacture thin products.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the length of carbon fibers mixed in the hardened gypsum and the bending strength of the hardened gypsum test piece. FIG. 2 is a graph showing the relationship between the weight ratio of carbon fiber mixed in gypsum to gypsum and the bending strength of the gypsum test piece. FIG. 3 is a diagram showing the relationship between the weight ratio of carbon fibers mixed in gypsum to gypsum and the water absorption performance of hardened gypsum (weight ratio of water that can be absorbed by gypsum to gypsum). FIG. 4 is a perspective view of a container for making gypsum slurry. FIG. 5A is a cross-sectional view of one molding step of a gypsum mold for casting a plastic oval plate, and FIG. 5B is a cross-sectional view of the molded gypsum mold. FIG. 6 (a) is a cross-sectional view of a gypsum mold for molding a plastic elliptical plate under pressure, wherein the molding surface is covered with a thin film of pure gypsum, (B) is a cross-sectional view of a molded gypsum mold. FIG. 7 shows a molding process of a plaster mold for plastic-molding a plate-shaped body having an engraved pattern. (A) is a master mold, (b) is a master mold, and (c) is a lower mold. The case die and (d) are cross-sectional views of the forming die, respectively. FIG. 8 is a diagram showing the principle of a mixing method utilizing oscillating rotation. FIG. 9 shows a molding process of a gypsum mold for cast-molding a silver alloy cup.
Is a prototype, (b) is a lower mold original mold, (c) is a lower mold case mold, and a cross section is a molding mold. FIG. 10 shows a molding process of a gypsum mold for molding a plastic casting mold, (a) is a master mold, (b) is a master mold,
(C) is a case type | mold, (D) is sectional drawing of the target metal mold, respectively. FIG. 11 is a scanning electron micrograph of a gypsum sample piece using β-type gypsum powder, and FIG. 12 is
It is a similar photograph when using α-type gypsum powder. Thirteenth
The figure is a measurement graph showing the change over time in transverse rupture strength in a bending test of a gypsum-type test piece with the weight ratio of carbon fibers mixed in the gypsum mold as a parameter. First
FIG. 4 is a graph showing the rate of change in length between the pure gypsum test piece and the carbon fiber reinforced gypsum test piece at each temperature. (Explanation of symbols of main parts) 3,3 ': Upper mold for plastic molding gypsum mold 4,4': Lower mold 6: Thin film 17: Lower mold for plastic cast molding 18: Upper mold 21: Bag 22: Shaking board 23: Rotating shaft 24: Shaking shaft 36: Silver alloy cup cast molding plaster mold lower mold 37: 〃 Upper mold 38: Silver alloy cup casting molding plaster mold 49 : Plastic casting mold

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] April 28, 1993

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Carbon fiber reinforced gypsum molding die and gypsum powder, and methods for producing the same

[Claims]

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbon fiber reinforced gypsum mold for molding polymer processed products other than ceramic products, non-ferrous metal products, fine ceramic products, paperware products, etc., and carbon fibers including ceramics. The present invention relates to a raw gypsum powder for a reinforced gypsum molding die and a method for producing these.

[0002]

2. Description of the Related Art Conventionally, plaster molding dies for general molding (hereinafter simply referred to as plaster dies) for molding polymer processed products other than ceramic products, non-ferrous metal products, fine ceramic products or paper ware products. ), There are various methods for increasing the strength, for example, β-type hemihydrate gypsum is the main component, and α-type hemihydrate gypsum is mixed therein to reduce the amount of water mixed,
There is a method of mixing cement or resin in gypsum, and a method of mixing natural fiber such as hemp or glass fiber in gypsum.

[0003]

However, when α-type hemihydrate gypsum is mixed with β-type hemihydrate gypsum to reduce the amount of mixed water, the strength itself slightly improves but the water absorption performance decreases. It has drawbacks such as Good water absorption performance of the gypsum mold is one of the most important factors for the plaster mold for casting such as pulp slurry. That is, when the water absorption performance of the gypsum mold is poor in the molding method utilizing the water absorption performance of gypsum,
The molding time per product becomes long, resulting in a decrease in molding efficiency, and the finished shape of the product also deteriorates. Therefore, in the cast molding method involving dewatering operation such as fine ceramics and paper containers, the deterioration of the water absorption performance of the gypsum mold is a fatal defect in product manufacture.

In the molding of investment casting molds of gold, silver and copper alloys for dental materials and jewelry, or for precision casting of non-ferrous metal products such as molds, machine parts in general, arts and crafts, etc. Breathability is one of the important factors to escape the gas generated at the interface between the mold and the cast metal. If adequate breathability is lacking, pressure or vacuum casting must be used.

Further, when cement or resin is mixed in gypsum, the strength itself can be improved, but similarly, the water absorption performance is lowered and the physical properties of other gypsum are also changed. There is. When natural fibers such as hemp are mixed in gypsum, the tensile strength of natural fibers is smaller than that of synthetic fibers, so the strength cannot be increased unless the amount of gypsum mixed is large. At the same time, an increase in the amount of natural fibers mixed inevitably leads to a decrease in the water absorption performance of the gypsum type. Moreover, since the natural fibers are thick monofilaments themselves, the ends of the fibers that have entered the surface layer of the gypsum type are The surface of the molded product is damaged by the exposed fiber ends, and the surface properties become inhomogeneous due to the lack of water absorption at the exposed fiber ends. .

When glass fibers are further mixed in the gypsum, the strength of the gypsum mold is slightly improved, but since the glass fibers have rigidity, the ends of the glass fibers that have entered the surface layer are exposed on the molding surface. Then, there is a drawback that the surface of the molded product is damaged.

The present invention has excellent strength characteristics, flexibility, light weight, low thermal expansion property, and further, carbon fibers having an extremely small diameter are cut into a length of 5 to 100 mm to form 0.008 to 0.9 in a set gypsum matrix. By uniformly dispersing and mixing in the state of monofilament in the ratio of wt%, the water absorption performance which is the main physical property of the paper container mold, or the mold for investment casting of dental materials and accessories, or the precision casting of metalware. The material mechanical strength of the gypsum mold is increased without deteriorating the ventilation performance, which is an important physical property in the mold, and without changing other physical properties of the gypsum mold in the case of other general gypsum molds, and against mechanical external force. Both strength (durability) and strength (durability) against internal stress due to thermal strain are increased.

A first object of the present invention is to increase the mechanical strength of the gypsum mold by increasing the mechanical strength of the gypsum mold without deteriorating the original functions of the gypsum mold, such as high dimensional accuracy, low cost, and ease of molding by casting. By simultaneously increasing both the strength against external force and the strength against internal stress due to thermal strain, it is possible to prevent damage to the gypsum mold due to external pressure or internal pressure during molding, and at the time of paper container molding, gypsum after molding It is to shorten the drying time of the mold and improve the molding efficiency (productivity by the gypsum mold).

