JP7048869B2 - Injection molding method for mold assembly and molded products with hollow portions - Google Patents

Description

The present invention relates to a mold assembly and an injection molding method for a molded product having a hollow portion.

When molding a molded product based on an injection molding method using a molten thermoplastic resin, a pressurized gas is applied to the molten thermoplastic resin injected into the cavity in order to obtain a beautiful molded product with a beautiful appearance without sink marks or warpage. Widely used is an injection molding method for molded products having a hollow portion, which is introduced to form a hollow portion inside the molten thermoplastic resin in the cavity and releases the pressurized gas in the hollow portion to the atmosphere before opening the mold. Has been done. As a result of the molten thermoplastic resin being pressed against the cavity surface of the mold by the pressurized gas introduced into the molten thermoplastic resin injected into the cavity, it is possible to prevent sink marks and warpage in the obtained molded product.

By the way, in the conventional injection molding method of a molded product having a hollow portion, the hollow portion formed inside the thermoplastic resin in the cavity is substantially in a heat insulating state. As a result, there is a problem that it takes a long time to cool and solidify the thermoplastic resin in the cavity.

An injection molding method for solving this problem is well known, for example, from Japanese Patent Application Laid-Open No. 9-85771. In the technique disclosed in this Patent Publication, a plurality of molds are combined to form a closed cavity, and a fluid synthetic resin material is injected into the closed cavity from one material injection port, and then the material is injected. A gas of appropriate pressure such as compressed air is press-fitted into the synthetic resin material in the cavity from the first injection port near the inlet to form a hollow portion, and then the second injection at a position far from the material injection port in the hollow portion. Press in a gas of appropriate pressure such as compressed air from the mouth.

Japanese Unexamined Patent Publication No. 9-85771

However, in the technique disclosed in JP-A-9-85771, the structure of the mold becomes complicated, and the time for cooling and solidifying the thermoplastic resin in the cavity can be sufficiently shortened. I can't plan.

Therefore, an object of the present invention is a mold assembly and a hollow portion capable of effectively cooling and solidifying the thermoplastic resin in the cavity in a short time despite having a simple structure and structure. It is to provide the injection molding method of the molded article which has.

The injection molding method for a molded product having a hollow portion of the present invention for achieving the above object is
A process of injecting a molten thermoplastic resin into a cavity provided in a mold via a molten thermoplastic resin introduction portion, and a process of injecting the molten thermoplastic resin into the cavity.
The tip of the nozzle of the device that also serves as the pressurized gas introduction / discharge device and the liquid introduction / discharge device is positioned in the cavity , and the pressurized gas is inside the molten thermoplastic resin injected into the cavity. To form a hollow portion inside the molten thermoplastic resin injected into the cavity, and then discharge the pressurized gas to the outside from the nozzle located in the hollow portion.
It is characterized by a step of introducing a liquid into the hollow portion through the nozzle of the device also used , discharging the introduced liquid through the nozzle, and repeating removal to the outside a plurality of times. And.

Here, it is desirable that the plurality of times is twice, preferably three times or more. When the liquid is introduced into the hollow portion for the first time, the liquid introduced into the hollow portion is often vaporized by the heat of the thermoplastic resin injected into the cavity and becomes vapor. Therefore, in this case, the vapor vaporized by the liquid introduced into the hollow portion is removed to the outside, and this step is also included in the "step of removing the liquid introduced into the hollow portion to the outside".

The pressurized gas may be introduced during injection of the molten thermoplastic resin into the cavity, at the same time as the injection is completed, or after the injection is completed.

In the injection molding method of a molded product having a hollow portion of the present invention, a pressurized gas is introduced into the molten thermoplastic resin injected into the cavity, and the hollow portion is inside the molten thermoplastic resin injected into the cavity. After the skin layer is formed on the thermoplastic resin injected into the cavity, the pressurized gas in the hollow portion can be discharged to the outside. After the skin layer is formed in this way, the pressurized gas in the hollow portion is discharged to the outside, so that the shape of the hollow portion formed inside the thermoplastic resin can be kept stable.

In the injection molding method for a molded product having a hollow portion of the present invention including the above preferred embodiment, when the step of introducing a liquid into the hollow portion and then removing the liquid in the hollow portion to the outside is repeated a plurality of times, the liquid It is preferable to reuse.

In the mold assembly of the present invention, the liquid removing device may be in the form of an ejector having a drive port, a suction port, and a discharge port. Further, in the injection molding method of a molded product having a hollow portion of the present invention including various preferable forms described above, a form in which the liquid in the hollow portion is removed to the outside by an ejector having a drive port, a suction port and a discharge port. Can be.

A circulation system is formed in which the liquid stored in the liquid storage container (tank) is sent out from the drive port of the ejector via the pump and piping, and returned to the liquid storage container from the discharge port. Further, the liquid stored in the liquid storage container (tank) is introduced into the hollow portion via the pump and another pipe, and further via the liquid introduction / discharge device. Then, the liquid that has stayed in the hollow portion for a predetermined time is discharged from the hollow portion via the liquid introduction / discharge device, is sucked into the suction port of the ejector via another pipe, and is sucked into the liquid storage container from the discharge port. A discharged system to be returned is formed. In this way, the liquid sent to the drive port of the ejector and the liquid sucked to the suction port of the ejector are returned to the liquid storage container through the discharge port of the ejector.

