JP2012051268A - Method of manufacturing expandable plastic molding, expandable plastic molding, and injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an expandable plastic molding using a resin raw material to which a foaming agent is added, the expandable plastic molding, and an injection molding machine used for the manufacturing method.SOLUTION: The following processes are performed: a metering standby step in which the resin raw material to which a chemical foaming agent is added is supplied from a raw material supply part 21 of the injection molding machine 1 to the inside of a cylinder 2, the resin raw material pushes open a central part check valve 5 and a tip check valve 6 provided on a screw 3 ahead while melting to move to the tip side of the cylinder 2, a rotary action of the screw 3 finishes after a predetermined amount of the resin raw material melted and kneaded is filled between the tip check valve 6 and a nozzle 22 of the cylinder 2, and further, the resin raw material is pooled between the nozzle 22 and the tip check valve 6 while the tip check valve 6 and the central part check valve 5 are kept in a closed state; and following to the metering standby step, an injection step of injecting the resin raw material pooled between the tip check valve 6 and the nozzle 22 to a cavity 14 of a mold 10A.

Description

  The present invention relates to a method for producing a foamable plastic molded article using a resin raw material to which a chemical foaming agent is added in advance, a foamable plastic molded article produced by the production method, and an injection molding used in the production method. Related to the machine.

  Conventionally, the manufacturing method of the foamable plastic composition using the resin raw material to which the chemical foaming agent was added has already been disclosed (refer patent document 1). The foamable plastic composition disclosed in Patent Document 1 uses a thermoplastic plastic and a chemical foaming agent, and examples of the thermoplastic plastic include polypropylene and polyethylene, and examples of the chemical foaming agent include ammonium carbonate and Examples include inorganic compounds such as sodium bicarbonate, azo compounds, sulfohydrazide compounds, and the like. In the above configuration, a resin raw material to which a chemical foaming agent has been added in advance is introduced into a cylinder of an injection molding machine through a raw material supply unit such as a hopper, and the resin raw material is melt-kneaded in the cylinder and directly into a mold. Since the composition can be injected, there is an advantage that the production process of the foamable plastic composition is simple and the structure of the injection molding machine is not complicated.

  In addition to the above configuration, as foam molding, an inert gas such as carbon dioxide gas or nitrogen gas is dissolved in a molten synthetic resin, and then injected into a mold to form countless bubbles in the resin. Is disclosed (see Patent Document 2). Further, Patent Document 2 discloses an injection molding including a first backflow prevention mechanism between a plasticizing screw and a stirring screw, and a second backflow prevention mechanism between an injection nozzle and a stirring screw. A machine is disclosed. The above configuration can prevent the foaming agent (carbon dioxide) from flowing back by the first backflow prevention mechanism, and can prevent the foaming agent-dissolved resin from flowing back by the second backflow prevention mechanism. There is.

JP-A-8-300391 JP 11-34130 A

  However, although the molded body disclosed in Patent Document 1 has the above-described advantages, it is a molded body (structural foam) having a relatively low foaming ratio, and has a high foaming ratio (for example, 3) because the pressure difference during injection is small. There is a problem that it is difficult to obtain a foamable plastic composition of up to 5 times.

  Further, the configuration of Patent Document 2 requires a separate mechanism for supplying an inert gas to the cylinder filled with the molten resin raw material, which complicates the structure of the injection molding machine and reduces the cost. In addition, there is a problem that replacement of consumable parts (for example, parts related to the backflow prevention mechanism) is troublesome in the injection molding machine, which requires a lot of labor for maintenance.

  Therefore, the present invention is based on the premise that a foamable plastic molded body is obtained by using a resin raw material to which a chemical foaming agent has been added in advance in order to simplify the manufacturing process and the injection molding machine. It is an object of the present invention to provide a production method capable of efficiently and stably producing a foamed plastic molded article having a high expansion ratio by increasing the size, and an injection molding machine used in the production method.

  In the present invention, a screw is provided in a temperature-controllable cylinder so that the screw can be rotated and moved forward and backward by a driving means, a raw material supply unit is disposed at the root end of the cylinder, and an open / close valve is provided at the tip of the cylinder In addition, an injection molding machine in which a tip backflow prevention valve is arranged at the tip of the screw and a center backflow prevention valve is arranged at the center of the screw is used. The foamed plastic molded body is manufactured by the above-described method, wherein the screw is rotated by a driving means in a state where the on-off valve of the nozzle is closed and the screw is set at the foremost position. The added resin raw material is supplied from the raw material supply unit into the cylinder, and the resin raw material is fed to the tip side of the cylinder while being heated and melted and kneaded in the cylinder. While melting, push the central part backflow prevention valve and the front end backflow prevention valve forward to move to the front end side of the cylinder, and fill the front end of the cylinder with the resin material almost completely melted and kneaded At this time, the screw retreats, and after filling a predetermined amount of the melt-kneaded resin raw material between the tip backflow check valve and the nozzle of the cylinder, the rotation operation of the screw is finished. At this time, the backward movement of the screw is stopped, and the tip backflow prevention valve is pushed rearward by the internal pressure between the tip backflow prevention valve and the nozzle, and the tip portion is closed. Due to the internal pressure between the backflow prevention valve and the central backflow prevention valve, the central backflow prevention valve is pushed backward to change from the open state to the closed state. Further, the front end backflow prevention valve and the central backflow prevention valve The cylinder is kept closed A metering standby step for storing the resin raw material between the nozzle and the tip backflow prevention valve; and following the metering standby step, the nozzle on-off valve is opened, and the tip backflow prevention valve and the valve An injection step of injecting the resin raw material stored between the tip backflow prevention valve and the nozzle into the mold cavity while advancing the screw with a driving means while maintaining the central backflow prevention valve in the closed state And a method for producing a foamable plastic molded article.

