JP2012135940A - Method of manufacturing molding by transfer molding method, and molding manufactured by the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a molding by a transfer molding method that enables smoothing of a surface of the molding when manufacturing the molding by the transfer molding method, and a molding manufactured by the same.SOLUTION: In this method, a molding material containing a thermosetting resin as a binding material and an inorganic material as a non-plastic material is stored in a pot 15, the molding material is heated and melted to be injected in a cavity through a communication path 17 for making a bottom part of the pot communicate with the cavity, and set by keeping the temperature and pressure thereof for a certain period after injection completion, and thereafter die opening is performed. In the method, the surfaces of the powder particle-like inorganic material are covered with the thermosetting resin by setting the mixture ratio of the thermosetting resin to the inorganic material at 18-35 mass%, an air passage for sucking and exhausting gas on the cavity side is formed in a parting part of a die, and a molten substance of the molding material is injected while sucking the air from the air passage.

Description

  The present invention relates to a method for producing a molded product by a transfer molding method using a molding material obtained by coating a carbon material such as graphite, a ceramic material such as mica, and other inorganic materials with a thermosetting resin, and the manufacturing method. It relates to the manufactured molded article.

  The transfer molding method is a method in which a pot is provided separately from the cavity portion of the mold, the molding material in the pot is heated and melted, and the mold is injected into the mold with a plunger. An example of such a transfer molding method or apparatus is disclosed in Patent Documents 1 and 2, for example.

  Compared with the compression molding method, the transfer molding method can inject a uniformly molten molding material into the mold and apply pressure when flowing, so the molding material flow in the vertical and horizontal directions can be reduced. The density of the molding material becomes uniform, and the molded product is characterized by strength and good dimensional accuracy regardless of the flow direction of the molding material. Further advantages of the transfer molding method are that a molded product with a uniform thickness and a complex shape can be obtained, that it has excellent dimensional accuracy, especially in the direction across the parting line, and that the heating time is compression molding. It can be reduced by 10 to 30% compared to the above. The transfer molding method is employed when there are restrictions due to molding materials or when it is difficult to adopt the injection molding method because the molded product is large and thick.

  A method for producing a molded article by the transfer molding method as described above will be outlined. After the mold kept at a constant temperature is closed, the powdery molding material and the molding material tableted with the powder are stored in a pot, and the molding material is heated and melted. The molten molding material is poured into the cavity through a communication path that allows the bottom of the pot to communicate with the cavity with a plunger. The movement of the plunger is stopped at the timing when the molten material slightly protrudes from the gap provided on the parting surface of the mold. Then, after keeping and keeping the pressure for a certain period of time, the hydraulic cylinder is operated to open the mold, and the molded product is demolded during or after the mold opening.

In this way, in the transfer molding method, a gap is provided in the parting surface of the mold so that the molten material protrudes from the gap, so air and other gases existing in the cavity at the initial stage of molding are released from the gap. Discharged. Moreover, since the molding material of the transfer molding method is a powder or a tablet of the powder, the molding material itself contains air. The air contained in the molding material is discharged from a gap (about 0.01 to 0.02 mm) provided between the plunger and the pot (cylinder) in the middle of molding or at the end of molding. Further, in the transfer molding method, a gap of 1 to 2 mm is left between the distal end surface of the plunger and the bottom surface of the pot so that excessive pressure is not applied to the molded product. Therefore, air remains in the cull portion remaining in the gap, and air is prevented from moving to the molded product side.
As described above, in the transfer molding method, air and other gases in the cavity are discharged from the gap between the parting surfaces of the mold, so the air and other gases in the cavity are not forcibly discharged. Is common.

On the other hand, in the injection molding method using a thermosetting resin, when a molded product is manufactured, air or other gas may be forcibly discharged from the cavity. This is because in the injection molding method, there is no gap between the molds, and therefore it is necessary to positively discharge the gas in the molds.
The point that the gas in the cavity is forcibly discharged in such an injection molding method is described in Patent Document 3 as follows.
"In other words, in order to obtain homogeneous and high physical properties, it is important to ensure a good flow of the molding material while discharging gas such as air in the mold, such as phenolic resin that is a molten binder. While it is essential to improve the molding pressure of the binder, the air in the mold at the curing stage during injection molding and various by-product gases associated with the curing reaction of the binder may impede filling and For this reason, it is not sufficient to exhaust gas from the mating surface of the mold according to the pressure during molding, and it is not sufficient to provide a vent hole for decompression exhaust. It was necessary to provide at the filling position ”(see [0010] of Patent Document 3).

