JP2537333B2 - METHOD OF MOLDING MULTILAYER FOAM AND MULTILAYER FOAM MOLDING APPARATUS - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a multi-layer foam and a multi-layer foam molding apparatus in which a plurality of types of foams are integrally molded.

[0002]

2. Description of the Related Art A foamed molded product used as a cushioning material for packaging, artificial wood, etc., is prepared by filling pre-expanded resin beads such as styrene (hereinafter simply referred to as resin beads) in a mold.
The beads are completely foamed by blowing steam through a large number of small holes formed in the mold wall, and the beads are fused and molded together.
In this foam-molded product, for example, a surface layer portion or an end portion that requires relatively high strength is formed of a foam having a low expansion ratio or a virgin plastic foam, and a core portion that does not require high strength is formed. Forming with a lightweight, low-cost, high expansion ratio or recycled plastic foam is effective in reducing the weight of foam-molded products and reducing raw material costs. As described above, as a method for forming a multi-layered foam body in which different strengths, densities or colors are partially formed in one foam-molded article, a simultaneous foam molding method using different raw materials described in Japanese Patent Publication No. 3-55299. Japanese Patent Publication No. 59-23547 discloses a method for molding a synthetic resin foam-molded article.

[0003]

However, in the multilayer foam molded by the above-mentioned method, different foams are mixed with each other and the boundary tends to be unclear. In such a foam-molded article, for example, a predetermined strength cannot be obtained in a portion requiring high strength, and the ratio of expensive materials is increased in the end, so that sufficient weight reduction and large cost reduction cannot be expected. Of course, it is possible to mold such multilayer foams using complicated processes and equipment, but plastic foams generally have large cost constraints, and high productivity is achieved with simple equipment and easy operation. If it is not a molding method that is applicable, it is not practical. The present invention provides a simple and highly productive method of integrally forming a surface layer portion or an end portion and a central portion or a core with different kinds of foams, and a simple apparatus therefor.

[0004]

Means for Solving the Problems As a result of investigating the cause of difficulty in molding a multi-layered foam in which each layer is divided as desired, the inventor of the present invention sucks resin beads using an injector, It was found that the resin beads in the previously filled mold were disturbed because the mold was filled, and the layers were mixed together. As a result of further research, the hopper that stores the resin beads is pressurized, and the resin beads are pushed out by the pressure to fill the mold with pressure, and a special means is provided for the switching operation to the filling of different types of resin beads. The present invention has been completed by finding that it is possible to integrally form a multi-layer foam body in which each layer is laminated by using it. In the present invention, a foam molding die (hereinafter, simply referred to as a die) having a large number of small steam holes and vent holes for blowing steam is used as the die.

That is, the present invention comprises, as the first invention, a plurality of pressure hoppers 1 and 2 and a mold 11 having a plurality of resin bead charging holes 7 and 8 connected to the respective pressure hoppers. Using the foam molding apparatus, first, the required amount of the resin beads A is charged into the mold from the pressure hopper 1 that stores the resin beads A at the pressure applied to the pressure hopper 1. From the wall surface of the unfilled portion, the pressurized gas is fed into the mold, and then the feeding of the pressurized gas is stopped, and at the same time, the pressure applied to the pressurizing hopper 2 that stores the resin beads B, A predetermined amount of resin beads B are charged into the mold, and the above-described operation is repeated to charge a predetermined plurality of resin beads into the mold, and then the mold is heated so that the charged resin beads are mutually exchanged. A method for forming a multi-layered foam, which is characterized in that Subjected to.

Further, as a second invention, a foam molding apparatus comprising two pressure hoppers 1 and 2 and a mold 11 having resin bead charging holes 7 and 8 connected to the respective pressure hoppers. First, after a pressurized gas is fed into the mold, a predetermined pressure is applied to the pressurizing hopper 1 which stores the resin beads A, so that a required amount of the resin beads A is introduced from the resin bead charging hole 7. It is charged into the mold, and then the supply of the pressurized gas is stopped, and at the same time, a predetermined pressure is applied to the pressurizing hopper 2 to introduce the required amount of the resin beads B from the resin bead introducing hole 8.
There is provided a method for molding a two-layer foam, characterized in that after the addition of the resin beads B is completed, the inside of the mold is heated to fuse the introduced resin beads to each other.