A second object of the present invention is to produce a gypsum mold in which carbon fibers are mixed, in which a large number of monofilamentary carbon fibers are uniformly dispersed in gypsum slurry, whereby carbon is incorporated in the gypsum matrix. This is to uniformly mix and mix the fibers.

[0010]

The present invention has been made to achieve the above object, and the invention according to claim 1 has a length of 5 in the plaster structure of the base material of the plaster mold for molding. No
A carbon fiber reinforced gypsum molding die characterized in that 100 mm of carbon fibers are dispersed in a single fiber and uniformly mixed and dispersed at a ratio of 0.008 to 0.9% by weight with respect to gypsum.

Further, in the invention according to claim 2, the sizing agent applied after the carbon fiber is cut into a length of 5 to 100 mm is removed by heating, and the carbon fiber is stirred in water while applying ultrasonic vibration. To disperse the carbon fibers into innumerable monofilaments, and the gypsum powder, the carbon fibers dispersed in 0.01 to 1% by weight of the gypsum powder monofilaments, water, and, if necessary, other A gypsum slurry containing carbon fibers in which monofilaments of carbon fibers are uniformly dispersed by mixing with an additive is prepared, and a pure gypsum slurry is poured into a mother mold in advance to form a thin film, after which the carbon fibers are formed. Manufacture of a carbon fiber reinforced gypsum mold characterized by producing a gypsum mold with a thin film made of pure gypsum coated on the molding surface by pouring in gypsum slurry, curing and releasing the mold. Is the way.

In the invention according to claim 3, the carbon fibers dispersed in the gypsum powder into monofilaments having a length of 5 to 100 mm are uniformly added to the gypsum powder in a proportion of 0.01 to 5% by weight. This is a gypsum powder containing carbon fibers for a gypsum mold, which is mixed and dispersed.

Further, in the invention according to claim 4, the carbon fiber is cut into a length of 5 to 100 mm and preliminarily dispersed into an infinite number of single fibers, and the gypsum powder and 0.01 g of the gypsum powder are used.
To 5% by weight of the above-mentioned carbon fibers dispersed in monofilaments are introduced into a circulating jet air flow to uniformly mix the two and then recovered. It is a manufacturing method of the gypsum powder containing.

In the invention according to claim 5, the carbon fiber is cut into a length of 5 to 100 mm and preliminarily dispersed into an infinite number of single fibers, and the gypsum powder and 0.01 g of the gypsum powder are used.
1 to 5% by weight of the carbon fibers dispersed in the monofilament are put into a flexible bag body and oscillated and rotated to produce a gypsum powder containing carbon fiber for a plaster molding die. .

As the gypsum mold according to the present invention, a general cast molding gypsum mold, a metal precision casting gypsum mold, a press molding gypsum mold of powder or a plastic material, an extrusion molding gypsum mold,
Gypsum molds for injection molding, other so-called fine ceramics press molding gypsum molds for injection molding, so-called fine ceramics that do not contain clays in the raw material mixture of alumina, silicon carbide, silicon nitride, partially stabilized zirconia, sialon, etc. A gypsum mold for fine ceramics molding such as a plaster mold for molding is included.
Further, it includes a rocker molding die for fine ceramics, a casting molding die, and a casting molding die for producing a paper container from pulp slurry, which is carried out by utilizing the water absorption performance of gypsum itself.

The type of carbon fiber used in the present invention may be polyacrylonitrile-based, pitch-based, rayon-based or lignin-povar-based, but it has high strength or high elasticity because of the increase in the strength of the gypsum mold. Carbon fiber is desirable, specifically, tensile strength 200kgf / mm ² (K
g / mm ² ) or more, tensile elastic modulus 20,000 kgf / mm ² (Kg / mm ² )
The above is desirable.

In the present invention, it is extremely important that carbon fibers, which tend to form nodules, are uniformly dispersed and mixed in a single fiber state in the plaster mold (gypsum-type structure) of the base material without forming nodules. From this viewpoint, the length of the carbon fiber to be mixed in the gypsum mold as a reinforcing material and the weight ratio with respect to the gypsum are determined.

The carbon fibers are dispersed into a myriad of monofilaments and mixed in the plaster mold of the base material. The length of the carbon fibers is 5 to 100 mm, preferably 20 to 30 mm for the reasons described below. is necessary. Figure 1 consists of 100 parts by weight of gypsum, 60 parts by weight of water, and 0.5 parts by weight of carbon fiber.
A graph of the test results showing the relationship between the length of the carbon fiber in a 15 mm × 25 mm × 250 mm gypsum test piece and the bending strength (flexural strength) is shown. It can be seen that the bending strength sharply decreases when the thickness is 15 mm or less. Here, the length of the carbon fiber to be dispersed and mixed in the gypsum mold of the base material is limited to 5 to 100 mm, because when the length is less than 5 mm, the gypsum particles of the base material and the single fiber of the carbon fiber are Due to the shortage of the total adhesive area, it is not possible to improve the strength of the plaster mold sufficiently, and if the length is 100 mm or more,
This is because handling is difficult when the fibers are separated into single fibers, when they are mixed and stirred with gypsum powder and water, or when they are poured into a case mold, and uniform dispersion in the gypsum mold becomes difficult.

First, 5 carbon fibers produced by a conventional method are used.
After being cut to a length of 100 mm to 100 mm, it is separated into an infinite number of single fibers by a predetermined method. The following is an example of a method of dispersing the bundled carbon fibers into single fibers. First, the bundled carbon fibers are heated in an oxidizing atmosphere to oxidize and remove the sizing agent for handling and stabilizing applied on the surface, or the sizing agent is washed away with an acetone solvent to remove the sizing agent. The heating temperature when removing the sizing agent by heating is relatively determined by the relationship with the sizing agent applied to the surface, but it is around 300 ℃, which is the general maximum safe use temperature of carbon fiber. It is desirable to do in. The carbon fibers from which the sizing agent has been removed by heating are innumerable (typically 1,000 to 2
4,000) extremely small diameter (usually 5 to 10 μm)
Easily dispersed in single fibers.

Next, the sizing agent is removed and 5 to 10
When carbon fiber cut to a length of 0 mm was put into a water tank and gently rotated by a stirring blade while applying ultrasonic vibration, the sizing agent was removed by the previous heating and the carbon fiber was easily dispersed. Is dispersed in a myriad of single filaments having extremely small diameters without causing agglomeration due to the synergistic effect of ultrasonic vibration and gentle stirring. When stirring,
The number of rotations must be 40 to 60 rpm in a water tank having a diameter of about 60 cm so that the carbon fibers are not damaged by the stirring blades. After the dispersion treatment, the innumerable dispersed single fibers are taken out from the water tank, dehydrated and dried.

