Method and device for plasticizing resin

Abstract

To provide a method for plasticizing resin which can effectively remove impurities from resin and / or reinforcing fibers and can also satisfactorily disperse reinforcing fibers.SOLUTION: A device for plasticizing a resin according to the present invention has a gas emission nozzle at a tip of a heating cylinder, and the heating cylinder is temperature controlled so that a moisture contained in a resin raw material becomes subcritical or supercritical in at least an area including the gas emission nozzle and is then exhausted from the gas emission nozzle.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a resin plasticization method and apparatus for plasticizing and discharging a resin raw material. [Background technology]

[0002] There is a technique for adding reinforcing fibers such as glass fibers and carbon fibers to resin in order to increase the strength of resin molded products. For example, the following patent document describes a vent-type injection molding machine that supplies reinforcing fibers from a vent formed in the middle of a heating cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-166712 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned vent-type injection molding machine, impurities remain in the resin or reinforcing fibers, and the dispersion of the reinforcing fibers is insufficient, making it difficult to obtain high-quality molded products. In response to this, the object of the present invention is to provide a resin plasticization method and device that can effectively remove impurities from the resin or reinforcing fibers and also disperse the reinforcing fibers well. [Means for solving the problem]

[0005] The resin plasticization method according to the present invention is a resin plasticization method carried out while transporting a resin raw material brought to a predetermined moisture-absorbed state inside a heating cylinder with a gas emission nozzle at its tip, and is characterized by comprising the steps of: plasticizing the resin raw material; heating and pressurizing the plasticized resin; evacuating the moisture that has become subcritical or supercritical from the exhaust port of the gas emission nozzle; and discharging the resin after the moisture has been evacuated from the resin outlet of the gas emission nozzle. Furthermore, the resin plasticization apparatus according to the present invention is a resin plasticization apparatus for carrying out the resin plasticization method, characterized in that a gas emission nozzle is provided at the tip of a heating cylinder, and the heating cylinder is temperature controlled so that the moisture contained in the resin raw material becomes subcritical or supercritical at least in an area including the gas emission nozzle, and is then exhausted from the gas emission nozzle. Effect of the Invention

[0006] According to the present invention, impurities and the like can be effectively removed from the resin and reinforcing fibers, and the reinforcing fibers can also be dispersed well. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a vertical cross-sectional view showing the basic configuration of a resin plasticizing device. [Diagram 2] FIG. 2 is a flow diagram showing a resin plasticizing method using the resin plasticizing apparatus of FIG. [Diagram 3] FIG. 4 is a vertical cross-sectional view showing another example of the basic configuration of a resin plasticizing device. [Figure 4] FIG. 4 is a flow diagram showing a resin plasticizing method using the resin plasticizing device of FIG. [Diagram 5] 1 is a phase diagram of water. [Figure 6] 1(a) and 1(b) are cross-sectional views showing the dispersion state of reinforcing fibers in a resin. [Figure 7] 1 is a graph showing the relationship between the reinforcing fiber content of a resin and tensile strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Fig. 1 is a vertical cross-sectional view showing the basic configuration of a resin plasticizer according to the present invention. This plasticizer A constitutes an extrusion molding device that extrudes plasticized resin through a die B. The die B is the same as a conventional one. The plasticizer A can also be of a twin-screw type.

[0009] The plasticizer A has a hopper 11 at the base of a heating cylinder 10, a vent 12 at the middle, and a gas discharge nozzle 13 at the tip. An electric heater for heating the heating cylinder 10 is not shown in the figure.

[0010] The hopper 11 is a container for accumulating the resin raw material (pellets) to be charged into the heating cylinder 10, and its bottom is connected to the heating cylinder 10.

[0011] The vent portion 12 is an opening for releasing bubbles of air, moisture, impurities, etc. contained in the plasticized resin and flowing therethrough to the outside, and is formed on the side surface of the middle portion of the heating cylinder 10.