Further, as a third invention, it has a plurality of pressurizing hoppers and a plurality of resin bead charging holes connected to each pressurizing hopper capable of realizing the above-mentioned method for molding a multilayer foam. Provided is a multi-layer foam molding device including a foam molding die.

[0008]

Actions and Embodiments The following will specifically describe the method for molding a multilayer foam according to the present invention and a molding apparatus capable of realizing the same, with reference to the drawings and embodiments. FIG. 1 shows a flow sheet showing an example of a foam molding apparatus used for carrying out the present invention, and FIGS. 2 and 3 show examples of foam molded articles molded according to the present invention. The apparatus used in the method for molding a multilayer foam according to this example includes a plurality of pressure hoppers 1 and 2, and a mold 11 having a plurality of resin bead charging holes 7 and 8 connected to the respective pressure hoppers. It is also an embodiment of the third invention. The pressurizing hopper 1 is connected to the storage hopper 15 for storing the resin beads A via the raw material supply valve 17, and has a function of supplying the resin beads A exclusively to the mold 11. Similarly, the pressurizing hopper 2 is connected to the storage hopper 16 for storing the resin beads B via the raw material supply valve 18. The pressure in the pressurizing hoppers 1 and 2 is at least equal to or higher than the flow limit of the resin beads to be supplied, and normally the maximum pressure should be designed to be about 0.25 to 0.5 MPa.

A shutter 1 is provided at the bottom of the pressure hoppers 1 and 2.
2 and 13 are provided to supply and block the resin beads A and B. Although the shutter may be of any type, it is preferable that the pressure loss when supplying the resin beads is small. In particular, a method is preferable in which the resin beads to be filled later can be added in a short time. In the present embodiment example, the shutter 12 is a rotary shutter that opens and closes by rotating a disc having an opening.
A butterfly valve is used for the shutter 13.

The die 11 has piston valves 2
A plurality of resin bead charging holes 7 and 8 having holes 0a and 20b are provided, and a filler (resin bead charging portion) 5 and
It is connected to the pressure hoppers 1 and 2 via 6. The mold 11 has a large number of small vent holes on the wall surface, except that there are a plurality of resin bead charging holes 7 and 8, and is the same as a normal mold for molding a single-layer foam. In the present embodiment, the fillers 5 and 6 are provided with injectors because they are also used as a molding device for a single-layer foam, and in a dedicated mold intended only for carrying out the present invention, resin beads are used. It is not necessary to use an injector as a filler for charging. Further, in the present invention, the mold 1 is formed by using the resin bead charging hole.
Since gas is sent to 1, it is preferable to separate individual resin bead charging holes as far as possible unless there is a problem in the structure of the mold, because the boundary of layers can be easily adjusted.

The air valve 14 provided on the upstream side of the resin bead charging hole 8 has a function of sending gas from the resin bead charging hole 8 to the mold 11 via the raw material charging header 19. The gas may be fed in from a gas feed hole provided separately from the resin bead feed hole, but the structure of the mold becomes complicated. The blow air introduction ports 9 and 10 are used for pre-blowing for the purpose of removing steam and water droplets in the mold 11, or the resin beads remaining in the resin feeding pipes 3 and 4 are pressed into the pressure hopper 1, 2.
It is provided to blow back to 2. The piston valve 20a is used to open and close the resin bead charging hole 7 and the blow air introducing port 9, and operates so that when one of them is opened, the other is closed. The same applies to the piston valve 20b.

Next, the method for molding the multilayer foamed product of the first invention will be specifically described by taking the case of using two types of resin beads A and B as an example. In the following, reference to the behavior of the resin beads in the mold is based on estimation including the case of the second invention, and does not limit the configuration of the present invention. Further, the specific pressure ranges shown below are reference values obtained by the inventor's molding apparatus. Actually it is difficult to measure the pressure inside the mold, and
Since the optimum pressure for molding depends on the size of the mold, the number and area of vent holes in the mold, the accuracy of the joint part of the mold, etc.,
In actual molding, it is preferable to confirm the optimum pressure for each device by trial. At the time of molding, required amount of resin beads A and B are transferred from the storage hoppers 15 and 16 to the pressure hoppers 1 and 2 and stored therein.