JP 2000-299329 A JP-A-7-329100 JP 2010-179542 A

As described above, in the transfer molding method, air and other gases are not included in the molded product, but at the initial stage of molding, the molding material at the position of the communication path provided on the bottom surface of the pot is melted. When the molding material melts, it may be extruded into the cavity as it is. Furthermore, it is necessary to quickly fill the molding material up to the end of the mold after the start of injection. For this reason, the molding material needs to be given a good fluid state.
In addition, as a molding material, in a composite material that is a combination of a thermosetting resin and an inorganic material (particles), various gases of by-products generated by the resin curing reaction and air mixed in the resin at the time of injection are not contained in the resin material. Filling is inhibited and air bubbles remain in the molded product. When bubbles remain in the molded product in this way, the surface of the molded product is thinned by the pressure of the gas itself, particularly when the gas present near the surface of the molded product is released into the atmosphere by a demolding operation after molding. As shown in FIG. 11, the film may be inflated to form a dome-shaped protrusion 73, or the thin film may be damaged to form a scar 75, which may impair the smoothness of the surface of the molded product.

  The present invention has been made to solve such problems, and in the case of producing a molded article by a transfer molding method using a molding material comprising a thermosetting resin and an inorganic material, the surface of the molded article is It is an object of the present invention to obtain a method for producing a molded product by a transfer molding method which can be smoothed and a molded product produced by the production method.

  In transfer molding using a composite material that is a combination of a thermosetting resin and an inorganic material (particles) as a molding material, in order to smooth the surface of the molded product, the fluidity of the molding material is increased, and the molded product The remaining gas needs to move relative to each other as much as possible to discharge or compress bubbles, and to prevent air contained in the molding material from being contained in the molded product. The present invention is based on the above findings, and specifically comprises the following configuration.

(1) A method for producing a molded product by a transfer molding method according to the present invention includes a molding material containing a thermosetting resin as a binder and an inorganic material as a non-plastic raw material in a pot, The material is heated and melted and injected into the cavity through a communication path that allows the bottom of the pot to communicate with the cavity. It is a manufacturing method of a molded product by a transfer molding method in which mold opening is started and the molded product is demolded during or after mold opening,
The molding material covers the surface of the powdered inorganic material with the thermosetting resin, and the blending ratio of the thermosetting resin to the inorganic material is 18% by mass to 35% by mass,
The parting portion is provided with a suction / discharge passage for sucking and discharging the gas on the cavity side, and the melt of the molding material is injected while suctioning from the suction / discharge passage.
When the blending ratio of the resin is 18% by mass or less, the amount of resin adhering to the surface of the particles is not sufficient, friction is likely to occur on the particle surface, and movement of the relative position of the particles during filling or holding pressure is maintained. It becomes difficult to discharge or compress bubbles between particles. On the other hand, if the blending ratio of the resin exceeds 35% by mass, the amount of the resin adhering to the particles becomes excessive, and the physical properties of the resin are exerted more strongly than the physical properties of the inorganic material. ) Cannot be demonstrated.

For example, the inner pot of an electromagnetic induction heating rice cooker is formed using graphite as an inorganic material, and has a circular bottom portion and a side wall extending vertically from the periphery thereof, and the bottom portion for equalizing the flow length. The molding material is injected from the center of the plate, but since there is a bent part of approximately 90 degrees between the bottom part and the side wall part, pressure is applied to the side wall part compared to a flat plate like a grilled meat plate. It is difficult, and the packing density of the graphite particles on the side wall is lower than that of the bottom, so that the appearance after firing becomes rough. Therefore, in order to improve the appearance after firing, it is necessary to increase the filling degree of graphite and reduce the amount of resin after molding. On the other hand, since it is necessary to fill the mold end, it is necessary to ensure the fluidity of the molding material, and therefore the resin blending ratio is more preferably 18% by mass to 25% by mass.
Even if it is a molded product that has a bent part in the middle of the flow length like the inner pot of an electromagnetic induction heating rice cooker, and the pressure is difficult to be applied to the side wall part by changing the flow direction, the resin compounding ratio is 18% by mass. From 25% by mass, residual bubbles after molding can be reduced, and a product with a good appearance after firing can be obtained.

