JPH0121775Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Industrial Application Field) The present invention relates to a reaction injection molding apparatus for producing a synthetic resin molded article by injecting two or more reaction liquids into a mold and foaming and curing them. (Prior Art) An example of a reaction injection molding apparatus is described in Japanese Patent Publication No. 57-54293. This device sucks a portion of the unsolidified resin from the liner near the gate after the reaction liquid is injected, reducing the pressure difference between the cavity and the liner to prevent voids from forming in the molded product. That is. By the way, in reaction injection molding, the amount of catalyst mixed in the reaction liquid is increased to increase the reaction rate in the mold in order to shorten the molding time. Surface defects, or shallow dents (sink marks), may appear on the molded product near the mold gate. In the conventional technology described above, in order to prevent the surface defects, it is necessary to increase the suction force of the resin at the liner portion, and a large amount of resin sucked through the resin suction hole solidifies, making post-processing complicated. (Purpose of the invention) In view of this point, the present invention attempts to eliminate surface defects occurring in the resin molded product. That is, the present invention was made based on the following findings as a result of research on this surface defect. Since the reaction liquid is filled from the tip of the cavity far from the gate of the mold, there is a difference in filling time between the vicinity of the gate and the tip of the cavity. If you increase the amount of catalyst and increase the reaction rate,
In the vicinity of the gate, the reaction liquid is filled with a delay while foaming and hardening of the reaction liquid progresses from the tip of the cavity, so the internal pressure increases.
However, the temperature distribution of the mold is originally uneven due to hot water piping, etc., and the reaction liquid itself is highly reactive, making it easy for variations in the generation of reaction heat to occur. I don't expect much hardening. The cavity surface is affected by uneven application of the mold release agent, etc., and the release properties of the molded product are not uniform. It is recognized that the increase in internal pressure near the gate acts in the direction of inhibiting the homogeneous foaming and curing of the reaction liquid, causing uneven shrinkage force when curing the molded product, and reducing surface release properties. It is thought that the surface defects of the molded product are caused by a large shrinkage force acting on the high parts or by concentration of gas during foaming. Therefore, the present invention aims to solve the problem of surface defects that occur in resin molded products by providing a reaction injection molding device that prevents the internal pressure from increasing near the gate and promotes homogeneous foaming and curing near the gate. That is. (Structure of the invention) The reaction injection molding apparatus of the invention includes a first depressurization passage for exerting a depressurization effect near the gate of the mold;
A second pressure reduction passage for exerting a pressure reduction effect on the tip of the cavity far from the gate, and the first pressure reduction passage start the pressure reduction after injection is completed, and the second pressure reduction passage causes the pressure reduction to be lower than that on the first pressure reduction passage side. The present invention is characterized in that it is equipped with a control means that controls the operation from the time of injection. (Example) Hereinafter, an example of the present invention will be described based on the drawings. In the reaction injection molding apparatus 1 shown in FIGS. 1 and 2, reference numeral 2 denotes a molding die in which a cavity 5 is composed of a core mold 3 and a cavity mold 4. As shown in FIG. Molding mold 2
A mixing head 8 is attached to which mixes a plurality of reaction solutions and injects the mixture into the cavity 5 via the aftermixer 6 and gate 7 of the mold 2.
In this example, a urethane molded product is obtained, and the mixing head 8 has a pipe 9 for the isocyanate stock solution.
A pipe 10 for a polyol stock solution is connected to the pipe 10. Then, the end of the first decompression passage 12 extending from the decompression machine 11 communicates with the gate 7, and
A second pressure reduction passage 15 communicates with the cavity tip 5a located at a far distance from the gate 7 via an air vent passage 13 and an air reservoir 14, and the other end of this second pressure reduction passage 15 is connected to a pressure reduction machine 11. has been done.
A first pressure regulating valve 16 and a second pressure regulating valve 17 are interposed in the first pressure reducing passage 12 and the second pressure reducing passage 15, respectively, and both pressure regulating valves 16 and 17 constitute a pressure reducing value control means 18. . That is, immediately after the injection of the reaction liquid is completed, the first pressure regulating valve 16 exerts a pressure reducing effect in the vicinity of the gate via the first pressure reducing passage 12 to a value of about 100 to 250 mmHg reduced from atmospheric pressure, and the second pressure regulating valve 17 Before injection, a pressure reduction effect of about 100 to 250 mmHg is applied to the cavity tip 5a via the second pressure reduction passage 15, and at the same time as the start of injection, the pressure reduction value is reduced to 10 to 25 mmHg.
