Resin molding method and resin molding apparatus

Abstract

To provide a resin molding method for manufacturing a dense resin molded product free from foaming by enhancing the dispersibility of a molten resin, and a molding apparatus for performing the method.SOLUTION: The resin molding method is carried out by using a configuration in which a molding machine provided with a heating cylinder having a screw for charging a resin raw material containing a subcritical reaction substance and heating and melting the resin raw material is combined with a gas discharge nozzle having a resin injection port and a gas discharge port at a tip end of the molding machine. As the resin raw material, resin pellets, resin powder, resin pellets or resin powder containing reinforcing short fibers, or a resin raw material heated and melted and mixed with reinforcing fibers is used.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a novel resin molding method and a resin molding apparatus for carrying out the method. [Background technology]

[0002] There is a technology for incorporating reinforcing fibers such as glass fiber or carbon fiber into a resin material in order to increase the strength of a resin molded product. For example, the following patent document describes a vent-type injection molding machine in which continuous reinforcing fibers are supplied and kneaded from a vent formed in the middle of a heating cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-166712 Summary of the Invention [Problem to be solved by the invention]

[0004] However, resin molded products manufactured using vent-type injection molding machines often contain impurities. Also, when ultrafine fiber materials (hereinafter referred to as "reinforcing short fibers") are added to resin pellets as a resin raw material, the reinforcing short fibers tend to aggregate when the resin is melted, making it difficult to produce dense, high-quality resin molded products. In order to solve these problems, the first object of the present invention is to provide a method and an apparatus for carrying out the method that can significantly increase the fluidity of molten resin during the production of resin molded products. Second, the object is to provide a method and an apparatus for implementing the method that can improve the dispersibility of reinforcing short fibers even when resin pellets or resin powder containing reinforcing short fibers in advance is used as the resin raw material. [Means for solving the problem]

[0005] In order to achieve this object, the present inventors have conducted various studies and have arrived at the present invention. In other words, as a result of various studies on resin molded products, the inventors concluded that if the resin raw material contains a predetermined amount of moisture, and then in the resin molding process, the resin material is melted and high temperature and high pressure are applied, thereby bringing the moisture contained in the molten resin to a state close to subcritical or subcritical, the fluidity of the resin in a heated and molten state can be significantly increased.Based on this inference, as a result of trial and error, they were able to confirm that by adding a gas emission nozzle with a special structure to the tip of the heating cylinder and specifying the conditions for pressurizing and heating the molten resin, the moisture contained in the resin raw material can be changed to a subcritical state, significantly increasing the fluidity, and they obtained the following findings. That is, the first condition is that the resin raw material contains a predetermined amount of water. However, a similar effect can be obtained with any substance that can be safely changed to a subcritical state by controlling the pressure and temperature, and therefore in the present invention, such a substance is contained in the resin raw material as a subcritical reaction substance. The second condition is that the heated and melted resin is pressurized and passed through a gas discharge nozzle, and just before the molten resin is injected into a mold, the subcritical reactant is gasified and exhausted from the gas discharge nozzle. This brings the subcritical reactant contained in the molten resin into a state close to subcritical, significantly increasing the fluidity of the molten resin and making it possible to produce a molded product with a dense solid structure without bubbles. The present inventors have arrived at the present invention based on these findings, and propose a novel resin molding method and a novel resin molding apparatus for carrying out the method.