First, pre-blowing is performed prior to filling. Next, the shutter 12 and the resin bead charging hole 7 are opened, and a required amount of the resin beads A is charged from the pressure hopper 1 into the mold 11 through the resin charging pipe 3 with the pressure applied to the hopper 1. The flow rate of the resin beads A can be adjusted by the pressure applied to the pressure hopper 1, the opening time of the shutter 12, and the like. It is preferable to use a slide type rotary shutter as the shutter 12 because the flow rate can be easily adjusted. If the amount of resin beads A is extremely small, pressurizing hopper 1
It is advisable to adjust the charging time by lowering the pressure applied to the resin bead A to the flow limit. The injected resin beads A are accumulated around the resin bead injection hole 7 in the mold.

When the injection of the required amount of resin beads A is completed, the piston valve 20a is opened with the shutter 12 kept open.
Is operated to close the resin bead charging hole 7 to stop the supply of the resin beads A and at the same time to open the blow air introducing port 9. Compressed gas is fed from the blow air introduction port 9, the resin beads A remaining in the resin feeding pipe 3 are blown back to the pressure hopper 1, and the shutter 12 is closed. Further, the empty air valve 14 is opened at the same time when the piston valve 20a is operated, and the mold 1
A compressed gas is jetted into the inside 1, and the resin beads A previously charged are collected and held at the end portion on the resin bead charging hole 7 side by the pressure of the gas. Since the compressed air passes through the resin bead layer and flows out from the vent hole and the fitting gap, it is considered that the resin bead A is pressed and held against the wall surface or one end of the mold by the flow of this gas. Compressed gas usually has an original pressure of 0.3
Although it is set to 0.5 MPa, it is necessary to adjust the pressure loss of the pipe to the mold and the number of vent holes of the mold.

Next, at the same time as closing the empty air valve 14, the resin bead charging hole 8 and the shutter 13 are opened, and the resin bead B is charged from the pressure hopper 2 through the resin charging pipe 4 into the mold 11 to load the resin bead A. Fix it. Actually, it is considered that the injection of the resin beads B starts after the pressures in the mold 11 and the raw material feeding header 19 decrease after closing the empty air valve 14 and become lower than the pressure in the hopper 2. The original pressure of the resin beads B is preferably about 0.1 to 0.2 MPa. This is because if the pressure is too high, the density of the resin beads B becomes too high (overfilling), and if it is too low, the filling tends to be insufficient and a hollow portion tends to be formed in the molded product. Since the resin beads A previously charged are held at one end by the gas flow in the mold 11, they are not mixed with the resin beads B, and the resin beads A and the resin beads B are substantially mixed. It is filled as it is. After charging the required amount of the resin beads B, the piston valve 20b is operated with the shutter 13 kept open to close the resin bead charging hole 8 and at the same time open the blow air introducing port 10. The resin beads B remaining in the resin feeding pipe 4 are blown back from the blow air introduction port 10 to the pressure hopper 2.

By repeating the above operation, various kinds of resin beads can be filled. Although only two types of resin beads are used in this embodiment, it is also possible to integrally form using three or more types of resin beads. When the divided injection of the resin beads A and B is completed in this way, steam is introduced from the vent hole of the mold 11 and the beads are heated and fused to each other. Since the resin beads are filled layer by layer, the foam is divided into two layers and integrally fused. The molded product 21 shown in FIG. 2 is an example of an embodiment of a multilayer foam molded product composed of a portion 22 made of resin beads A and a portion 23 made of resin beads B.