The pressure is reduced to about mmHg, and even at this reduced pressure value, a reducing effect is exerted on the cavity tip 5a during injection and for a predetermined time after completion of injection. Then, the first pressure reduction passage 12 and the second pressure reduction passage 15 are
The diameter of the air vent passage 13 is approximately 0.2 to 0.3 mm. Next, the mode of reaction injection molding in the apparatus 1 of the above embodiment will be explained with reference to FIG. 4. - Degassing the Cavity - After the core mold 3 and the cavity mold 4 are closed, a depressurizing action of 100 to 250 mmHg is applied from the cavity tip 5a through the second decompression passage 15, and the cavity 5 is degassed. In this case, the period until the start of injection (10 to 20 seconds, 20 seconds in Figure 4).
to reach the above decompression value. At this time, the first
The pressure reducing passage 12 is closed by a first pressure regulating valve 16. - Injection and pressure reduction through the second pressure reduction passage - At the same time as injection from the mixing head 8 is started, the pressure reduction value through the second pressure reduction passage 15 is reduced to approximately 10 to 25 mmHg by the second pressure regulating valve 17. The injection time is about 1 to 3 seconds when the product weight is 3 to 6 kg. In this example, the amount of reaction liquid injected into the cavity was 5 kg, and the injection time was 2 kg as shown in Figure 4.
I made it into seconds. In this step, foaming due to the reaction of the reaction liquid begins at the cavity tip 5a during injection.
The reaction liquid in the cavity tip 5a is prevented from entering the air bleed passage 13 to a large extent because the pressure reduction value in the second pressure reduction passage 15 is relatively small and the passage diameter of the air bleed passage 13 is small. do not have. As the reaction liquid foams inside the cavity 5 and progresses from the tip 5a toward the gate 7, an increase in internal pressure can be seen near the gate, but due to the depressurization action in the second decompression passage 15, There is no significant increase in internal pressure near the gate. - Completion of injection, depressurization by first decompression passage - At the same time as completion of injection, the first pressure regulating valve 16 is set to the opening degree, and a depressurizing action by the first decompression passage 12 is applied to the vicinity of the gate. Its reduced pressure value is 100~250mmHg
It is. The pressure reduction by the second pressure reduction passage 15 may be stopped after the injection is completed, but in this example, the pressure reduction effect continues to be applied to the cavity tip 5a even after the injection is completed. The first vacuum passage 12 applies vacuum to the vicinity of the gate for about 20 seconds until foaming and gelation of the reaction solution (formation of a dense skin on the surface of the molded product) is completed. In this step, since the reaction liquid in the cavity 5 has started foaming from the tip 5a,
At the time of completion of injection, the internal pressure has increased in the vicinity of the gate and the area is in an overpressurized state, but when foaming begins in the vicinity of the gate (after completion of injection), the depressurization effect by the first depressurization passage 12 reaches the vicinity of the gate. Since the overpressurized state is eliminated, the reaction proceeds near the gate under approximately the same pressure conditions as the cavity tip 5a, resulting in homogeneous foaming, creaming, gelling, and
Curing takes place. And the second at the time of injection
Because the pressure reduction effect of the pressure reduction passage 15 suppresses a large increase in the internal pressure near the gate,
The pressure reduction value by the first pressure reduction passage 12 does not need to be so high. Therefore, the reaction liquid near the gate is similar to the reaction liquid in the cavity tip 5a at the start of injection, due to the small passage diameter of the first decompression passage 12 and the fact that the decompression value is not so high. Decompression passage 1
There is no significant intrusion into 2. -Curing, Mold Release- In this example, the curing of the reaction liquid is completed in about 30 seconds after injection is completed, and the mold becomes ready for release.After the mold is opened, the synthetic resin molded product is released, and burrs etc. remove. Next, a description will be given of tests to investigate the occurrence of defects in synthetic resin molded products under various reduced pressure conditions and the results thereof. -Test- In this test, a urethane molded product 19 shown in FIG. 3 was obtained. In the dimension symbol in the same figure, L ₁ = 1200
mm, L ₂ = 300mm, W = 600mm, T ₁ = 5mm, T ₂ = 2.5
mm. In addition, in the same figure, 20 is a thick part;
21 is a thin wall portion, 22 is a through hole, 23 is a gate portion,
24 is an after mixer section. The molding conditions are shown in Table 1.