In the injection molding method of the mold assembly of the present invention including the various preferred forms described above or the molded product having the hollow portion of the present invention, the amount of the molten thermoplastic resin to be injected into the cavity completely fills the cavity. It is preferable that the amount is not filled (short shot method). That is, the volume V ₁ of the molten thermoplastic resin injected into the cavity is preferably less than the volume V ₀ of the cavity, and is not specifically limited.
0.7 ≤ V ₁ / V ₀ <1
It is more preferable to satisfy. When the overflow cavity portion described below is provided, the amount of the molten thermoplastic resin to be injected into the cavity may be an amount that does not completely fill the cavity, or the cavity is completely filled, but overflow. The amount may not completely fill the cavity, and the volume V ₁ of the molten thermoplastic resin injected into the cavity is not specifically limited, but is not limited.
0.7 ≤ V ₁ / V ₀ ≤ 1.1
It is more preferable to satisfy. Further, the amount of the molten thermoplastic resin to be injected into the cavity is not limited to the short shot method, and may be an amount that completely fills the cavity (full shot method).

Further, in the injection molding method of the mold assembly of the present invention including the various preferable forms described above or the molded product having the hollow portion of the present invention, the mold is provided with an overflow cavity portion ("". It can be in the form of being provided with a "discard cavity portion"). That is, the pressurized gas is introduced into the molten thermoplastic resin in the cavity during the injection of the molten thermoplastic resin into the cavity, at the same time as the injection is completed, or after the injection is completed. The molten thermoplastic resin in the cavity pushed away by the introduction is discharged to the overflow cavity portion. By providing the overflow cavity portion in this way, injection molding of the molded product can be performed more stably. The overflow cavity portion is provided at the end of the molten thermoplastic resin injected into the cavity in the flow direction. However, it does not have to be a portion strictly corresponding to the end. That is, it may be a portion corresponding to the vicinity of the end in the flow direction of the molten thermoplastic resin. Further, a valve mechanism that can be opened and closed may be provided between the cavity and the overflow cavity portion, whereby the inflow of the molten thermoplastic resin into the overflow cavity portion can be accurately controlled.

The mold is composed of a first mold portion (for example, a fixed mold portion) and a second mold portion (for example, a movable mold portion). The first mold portion and the second mold portion can be made of a well-known metal material such as carbon steel, stainless steel, aluminum alloy, and copper alloy.

The melt thermoplastic resin introduction portion may be disposed in the first mold portion, may be disposed in the second mold portion, or may be disposed in the first mold portion and the second mold portion. It may be arranged in the mold portion. The structure of the molten thermoplastic resin introduction portion (specifically, the gate portion) can be any known type of gate structure, for example, a direct gate structure, a side gate structure, a jump gate structure, or a pinpoint gate structure. , Tunnel gate structure, ring gate structure, fan gate structure, disk gate structure, flash gate structure, tab gate structure, film gate structure can be exemplified.

The pressurized gas introduction / discharge device may be disposed in the first mold portion, the second mold portion, the first mold portion, and the second mold portion. It may be arranged in the mold portion of. In the pressurized gas introduction / discharge device, the part where the pressurized gas is introduced into the molten thermoplastic resin injected into the cavity in order to form a hollow part inside the molten thermoplastic resin injected into the cavity. The portion of the hollow portion for discharging the pressurized gas to the outside may be composed of the same parts or different parts. The liquid introduction / discharge device may also be arranged in the first mold portion, the second mold portion, the first mold portion and the second mold. It may be arranged in the mold portion. In the liquid introduction / discharge device, the portion for introducing the liquid into the hollow portion and the portion for discharging the liquid in the hollow portion may be composed of the same parts or different parts. Further, the liquid introduction / discharge device may be used in combination with the pressurized gas introduction / discharge device, and the device in which the liquid introduction / discharge device and the pressurized gas introduction / discharge device are used in combination is described below for convenience. , Called "fluid introduction / discharge device".

As an example of disposing the fluid introduction / discharge device into the mold assembly, the fluid introduction / discharge device is provided so that the tip of the fluid introduction / discharge device is arranged in the cavity or near the cavity surface of the mold. It may be configured to be arranged in the mold portion of 1, the second mold portion, or the first mold portion and the second mold portion. The fluid introduction / discharge device can be, for example, a well-known gas injection nozzle. If necessary, a heating means (for example, an electric heater) for heating the tip portion may be attached to the tip portion. By arranging the heating means in this way, it is possible to avoid the start of instantaneous solidification of the molten thermoplastic resin in the vicinity of the fluid introduction / discharge device, and it is added to the molten thermoplastic resin in the cavity via the fluid introduction / discharge device. The pressure gas can be reliably introduced, and the pressurized gas in the hollow portion can be reliably discharged to the outside of the system via the fluid introduction / discharge device. Further, in some cases, the fluid introduction / discharge device may be arranged so that the tip portion thereof is arranged in the molten thermoplastic resin introduction portion, or the tip portion thereof is the tip portion of the injection cylinder. It may be arranged so as to be arranged in the (nozzle portion), or may be arranged so that the tip portion thereof is arranged in the resin flow path connecting the injection cylinder and the molten thermoplastic resin introduction portion. ..