(2) Moreover, the thing as described in said (1) WHEREIN: The said thermosetting resin is a phenol resin, It is characterized by the above-mentioned. There are novolak resin and resol resin in phenol resin, but novolak resin is a polynuclear phenol (2 to 8 mer), and it is necessary to add a curing agent to cause a curing reaction. On the other hand, the resol resin is multimethylol (1 to 4 mer), and a curing reaction occurs without adding a curing agent. In addition, the phenol resin can be changed from those mainly composed of the glassy phase to insoluble and infusible materials mainly composed of the rubbery phase by setting the curing reaction conditions. In the curing reaction of the novolak resin, various gases are generated due to decomposition of the curing agent in addition to the condensation polymerization reaction. On the other hand, in the curing reaction of the resole resin, methylol groups are polycondensed to become —CH ₂ OCH ₂ —, —CH ₂ —, CH═CH—, etc., and water vapor and other gases are generated by the dehydration reaction.

(3) Further, in the above (1) or (2), the inorganic material is ceramic particles such as quartz, burned powder and feldspar.

(4) Further, in the above (1) or (2), the inorganic material is graphite or another carbon material.

(5) The molded product according to the present invention is characterized by being manufactured by the method for manufacturing a molded product by the transfer molding method described in any one of (1) to (4) above.

In the method for producing a molded product by the transfer molding method according to the present invention, the molding material is made to have a blending ratio of the thermosetting resin to the inorganic material of 18% by mass to 35% by mass to reduce friction between particles. Therefore, the fluidity of the molding material can be increased so that the molding material can be quickly filled up to the end of the mold, and the particles can move relative to each other by the holding pressure after injection and after filling to discharge or compress the bubbles between the particles. Allow movement.
In addition, since the molding material melt is injected into the mold while sucking from the suction / discharge flow path at the initial stage of molding, the middle stage of molding, and the final stage of molding, The air and reaction product gas contained in the molding material can be forcibly exhausted, and thus the bubbles contained in the molded product can be compressed or eliminated, which increases the packing density of particles and increases the surface of the molded product. Can be smoothed.

It is explanatory drawing of the manufacturing method of the molded article by transfer molding which concerns on one embodiment of this invention. It is an enlarged view of the A section enclosed with the circle of FIG. It is a figure which shows the metal mold | die in the state which formed the cavity in the transfer molding machine which concerns on one embodiment of this invention. It is an enlarged view which expands and shows the B section enclosed with the circle in FIG. It is drawing which follows the arrow AA line in FIG. It is explanatory drawing explaining the mechanism of the air discharge | emission in the molding material of one embodiment of this invention. It is explanatory drawing of the transfer molding method of one embodiment of this invention. FIG. 8 is an enlarged view of a portion C surrounded by a circle ○ in FIG. 7. It is explanatory drawing of the falling ball test method about a plate-shaped test piece. It is explanatory drawing of the falling ball test method about the inner pot of an electromagnetic induction heating rice cooker. It is explanatory drawing of the subject which invention intends to solve.

The main part of the transfer molding machine 1 which manufactures the molded article which concerns on this Embodiment is demonstrated based on FIG. In FIG. 1, the transfer molding machine 1 is provided with a mold for molding the inner pot of the electromagnetic induction heating rice cooker.
The transfer molding machine 1 is a male which can be moved up and down by being guided by a hydraulic cylinder installed on a base (not shown) and a pole (not shown) fixed to the rod 3 of the hydraulic cylinder and standing on the base. A mold receiver 5, a male mold 7 fixed on the upper surface of the male mold receiver 5, a projecting pin 9 that can move up and down through the male mold 7, and a pole (not shown) erected on the base None) in the middle portion of the floating plate 11 that can be brought into contact with and separated from the male die receiver 5, the female die 13 that is installed on the lower side of the floating plate 11, and the upper side of the floating plate 11 The pot 15 is provided.
The top of the female mold 13 and the bottom of the pot 15 are communicated with each other through a communication passage 17 that communicates the two.
As shown in FIG. 2, the communication path 17 is gradually reduced in diameter from the bottom side of the pot 15 toward the lower side, and a minimum diameter part 19 is formed in the middle of the communication path 17 so that the path diameter is minimum. The diameter is increased from the minimum diameter portion 19 toward the female mold 13 side so as to reach the female mold 13. That is, the communication path 17 has a funnel shape from the bottom of the pot 15 to the minimum diameter portion 19, and has a truncated cone shape from the minimum diameter portion 19 to the female mold 13.

