JPH0825230B2 - Hollow molded article in which foam cells on the inner peripheral surface are ruptured and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hollow molded article having a ruptured foam cell in at least a part of an inner peripheral surface thereof and a method for manufacturing the hollow molded article, which is particularly used as an air intake duct having a sound absorbing effect. The present invention relates to a hollow molded article suitable for, and a method for producing the same.

2. Description of the Related Art Conventionally, an intake duct for introducing outside air into an automobile engine has been used. When outside air is sucked through the intake duct, intake noise is generated, which causes noise. Therefore, a muffler is used to absorb the intake sound of the intake duct and reduce the noise level.
A typical example of a conventional sound absorber is shown in FIG. 4, and it has a roughly double pipe structure, and a plurality of through holes are formed in the circumferential direction of the intake duct 18 to form an inside of the outer pipe 19. It is in communication. However, since such a silencer has a relatively large structure and its structure is a double pipe structure, it is relatively difficult to manufacture, and therefore the cost is high. However, there are drawbacks such as occupying a relatively large space, requiring a lot of man-hours for attaching the silencer to the intake duct, and lacking reliability.

The present invention has been made in view of the above points, eliminates the drawbacks of the prior art as described above, and at least an inner peripheral surface suitable for use as a duct having a sound deadening or sound absorbing effect. An object of the present invention is to provide a hollow molded article having a partially ruptured foam cell and a method for producing the same.

Structure According to the present invention, there is provided a hollow molded article that comprises foam cells that are at least partially ruptured on the inner peripheral surface. Such hollow moldings have a plurality of small cavities defined by ruptured foam cells on the inner peripheral surface thereof, and these cavities cause noise that may generate gas passing through the hollow moldings. Has the effect of significantly reducing the level of noise generated by absorbing or absorbing sound. Therefore, such a hollow molded article can be used, for example, as a part of an intake duct of an automobile engine. The hollow molded article of the present invention is not limited to the intake duct of the engine, and can be used at any other place where gas may pass therethrough and generate noise, so that the hollow molded article exhibits a sound absorbing or absorbing effect. It is possible.

The hollow molded article of the present invention can be made of not only a plastic such as a thermoplastic resin and other resins, but also an elastomer and other arbitrary substances. In particular, forming foam cells on at least a part of the inner peripheral surface of the hollow molded article,
Since it is characterized in that at least a part of the foam cells is ruptured, it is desirable that the material of the hollow molded article at least partially contain a foaming agent. For example, when a hollow molded article is molded from a parison by blow molding, a foaming agent is contained on at least the inner peripheral surface of the parison, and the foaming agent is foamed to form a foam cell, at least a part of which is formed. It is better to burst the foam cells.

According to the present invention, there is provided a method for producing a hollow molded article having a ruptured foam cell on at least a part of its inner peripheral surface.
In accordance with the principles of the method of the present invention, a parison is formed that at least partially contains a blowing agent, and the parison is housed in a cavity defined by mold assembly, with a pressure differential between the interior and exterior of the parison. By generating and pressing the parison against the wall surface of the cavity to determine the outer shape of the parison, further reducing the pressure inside the parison, at least a part of the foam cells formed in at least a part of the inner peripheral surface of the parison Explode. After that, when the parison is cured and preferably has a self-shape retention ability, the mold is opened and the molded article is taken out from the parison.

As a mold, a pair of half molds is usually used, and a cavity is formed by matching the pair of half molds. When matching a pair of these half molds,
The parison may be stored only in the cavity, or at least a part of the parison may protrude from the cavity and be sandwiched between the pair of mold halves. Furthermore, when the parison is housed in the cavity of the mold and a pressure difference is generated between the inside and outside of the parison to press the parison against the wall surface of the cavity to determine the external shape of the parison, a predetermined pressure is applied within the parison in a short time. It is advisable to adopt a configuration in which the gas is introduced and the gas inside the cavity is exhausted outside the parison to generate pressure inside and outside the parison to press the parison against the wall surface of the cavity.
Further, after the parison is housed in the cavity of the mold, the mold is cooled at a predetermined timing to cool the outer surface of the parison pressed against the wall surface of the cavity to harden the outer surface of the parison. It is preferable to form a skin layer that does not substantially foam.