[Table] In Table 1, primary reduced pressure means reduced pressure up to the start of injection, and secondary reduced pressure means reduced pressure from the start of injection. -Test Results- Table 2 shows the test results under different pressure reduction conditions. In addition, in Table 2, the numerical value in the section of the vacuum passage is the vacuum value, and the unit is mmHg.

【table】

[Table] In Table 2, test numbers 3 and 4 had almost no surface defects (sink marks) or voids (0
In addition, the sink marks that occurred were extremely thin and did not pose any problems as a product. Also, the diameter of the dent in test number 2 is 20
The dent in Test No. 3 was about 15 mm in diameter. Furthermore, in Test No. 5, clogging due to inflow of resin occurred at each opening (communication port) of the first reduced pressure passage and the second reduced pressure passage. Therefore, from the above results, it can be seen that the pressure reduction value in the first pressure reduction passage is preferably 100 to 300 mmHg, and the pressure reduction value of the secondary pressure reduction in the second pressure reduction passage is 10 to 30 mmHg. In addition, in the conventional method without reducing the pressure, the incidence of sink marks and voids was about 20 to 30%, depending on the properties of the reaction solution. Of course, the present invention can also be used in a reaction injection molding apparatus called R-RIM, which is filled with a reinforcing material. In addition, in the above example, two types of reaction liquids, an isocyanate-based stock solution and a polyol-based stock solution, were injected, but auxiliary agents such as catalysts were routed through a separate route, and three types of reaction liquids, ie, isocyanate-based, polyol-based, and auxiliary agents, were injected. The reaction solution may be injected into a mold. (Effects of the invention) According to the invention, since the depressurizing passage is communicated with both the tip of the cavity and the vicinity of the gate, the pressure within the cavity is kept approximately uniform throughout the cavity, allowing foaming and curing to proceed. At the same time, the gas present between the mold and the molded product can be vented from the tip of the cavity, making it possible to obtain a molded product without surface defects (sink marks) or voids. Further, since the reduced pressure is applied from the tip of the cavity into the cavity, the reduced pressure value on the gate side can be reduced, and the reaction liquid can be prevented from flowing into the reduced pressure passage.

[Brief explanation of the drawing]

The drawings illustrate embodiments of the present invention, in which Fig. 1 is a longitudinal sectional view of a reaction injection molding apparatus, Fig. 2 is a plan view of the same apparatus, Fig. 3 is a perspective view of a test molded product, and Fig. 4 is a reduced pressure FIG. 2 is a diagram showing the relationship between conditions, injection of a reaction liquid, and reaction progress status on a time axis. 1... Reaction injection molding device, 2... Molding mold, 5...
...Cavity, 5a...Cavity tip, 7...
...Gate, 11...Pressure reducing machine, 12...First pressure reducing passage, 15... Second pressure reducing passage, 16... First pressure regulating valve, 17... Second pressure regulating valve, 18... Control means.

Claims (1)

[Scope of utility model registration request] A reaction injection molding device that injects two or more reaction liquids into the cavity of a mold and foams and hardens them to produce a synthetic resin molded product, with one end communicating with the vicinity of the gate of the mold and the other end connected to a pressure reducing machine. a first reduced pressure passage connected to the cavity, one end of which communicates with the tip of the cavity far from the gate, and the other end of which is connected to the pressure reduction machine;
A control means is provided to cause the pressure reduction through the first pressure reduction passage to start after the completion of injection, and to perform the pressure reduction through the second pressure reduction passage from the time of injection by setting the pressure reduction value from atmospheric pressure to a value smaller than that on the first pressure reduction passage side. A reaction injection molding device characterized by: