JPH10156856A - Method for molding of synthetic resin molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding a synthetic resin molding wherein since highly expensive equipment is not required, cost reduction of a product can be planned, and a molding cycle can be also shortened. SOLUTION: After casting or charging molten materials (a) into a cavity of a mold 1, and a suitable amount of water (b) is casted inside the molten materials (a) and blocked. The water (b) is vaporized with heat of the molten materials (a), and sudden rise in pressure following that is utilized for molding pressure to carry out molding. After molding, steam is released from inside the molded product to lower pressure inside the molded product and that is released from the mold. A foaming agent (c) is added to the suitable amount of water (b) which is casted into the molten materials (a) to be blocked, the foaming agent (c) is foamed following vaporization of water with heat of the molten materials (a), and rise in pressure owing to vaporization is supplemented by this foaming.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for molding a synthetic resin molded article. More specifically, the present invention relates to a molding method in which water is vaporized in a molten raw material and the generated pressure is used for molding.

[0002]

2. Description of the Related Art In molding a synthetic resin molded article, a molten material is injected into a cavity of a mold to form a molding base, and a pressurized gas is fed into the center of the molding base by a hollow needle, and the molding base is placed inside. A method of obtaining a hollow product by discharging gas from the inside after pressurizing and expanding the material to match the cavity is described in Japanese Patent No. 10755.
No. 88 is known.

[0003]

However, in this method, the molten raw material (molding base) injected into the cavity is brought into pressure contact with the cavity by a pressurized gas, so that the method includes a compressor capable of obtaining a high pressure necessary for molding. Thus, gas injection must be performed. For this reason, not only does the equipment cost increase and the cost of the product increases, but also molding takes several seconds or more, and it is necessary to set the raw material temperature high to compensate for the temperature decrease during this time. There is a problem that the molding cycle is extended and the production efficiency is reduced.

[0004] In order to solve the above problems, the present invention is to steam the water in the molten raw material to cause a rapid pressure rise, and to use this pressure rise as a molding pressure to form the raw material. As a result, the cost of the product can be reduced because expensive equipment is not required, and since the molding is completed instantly, there is no need to set the raw material temperature high, and the heat of the raw material is removed by steaming water. An object of the present invention is to provide a method of molding a synthetic resin molded article that can shorten a molding cycle and greatly contribute to increasing production capacity because the molded article is cooled.

[0005]

In order to solve the above problems, the present invention is characterized by employing the following method. (1) Inject or fill the molten material into the mold cavity
In the method for molding a synthetic resin molded article in which a molded article is obtained by charging and expanding a hollow molten raw material, after injecting or charging the molten raw material into the cavity, an appropriate amount of water is injected into the molten raw material. The water is turned into steam by the heat of the molten raw material, and the resulting rapid rise in pressure is used as the molding pressure to form the raw material. Release the pressure after lowering the pressure. (2) A foaming agent is added to an appropriate amount of water to be injected and sealed inside the molten raw material, and the foaming agent is foamed with the steaming of the water by the heat of the molten raw material. Let me supplement you.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for molding a synthetic resin molded product according to the present invention will be described below with reference to the drawings.

[0007] One of the molding methods to which the present invention is applied is a method in which an injection mechanism feeds polypropylene,
This is injection molding to obtain a product by injecting and filling ABS plastic, polystyrene, polycarbonate, vinyl chloride, and other synthetic resin raw materials that have been melt-plasticized. In this injection molding, as shown in FIGS. 1 to 3, the molten raw material a is injected into the cavity 2 of the mold 1 from the injection mechanism 3 through the sprue 4, the runner 5, and the gate 6.
In a state where a space 7 exists in a part of the opening 5, the on-off valve 8 of the gate 5 is closed as shown in FIG. 2 to prevent the molten raw material a from flowing back to the injection side. Then, a water injection needle 9 supported on the mold 1 so as to be able to advance and retreat is drawn out as shown in FIG. 1 and its tip is inserted into the inside of the melted raw material a injected into the cavity 2. And open 0,0 for 100 g of product weight.
22 to 0.53 cc of water b is injected as it is or in the form of a mist. The needle 9 for performing this injection is 1 in the figure.
Although only one needle is used, the number of injection needles 9 is increased to a plurality according to the area of the cavity 2 and arranged at a predetermined interval. Is injected so that steaming occurs on average in the entire large volume of the molten raw material, but the drawing of this embodiment is omitted. When the injection of the water b is completed, the on-off valve 11 is closed, the injection needle 9 is removed from the molten raw material, and the needle hole is closed. Then, the injected water b is 180 ~
The heat of vaporization is obtained from the molten raw material a having a high temperature of 240 ° C. to vaporize instantaneously.
° C, pressure = p, mass = w, molecular weight of water = 18,