[0006] In order to achieve the above object, the present inventors propose the following method and apparatus as the present invention. That is, claims 1 to 6 propose a resin molding method using a resin material containing a subcritical reaction substance and a gas discharge nozzle, which increases the fluidity of the molten resin and makes it possible to obtain a resin molded product with a dense structure without foaming. ●Claim 1 A resin molding method in which a resin raw material is charged into a heating cylinder of a molding machine and heated and melted while being transported inside the cylinder, The resin raw material contains water or a subcritical reactant that safely changes to a subcritical state under pressure and temperature lower than those of water, The heating cylinder has a resin injection port and a gas discharge nozzle having a gas discharge port at its tip, charging the resin raw material into a heating cylinder; a step of heating and kneading the resin raw material in the heating cylinder to plasticize it; Further heating and melting the plasticized resin raw material in the pressure cylinder; and a step of pressurizing the thus-molten resin and feeding it into the gas discharge nozzle. By performing these steps, the molten resin is passed through the gas discharge nozzle and then injected toward a mold from the resin injection port, while the subcritical reactant contained in the molten resin is exhausted as a gas from the gas discharge port. In the present invention, the resin raw material must contain a subcritical reaction material in a predetermined ratio, and the resin raw material can be resin pellets or resin powder that do not contain reinforcing short fibers, resin pellets or resin powder that contain reinforcing short fibers, or those that have been heated and melted to mix in continuous reinforcing fibers. Furthermore, in the present invention, it is sufficient if a gas discharge nozzle is provided at the tip of the heating cylinder of the injection molding machine, and the subcritical reactant contained in the resin raw material is brought into a state close to subcriticality or a subcritical state by heating the molten resin to a certain temperature and pressurizing it, and the present invention does not exclude these conditions. ●Claim 2 In claim 1, A resin molding method, wherein the subcritical reactant is carbonated water or carbon dioxide gas. ●Claim 3 In claim 1, A resin molding method, wherein the subcritical reactant is a hydrocarbon. ●Claim 4 In claim 1, A resin molding method, wherein the subcritical reactant is an organic solvent. ●Claim 5 In any one of claims 1 to 4, The resin raw material is a thermoplastic resin pellet, a resin powder, or a thermoplastic resin pellet or a resin powder containing reinforcing short fibers. ●Claim 6 In any one of claims 1 to 5, A resin molding method in which continuous reinforcing fibers are mixed into the plasticized resin raw material.

[0007] Claims 7 to 13 propose a resin molding device for carrying out the present invention. Here, claims 7 and 8 propose a heating cylinder without a vent, claim 9 proposes a heating cylinder with a vent, and claim 10 proposes a heating cylinder characterized by the screw shaft diameter. Claim 11 proposes mixing reinforcing fibers into the resin raw material, claim 12 proposes an extrusion molding device, and claim 13 proposes an application to an injection molding device. ●Claim 7 A resin molding apparatus for carrying out the resin molding method according to any one of claims 1 to 6, comprising: a molding machine equipped with a heating cylinder having a heating means for heating, kneading, and melting a resin raw material introduced from a material introduction hopper, and a screw; a gas discharge nozzle provided at the tip of the heating cylinder and having a resin injection port and a gas discharge port; The heating cylinder controls the heating temperature and pressure to change the subcritical reactant contained in the molten resin to at least a state close to subcritical, The resin molding device is configured such that the molten resin passes through the gas discharge nozzle and is then injected toward a mold from the resin injection port, while the subcritical reactant contained in the molten resin becomes gas and is exhausted from the gas discharge port. ●Claim 8 In claim 7 The shaft diameter of the screw of the heating cylinder is larger on the gas discharge nozzle side than on the material input hopper side, A resin molding device, wherein the gas discharge port of the gas discharge nozzle is connected to a suction means. ●Claim 9 In claim 7 or 8, The heating cylinder has a vent portion at its middle portion, The resin molding device is configured to supply continuous reinforcing fibers from the vent portion and mix them into the molten resin. ●Claim 10 In any one of claims 7 to 9 A resin molding device, wherein the shaft diameter of the screw of the heating cylinder is narrower at a portion corresponding to the vent portion than at other portions. ●Claim 11 In any one of claims 7 to 9, The resin molding device is characterized in that the molten resin contains reinforcing fibers cut into pieces of about 2 to 3 mm. ●Claim 12 In any one of claims 7 to 11, A resin molding device that constitutes an extrusion molding device. ●Claim 13 In any one of claims 7 to 11, A resin molding device that constitutes an injection molding device. [Effects of the Invention]