  In the weighing standby step, when the rotational operation of the screw is finished, the movement of the resin raw material to the cylinder front end side stops, so that the front end backflow prevention valve has an internal pressure between the front end backflow prevention valve and the nozzle. Is pushed backwards to be in a closed state. For this reason, the tip portion backflow prevention valve prevents the resin material existing between the tip portion backflow prevention valve and the nozzle from flowing back toward the root end portion of the cylinder, and the tip portion backflow prevention valve and the nozzle The internal pressure during is not reduced. In addition, the central backflow prevention valve is also pushed rearward by the internal pressure between the front end backflow prevention valve and the central backflow prevention valve to be in a closed state. For this reason, the central backflow prevention valve prevents the resin material existing between the front end portion backflow prevention valve and the central portion backflow prevention valve from flowing back toward the root end portion of the cylinder. The internal pressure between the central backflow prevention valve is not reduced. Therefore, in the present invention, the resin raw material can be compressed and maintained in the cylinder at a high pressure, and the pressure difference when the resin raw material is injected becomes large, resulting in an extremely high expansion ratio. It becomes possible to provide a foamable plastic molding.

  Moreover, it is desirable that the internal pressure between the tip portion backflow prevention valve and the nozzle immediately before the start of the injection process is set to a pressure in the range of 10 to 50 MPa.

  If it is the said structure, the resin raw material will be in a suitable compression state in a cylinder immediately before injection | pouring, and the foaming plastic molding of a high expansion ratio can be obtained stably.

  Further, in the method for producing a foamable plastic molded body, the tip is pushed further forward by a driving means while the on-off valve of the nozzle is closed between the measurement standby step and the injection step. The resin raw material filled between the backflow prevention valve and the nozzle is pressurized, and the internal pressure between the front end portion backflow prevention valve and the nozzle is changed to the front end portion backflow prevention valve and the A pre-pressurizing step for making the pressure higher than the internal pressure between the nozzles may be further added.

  If it is the said structure, since the internal pressure in a cylinder can be reliably raised immediately before injecting a resin raw material, the pressure difference at the time of injection can be enlarged more stably.

  Further, when the resin raw material is injected into the cavity of the mold, the cavity may be enlarged.

  As said structure, there exists a core back type, for example, and the foaming plastic molding of a much higher foaming ratio can be obtained.

  Moreover, this invention is a foamable plastic molding manufactured by the said manufacturing method, Comprising: Foaming magnification is 2.5 times-5 times, It is a foamable plastic molding characterized by the above-mentioned.

  Thus, the foamable plastic molded article obtained by the production method of the present invention becomes a molded article having a higher expansion ratio than a molded article (structural foam) having a low expansion ratio.

  Moreover, in the said foaming plastic molded object, it is desirable that the resin raw material containing 100 mass parts of thermoplastic resins and 0.1-20 mass parts of chemical foaming agents is used, and melting temperature is 230 degrees C or less. .

  By setting it as the said mixture ratio, the foaming plastic molding of a high expansion ratio can be obtained stably.

  Further, the present invention is an injection molding machine used in the above manufacturing method, wherein the screw is based on the length of the portion where the flight is located on the root end side from the central portion backflow prevention valve. The injection molding machine is characterized in that the ratio of the length of the portion where there is a flight between the valve and the tip backflow prevention valve is set to 15 to 50%.

  If it is set as the said structure, a chemical foaming agent can be melt | dissolved in resin and knead | mixed by making a resin raw material fully a molten state between this raw material supply part and this center part backflow prevention valve.

  Moreover, it is desirable that the cross-sectional area of the resin flow path formed in the central part backflow prevention valve is larger than the cross-sectional area of the resin flow path formed in the tip part backflow prevention valve.

  In the above configuration, even if a pellet raw material that is not completely melted on the cylinder root end side than the central backflow prevention valve is mixed in the resin raw material, the resin raw material containing the pellet raw material is smooth. It is possible to pass through the central part check valve.

  Since the present invention can increase the pressure difference during injection, a foamable plastic molded article having a high expansion ratio can be produced even when a resin raw material to which a chemical foaming agent has been added in advance is used. In addition, the present invention can produce an expandable plastic molded article having a higher expansion ratio than the conventional one, and can provide an injection molding machine having a simple structure.