[0012] The gas emission nozzle 13 is a special nozzle that is provided with a fine vent member 13a in the material flow path of the injection nozzle, and is configured to increase the flow rate of the resin that has completed plasticization and to gasify and remove moisture and the like in the resin. The gas emission nozzle 13 is formed with a gas emission port 13b and a resin emission port 13c.

[0013] The gas discharged from the vent portion 12 and the gas discharge nozzle 13 is sucked by an air pump 16 through a pipe 15 having a harmful substance filter 14 in the middle thereof, and is discharged to the outside.

[0014] The screw 17 has different shaft diameters (and pitch) 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 18 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 in the direction of the gas emission nozzle 13, and is processed, such as plasticized, along the way.

[0015] The resin to be plasticized is assumed to be a thermoplastic resin such as polypropylene, polyethylene, ABS, acrylic, polyamide, polycarbonate, polyphenylene sulfide, polyether ether ketone, polybutylene terephthalate, etc., but since the present invention utilizes the moisture contained in the resin raw material, it is desirable that the resin raw material is in a certain moisture absorption state, and there is no need to dry it in advance. For example, the water absorption rate of polypropylene is about 0.02%, that of polyethylene is about 0.04%, and that of ABS is about 0.33%, but if it is stored in air for a certain period of time or more, any resin will absorb water until it is almost saturated, so it can be used as it is. The resin raw material may also contain reinforcing fibers such as carbon fibers, glass fibers, etc. In this case, the reinforcing fibers may have a diameter of about 0.05 to 10 microns.

[0016] Next, the plasticization process in the plasticizer A will be described in detail. Here, the processing target is assumed to be a polypropylene resin raw material containing reinforcing fibers. The reinforcing fibers may be supplied from the vent 12.

[0017] The heating cylinder 10 and the gas discharge nozzle 13 are temperature-controlled for each part for plasticizing the resin and subsequent processing. Specifically, the heating cylinder 10 and the gas discharge nozzle 13 are divided into a plurality of regions I to V, and the temperature is controlled for each region. Also, the screw 17 has different axial diameters for each part to suit these regions.

[0018] Specifically, in order to plasticize the resin raw material in region I, the temperature of the heating cylinder 10 is controlled so as to gradually increase from 100°C to 240°C, while the screw 17 has a small shaft diameter. The air between the resin raw materials is mainly exhausted from the hopper 11. In region II, in order to pressurize the plasticized resin, the heating cylinder 10 is temperature-controlled at 240° C., while the screw 17 has a large shaft diameter. Region III includes the vent 12, and in order to release impurities, air, and moisture bubbles contained in the resin to the outside, the heating cylinder 10 is temperature-controlled at 240°C, while the screw 17 has a narrow shaft diameter. In this region, the resin is decompressed to prevent the resin from spraying out of the vent 12. In region IV, the temperature of the heating cylinder 10 is controlled at 220°C to pressurize the resin again, while the screw 17 has a large shaft diameter. The reason why the temperature in this region is lower than that in region III is to prevent carbonization, which becomes more likely to occur due to the reduction in moisture in the resin. In region V, the gas emission nozzle 13 is temperature-controlled to 200° C. in order to reduce the pressure of the resin. The above temperature control is merely an example, and the temperature control of the heating cylinder 10 may be appropriately set depending on the type of resin, etc.

[0019] In the present invention, the resin raw material contains more moisture than usual, so that by performing the above-mentioned temperature control and pressure control, the moisture becomes subcritical in regions II and V, and exhibits a favorable effect. In other words, since subcritical water has the properties of both liquid and gas, i.e., high fluidity and high solubility, it penetrates well into the gaps between the resin and the reinforcing fibers, dissolving impurities and promoting the dispersion of the reinforcing fibers. Then, the moisture that has absorbed the impurities leaves the subcritical state and is released to the outside as gas from the vent portion 12 or the gas release port 13b of the gas release nozzle 13. On the other hand, the resin from which the moisture has been removed is released from the resin release port 13c.