The communication path 17 as described above is formed by a hole 21 formed in the bottom of the pot 15 and a through hole 25 provided in a gate insert 23 installed between the pot 15 and the female mold 13. .
As shown in FIG. 2, the hole 21 formed in the bottom of the pot 15 is gradually reduced in diameter downward, and the through hole 25 provided in the gate insert 23 continues to the hole 21. Yes.
The gate insert 23 has a head portion 27 whose upper end is enlarged in diameter, and a main body portion 29 is formed in the lower portion of the head portion 27. The vertical section has a substantially T-shape. The gate insert 23 has the body portion 29 inserted into the opening 31 provided in the female die, and the head 27 and the female die so that the head portion 27 fits into the recess 33 provided in the bottom surface of the pot 15. It is installed between.
The gate insert 23 is formed with a through hole 25 that forms a part of the communication path 17 at the center thereof. The shape of the through hole 25 is gradually reduced from the head 27 side downward, and a minimum diameter portion 19 having a minimum hole diameter is formed in the middle, and the diameter extends from the minimum diameter portion 19 toward the lower end. It has a diameter.

The inner diameter of the minimum diameter portion 19 in the communication path 17 is related to the particle size of the inorganic material. When the inorganic material having a maximum length of 500 μm is used, the inner diameter is 4.0 to 7.0 mm, preferably Is from 5.0 to 6.5 mm.
Further, the gradient angle and length of the hole from the minimum diameter portion 19 to the female mold 13 may be determined in consideration of fluctuations in actual molding conditions and lot fluctuations in the molding material. The gradient angle is 30 degrees. It is practical to set the length to -50 degrees and the length from 5 mm to 15 mm.

A fixed platen 35 is fixed above the floating plate 11 at an upper position of a pole (not shown), and a plunger 37 is installed on the lower surface of the fixed platen 35. A take-out groove 39 having an inverted trapezoidal vertical cross section is formed at the center of the top surface of the plunger 37.
A gap of about 0.01 to 0.02 mm is formed between the plunger 37 and the pot 15.
Further, in order to prevent excessive pressure from being applied to the molded product, a gap of 1 to 2 mm is formed between the distal end surface of the plunger 37 and the bottom surface of the pot 15 when the plunger 37 is moved down most. It is like that.

On the parting surface, as shown in FIGS. 3 and 4, the male mold 7 and the female mold are formed in a state where the male mold 7 is closest to the female mold 13 and the cavity 41 is formed (see FIG. 3). 13 is formed with a slight gap 43 (about 0.02 mm). The gap 43 serves as a gas discharge path in the cavity 41 during molding and an outflow path through which a melt of the molding material flows out at the end of molding.
A ring-shaped edge 45 having a width of 0.5 mm is formed outside the final filling portion on the male mold 7 side, and a ring-shaped suction channel 47 is provided along the edge 45 on the outer side. Yes. A radial flow path 49 that communicates with the suction flow path 47 and extends in the radial direction is formed, and the radial flow path 49 is connected to the vacuum ejector 53 via an L-shaped connection flow path 51.

  As shown in the enlarged cross-sectional view of FIG. 5, the vacuum ejector 53 has an air flow path 55 extending in a direction orthogonal to the connection flow path 51, and a flow path diameter of a connection portion between the air flow path 55 and the connection flow path 51. Has a reduced diameter portion 57 that rapidly decreases in diameter. Then, by flowing air at a high speed in the direction indicated by the arrow in FIG. 5 through the air flow path 55, the connection flow path 51 becomes negative pressure, which causes the radial flow path 49, the suction flow path 47, and the edge 45 to flow. The gas in the cavity 41 is sucked through the formed gap 43 and discharged to the air flow path 55. The gap 43, the suction channel 47, the radial channel 49, the connection channel 51, and the air channel 55 correspond to the suction / discharge channel of the present invention.

