JP2021024240A - Foam molded body production device - Google Patents

Abstract

To provide a production device capable of realizing good foam molding in which fine cells are formed inside a molded body without reduction in a forming capability in the molded body, even if a size of the device that performs foam molding by compressing a molten resin with a physical foaming agent at a constantly fixed pressure in a starved zone is increased.SOLUTION: There is provided a production device (1, 500) that comprises: a starved zone (16, 516) in a molten resin-starved state; a cylinder (10, 510) in which an inlet of a physical foaming agent for the starved zone is provided; and a screw (20, 520) having a screw outer diameter of φ50 mm or more, which is installed inside the cylinder, in which the screw has a multi-row flight structure in the starved zone, and in the multi-row flight structure of the screw, a volume per axis circumference between adjacent screw flights is 5 cm3 or more and 100 cm3 or less.SELECTED DRAWING: Figure 10

Description

The present invention relates to an apparatus for producing a foam molded product.

As a method of foam injection molding using nitrogen or carbon dioxide as a physical foaming agent, there is a method of shearing and kneading a high-pressure fluid which is a supercritical fluid with a molten resin to dissolve it. On the other hand, Patent Document 1 discloses a method of molding a foam molded product using nitrogen, carbon dioxide, or the like having a relatively low pressure without requiring a supercritical fluid. According to this method, fine foam cells can be formed in a molded product by a simple process using a low-pressure physical foaming agent without using a special high-pressure device.

FIG. 12 is a reference schematic configuration diagram showing an example of a molding machine that performs foam molding using a relatively low-pressure physical foaming agent. In the molding machine 100, the resin pellets supplied from the hopper 130 are given residual heat in the feed zone 112, and are melt-compressed through the compression zone 113 and the measurement zone 114. Then, the amount of the molten resin supplied downstream is limited in the seal zone 115, and the density of the molten resin is reduced in the starvation zone 116. In the starvation zone 116, the relatively low-pressure physical foaming agent introduced through the introduction port 102 stays in contact with the low-density molten resin and permeates (dissolves) inside the molten resin. .. The molten resin infiltrated with the physical foaming agent passes through the recompression zone 117 and the reweighing zone 118 and is re-kneaded so that the dissolved amount of the physical foaming agent becomes stable. The recompressed molten resin moves to the front of the screw 120 via the check ring 119. At this time, the internal pressure of the molten resin is controlled as the back pressure of the screw.

Japanese Patent No. 6139038

By the way, in the molding machine 100 shown in FIG. 12, the screw 120 is a single flight in the starvation zone 116. When the molding machine 100 is made larger in order to be able to mold relatively large parts such as automobile parts, that is, when the outer diameter (screw diameter) of the screw 120 is made larger, the depth of the screw flight 121 is As the diameter becomes deeper, the absolute amount of molten resin deposited between each screw flight 121 in the screw 120 increases. In this case, since the rate of increase in the surface area of the molten resin is small with respect to the rate of increase in the volume of the molten resin, the contact area between the physical foaming agent and the molten resin with respect to the molten resin per unit volume decreases. As a result, the permeation time of the physical foaming agent into the molten resin is insufficient, and there is a possibility that the physical foaming agent may not sufficiently permeate. Such a problem becomes a factor that lowers the foaming performance of the molded product. If the above problem is to be avoided by reducing the amount of molten resin supplied to the starvation zone 116 and reducing the amount of molten resin staying between the screw flights 121, the cylinder 110 in the starvation zone 116 Due to the decrease in the frictional resistance between the resin and the molten resin, there arises a problem that the moving speed of the molten resin in the starvation zone 116 decreases and the plasticization time becomes long. This is not preferable because it causes problems such as a long molding cycle time and difficulty in changing the resin.

Here, with reference to FIG. 13, the maximum amount of molten resin that moves with one rotation of the screw 120 will be described. In the measuring zone 114, the maximum amount of resin that moves downstream with one rotation of the screw 120 is the volume A per axial circumference between adjacent screw flights 121. Further, in the starvation zone 116, the maximum amount of resin that moves to the downstream side as the screw 120 makes one rotation is the volume B per axial circumference between the adjacent screw flights 121. At this time, if the difference between the volume A and the volume B is increased, that is, if the volume B is increased with respect to the volume A, the starvation zone 116 is likely to be in a starvation state. The “starvation state” means a state in which the molten resin is not filled in the starvation zone 116 and is not filled, or a state in which the density of the molten resin is reduced. However, if the difference between the volume A and the volume B becomes too large, the amount of molten resin staying there is significantly reduced with respect to the volume of the starvation zone 116, and the amount of the physical foaming agent staying in the starvation zone 116 increases. It ends up. In this case, a large amount of undissolved physical foaming agent (surplus gas) is involved in the recompression zone 117 (see FIG. 12), so that bubbles (large-diameter voids) are generated in the molded product, and the molded product is formed. There was a risk that the foaming performance of the product would deteriorate. Such a problem may occur even when the molding machine 100 is a molding machine that performs extrusion molding.

The present invention has been made in view of the above circumstances, and even when the manufacturing apparatus for molding by constantly pressing the molten resin with a physical foaming agent at a constant pressure in the starvation zone is made larger, that is, the screw. It is an object of the present invention to provide a manufacturing apparatus capable of realizing good molding in which fine cells are formed inside a molded body even when the diameter is made larger, and the foaming performance of the molded body is not deteriorated.

In order to solve the above problems, the foam molding manufacturing apparatus of the present invention has a plasticized zone in which the thermoplastic resin is plasticized and melted to become a molten resin, and a starvation zone in which the molten resin is starved. Then, a cylinder provided with an introduction port for the physical foaming agent into the starvation zone, a screw having a screw outer diameter of φ50 mm or more arranged inside the cylinder, and the physical foaming agent having a constant pressure are used. It is provided with a pressure adjusting container that is introduced into the starvation zone through an inlet and keeps the starvation zone at the constant pressure at all times, and the screw has a multi-row flight structure in the starvation zone, and the screw of the screw. In the multi-row flight structure, the volume per axis circumference between adjacent screw flights is 5 cm ³ or more and 100 cm ³ or less.

According to such a configuration, when the extrusion manufacturing apparatus for molding by constantly pressing the molten resin with a physical foaming agent at a constant pressure in the starvation zone is made larger, that is, when the screw diameter is made larger. However, since the flight structure in the starvation zone is a multi-row flight structure, the same amount of molten resin as in the case of single flight is divided into multiple parts and transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited therein can be reduced. Therefore, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed, and the permeation time of the physical foaming agent into the molten resin is secured. As a result, good foam molding in which fine cells are formed inside the foam molded product can be realized, and deterioration of the foaming performance of the foam molded product can be suppressed. In other words, in an extrusion manufacturing device that pressurizes the starvation zone with a relatively low pressure physical foaming agent, the flight structure in the starvation zone is multi-row flight even if the device is made larger, that is, the screw diameter is made larger. Due to the structure, the same amount of molten resin as in the case of single flight is divided into a plurality of pieces and transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited therein can be reduced. Therefore, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed, and the permeation time of the physical foaming agent into the molten resin is secured. As a result, good foam molding without deteriorating the foaming performance of the molded product can be realized, and fine foam cells can be stably formed inside the molded product. Further, since the volume of the axis per one rotation between screw flights adjacent in starvation zone is in the 5 cm ³ 100 cm ^3, in hunger zones, while maintaining the starved, capable to supply molten resin to the downstream While being maintained, a decrease in the penetration efficiency of the physical foaming agent due to an excessive amount of resin deposited between adjacent screw flights is suppressed. As a result, it is possible to more reliably suppress the enlargement of the foam cell size and the occurrence of foam breakage in the molded product, and it is possible to obtain a molded product in a good foamed state.

According to the present invention, even when the manufacturing apparatus for molding by constantly pressurizing the molten resin with a physical foaming agent at a constant pressure in the starvation zone is made larger, that is, when the screw diameter is made larger, foam molding is performed. It is possible to realize good foam molding in which fine cells are formed inside the body, and it is possible to suppress deterioration of the foaming performance of the foam molded product.

It is a schematic block diagram which shows the manufacturing apparatus of the foam compact which concerns on 1st Embodiment of this invention. It is a flowchart which shows the manufacturing method of the foam compact. It is the schematic which shows the whole screw. The same shows a part of the screw, and is a schematic diagram for explaining the dimensions of the screw. It shows a part of a screw, and is the schematic diagram for demonstrating the volume per one circumference around an axis between adjacent screw flights. It is a schematic diagram which shows a part of the two-row flight structure part of the screw used in the manufacturing apparatus of the foam molded article which concerns on 1st Embodiment of this invention. It is a schematic block diagram which shows the modification of the manufacturing apparatus of the foam compact which concerns on 1st Embodiment of this invention. It is the schematic which shows a part of the 3rd flight structure part of the screw. It is a figure which shows the condition and result of the evaluation performed using the manufacturing apparatus of the foam molded article which concerns on 1st Embodiment of this invention. It is a schematic block diagram which shows the manufacturing apparatus of the foamed molded article which concerns on 2nd Embodiment of this invention. It is the schematic which shows the whole screw. It shows a molding machine, and is a reference schematic block diagram for explaining a problem. It is the schematic which shows a part of the screw.