[0008]

(Equation 1)

[0009] The volume determined by Equation 1 is, for example, 5 ml.
Considering that you keep it in the container of

[0010]

(Equation 2)

Accordingly, Table 1 shows the results obtained by calculating the pressure when changing the volume to be confined in the container by Equation 2 and creating a table.

[0012]

[Table 1]

However, the above numerical value of the pressure is a theoretical value when it is considered that the water vapor is sealed in the container. In practice, the conditions are different because the water vapor can be sealed in a fluid synthetic resin. Since the pressure is considered to be lower than the value, the pressure is compensated by increasing the amount of water vapor. This pressure is applied to the normal molding pressure 5 of the raw synthetic resin.
If the value is set to a value suitable for the raw material within 0 to 100 kg / cm ² , the molten raw material a injected into the cavity 2 is pressurized from the inside to the outside by an appropriate pressure.
And fills the cavity 2 by spreading to every corner of the cavity 2, and presses each part of the raw material a against the wall of the cavity 2 with an average force to improve the mold transferability, and water is turned into steam. Then, the molded product cools by taking heat from the molten raw material and acts to promote its hardening. Therefore, an injection molded product having high fidelity such as shape and texture to the cavity 2 and having excellent uniform accuracy and quality as a whole is efficiently molded, and the product molded as described above Since the inside of the hollow portion is formed into a hollow shape as shown in FIG. 2 by water vapor, not only the material of this hollow portion is saved, but also the hollow portion reduces the weight of the product, heat insulation, sound insulation, and the like.
Contributes to improvement of cushioning properties.

In the present invention, if high-pressure steam is left in the internal cavity 12 even after the product is formed in the cavity 2 as described above, the mold 1 is opened to release the product. Since the product may swell and deform due to the internal water vapor pressure, the air release pipe 13 is branched from the water supply pipe 10, and an on-off valve 14 is provided in the branch pipe 13 and placed. Detection is performed at a set time or at a molding pressure set by the pressure detecting means. Upon completion of molding, the injection needle 9 is inserted into the molten raw material, the on-off valve 14 is opened, and the water vapor in the cavity 12 is released. By doing so, it is possible to perform injection molding without causing deformation of the product due to opening of the mold at the time of demolding.

Further, as described above, if the molten raw material is molded by utilizing the pressure of the steam and the steam is released after the molding, a foaming agent is mixed into the raw material and the product is made porous by foaming. In the case of a foamed synthetic resin molded article, foaming of the raw material is suppressed by the steam pressure during molding, and the outer shape is formed exclusively by the unfoamed skin layer. When the pressure of 12 is reduced, the foaming of the molten raw material a is promoted along with this, so that the raw material expands inside by foaming to form a product in which the volume of the cavity 12 is reduced. A product that fills the cavity 12 with a foam layer can be formed by setting the height higher.

The opening / closing valve 14 of the air release pipe 13 for releasing the water vapor formed as described above after the formation is provided with a pressure-sensitive sensor 15 at an appropriate position in the cavity 2. When pressurization is achieved by the arrival of pressure, the end of forming can be sensed, and a valve that opens and closes the on-off valve 14 to release water vapor can be used. When this is done, any device that can automatically detect this and release the residual water vapor within cavity 12 can be used. When the water injection needle 9 is used for discharging the water vapor, if it takes too much time to discharge the water, an air release pipe (not shown) provided with an open / close valve is provided separately from the injection needle 9, and this water discharge pipe allows the water vapor to be quickly discharged. Make sure to discharge.