  A molding method for molding the inner pot of the electromagnetic induction heating rice cooker with the transfer molding machine 1 having the above-described components will be described. Graphite powder is used as an inorganic material that exhibits electromagnetic induction. The graphite powder can be used without excluding fine particles having a specific particle size or less after being pulverized to 500 μm or less. The surface of the graphite powder is made of a thermosetting resin such as a phenol resin, and the blending ratio of the thermosetting resin to the inorganic material is 18% by mass to 35% by mass, preferably 18% by mass to 25% by mass. It is formed by coating an inorganic material with a thermosetting resin. By setting the resin blending ratio to 18% by mass to 35% by mass, when pressurizing under heating at a melting temperature or higher, as shown in FIG. 6, the surface of the graphite particles 59 is covered with the thermosetting resin 61, The graphite particles 59 easily move to a suitable position due to the fluidity of the resin. As a result, as shown in FIG. 6A, the bubble 63 is shifted from the large state to the state shown in FIG. If the bubble 63 is an open cell, the air contained in the molding material by being filled is discharged by the gap between the pot 15 and the plunger 37 or the vacuum ejector 53. For this reason, the gas contained in a molded article can be suppressed to the minimum, and the smoothness of the surface of a molded article can be improved. Actual graphite particles are not spherical but irregular, but are typically spherical for ease of explanation. In addition, when the bubble 63 is a closed cell, the bubble is compressed and its volume decreases.

  The male and female molds, the pot 15 and the plunger 37 are heated in advance to a temperature suitable for the molding material, and the molding material formed on the tablet is put into the pot 15. The molding material to be put into the pot consists of a mixture of an inorganic material of graphite particles and a thermosetting resin powder of phenolic resin, and the heat temperature is as high as possible unless there is partial curing or flow stoppage during filling. Set. The rod 3 of the hydraulic cylinder is extended to raise the male mold receiver 5, and the male mold receiver 5 is brought into contact with the floating plate 11 to form a cavity 41. When the cavity 41 is formed, the vacuum ejector 53 starts to discharge the gas in the cavity 41. By further extending the rod 3 of the hydraulic cylinder, the male mold receiver 5 and the floating plate 11 are raised together, and the plunger 37 is inserted into the pot 15. The molding material that is easy to flow due to the heat of the pot 15 is gradually injected into the cavity 41 through the communication path 17. In this injection process, as described above, the gap 63 in the molding material becomes small, and the gas pushed out by the gap is discharged by the gap between the pot 15 and the plunger 37 or the vacuum ejector 53. The injection rate of the molding material is determined in consideration of the thickness of the molded product and the curing rate of the curable resin.

  The molten molding material passing through the communication path 17 is compressed at the minimum diameter portion 19 and released at once in the expanded diameter flow path immediately after passing through the minimum diameter portion 19, while maintaining high fluidity, It flows toward the mold end. In a state where the melted molding material is filled in the mold, it is cured by holding the pressure for about 6 to 8 minutes. The lowest movement position of the top surface of the plunger 37 with respect to the bottom surface of the pot 15 is set to be 1 to 2 mm above the bottom surface of the pot 15, and the bottom surface of the pot 15 even when the plunger 37 is moved to the lowest position. A gap is formed between the two. Due to this gap, a curl portion 65 made of a cured product of the molding material is formed. The cal part 65 refers to a part above the part indicated by a broken line in the figure showing the cal part 65 in FIG. Cull thickness (material charge) is typically 1 to 2 mm, and if it is thicker than this, excessive pressure is applied, resulting in increased internal stress of the molding material to be filled. When it is thin, insufficient filling occurs and the density of the molding material to be filled is lowered.

  The cured product that has become insoluble and infusible by the curing reaction is connected to the bottom of the pot 15, the communication path 17, and the cavity 41. When the hydraulic cylinder is operated in this state and the floating plate 11 and the male mold receiver 5 are lowered together, the cull portion 65 is fixed to the plunger 37 by the take-out groove 39, so that the cured product is absorbed by the cull portion 65. The upper part is fixed and pulled downward, and as a result, it breaks at the smallest diameter part 19 having the smallest cross section (see FIG. 7). As a result, the inverted frustoconical cured product 43 formed by the portion above the minimum diameter portion 19 in the cull portion 65 and the communication path 17 is held on the plunger 37 side, and the flow below the minimum diameter portion 19 is maintained. The frustoconical projection 69 formed by the path is held on the floating plate 11 side together with the molded product 71.