[0008] According to the resin molding method and apparatus of the present invention, the properties of the base resin are improved, and it is possible to manufacture a resin molded product that is dense and solid without bubbles. That is, in the resin molding method according to the present invention, the resin that has been heated and melted in the heating cylinder is subjected to a large pressure as it passes through the gas discharge nozzle, and the heating temperature is further increased, so that the subcritical reactants contained in the heated and melted resin are changed to a subcritical or near-subcritical state, and as a result, the fluidity of the heated and melted resin can be significantly increased. Furthermore, the subcritical reactant, which has thus increased the fluidity of the flowing resin, turns into gas and is released all at once from the gas discharge port of the gas discharge nozzle just before the molten resin is injected into the mold, and does not flow back into the heating cylinder, so that foaming does not occur in the molded product. Furthermore, the gas discharge nozzle has a filter function, so impurities contained in the molten resin and water are removed before the molten resin is injected into the mold, so no impurities remain in the molded product produced. Furthermore, the subcritical reactant contained in the molten resin reaches a state close to subcritical when injected from the gas discharge nozzle, decomposing impurities, resulting in a pure molded product free of impurities. Furthermore, when short reinforcing fibers are added to the resin raw material or when reinforcing fibers are mixed into the molten resin raw material, the dispersion of these fibers within the base resin is enhanced three-dimensionally, with almost no aggregation, significantly improving the strength of the resin molded product produced. Therefore, the present invention realizes the manufacturing of screw fasteners as resin molded products. When manufacturing resin-molded screws, the method of the present invention significantly increases the fluidity of the base resin, making it possible to evenly distribute reinforcing short fibers and reinforcing fibers on the screw body and the complex threads that protrude continuously and spirally from the screw body, thereby enabling mass production of screw parts that take advantage of the corrosion resistance and light weight of resin. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a vertical cross-sectional view showing a basic configuration of a resin molding device. [Figure 2] 2 is a flow diagram showing a resin molding method using the resin molding device of FIG. 1. [Figure 3] FIG. 10 is a vertical cross-sectional view showing another example of the basic configuration of a resin molding device. [Figure 4] 4 is a flow diagram showing a resin molding method using the resin molding device of FIG. 3. [Figure 5] FIG. 1 is an explanatory diagram of a phase change of water. [Figure 5A] FIG. 1 shows an example of a subcritical reactant. [Figure 6] 1(a) and 1(b) are cross-sectional views showing the dispersion state of reinforcing fibers in the matrix resin. [Figure 7] 1 is a graph showing the relationship between the reinforcing fiber content of a resin and tensile strength. [Figure 8] 1 is a photograph showing the appearance of a resin molded product, showing the results of a tensile strength test comparing the strength of a resin molded product produced by the method of the present invention with that of a resin molded product produced by a conventional method. [Figure 9] 1 is a graph showing tensile test data comparing the strength of a resin molded article produced by the method of the present invention with that produced by a conventional method. DETAILED DESCRIPTION OF THE INVENTION

[0010] Fig. 1 is a longitudinal cross-sectional view showing the basic configuration of a resin molding apparatus of the present invention for carrying out the method of the present invention. This apparatus A constitutes an extrusion molding apparatus that extrudes heated molten resin through a die B. The die B is the same as a conventional die. The resin molding apparatus A can also be a multi-screw type with two or more axes.

[0011] In the molding device A, a material input hopper 11 is provided at the base of a heating cylinder 10, a vent section 12 is provided in the middle, and a gas discharge nozzle 13 is provided at the tip. Note that an electric heater, which is the heating means for the heating cylinder 10, is not shown.

[0012] The hopper 11 is a container for storing the resin raw material (pellets) to be charged into the heating cylinder 10, and its bottom is connected to the heating cylinder 10. Here, the resin raw material may be resin pellets containing no reinforcing short fibers or resin pellets containing reinforcing short fibers, depending on the resin molded product to be produced.

[0013] Vent 12 is an opening for releasing bubbles such as air, moisture, and miscellaneous gases generated during plasticization contained in the resin plasticized in cylinder 10 to the outside, and is formed on the side surface of the middle part of heating cylinder 10. In the example of Fig. 1, continuous reinforcing fibers 18 are supplied from vent 12 and mixed into the molten resin in cylinder 10, and the continuous reinforcing fibers mixed into the molten resin are cut to an appropriate size (for example, about 2 to 3 mm) in cylinder 10.