That is, according to one specific embodiment of the method of the present invention, (a) a step of forming a parison containing a foaming agent at least along the inner peripheral surface, (b) a mold is clamped to form the parison. Inserting into the cavity of the mold, (c) generating a pressure difference between the inside and outside of the parison to press the parison against the wall surface of the cavity to define an external shape, (d) the inner circumference of the parison A step of foaming the foaming agent in at least a part of the above to form a foamed cell and rupturing at least a part of the foamed cell. That is, according to the method of the present invention, the outside of the parison is molded by the cavity of the mold,
A preferred example is characterized in that the inside of the parison is evacuated to reduce the pressure, at which time the foam cells on the inner peripheral surface of the parison are at least partially ruptured.

Examples Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is constructed according to one embodiment of the present invention, and a hollow molded article having a foam cell at least partially ruptured in at least a part of an inner peripheral surface of the present invention is manufactured by a blow molding method. The manufacturing apparatus which does is shown. As shown in the figure, a screw 1 communicating with a hopper (not shown) for containing the material for molding the hollow molded article of the present invention is provided, and the screw 1 is rotationally driven in a predetermined direction. , The material is supplied into the nozzle or the supply passage 3 defined in the die head 2. The material in this case may be any material capable of molding a desired hollow molded article, for example, a thermoplastic resin such as polyethylene or polystyrene, other plastic material or elastomer, and any other material. Can be any desired material. Further, in the illustrated example, an appropriate amount of foaming agent is mixed in this material.

The foaming agent is uniformly mixed in the material supplied to the supply passage 3 of the head 2, and the foaming agent is poured out from the supply port 4 of the die head 2 to form a cylindrical parison 9. The parison 9 in this case is formed of a material in which the foaming agent is uniformly mixed, but as another embodiment,
It is also possible that the parison 9 has a multi-layered structure of two or more layers and at least the innermost layer thereof contains a foaming agent.

A through hole 2a is formed in the center of the die head 2, and the through hole 2a can communicate with the compressor 6 via the heater (or temperature controller) 17 and also with the vacuum pump 12. Therefore, the compressed air supplied from the compressor 6 can be heated to a predetermined temperature by the heater 17 and supplied to the through hole 2a, and can also be exhausted from the through hole 2a by the vacuum pump 12.

A die 5 is arranged below the die head 2,
The mold 5 can be formed by, for example, matching a pair of half molds to form a cavity therebetween. The walls of this cavity are defined by the mating surfaces of the respective halves and the parison is pressed into this cavity to define the external shape of the molded part. The mold 5 can be a split mold of three or more. Incidentally, FIG. 1 shows a state where these split molds are matched with each other.
In this embodiment, an appropriate number of suction holes 5a are formed in the die 5. In the illustrated example, a plurality of suction holes 5a are formed, one end of each of which is in communication with the cavity of the mold 5 and the other end is in communication with the vacuum pump 12.
Therefore, when the vacuum pump 12 is operated, the gas in the cavity is exhausted and the pressure in the cavity is lowered, that is, the pressure becomes negative with respect to the atmosphere. Therefore, the parison 9 stored in the cavity of the mold 5 is adsorbed on the wall surface of the cavity.

Further, an appropriate number of cooling chambers 11a are formed inside the mold 5, and these cooling chambers 11a are communicated with the chiller 10 via a pipe line 11b. Therefore, when the chiller 10 is operated, the cooling medium passes through the cooling chamber 11a, thereby cooling the required part of the mold 5 and the parison 9 housed in the mold 5. Especially, since the outer peripheral surface of the parison 9 is in contact with the cavity, the outer peripheral surface portion of the parison 9 is cooled.

A pin 7 communicating with the through hole 2a is provided at the lower end of the die head 2, and the pin 7 is inside the parison 9 housed in the cavity of the mold 5 in a state where the mold 5 is matched. The length is set so that the tip part is located in the. Therefore, as shown in FIG. 1, with the parison 9 housed inside the cavity of the mold 5, the tip of the pin 7 communicates with the inside of the parison 9, and therefore the parison housed inside the cavity. The inside of 9 communicates with the through hole 2a through the pin 7. Further, a controller 20 for controlling the entire operation of the blow molding machine is provided, and the controller 20 includes the screw 1, the compressor 6, the vacuum pump 12, and the mold 5.
(When the molds are automatically matched and released), they are operatively connected to the vacuum pump 12, the chiller 10 and the like, and the respective devices are controlled to operate according to a required program. Such a controller 20 can be configured using, for example, a microcomputer or a CPU. Note that FIG. 2 shows the same blow molding machine as in FIG. 1, but shows different steps in blow molding, and therefore a part of it is omitted.