  The communication passage 17 is expanded in diameter on the downstream side of the minimum diameter portion 19, and is communicated with the cavity 41 through a truncated cone-shaped channel after being expanded. For this reason, when the mold is opened, a molding defect occurs in the vicinity of the minimum diameter portion due to the cutting of the communication path, but this does not affect the molded product 71 side. Since the truncated cone-shaped convex portion 69 formed by the flow path below the minimum diameter portion 19 is removed after demolding, the mechanical strength due to molding failure is reduced in the vicinity of the communication flow path in the molded product 71. There is nothing.

  Next, when the floating plate 11 is fixed at an intermediate position of the pole and the hydraulic cylinder is further operated to move the male mold receiver 5 downward, a molded product 71 in which the truncated cone-shaped projection 69 is integrally formed. Is exposed in a state of being fixed to the male mold 7 side. In this state, the protruding pin 9 is protruded to remove the molded product 71. After the molded product 71 is removed from the mold, it is left to cool. Thereafter, the truncated cone-shaped convex portion 69 is cut off at the base to obtain a molded product 71. As described above, even if a defective molding portion occurs, the defective molding portion is concentrated on the top of the truncated cone-shaped convex portion 69, and the convex portion 69 is cut out to cause defective molding on the molded product 71 side. There is nothing. For this reason, it becomes possible to raise the injection pressure at the time of shaping | molding, and by adjusting the compounding ratio of the thermosetting resin with respect to an inorganic material, from the front-end | tip part of the molded product 71 with long flow length, or the molded product 71 from the communicating path 17. A molded product 71 (for example, a pot or an inner pot) having a bent portion between the front end portions of the can be molded.

  In the present embodiment, the pot 15 and the cavity 41 are arranged in the vertical direction via the communication path 17, and the communication path 17 is arranged in the center of the cavity 41. It is possible to evenly inject into the respective end portions and the molded product 71 having a bent portion between the communication passage 17 and the distal end portion of the molded product 71. Further, in the present embodiment, the blending ratio of the thermosetting resin to the inorganic material in the molding material is set to 18 mass% to 35 mass%, and the gas in the cavity 41 is forcibly forced by the vacuum ejector 53. Since the exhaust is performed, the gas remaining in the molded product can be reduced to smooth the surface of the molded product (see FIG. 8).

  Hereinafter, examples of the present invention will be described in detail by taking as an example a grilled meat plate formed by a transfer molding method using graphite particles as an inorganic material and an inner pot of an electromagnetic induction heating rice cooker. In addition, although the example of the inner pot of the electromagnetic induction heating rice cooker was given this time, as the electromagnetic induction heating cooker, a plate for frying pan, pan, yakiniku, takoyaki, kettle, etc. are also suitable for the present invention. Yes.

<Process for preparing molding material>
Two types of graphite are used. The first is graphite made in China, and isotropically pulverized to 20 μm or less by a jet mill. The second one is Japanese graphite, and the chips produced when the electrode is shaved from the graphite ingot are selected by flotation to obtain graphite particles of 200 μm or less. The graphite particles contain 40 to 65% of particles of 50 μm or less when used without excluding fine particles of a specific particle size or less after being pulverized to 200 μm or less. This is mixed with a tri- to pentameric resole resin diluted with a lower alcohol, for example, ethanol.

  The pulverized particles are used without being classified as they are. As the quaternary ammonium salt type cationic activator used here, a cationic activator containing an alkyltrimethyl group and an alkyldimethylbenzyl group was used. The surfactant has protective colloid properties, and exhibits a polyelectrolyte behavior in the solution to form an anionic water-soluble resin and a polyion complex, so that the resin dispersed in the solution is not excessively large. If it is the particle | grains of 200 micrometers or less comparable as the graphite particle used by embodiment, since it acts so that a spherical shape may be comprised, it is preferable.

  Next, it stirs so that a graphite particle may disperse | distribute uniformly, heating at arbitrary temperature, and coat | covers the whole surface of a graphite particle with a resole resin. This coating exhibits suitable fluidity and viscosity. This was transferred to a rotary dryer at a low temperature of about 10 to −10 ° C. and subjected to a drying process in which lower alcohols as solvents were scattered under reduced pressure.