[0020] The temperature control (region V) of the gas emission nozzle 13 is in the range of +40° C. to −40° C. relative to the heating cylinder 10, preferably in the range of −20° C. to −30° C., and the optimum temperature should be experimentally determined.

[0021] FIG. 2 is a flow diagram showing a resin plasticizing method using the resin plasticizing apparatus of FIG. This resin plasticization method is carried out while transporting a resin raw material that has been brought to a predetermined moisture-absorbed state inside a heating cylinder that has a vent in the middle and a gas emission nozzle at the tip. Specifically, the process includes step S1 of feeding the resin raw material into a heating cylinder, step S2 of heating and plasticizing the resin raw material, step S3 of further heating and pressurizing the plasticized resin, step S4 of evacuating impurities and the like from an exhaust port in the vent section, step S5 of heating and pressurizing the resin again, step S6 of evacuating moisture in a subcritical or supercritical state from an exhaust port of the gas emission nozzle, and step S7 of discharging the resin from which the moisture has been evacuated through the resin discharge port of the gas emission nozzle. Here, steps S2 to S6 correspond to the processes in the above-mentioned areas I to V, respectively.

[0022] In this resin plasticization method, the resin raw material may contain reinforcing fibers. In that case, in the plasticized resin discharged to the outside, most of the reinforcing fibers are cut into short fibers of 3 mm or less by shearing at the boundary between the screw and the heating cylinder. Such short fibers are very useful for reinforcing the details of the final resin product when it is molded. Furthermore, by performing such resin plasticization and extrusion molding, the resin can be extruded into long string-like shapes called strands, cooled, and cut with a strand cutter to produce high-quality resin pellets containing short fibers.

[0023] 3 is a vertical cross-sectional view showing another example of the basic configuration of a resin plasticizing device according to the present invention. This plasticizing device A constitutes an injection molding device that injects plasticized resin into a mold C. Elements common to the above example are given the same reference numerals and their explanations are omitted.

[0024] Unlike the previous example, this example does not use a bent portion, and therefore the screw 17 does not have a thin shaft diameter in the middle.

[0025] In region VI, in order to plasticize the resin raw material, the temperature of the heating cylinder 10 is controlled so as to gradually increase from 100° C. to 240° C., 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 at a temperature of 240° C., while the screw 17 has a large shaft diameter. When the screw 17 advances to inject the resin in regions VII and VIII, the moisture becomes subcritical.

[0026] FIG. 4 is a flow diagram showing a resin plasticizing method using the resin plasticizing apparatus of FIG. This resin plasticization method is carried out while transporting a resin raw material that has been brought to a predetermined moisture-absorbed state inside a heating cylinder having a gas emission nozzle at the tip. Specifically, the process includes step S8 of feeding the resin raw material into a heating cylinder, step S9 of plasticizing the resin, step S10 of heating and pressurizing the resin, step S11 of evacuating the moisture in a subcritical or supercritical state from the exhaust port of the gas emission nozzle, and step S12 of discharging the resin from the resin outlet of the gas emission nozzle after the moisture has been evacuated. Here, steps S9 to S11 correspond to the processes in areas VI to VIII.

[0027] As described above, in the resin plasticization apparatus and resin plasticization method according to the present invention, the effect of subcritical water makes the final molded product high quality with few impurities and bubbles. In addition, when reinforcing fibers are contained, the sizing agent (mainly epoxy resin) that binds the reinforcing fibers is also removed, improving the bond between the resin and the reinforcing fibers.