Cross section of injection molding machine a) is an enlarged view of the central part check valve, and b) is an enlarged view of the tip check valve. Explanatory drawing which shows the manufacturing process (core back system) of an expandable plastic molding Explanatory drawing which shows the manufacturing process (non-core back system) of the foamable plastic molding of another form

An injection molding machine according to the present invention will be described with reference to the accompanying drawings.
〔Injection molding machine〕
As shown in FIG. 1 and the like, the injection molding machine 1 includes a cylinder 2. A plurality of heating portions 23 are attached to the outer surface of the cylinder 2 so that the temperature in the cylinder 2 can be controlled. A raw material supply unit 21 having a hopper is provided at the root end of the cylinder 2. Further, a nozzle 22 provided with an on-off valve 22A is formed at the tip of the cylinder 2.

  A screw 3 is provided in the cylinder 2 so as to be rotatable and capable of moving forward and backward. The screw 3 is connected to the first screw part 31 disposed on the root end side, the second screw part 32 connected to the tip of the first screw part 31, and the tip of the second screw part 32. It is comprised with the front-end | tip part 33. FIG. A pointed head 34 is formed at the tip of the tip 33.

  More specifically, a screw hole (not shown) is formed at the tip of the first screw part 31, and a screw (not shown) formed at the root end of the second screw part 32 in the screw hole. The first screw part 31 and the second screw part 32 are connected and fixed by screwing. Further, a position / pressure control means 24 for controlling the front-rear position and pressure of the screw 3 is provided at the root end of the first screw portion 31. The position / pressure control means is constituted by an injection servo motor or the like. Further, the position / pressure control means 24 is provided with a pressure detection unit 4 for detecting a pressure in the direction toward the root end (rear) acting on the screw 3.

Further, a screw rotating means (not shown) constituted by a measuring servo motor or the like is provided at the root end of the first screw portion 31.
The drive means according to the present invention comprises the position / pressure control means and screw rotation means of this embodiment.

  Further, the screw diameter of the first screw portion 31 is the same from the root end to the middle. Further, the portion further from the same diameter portion becomes larger toward the tip, and accordingly, the flight depth gradually decreases toward the tip.

  Furthermore, a central part backflow prevention valve 5 is provided at a connection point between the first screw part 31 and the second screw part 32. The central backflow prevention valve 5 is constituted by a known ring valve, and specifically, a ring portion 51 disposed on the inner periphery of the cylinder 2 so as to be movable back and forth, and a root end of the second screw portion 32. A valve portion 52 that protrudes around the portion and a valve seat 54 that protrudes around the tip of the first screw portion 31 are provided. And if this ring part 51 moves ahead with respect to the valve seat 54 and this center part backflow prevention valve 5 is pushed open toward the front, a resin flow path will be ensured and it will be in an open state. On the other hand, when the ring portion 51 moves rearward and comes into contact with the valve seat 54, the resin flow path is closed and the central portion backflow prevention valve 5 is closed.

As shown in FIG. 2a, in the central part backflow prevention valve 5, the thickness D1 of the ring part 51 is D1 = 2.85 mm, and the axial center outer diameter D2 of the second screw part 32 corresponding to the inside of the ring part 51 is D2 = 19 mm, the inner diameter D3 of the ring portion 51 is set to D3 = 22.3 mm, and the stroke D4 of the ring portion 51 is set to D4 = 6 mm. Further, in the central part check valve 5, the cross-sectional area of the resin flow path 53 (see FIG. 2a) through which the molten resin material passes is set to 107.0 mm ² .

  Further, as shown in FIG. 1, a tip portion backflow prevention valve 6 is provided at a connection portion between the second screw portion 32 and the tip portion 33. The front end backflow prevention valve 6 is also constituted by a known ring valve, and specifically comprises a ring portion 61 disposed on the inner periphery of the cylinder 2 so as to be movable back and forth, and a root end portion of the head 34. And a valve seat 64 protruding around the tip of the second screw portion 32. Then, when the ring portion 61 moves forward and the tip portion backflow prevention valve 6 is pushed forward, the resin flow path is secured and the open state is established, and the ring portion 61 moves rearward and the valve When abutting against the seat 64, the resin flow path is closed, and the tip portion backflow prevention valve 6 is closed. The injection molding machine 1 is also provided with an internal pressure detector (not shown) that detects the internal pressure between the tip 22 backflow check valve 6 at the tip of the cylinder 2 and the nozzle 22. . The internal pressure detector may be configured by attaching a pressure sensor between the tip backflow check valve 6 and the nozzle 22, or based on the pressure detected by the pressure detector 4. It may be configured to be able to grasp the above, or may be configured to employ other means.