(First Embodiment)
Hereinafter, the first embodiment of the present invention will be described with reference to the drawings.
In the present embodiment, the foam molded product is manufactured using the manufacturing apparatus 1 shown in FIG. The manufacturing apparatus 1 is an injection molding apparatus (injection manufacturing apparatus). The manufacturing apparatus 1 mainly includes a plasticized cylinder (cylinder) 10, a plasticized screw (cylinder) 20 which is arranged inside the cylinder 10 so as to be rotatable around an axis and movable back and forth in an axial direction, and a physical foaming agent. A cylinder (physical foaming agent supply mechanism) 50 for supplying the cylinder 10 to the cylinder 10, a mold clamping unit provided with a mold (not shown), and a control device for operating the cylinder 10 and the mold clamping unit (not shown). It has a cylinder.
In the cylinder 10, the plasticized and melted molten resin flows from the right hand to the left hand in FIG. Hereinafter, inside the cylinder 10, the right hand in FIG. 1 is referred to as “upstream” or “rear”, and the left hand in FIG. 1 is referred to as “downstream” or “forward”.

In the manufacturing apparatus 1, the rotation of the screw 20 in the cylinder 10 plasticizes and melts the resin pellets, and the molten resin is sent to the front side in the cylinder 10. Further, the molten resin is sent to the front side in the cylinder 10, and the screw 20 moves to the rear to measure the molten resin. Further, the screw 20 is designed to move forward at the time of injection.

The cylinder 10 has a plasticization zone 40 provided on the upstream side and a hunger zone 16 provided on the downstream side. The plasticization zone 40 is a zone in which the thermoplastic resin is plasticized and melted to become a molten resin. The starvation zone 16 is a zone in which the molten resin is starved. The "starvation state" means a state in which the molten resin is not filled in the starvation zone 16 and is not filled, or a state in which the density of the molten resin is reduced. Therefore, in the starvation zone 16, a space other than the portion occupied by the molten resin may exist.

The cylinder 10 includes a feed zone 12, a compression zone 13, a weighing zone 14, a seal zone 15, a starvation zone 16, a recompression zone 17, and a reweighing zone 18 in this order from the upstream side to the downstream side. have. The feed zone 12, the compression zone 13, and the weighing zone 14 form a plasticizing zone 40. The feed zone 12 is a zone in which residual heat is given to the pellets of the thermoplastic resin. The compression zone 13 is a zone in which the thermoplastic resin is sheared and kneaded to be plasticized and melted, and the molten resin is compressed. The measuring zone 14 is a zone in which the density of the compressed molten resin is kept constant. The seal zone 15 is a zone in which the supply amount of the molten resin to the downstream is limited. The recompression zone 17 is a zone in which the molten resin is recompressed. The reweighing zone 18 is a zone in which the molten resin is weighed.
Although not shown, a zone for adjusting the moving speed of the molten resin and a zone provided with a flight structure for kneading the molten resin may be further provided between the seal zone 15 and the starvation zone 16. ..

The cylinder 10 is provided with an introduction port 2 as an opening for introducing a physical foaming agent into the starvation zone 16. A pressure adjusting container 5, which will be described later, is connected to the introduction port 2. A cylinder 50 is connected to the pressure adjusting container 5 by a pipe 54 via a pressure reducing valve 51 and a pressure gauge 52. The cylinder 50 supplies the physical foaming agent into the cylinder 10 via the pressure adjusting container 5.

The method for producing the foamed molded product of the present embodiment will be described with reference to the flowchart shown in FIG.
(1) The thermoplastic resin is plasticized and melted.
First, in the plasticization zone 40 of the cylinder 10, the thermoplastic resin is plasticized and melted to obtain a molten resin (step S1 in FIG. 2). As the thermoplastic resin, various resins can be used depending on the target heat resistance and the intended use of the molded product. Specifically, for example, polypropylene, polymethylmethacrylate, polyamide, polyethylene, polycarbonate, polybutylene terephthalate, amorphous polyolefin, polyetherimide, polyethylene terephthalate, polyetheretherketone, ABS resin (acrylonitrile / butadiene / styrene copolymer resin). , Polyphenylensulfide, polyamideimide, polylactic acid, thermoplastic resins such as polycaprolactone, and composite materials thereof can be used. In particular, crystalline resin is desirable because it easily forms fine cells. These thermoplastic resins may be used alone or in combination of two or more. Further, those obtained by kneading these thermoplastic resins with various inorganic fillers such as glass fiber, talc, carbon fiber and ceramic, and organic fillers such as cellulose nanofibers, cellulose and wood flour can also be used. It is preferable to mix the thermoplastic resin with an inorganic filler that functions as a foam nucleating agent, an organic filler, and an additive that increases the melt tension. By mixing these, the foam cell can be made finer. Further, the thermoplastic resin may contain various other general-purpose additives, if necessary.

The thermoplastic resin is plasticized and melted in the cylinder 10 in which the screw 20 is installed. A band heater (not shown) is provided on the outer wall surface of the cylinder 10, whereby the cylinder 10 is heated, shearing heat is added due to the rotation of the screw 20, and the thermoplastic resin is plasticized and melted. It has become.

(2) Maintain pressure in the hunger zone.
Next, a constant pressure physical foaming agent is supplied to the pressure adjusting container 5, a pressurized fluid having a constant pressure is introduced from the pressure adjusting container 5 into the starvation zone 16, and the starvation zone 16 is held at the constant pressure (FIG. Step S2 of 2.

A pressurized fluid is used as the physical foaming agent. In the present embodiment, the "fluid" means any of a liquid, a gas, and a supercritical fluid. Further, the physical foaming agent is preferably carbon dioxide, nitrogen or the like from the viewpoint of cost and environmental load. Since the pressure of the physical foaming agent of the present embodiment is relatively low, for example, a cylinder 50 in which a fluid such as a nitrogen cylinder, a carbon dioxide cylinder, or an air cylinder is stored is depressurized to a constant pressure by a pressure reducing valve 51. The extracted fluid can be used. In this case, since the booster is not required, the cost of the entire manufacturing apparatus can be reduced. If necessary, a fluid pressurized to a predetermined pressure may be used as the physical foaming agent. For example, when nitrogen is used as the physical foaming agent, the physical foaming agent can be produced by the following method. First, nitrogen is purified through a nitrogen separation membrane while compressing the air in the atmosphere with a compressor. Next, the purified nitrogen is boosted to a predetermined pressure using a booster pump, a syringe pump, or the like to generate a physical foaming agent.

The pressure of the physical foaming agent introduced into the starvation zone 16 is constant, and the pressure of the starvation zone 16 is maintained at the same constant pressure as the introduced physical foaming agent. The pressure of this physical foaming agent is preferably 0.5 MPa to 12 MPa, more preferably 1 MPa to 10 MPa, and even more preferably 1 MPa to 8 MPa. The optimum pressure differs depending on the type of molten resin, but by setting the pressure of the physical foaming agent to 1 MPa or more, the amount of physical foaming agent required for foaming can be permeated into the molten resin, and it is 12 MPa or less. By doing so, the heat resistance of the foamed molded product can be improved. When manufactured at a pressure (high pressure) higher than 12 MPa, the foam cell itself of the foamed molded product is in a high pressure state, and when the foamed molded product is heated to a high temperature, a phenomenon of post-swelling occurs, so that the heat resistance of the foamed molded product is lowered. To do. On the other hand, when foaming is performed at a pressure (low pressure) of 12 MPa or less, the occurrence of such a phenomenon is suppressed and the heat resistance of the foamed molded product is improved.
The pressure of the physical foaming agent that pressurizes the molten resin is "constant", which means that the fluctuation range of the pressure with respect to the predetermined pressure is preferably within ± 20%, more preferably within ± 10%. .. The pressure in the starvation zone 16 is measured, for example, by a pressure sensor (not shown) provided at a position facing the introduction port 2 of the cylinder 10.

The physical foaming agent is supplied from the cylinder 50 to the starvation zone 16 via the pressure adjusting container 5 and the introduction port 2. The physical foaming agent is depressurized to a predetermined pressure using the pressure reducing valve 51, and then introduced into the starvation zone 16 from the introduction port 2 without passing through a booster or the like. In the present embodiment, the introduction amount, introduction time, etc. of the physical foaming agent to be introduced into the cylinder 10 are not controlled. Therefore, a mechanism for controlling them, for example, a drive valve using a check valve or a solenoid valve, is unnecessary, and the introduction port 2 does not have a drive valve and is always open. In the present embodiment, the physical foaming agent supplied from the cylinder 50 is maintained at a constant pressure of the physical foaming agent from the pressure reducing valve 51 through the pressure adjusting container 5 to the starvation zone 16 in the cylinder 10.