The pressurized gas is a gas substance at normal temperature and pressure, and it is desirable that the pressurized gas does not react or mix with the thermoplastic resin used. Specific examples thereof include nitrogen gas, air, carbon dioxide gas, and helium gas, but nitrogen gas and helium gas are preferable in consideration of safety and economy. It may also contain a gas liquefied under high pressure. As the liquid introduced into the hollow portion, water (hot water) set to an appropriate temperature can be mentioned.

In carrying out the injection molding method of the present invention, the amount, temperature, pressure or injection rate of the molten thermoplastic resin at the time of injection molding, the amount of pressurized gas to be introduced to form the hollow portion, pressure or speed, gold. Various conditions such as the cooling time of the mold need to be appropriately selected and controlled depending on the type of the thermoplastic resin used, the shape of the mold, and the like, and cannot be uniquely determined.

The structure of the mold assembly may be one molded product or a large number of molded products.

The molded product obtained by the injection molding method of the present invention is not particularly limited, and examples thereof include a handle-formed molded product, a long molded product, and a thin-walled molded product having a partially thickened portion. be able to. Here, the handle-formed molded product is a product in which a thick grip portion and at least one mounting portion are integrated, and the grip portion corresponds to the thickest portion of the molded product, and the thickest portion thereof. The (grip portion) is provided with a hollow structure. This molded product is attached to an automobile, an electric appliance, a door of a building, or the like at its attachment portion. Then, the user grips the grip portion and opens and closes the door and the like. Molds usually have the shape of a handle or lever. On the other hand, as a long molded product, a roof rail attached to a roof portion of an automobile and various pipes can be mentioned, and as a thin molded product having a partially thickened portion, an outer plate such as a bonnet and various covers can be mentioned. be able to. However, the molded product is not limited to these.

Examples of the thermoplastic resin suitable for use in the present invention include crystalline thermoplastic resin and amorphous thermoplastic resin, and specifically, polyolefin resins such as polyethylene resin and polypropylene resin; polyamide 6, Polyamide resin such as polyamide 66 and polyamide MXD6; polyoxymethylene (polyacetal, POM) resin; polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin and other polyester resin; polyphenylene sulfide resin; polystyrene resin, ABS resin , AES resin, AS resin and other styrene resins; methacrylic resin; polycarbonate resin; modified polyphenylene ether (PPE) resin; polysulfone resin; polyether sulfone resin; polyallylate resin; polyetherimide resin; polyamideimide resin; polyimide resin The polyether ketone resin; the polyether ether ketone resin; the polyester carbonate resin; the liquid crystal polymer can be exemplified.

Further, a thermoplastic resin made of a polymer alloy material can be used. Here, the polymer alloy material comprises a blend of at least two kinds of thermoplastic resins, or a block copolymer or a graft copolymer in which at least two kinds of thermoplastic resins are chemically bonded. Polymer alloy materials are widely used as high-performance materials that can combine the unique performance of each single thermoplastic resin. As the thermoplastic resin constituting the polymer alloy material in which at least two kinds of thermoplastic resins are blended, styrene resins such as polystyrene resin, ABS resin, AES resin and AS resin; polyolefin resins such as polyethylene resin and polypropylene resin; methacrylic resin Polycarbonate resin; Polyamitone resin such as polyamide 6, polyamide 66, polyamide MXD6; modified PPE resin; polyester resin such as polybutylene terephthalate resin and polyethylene terephthalate resin; polyoxymethylene resin; polysulfone resin; polyimide resin; polyphenylene sulfide resin; Polyarylate resin; polyether sulfone resin; polyether ketone resin; polyether ether ketone resin; polyester carbonate resin can be mentioned. As a polymer alloy material in which two types of thermoplastic resins are blended, a polymer alloy material of a polycarbonate resin and an ABS resin can be exemplified. In addition, such a combination of resins is referred to as polycarbonate resin / ABS resin. The same applies to the following. Further, as a polymer alloy material in which at least two types of thermoplastic resins are blended, polycarbonate resin / PET resin, polycarbonate resin / PBT resin, polycarbonate resin / polyamide resin, polycarbonate resin / PBT resin / PET resin, modified PPE resin / HIPS Examples thereof include resins, modified PPE resins / polyamide resins, modified PPE resins / PBT resins / PET resins, modified PPE resins / polyamide MXD6 resins, polyoxymethylene resins / polyurethane resins, and PBT resins / PET resins.

Additives, fillers, and strengthening agents can also be added to the various thermoplastic resins described above.

As additives, plasticizers; stabilizers; antioxidants: UV absorbers; organic nickel compounds such as nickel bis (octylphenyl) sulfide, UV stabilizers such as hindered amine compounds; antistatic agents; flame retardants; binazine, preben Antifungal agents such as tall and thiabendazole; lubricants such as liquid paraffin, polyethylene wax and fatty acid amide; organic foaming agents such as ADCA; transparent nucleating agents; various coloring agents such as organic pigments and inorganic pigments; cross-linking agents; acrylic graft polymers, Impact resistant enhancers such as MBS can be mentioned.