As shown in FIG. 2b, in the tip backflow prevention valve 6, the thickness D5 of the ring portion 61 is D5 = 4.35 mm, and the shaft core outer diameter D6 of the tip portion 33 corresponding to the inside of the ring portion 61 is D6 = 16. The inner diameter D7 of the ring portion 61 is set to D7 = 19.3 mm, and the stroke D8 of the ring portion 61 is set to D8 = 5.6 mm. In the tip portion backflow prevention valve 6, the cross-sectional area of the resin flow path 63 (see FIG. 2b) through which the molten resin material passes is set to 83.8 mm ² . In the second screw portion 32, the screw diameter increases toward the tip, and accordingly, the flight depth gradually decreases toward the tip.

  In the above-described configuration, the first core portion 31 and the second screw portion 32 are set such that the shaft outer diameter D2 of the central portion check valve 5 is set larger than the shaft outer diameter D6 of the tip check valve 6. This is to ensure sufficient connection strength at the connection point. In addition, regarding the cross-sectional areas of the resin flow paths 53 and 63 of the front end backflow prevention valve 6 and the central backflow prevention valve 5, the resin flow path 53 of the central backflow prevention valve 5 is more resinous of the front end backflow prevention valve 6. It is set to be larger than the flow path 63. This is because even if a pellet-shaped raw material that is not completely melted in the molten resin on the root end side from the central part backflow prevention valve 5 is mixed in the resin raw material, the resin raw material is not connected to the central part backflow prevention valve 5. This is so that it can pass smoothly.

  Further, as shown in FIG. 1, the length of the flight portion of the first screw portion 31 (only the flight portion) L1 is set to L1 = 364 mm, and the flight portion of the second screw portion 32 Is set to L2 = 154 mm. That is, the L2 length ratio (L2 / L1) based on L1 is set to be in the range of 15 to 50%. The total length Lt of the screw 3 with the flight diameter L3 as a reference is set to Lt / L3 = 20. Moreover, the pitch ratio (pitch interval L4 / flight diameter L3) of the screw 3 is set to 0.75 in order to improve plasticization. The groove depth of the metering zone of the screw 3 (the portion where the groove of the screw 3 is the shallowest) is set to 2 mm for the first screw portion 31 and 2.5 mm for the second screw portion 32. The shear heating capacity of the screw part 31 is set to be higher than that of the second screw part 32.

  Further, as shown in FIG. 1 and the like, a mold 10A is disposed in front of the nozzle 22 of the cylinder 2. The mold 10A is a core back mold, and the cavity 14 can be expanded by retracting the core 12.

Next, the raw material and manufacturing method of the foamable plastic molding according to the present invention will be described.
[Raw material]
As the resin raw material, a material containing a thermoplastic resin and a chemical foaming agent is used.
Examples of the thermoplastic resin include general polypropylene, polyethylene, acrylonitrile-styrene-butadiene block copolymers, polyamides such as polystyrene and nylon, polyvinyl chloride, polycarbonate, acrylic resins, styrene-butadiene block copolymers, and the like. And thermoplastic elastomers, thermoplastic elastomers such as ethylene / propylene rubber (EPM, EPDM), mixtures thereof, and polymer alloys using these. These can be used alone or in combination.
Examples of the chemical foaming agent include azodicarboxylic acid amide, oxybisbenzenesulfonyl hydrazide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, paratoluenesulfonyl hydrazide and the like. Also, polycarboxylic acids such as citric acid, oxalic acid, fumaric acid, phthalic acid, malic acid, tartaric acid, cyclohexane 1,2 dicarboxylic acid, camphoric acid, ethylenediaminetetraacetic acid, triethylenetetramine hexaacetic acid, nitrilolic acid, and hydrogen carbonate Examples thereof include a mixture of inorganic carbonic acid compounds such as sodium, sodium aluminum hydrogencarbonate and potassium hydrogencarbonate, and salts of polycarboxylic acids such as sodium dihydrogen citrate and potassium oxalate.

[Combination ratio]
The mixing ratio of the thermoplastic resin and the chemical foaming agent is, for example, preferably a resin raw material containing 100 parts by weight of a thermoplastic resin and 0.1 to 20 parts by weight of a chemical foaming agent, and further has a melting temperature of 230 ° C. or lower. Things are desirable. In addition, fillers (for example, talc, silica powder, etc.) that can be the starting point / starting point of foaming nuclei can be appropriately added. Further, various additives such as various commonly used pigments, lubricants, antistatic agents and stabilizers may be contained. In addition, if the chemical foaming agent is less than 0.1 part by mass with respect to 100 parts by mass of the thermoplastic resin, a molded body having insufficient foaming is obtained, and if the chemical foaming agent exceeds 20 parts by mass, the molding stability becomes insufficient. .

〔Molding condition〕
For example, the molding conditions of the foamable plastic molding according to the present invention are as follows.
a) Used injection molding machine: Electric injection molding machine manufactured by Meiki Seisakusho Co., Ltd. b) Set temperature of cylinder: 150-220 ° C
c) Mold temperature: 40-80 ° C
d) Screw rotation speed: 80 rpm
e) Cooling time: 360 sec
f) Injection rate: 145 cm ³ / sec

〔Manufacturing process〕
The manufacturing process of the present embodiment has a configuration including a weighing standby process and an injection process. As will be described in detail later, the manufacturing process shown in FIG. 3 has a configuration employing a core back method, and the manufacturing process shown in FIG. 4 has a configuration not using the core back method.