As another method of separating the bundled carbon fibers into single fibers, there is a method of pre-sizing the carbon fibers with a water-soluble sizing agent. That is, the bundle-like carbon fibers sized with a water-soluble sizing agent are cut into a length of 5 to 100 mm, and the carbon fibers suitable for one mixing ratio are weighed in advance, and the weighed carbon fibers are weighed. When the carbon fibers are put into a container 1 (see FIG. 4) containing water that is suitable for one mixing ratio and gently stirred by a stirring blade, the water-soluble sizing agent applied to the carbon fibers is Immediately elutes in water and self-diffuses, and the bundle-like carbon fibers are uniformly dispersed in the countless single filaments having extremely small diameters in water without agglomeration by the stirring action of the stirring blades. Also in this method, it is necessary to set the rotation speed to 40 to 60 rpm in a container having a diameter of about 60 cm so that the carbon fibers are not damaged by the stirring blade during stirring. When the carbon fibers are dispersed into single fibers by this method, the gypsum powder, which is suitable for a single mixing amount, and a setting retarder are directly placed in a container 1 in which the single fibers of carbon fibers are uniformly dispersed in water. The gypsum slurry is prepared by adding the above-mentioned additive and stirring.

Next, if a method for producing a gypsum slurry in which carbon fibers dispersed in single fibers are mixed is described, the ratio of carbon fibers to gypsum powder is 0.
It is necessary that the content is 01 to 1% by weight (approximately 0.008 to 0.9% by weight when converted to the ratio of carbon fiber to gypsum of the hardened gypsum type base material), and preferably 0.1 to 0.3% by weight. Fig. 2 shows a mixture of 100 parts by weight of gypsum powder and 60 parts by weight of water, and 15 mm × 25 mm × 250 mm in which carbon fibers 20 mm in length were mixed in a required ratio (various parts by weight).
3 is a graph of test results showing the relationship between the weight percentage of the mixed carbon fibers in the gypsum test piece with respect to the gypsum powder and the bending strength. FIG. 3 is a graph of test results showing the relationship between the weight ratio of carbon fibers mixed in the gypsum powder and the water absorption rate, that is, the water absorption performance (% by weight of water that can be absorbed by the test piece of hardened gypsum). As is clear from FIGS. 2 to 3, it is understood that as the weight ratio of the carbon fibers mixed in the gypsum powder increases, the bending strength increases and the water absorption increases.

The fact that the water absorption capacity of gypsum is increased by the incorporation of carbon fibers is because the particles of gypsum are needle-shaped and the cross-sectional shape of carbon fibers is circular or a shape close to this.
Moreover, since the size of the gypsum particles and the diameter of the carbon fibers are not so different, it is considered that this is due to the formation of new voids between the carbon fibers and the gypsum particles due to the mixing of the carbon fibers. To be done.

Here, the mixing ratio of the carbon fiber to the gypsum powder is set to 0.01 to 1% by weight. When the mixing ratio of the carbon fiber is less than 0.01% by weight, the ratio of the carbon fiber to the gypsum powder is too small and the ratio of the gypsum type is small. If the strength cannot be improved sufficiently, and if the mixing ratio of carbon fibers exceeds 1% by weight, the ratio of carbon fibers is too large when making gypsum slurry, and carbon fibers are incorporated into the gypsum slurry as single fibers. In that state, it is not possible to uniformly disperse the carbon fibers, and it becomes easy for agglomerates of carbon fibers to be generated, and the fluidity when pouring the gypsum slurry into the master mold becomes poor, making the casting operation difficult, and further molding gypsum. The physical properties of the mold such as water absorption or capillary (capillary porosity) change and the conditions as a molding material when air permeability and water absorption are utilized are no longer satisfied, and carbon is contained inside the molded gypsum mold. fiber Easily Nodules occurs, it will not satisfy the function as mold precision product becomes heterogeneous state.

To remove the sizing agent and prepare the gypsum slurry in which the carbon fibers are uniformly dispersed by using the carbon fibers dispersed in advance in the single fiber, the container 1 as shown in FIG. 4 is prepared. , Water suitable for the mixing amount at one time and necessary additives such as a curing retarder and a water reducing agent are put in advance, and then,
Into this container 1, carbon fibers dispersed in a predetermined amount of pre-measured monofilaments are charged, and finally a predetermined amount of gypsum powder is charged to mount this container 1 on a vacuum stirrer and stir it. When the blades are rotated at low speed and mixed and stirred, a gypsum slurry in which single carbon fibers are uniformly dispersed in the gypsum slurry is obtained without forming agglomerates. The reason why the carbon fibers are uniformly dispersed in the gypsum slurry without producing agglomerates is that the ratio of the carbon fibers to the gypsum powder is extremely small.

Next, in the case of manufacturing a plastic cast molding gypsum mold for molding a dish, the above-mentioned gypsum slurry in which carbon fibers are uniformly dispersed is used as an upper mold as shown in FIG. After gently pouring into the case die 2 for molding and allowing it to stand for a predetermined period of time, a slight impact is applied after curing to disperse the case die 2 in the upper and lower directions, and then the mold is removed. The upper mold 3 of the plaster mold for plastic molding for casting the plate as shown in FIG. Since carbon fiber has rich flexibility, it is understood that it deforms freely even after casting, and it is reasonably inserted between the particles of gypsum, and it is also mixed in the surface layer part of the cast gypsum mold. The end of the carbon fiber thus formed is hardly exposed on the molding surface, but even if it is exposed, the diameter of the single fiber of the carbon fiber is extremely small as described above, and since it has abundant flexibility. The surface of a polymer molded product such as plastic or rubber is hardly damaged by the carbon fiber exposed on the molding surface. Similarly, the lower mold 4 of the plaster mold for plastic casting is molded using the case mold for molding the lower mold. still,
The lower mold 4 is provided with a molten plastic injection hole 5. When injecting at normal pressure, FIG. 5B is actually used in an inverted state.

As described above, even if the ends of the carbon fibers are exposed to the molding surface, the surface of the molded product is hardly damaged. In particular, the molded product is a high-grade product and extremely precise and smooth molding. When it is necessary to obtain a surface, as shown in FIG. 6 (a), a small amount of pure gypsum slurry is poured while the case mold 2 is rotated at a low speed to form a thin film 6 having a thickness of 1 to 3 mm in advance. Then, after stopping the rotation of the case mold 2, the plaster slurry in which the carbon fibers are uniformly dispersed is immediately poured into the case mold 2, and the same operation as above is performed thereafter to mold the upper mold 3'of the plaster mold for plastic molding. To be done. When the lower mold 4'is molded in the same manner, as shown in FIG. 6 (b), a gypsum mold for plastic pressure casting in which the thin film 6 made of pure gypsum is coated on the outer peripheral surface which is the molding surface is obtained. It is possible to reliably prevent the carbon fibers from being exposed on the molding surface. In addition, a beryllium copper alloy, aluminum alloy, zinc alloy plastic injection molding die or non-ferrous alloy container can be molded with a plaster mold whose molding surface is covered with a thin gypsum mold. In this case, the molding surface of the molded mold or the surface of the container is not damaged by the end of the carbon fiber.