As plasticizers, phthalates such as diethyl phthalate, di-n-butyl phthalate, -2-ethylhexyl phthalate, diisononyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate; triethyl phosphate, tributyl phosphate, phosphate Phthalic acid esters such as triclesyl and triphenyl phosphate; fatty acid base esters such as butyl oleate, dibutyl adipate, -n-hexine adipate, di-2-ethylhexyl adipate; alcohol esters such as diethylene glycol dibenzoate Oxyrate esters such as acetyltriethyl citrate and dibutyl maleate; trimellitic plasticizers; polyester plasticizers; epoxy plasticizers; paraffin chloride plasticizers.

As stabilizers, organic tin-based stabilizers such as di-n-octyltin compounds, di-n-butyltin compounds, and dimethyltin compounds; lead compounds such as tribasic lead sulfate, dibasic lead phosphite, and lead silicate. Stabilizers; metal soap-based stabilizers such as cadmium soap, lead soap, zinc soap; trisnonyl phosphate; trisnonylphenyl phosphate and the like can be mentioned.

As antioxidants, phenolic antioxidants such as dibutylcresol and butylhydroxyanisole; bisphenolic antioxidants such as methylenebis (methylbutylphenol) and thiobis (methylbutylphenol); tris (methylhydroxybutylphenyl) butane, tocophenol and the like. Polyphenolic antioxidants; organic sulfur compounds such as dimyristylthiodipropionate; organic phosphorus compounds such as tris (mono / dinonylphenyl) phosphite.

As UV absorbers, salicylic acid-based UV absorbers such as phenyl salicylate and butylphenyl salicylate; benzophenone-based UV absorbers such as dihydroxybenzophenone; benzotriazole-based UV absorbers such as (hydroxymethylphenyl) benzotriazole; ethylhexyl cyanodi acrylate. Examples thereof include cyanoacrylate-based ultraviolet absorbers such as phenonyl.

Non-ionic surfactant-based antistatic agents such as poly (oxyethylene) alkylamine and poly (oxyethylene) alkylphenyl ether as antistatic agents; negatives such as alkyl sulfonates, alkylbenzene sulfonates, and alkyl phosphates. Ionic surfactant-based antistatic agents; cationic surfactant-based antistatic agents such as quaternary ammonium chloride; amphoteric surfactants; conductive resins.

As flame retardants, halogen-based flame retardants such as tetrabromobisphenol A, polybromobiphenol, bis (hydroxydibromophenyl) propane, and paraffin chloride; phosphorus-based flame retardants such as ammonium phosphate and tricresyl phosphate; antimony trioxide; red phosphorus ; Can be mentioned such as tin oxide.

In addition, as fillers and reinforcing agents, inorganic materials; stainless steel fibers, high-strength amorphous metal fibers, stainless steel foils, steel foils, copper foils and other metal-based materials; high-molecular-weight polyethylene fibers, high-strength polyarrate fibers, all para-based materials. Organic materials such as aromatic polyamide fibers, aramid fibers, PEEK fibers, PEI fibers, PPS fibers, fluororesin fibers, phenol resin fibers, vinylon fibers, polyacetal fibers; and powder materials can be mentioned.

Here, as an inorganic filler and a reinforcing agent, glass-based materials such as glass fiber, long glass fiber, and quartz glass fiber; carbon-based materials such as PAN-based carbon fiber, pitch-based carbon fiber, and graphite whisker; silicon carbide fiber. Silicon carbide-based materials such as continuous silicon carbide, silicon carbide whisker, silicon carbide whisker sheet; boron-based materials such as boron fiber; Si-Ti—CO-based material such as Si—Ti—CO fiber; potassium titanate. Potassium titanate-based materials such as fiber, potassium titanate whisker, potassium titanate conductive whiskers; silicon nitride-based materials such as silicon nitride whisker, silicon nitride whisker sheet; calcium sulfate-based materials such as calcium sulfate whisker can be mentioned. ..

In addition, as powder-based fillers and fortifiers, mica flakes, mica powder, silas balloons, silica powder, talc powder, aluminum hydroxide powder, magnesium hydroxide powder, magnesium silicate powder, calcium sulfate powder, spherical hollow glass powder, Metallized powder, high-purity synthetic silica powder, tungsten disulfide powder, tungsten carbide powder, zirconia powder, zirconia powder, partially stabilized zirconia powder, alumina-zirconia composite powder, composite metal powder, iron powder, aluminum powder, molybdenum Examples thereof include metal powder, tungsten powder, aluminum nitride powder, nylon fine particle powder, silicone resin powder, spinel powder, amorphous alloy powder, aluminum flakes, and glass flakes.

Since the mold assembly of the present invention is provided with a liquid introduction / discharge device for introducing and discharging a liquid into the hollow portion and a liquid removing device for removing the liquid discharged from the hollow portion to the outside, the mold assembly is also provided. In the injection molding method for a molded product having a hollow portion of the present invention, the steps of introducing a liquid into the hollow portion and then removing the liquid introduced into the hollow portion to the outside are repeated a plurality of times. Despite its simple structure and structure, the thermoplastic resin in the cavity can be effectively cooled and solidified in a short time.