Further, the introduction port 2 of the physical foaming agent has a larger inner diameter than the introduction port of the physical foaming agent of the conventional manufacturing apparatus. Therefore, even a relatively low-pressure physical foaming agent is efficiently introduced into the cylinder 10. Further, even when a part of the molten resin comes into contact with the introduction port 2 and solidifies, the inner diameter is large, so that the molten resin functions as an introduction port without being completely blocked. For example, when the inner diameter of the cylinder 10 is large, that is, when the outer diameter of the cylinder 10 is large, it is easy to increase the inner diameter of the introduction port 2. On the other hand, if the inner diameter of the introduction port 2 is too large, the molten resin stays and causes molding defects, and the pressure adjusting container 5 connected to the introduction port 2 becomes large, which increases the cost of the entire device. It ends up. Specifically, the inner diameter of the introduction port 2 is preferably 20% to 100%, more preferably 30% to 80% of the inner diameter of the cylinder 10. Alternatively, the inner diameter of the introduction port 2 does not depend on the inner diameter of the cylinder 10, and is preferably 3 mm to 150 mm, more preferably 5 mm to 100 mm. When the introduction port 2 is an elongated hole or an elliptical hole, these inner diameters indicate the diameter on the minor axis side.

Next, the pressure adjusting container 5 (introducing speed adjusting container) connected to the introduction port 2 will be described. The pressure adjusting container 5 has a function of keeping the pressure of the physical foaming agent and the pressure of the starvation zone 16 in the cylinder 10 at the same constant pressure and holding the starvation zone 16 at the constant pressure. For example, when a large amount of the physical foaming agent is consumed in the starvation zone 16, the physical foaming agent may not be supplied in time and the pressure in the starvation zone 16 may suddenly decrease, but the pressure adjusting container 5 stabilizes the physical foaming agent. The pressure fluctuation in the hunger zone 16 can be suppressed. Further, the pressure adjusting container 5 is formed so as to have a certain volume or more, the flow velocity of the physical foaming agent introduced into the cylinder 10 is moderated, and the time for the physical foaming agent to stay in the pressure adjusting container 5 is secured. ing. The pressure adjusting container 5 is directly connected to a cylinder 10 heated by a band heater (not shown) arranged around the cylinder 10, and the heat of the cylinder 10 is also conducted to the pressure adjusting container 5. As a result, the physical foaming agent inside the pressure adjusting container 5 is heated, the temperature difference between the physical foaming agent and the molten resin is reduced, and the temperature of the molten resin in contact with the physical foaming agent is suppressed from being extremely lowered. , The amount of the physical foaming agent dissolved in the molten resin (permeation amount) is stable. That is, the pressure adjusting container 5 functions as a buffer container having a heating function of the physical foaming agent. On the other hand, if the volume of the pressure adjusting container 5 is too large, the cost of the entire device increases. The volume of the pressure adjusting container 5 depends on the amount of the molten resin present in the starvation zone 16, but is preferably 5 mL to 20 L, more preferably 10 mL to 2 L, and even more preferably 10 mL to 1 L. By setting the volume of the pressure adjusting container 5 within this range, it is possible to secure a time for the physical foaming agent to stay while considering the cost. Further, the pressure adjusting container 5 is connected to the introduction port 2 and is provided adjacent to the tubular first straight portion 5a having a constant inner diameter thereof and the first straight portion 5a, and is separated from the introduction port 2. Therefore, it has a tapered portion 5b whose inner diameter is increased, and a tubular second straight portion 5c which is provided adjacent to the tapered portion 5b and whose inner diameter is constant. In the pressure adjusting container 5, the first straight portion 5a having a small inner diameter and the second straight portion 5c having a large inner diameter are provided so that their central axes are on the same straight line, and the first straight portion 5a and the second straight portion 5a are provided. The straight portion 5c is connected to the tapered portion 5b. The maximum value of the inner diameter of the pressure adjusting container 5 (that is, the inner diameter of the second straight portion 5c) is larger than the inner diameter of the introduction port 2. Therefore, even when the molten resin invades the inside of the pressure adjusting container 5, it is easy to secure a flow path for the physical foaming agent. That is, it is possible to prevent the introduction path of the physical foaming agent from being blocked by the solidified molten resin. Further, a larger amount of the physical foaming agent tends to stay in the lower part of the pressure adjusting container 5. Since the heat from the cylinder 10 is transferred to the lower part of the pressure adjusting container 5, a larger amount of the physical foaming agent can be efficiently heated. As a result, the amount of the physical foaming agent dissolved in the molten resin (permeation amount) becomes more stable.

Further, the physical foaming agent comes into contact with the molten resin and permeates, so that it is consumed in the cylinder 10. In order to keep the pressure in the starvation zone 16 constant, the consumed physical foaming agent is introduced from the pressure adjusting container 5 into the starvation zone 16. If the volume of the pressure adjusting container 5 is too small, the replacement frequency of the physical foaming agent becomes high, so that the temperature of the physical foaming agent becomes unstable, and as a result, the supply of the physical foaming agent may become unstable. Therefore, it is preferable that the pressure adjusting container 5 has a volume in which the amount of the physical foaming agent consumed in the plasticizing cylinder can be retained in 1 to 10 minutes. Further, for example, the volume of the pressure adjusting container 5 is preferably 0.1 to 5 times, more preferably 0.5 to 2 times the volume of the starvation zone 16 to which the pressure adjusting container 5 is connected. In the present embodiment, the volume of the starvation zone 16 is a portion (deep groove portion 20D described later) in which the diameter of the shaft of the screw 20 and the depth of the screw flight are constant in the empty cylinder 10 containing no molten resin. ) Is the volume of the area where it is located. The pressure adjusting container 5 may be a container separate from the cylinder 10 or may be formed integrally with the cylinder 10 to form a part of the cylinder 10.

(3) The molten resin is starved.
Next, the molten resin is allowed to flow into the starvation zone 16 to starve the molten resin in the starvation zone 16 (step S3 in FIG. 2). In the present embodiment, the molten resin is starved in the starvation zone 16 by providing the compression zone 13 in which the molten resin is compressed and the pressure is increased upstream of the starvation zone 16. The starvation state is determined by the balance between the feed amount of the molten resin from the upstream of the starvation zone 16 to the starvation zone 16 and the feed amount of the molten resin from the starvation zone 16 to the downstream thereof. The hunger zone 16 becomes hungry when the former is less.

The screw 20 is a screw used in the manufacturing apparatus 1 in which a low-density resin in a plasticized and melted state is constantly pressurized with a physical foaming agent at a constant pressure in a starvation zone 16. As shown in FIG. 3, the screw 20 includes a first transition portion (first groove depth transition portion) 20A located on the upstream side, a first shallow groove portion 20B adjacent to the downstream side of the first transition portion 20A, and the like. A seal portion 20C adjacent to the downstream side of the first shallow groove portion 20B, a deep groove portion 20D adjacent to the downstream side of the seal portion 20C, and a second transition portion (second groove depth transition) adjacent to the downstream side of the deep groove portion 20D. Part) 20E and a second shallow groove part 20F adjacent to the downstream side of the second transition part 20E. The first transition unit 20A is located in the compression zone 13. The first shallow groove portion 20B is located in the measuring zone 14. The seal portion 20C is located in the seal zone 15. The deep groove portion 20D is located in the starvation zone 16. The second transition unit 20E is located in the recompression zone 17. The second shallow groove portion 20F is located in the reweighing zone 18.

Here, as shown in FIG. 4, in the screw 20, the screw diameter is D, the screw shaft diameter is d (the diameter of the groove in the screw 20), the screw flight depth (flight depth) is h, and the screw pitch. (Interval between adjacent screw flights) Let P. The flight depth h is represented by h = (Dd) / 2. Note that D can be referred to as the screw outer diameter, and d can also be referred to as the screw inner diameter. In the present embodiment, the screw outer diameter is φ50 mm or more.

A description will be given by returning to FIG. The portion of the screw 20 corresponding to the plasticization zone 40, the recompression zone 17 and the reweighing zone 18 has a single flight structure, that is, a structure in which one screw flight 7 is formed on the outer peripheral surface of the screw 20.
The first transition portion 20A is formed so that the diameter d of the screw shaft gradually increases and the flight depth h gradually decreases from the upstream side to the downstream side. In the first transition portion 20A, the diameter d of the screw shaft is larger and the flight depth h is smaller than the portion located in the feed zone 12 on the upstream side. It can also be said that the first transition portion 20A is formed so that the groove between the adjacent screw flights 7 gradually becomes shallower from the upstream side to the downstream side. Since the second transition unit 20E is substantially the same as the first transition unit 20A, a duplicate description will be omitted.