Next, with reference to FIG. 1 and FIG. 2, a manufacturing method for molding a hollow molded article having foam cells at least partially ruptured on at least a part of an inner peripheral surface thereof by using the blow molding machine will be described. I will explain it. As described above, in the present embodiment, the screw 1 is rotationally driven to supply a material such as a thermoplastic resin, in which an appropriate amount of the foaming agent is uniformly mixed, to the supply passage 3 of the die head 2 and the supply port 4 And parison 9 is formed. Therefore, in the illustrated example, the parison 9 contains a foaming agent which is distributed substantially uniformly throughout. When the parison 9 is poured out from the die head 2 by a predetermined amount, the mold 5 is matched and the parison 9 is housed in the cavity defined in the mold 5. In the illustrated example, the mold 5 is arranged vertically, but the mold 5 is arranged other than vertically so that the parison 9 is first supplied onto one of the split molds, and then the remaining split molds are formed. In addition, the parison 9 may be housed inside the cavity.

In the state where the die 5 is fitted and clamped, the tip of the blow pin 7 extending from the lower end of the die head 2 is located inside the parison 9, so that the interior of the parison 9 penetrates the die head 2. It is maintained in communication with the hole 2a. After the mold 5 is clamped, a relatively low pressure gas (for example, 1 to 3 kg) of a relatively low pressure is discharged from the compressor 6 through the blow pin 7 for a predetermined time (for example, 30 seconds or less). It is blown inside. This state is shown by the dotted line in the graph of FIG. That is, after mold clamping,
After time t _1, the pressure inside the parison 9 is increased from atmospheric pressure to 1.2 times the pressure. In this case, the heater
It is preferable to operate 17 to heat the compressed air supplied from the compressor 6 into the parison 9 to a predetermined temperature. The predetermined temperature may be set to a temperature suitable for the compressed air supplied into the parison 9 to foam the foaming agent contained in the parison 9.

On the other hand, the compressed air heated as desired is supplied to the inside of the parison 9, and at the same time, the vacuum pump 12 is operated to evacuate the cavity of the mold 5 through the suction hole 5a. The gap 1 between and is evacuated to a negative pressure state (for example, 0.3 kg / cm ² or less). This state is shown in the graph of Fig. 5, and the pressure inside the cavity outside the parison 9 is 0.3 kg / cm ₂ t ₂ hours after mold clamping.
It is set to the negative pressure state of ² . In this way, a pressure difference (that is, a pressure in which the inside is higher in absolute value than the outside) is set inside and outside the parison 9 housed in the cavity inside the mold 5, so that the parison 9 is pressed against the wall surface of the cavity, and The external shape of the parison 9 will be defined. In this case, the step of supplying the compressed air to the inside of the parison and the step of generating the negative pressure outside the parison do not necessarily have to be performed at the same time, and they can be performed at different times in time. Further, it is also possible to press the parison 9 against the wall surface of the cavity by only one of the steps to define the external shape.

As described above, in the illustrated preferred embodiment, the air blow and the suction are performed at the same time, whereby the parison 9 is pressed against the wall surface of the cavity of the mold 5, so that the shape conforming to the wall surface is formed. Defined. Further, in the illustrated preferred embodiment, the cooling chamber 11a is formed inside the mold 5, and the cooling medium is circulated in the cooling chamber 11a, so that the mold 5 and especially the wall surface of the cavity have a predetermined shape. It is maintained at a low temperature. Therefore, when the parison 9 is pressed against and brought into contact with the wall surface of the cavity as described above, the outer peripheral surface of the cavity 9 is cooled to a predetermined temperature and the surface layer on the outer peripheral surface of the parison is cured to form a skin layer. It
As a result, the foaming agent contained in the surface layer on the outer peripheral surface of the parison 9 is in a state where its foaming ability is substantially blocked, and in the skin layer, foaming is substantially prohibited.

As described above, the compressed air having a relatively low pressure is blown for a predetermined time, the compressor 6 is stopped, and then the vacuum pump 12 is operated at a predetermined timing as shown in FIG. The interior 8 of the parison 9 is exhausted via the blow pin 7 and the pressure inside the parison 9 is reduced. In this embodiment, as shown in FIG. 5, the inside 8 of the parison 9 is in a negative pressure state, and after t ₃ hours,
The pressure is set to about 0.5 kg / cm ² . It is important to note that, in this case, the pressure in the gap 13 between the outside of the parison 9 and the inside of the cavity is still maintained at a low pressure state, which is lower than the pressure inside the parison 9. To prevent the parison 9 from coming off the cavity wall. In the illustrated example, the negative pressure state (0.3 kg / cm ² ) set for t ₂ hours is maintained as it is. By maintaining the pressure difference between the inside and the outside of the parison 9 in this way, it is possible to prevent the external shape of the parison 9 from being deformed.