FIG. 1 is a conceptual diagram of the mold assembly of the first embodiment. 2A, 2B and 2C show a state in which the molten thermoplastic resin is injected into the cavity, and a pressurized gas is introduced into the molten thermoplastic resin injected into the cavity to form a hollow portion. It is a figure which shows typically the state which is, and the state which the pressurized gas is discharged from a hollow part. 3A and 3B are diagrams schematically showing a state in which the liquid is introduced into the hollow portion and a state in which the liquid is discharged from the hollow portion. FIG. 4 is a conceptual diagram of a mold in a modified example of the mold assembly of the first embodiment. FIG. 5 is a principle diagram of the ejector.

Hereinafter, the present invention will be described with reference to the drawings, but the present invention is not limited to the examples, and various numerical values and materials in the examples are exemplified.

The first embodiment relates to the mold assembly of the present invention and the method of molding an injection-molded article having a hollow portion of the present invention. A conceptual diagram of the mold assembly of the first embodiment is shown in FIG. 1, and schematic end views of a mold or the like for explaining the injection molding method in the first embodiment are shown in FIGS. 2A, 2B, 2C, and 3A. And shown in FIG. 3B.

Specifically, the molded product obtained by the molding method of Example 1 is, for example, a handle-formed product. Here, the handle-formed molded product is a product in which a thick grip portion and at least one mounting portion are integrated, and the grip portion corresponds to the thickest portion of the molded product, and the thickest portion thereof. The (grip portion) is provided with a hollow structure. This handle-formed product is attached to an automobile, an electric appliance, a door of a building, or the like at its attachment portion. Then, the user grips the grip portion and opens and closes the door and the like. The handle-formed product has a handle shape.

The mold assembly of the first embodiment is
Mold 10, provided with a cavity 14.
The molten thermoplastic resin introduction unit 13, which injects the molten thermoplastic resin into the cavity 14.
A pressurized gas is introduced into the molten thermoplastic resin 16 injected into the cavity 14 in order to form the hollow portion 17 inside the molten thermoplastic resin 16 injected into the cavity 14, and the inside of the hollow portion 17 is formed. Pressurized gas introduction / discharge device that discharges pressurized gas to the outside,
A liquid introduction / discharge device that introduces and discharges liquid into the hollow portion 17, and a liquid introduction / discharge device, and
A liquid removing device that removes the liquid discharged from the hollow portion 17 to the outside.
It is equipped with.

Here, the mold 10 is composed of a first mold portion (fixed mold portion) 11 and a second mold portion (movable mold portion) 12, and is composed of the first mold portion 11 and the first mold portion 11. The cavity 14 is formed by mold-fastening the mold portion 12 of 2.

In the first embodiment, the molten thermoplastic resin introduction portion 13 more specifically has a side gate structure opened in the cavity 14. The molten thermoplastic resin introduction unit 13 communicates with the injection cylinder (not shown) via the resin flow path 13A.

The pressurized gas introduction / discharge device and the liquid introduction / discharge device may be arranged in the first mold portion 11, may be arranged in the second mold portion 12, or may be arranged in the second mold portion 12. Although it may be arranged in the mold portion 11 of 1 and the second mold portion 12, in the first embodiment, the pressurized gas introduction / discharge device and the liquid introduction / discharge device are one device. (Fluid introduction / discharge device 21) is also used, and the fluid introduction / discharge device 21 is arranged in the second mold portion 12. The fluid introduction / discharge device 21 includes a well-known pressurized gas injection nozzle having a tip opened in the cavity 14.

The tip of the fluid introduction / discharge device (pressurized gas injection nozzle) 21 is arranged so as to be arranged in the cavity 14. The fluid introduction / discharge device 21 is provided with a hydraulic cylinder (not shown), and the fluid introduction / discharge device 21 is positioned at the forward position and the backward position by the operation of the hydraulic cylinder. When in the forward position, the tip of the fluid introduction / discharge device 21 is located in the cavity 14. When in the retracted position, the tip of the fluid introduction / discharge device 21 is located in the same plane as the cavity surface of the mold (specifically, the second mold portion 12).

The liquid removing device is composed of an ejector 40 having a drive port 41, a suction port 42, and a discharge port 43. FIG. 5 shows a principle diagram of the ejector 40. A liquid (specifically, water or hot water having a predetermined temperature) pressurized from the pump 31 is supplied to the drive port 41 via the pipe 62. The inside of the drive port 41 has a nozzle shape in which the inner diameter gradually decreases toward the end 41B from the open end 41A, and the minimum diameter is reached at the end 41B. The reduced diameter portion 44 has the same inner diameter as the terminal 41B of the drive port 41. The suction port 42 is open to the reduced diameter portion 44, and the liquid that has passed through the pipe 68, that is, the liquid that has existed in the hollow portion 17, is sucked. The discharge port 43 discharges the sucked liquid together with the liquid from the drive port 41. The discharge port 43 has a shape opposite to that of the drive port 41, that is, a shape in which the inner diameter gradually increases from the end portion 43B on the reduced diameter portion side of the discharge port 43 toward the opening end 43A. In the ejector 40, the liquid introduced from the drive port 41 heads toward the reduced diameter portion 44. Since the inner diameter of the reduced diameter portion 44 is narrowed, the flow velocity of the liquid in the reduced diameter portion 44 increases. Then, as the flow velocity increases, the pressure of the reduced diameter portion 44 decreases based on Bernoulli's theorem, so that the pressure at the suction port 42 opened in the reduced diameter portion 44 decreases, and the liquid is sucked through the pipe 68. To. The sucked liquid is discharged from the discharge port 43 together with the liquid supplied to the drive port 41.