Next, the method for molding the multi-layer foam of the second invention will be specifically described. First, fully close the mold 11,
Open the empty air valve 14 and pass the filler 6 through the mold 11
A gas is ejected at a predetermined pressure inside. The source pressure of the supply gas is preferably about 0.3 to 0.5 MPa. Next, preferably with the gas being blown into the mold 11,
A required amount of resin beads A is charged into the mold 11 from the pressure hopper 1. The pressure in the mold is estimated to be 0.01 MPa or less. The injected resin beads A collect at the end portion on the resin bead injection hole 7 side and near the wall surface of the mold due to the gas flow in the mold described above. The pressure of the hopper 1 needs to be determined in consideration of the height h of the covering portion. When it is desired to increase the height h of the covering portion, an empirical method has been found to increase the pressure of empty air in the mold or lower the pressure of the hopper 1 to the pressure in the mold and the equilibrium limit pressure. Was issued. Even during the injection of the resin beads A, the empty air valve 14 is opened and the gas is jetted into the mold to maintain the gas flow from the center of the mold to the wall surface direction. After the resin beads A have been charged, the piston valve 20a is operated with the shutter 12 open,
The resin bead charging hole 7 is closed to stop the supply of the resin beads A, and at the same time, the blow air introducing port 10 is opened. Compressed gas is fed from the blow air introduction port 10 to blow back the resin beads A remaining in the resin feeding pipe 3. Next, the empty air valve 14 is closed, and at the same time, the resin beads B are charged under pressure while the gas flow remains in the mold 11, and the resin beads A previously charged are filled with the resin beads B. Fixed by. Prior to the introduction of the resin beads B, the mold is opened as needed to facilitate the introduction. The original pressure of the resin beads B is larger than the pressure applied to the hopper 1,
About 0.2 to 0.25 MPa is preferable. The reason is the same as that of the first invention. When air pockets due to gas are generated on the side where the resin beads A are charged in the mold 11, the resin beads A are additionally filled by the resin bead charging hole 7.

After the divided injection of the resin beads A and B is completed in this manner, steam is introduced from the vent hole of the mold 11 to heat the beads and fuse them to each other. The foamed molded product 31 including the portion 32 made of the resin beads A and the portion 33 made of the resin beads B is molded.

As the resin beads, those having a specific gravity of 0.2 to 0.005 which are obtained by pre-expanding a foaming thermoplastic resin such as polystyrene or polyethylene are usually used. Further, the divided shape of the plurality of types of resin beads A, B, etc. in the foamed molded product 21 in the first invention can be changed by changing the positions and numbers of the resin charging holes 7, 8, and the pressures of the pressurizing hoppers 1, 2. It can be changed, and a predetermined division pattern can be configured in the vertical and horizontal directions. The same applies to the second invention.

According to a third aspect of the present invention, there is provided a multi-layer foam molding device.
It has a plurality of pressurizing hoppers, and a foam molding die having resin bead charging holes connected to the pressurizing hoppers. This device is a conventional single-layer foam molding device, in which a plurality of resin bead charging holes are provided in a mold, and a plurality of pressure hoppers are provided between the hopper for storing resin beads and the resin bead charging hole of the mold. It can be easily obtained by connecting. Therefore, the existing equipment can be used, and it is not necessary to manufacture a completely new one. Furthermore, it can also be used as a commonly used single-layer foam molding device.

[0021]

EXAMPLES The method for molding the multilayer foam of the second invention will be described in detail with reference to Examples. The molding machine used in this example is almost the same as that shown in FIG. The raw material used was polystyrene for foam molding (ESC180 (g /
1) and HDM200 (g / l) orange: manufactured by Sekisui Plastics Co., Ltd., and used as a mold for polystyrene foam molding to form a packing cushioning material for home electric televisions by the method for molding a multilayer foam of the second invention. Manufactured. The manufacturing process of this embodiment will be described below with reference to FIG.