Further, in the case of producing a large number of plaster molds for plastic-molding a plate-shaped body having an engraved pattern, the following steps are carried out. In FIG. 7, a gypsum prototype or prototype (first mold) 11 to a master mold in which carbon fibers are uniformly dispersed and mixed, or only the inside uses carbon fiber-containing gypsum and pure gypsum is used for the surface layer part (Prototype female mold) {Second mold}
Duplicate 12a and 12b. In the case of precision casting of metal, these master molds 12a and 12b are called master molds. The entire gypsum female mold of this original mold is divided into upper and lower halves to form a female mold 16 (not shown) corresponding to the upper male mold portion 12b and a male mold 16a corresponding to the lower female mold 12a. To manufacture. This lower female mold 14
Has a gypsum slurry inlet 15. This mold 16 is a so-called case mold (third mold) in ceramic molding. In the following, metal or plastic other than ceramic and paper container molding are also referred to as case type.

The above-mentioned gypsum slurry in which carbon fibers are uniformly dispersed is injected into the case mold 16 through the gypsum slurry injection port 15.
When injecting gypsum slurry under normal pressure (atmospheric pressure), see Fig. 7.
The case mold 16 shown in (C) must be turned upside down. After leaving for a specified time to cure, upper mold 13 and lower mold 14
And are separated, and the lower die 17 of the forming die (fourth die) is taken out.
Similarly, a case mold is molded from the upper part 12b of the original mold, and gypsum slurry in which carbon fibers are uniformly dispersed is poured into the case mold to mold the upper mold 18 of the mold. A combination of the upper mold 18 and the lower mold 17 of this mold is a so-called "use mold" in ceramic molding. The gypsum mold reinforced with the carbon fiber according to the present invention has a small volume expansion coefficient in the curing process, and further, the thermal expansion coefficient of the cured gypsum mold is small. If gypsum that is uniformly dispersed and mixed is used, it is possible to duplicate a highly accurate mold from the original mold to the molding mold with little dimensional change.

Further, in the case of a gypsum mold for molding a molding die such as a plastic injection molding mold made of beryllium copper alloy, aluminum alloy or zinc alloy, as compared with the case of direct molding by a gypsum mold, Since the shape duplication process is more and more complicated, the volume expansion coefficient in the hardening process of the gypsum mold and the small thermal expansion coefficient of the hardened gypsum mold are more important characteristics in high-precision duplication.

When a gypsum slurry in which carbon fibers are uniformly dispersed is produced by the above-mentioned method, a small amount of carbon fiber must be accurately weighed each time the gypsum slurry is produced, which is troublesome. Therefore, using a jet air flow or oscillating rotation that circulates carbon fibers, which are lightweight and highly floating, and are difficult to handle, they are mixed and dispersed in advance in the gypsum powder evenly in the single fiber state, and this is used as the raw gypsum powder. You may use. As a result, it is possible to eliminate the troublesome operation of measuring only a small amount of carbon fiber suitable for one mixing amount each time gypsum slurry is produced.

A mixing method using a circulating jet air flow will be specifically described. Gypsum powder and carbon fibers dispersed into single fibers are added to the gypsum powder in an amount of 0.01 to
When added to the mixing device at a ratio of 5% by weight, the gypsum powder and the carbon fibers dispersed in the single fibers are appropriately mixed while circulating a number of times in a state of being scattered by the jet air flow,
After that, when separated and collected from the air flow by a cyclone or a back filter, a gypsum powder containing carbon fibers is obtained in which the gypsum powder and the carbon fibers dispersed in the single fibers are uniformly mixed. Here, the pressure of the jet air flow is 1 to
It is necessary to have a low pressure of ² kgf / cm ² (Kg / cm ² ), and when the air pressure is increased, the gypsum particles or the gypsum particles and the carbon fibers collide with each other at the time of mixing, and the gypsum becomes large. Both the particles and the carbon fibers are crushed to change the physical properties of the gypsum mold material, which is not preferable.

Another method for uniformly mixing the carbon fiber with the gypsum powder is a mixing method utilizing oscillating rotation. This is a flexible bag 21 as shown in FIG.
The gypsum powder and the carbon fibers dispersed in the monofilament are charged into the gypsum powder at a ratio of 0.01 to 5% by weight, and the rocking plate 22 attached to the bottom of the bag body 21 is Rotating shaft 23
When oscillatingly rotated by the oscillating shaft 24 mounted eccentrically, the mixture in the bag body 21 is accelerated, and the magnitude and direction of its velocity are arbitrarily changed, whereby the gypsum powder in the bag body 21 is changed. And the carbon fibers are evenly mixed. When carbon fibers are mixed in the gypsum powder, it is possible to simultaneously mix necessary additives such as a set retarder and a water reducing agent.

In addition, the above-mentioned gypsum powder is a mixture of innumerable single carbon fibers dispersed uniformly in the gypsum powder. However, the water content of polyvinylpyrrolidone, polyvinyl alcohol, etc. In the case of carbon fiber sizing treated with a water-soluble sizing agent, it is not necessary to disperse into pre-formed single fibers, and the water-soluble sizing agent has the property of elution into water and self-diffusion when making gypsum slurry,
It can be put and mixed in the gypsum powder in the bag as a bundle. Furthermore, when using the raw gypsum powder mixed and dispersed in the gypsum powder in a proportion higher than the weight ratio when using the carbon fiber, the gypsum powder is mixed again during use, and the gypsum powder and the carbon fiber are mixed with gypsum. The carbon fiber must be diluted to a ratio of 0.01 to 1% by weight with respect to the powder, but this method can reduce the transportation cost of the gypsum powder in which the carbon fiber is mixed.

Here, the ratio of carbon fiber to gypsum powder is
The reason why the content is 0.01 to 5% by weight is that if it exceeds 5% by weight, it is difficult to mix it in a single fiber state, and if it is less than 0.01% by weight, it cannot be used as it is for molding. When it is used as it is without being diluted, the mixing ratio of carbon fiber to the gypsum powder is 0.01 to 1% by weight.

When gypsum mixed with carbon fiber is used as a mold material for a general molding die or a molding die, a ceramic molding die is further produced from the gypsum mold to polymer processing or precision metal casting. Alternatively, when performing cast molding of ceramics other than ceramics, that is, glass, fine ceramics, or when performing blow molding of high-grade glassware, the expansion coefficient during hydration hardening of gypsum mixed with carbon fibers, and Since the expansion rate during cooling and demolding and the subsequent drying shrinkage rate / expansion rate are both small, the accuracy of the replicated product when casting into the mother mold (female mold) and repeating the mold is good, and an accurate replicated product is obtained. it can. In addition, since the coefficient of thermal expansion of the mold itself is small, expansion and contraction due to temperature change is small, which enables highly accurate replication and improves the accuracy of the molding mold itself.