As shown in the conceptual diagram in FIG. 1, the fluid introduction / discharge device 21 (more specifically, the rear end portion of the pressurized gas injection nozzle) is pressurized through the pipes 65 and 64 constituting the gas flow path. It is connected to the gas supply device 50. The pressurized gas is composed of nitrogen gas, and the pressurized gas source (not shown) in the pressurized gas supply device 50 is composed of, for example, a PSA type nitrogen gas generator.

Further, in the middle of the pipes 64 and 65, a control pressure reducing valve 70, a first switching valve 71 and a first on-off valve 73 are arranged from the pressurized gas supply device side. The first switching valve 71 further communicates with the liquid discharge portion of the flow rate control device 32 via the pipe 63. Further, the pipe 66 is branched from the middle of the pipe 65, and the pipe 66 is connected to the second switching valve 72 via the second on-off valve 74, and is connected to the second switching valve 72 and the outside (outside the system). Is connected by a pipe 67. Further, the second switching valve 72 and the suction port 42 of the ejector 40 are connected by a pipe 68.

The liquid stored in the liquid storage container 30 is delivered to the drive port 41 of the ejector 40 via the pipe 60, the pump 31, and the pipe 62. Further, the liquid stored in the liquid storage container 30 passes through the pipe 60, the pump 31, the pipe 61, the flow control device 32, the pipe 63, the first switching valve 71, the pipe 65, and the first on-off valve 73, and further. , Is introduced into the inside of the thermoplastic resin 16 in the cavity 14 via the liquid introduction / discharge device (fluid introduction / discharge device 21). Then, the liquid staying in the hollow portion 17 for a predetermined time is discharged from the hollow portion 17 via the liquid introduction / discharge device (fluid introduction / discharge device 21) to the pipe 66, the second on-off valve 74, and the second switching valve. It is sucked into the suction port 42 of the ejector 40 constituting the liquid removing device through 72 and the pipe 68. Then, the liquid sent to the drive port 41 of the ejector 40 and the liquid sucked to the suction port 42 of the ejector 40 are returned to the liquid storage container 30 via the discharge port 43 of the ejector 40 and the pipe 69.

Hereinafter, a method for molding an injection-molded article having a hollow portion according to the first embodiment will be described with reference to FIGS. 2A, 2B, 2C, 3A and 3B. In Example 1, a polycarbonate resin manufactured by Mitsubishi Engineering Plastics Co., Ltd. (trade name: Iupiron S-3000) was used as the thermoplastic resin, and the injection conditions were as shown in Table 1 below.

[Table 1]
Molten thermoplastic resin temperature: 280 ° C
Mold temperature: 80 ° C
Injection time: 6 seconds

[Step-100]
First, the molten thermoplastic resin 16 is injected into the cavity 14 provided in the mold 10 via the molten thermoplastic resin introducing portion 13. Specifically, the first mold portion 11 and the second mold portion 12 are molded (see FIG. 1). Then, after the thermoplastic resin 16 is plasticized, melted, and weighed in an injection cylinder (not shown), the molten thermoplastic resin 16 is formed in the cavity 14 from the injection cylinder via the resin flow path 13A and the molten thermoplastic resin introduction portion 13. (See FIG. 2A). Here, the amount of the molten thermoplastic resin 16 to be injected into the cavity 14 is an amount that does not completely fill the cavity 14 (short shot method). That is, the volume V ₁ of the molten thermoplastic resin 16 injected into the cavity 14 is less than the volume V ₀ of the cavity 14, specifically.
0.7 ≤ V ₁ / V ₀ <1
To be satisfied. More specifically, the volume of the cavity 14 is 96 cm ³ , and the volume of the molten thermoplastic resin 16 injected into the cavity 14 is 67 cm ³ .

The tip of the fluid introduction / discharge device (pressurized gas injection nozzle) 21 is arranged so as to be arranged in the cavity 14. The fluid introduction / discharge device 21 is provided with a hydraulic cylinder (not shown), and the fluid introduction / discharge device 21 is positioned at the forward position and the backward position by the operation of the hydraulic cylinder. When in the forward position, the tip of the fluid introduction / discharge device 21 is located in the cavity 14. When in the retracted position, the tip of the fluid introduction / discharge device 21 is located in the same plane as the cavity surface of the mold (specifically, the second mold portion 12). In the state shown in FIG. 2A, the fluid introduction / discharge device 21 is in the retracted position, and the tip portion of the fluid introduction / discharge device 21 is the cavity surface of the mold (specifically, the second mold portion 12). Located in the same plane. The pipe 64 and the pipe 65 are in a communicating state by the first switching valve 71, but by closing the first on-off valve 73, the pressurized gas from the pressurized gas supply device 50 is introduced and discharged from the fluid. It is in a state where it does not flow into. The second on-off valve 74 is kept closed. Further, the pipe 66 and the pipe 67 are kept connected to each other via the second switching valve 72.