In the injection molding, when a thin product is molded by a mold 1 having a shallow cavity 2 as shown in FIGS. 4 to 6, the shallow cavity 2 is passed through a runner 5 and a sprue 4 to form a well-known open / close nozzle (FIG. 4). (Omitted in the drawing). In the mold 1, the nozzle of the injection mechanism 3 is opened to inject the molten raw material a into the cavity 2 through the sprue 4 and the runner 5, and the raw material is injected while a space 7 exists in a part of the cavity 2. When stopped, the nozzle closes to prevent backflow of raw material to the injector. At this time, the water injection needle 9 supported in the mold 1 so as to be able to move forward and backward is inserted into the molten raw material in the sprue 4, and the on-off valve 11 provided in the water supply pipe 10 is opened, and 0.22 to 100 g of the product weight.
After injecting 0.53 cc of water b as it is or in the form of a mist, the on-off valve 11 is closed, the injection needle 9 is removed from the molten raw material a, and the needle hole is closed. Then, the water b takes heat from the molten raw material a at 180 to 240 ° C., instantaneously turns into steam in the raw material, and flows through the molten raw material in the runner 5 as shown in FIG. 50 to 10 which are required for molding in the raw material a in the cavity 2 after flowing into the raw material.
A pressure of 0 kg / cm ² is generated, and the molten raw material a is pressurized from the inside to the outside and spreads to every corner of the cavity 2 to fill the cavity 2, and each part is pressed against the wall of the cavity 2 on average to form a mold. In order to improve the transferability, water acts to remove heat from the molten raw material to turn it into steam, thereby cooling the molded article and promoting its hardening. Therefore, even in the case of a thin product, the fidelity to the shape and texture of the cavity 2 is high, and each part is formed efficiently with uniform accuracy and high quality. Are formed on average, contributing to material saving, product weight reduction, heat insulation, sound insulation, cushioning, and the like.

In this embodiment as well, when the molding of the raw material by the pressure of the steam is completed, the air discharging needle 16 supported on the portion corresponding to the cavity 2 of the mold 1 so as to be able to move forward and backward can be used.
2 is inserted into the molded article so as to pass through to the opening and closing valve 14 of the air release pipe 13 by a timer, a pressure detecting means, a pressure sensor and the like.
Is opened to release water vapor, and the product is demolded so that it does not remain in the cavity 12 so that the product is not deformed by the water vapor pressure even when the mold is opened. Accordingly, when the raw material is a foamed synthetic resin, the pressure inside the molded article is reduced by the release of the pressure steam from the cavity 12 to promote foaming.
2 can be formed, or a product in which the cavity 12 is filled with a foam layer.

As described above, when water b is injected into the molten raw material a in the sprue 4 and steam is allowed to flow into the molten raw material a in the cavity 2 via the molten raw material in the runner 5, When the runner 5 is cut off, the hole through which the water vapor has passed is exposed. Therefore, in the case of a product in which the presence of this hole is not allowed, the pressing piece 17 is movably provided at the end of the runner 5 (the cavity 2 side). Is positioned outside the runner 5 during molding, and is moved into the runner 5 as shown in FIG. 6 when the molding is completed, and the raw material in this portion is crushed. It will not be exposed to goods.

Another molding method which is the object of the present invention is a parison formed by injecting or extruding polypropylene, ABS resin, polystyrene, polycarbonate, vinyl chloride, or other synthetic resin materials melted and plasticized. Or by loading the molten material in the inner space where a plurality of extruded films are stacked into a mold cavity, sending a pressurized gas into the inner space between the parison or the film, and pressing against the cavity wall to produce a product. Is blow molding. This blow molding is performed by using a mold 1 as shown in FIGS.
The parison a is inserted into the cavity 2 as shown in FIG. Then, the water injection needle 9 supported by the mold 1 is inserted into the parison a, and the open / close valve 1 of the water supply pipe 10 connected thereto is inserted.
1 is opened and 0.27 to 0.36 cc of water b is injected into the parison a with a cavity volume of 1 cm ³ as it is or in a mist state, and the on-off valve 6 is closed. Then, the injected water b deprives the high-temperature parison a of vaporization heat and instantaneously turns into steam.
A pressure of ² cm ² was generated to press the parison a against the wall of the cavity 2 as shown in FIG. 8, and the parison a spread all over the cavity 2 and each part of the parison a was averaged to the wall of the cavity 2. Press transfer with force improves mold transferability. Therefore, a blow-molded product having a high degree of fidelity of the shape and texture with respect to the cavity 2 and excellent in uniform accuracy and quality in each part is efficiently formed. Then, the on-off valve 11 is opened by a timer, a pressure detecting means, a sensor, etc., to release the water vapor in the molded product. Also, the product can be formed by utilizing the steaming of water by the heat of the raw material, and the product can be prevented from being deformed at the time of demolding.