[Weighing standby process]
As shown in FIGS. 3 a and 4 a, the resin raw material (pellet shape) to which the chemical foaming agent has already been added is introduced into the cylinder 2 through the raw material supply unit 21. At the same time, the resin raw material supplied from the raw material supply unit 21 by closing the on-off valve 22A of the nozzle 22 and rotating the screw 3 by the driving means after setting the screw 3 to the foremost position. Are sequentially transferred toward the tip of the cylinder 2 to fill the tip of the cylinder 2 with the resin material. At this time, by the heating by the heating unit 23 and the rotation operation of the screw 3, the resin raw material that was initially in the form of pellets is heated and melted and kneaded in the cylinder 2 to be in a substantially uniform molten state without any bias. Further, in the process of filling the resin material, the resin material moves to the front end side of the cylinder 2 by pushing the center backflow prevention valve 5 and the front end backflow prevention valve 6 forward. Moreover, the screw 3 which was initially in the foremost position is pushed backward by the resin material in a completely melted state, which is sequentially filled in the tip of the cylinder, and sequentially retreats.

  In the section A (see FIGS. 3 and 4) between the raw material supply unit 21 and the central backflow prevention valve 5, the pellet-shaped resin raw material is sufficiently obtained by the heating by the heating unit 23 and the rotation operation of the screw 3. A configuration in which the mixture is kneaded by heating and melting is desirable.

  When a predetermined amount of the melted and kneaded resin raw material is charged and measured between the tip portion backflow check valve 6 and the nozzle 22 of the cylinder 2, the rotational operation of the screw 3 is then terminated, and the resin raw material cylinder Stop moving in the tip direction. At this time, the backward movement of the screw 3 stops. And it waits for a predetermined time in this state.

  When the rotation operation of the screw 3 is stopped, in the B section (see FIGS. 3 and 4) between the tip portion backflow prevention valve 6 and the center portion backflow prevention valve 5, the tip portion backflow prevention valve 6 and the center The central backflow prevention valve 6 is pushed backward by the internal pressure between the partial backflow prevention valve 5 and changes from the open state to the closed state. Therefore, the central backflow prevention valve 5 prevents the resin material existing between the front end portion backflow prevention valve 6 and the central portion backflow prevention valve 5 from flowing back toward the root end portion of the cylinder 2. The internal pressure between the prevention valve 6 and the central backflow prevention valve 5 is not reduced. At the same time, in the section C (see FIGS. 3 and 4) between the tip portion backflow prevention valve 6 and the nozzle 22, the tip is caused by the internal pressure between the tip portion backflow prevention valve 6 and the nozzle 22. The partial backflow prevention valve 6 is pushed rearward to change from the open state to the closed state. Therefore, the tip portion backflow prevention valve 6 prevents the resin material existing between the tip portion backflow prevention valve 6 and the nozzle 22 from flowing back toward the root end portion of the cylinder 2, and the tip portion backflow prevention valve 6. The internal pressure between the nozzle 22 and the nozzle 22 is not reduced.

In this step, the internal pressure between the tip portion backflow prevention valve 6 and the nozzle 22 is set to a pressure in the range of 1 to 50 MPa while being monitored by the pressure detection unit 4. More desirably, the pressure is set in the range of 1 to 30 MPa. If the pressure value is less than or greater than the pressure range, the metering control is not stable.
As a more preferable form, in the state where the screw 3 is rotating in the measurement standby step (during measurement), the internal pressure between the tip backflow prevention valve 6 and the nozzle 22 is in the range of 5 to 30 MPa. Set to the pressure of. If the internal pressure is larger or smaller than this pressure range when the screw 3 is rotating, the measuring operation tends to become unstable. Further, when the internal pressure is larger than this pressure range, the time required for the measuring operation becomes long.
On the other hand, in the state where the rotation operation of the screw 3 is stopped (waiting) in the weighing standby step, the internal pressure between the tip portion backflow prevention valve 6 and the nozzle 22 is a pre-pressurizing step which will be described later. In the case of a configuration that does not include, the pressure is set in the range of 10 to 50 MPa. When the rotational operation of the screw 3 is stopped, if the internal pressure is excessively lower than the pressure range, the screw 3 moves backward from the proper position, and if it is excessive, the energy cost is unnecessarily high. .

[Injection process]
Subsequent to the weighing standby step, the injection step shown in FIG. 3b or 4b is performed. In the injection step, the nozzle 22 is opened, and the screw 3 stopped at the standby position is advanced while the tip portion backflow prevention valve 6 and the center portion backflow prevention valve 5 are kept closed, The resin raw material between the tip portion backflow prevention valve 6 and the nozzle 22 stored in the weighing standby step is injected into the cavity 14 of the mold 10. At this time, since the resin raw material is compressed in the cylinder 2 at a high pressure, the pressure difference during injection becomes extremely large.