[Process-110]
Next, a pressurized gas is introduced into the molten thermoplastic resin 16 injected into the cavity 14 to form a hollow portion 17 inside the molten thermoplastic resin 16 injected into the cavity 14. That is, during the injection of the molten thermoplastic resin 16, at the same time as the injection is completed, or after the injection is completed, a pressurized gas is introduced into the molten thermoplastic resin 16 in the cavity 14, and a hollow portion is formed inside the molten thermoplastic resin 16. 17 is formed. Specifically, the hydraulic cylinder (not shown) constituting the fluid introduction / discharge device (pressurized gas injection nozzle) 21 is operated to be positioned at the forward position. At the same time, the first on-off valve 73 is opened, and the pressurized gas from the pressurized gas supply device 50 is introduced into the pipe 65 by the operation of the control pressure reducing valve 70. Then, the introduction of the pressurized gas into the molten thermoplastic resin 16 in the cavity 14 is started via the fluid introduction / discharge device 21, and the hollow portion 17 is formed inside the molten thermoplastic resin 16 in the cavity 14 (. See FIG. 2B). Specifically, in the first embodiment, at the same time as the injection of the molten thermoplastic resin 16 is completed, the first on-off valve 73 is opened and the control pressure reducing valve 70 is operated. Further, the second on-off valve 74 is left in the closed state.

[Step-120]
Next, the pressurized gas in the hollow portion 17 is discharged to the outside (see FIG. 2C). That is, the operation of the control pressure reducing valve 70 is stopped, the first on-off valve 73 is closed, and the second on-off valve 74 is opened. As a result, the pressurized gas in the hollow portion 17 is discharged to the outside (outside the system) via the fluid introduction / discharge device 21, the pipe 66, the second on-off valve 74, the second switching valve 72, and the pipe 67.

A hollow portion 17 is formed inside the molten thermoplastic resin injected into the cavity 14, and a skin layer is formed on the thermoplastic resin injected into the cavity 14, and then the pressurized gas in the hollow portion 17 is formed. Is preferably discharged to the outside, whereby the shape of the hollow portion 17 formed inside the thermoplastic resin can be kept stable.

[Process-130]
After that, the steps of introducing the liquid into the hollow portion 17 and then removing the liquid introduced into the hollow portion 17 to the outside are performed a plurality of times (specifically, in the first embodiment, for example, three times). ,repeat.

Specifically, the first switching valve 71 is switched so that the pipe 63 and the pipe 65 communicate with each other. Further, the first on-off valve 73 is opened, the second on-off valve 74 is closed, and the pipe 66 and the pipe 68 are connected via the second switching valve 72. Further, the pump 31 is operated. The liquid in the liquid storage container (tank) 30 is hollow through the pipe 60, the pump 31, the pipe 61, the flow rate control device 32, the pipe 63, the first switching valve 71, the pipe 65, and the fluid introduction / discharge device 21. It is sent into the 17 and cools the thermoplastic resin in the cavity 14. On the other hand, the liquid in the liquid storage container (tank) 30 is sent to the drive port 41 of the ejector 40 via the pipe 60, the pump 31, and the pipe 62, and is stored in the liquid through the discharge port 43 and the pipe 69 of the ejector 40. Returned to container 30.

After a predetermined time has elapsed, the first on-off valve 73 is closed and the second on-off valve 74 is opened. Then, the liquid in the hollow portion 17 is sucked by the operation of the ejector 40. Specifically, the liquid in the hollow portion 17 is sucked into the suction port 42 of the ejector 40 via the fluid introduction / discharge device 21, the pipe 66, the second on-off valve 74, the second switching valve 72, and the pipe 68. To. Then, the liquid sent to the drive port 41 of the ejector 40 and the liquid sucked to the suction port 42 of the ejector 40 are returned to the liquid storage container 30 via the discharge port 43 of the ejector 40 and the pipe 69.

In this way, the liquid in the hollow portion 17 is removed to the outside by the ejector 40 having the drive port 41, the suction port 42, and the discharge port 43. Further, when the step of introducing the liquid into the hollow portion 17 and then removing the liquid in the hollow portion 17 to the outside is repeated a plurality of times ([step-130]), the liquid is reused.

Next, by opening the first on-off valve 73 and closing the second on-off valve 74 again, the liquid is sent into the hollow portion 17 and the thermoplastic resin in the cavity 14 is cooled. Further, by closing the first on-off valve 73 and opening the second on-off valve 74 again, the liquid in the hollow portion 17 is removed to the outside. This operation is repeated a desired number of times in Example 1, specifically three times.

[Process-140]
After that, the fluid introduction / discharge device 21 is positioned at the retracted position, the mold is opened, and the molded product is taken out. In this way, a molded product having the hollow portion 17 can be obtained.

No sink marks or warpage were observed in the obtained molded product (handle-formed product), and a desired hollow portion 17 was formed inside the molded product (handle-formed product).

After forming the hollow portion 17, the introduction of pressurized gas is continued to cool the thermoplastic resin in the cavity 14, and then the fluid introduction / discharge device 21 is positioned at the retracted position, the mold is opened, and molding is performed. When a comparative test such as taking out a product was performed and the injection molding time (time required from the start of injection of the molten thermoplastic resin to the opening of the mold) in the comparative test was 100%, the injection molding method of Example 1 was performed. The injection molding time in the above was 70%, and the time for cooling and solidifying the thermoplastic resin in the cavity could be shortened.