The first shallow groove portion 20B has substantially the same diameter d and flight depth h of the screw shaft as the large diameter portion (the most downstream portion of the first transition portion 20A) in the first transition portion 20A. It can also be said that the first shallow groove portion 20B is formed so that the groove between the adjacent screw flights 7 becomes shallow. Since the second shallow groove portion 20F is substantially the same as the first shallow groove portion 20B, overlapping description will be omitted.

No screw flight is formed in the portion of the screw 20 corresponding to the seal zone 15. The seal portion 20C has substantially the same diameter d of the screw shaft as the first shallow groove portion 20B, and a plurality of shallow grooves are formed on the screw shaft instead of the screw flight. The diameter of the screw shaft of the first shallow groove portion 20B and the seal portion 20C is large, and the clearance between the inner wall of the cylinder 10 and the screw 20 is reduced, so that the amount of resin sent downstream is reduced. As a result, the flow resistance of the molten resin increases. In the present embodiment, the first shallow groove portion 20B and the seal portion 20C are mechanisms for increasing the flow resistance of the molten resin. The seal portion 20C also has an effect of suppressing the backflow of the physical foaming agent, that is, the movement of the physical foaming agent from the downstream side to the upstream side of the seal portion 20C. The seal portion 20C may have a structure in which a ring (provided with a plurality of grooves) of a member different from the screw 20 is provided instead of the screw flight.

When the diameter d of the shaft of the screw 20 is increased or when a ring of a member different from the screw 20 is provided, the clearance between the inner peripheral surface of the cylinder 10 and the screw 20 is reduced, and the amount of resin supplied downstream is reduced. Is reduced. As a result, the flow resistance of the molten resin increases. In the present embodiment, at least the first transition portion 20A is a mechanism for increasing the flow resistance of the molten resin. Due to the presence of the first transition portion 20A, the first shallow groove portion 20B, and the seal portion 20C, the flow rate of the resin supplied from the upstream side to the starvation zone 16 decreases, the molten resin is compressed on the upstream side, the pressure increases, and the downstream side. In the starvation zone 16 of the above, the molten resin becomes unfilled (that is, starved).

The mechanism for increasing the flow resistance of the molten resin is particularly limited as long as it is a mechanism for temporarily reducing the flow path area through which the molten resin passes in order to limit the flow rate of the resin supplied from the upstream side to the starvation zone 16. Not done. Examples of the mechanism for increasing the flow resistance include a structure in which the screw flight is provided in the opposite direction to the other portion, a labyrinth structure provided on the screw, and the like.

Further, a mechanism for increasing the flow resistance of the molten resin may be provided on the screw as a ring or the like of a member separate from the screw, or may be provided integrally with the screw as a part of the structure of the screw. If a mechanism for increasing the flow resistance of the molten resin is provided as a ring or the like which is a member separate from the screw, the size of the clearance which is the flow path of the molten resin can be changed by changing the ring, so that the flow of the molten resin can be easily performed. There is an advantage that the magnitude of the resistance can be changed.

The deep groove portion 20D (the portion corresponding to the starvation zone 16) in the screw 20 has a diameter d of the screw shaft as compared with the portion located in the plasticization zone 40 on the upstream side in order to promote the starvation state of the molten resin. It is getting smaller and the flight depth h is getting bigger. The deep groove portion 20D has a double-row flight structure described later, and it can be said that the deep groove portion 20D is formed so that the groove between the adjacent screw flights 21 and 22 becomes deep.

The deep groove portion 20D has a smaller screw shaft diameter d at the portion located in the starvation zone 16 and a flight depth h over the entire starvation zone 16 as compared with the first transition portion 20A and the first shallow groove portion 20B. It is preferable that the screw has a large structure. Further, in the deep groove portion 20D, it is preferable that the diameter d of the shaft of the screw 20 and the flight depth h are substantially constant over the entire starvation zone 16. As a result, the pressure in the starvation zone 16 can be kept substantially constant, and the starvation state of the molten resin can be stabilized. In the present embodiment, the deep groove portion 20D corresponding to the starvation zone 16 has a constant shaft diameter d and flight depth h of the screw 20.

Here, the maximum amount of molten resin that moves with one rotation of the screw will be described with reference to FIG. FIG. 5 is a diagram showing a part of the screw 20 corresponding to the weighing zone 14, a part corresponding to the seal zone 15, and a part corresponding to the hunger zone 16. In FIG. 5, for the sake of explanation, the portion corresponding to the hunger zone 16 is a single flight instead of a multi-row flight.
In the measuring zone 14, the maximum amount of molten resin that moves (is sent out) to the downstream side as the screw makes one rotation is the volume per axial circumference between the adjacent screw flights 7. (This is referred to as volume A.) Further, in the starvation zone 16, the maximum amount of molten resin that moves (is sent out) to the downstream side as the screw makes one rotation is the axial circumference 1 between the adjacent screw flights 21. It is the volume per circumference. (This is referred to as volume B.)

(Multi-article flight structure)
A description will be given by returning to FIG. In the present embodiment, the deep groove portion 20D (the portion corresponding to the hunger zone 16) has a multi-row flight structure. In FIG. 3, a two-row flight structure (double flight structure) is used as an example of the multi-row flight structure. The deep groove portion 20D includes a first screw flight 21 and a second screw flight 22 formed on the outer peripheral surface thereof. According to the multi-row flight structure, the molten resin can be distributed and transferred to a plurality of flights. Further, by adopting the multiple flight structure, the same amount of molten resin as in the case of single flight can be divided into a plurality of pieces and transferred. As a result, even when the manufacturing apparatus 1 is made larger and the screw diameter D is made larger, the molten resin can be sent downstream without excessively increasing the volume between adjacent screw flights. Further, according to the multi-row flight structure, even when the screw diameter D is made larger, it is possible to suppress an increase in the volume between adjacent flights. Therefore, the amount of molten resin deposited between adjacent flights can be reduced, and the starvation state can be stabilized. As a result, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed (the contact area between the physical foaming agent and the molten resin can be increased), and the permeation time of the physical foaming agent into the molten resin is secured. Therefore, the permeability of the physical foaming agent in the starvation zone 16 can be enhanced.

FIG. 6 is an enlarged view of a part of the two-article flight. There are two routes for transferring the molten resin, one is transferred by the first screw flight 21 and the other is transferred by the second screw flight 22. Here, the "volume per circumference around the axis between adjacent screw flights" is defined as the volume C. The volume C is the volume per circumference around the axis between the first screw flight 21 and the second screw flight 22. In FIG. 6, the volume C at one location is shaded. At this time, in the starvation zone 16, the maximum amount of molten resin that moves downstream with one rotation of the screw, that is, the volume B shown in FIG. 5, is the volume C multiplied by the number of screws "2". It will be a screw.

Here, as another example of the multi-row flight structure, a case where the deep groove portion 20D (the portion corresponding to the hunger zone 16) is a three-row flight will be described. FIG. 7 is an overall view of the manufacturing apparatus 1 provided with the screw 20 in which the deep groove portion 20D is a three-row flight, and FIG. 8 is an enlarged view of a part of the three-row flight. The deep groove portion 20D is provided with a first screw flight 21, a second screw flight 22, and a third screw flight 23. In this case, the routes to which the molten resin is transferred include a route transferred by the first screw flight 21, a route transferred by the second screw flight 22, and a route transferred by the third screw flight 23. There is a route. In this case, the volume C per axial circumference between adjacent screw flights is the volume per axial circumference between the first screw flight 21 and the second screw flight 22, and the second screw flight 22 and the second screw flight 22. There is a volume per circumference around the axis between the three screw flights 23 and a volume per circumference around the axis between the third screw flight and the first screw flight. In FIG. 8, the volume C at one location is shaded. At this time, in the starvation zone 16, the maximum amount of molten resin that moves downstream with one rotation of the screw, that is, the volume B shown in FIG. 5, is obtained by multiplying the volume C by the number of screws "3". It will be a screw. In generalization, the volume B is the volume C × n in the case of n-row flight (n is an integer of 2 or more).

In the present embodiment, the volume C per axial circumference between adjacent screw flights in the multi-row flight structure is 5 cm ³ or more and 100 cm ³ or less. The optimum value of the volume C varies depending on the screw diameter D, but it is preferably ^{at least 5 cm 3 or more.} When the volume C is ^{less than 5 cm 3} , it becomes difficult to maintain both the starvation state in the starvation zone 16 and the supply capacity for sending the molten resin downstream in the starvation zone 16. Is. Further, the volume C is ^{preferably 100 cm 3} or less. When the volume C is ^{larger than 100 cm 3} , the amount of resin deposited between adjacent screws becomes excessive, and the penetration efficiency of the physical foaming agent in the starvation zone 16 decreases. Further, the volume C is ^{more preferably 10 cm 3} or more and 50 cm ³ or less.