[0014] The gas discharge nozzle 13 is provided with a material flow path 13a for passing the molten resin, a resin injection port 13b, and a gas discharge port 13c. Here, material flow path 13a has branch paths with multiple inlets, and when the molten resin passes through the branch paths, subcritical reactants such as water contained in the molten resin are gasified, passed through a filter, and released from gas release port 13c. The molten resin passing through the branch paths is finally merged into one and injected from resin injection port 13b, and this special structure changes the subcritical reactants contained in the molten resin to a state close to subcritical. In other words, when the molten resin that has been heated and melted in the heating cylinder 10 and accumulated in the resin reservoir is pressed by the screw 17, the pressure is suddenly increased as it passes through the narrow material flow path 13a formed in the gas emission nozzle 13. Due to this structure, when a resin raw material containing a predetermined amount of moisture is used, the moisture in the molten resin changes from water vapor to a state close to subcritical, increasing the fluidity of the molten resin, and then runs through the molten resin at high speed, turning into gas as it passes through the shunt channel and is released from gas release port 13c. Due to this action, even if the reinforcing short fibers that were previously contained in the resin pellets or the reinforcing fibers that were mixed into the molten resin at an intermediate stage are aggregated, they are dispersed into pieces.Furthermore, the gas discharge nozzle 13 functions as a filter, so impurities are removed and even substances that have reached a subcritical state are decomposed. In addition, the subcritical reactant contained in the molten resin becomes a gas and passes through the molten resin at high speed, and then is released at high speed from the gas release port 13c, so it does not flow back into the heating cylinder 10, and therefore the molded product does not become foamed. The resin molded in this way is modified to become a dense, solid molded product without bubbles, and the reinforcing short fibers and reinforcing fibers are no longer clumped together, resulting in a molded product with high strength, no bubbles, and the fibers are evenly distributed in three dimensions.

[0015] The gas released from the vent section 12 and the gas release nozzle 13 is sucked through a pipe 15 having a harmful substance filter 14 in the middle to prevent outside air from entering through the vent section 12, and is forcibly exhausted to the outside by an air pump 16, which is a suction means.

[0016] The screw 17 has different shaft diameters (and pitches) at different locations in order to control the pressure of the plasticized resin. The base of the screw 17 is connected to a drive unit 19 that rotates and moves the screw 17 forward and backward. By rotating the screw 17, the resin raw material put into the hopper 11 is transported inside the heating cylinder 10 toward the gas discharge nozzle 13, where it is subjected to processes such as plasticization.

[0017] Suitable thermoplastic resins used as the resin raw material in the present invention include polypropylene, polyethylene, ABS, acrylic, polyamide, polycarbonate, polyphenylene sulfide, polyether ether ketone, and polybutylene terephthalate. However, since the present invention utilizes the moisture contained in the resin raw material, the optimal moisture content varies depending on the type of thermoplastic resin. For example, the water absorption rate of polypropylene is approximately 0.02%, that of polyethylene is approximately 0.04%, and that of ABS is approximately 0.33%. Resin raw materials such as resin pellets and resin powder will absorb water until they are nearly saturated if stored in air for a certain period of time, so some resin raw materials may be used as is. The resin raw material may be a mixture of resin pellets or powdered resin with reinforcing fibers such as carbon fiber or glass fiber, and the reinforcing fibers may have a diameter of about 0.05 to 10 microns.

[0018] Next, a description will be given of the molding process in molding device A. The resin raw material is assumed to be polypropylene, and reinforcing fibers are supplied from vent portion 12 when the resin pellets are plasticized.

[0019] The heating cylinder 10 is controlled for heating temperature and pressure at each location for plasticizing the resin and subsequent processing. Specifically, the heating cylinder 10 and gas discharge nozzle 13 are divided into multiple zones I to V, and the temperature in each zone is controlled within a temperature range that will not carbonize the heated and melted resin. The screw 17 also has different shaft diameters at each location to suit these zones.

[0020] In region I, the temperature of the heating cylinder 10 is controlled to gradually increase from 160°C to 280°C in order to plasticize the resin raw material, while the screw 17 has a small shaft diameter. Air contained in the resin raw material is mainly exhausted from the hopper 11. In region II, the screw 17 has a large shaft diameter and the heating cylinder 10 is controlled to a temperature of 240°C in order to pressurize the plasticized resin. Region III is a region including the vent portion 12, in which the temperature of the heating cylinder 10 is controlled to 240°C and the screw 17 has a small shaft diameter in order to release impurities, air, and moisture bubbles contained in the resin to the outside. In this region, the shaft diameter of the screw 17 is made small to reduce the pressure applied to the resin, thereby preventing the molten resin from spraying out of the vent portion 12. In region IV, the molten resin is pressurized again, so the temperature of the heating cylinder 10 is controlled to 220°C, while the screw 17 has a thick shaft diameter. The reason why the temperature in this region is lower than in region III is to prevent carbonization of the resin, which has become more susceptible to carbonization as a result of the reduction in moisture in the molten resin. In region V, the gas discharge nozzle 13 is temperature-controlled to 200° C. in order to reduce the pressure of the molten resin. The above temperature control is an example, and the temperature control of the heating cylinder 10 may be set appropriately depending on the type of resin, etc.