The method according to the present invention comprises the injection molding described above,
Water b injected and sealed into molten raw material a in blow molding
Further, when a foaming agent c, which evaporates and expands its volume when heated by the molten raw material a, is added, the volume expansion due to the vaporization of the water b is added to the volume expansion due to the vaporization of the foaming agent c to promote a rapid pressure rise. Will do. Therefore, it is preferable to add a foaming agent c to water since the effect of molding using a rapid pressure rise for molding pressure is promoted. As the foaming agent c, sodium bicarbonate, ammonium carbonate, and the like, The same effective agents can be used.

[0022]

【The invention's effect】

Advantageous Effects of Claim 1 (1) Water is injected and sealed into the molten raw material injected or charged into the cavity, and this water is steamed by the heat of the molten raw material to generate a rapid pressure rise in the raw material. The raw material is molded by using the pressure rise as the molding pressure, and when molding is completed, water vapor is discharged and the internal pressure is removed from the molded product, and the mold is released. The hollow molded article formed on average can be easily molded with high accuracy and quality. (2) Since it has a simple structure in which a means for injecting water into a molten material and a means for discharging water vapor from a molded article are simply added to an ordinary mold, the apparatus is installed at a low cost and the cost of the product can be reduced. It is valid. (3) Forming by water vaporization is instantaneous, and there is no need to raise the temperature of the raw material. In addition, since the water of the molten raw material deprives the heat of the water for vaporization, the cooling of the molded product is promoted. The cycle can be greatly reduced. (4) Since the pressure rise due to water vaporization is used for the molding pressure, the injection mechanism only needs to inject the molten raw material into the cavity, and the driving force of the injection mechanism is reduced. The foaming agent added to the water to be injected and sealed into the molten raw material is vaporized with the steaming of the water and supplements the rapid pressure rise in the raw material due to the steaming. The effect of forming by utilizing is improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which a molten raw material is injected into a cavity and water is injected and sealed therein in an embodiment in which the method according to the present invention is utilized by injection molding.

FIG. 2 is an explanatory view showing a state in which water sealed and injected into a molten raw material is steamed into a molten raw material in the embodiment to form a hollow molded article under a pressure generated by volume expansion.

FIG. 3 is an explanatory diagram showing a state in which pressure water vapor is released from an internal cavity and the cavity is depressurized as a molded product is formed in the embodiment.

FIG. 4 is an explanatory view showing a state in which water is injected and blocked into a molten raw material in a sprue connected to a cavity in an embodiment in which a thin product is injection-molded.

FIG. 5 is an explanatory view showing a state in which water injected and sealed into the molten raw material in the embodiment is steamed to form a hollow molded article under a pressure generated by volume expansion.

FIG. 6 is an explanatory view showing a state in which pressure steam is released from an internal cavity and the cavity is depressurized with molding of a molded product in the embodiment.

FIG. 7 is an explanatory diagram showing a state in which a parison is charged into a cavity and water is injected into the parison in an embodiment in which the method according to the present invention is used for blow molding.

FIG. 8 is an explanatory view showing a state in which water injected and sealed into the parison is vaporized in the embodiment and a hollow molded article is formed by pressure generated by volume expansion.

[Explanation of symbols]

 Reference Signs List 1 mold 2 cavity a molten raw material b water c blowing agent 9 water injection needle 10 water supply pipe 11 water supply pipe open / close valve 13 air release pipe 14 air release pipe open / close valve

Claims (2)

[Claims] 1. A method for molding a synthetic resin molded article in which a molten material is injected into a cavity of a mold or a hollow molten material is charged and expanded to obtain a molded article. After injecting or charging, a suitable amount of water is injected and sealed into the inside of the molten raw material, and this water is vaporized by the heat of the molten raw material, and the rapid pressure rise accompanying this is used as a molding pressure for melting. A method for molding a synthetic resin molded article, comprising: forming a raw material; releasing the water vapor from the molded article when the molding is completed; reducing the internal pressure; and releasing the molded article. 2. A foaming agent is added to an appropriate amount of water to be injected and sealed inside the molten raw material, and the foaming agent is foamed with the steaming of the water by the heat of the molten raw material. The method for molding a synthetic resin molded product according to claim 1, wherein the rise is supplemented.