In the present embodiment, the value (A / B) obtained by dividing the volume A by the volume B is 0.1 or more and 1.0 or less. This is because the deterioration of the foaming performance of the foamed molded product can be suppressed, and the occurrence of vent-up (a phenomenon in which the molten resin swells from the introduction port 2 of the starvation zone 16) can be suppressed. Further, the A / B is more preferably 0.4 or more and 0.9 or less. When the A / B is less than 0.4, the amount of molten resin in the starvation zone 16 becomes small and the starvation rate becomes high, but the excess gas increases, so that the foaming efficiency decreases and the foamed molded product breaks bubbles. Tends to occur easily. On the other hand, when A / B is larger than 0.9, the starvation rate and the solubility of the physical foaming agent tend to decrease, and vent-up tends to occur easily.

Further, the inner diameter of the cylinder 10 in which the screw 20 is installed (screw diameter D of the screw 20) is 40 mm to 300 mm. In the present invention, for example, it is defined as follows. When the manufacturing apparatus 1 is a medium size, the inner diameter of the cylinder 10 is about 40 mm to about 60 mm. When the manufacturing apparatus 1 is made large, the inner diameter of the cylinder 10 is about 60 mm to about 300 mm. The effect of the present invention is sufficiently exhibited even when the manufacturing apparatus 1 is made medium-sized, but when the manufacturing apparatus 1 is made large-sized, the contact area between the physical foaming agent and the molten resin is more significantly reduced. The effect of the invention will be more exerted. When the inner diameter of the cylinder 10 is, for example, less than about 40 mm, the volume between adjacent flights in the starvation zone 16 is small even if the portion of the screw 20 corresponding to the starvation zone 16 is not a multi-row flight but a single flight. Since the amount of resin deposited there is small, there is a tendency that no deterioration in the foaming performance of the molded product is observed. The upper limit of the inner diameter of the cylinder 10 is set to 300 mm because the inner diameter of the cylinder 10 is practically a maximum of 300 mm in the foam injection molding machine.

Further, the value (P / D) obtained by dividing the screw pitch P (see FIG. 4) in the multi-row flight portion by the screw diameter D of the screw 20 may be made larger than 1.0. The P / D is generally around 1.0, but when distributing flights to multiple flights, it is necessary to make the P / D larger than 1.0 and secure the minimum volume required between adjacent flights. Because there is. Further, the P / D in the hunger zone 16 may be larger than the P / D in the measurement zone 14. In that case, the feed rate of the molten resin in the starvation zone 16 becomes high, and the starvation rate in the starvation zone 16 can be increased.

In the screw 20, the multi-row flight structure of the deep groove portion 20D (the portion corresponding to the hunger zone 16) may be three-row flight or more. Further, other parts other than the hunger zone 16 may have a multi-row flight structure. The other portion is, for example, a portion corresponding to the recompression zone 17, the reweighing zone 18, etc. in the screw 20. Further, in the multi-row flight structure, the thickness of the sub flight may be formed thinner than the thickness of the main flight. The thickness means the width of the screw 20 in the axial direction. For example, in the case of a two-row flight (see FIG. 6), the thickness of the second screw flight 22 may be formed thinner than the thickness of the first screw flight 21.

Further, in order to stabilize the starvation state of the molten resin in the starvation zone 16, the supply amount of the thermoplastic resin supplied from the hopper 30 to the cylinder 10 may be controlled. This is because if the supply amount of the thermoplastic resin is too large, it becomes difficult to maintain the starvation state. In the present embodiment, a general-purpose feeder screw (not shown) is used to control the supply amount of the thermoplastic resin. By limiting the supply amount of the thermoplastic resin, the weighing rate of the molten resin in the reweighing zone 18 becomes higher than the plasticizing rate in the compression zone 13. As a result, the density of the molten resin in the starvation zone 16 is stably reduced, and the permeation of the physical foaming agent into the molten resin is promoted. It is not preferable to reduce the amount of the thermoplastic resin supplied from the hopper 30 to the cylinder 10 too much because the plasticizing time becomes long.

Further, in the present embodiment, the length of the starvation zone 16 in the flow direction of the molten resin is preferably long in order to secure the contact area and contact time between the molten resin and the physical foaming agent, but if it is too long, the molding cycle And the adverse effect of increasing the screw length occurs. Therefore, the length of the starvation zone 16 is preferably 2 to 12 times, more preferably 4 to 10 times the inner diameter of the cylinder 10. Also, the length of the starvation zone 16 preferably covers the entire range of weighing strokes in injection molding. That is, the length of the starvation zone 16 in the flow direction of the molten resin is preferably equal to or longer than the length of the measuring stroke in injection molding.

Further, the screw 20 moves forward and backward with the plasticization measurement and injection of the molten resin, but by setting the length of the starvation zone 16 to be equal to or longer than the length of the measurement stroke, the screw 20 is always manufactured during the production of the foam molded product. , The inlet 2 can be placed in the starvation zone 16. In other words, even if the screw 20 moves forward and backward during the production of the foam molded product, the zones other than the starvation zone 16 do not come to the position of the introduction port 2. As a result, the physical foaming agent introduced from the introduction port 2 is always introduced into the starvation zone 16 during the production of the foamed molded product. By providing the starvation zone 16 having a sufficient and appropriate size (length) in this way and introducing a physical foaming agent having a constant pressure therein, the starvation zone 16 can be easily held by a constant pressure. In the present embodiment, the length of the starvation zone 16 is substantially the same as the length of the portion of the screw 20 where the diameter of the shaft of the screw 20 and the depth of the screw flight are constant, that is, the length of the deep groove portion 20D. It has become.

In the present embodiment, it is assumed that the manufacturing apparatus 1 has one hunger zone 16, but the number of hunger zones 16 is not limited to this. For example, in order to promote the penetration of the physical foaming agent into the molten resin, a plurality of starvation zones 16 and introduction ports 2 may be provided, and the physical foaming agent may be introduced into the cylinder 10 through the plurality of introduction ports 2. ..

(4) The molten resin and the physical foaming agent are brought into contact with each other.
Next, while the starvation zone 16 is held at a constant pressure, the starved molten resin and the physical foaming agent at a constant pressure are brought into contact with each other in the starvation zone 16 (step S4 in FIG. 2). That is, in the starvation zone 16, the molten resin is pressurized with a physical foaming agent at a constant pressure. In the starvation zone 16, since the molten resin is unfilled (starvation state) and there is a space in which the physical foaming agent can exist, the physical foaming agent and the molten resin can be efficiently brought into contact with each other. The physical foaming agent in contact with the molten resin permeates the molten resin and is consumed. When the physical foaming agent is consumed, the physical foaming agent staying in the pressure adjusting container 5 is smoothly supplied to the starvation zone 16. As a result, the pressure in the starvation zone 16 is maintained at a constant pressure, and the molten resin continues to come into contact with the physical foaming agent at a constant pressure.

In the conventional foam molding using a physical foaming agent, a predetermined amount of a high-pressure physical foaming agent is forcibly introduced into a plastic cylinder within a predetermined time. Therefore, it is necessary to pressurize the physical foaming agent to a high pressure and accurately control the introduction amount, introduction time, etc. into the molten resin, and the physical foaming agent comes into contact with the molten resin only in a short introduction time. It was. On the other hand, in the present embodiment, instead of forcibly introducing the physical foaming agent into the cylinder 10, the physical foaming agent having a constant pressure is continuously applied to the cylinder 10 so that the pressure in the starvation zone 16 becomes constant. The physical foaming agent is continuously brought into contact with the molten resin. Thereby, the amount of the physical foaming agent dissolved (permeation amount) in the molten resin, which is determined by the temperature and pressure, can be stabilized. Further, in the present embodiment, since the physical foaming agent is always in contact with the molten resin, a necessary and sufficient amount of the physical foaming agent permeates into the molten resin. As a result, the foamed molded product produced by the manufacturing apparatus 1 according to the present embodiment foams even though it uses a low-pressure physical foaming agent as compared with the conventional molding method using a physical foaming agent. The cell is fine.

Further, according to the manufacturing method according to the present embodiment, since it is not necessary to control the introduction amount, introduction time, etc. of the physical foaming agent, a drive valve such as a check valve or a solenoid valve, and a control mechanism for controlling these are further provided. Is unnecessary, and the equipment cost can be suppressed. Further, the physical foaming agent used in the present embodiment has an advantage that the device load is small because the pressure is lower than that of the conventional physical foaming agent.