Therefore, even if the repetitive duplication is repeated several times, the duplication error between the first die (prototype) and the final die (molding die) is small. This point is the most important as a mold material for molding a metal mold or a ceramic mold in precision casting.

When the plaster mold according to the present invention is used as a press mold, the raw material for molding metal, plastic, ceramics or the like may be in the form of dry powder or paste such as china clay. Further, it may be in the form of a sheet.

Further, although the present invention has a direct purpose of reinforcing the molding die itself with carbon fiber, a member constituting the molding die such as a ceramic core (core) in an investment mold or a molding die. The jig-like member for holding or positioning may be made of gypsum reinforced with carbon fiber.

[0040]

EXAMPLES Next, examples of the present invention and comparative examples will be described. <Example 1> Polyacrylonitrile-based fibers were heat treated at about 300 ° C and then further heat-treated at about 1300 ° C in a nitrogen gas atmosphere to be graphitized, and about 6000 single fibers each having a diameter of 7 µm were bundled into a carbon fiber. Was used. The physical properties of this carbon fiber are: tensile strength 300 kgf / mm ² (Kg / mm ² ), tensile elastic modulus 23,000.
kgf / mm ² (Kg / mm ² ), density 1.75 g / cm ³ , linear expansion coefficient −0.
1 × 10 ^-6 / ℃, thermal conductivity 15Kcal / (m ・ hr ・ ℃) (17.4
5 W / (m · K), specific heat 0.17 cal / (g · ° C) (0.71
It was kJ / (kg · K)). In the following, regarding the unit display, “Kcal / (m · hr · ° C)” is expressed as “Kcal / mhr ° C”, “W / (m · K)” is expressed as “W / mK”, and “cal” /
(G ・ ° C) "is expressed as" cal / g ° C ", and" kJ / (kg ・
K) ”is expressed as“ kJ / kgK. ”This carbon fiber is cut into a length of about 20 mm and dispersed in water into an infinite number of single fibers by the synergistic effect of ultrasonic vibration and stirring. 100 parts by weight of β-gypsum powder, 60 parts by weight of water, 0.1 part by weight of carbon fiber,
Borax (hardening retarder) 0.2 parts by weight is mixed and stirred to make a gypsum slurry in which carbon fibers are uniformly dispersed. The gypsum slurry is poured into a case mold and a plastic oval plate is cast. A cast plaster mold for molding was obtained. In this cast molding gypsum mold, single fibers of carbon fibers were uniformly dispersed over the entire cut cross section, and this dispersion state was visible to the naked eye.

Example 2 A gypsum slurry in which monofilaments of carbon fibers were uniformly dispersed was prepared under the same conditions and methods as in Example 1, and a case mold was rotated at a low speed while pure carbon fibers were not mixed. Pour plaster slurry in advance to a thickness of 1
A thin film having a thickness of 3 to 3 mm was formed, and after that, the rotation of the case mold was stopped and the gypsum slurry mixed with carbon fiber was poured to obtain a cast plaster mold for casting a plastic elliptical dish. . The molding surface of this cast molding gypsum mold was covered with a thin film of pure gypsum, and carbon fibers were not exposed at all on the molding surface.

Example 3 Polyacrylonitrile fiber was heat treated at about 300 ° C. and then special heat treated at about 2500 ° C. in a nitrogen gas atmosphere for graphitization to obtain a diameter of about 7 μm.
The carbon fibers obtained by sizing monofilaments of m with polyvinylpyrrolidone to make a bundle of about 6000 fibers were used. The physical properties of this carbon fiber are: tensile strength 250 kgf / mm ² (Kg / mm ² ), tensile elastic modulus 35,000 kgf / mm ² (Kg / mm ² ), density 1.77 g / c.
m ³ , linear expansion coefficient −0.1 × 10 ^-6 / ℃, thermal conductivity 100 Kcal /
The mhr ℃ (116W / mK) and the specific heat 0.17cal / g ℃ (0.71kJ / kgK). This bundle of carbon fibers is cut into a length of 25 mm, and the carbon fibers are weighed in advance so that the ratio of the carbon fibers to 100 parts by weight of β-gypsum powder is 0.3 parts by weight. When put into a container containing measured water and stirred supplementarily, the bundled carbon fibers self-diffuse and are dispersed into innumerable single fibers, and evenly dispersed in water by the stirring action. did. Then, gypsum powder, borax (hardening retarder) and Melment F-20 (water reducing agent) manufactured by Showa Denko KK are added and mixed and stirred to obtain 10 gypsum powders.
A homogeneous gypsum slurry was prepared consisting of 0 parts by weight, 60 parts by weight of water, 0.3 parts by weight of carbon fiber, 0.2 parts by weight of set retarder and 0.2 parts by weight of water reducing agent. First, as shown in FIG. 9, a lower mold of the original mold (second intermediate mold) 32 is manufactured from the original mold 31 of the cup using the gypsum slurry, and the original mold 32 is used to form the case mold (the third intermediate mold). The lower mold of the mold 33 was manufactured using the above plaster slurry. This case type 33 combined with the upper case 34
While rotating at low speed at 100 rpm, pure gypsum slurry is poured to form a thin film 35 having a thickness of 1 mm in advance, and then the gypsum slurry is poured to form a lower mold 36 for a casting plaster mold 38 for molding a silver alloy cup. Obtained. The state of dispersion of the carbon fibers mixed in the lower mold 36 for the cast molding gypsum mold was almost uniform as in Example 1. Similarly, the upper mold 37 is manufactured, and the upper mold 37,
The lower mold 36 was combined to cast a silver alloy cup as a unit. A fine silver alloy cup was obtained in which the fine pattern on the outer surface was precisely reproduced.

<Example 4> In order to form a gypsum slurry in which monofilaments of carbon fibers are uniformly dispersed by the same conditions and methods as in Example 3 and cast this into a mother mold to cast a synthetic rubber ball. A plaster mold of

<Embodiment 5> Gypsum slurry in which monofilaments of carbon fibers are uniformly dispersed is prepared under the same conditions and methods as in Embodiment 3, and the plaster slurry is poured into a mother die to apply a ceramic ball to an isostatic press (etc.). A gypsum mold for casting a polyurethane / rubber mold for hydrostatic pressing was obtained.

Example 6 Gypsum slurry in which single carbon fibers were uniformly dispersed was prepared under the same conditions and methods as in Example 3, and the gypsum slurry was poured into a mother die to cast a crystal glass blow molding die made of Sialon. A plaster mold for filling was obtained.

<Comparative Example 1> 100 parts by weight of β-gypsum powder, 60 water
A gypsum mold for injection molding for mixing and stirring 0.2 part by weight of borax to make a pure gypsum slurry without carbon fiber and pouring the gypsum slurry into a case mold to injection-mold a plastic elliptical dish. Got

Example 7 Polyacrylonitrile fiber was heat treated at about 300 ° C. and then further heat treated at about 1300 ° C. in a nitrogen gas atmosphere to be graphitized to form a bundle of about 6000 single fibers having a diameter of about 7 μm. Used carbon fiber. The physical properties of this carbon fiber are as follows: tensile strength 300 kgf / mm ² (Kg / mm ² ), tensile elastic modulus 23,000 kgf / mm ² (Kg / mm ² ), density 1.75 g / cm ³ , linear expansion coefficient −0.1 × 10. ^-6 / ℃, thermal conductivity 15Kcal / mhr ℃ (17.
The specific heat was 45 W / mK) and the specific heat was 0.17 cal / g ° C (0.71 kJ / kgK). This carbon fiber was cut into a length of about 20 mm, and was separated into innumerable single fibers by the synergistic effect of ultrasonic vibration and stirring in water. β-gypsum powder 100 parts by weight, water 60 parts by weight, carbon fiber
0.1 part by weight and 0.2 part by weight of borax (setting retarder) were mixed and stirred to prepare a gypsum slurry in which single carbon fibers were uniformly dispersed.

Then, as shown in FIG.
Embedded in clay or gypsum up to the dividing surface, cast the gypsum slurry as it is to mold the upper half surface of the prototype 41, and then reverse the prototype 41 and perform the same operation to make the lower half surface of the prototype 41. The master 42 is produced by performing the mold making. The plaster slurry is poured into the original mold 42 to lower the case 43,4
Upper case 4 manufactured separately and separately
When combined with 5,46, it becomes a case type 47,48. In the case types 47 and 48, the carbon fibers were uniformly dispersed throughout the entire surface including the cross section, and this dispersion state was visible to the naked eye. The case molds 47, 48 were used as casting molds while rotating at a low speed, and a molten metal of aluminum was cast to manufacture a plastic casting mold 49.
The pattern on the surface of the master 41 was accurately transferred to the mold 49 as it was.

Comparative Example 2 100 parts by weight of β-gypsum powder, 60 water
1 part by weight and 0.2 part by weight of borax are mixed and stirred to prepare a pure gypsum slurry containing no carbon fiber, and the gypsum slurry is poured into the original mold produced in the same manner as in Example 7 to make the lower case and the case. An upper mold was manufactured, and a separately manufactured upper case was combined to obtain a case mold, and an aluminum alloy melt was cast into the case mold to manufacture a plastic casting mold.

The rate of change in length and the replication accuracy at each temperature during dry release of the gypsum case molds of Example 7 and Comparative Example 2 were as follows. Regarding the rate of change of length,
At the time of maximum heat generation of the case type (53.2 ° C), 0.076% (0.38 m for 500 mm) of the conventional product that does not contain carbon fiber
m) Swelling (expansion rate upon curing), the product of the present invention has expanded by 0.066% (0.33 mm against 500 mm), and after cooling at room temperature (23.5 ° C), it is dried and demolded. At that time, the conventional product expanded 0.025% (0.125 mm for 500 mm), while the product of the present invention expanded 0.018% (0.09 mm for 500 mm). After that, it was dried in a hot air dryer at 50 ° C for about 10 days.
The product of the present invention had a dry shrinkage of 0.06 mm and an expansion of 0.065 mm with respect to the master mold, whereas the product of the present invention had a dry shrinkage of 0.04 mm with respect to 500 mm and an expansion of 0.05 mm to the master mold. As is clear from this, it is understood that the product of the present invention has a small expansion during hydration hardening and has a good replication accuracy.

Examples 1 to 6 and Comparative Example 1
The physical properties of the gypsum molds such as bending strength, water absorption capacity, breaking temperature difference in the atmosphere, bulk specific gravity and expansion coefficient upon hardening were as shown in the table below. The water absorption capacity is measured by immersing the test piece under normal temperature and pressure.
It is the weight percentage of absorbed water. The rupture temperature difference represents the minimum temperature difference that results in rupture when a test piece heated in a high temperature atmosphere is quickly taken out into a room and left in a room temperature atmosphere.
The expansion coefficient at the time of hardening is the ratio of the length of the master mold to the length measured when the gypsum slurry was cast into the master mold, hardened and then demolded, and immediately before drying. As is clear from the above table, the gypsum mold mixed with carbon fiber has greatly improved the transverse rupture strength and the difference in fracture temperature in the atmosphere as compared with the gypsum mold not mixed with carbon fiber, and also in other physical properties. It turned out to be excellent.

FIG. 11 is a photograph of a thin piece produced from the cut surface of the gypsum hardened body of Example 1 taken at a magnification of 2000 with a scanning electron microscope. A slender straight cylinder extending from the upper left corner to the center is a mixed carbon single fiber, and the shard-like crystals are β-type dihydrate gypsum. FIG. 12 shows Example 1 except that α-type gypsum powder was used.
That is, it is the same as that of FIG. In addition, FIG. 13 is 15 mm × 25 mm × 100 mm by weight of gypsum, 60 parts by weight of water, and 15 mm × 25 mm × cast gypsum slurry mixed with a predetermined weight part of pitch-based carbon fiber having a length of 25 mm.
The relationship between the elapsed time and the transverse rupture strength when a 250 mm gypsum test piece was subjected to a bending test with a bending tester is shown, and is the test result when the weight ratio of the mixed carbon fiber was used as a parameter. As is clear from the graph of FIG. 13, the larger the proportion of the mixed carbon fibers, the larger the transverse rupture strength, and the fragility of simple fracture at the maximum transverse rupture force is eliminated, and so-called stickiness as a material occurs. Recognize. The suban of this test was 200 mm, the load was applied to the center, and the displacement speed at the load point was 1 mm / min.

FIG. 14 shows a curve showing the rate of change in length at each temperature between a pure gypsum test piece and a carbon fiber-reinforced gypsum test piece, and the gypsum test piece mixed with carbon fiber is shown. It can be seen that the rate of change (expansion) in length is slightly smaller in both the positive and negative cases than the rate of change (expansion) in the length of the gypsum test piece containing no carbon fiber.
It is understood that this is because the carbon fibers having a coefficient of thermal expansion almost equal to zero enter between the particles of the gypsum, and the carbon fibers suppress expansion or contraction of the gypsum. Therefore, the gypsum mold mixed with carbon fiber has a small expansion or contraction due to temperature, and the dimensional accuracy of the molded product is improved.