In this way, when the pressure inside the parison 9 is reduced,
The foaming agent on the inner peripheral surface of the parison 9 expands to form foamed cells 14, and these foamed cells 14 are overexpanded to form foamed cells.
14 bursts. As a result, a large number of small cavities are formed on the inner peripheral surface of the parison 9 due to the ruptured foam cells. In this case, it is not necessary that all of the foam cells formed on the inner peripheral surface of the parison 9 burst, but as many foam cells as possible burst and as many cavity portions are formed. It is desirable to be done. A partial cross-sectional view of the hollow molded product thus formed is shown in FIG. That is, as shown in FIG.
The ruptured foam cells 14 'are arranged along the inner peripheral surface of and the skin layer 16 is formed along the outer peripheral surface thereof. It is desirable that the skin layer 16 does not contain foam cells, but even when it contains foam cells, it is desirable that the degree of foaming is low and extremely small. That is, it is sufficient that the skin layer 16 has a minimum continuous composition and that the hollow molded article to be molded can keep the inside and the outside from communicating with each other by the skin layer 16. However, when the hollow molded article to be molded is required to have rigidity and the like, it is desirable that foam cells are not formed in the skin layer 16 or that the degree thereof is extremely small even if formed. It is also possible to have one or more intermediate layers between the skin layer 16 and the ruptured foam cells 14 ', one or more of which being unruptured. It is possible to contain foam cells. In the case of such a configuration,
The ruptured foam cells 14 'can exert a sound absorbing or silencing effect, and the intermediate layer including the foam cells can exert a heat retaining or heat insulating effect.

Then, as shown in FIG. 5, the interior 8 of the parison 9 is opened to the atmosphere at time t ₄ , so that its pressure is increased at time t ₅
At atmospheric pressure is restored. On the other hand, the pressure outside the parison 9, that is, the pressure in the gap between the parison 9 and the cavity is released to the atmosphere at time t ₅ . Then, at time t ₆ , the mold 5 is opened and the molded product is molded into the mold 5.
Take out from.

As the foaming agent usable in the present invention, there are a volatile foaming agent and a decomposable foaming agent, and among the volatile foaming agents, carbon dioxide gas, propane, Freon 12, butane, Freon 11, Freon. Gas such as 113, and isopentane,
There are volatile liquids such as ether, n-pentane, petroleum ether, acetone, hexane, benzene and heptane. On the other hand, as decomposable foaming agents, there are inorganic foaming agents such as ammonium bicarbonate, sodium bicarbonate, sodium nitrite, and ammonium chloride, and other dinitrosopentamethylenetetraamine, asodicarbonamide, P-toluenesulfonylhydrazide, P, There are organic foaming agents such as P'-oxybisbenzenesulfonyl hydride, radig, trihydrazinotriazine, and hydrazodicarbonamide. Furthermore, examples of combinations of molding materials, foaming agents and molding conditions in the preferred embodiments applicable to the present invention are as follows.

In Examples 1 and 2 shown in the above table, the parison has a single layer, but in Examples 3 and 4, it has a two-layer structure of an outer layer and an inner layer. In Examples 3 and 4, the foaming agent can be mixed only with the resin for the inner layer. In this case, two cylindrical supply passages are provided in the die head 2 shown in FIGS. 1 and 2, and only the resin material is supplied to the outer cylindrical passage, while the inner cylindrical passage is provided. By supplying a resin material mixed with a foaming agent to the passage, it is possible to easily form a parison having a two-layer structure and containing the foaming agent only in the inner layer.

Effect As described above in detail, according to the present invention, there is provided a hollow molded article having at least a partially ruptured foam cell on at least a part of the inner peripheral surface thereof, which is used for a gas passage duct. In this case, it is possible to absorb or muffle the noise generated by the passing gas, which is particularly effective as a measure against noise. Further, the hollow molded article having the ruptured foam cells of the present invention has a simple structure, is easy to manufacture and is low in cost, and has an integral structure, so that it has high strength and high reliability. Further, the overall size is small, the installation space is minimized, and the flexibility is made by selecting materials appropriately, by selecting the wall thickness, or by providing an appropriate bellows structure. It is possible to impart the property, and it is possible to easily improve the attachment performance. Further, in the method of the present invention, it is only necessary to maintain the inner and outer pressures of the parison at an appropriate level and lower the pressure inside the parison to rupture the foam cells. It can be carried out by appropriately setting the operating conditions with a slight change, and its practical value is particularly high. Further, one embodiment of the apparatus used in the present invention is characterized in that the pressure inside the cavity is lowered to press the parison against the cavity wall surface to form the shape outside the parison,
It is possible to form the external shape of the parison evenly and accurately with the detailed shape.