A pre-pressurization step may be further added between the weighing standby step and the injection step.
In the preliminary pressurizing step, after the weighing standby step, the screw 3 is pushed further forward by the position / pressure control means 24 while the on-off valve 22A of the nozzle 22 is closed, and the tip backflow prevention valve 6 is pushed. And pressurizing the resin raw material filled between the nozzle 22 and the internal pressure between the tip portion backflow prevention valve 6 and the nozzle 22 and the tip portion backflow prevention valve 6 in the metering standby step. This is a step of making the pressure higher than the internal pressure between the nozzles 22. With such a configuration, the internal pressure of the cylinder 2 can be reliably increased immediately before injecting the resin raw material, so that the pressure difference during injection can be increased more stably. For example, in the configuration including the pre-pressurization step, when the rotational operation of the screw 3 is stopped (waiting) in the weighing standby step, the inside between the tip backflow prevention valve 6 and the nozzle 22 The pressure can be set in the range of 1 to 20 MPa, and the internal pressure can be set in the range of 10 to 50 MPa in the pre-pressurization step. Here, in order to manufacture the foamable plastic molded body 7 having a high foaming ratio with good reproducibility, the internal pressure between the tip portion backflow prevention valve 6 and the nozzle 22 immediately before the start of the injection process is 10 to 50 MPa. It is desirable to be in range. Therefore, in the case of a configuration that does not include the preliminary pressurizing step, it is necessary to set the internal pressure to a pressure in the range of 10 to 50 MPa in the weighing standby step. On the other hand, in the case of the configuration including the pre-pressurization step, the internal pressure is set to a pressure in the range of 1 to 20 MPa in the weighing standby step, and the internal pressure is set to a range of 10 to 50 MPa in the pre-pressurization step. What is necessary is just to set to the pressure of. For this reason, the configuration including the pre-pressurization step does not require the internal pressure to be set to a desired high pressure value in the measurement standby step, and therefore it is possible to suppress the energy cost necessary for maintaining the internal pressure.

  In the injection step, when the resin raw material is injected into the mold 10, as shown in FIG. 3 b, the core 12 may be retracted (core back) to enlarge the cavity 14. Such a core back system is a preferable configuration in that the expansion ratio of the foamable plastic molding 7 to be obtained can be increased. The maximum enlargement width of the cavity is 25 mm, the cavity enlargement speed is 0.25 to 25.0 mm / min, and the core 12 can be retracted at any time in the injection process. The configuration shown in FIG. 4 is a configuration in which the core 12 is not retracted (core back).

Then, as shown in FIG. 3 c or 4 c, after the molded product is cooled, the foamable plastic molded body 7 as a molded product is taken out from the mold 10.
When the foamable plastic molded body 7 of the present invention is continuously manufactured, it is efficient that the foamable plastic molded body 7 is cooled and taken out during the weighing standby process in the next cycle. desirable.

[Foaming plastic molding]
The foamable plastic molded body 7 produced by the above production method has an expansion ratio of 2.5 to 5 times. The expansion ratio is indicated by a value obtained by measuring the specific gravity with a specific gravity meter (manufactured by Mirage Trading Co., Ltd., electronic specific gravity meter EW-200SG) and dividing by the specific gravity of the unfoamed molded product.

  Hereinafter, Examples 1-3 and Comparative Examples 1-7 of a foamable plastic molding are demonstrated concretely.

In order to obtain the foamable plastic molding 7, first, a master batch of filler was prepared. The contents of the blend are as follows.
a) KRATON MD6698
(Manufactured by Kraton Polymers): 80 parts by mass b) Talkan Hayashi (manufactured by Hayashi Kasei Co., Ltd.): 20 parts by mass c) ADK STAB PEP-36 (manufactured by Adeka Co., Ltd.): 0.2 parts by mass d) Total: 100.2 parts by mass However, KRATON MD6698 is a high melt tension hydrogenated styrene / butadiene block copolymer, Talkan Hayashi is talc for foaming nucleating agent (average particle diameter D50... 11.0 μm), and ADK STAB PEP-36 is a phosphite type. It is an antioxidant.

Next, a thermoplastic elastomer (TPE) for foam molding was produced using the master batch.
a) KRATON MD6698
(Manufactured by Kraton Polymers): 85 parts by mass b) talc masterbatch: 15 parts by mass c) Polyslen EV306G (manufactured by Eiwa Kasei Kogyo Co., Ltd.): 6.0 parts by mass d) Polyslen EV405D (manufactured by Eiwa Kasei Kogyo Co., Ltd.): 1. 5 parts by mass e) Talkan Hayashi (manufactured by Hayashi Kasei Co., Ltd.): 0.5 parts by mass f) Total: 108 parts by mass However, the talc masterbatch is the same as the masterbatch of the filler, and the polyslen EV306G is a foaming agent. Master batch, azodicarboxylic acid amide ADCA 20% master batch (base resin: ethylene-vinyl acetate copolymer EVA, decomposition temperature d.p. 150 ° C., generated gas amount GV 66 cm ³ / g), Polyslen EV405D is foamed Agent masterbatch, sodium bicarbonate 20% masterbatch Base resin: ethylene - vinyl acetate copolymer EVA, decomposition temperature D.P.155 ° C., a generated gas amount GV52cm ³ / g), Tarkan Hayashi, talc pellets sticking prevention (average particle diameter D50 ... 11. 0 μm).