Here, when the gypsum mold is used as a metal forming mold, a polymer processing forming mold, or a paper container forming mold, the material strength of the gypsum mold is increased due to the drastic improvement of the bending strength and the bending strength. By increasing the mechanical strength of the part that was conventionally damaged by external pressure or internal pressure during molding, damage to the gypsum mold can be prevented, and high (fast) cycle molding becomes possible and molding efficiency ( Productivity) and the life of the plaster mold is extended. In addition, damage to the molding machine such as pressure casting, centrifugal casting, vacuum casting, and injection molding due to breakage of the plaster mold during molding can be prevented from being interrupted by production, and damage to the molding machine can be prevented. It is possible to save the trouble of replacing the parts and readjusting them. Furthermore,
By significantly improving the mechanical strength, it is possible to reduce the thickness of the gypsum mold, which in turn reduces the amount of gypsum used.

The difference in fracture temperature in the atmosphere due to the incorporation of carbon fiber is improved because the gypsum itself expands by a predetermined amount due to the temperature rise, but the carbon fiber itself hardly expands. In addition to the tensile force applied to the fiber in the length direction, the compressive force is applied to the gypsum, which causes an internal stress in the length direction of the carbon fiber, resulting in a state where prestress is introduced just like PS concrete. It is understood that it is because it has become.

A large increase in the breaking temperature difference in the atmosphere means that the plaster mold can withstand a large temperature difference. It is possible to raise the temperature.
Therefore, the drying time of the gypsum mold for each molding can be shortened, the number of molding dies to be held in the drying device can be reduced, and the molding efficiency (productivity) can be improved. Therefore, it is possible to reduce the number of operating gypsum molds with respect to the number of molded products such as fine ceramics and paper containers, which is suitable for molding a large number of small-volume products, and at the same time, it is possible to reduce the product cost.

Further, the reduction of the bulk specific gravity reduces the weight of the gypsum mold, and the transportation or handling of the gypsum mold is improved. Further, due to the slight decrease in expansion during hardening, the pressure applied to the case mold during molding of the gypsum mold is reduced, which facilitates demolding, and at the same time prevents damage to the case mold. The same effect can be obtained in the case of manufacturing other molds for non-ferrous metal casting.

[0058]

Summarizing the above, the present invention has the following effects. (1) The material mechanical strength of the gypsum mold is greatly increased to prevent damage to the gypsum mold due to external pressure or internal pressure during molding, and at the same time, strength (durability) against internal stress due to temperature difference, etc. Greatly increased, it is possible to raise the drying temperature of the gypsum mold for each molding in the molding that utilizes the water absorption performance of the gypsum mold, such as cast molding of fine ceramics and paper containers, and shorten the drying time In addition to the above, complete drying is possible, and the molding efficiency can be remarkably improved.

(2) As the gypsum-type reinforcing material, since carbon fiber having an extremely small diameter, a large strength and a high flexibility is used, even if the mixing ratio of the reinforcing material to the gypsum is small, the gypsum-type The mechanical external force and the strength against thermal inhomogeneity can be increased, and the mixing ratio of the reinforcing material is small. Therefore, by mixing carbon fiber, water absorption is used as in the casting of fine ceramics and paper containers. The water absorption performance, which is the basic performance of the plaster mold for molding, or the ventilation performance when molding non-ferrous metal products, does not deteriorate.

(3) When the surface layer portion, which is the molding surface of the gypsum mold, is covered with a thin film of pure gypsum, it is possible to reliably prevent the end portion of the carbon fiber from being exposed on the molding surface, and The surface can be smoothed.

(4) Since carbon fiber having a high temperature heating and burning property is mixed as a reinforcing material, it may be damaged during use,
Alternatively, the unusable gypsum mold can be crushed and gently heat-treated over a long period of time to easily burn off and remove only the carbon fibers mixed in the interior, and the gypsum hardened product It can be reused. In this case, when a material having no heat-burning property such as glass fiber is mixed as a reinforcing material, it is extremely difficult or impossible to recycle or reuse the plaster mold by removing only the mixed reinforcing material. .

(5) The carbon fiber is cut into a length of 5 to 100 mm, the sizing agent is removed by heating, and ultrasonic vibration is applied in water while stirring to obtain an extremely small diameter and flexibility. Rich bundles of carbon fibers can be easily dispersed into innumerable monofilaments, which allows even innumerable carbon fibers to be evenly dispersed in gypsum slurry, which in turn allows the carbon fibers to be evenly mixed in the plaster mold. Can be made.

(6) When carbon fibers sized with a water-soluble sizing agent are used, the carbon fibers are cut into a length of 5 to 100 mm and then put into water to elute the water-soluble sizing agent into water. At least disperse the bundled carbon fibers into innumerable single fibers, and then add the gypsum powder and mix and stir to create a gypsum slurry in which the carbon fibers are uniformly mixed and dispersed. It is not necessary to carry out a pretreatment only to disperse the carbon fibers in the shape of innumerable single fibers.

(7) The carbon fiber is cut into a length of 5 to 100 mm and dispersed in advance into innumerable monofilaments to obtain gypsum powder and monofilaments having a predetermined weight ratio with respect to the gypsum powder. The dispersed carbon fibers are put into a circulating jet air flow to uniformly mix them, and then collected.
By uniformly mixing and dispersing the carbon fibers dispersed in the gypsum powder into single fibers, it is not necessary to measure only a small amount of carbon fibers that is suitable for one mixing amount each time gypsum slurry is made. be able to.

(8) Conventionally, to cast the gypsum slurry into the mother mold, the gypsum slurry is poured into the mother mold to form the surface layer 5 or 5.
Gypsum is made by making a first layer with a thickness of 100 mm, then making a second layer in the same manner, and spreading a reinforcing material obtained by cutting fibers such as hemp on the second layer and thrusting it with a finger. The reinforcing material was mixed in the slurry, and then the third layer, the fourth layer, and the gypsum layer containing the reinforcing material were sequentially laminated in the same manner to form a desired thickness. On the other hand, in the present invention, since carbon fiber as a reinforcing material is mixed in advance in the gypsum slurry, the stirring slurry is poured to form a relatively thick first layer, and then the stirring slurry is simply poured. The second layer may be laminated and molded to a required thickness. Therefore, according to the present invention, a large amount of sludge can be poured into the mother die at a time, and the working time can be shortened.

(9) Since the gypsum of the present invention in which carbon fibers are dispersed and mixed has a small expansion coefficient during hydration hardening, there is little error when replicating from the original mold to the original mold, the case mold, and the molding mold, and accuracy is improved. It is possible to manufacture a molding die with good quality. The same can be said for other synthetic rubber molding dies used in precision pressure casting of metals, pulp slurry casting, plastic injection molding, synthetic rubber casting, isostatic molding of fine ceramics and the like.