Further, in the present embodiment, the starvation zone 16 is always maintained at a constant pressure during the production of the foam molded product. That is, in order to supplement the physical foaming agent consumed in the cylinder 10, all the steps of the method for producing a foamed molded product are carried out while continuously supplying the physical foaming agent at a constant pressure. Further, in the present embodiment, for example, in the case of continuously performing injection molding of a plurality of shots, the molten resin for the next shot is performed while the injection step, the cooling step of the molded body, and the taking-out step of the molded body are being performed. Is prepared in the cylinder 10, and the molten resin for the next shot is pressurized at a constant pressure by the physical foaming agent. That is, in the injection molding of a plurality of shots performed continuously, the molten resin and the physical foaming agent having a constant pressure are always present and in contact with each other in the cylinder 10, that is, the molten resin is formed by the physical foaming agent in the cylinder 10. One cycle of injection molding is performed, including a plasticization weighing step, an injection step, a cooling step of a molded body, a taking-out step, and the like, under constant pressure at a constant pressure. Similarly, when continuous molding such as extrusion molding is performed, the molten resin and the physical foaming agent having a constant pressure are always present and in contact with each other in the cylinder 10, that is, the molten resin is physically in the cylinder 10. Molding is performed in a state of being constantly pressurized at a constant pressure by a foaming agent.
Even when the manufacturing apparatus 1 is made large, molding is performed in a state where the molten resin is constantly pressurized at a constant pressure by a physical foaming agent in the cylinder 10 by providing a pressure adjusting container 5 having an appropriate size. This is ensured, and it is possible to enjoy the effect of a molding method using a low-pressure physical foaming agent, which enables good foam molding in which fine cells are formed inside the molded body. For example, when a large amount of the physical foaming agent is consumed in the starvation zone 16, the supply of the physical foaming agent may not be in time and the pressure in the starvation zone 16 may suddenly decrease, but the pressure adjusting container 5 stabilizes the physical foaming. The agent is supplied, the pressure fluctuation in the starvation zone 16 is suppressed, and the molten resin can be molded in the cylinder 10 in a state of being constantly pressurized at a constant pressure by the physical foaming agent.

(5) The molten resin is molded into foam molding.
Next, the molten resin contacted with the physical foaming agent is molded into a foamed molded product (step S5 in FIG. 2). The cylinder 10 is provided with a recompression zone 17 adjacent to the downstream of the starvation zone 16. Due to the rotation of the screw 20, the molten resin in the starvation zone 16 flows into the recompression zone 17. In the recompression zone 17, the molten resin is recompressed and the pressure is increased. The molten resin containing the physical foaming agent is pressure adjusted in the recompression zone 17 and extruded to the front of the screw 20 to be weighed. The cylinder 10 is provided with a reweighing zone 18 adjacent to the downstream of the recompression zone 17 as a zone for performing the weighing.

At this time, the internal pressure of the molten resin extruded to the front of the screw 20 is controlled as the back pressure of the screw by a hydraulic motor, a hydraulic cylinder or an electric motor (not shown) connected to the rear of the screw 20. In the present embodiment, the internal pressure of the molten resin extruded in front of the screw 20, that is, the back pressure of the screw is constant in order to uniformly phase the physical foaming agent from the molten resin without separating it and stabilize the resin density. It is preferable to control the pressure so as to be about 1 to 6 MPa higher than the pressure of the starvation zone 16 held in. In the present embodiment, a check ring 19 is provided at the tip of the screw 20 so that the compressed resin in front of the screw 20 does not flow back to the upstream side. As a result, the pressure in the starvation zone 16 at the time of weighing is not affected by the resin pressure in front of the screw 20.

In the present embodiment, the molten resin weighed in the reweighing zone 18 is injection-filled from the cylinder 10 into a cavity (not shown) in the mold to perform injection foam molding. For injection foam molding, a short shot method is used in which the mold cavity is filled with a molten resin having a filling capacity of 75% to 95% of the mold cavity volume, and the mold cavity is filled while the bubbles expand. You may. Further, a core back method may be used in which the molten resin is filled with a filling amount of 90% to 100% of the mold cavity volume, and then the cavity volume is expanded and foamed. The obtained foam molded product has a foam cell inside, and shrinkage of the thermoplastic resin during cooling is suppressed and cooling strain is alleviated, so that sink marks and warpage are reduced, and a foam molded product having a low specific gravity can be obtained. Obtainable.

In the manufacturing method according to the present embodiment, it is not necessary to control the introduction amount, introduction time, etc. of the physical foaming agent into the molten resin, so that a complicated control device can be omitted or simplified, and the device cost can be reduced. it can. Further, while the starvation zone 16 is held at a constant pressure, the starved molten resin and the physical foaming agent at a constant pressure are brought into contact with each other in the starvation zone 16. As a result, the amount of the physical foaming agent dissolved in the molten resin (permeation amount) can be stabilized by a simple mechanism.

(Evaluation of foam molded product)
The evaluation method of the (injection) foam molded article (molded article) produced by the manufacturing apparatus 1 will be described. As the thermoplastic resin, polypropylene mixed with 20% talc (manufactured by Idemitsu Lion Composite, 4700G) was used. The thickness (2.5 mm) of the molded product was kept constant, and the size of the molded product was changed (150 mm square to 800 mm square) according to the diameter of the screw cylinder. The state of the foam cell of the molded product at the gate portion, the central portion and the flow end portion was evaluated by cross-sectional SEM. Foaming cells in a field of view of 1 mm square were observed, and an average cell of 50 μm or less was regarded as acceptable. Further, regarding the uniformity of the foam cell, the molded product was visually confirmed through the molded product, and it was evaluated whether or not foam rupture could be confirmed.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples and comparative examples described below. FIG. 9 is a diagram summarizing examples and comparative examples.

[Example 1]
In Example 1, foam injection molding was performed using a screw having a screw cylinder inner diameter of φ56 mm. The screw in the hunger zone 16 has a double flight structure. Regarding the maximum capacity of the molten resin that moves with one rotation of the screw, the volume A in the measuring zone 14 was set to 30 cm ^3, and the volume B (volume C × 2 path) in the starvation zone 16 was set to 38 cm ³ . Further, A / B (preferably 0.1 to 1.0) was set to 0.78. Further, the volume per one rotation axis between the screw flight adjacent the multiple lead flight starvation zone 16 ^C a (preferably 5 cm 3 100 cm ^3), was 19cm ^3.
A 150 mm square flat plate is used for the mold, and the pressure of the physical foaming agent by nitrogen adjusted by adjusting the pressure reducing valve 51 is 8 MPa, the back pressure of the screw is 10 MPa, the resin temperature is 180 to 210 ° C, and the mold temperature is 40 ° C. After the plasticization measurement, injection filling was performed at an injection speed of 50 mm / s. After applying at a pressure of 20 MPa for 2 seconds, the mold was opened by 5 mm and core back foaming was performed three times.

When the cell diameter of the molded product of Example 1 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 22 μm, which was good. In addition, no bubble rupture was observed. In addition, 100 shots were continuously molded, but no vent-up occurred.

[Example 2]
In Example 2, a screw having a screw cylinder inner diameter of φ80 mm was used. The screw in the hunger zone 16 has a double flight structure. Further, the volume A in the measurement zone 14 was set to 43 cm ^3, and the volume B in the starvation zone 16 (volume C × 2 path) was set to 52 cm ³ . Further, A / B was set to 0.82. The volume C was set to 26 cm ³ . The other parts were the same as in Example 1, and core back foaming was performed.

When the cell diameter of the molded product of Example 2 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 28 μm, which was good. In addition, no bubble rupture was observed. In addition, 100 shots were continuously molded, but no vent-up occurred.

[Example 3]
In Example 3, a screw having a screw cylinder inner diameter of φ100 mm was used. The screw in the hunger zone 16 has a double flight structure. Further, the volume A in the measurement zone 14 was set to 55 cm ^3, and the volume B (volume C × 2 path) in the starvation zone 16 was set to 86 cm ³ . Further, A / B was set to 0.63. The volume C was set to 43 cm ³ . Moreover, a flat plate of 250 × 400 mm square was used as the mold. The other parts were the same as in Example 1, and core back foaming was performed.

When the cell diameter of the molded product of Example 3 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 35 μm, which was good. In addition, no bubble rupture was observed. In addition, 100 shots were continuously molded, but no vent-up occurred.

[Example 4]
In Example 4, a screw having a screw cylinder inner diameter of φ200 mm was used. The screw in the hunger zone 16 has a triple flight structure. Further, the volume A in the measurement zone 14 was set to 110 cm ^3, and the volume B in the starvation zone 16 (volume C × 3 path) was set to 171 cm ³ . Further, A / B was set to 0.64. The volume C was set to 57 cm ³ . A flat plate of 800 mm square was used as the mold. The other parts were the same as in Example 1, and core back foaming was performed.

When the cell diameter of the molded product of Example 4 was evaluated by a cross-sectional SEM, the average cell diameter was as small as 38 μm, which was good. In addition, no bubble rupture was observed. In addition, 100 shots were continuously molded, but no vent-up occurred.

[Comparative Example 1]
In Comparative Example 1, a screw having a screw cylinder inner diameter of φ100 mm was used. The screw in the hunger zone 16 has a single flight structure. Further, the volume A in the measurement zone 14 was set to 55 cm ^3, and the volume B in the starvation zone 16 was set to 86 cm ³ . Further, A / B was set to 0.63. The other parts were the same as in Example 3, and core back foaming was performed.

When the cell diameter of the molded product of Comparative Example 1 was evaluated by a cross-sectional SEM, the average cell diameter was 47 μm, which was slightly enlarged. In addition, bubble rupture was observed at the end of the flow. This is because in a single flight, the difference between the volume A and the volume B is large, so that the amount of resin deposited between adjacent flights in the starvation zone 16 decreases, and the amount of the physical foaming agent that stays increases. It is presumed that the excess gas that could not be completely dissolved was involved during recompression.