  And the following results were obtained by performing the said manufacturing process according to the said manufacturing conditions.

  However, in Table 1, the screw type X is the case where the screw 3 provided with the tip portion backflow prevention valve 6 and the central portion backflow prevention valve 5 according to the present invention is used, and the screw type Y is the tip portion backflow prevention valve. It is a case where the screw provided only with is used. The pressure value (MPa) immediately before the injection process is the internal pressure (MPa) between the tip portion backflow prevention valve 6 and the nozzle 22 immediately before the start of the injection process.

In Table 1, the contents of the molding stability evaluation are as follows.
○: A completely filled product is obtained almost stably.
Δ: An unfilled product of 1 shot is generated every 5 to 10 consecutive shots.
X: One shot of unfilled product occurs every second or third shot.
XX: Product volume differs for each shot.

In Examples 1 to 3, the nozzle 22 having the on-off valve 22A is employed, the on-off valve of the nozzle 22 is closed, the resin material is pressurized, and the pressure value is set within an appropriate range (1 to 30 MPa). In addition, since the screw type was X and the cavity was expanded at the time of injection, a molded article having a high expansion ratio was stably obtained.
In Comparative Example 1, since the nozzle on-off valve was always open, the foaming gas leaked through the nozzle, the expansion effect by the foaming gas was reduced, and the foaming ratio of the resulting molded article was low. In Comparative Example 2, no pressure was applied to the resin raw material, and the foaming gas was not sufficiently dissolved in the resin raw material. Therefore, the pressure difference during injection was small, and the foaming ratio was small. In Comparative Examples 3 to 7, a molded article having a high expansion ratio can be obtained due to the expansion effect of the cavity, but since the screw type is Y, the pressure of the resin raw material cannot be properly maintained, and the molding stability is insufficient. there were.

  Examples 4 to 6 and comparative examples 8 to 14 will be described below.

A general-purpose polystyrene (GPPS) for foam molding was prepared.
a) Polystyrene BX970X (manufactured by Nippon Polystyrene Co., Ltd.): 100 parts by mass b) Vinyl Hall AC # LQ (manufactured by Eiwa Kasei Kogyo Co., Ltd.): 2.4 parts by mass c) Cellbon FE-507 (manufactured by Eiwa Kasei Kogyo Co., Ltd.): 0.8 parts by mass d) Talkan Hayashi (manufactured by Hayashi Kasei Co., Ltd.): 1.0 part by mass e) Total: 104.2 parts by mass However, polystyrene BX970X is a high melt tension hydrogenated general-purpose polystyrene HMS-GPPS, VINYHOLE AC # LQ is a chemical foaming agent (azodicarboxylic acid amide, decomposition temperature d.p. 200 ° C., generated gas amount GV210 cm ³ / g), and Cellbon FE-507 is a chemical foaming agent (sodium bicarbonate, decomposition). temperature D.P.150 ° C., a generated gas amount GV150cm ³ / g), Tarkan Hayashi, foam nucleating agent talc (average particle Child diameter D50... 11.0 μm).

And the following results were obtained by performing the said manufacturing process according to the said manufacturing conditions.

  However, the screw types X and Y in Table 2 are the same as in Table 1. In Table 2, the contents of the molding stability evaluation are the same as in Table 1.

In Examples 4 to 6, the nozzle 22 having the on-off valve 22A is employed, the on-off valve 22A of the nozzle 22 is closed to pressurize the resin material, and the pressurization value (immediately before the start of the injection process) is within an appropriate range (10 Since the screw type was set to X and the cavity was expanded at the time of injection, a molded article having a high expansion ratio was stably obtained.
In Comparative Example 8, since the nozzle was normally open and the foaming gas leaked through the nozzle, the expansion effect by the foaming gas was reduced, and the foaming ratio of the obtained molded article was low. In Comparative Example 9, no pressure was applied to the resin raw material, and the foaming gas was not sufficiently dissolved in the resin. Therefore, the pressure difference at the time of injection was reduced and the expansion ratio was reduced. In Comparative Examples 10 to 14, although a molded article having a high expansion ratio can be obtained due to the expansion effect of the cavity, since the screw type is Y, the pressure of the resin raw material cannot be properly maintained, and the molding stability is insufficient. there were.

  When a manufacturing method (see FIG. 4) in which the cavity 14 of the mold 10B is not expanded at the time of injection is employed, the foamable plastic molded body 7 shown below was obtained.