  The molding material obtained by the above method is a granular molding formed by holding the surface of graphite powder in a wet state with the resol resin raw material liquid so that it is held as a film on the outer peripheral surface of the graphite powder. Become a material. At this time, the resin adhesion rate in the molding material adjusted the compounding ratio of a graphite particle and a resole resin raw material. In the present invention, from the knowledge that the smoothness of the surface after firing is related to the blending ratio of the resole resin to the graphite particles, the blending ratio of the resole resin to the graphite particles is in the range of 18% to 35% by weight. Then, the yakiniku plate and the inner pot of the electromagnetic induction heating rice cooker were molded, and after firing, the appearance of their surfaces was visually inspected.

<Molding process>
Next, a pot-shaped molded product (inner pot) is molded from the molding material. The male and female molds are heated to a curing temperature of about 160 ° C., and a predetermined amount of molding material (tablet) is charged. At this time, in the present embodiment, the time during which the viscosity at the time of flow accompanying the progress of the reaction does not become excessively high in the present embodiment is promoted to release gas such as water vapor as a by-product in the initial reaction stage before the resol resin reaches curing. High pressure for obtaining a molded product having a dense internal structure by increasing the packing density after holding for 80 to 90 seconds at a contact pressure that maintains the state in which the graphite particles have sufficient bubbles. In the form, the injection pressure is 200 tons (converted to the resin pressure is 85 MPa. The resin pressure is the value obtained by dividing the injection pressure by the cross-sectional area of the inner hook), and after 6 minutes of flow, complete curing is achieved for 6 minutes. After the holding time, mold opening starts. After the communication portion is broken at the minimum diameter portion, the molded product in which the truncated cone-shaped projection 45 is integrated is removed from the mold, and the truncated cone-shaped projection 69 is cut off at the root portion. The thermosetting resin is gelled by a curing reaction and becomes rubbery when the curing reaction proceeds, and becomes glassy and completely cured when the reaction proceeds further. When the curing temperature is higher than the glass transition point, curing of the resin can be completed while remaining rubbery without becoming glassy. If the cured state is completed in the form of rubber instead of glass, the impact resistance of the molded product can be improved.

<Baking process>
The obtained molded product was allowed to stand in an oxygen-free atmosphere at 1000 to 1200 ° C. to condense or carbonize the resole resin that became an insoluble and infusible cured product, thereby connecting the graphite particles to each other, A graphite aggregate in the form of a pan was obtained. At this time, when the resol resin is condensed or carbonized, if there is a cracked gas that is not dissipated from the molded product and stays inside, the cracked gas causes a local bulge caused by a fault crack. In order to prevent this, the temperature is gradually raised over one month. The resole resin used as the binder generates shrinkage due to the curing reaction, that is, a curing stress accompanying the curing shrinkage, in the reaction curing process at the time of molding. A molding material that is a combination of a resin and graphite particles generates a large curing stress. If the curing stress is excessive, it is released during the firing process, causing a phenomenon of explosion, resulting in a defective product.

Table 1 shows the appearance of the surface after firing according to the relationship between the blending ratio of the graphite particles and the resol resin.
In Table 1, the particle size is the particle size of the graphite particles. In the evaluation of the appearance after firing, ○ means that the appearance is beautiful, and Δ is inferior to ○, but within the allowable range. I mean.
The thickness of the molded product is 4 mm.

The falling ball test shown in Table 1 will be described.
FIG. 9 shows the case where the test object is a flat yakiniku plate (numbers 1 and 2 in Table 1), and FIG. 10 shows the case where the test object is an inner pot of an electromagnetic induction heating rice cooker (numbers 3 to 6 in Table 1). ). In either case, the test object 83 is placed on the cushion mat 81, the cylinder 85 is erected on the test object, and the steel is placed on the drawing plate 87 arranged at a predetermined height. The ball 89 was dropped by pulling out the pull-out plate 87, and the limit height (mm) at which no crack occurred was defined as the falling ball strength.