The specific embodiments of the present invention have been described above in detail, but the present invention should not be limited to these specific examples, and various modifications can be made without departing from the technical scope of the present invention. Of course, it is possible.

[Brief description of drawings]

1 and 2 are schematic diagrams showing an apparatus for carrying out one embodiment of the method of the present invention constructed based on one embodiment of the present invention, and FIG. 3 is one embodiment of the present invention. FIG. 4 is a partial cross-sectional schematic view showing a part of a hollow molded product having a foam cell which is at least partially ruptured in at least a part on an inner peripheral surface formed according to FIG. FIG. 5 is a schematic perspective view shown, and FIG. 5 is a graph useful for explaining a process in one embodiment of the present invention. (Explanation of symbols) 2: Dice head 5: Mold 7: Blow pin 9: Parison

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Claims (15)

[Claims] 1. A hollow molded article, wherein foamed cells are formed on at least a part of the inner circumference of the hollow molded article and at least a part of the foamed cells is ruptured. 2. The hollow molded article according to claim 1, wherein the hollow molded article is formed of a plastic material, and a predetermined amount of a foaming agent is mixed with the plastic material. 3. The hollow molded product according to claim 1 or 2, wherein the hollow molded product is an intake duct having a sound absorbing function. 4. A method for producing a hollow molded article, comprising: (a) forming a parison containing a foaming agent along at least a part of an inner peripheral surface; (b) clamping the mold to form the parison. At least partially accommodating in the cavity of the mold, (c) a pressure difference is generated between the inside and outside of the parison contained in the cavity to press the parison against the wall surface of the cavity to define an external shape. And (d) rupturing at least a part of the foam cells formed from the foaming agent in at least a part of the inner circumference of the parison, The method for producing a hollow molded article, comprising: . 5. The method according to claim 4, wherein in step (a), the parison is formed by extracting a plastic material mixed with a foaming agent from a nozzle. 6. The method according to claim 4 or 5, wherein in the step (c), the gas is introduced into the parison at a relatively low pressure and the pressure in the cavity is simultaneously provided outside the parison. The pressure is lowered to press the parison against the wall surface of the cavity. 7. The method according to claim 4, wherein in step (c), the pressure in the parison is atmospheric pressure or a positive pressure higher than atmospheric pressure. A method of producing a negative pressure inside the cavity outside the parison. 8. A method according to any one of claims 4 to 7, characterized in that in the step (c), the gas is introduced into the parison rapidly. . 9. The gas inside the parison according to any one of claims 4 to 8 is exhausted when the pressure inside the parison is reduced in the step (d). And maintaining the pressure inside the parison higher than the pressure inside the cavity outside the parison. 10. The pressure according to claim 9, wherein the pressure inside the parison is first exhausted by exhausting from the inside of the parison.
A negative pressure state, wherein the first negative pressure state is lower than the second negative pressure state which is the pressure inside the cavity outside the parison. 11. The parison according to any one of claims 4 to 10 which cools a predetermined part of the mold at a predetermined timing and contacts the wall surface of the cavity. A method of curing an outer peripheral surface to substantially prevent the foam cells from bursting on the outer peripheral surface. 12. The method according to any one of claims 4 to 11, wherein in the step (a),
A method characterized in that the temperature of the parison is raised to a temperature close to the temperature at which the foam cells are ruptured by the foaming pressure of the foaming agent, and the foam cells on the inner peripheral surface of the parison are set in a more easily rupturable state. 13. The foam cell at the inner periphery of the parison is further ruptured by using a resin having a small melt tension as a plastic material according to any one of claims 4 to 12. A method characterized by setting it in an easy-to-use state. 14. The method according to any one of claims 4 to 13, wherein in the step (c),
A method comprising heating the gas introduced into the parison to a predetermined temperature and introducing the gas into the parison. 15. The method according to any one of claims 4 to 14, wherein in the step (a),
The method, wherein the parison has at least a two-layer structure, and at least the innermost layer contains a foaming agent.