JPH0751298Y2 - Nozzle for high pressure gas injection of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a high pressure gas injection nozzle used for high pressure gas injection molding of an injection molding machine.

(Prior Art) In a process of injecting a molten resin into a mold cavity in injection molding, high-pressure gas is introduced from a high-pressure gas generator to a nozzle, and the high-pressure gas is injected together with the molten resin. In order to inject the high-pressure gas into the molten resin, the pressure P _G of the high-pressure gas needs to be higher than the molten resin pressure P ₁ of the high-pressure gas inlet 11 in FIG.

(Problems to be solved by the invention) However, in the conventional high-pressure gas injection nozzle shown in FIG. 5, the molten resin pressure P _{2 in} the passage 10 on the screw side upstream from the high-pressure gas injection port 11 and the molten resin in the injection port 11 are increased. Since the difference with the pressure P ₁ is small, if the pressure P _G of the injected gas is made higher than the molten resin pressure P ₁ of the injection port 11, the gas pressure P _G will be
The pressure also becomes higher than the molten resin pressure P _{2 of} 10, the high-pressure gas also flows to the screw side, and the gas is mixed into the molten resin there. When the molten resin mixed with gas is injected and injected into the mold cavity in the next step, there is a problem that a defective appearance such as flashing occurs on the surface of the molded product.

In Therefore fifth near the high-pressure gas inlet 11 of a conventional high-pressure gas injection nozzle shown in FIG., A molten resin pressure P ₂ upstream of passage 10, the difference of the molten resin pressure P ₁ downstream of inlet 11 becomes larger and thus, the pressure P _G in the high pressure gas, increasing the difference of the molten resin pressure P ₂ of the molten resin pressure P ₁ and the upstream passage 10 of P ₁ <P _G <settable to P _2, and the inlet 11 Therefore, it is necessary to increase the setting range of the gas pressure P _G to facilitate the setting. By maintaining the state of P _G <P _{2 in} this way, high-pressure gas is prevented from being mixed in the upstream molten resin, and molding defects can be reduced.

This invention is in the vicinity of a pressure gas inlet of the high pressure gas injection nozzle, a molten resin pressure P ₂ upstream of the passage, in order to be the difference between the molten resin pressure P ₁ downstream of the inlet becomes large, and the upstream By providing a narrowed portion of the passage in which the cross-sectional area of the molten resin passage is reduced downstream, a high-pressure gas injection nozzle that can solve the above-mentioned conventional problems is provided.

(Means for Solving the Problems) Therefore, the present invention is an injection molding having a nozzle section for injecting a molten resin into a mold and a nozzle provided in the nozzle section for injecting high-pressure gas into the molten resin during an injection step. High-pressure gas injection nozzle of a machine, a resin passage having a cross-sectional area between the resin passage of the high-pressure gas inlet and the resin passage upstream thereof, which is smaller than the resin passage of the inlet and smaller than the upstream resin passage. Is arranged so that the pressure value of the molten resin flowing at the time of high-pressure gas injection is higher than the pressure value of the molten resin at the gas injection port, and this is the means for solving the problem. is there.

(Operation) In the injection process of the molten resin, when the molten resin flows from the upstream side of the nozzle toward the high pressure gas injection port of the downstream side,
Flow resistance ΔP is generated in the narrowed portion of the passage. This flow resistance ΔP increases as the cross-sectional area of the narrowed portion of the passage decreases. Since in this way provided the constricted portion of the passage, a molten resin pressure P ₂ upstream of the passage, the difference in the molten resin pressure P ₁ downstream inlet is increased, the pressure P _G in the high pressure gas
It becomes easily sets to _{P 1 <P G <P 2} .

(Embodiment) The present invention will be described below with reference to the embodiments of the drawings. FIG. 1 shows a first embodiment of the present invention. Now, in FIG. 1, a high pressure gas injection nozzle 2 is attached to the injection molding apparatus 1,
The nozzle 2 comprises a body 3, a nozzle tip 4, a plunger 5, a lever 6 and a gas injection block 7. Also, there are gas passages 8 and 9 in the plunger 5 and the block 7,
During injection, the high-pressure gas is injected from a high-pressure gas generator (not shown) through the gas passages 8 and 9 into a mold cavity (not shown) together with the molten resin. The tip of the plunger 5 contacts the inner wall of the nozzle tip 4 to close the upstream passage 10 for the molten resin. When the plunger 5 is moved to the right in FIG. Separated from the inner wall of the chip 4, the molten resin upstream passage 10 communicates with the injection port 11 (FIG. 2). As shown in FIG. 2, since the inner diameter D ₁ of the tip portion of the nozzle tip 4 is smaller than the inner diameter D ₂ of the passage 10 portion, the passage 12 formed by the outer peripheral portion of the plunger 5 and the inner diameter D ₁ portion. The cross-sectional area of is narrower than the cross-sectional area of the other part (the cross-sectional area of the inlet 11 and the upstream passage 10).