[0028] Figure 5 is a phase diagram of water. Water can be in three phases, solid, liquid, and gas, depending on temperature and pressure, but in the temperature and pressure range above the critical point (374°C, 22MPa), it becomes a supercritical state. In the supercritical state, water exhibits both gas and liquid properties, such as gas properties such as elasticity and high permeability (low surface tension), and liquid properties such as high solubility. However, in the case of polypropylene, which is used as an example, water cannot be put into a supercritical state due to the resin properties, so it is used in a subcritical state with lower temperature and pressure. Such a subcritical state is shown as the shaded area X in the figure. Water in this subcritical state is almost liquid, but it exhibits sufficient supercritical properties compared to normal water. Water in the subcritical state becomes a gas state by reducing the pressure in the vent section and gas emission nozzle. Depending on the type of resin, it may be possible to bring the water in the resin into a supercritical state using a similar device, in which case the effects of the present invention will be even more pronounced.

[0029] 6(a) and 6(b) are both cross-sectional views showing the dispersion state of reinforcing fibers in a resin. 6(a) is a cross-sectional view of resin discharged from a conventional plasticizer not equipped with a gas discharge nozzle, in which reinforcing fibers F are localized in multiple locations in the resin M. This is thought to be due to the fact that the reinforcing fibers F are coated with a sizing agent, and that it is difficult for the resin M to penetrate between the reinforcing fibers F. 6(b) is a cross-sectional view of the resin discharged from a plasticizer equipped with a gas discharge nozzle according to the present invention, in which the reinforcing fibers F are dispersed almost uniformly in the resin M. This is believed to be due to the penetration of subcritical water between the reinforcing fibers F, the absorption of the sizing agent by water, and the like, which makes the reinforcing fibers F more easily dispersed.

[0030] Fig. 7 is a graph showing the relationship between the reinforcing fiber content of a resin and the tensile strength. In the graph, the data distribution of a molded product made by a conventional plasticizer and the data distribution of a molded product made by the plasticizer according to the present invention are shown in the shaded areas Y and Z, respectively. In terms of the relationship between the reinforcing fiber content and the tensile strength, it is believed that the tensile strength is basically maximized at a certain reinforcing fiber content, but the molded products made by the plasticizer according to the present invention generally exhibit higher tensile strength than the molded products made by the conventional plasticizer. This is believed to be because the latter has higher dispersion of the reinforcing fibers and the bond between the reinforcing fibers and the resin is stronger due to the removal of the sizing agent, etc. [Explanation of symbols]

[0031] A Resin plasticizing equipment 10 Heating Cylinder 13 Gas discharge nozzle

Claims

1. A method for plasticizing a resin, the method being carried out while transporting a resin raw material that has been brought into a predetermined moisture-absorbed state inside a heating cylinder having a gas emission nozzle at its tip, comprising the steps of: plasticizing the resin raw material; heating and pressurizing the plasticized resin; A step of exhausting the moisture in a subcritical or supercritical state from an exhaust port of the gas ejection nozzle; Discharging the resin from which the moisture has been exhausted through a resin discharge port of the gas discharge nozzle; A resin plasticization method comprising the steps of:

2. In claim 1, The resin plasticization method, wherein the resin raw material contains reinforcing fibers.

3. In claim 2, A method for plasticizing resin, characterized in that in the resin discharged to the outside, most of the reinforcing fibers are cut into short fibers having a length of 3 mm or less.

4. A resin plasticizing apparatus for carrying out the resin plasticizing method according to claim 1, A gas emission nozzle is provided at the tip of the heating cylinder. A resin plasticization apparatus characterized in that the heating cylinder is temperature controlled so that the moisture contained in the resin raw material becomes subcritical or supercritical in at least an area including the gas ejection nozzle and is then exhausted from the gas ejection nozzle.

5. In claim 4, A resin plasticizing apparatus characterized in that the resin raw material is introduced into the heating cylinder in a predetermined moisture absorption state.

6. In claim 4, A resin plasticizing apparatus, wherein the resin raw material contains reinforcing fibers.

7. In claim 4, The resin plasticizing device is characterized in that it constitutes an extrusion molding device.

8. In claim 4, The resin plasticizing device is characterized in that it constitutes an injection molding device.

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