[0021] In the present invention, the subcritical reactant contained in the resin raw material is converted to a state at least close to subcritical, giving it the properties of both a liquid and a gas, i.e., high fluidity and high solubility, so that it not only penetrates into the gaps between the resin and reinforcing fibers at high speed, but also has the effect of dissolving impurities. Therefore, it has the effect of eliminating impurities, preventing aggregation of reinforcing short fibers and reinforcing fibers, and promoting three-dimensional dispersion.

[0022] The temperature control (area V) of the gas discharge nozzle 13 is preferably in the range of +40°C to -40°C relative to the heating cylinder 10, more preferably in the range of -20°C to -30°C, but the optimum temperature may be determined experimentally.

[0023] FIG. 2 is a flow diagram showing the resin molding method of FIG. In this method, the reinforcing fibers are supplied through the vent portion. The specific steps include step S1 of feeding the resin raw material into a heating cylinder, step S2 of heating and kneading the resin raw material to plasticize it, step S3 of further heating and pressurizing the plasticized resin, step S4 of venting miscellaneous gases and impurities from the opening of the vent, step S5 of reheating and pressurizing the resin, step S6 of venting moisture that has reached a near-subcritical state from the exhaust port of the gas discharge nozzle, and step S7 of injecting the resin after the moisture has been vented from the resin injection port of the gas discharge nozzle. Note that in Figure 1, continuous reinforcing fibers 18 are supplied from the vent 12, but this step is not shown in the flow diagram. Additionally, remaining solid impurities are captured by a filter structure in the gas discharge nozzle, but this step is also not shown in the flow diagram. Steps S2 to S6 correspond to the processes in areas I to V in FIG. 1, respectively.

[0024] The screw is designed so that the continuous reinforcing fibers supplied from the vent are cut into pieces of about 2 to 3 mm by the shearing action at the boundary between the screw and the heating cylinder. The reinforcing fibers mixed into the plasticized resin raw material are dispersed into the fine details of the base resin, and are therefore extremely useful in improving the strength of the resin molded product. Furthermore, by using such resin plasticization and extrusion molding, high-quality resin pellets containing reinforcing short fibers can be produced by extruding the resin into long string-like shapes called strands, cooling them, and cutting them with a strand cutter.

[0025] 3 is a longitudinal sectional view showing another example of the basic configuration of a resin molding apparatus according to the present invention. This apparatus A constitutes an injection molding apparatus that injects heated and molten resin into a mold C. Parts that are common to the above-mentioned embodiment are given the same reference numerals and their explanations will be omitted.

[0026] Unlike the example in Figure 1, this example does not have a vent, so no reinforcing fibers are mixed into the plasticized resin. Therefore, there is no thin shaft diameter portion in the middle of the screw 17.

[0027] In region VI, the temperature of the heating cylinder 10 is controlled to gradually increase from 160° C. to 280° C. in order to plasticize the resin raw material, while the screw 17 has a small shaft diameter. In region VII, in order to pressurize the plasticized resin, the heating cylinder 10 is controlled to a temperature of 240°C, while the screw 17 has a large shaft diameter. In regions VII and VIII, the pressure applied to the molten resin is increased when the screw 17 is advanced to inject the resin, in order to bring the water contained in the molten resin into a state close to subcritical.

[0028] FIG. 4 is a flow diagram showing a resin molding method using the resin molding apparatus of FIG. In this method, the resin raw material adjusted to a predetermined moisture content is conveyed inside a heating cylinder provided with the gas discharge nozzle at the tip thereof. The specific steps include step S8 of feeding the resin raw material into a heating cylinder, step S9 of kneading and heating the fed resin raw material to plasticize it, step S10 of further heating and pressurizing the plasticized resin raw material to melt it, step S11 of venting the moisture contained in the molten resin from the exhaust port of the gas emission nozzle, and step S12 of discharging the molten resin from the resin injection port of the gas emission nozzle after the moisture has been removed. Here, steps S9 to S11 correspond to the processes in regions VI to VIII, and the remaining solid impurities are captured by the filter structure of the gas emission nozzle 13, but this process is not shown in the flow diagram.