In the injection process of the molten resin, when the molten resin flows from the upstream side of the nozzle toward the high-pressure gas inlet 11 of the downstream side, the flow resistance ΔP is generated in the narrowed portion of the passage 12.
This flow resistance ΔP becomes larger as the drawing becomes stronger and the viscosity of the molten resin becomes higher.

According to one embodiment, the outer diameter of the plunger is 8 mm and the aperture clearance is 0.5.
mm, drawing length 15 mm, injection rate 60 cm ² / sec, flow resistance ΔP of high density PP (resin temperature 250 ° C.) used resin is 2 MPa higher than when drawing gap 2 mm. When the flow resistance ΔP increases in this way, the setting range of the high-pressure gas injection pressure also increases and the setting is easy, and the difference between the molten resin pressure P _{1 at the} injection port 11 and the gas pressure P _G , and the gas pressure. The difference between the pressure P _G and the molten resin pressure P _{2 in} the upstream passage 10 can be increased.

FIG. 3 shows a second embodiment of the present invention. This is provided with a replaceable nozzle piece 14 at the tip of the nozzle tip 4 of the first embodiment shown in FIG. ₁ , and the nozzle pieces 14 having different inner diameters D ₁ of the narrowed portion are replaced to change the degree of narrowing of the passage. The flow resistance ΔP can be adjusted by changing the flow resistance.

(Effects of the Invention) As described in detail above, according to the present invention, in the high-pressure gas injection nozzle, the portion where the passage of the molten resin is narrowed is arranged near the gas injection port. A flow resistance ΔP is generated in the narrowed portion of the throttle valve, and the difference between the molten resin pressure P _{2 in} the upstream passage of the throttle and the molten resin pressure P _{1 in} the downstream inlet becomes large, and the injection gas pressure P _{G is changed} to P ₁ <P _G <P ₂
Easily configurable. By thus difference molten resin pressure P ₂ of the molten resin pressure P ₁ and the upstream passage inlet to increase, by increasing the setting range of the pressure P _G in the gas, the upper flow and the pressure P _G in the gas Since the difference in the molten resin pressure P _{2 in} the passage can be easily maintained to be large, high-pressure gas will not mix into the upstream molten resin, and molding defects can be reduced.

[Brief description of drawings]

1 is a side sectional view of a high pressure gas injection nozzle according to a first embodiment of the present invention, FIG. 2 is an enlarged sectional view of a nozzle tip portion of FIG. 1, and FIG. 3 is a second embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view of the tip of the high-pressure gas injection nozzle, FIG. 4 is an explanatory view showing the cross-section of the nozzle tip in the first embodiment of the present invention and the corresponding passage cross-section changes and pressure changes, and FIG. FIG. 6 is an enlarged cross-sectional view of a conventional high-pressure gas injection nozzle tip portion, and FIG. 6 is an explanatory diagram showing a concept of a conventional nozzle tip portion and corresponding passage cross-section changes and pressure changes. Description of main parts of the figure 1 …… Injection molding device 2 …… High pressure gas injection nozzle 3 …… Nozzle body 4 …… Nozzle tip 5 …… Plunger 6 …… Lever 9 …… Gas passage 10 …… Molten resin passage 11 …… Injection port 14 …… Nozzle piece P ₁ …… Injection port 11 molten resin pressure P ₂ …… Passage 10 molten resin pressure P _G …… Gas pressure

Claims (1)

[Scope of utility model registration request] 1. A high-pressure gas injection nozzle of an injection molding machine, comprising: a nozzle section for injecting a molten resin into a mold; and a nozzle provided in the nozzle section for injecting a high-pressure gas into the molten resin during an injection process. Between the resin passage of the gas injection port and the resin passage of the upstream, smaller than the resin passage of the same injection port,
In addition, a resin passage having a smaller cross-sectional area than the upstream resin passage is arranged so that the pressure value of the molten resin flowing at the time of high-pressure gas injection is higher than the pressure value of the molten resin at the gas inlet. A high-pressure gas injection nozzle for injection molding machines.