[Comparative Example 2]
In Comparative Example 2, a screw having a screw cylinder inner diameter of φ200 mm was used. The screw in the hunger zone 16 has a double flight structure. The volume C was set to 105 cm ³ . The other parts were the same as in Example 4, and core back foaming was performed.

When the cell diameter of the molded product of Comparative Example 2 was evaluated by a cross-sectional SEM, the cell diameter was large and bubbles were scattered. It is presumed that this is because the amount of resin staying between adjacent screws in the starvation zone 16 increased and the contact area with the physical foaming agent decreased, resulting in an insufficient amount of dissolved physical foaming agent. To. In addition, it is presumed that the amount of the physical foaming agent that stays is too large and excess gas is involved during recompression.

[Comparative Example 3]
In Comparative Example 3, a screw having a screw cylinder inner diameter of φ56 mm was used. The screw in the hunger zone 16 has a double flight structure. The volume B in the hunger zone 16 was set to 28 cm ³ . In addition, A / B was set to 1.07 (that is, the hunger rate was lowered). Other than that, core back foaming was performed in the same manner as in Example 1.

In Comparative Example 3, vent-up occurred frequently, and it was difficult to continuously mold the resin unless the supply amount of the resin was narrowed down considerably.

As described above, in the manufacturing apparatus and manufacturing method according to the present embodiment, the apparatus for performing foam molding by constantly pressurizing the molten resin with a physical foaming agent at a constant pressure in the starvation zone 16 is made larger. In other words, even if the screw diameter is made larger, the flight structure in the starvation zone 16 has a multi-row flight structure, so that the same amount of molten resin as in the case of single flight is divided into a plurality of parts. And be transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited therein can be reduced. Therefore, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed, and the permeation time of the physical foaming agent into the molten resin is secured. Therefore, it is possible to realize good foam molding in which fine cells are formed inside the foam molded product (molded product), and it is possible to suppress deterioration of the foaming performance of the foam molded product.
In other words, in a manufacturing apparatus (manufacturing method) in which the starvation zone 16 is pressurized with a relatively low-pressure physical foaming agent, even when the apparatus is made larger, that is, when the inner diameter (scru diameter) of the screw cylinder is made larger. Since the flight structure in the starvation zone 16 is a multi-row flight structure, the same amount of molten resin as in the case of single flight is divided into a plurality of and transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited therein can be reduced. Therefore, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed, and the permeation time of the physical foaming agent into the molten resin is secured. As a result, good foam molding without deteriorating the foaming performance of the molded product can be realized, and fine foam cells can be stably formed inside the molded product.

Further, since the volume per one revolution about the axis of the adjacent screw flights of the starvation zone 16 (volume C) is in the range of ^{5 cm} 3 100 cm ^3, the starvation zone 16, while maintaining the starved, melting The ability to supply the resin downstream is maintained, and the decrease in the penetration efficiency of the physical foaming agent due to the excessive amount of resin deposited between adjacent screw flights is suppressed. As a result, it is possible to more reliably suppress the enlargement of the foam cell size and the occurrence of foam breakage in the molded product, and it is possible to obtain a molded product in a good foamed state.

Further, the volume A per axial circumference between adjacent screw flights in the weighing zone 14 and the volume B per axial circumference between adjacent screw flights in the starvation zone 16 are multiplied by the number of screws. Since the ratio A / B with and is in the range of 0.1 to 1.0, the excess of the physical foaming agent in the starvation zone 16 is suppressed, and the occurrence of vent-up is suppressed. As a result, the occurrence of foam breakage in the molded product can be more reliably suppressed, a molded product in a good foamed state can be obtained, and the productivity of the molded product can be improved.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to the drawings. In the present embodiment, a case where the manufacturing apparatus is an extrusion molding apparatus will be described.

The manufacturing apparatus 500 shown in FIG. 10 is an extrusion molding apparatus (extrusion manufacturing apparatus). The manufacturing apparatus 500 includes a plasticized cylinder (cylinder) 510 in which a screw 520 is installed, a physical foaming agent supply mechanism 600 for supplying a physical foaming agent to the cylinder 510, and a control device (not shown) for controlling the operation of the cylinder 510. Etc. are provided. The molten resin plasticized and melted in the cylinder 510 flows from the right hand to the left hand in FIG. Inside the cylinder 510 of this example, the right hand in FIG. 10 is "upstream" or "rear" and the left hand is "downstream" or "forward".

A die 590 is provided at the tip of the cylinder 510, and the molten resin is extruded by extruding the molten resin from the die 590 into the atmosphere. The tip of the die 590 has a hole whose outlet is narrowed so that the resin pressure increases, and a string-shaped (rod-shaped) molded body is formed.
On the upper side surface of the cylinder 510, a resin supply port 501 for supplying the thermoplastic resin to the cylinder 510 and an introduction port 502 for introducing the physical foaming agent into the cylinder 510 are provided in this order from the upstream side. ..

A hopper 591 for supplying resin and a feed screw 592 are arranged in the resin supply port 501, and a pressure adjusting container (introduction speed adjusting container) 550 is arranged in the introduction port 502. The pressure adjusting container 550 has a structure similar to that of the pressure adjusting container 5 shown in FIG. A physical foaming agent supply mechanism 600 is connected to the pressure adjusting container 550 via a pipe 554, a pressure reducing valve 551, a pressure gauge 552, and a buffer tank 553. Further, a sensor (not shown) for monitoring the pressure may be provided at a position facing the introduction port 502 of the cylinder 510.

The cylinder 510 has a feed zone 512, a compression zone 513, a weighing zone 514, a starvation zone 516, a recompression zone 517, and a reweighing zone 518 in this order from the upstream side to the downstream side. .. The feed zone 512 and the compression zone 513 form a plasticization zone 540. The plasticizing zone 540 may further include a measuring zone 514.
The feed zone 512 is a zone in which residual heat is given to the pellets of the thermoplastic resin. The compression zone 513 is a zone in which the thermoplastic resin is sheared and kneaded to be plasticized and melted, and the molten resin is compressed. The measuring zone 514 is a zone in which the density of the compressed molten resin is kept constant. The starvation zone 516 is a zone in which the molten resin is starved. The recompression zone 517 is a zone in which the molten resin is recompressed. The reweighing zone 518 is a zone in which the molten resin is weighed.

The screw 520 is a screw used in the manufacturing apparatus 500 that pressurizes a low-density resin in a plasticized and melted state with a physical foaming agent at a constant pressure at all times in a starvation zone 516. As shown in FIG. 11, the screw 520 includes a first transition portion (first groove depth transition portion) 520A located on the upstream side, a first shallow groove portion 520B adjacent to the downstream side of the first transition portion 520A, and the like. On the downstream side of the deep groove portion 520C adjacent to the downstream side of the first shallow groove portion 520B, the second transition portion (second groove depth transition portion) 520D adjacent to the downstream side of the deep groove portion 520C, and the second transition portion 520D. It has a second shallow groove portion 520E adjacent to it. The first transition unit 520A is located in the compression zone 513. The first shallow groove portion 520B is located in the measuring zone 514 and also serves as a seal. The deep groove portion 520C is located in the starvation zone 516. The second transition unit 520D is located in the recompression zone 517. The second shallow groove portion 520E is located in the reweighing zone 518.

The screw 520 is rotatably arranged in the cylinder 510 in order to promote plasticizing and melting of the thermoplastic resin. In other words, the screw 520 is rotatably arranged (supported) in the cylinder 510. Further, the screw 520 has a first transition portion (first large diameter portion) 520A, a first shallow groove portion 520B, and a second transition portion (second large diameter portion) as a mechanism for increasing the flow resistance and pressure of the molten resin. Part) 520D and a second shallow groove part 520E are provided.

The explanation will be returned to FIG. In the cylinder 510, the thermoplastic resin is supplied from the resin supply port 501 into the cylinder 510, and the thermoplastic resin is plasticized by a band heater (not shown) to become a molten resin, and the screw 520 rotates in the forward direction to the downstream. Sent. In the molten resin, the molten resin is compressed and the pressure increases on the upstream side of the first shallow groove portion 520B, and the molten resin becomes unfilled (starvation state) on the downstream side of the first shallow groove portion 520B. The molten resin sent further downstream is compressed by the presence of the second transition portion 520D of the screw 520 to increase the pressure, and is adjusted so that the physical foaming agent and the molten resin do not separate. The resin sent further downstream is extruded from the die 590.

Further, the introduction port 502 into which the physical foaming agent is introduced is provided in the starvation zone 516. As described above, the cylinder 510 has one starvation zone 516 and one introduction port 502, and the physical foaming agent is introduced through the introduction port 502.