[0029] As described above, in the resin molding method of the present invention, the heating and pressurizing control by the heating cylinder is combined with the gas release nozzle to heat and melt the resin raw material and control the water contained therein to a state as close to subcritical as possible, so that the final molded product is a modified, high-quality product with almost no impurities or bubbles. Furthermore, when reinforcing fibers are mixed into the resin material during the kneading and melting process, the sizing agent (mainly epoxy resin) that holds the reinforcing fibers together is also decomposed and removed by the water that has reached a near-subcritical state, significantly improving the bonding and adhesion with the base resin.

[0030] Figure 5 is an explanatory diagram of water's phase changes. Water can be in three phases - solid, liquid, or gas - depending on the temperature and pressure, but it enters a supercritical state at temperatures and pressures above its critical point (374°C, 22 MPa). In the supercritical state, water exhibits the properties of both a gas and a liquid, such as gas properties such as elasticity and high permeability (low surface tension) and liquid properties such as high solubility. In the present invention, it is sufficient to change the state to a subcritical state. The polypropylene used in the examples was used in a subcritical state. In the figure, the subcritical state is shown as the shaded area X. In this state, the water is almost liquid, but it not only significantly improves the dispersibility of the molten resin, but also has the effect of decomposing organic impurities. Furthermore, the water that has reached a state close to subcritical becomes gaseous when decompressed in the vent and gas release nozzle. In order to change water into a subcritical state, high pressure and high temperature must be applied. However, the present inventors discovered that when water is present in molten resin, the resin does not carbonize but has the effect of significantly increasing its fluidity, which led to the present invention.

[0031] FIG. 5A is a table showing examples of substances that can be used as subcritical reactants in the present invention. In the table, the critical conditions for water are a pressure of 218.3 atm and a temperature of 374.2°C. Carbon dioxide has a pressure of 72.8 atm and a temperature of 31.0°C. Methane, a hydrocarbon, has a pressure of 45.4 atm and a temperature of -82.6°C, and methanol, an organic solvent, has a pressure of 79.8 atm and a temperature of 239.6°C. All of these gases transition to a critical state at lower pressures and temperatures than water. As a subcritical reactant, highly volatile gases are undesirable from a safety standpoint, but carbonated water, nonionic surfactants, and other substances that can be safely converted to a subcritical state can also be used, and the proportion contained in the resin raw material will vary depending on the substance.

[0032] 6(a) and 6(b) are cross-sectional views showing the dispersion of short reinforcing fibers and reinforcing fibers in the base resin. Figure 6(a) is a cross-sectional schematic diagram of resin discharged from a conventional plasticizing device that does not have a gas discharge nozzle, and shows that the reinforcing fibers F are in a state of agglomeration F' in multiple locations within the base resin M. This is thought to be due to factors such as insufficient dispersibility of the molten resin, the reinforcing fibers F being coated with a sizing agent, and the resin M not easily penetrating between the reinforcing fibers F. 6(b) is a cross-sectional schematic diagram of molten resin discharged from a molding apparatus according to the present invention equipped with a gas discharge nozzle, showing that the reinforcing fibers F are dispersed almost uniformly without aggregation in the matrix resin M. This is presumably due to the fact that the fluidity of the molten resin is improved by the water reaching a near-subcritical state thoroughly penetrating between the reinforcing fibers F, and that the sizing agent that coated the reinforcing fibers is decomposed by the decomposition action caused by the water reaching a near-subcritical state.

[0033] FIG. 7 is a graph showing the relationship between the reinforcing fiber content and the tensile strength of a resin molded product. The graph shows the data distribution Y of products molded using a conventional molding machine and the data distribution Z of products molded using the molding device according to the present invention. In terms of the relationship between the reinforcing fiber content and tensile strength, it is generally believed that the tensile strength is maximized at a certain reinforcing fiber content, but the products molded according to the present invention generally showed higher tensile strength than the products molded using the conventional molding machine. This is presumably because the latter has significantly higher dispersibility of the reinforcing fibers and the decomposition of the sizing agent results in stronger bonding and adhesion between the reinforcing fibers and the base resin.