(10) In the case of manufacturing a metal casting mold such as precision metal casting, a master mold (corresponding to a master mold of ceramics) that replicates a model and a master mold for molding a mold that replicates the master mold If the carbon fiber reinforced gypsum mold according to the present invention is used in place of the metal mold as the molding mold (corresponding to the case mold of ceramics) and these molds, these molds can be manufactured very easily and accurately, and the product is also the same. It can be manufactured easily and accurately. Therefore, a prototype of a cast product, that is, a prototype of a product can be extremely easily prototyped in a short time, and further, a subsequent design change can be promptly and economically dealt with. Moreover, it is possible to make prototypes with higher accuracy than either sand molds or metal molds.
It is also suitable for the non-ferrous metal plaster molding method for high-mix low-volume production because it can produce small lots.

(11) If there is a complicated pattern such as deep undercut engraving, silicon rubber or the like is used for the part corresponding to the pattern part of the original mold, which is the intermediate mold of the used mold manufacturing, the case mold, etc. However, if the carbon fiber reinforced gypsum mold according to the present invention is used for the mold, it is much easier and more precise than the mold made of pure gypsum. The pattern can be reproduced.

(12) When molding a non-ferrous metal mold,
Since high precision is particularly required, the gypsum molding die according to the present invention, which has a small volume expansion during curing, a small drying shrinkage, and a small thermal expansion coefficient, can be manufactured with a high precision.

(13) Compared with the case of using a sand mold or a metal mold, the surface is extremely smooth, and even fine wood grain and fingerprint patterns can be accurately cast, and the draft angle is 2 ° or less, depending on the case. Molding / demolding is possible even if there is no draft.

(14) Compared with the sand mold, since the cooling rate of the casting is slower, the casting strain is small, the structure and mechanical properties are uniform, and the product with a thin wall thickness can be manufactured.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the length of carbon fibers mixed in a hardened gypsum and the bending strength of a hardened gypsum test piece.

FIG. 2 is a graph showing the relationship between the weight ratio of carbon fiber mixed in gypsum to gypsum and the bending strength of a gypsum test piece.

FIG. 3 is a diagram showing the relationship between the weight ratio of carbon fibers mixed in gypsum to gypsum and the water absorption performance of hardened gypsum (the weight ratio of water that can be absorbed by gypsum to gypsum).

FIG. 4 is a perspective view of a container for making gypsum slurry.

FIG. 5A is a cross-sectional view of one molding step of a gypsum mold for casting a plastic oval plate, and FIG. 5B is a cross-sectional view of the molded gypsum mold.

FIG. 6 (a) is a cross-sectional view of one molding step of a gypsum mold for press-molding a plastic oval plate, the molding surface of which is covered with a thin film of pure gypsum.
(B) is a cross-sectional view of a molded gypsum mold.

FIG. 7 shows a molding process of a plaster mold for plastic-molding a plate-shaped body having an engraved pattern, (a) is a prototype, (b) is a master, and (c) is a lower mold case. The mold and (d) are cross-sectional views of the mold.

FIG. 8 is a diagram showing the principle of a mixing method using oscillating rotation.

FIG. 9 shows a molding process of a gypsum mold for cast-molding a silver alloy cup, (a) is a prototype, (b) is a lower mold original mold, and (c) is a lower mold case mold. , (D) are cross-sectional views of the respective molding dies.

FIG. 10 shows a molding process of a plaster mold for molding a plastic casting mold, in which (a) is a master mold,
(B) is a cross-sectional view of the original mold, (C) is a case mold, and (D) is a target mold.

FIG. 11 is a scanning electron micrograph of a gypsum sample piece using β-type gypsum powder.

FIG. 12 is a similar photograph when α-type gypsum powder is used.

FIG. 13 is a measurement graph showing the change over time in the transverse rupture strength in a bending test of a gypsum-type test piece using the weight ratio of carbon fibers mixed in the gypsum mold to gypsum as a parameter.

FIG. 14 is a graph showing the rate of change in length between the pure gypsum test piece and the carbon fiber reinforced gypsum test piece at each temperature.

[Explanation of reference symbols] 3,3 'Upper mold for plastic molding gypsum mold 4,4' Lower mold for plastic molding gypsum mold 6 Thin film 17 Lower mold for plastic molding gypsum mold 18 Plastic molding gypsum mold Upper mold 21 Bag 22 Swing plate 23 Rotating shaft 24 Swing shaft 36 Lower mold of gypsum mold for silver alloy cup casting 37 Upper mold of gypsum mold for silver alloy cup casting 38 Silver alloy cup casting Plaster mold 49 Plastic casting mold

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Figure 4]

[Figure 8]

[Fig. 2]

[Figure 3]

[Figure 5]

[Figure 6]

[Figure 7]

[Figure 9]

[Figure 10]

FIG. 11

[Fig. 12]

[Fig. 13]

FIG. 14

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B29C 33/38 8823-4F 47/12 8016-4F C04B 11/00 (C04B 28/14 14:38 ) A 2102-4G

Claims (1)

Claims (1): Carbon fiber having a length of 5 to 100 mm dispersed in monofilament in a plaster structure of a base material of a plaster mold for molding is 0.008 to 0.9 with respect to gypsum. Molding die made of carbon fiber reinforced gypsum characterized by being uniformly mixed and dispersed in a weight percentage. (2) The sizing agent applied after cutting the carbon fibers to a length of 5 to 100 mm is removed by heating, and the carbon fibers are agitated in water while applying ultrasonic vibration to countless carbon fibers. The gypsum powder is dispersed in fibers, and the gypsum powder, the carbon fibers dispersed in 0.01 to 1% by weight based on the gypsum powder, the carbon fiber, water and other additives as necessary are stirred. Make a carbon fiber-containing gypsum slurry in which monofilaments of carbon fibers are evenly dispersed, pour pure gypsum slurry in advance into the mold to form a thin film, and then pour the carbon fiber-containing gypsum slurry, after curing A method for producing a carbon fiber reinforced gypsum molding die, characterized by producing a gypsum molding die having a molding surface coated with a thin film of pure gypsum by demolding and drying. (3) The carbon fiber dispersed in the gypsum powder into monofilaments having a length of 5 to 100 mm is 0.0 with respect to the gypsum powder.
A gypsum powder containing carbon fiber for a gypsum mold, which is uniformly mixed and dispersed in a proportion of 1 to 5% by weight. (4), carbon fiber is cut into a length of 5 to 100 mm and preliminarily dispersed into innumerable monofilaments, and gypsum powder,
It is characterized in that 0.01 to 5% by weight of the gypsum powder, and the carbon fibers dispersed in monofilaments are introduced into a circulating jet air flow to uniformly mix the two and then recovered. A method for producing a gypsum powder containing carbon fiber for a plaster mold. (5), carbon fiber is cut into a length of 5 to 100 mm and preliminarily dispersed into an infinite number of single fibers, and gypsum powder,
Carbon for a gypsum molding die, characterized in that 0.01 to 5% by weight of the gypsum powder and the carbon fibers dispersed in the monofilament are put into a flexible bag and oscillated and rotated. A method for producing a gypsum powder containing fibers.