In the present embodiment, the outer diameter of the screw 520 (screw outer diameter) is φ50 mm or more. The outer diameter of the screw 520 is, for example, φ115 mm. The parts of the screw 520 corresponding to the plasticization zone 512, the compression zone 513, the weighing zone 514, the recompression zone 517, and the reweighing zone 518 have a single flight structure, that is, one screw flight 507 on the outer peripheral surface of the screw 520. It has a formed structure.

In order to promote the starvation state of the molten resin, the deep groove portion (small diameter portion) 520C has a smaller diameter d (see FIG. 4) of the screw shaft as compared with the first shallow groove portion 520B on the upstream side, and the flight The depth h (see FIG. 4) is increased. In the present embodiment, the deep groove portion 520C has a double flight structure (double flight structure). In other words, the deep groove portion 520C is formed so that the groove pitch between the adjacent screw flights 531 and 532 is narrowed.

The deep groove portion 520C has a smaller screw shaft diameter d at the portion located in the starvation zone 516 and a flight depth h over the entire starvation zone 516 as compared with the first shallow groove portion 520B and the second shallow groove portion 520E. It is preferable that the screw has a large structure. In the present embodiment, the deep groove portion 520C corresponding to the starvation zone 516 has a constant screw shaft diameter d and flight depth h. However, the diameter d of the screw shaft and the flight depth h in the starvation zone 516 do not necessarily have to be constant as long as the starvation state of the molten resin, that is, the state in which the resin is not compressed is maintained within a certain range.

The deep groove portion 520C includes a first screw flight 531 and a second screw flight 532 formed on the outer peripheral surface thereof. According to the multi-row flight structure, the molten resin can be distributed and transferred to a plurality of flights. Further, by adopting the multiple flight structure, the same amount of molten resin as in the case of single flight can be divided into a plurality of pieces and transferred. As a result, even when the manufacturing apparatus 500 is made larger and the screw diameter D is made larger, the molten resin can be sent downstream without excessively increasing the volume between adjacent screw flights. Further, according to the multi-row flight structure, even when the screw diameter D is made larger, it is possible to suppress an increase in the volume between adjacent flights. Therefore, the amount of molten resin deposited between adjacent flights can be reduced, and the starvation state can be stabilized. As a result, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed (the contact area between the physical foaming agent and the molten resin can be increased), and the permeation time of the physical foaming agent into the molten resin is secured. Therefore, the permeability of the physical foaming agent in the starvation zone 516 can be enhanced. In the present embodiment, the multi-row flight structure of the deep groove portion 520C is a two-row flight, but it may be a three-row flight or more.

The physical foaming agent supply mechanism 600 includes a cylinder 601, an air-driven booster pump 602 that boosts nitrogen to a predetermined pressure, a pressure gauge 603, and a pressure reducing valve 604. Further, in the present embodiment, a die 590 having a hole-shaped extrusion port is used so that a string-shaped molded product can be obtained. The size of the gap of the extrusion port corresponding to the thickness of the string is, for example, 0.2 mm.

Next, the production of the foam molded product using the production apparatus 500 will be described. In the present embodiment, the string-shaped foam molded product is continuously manufactured by extrusion molding using the manufacturing apparatus 500. As the thermoplastic resin, for example, non-reinforced polyamide 6 (PA6) (manufactured by Toray Industries, Inc., Amylan CM1021FS) is used. The resin pellets of the thermoplastic resin are supplied from the resin supply hopper 591, and the screw 520 is rotated in the forward direction. In the feed zone 512, the thermoplastic resin is heated and kneaded to obtain a molten resin. In order to keep the starvation state of the starvation zone 516 stable, the feed screw 592 may be used to limit the supply of resin pellets from the hopper 591 to the cylinder 510. By reducing the feed amount of the resin pellets, the amount of molten resin in the feed zone 512 can be reduced. This stabilizes the starvation state in the downstream starvation zone 516. By continuing the forward rotation of the screw 520 at a rotation speed of 150 rpm, the molten resin is made to flow from the feed zone 512 to the compression zone 513, and further to the starvation zone 516.

Since the molten resin flows into the starvation zone 516 from the gap between the first shallow groove portion 520B of the screw 510 and the inner wall of the cylinder 510, the supply amount of the molten resin to the starvation zone 516 is limited. As a result, the molten resin is compressed in the compression zone 513 on the upstream side of the first shallow groove portion 520B to increase the pressure, and the molten resin becomes unfilled (starvation state) in the starvation zone 516 on the downstream side. In the starvation zone 516, since the molten resin is unfilled (starvation state), nitrogen introduced from the introduction port 502 exists in a space where the molten resin does not exist, and the molten resin is pressurized by the nitrogen. Further, the molten resin is sent downstream and recompressed in the recompression zone 517.

Further, the molten resin is sent to the recompression zone 517, recompressed, and then continuously extruded from the die 590 into the atmosphere to obtain a string-shaped foam molded product having a predetermined length. For example, the molten resin can be foamed to 5 times the size of the gap between the extrusion ports of the die 590 to obtain a string-shaped molded product having a diameter of 1.0 mm.

According to the extrusion manufacturing apparatus 500 of the present embodiment, as in the case of Examples 1 to 4 (see FIG. 9) of the injection manufacturing apparatus 1 shown in the first embodiment, a good molded product (see FIG. 9). Molded product) can be obtained.

As described above, in the manufacturing apparatus 500 according to the present embodiment, when the apparatus for molding by constantly pressing the molten resin with a physical foaming agent at a constant pressure in the starvation zone 516 is made larger ( That is, even when the outer diameter of the screw is made larger), the flight structure in the starvation zone 516 is a multi-row flight structure, so that the same amount of molten resin as in the case of single flight is divided into a plurality of pieces. Will be transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited therein can be reduced. Therefore, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed, and the permeation time of the physical foaming agent into the molten resin is secured. Therefore, it is possible to realize good foam molding in which fine cells are formed inside the foam molded product (molded product), and it is possible to suppress deterioration of the foaming performance of the foam molded product.

In other words, in the manufacturing apparatus 500 (manufacturing method) in which the starvation zone 516 is pressurized with a relatively low-pressure physical foaming agent, when the apparatus is made larger, that is, the inner diameter of the screw cylinder (outer diameter of the screw) is made larger. Even in this case, since the flight structure in the starvation zone 516 is a multi-row flight structure, the same amount of molten resin as in the case of single flight is divided into a plurality of and transferred. At this time, since the volume between adjacent screw flights does not become excessively large, the amount of molten resin deposited therein can be reduced. Therefore, the decrease in the contact area between the physical foaming agent and the molten resin is suppressed, and the permeation time of the physical foaming agent into the molten resin is secured. As a result, good foam molding without deteriorating the foaming performance of the molded product can be realized, and fine foam cells can be stably formed inside the molded product.

Further, since the volume per one revolution about the axis of the adjacent screw flights of the hunger zone 516 is in the range of ^{5 cm} 3 100 cm ^3, the starvation zone 516, while maintaining the starved, the molten resin to the downstream The ability to send (supply) is maintained, and the decrease in the penetration efficiency of the physical foaming agent due to the excessive amount of resin deposited between adjacent screw flights is suppressed. As a result, it is possible to more reliably suppress the enlargement of the foam cell size and the occurrence of foam breakage in the molded product, and it is possible to obtain a molded product in a good foamed state.

Further, the volume A per axial circumference between adjacent screw flights in the weighing zone 514 and the volume B per axial circumference between adjacent screw flights in the starvation zone 516 multiplied by the number of screws. Since the ratio A / B with and is in the range of 0.1 to 1.0, excess of the physical foaming agent is suppressed in the starvation zone 516, and the occurrence of vent-up is suppressed. As a result, the occurrence of foam breakage in the molded product can be more reliably suppressed, a molded product in a good foamed state can be obtained, and the productivity of the molded product can be improved.

1 Injection manufacturing equipment 500 Extrusion manufacturing equipment 2,502 Inlet 5,550 Pressure adjusting container 10,510 Plasticized cylinder (cylinder)
40,540 Plasticization Zone 16,516 Hunger Zone 20,520 Screw

Claims (2)

It is a manufacturing device for foam molded products.
A cylinder having a plasticization zone in which a thermoplastic resin is plasticized and melted to become a molten resin and a starvation zone in which the molten resin is in a starvation state, and a port for introducing a physical foaming agent into the starvation zone is provided. ,
A screw having a screw outer diameter of φ50 mm or more, which is arranged inside the cylinder,
The physical foaming agent having a constant pressure is introduced into the starvation zone through the introduction port, and the pressure adjusting container for keeping the starvation zone at a constant pressure at all times is provided.
The screw has a multi-row flight structure in the starvation zone.
The multi-row flight structure of the screw is an apparatus for manufacturing a foam molded product, characterized in that ^{the volume per axial circumference between adjacent screws is 5 cm 3} or more and 100 cm ^{3 or less.} The foam molding manufacturing apparatus according to claim 1, wherein the manufacturing apparatus is an extrusion manufacturing apparatus.

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