[0034] Supported by test data Figure 8 shows the results of a comparison of the strength of molded products produced by the present invention and conventional methods. In this comparative example, the molded products were molded into dumbbell test pieces and subjected to a tensile test in which they were pulled at a constant speed. Both dumbbell test pieces used PP as the base resin and contained 1% cellulose nanofiber as reinforcing short fibers, and the appearance of both the products produced by the present invention and conventional methods was the same. S0 shows the appearance of the dumbbell test piece before tensioning, S1 shows a dumbbell test piece manufactured by a conventional method that was subjected to a tensile test, and S2 shows a dumbbell test piece manufactured by the method of the present invention that was subjected to a tensile test. As is clear from comparing S1 and S2, S1 broke linearly with only a slight stretch in the middle, whereas S2 broke with a significant stretch in the middle, with the middle branching into multiple branches, clearly showing an increase in tensile strength. Therefore, it was confirmed from the appearance that the manufacturing method of the present invention significantly increased the strength of resin molded products compared to conventional methods. FIG. 9 shows test data from the tensile test of the dumbbell test piece, with the vertical axis representing the pressure applied during the tensile test (MPa) and the horizontal axis representing the elongated length (mm). S2 barely stretches even when the pressure is increased at first, but when the pressure is further increased, it reaches a peak value and can withstand a pressure of 1400 MPa without breaking even when stretched beyond 30 mm. It can be seen that S1 gradually elongates as the applied pressure increases, and breaks before reaching 12 mm of elongation. From this test data, it is clear that the resin molded article produced by the method of the present invention is modified to have a significantly improved mechanical strength. [Explanation of symbols]

[0035] A Resin molding equipment 10 Heating Cylinder 13 Gas discharge nozzle 13b Resin outlet 13c Gas outlet 18 Reinforcing fibers

Claims

1. A resin molding method in which a resin raw material is charged into a heating cylinder of a molding machine and heated and melted while being transported inside the cylinder, The resin raw material contains water or a subcritical reactant that changes to a subcritical state under pressure and temperature lower than those of water, The heating cylinder has a resin injection port and a gas discharge nozzle having a gas discharge port at its tip, charging the resin raw material into a heating cylinder; a step of heating and kneading the resin raw material in the heating cylinder to plasticize it; Further heating and melting the plasticized resin raw material in the pressure cylinder; and a step of pressurizing the thus-molten resin and feeding it into the gas discharge nozzle. By carrying out these steps, the molten resin is passed through the gas discharge nozzle and then injected toward a mold from the resin injection port, while the subcritical reactant contained in the molten resin is gasified and exhausted from the gas discharge port, in this resin molding method.

2. In claim 1, A resin molding method, wherein the subcritical reactant is carbonated water or carbon dioxide gas.

3. In claim 1, A resin molding method, wherein the subcritical reactant is a hydrocarbon.

4. In claim 1, A resin molding method, wherein the subcritical reactant is an organic solvent.

5. In any one of claims 1 to 4, The resin molding method, wherein the resin raw material is a thermoplastic resin pellet or resin powder, or a thermoplastic resin pellet or powder containing reinforcing short fibers.

6. In any one of claims 1 to 5, A resin molding method characterized in that the molten resin contains reinforcing fibers mixed therein.

7. A resin molding apparatus for carrying out the resin molding method according to any one of claims 1 to 6, a molding machine equipped with a heating cylinder having a heating means for heating and kneading the resin raw material fed from a material feeding hopper to melt it, and a screw; a gas discharge nozzle provided at the tip of the heating cylinder and having a resin injection port and a gas discharge port; The heating cylinder controls the heating temperature and pressure to change the subcritical reactant contained in the molten resin to at least a state close to subcritical, The resin molding device is configured such that the molten resin passes through the gas discharge nozzle and is then injected toward a mold from the resin injection port, while the subcritical reactant contained in the molten resin becomes gas and is exhausted from the gas discharge port.

8. In claim 7 The shaft diameter of the screw of the heating cylinder is larger on the gas discharge nozzle side than on the material input hopper side, A resin molding device, wherein the gas discharge port of the gas discharge nozzle is connected to a suction means.

9. In claim 7 or 8 The heating cylinder has a vent portion at its middle portion, A resin molding device in which continuous reinforcing fibers are supplied from the vent portion and mixed into the molten resin.

10. In any one of claims 7 to 9 A resin molding device, wherein the shaft diameter of the screw of the heating cylinder is narrower at a portion corresponding to the vent portion than at other portions.

11. In any one of claims 7 to 10 A resin molding apparatus characterized in that the molten resin contains reinforcing fibers cut to about 2 to 3 mm.

12. In any one of claims 7 to 11 A resin molding device that constitutes an extrusion molding machine.

13. In any one of claims 7 to 11 A resin molding device that constitutes an injection molding machine.

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