As described above, in the first embodiment, the liquid introduction / discharge device for introducing and discharging the liquid into the hollow portion and the liquid removing device for removing the liquid discharged from the hollow portion to the outside are provided. Further, in the injection molding method of the molded product of Example 1, the steps of introducing the liquid into the hollow portion and then removing the liquid introduced into the hollow portion to the outside are repeated a plurality of times, which is simple. Despite its structure and structure, the thermoplastic resin in the cavity can be effectively cooled and solidified in a short time.

Example 2 is a modification of Example 1. A conceptual diagram of the mold assembly of the second embodiment is shown in FIG. In the mold assembly of the second embodiment, the cavity is composed of a main cavity portion 15A into which the molten thermoplastic resin is injected, and an overflow cavity portion (discarded cavity portion) 15B communicating with the main cavity portion 15A.

In the injection molding method of Example 2, in the same step as [Step-100] of Example 1, the molten thermoplastic resin is injected into the main cavity portion 15A, and [Step-110] of Example 1 is performed. In the same step as above, a pressurized gas is introduced into the molten thermoplastic resin 16 in the cavity to form a hollow portion 17 inside the molten thermoplastic resin 16. The molten thermoplastic resin 16 extends to the overflow cavity portion 15B. After that, by executing the same steps as in [Step-120] to [Step-140] of Example 1, a molded product having the hollow portion 17 can be obtained.

When the overflow cavity portion 15B is provided in this way, the amount of the molten thermoplastic resin to be injected into the main cavity portion 15A may be an amount that does not completely fill the main cavity portion 15A, or may be an amount that does not completely fill the main cavity portion 15A. The amount may be such that the portion 15A is completely filled, but the overflow cavity portion 15B is not completely filled.

Except for the above points, the configuration and structure of the mold assembly of the second embodiment can be the same as the configuration and structure of the mold assembly described in the first embodiment, and the mold assembly of the second embodiment can be used. Since the injection molding method using a three-dimensional object can be the same as the injection molding method using the mold assembly of the first embodiment, detailed description thereof will be omitted.

Although the present invention has been described above based on preferred examples, the present invention is not limited to these examples. Structure and configuration of mold assembly and mold described in Examples, pressurized gas introduction / discharge device, liquid introduction / discharge device, liquid removal device, etc., thermoplastic resin used in Examples, injection molding conditions , Cooling / solidification conditions, shape of molded product, cavity size, etc. are examples and can be changed as appropriate. In the embodiment, the mold assembly is configured by taking one molded product, but it can also take a large number of molded products.

10 ... Mold assembly, 11 ... First mold part (fixed mold part), 12 ... Second mold part (movable mold part), 13 ... Melt thermoplastic Resin introduction part, 13A ... resin flow path, 14 ... cavity, 15A ... main cavity part, 15B ... overflow cavity part (discarded cavity part), 16 ... molten thermoplastic resin, 17. ... Hollow part, 21 ... Fluid introduction / discharge device, 30 ... Liquid storage container (tank), 31 ... Pump, 32 ... Flow control device, 40 ... Ejector, 41 ... Drive port, 42 ... Suction port, 43 ... Discharge port, 44 ... Reduced diameter part, 50 ... Pressurized gas supply device, 60,61,62,63,64,65,66,67 , 68, 69 ... Piping, 70 ... Control pressure reducing valve, 71, 72 ... Switching valve, 73, 74 ... On-off valve

Claims (6)

A process of injecting a molten thermoplastic resin into a cavity provided in a mold via a molten thermoplastic resin introduction portion, and a process of injecting the molten thermoplastic resin into the cavity.
The tip of the nozzle of the device that also serves as the pressurized gas introduction / discharge device and the liquid introduction / discharge device is positioned in the cavity, and the pressurized gas is inside the molten thermoplastic resin injected into the cavity. To form a hollow portion inside the molten thermoplastic resin injected into the cavity, and then discharge the pressurized gas to the outside from the nozzle located in the hollow portion.
It is characterized by a step of introducing a liquid into the hollow portion through the nozzle of the device also used, discharging the introduced liquid through the nozzle, and repeating removal to the outside a plurality of times. A method for injection molding a molded product having a hollow portion. A pressurized gas is introduced into the molten thermoplastic resin injected into the cavity, a hollow portion is formed inside the molten thermoplastic resin injected into the cavity, and the thermoplastic injected into the cavity. The injection molding method for a molded product having a hollow portion according to claim 1 , wherein the pressurized gas in the hollow portion is discharged to the outside after the skin layer is formed on the resin. 1 or claim 1, wherein the liquid is reused in a step of repeatedly introducing the liquid into the hollow portion, discharging the introduced liquid from the hollow portion, and removing the liquid to the outside. 2. The injection molding method for a molded product having a hollow portion according to 2. The molded product having a hollow portion according to any one of claims 1 to 3 , wherein the liquid in the hollow portion is removed to the outside by an ejector having a drive port, a suction port, and a discharge port. Injection molding method. The hollow portion according to any one of claims 1 to 4 , wherein the volume V ₁ of the molten thermoplastic resin injected into the cavity is less than the volume V ₀ of the cavity. Injection molding method for molded products. 0.7 ≤ V ₁ / V ₀ <1
The injection molding method for a molded product having a hollow portion according to claim 5 , wherein the molding product is characterized by satisfying the above.

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