First, the mold 11 is fully closed and the original pressure is 0.4MP.
After blowing the compressed air of a for 2 seconds, the resin beads A of the pre-foamed raw material were put into the mold for 0.8 seconds from the hopper pressurized to 0.06 MPa while ejecting the compressed air.
After the injection of the resin beads A is completed, the blowback of the resin beads A remaining in the resin injection pipe 3 is changed to 0.6MPa.
It was performed for 3 seconds with the air of a. Next, the empty air valve 14 was closed to stop the ejection of compressed air, and at the same time, the resin beads B were charged into the mold for 3.5 seconds from the hopper pressurized to 0.2 MPa. After the addition of the resin beads B was completed, the resin beads B remaining in the resin supply pipe 4 were blown back for 2.0 seconds with air having an original pressure of 0.6 MPa. Further, the empty air valve 14 was opened again with the shutter 13 kept open, and the raw material charging header 19 was cleaned for 2.0 seconds. Then, steam heating was performed by a commonly used method, cooling was performed, and foam molding was completed. The cycle of the manufacturing process of this example was 350 seconds, and the total heating time was 21.0 seconds.
In the foamed molded product obtained in this example, the low expansion ratio resin on the outside and the high expansion ratio resin on the inside were separated by a clear boundary line, and it was the most suitable as a cushioning material for packaging for home electric televisions. .

[0023]

In the method for molding a multilayer foam of the present invention, a structure unique to a foam molding mold having a large number of small vent holes and a gas flow in the mold based on the structure are used, and a plurality of foam molds are used. Since the required amount of resin beads is sent into the mold using the pressure hopper, different types of resin beads are not agitated by air and mixed, and the foamed molded product has a clear boundary line between multiple types of resin. Can be obtained. Further, a required amount of resin beads can be charged into the mold, and the mixing ratio and mixing amount of a plurality of types of resin beads can be manipulated as desired. Therefore, it becomes possible to use the high-expanded beads and the recycled beads without anxiety, and it is possible to produce a lightweight multi-layer expanded molded article having a low raw material cost with high production efficiency. Furthermore, the molding apparatus used for carrying out the method of the present invention is easy to operate, can produce a normal single-layer foam, and uses most of the normally used foam molding apparatus. Is not expensive.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of a foam molding apparatus used for carrying out the present invention.

FIG. 2 is a foam-molded article molded according to the first invention.

FIG. 3 is a cross-sectional view of a foam molded product molded according to the second invention.

[Explanation of symbols]

1, 2: Pressurizing hopper 3, 4: Resin injection pipe 5,
6: Filler 7, 8: Resin bead charging hole 9, 10: Blow air inlet 11: Mold 12, 13: Shutter 14: Empty air valve 15, 16: Storage hopper 17, 18: Raw material supply valve 19: Raw material feeding header 20a, b: Piston valve 21: Foam molded article molded by the first invention 2
2: Low-magnification foamed part 23: High-magnification foamed part 31: Foam-molded article molded by the second invention 32: Low-magnification foamed part 33: High-magnification foamed part

Claims (3)

(57) [Claims] 1. A plurality of pressure hoppers 1, 2, and a plurality of resin bead charging holes 7 connected to the respective pressure hoppers.
Using a foam molding apparatus including a mold 11 having a mold 8, a pressure type hopper 1 for storing the resin beads A is used to apply a required amount of resin beads A to a metal mold with pressure applied to the pressure type hopper 1. A pressure type that is charged into the mold, and pressurized gas is fed into the mold from the wall surface of the unfilled part in the mold, and then the feeding of pressurized gas is stopped and at the same time the resin beads B are stored. With the pressure applied to the hopper 2, a required amount of resin beads B is charged into the mold, and the above operation is repeated to charge a predetermined plurality of resin beads into the mold, and then the inside of the mold is filled. A method for molding a multi-layer foam, which comprises heating to fuse the filled resin beads to each other. 2. A foam molding apparatus comprising two pressurizing hoppers 1 and 2 and a mold 11 having resin bead charging holes 7 and 8 connected to the pressurizing hoppers. After the pressurized gas is fed into the mold, a predetermined pressure is applied to the pressurizing hopper 1 that stores the resin beads A, and the required amount of the resin beads A is introduced from the resin bead charging hole 7.
Then, the feeding of the pressurized gas is stopped, and at the same time, a predetermined pressure is applied to the pressurizing hopper 2 to feed the required amount of the resin beads B from the resin bead feeding hole 8 to obtain the resin beads. A method for molding a two-layer foam, characterized in that after the addition of B is completed, the inside of the mold is heated to fuse the filled resin beads to each other. 3. A multi-layer foam molding apparatus comprising a plurality of pressure hoppers and a foam molding die having a plurality of resin bead charging holes connected to the respective pressure hoppers.