As shown in Table 1, the appearance after firing was beautiful when the resin compounding ratio relative to graphite was in the range of 19.5 mass% to 35 mass%. In this range, the falling ball strength is 100 mm or more, so that it can withstand practical use.
On the other hand, when the resin blending ratio was 18% by mass, the falling ball strength was 50 mm and the appearance was slightly inferior, but all were within the allowable range.
Regarding the particle size of graphite, 20 μm tends to be slightly better in falling ball strength in the case of 20 μm and 200 μm, but if the resin compounding ratio to graphite is in the range of 18% by mass to 35% by mass. For any particle size, both falling ball strength and appearance after firing are acceptable.

  From the above consideration, it can be seen that if the resin blending ratio with respect to graphite is in the range of 18% by mass to 35% by mass, at least the appearance is suitable for practical use. On the other hand, regarding the strength, whether or not it is appropriate is determined according to the intended use. Therefore, when high strength is required, it is desirable to increase the resin blending ratio.

  A molding material having a resin blending ratio of 18% by mass to 35% by mass easily moves graphite particles to a suitable position in the mold when pressed under heating at a temperature equal to or higher than the melting temperature, that is, excellent in fluidity. Therefore, the appearance of the surface of the molded product after firing is considered good. In addition, the molding material according to the present embodiment in which the resole resin is arranged on the surface of the graphite particles is excellent in fluidity because it is homogeneous, and also in this respect, the appearance of the surface of the molded product after firing is considered to be improved. It is done.

<Coating process>
The inner surface coating process of the inner pot of the electromagnetic induction heating rice cooker will be described. First, the base coating for cooking is performed. 10 vol% of tetrafluoroethylene / hexafluoropropylene copolymer (4.6 fluoride) (FEP) fine powder is dispersed in an aqueous dispersion of polyethersulfone (PES) to form an undercoat having a low viscosity of 200 centipoise The resin is sprayed several times using a spray until it remains thin on the surface.

Next, surface coating is performed. The liquid resin used for the base coating is in an undried state, and a fine powder of tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) compatible with FEP is uniformly adhered to the surface of the liquid resin to absorb the liquid resin. And fix. Thereafter, drying is performed in a 200 ° C. oven for 10 minutes.
Subsequently, it is put into a 360 ° C. furnace in order to perform the fusion treatment. As a result, PES and FEP are melted and joined so as to fit into the pores of the graphite aggregate, and a coating film not containing pores such as pinholes is formed, so that liquid ingredients used for cooking do not penetrate during cooking. Form an embodiment.

DESCRIPTION OF SYMBOLS 1 Transfer molding machine 5 Male mold receiver 7 Male mold 9 Projection pin 11 Floating board 13 Female mold 15 Pot 17 Communication path 19 Minimum diameter part 21 Hole 23 Gate insert 25 Through-hole 27 Head 29 Main part 31 Opening hole 33 Concavity 35 Fixed platen 37 Plunger 39 Extraction groove 41 Cavity 43 Clearance 45 Edge 47 Suction flow path 49 Radial flow path 51 Connection flow path 53 Vacuum ejector 55 Air flow path 57 Reduced diameter part 59 Inorganic material 61 Thermosetting resin 63 Bubble 65 Cull 69 Projection 71 Molded product 73 Projection 75 Scar mark 81 Cushion mat 83 Test object 87 Pull-out plate 89 Steel ball

Claims (5)

A molding material containing a thermosetting resin as a binder and an inorganic material as a non-plastic raw material is placed in a pot, and the molding material is heated and melted to communicate between the bottom of the pot and the cavity. Injecting into the cavity through the communication path, and after the injection is completed, the mold is opened after holding and curing for a certain period of time, and then mold opening,
The molding material covers the surface of the inorganic material in a granular form with the thermosetting resin, and the blending ratio of the thermosetting resin to the inorganic material is 18% by mass to 35% by mass,
According to a transfer molding method, wherein the parting portion is provided with a suction / discharge channel for sucking and discharging the gas on the cavity side, and the melt of the molding material is injected while suctioning from the suction / discharge channel. Manufacturing method of molded products.   2. The method for producing a molded article by transfer molding according to claim 1, wherein the thermosetting resin is a phenol resin.   The method for producing a molded article by the transfer molding method according to claim 1 or 2, wherein the inorganic material is ceramic powder such as quartz, burned powder, and feldspar.   The method for producing a molded product by transfer molding according to claim 1 or 2, wherein the inorganic material is graphite or other carbon particles.   A molded product produced by the method for producing a molded product according to the transfer molding method according to claim 1.

Images