  However, the screw types X and Y in Table 3 are the same as those in Tables 1 and 2. In Table 3, the contents of the molding stability evaluation are the same as those in Tables 1 and 2.

  The seventh embodiment has a configuration in which the cavity is not expanded at the time of injection, and the other conditions are the same as those of the first embodiment.

  In Example 8, the cavity is not expanded at the time of injection, and the other conditions are the same as in Example 4.

  In Examples 7 and 8, the on-off valve 22A of the nozzle 22 is closed to pressurize the resin material, and the pressurization value (immediately before the start of the injection process) is set within an appropriate range (10 to 50 MPa). Since X was X, a molded article having a high expansion ratio was stably obtained.

The present invention is not limited to the above-described embodiments, and can be appropriately modified within the scope of the gist of the present invention.
For example, the driving means of the injection molding machine 1 can be easily configured by a driving device such as a known hydraulic cylinder, electric cylinder, air cylinder, servo motor or the like.

DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Cylinder 3 Screw 5 Center part backflow prevention valve 6 Tip part backflow prevention valve 7 Foaming plastic molding 10A, 10B Mold 14 Cavity 21 Raw material supply part 22A On-off valve 22 Nozzle

Claims (8)

A screw is installed in a temperature-controllable cylinder so that it can be rotated and moved forward and backward by drive means. A raw material supply unit is arranged at the root end of the cylinder, and an opening / closing valve is arranged at the tip of the cylinder. In addition, a foamable plastic using an injection molding machine in which a tip backflow prevention valve is disposed at the tip of the screw and a center backflow prevention valve is disposed at the center of the screw. A method for producing a molded body, comprising:
With the on-off valve of the nozzle closed and the screw set to the foremost position, the screw is rotated by a driving means, and a resin raw material to which a chemical foaming agent is added is supplied from the raw material supply unit. The resin raw material is fed into the cylinder and heated to the front end side of the cylinder while being melted and kneaded in the cylinder. At this time, the resin raw material is melted while the central part backflow prevention valve and the front end part backflow prevention valve are Pushed forward and moved to the tip side of the cylinder, and the resin raw material was almost completely melted and kneaded to fill the tip of the cylinder. At this time, the screw was retracted and melted and kneaded. After filling a predetermined amount of the resin raw material between the tip portion backflow prevention valve and the nozzle of the cylinder, the rotation operation of the screw is terminated, and at this time, the backward movement of the screw stops, and the tip portion backflow prevention valve And the The tip backflow check valve is pushed rearward by an internal pressure between the tip and the closed state, and the center pressure between the tip backflow check valve and the center backflow check valve The backflow prevention valve is pushed backward to change from the open state to the closed state, and further, the tip of the backflow prevention valve and the central portion of the backflow prevention valve are kept closed, A weighing standby step of storing the resin raw material between,
Following the metering standby step, with the nozzle open / close valve opened, and with the tip backflow prevention valve and the center backflow prevention valve kept closed, the screw is advanced by the drive means, An injection step of injecting a resin raw material stored between the tip backflow prevention valve and the nozzle into a cavity of a mold;
A method for producing a foamable plastic molded article comprising:   2. The method for producing a foamable plastic molded body according to claim 1, wherein an internal pressure between the tip portion backflow prevention valve and the nozzle immediately before the start of the injection process is set to a pressure in a range of 10 to 50 MPa. In the manufacturing method of the foamable plastic molding of Claim 1 or Claim 2,
Between the weighing standby process and the injection process,
With the nozzle on-off valve closed, the screw is pushed further forward by driving means to pressurize the resin material filled between the tip backflow check valve and the nozzle, and the tip backflow check valve A method for producing a foamable plastic molded body, further comprising a pre-pressurizing step for making the internal pressure between the nozzle and the nozzle higher than the internal pressure between the tip backflow check valve and the nozzle in the weighing standby step .   The method for producing a foamable plastic molded body according to any one of claims 1 to 3, wherein the cavity is enlarged when a resin raw material is injected into the cavity of the mold. A foamable plastic molded article produced by the production method according to any one of claims 1 to 4,
A foamable plastic molded article having an expansion ratio of 2.5 to 5 times.   The foamable plastic molded article according to claim 5, wherein a resin raw material containing 100 parts by mass of a thermoplastic resin and 0.1 to 20 parts by mass of a chemical foaming agent is used, and a melting temperature is 230 ° C or lower. An injection molding machine used in the method for producing a foamable plastic molded body according to any one of claims 1 to 4,
The screw is
The ratio of the length of the part with the flight between the central part backflow prevention valve and the tip part backflow prevention valve based on the length of the part with the flight at the root end side from the central part backflow prevention valve is 15 to 15 An injection molding machine characterized by being set to 50%.   8. The injection molding machine according to claim 7, wherein a cross-sectional area of the resin flow path formed in the central portion check valve is set to be larger than a cross-sectional area of the resin flow path formed in the tip check valve.