JPS6360724A - Injection molding method - Google Patents

Abstract

PURPOSE:To improve a quality by preventing a weld line, flow mark, etc., by performing injection molding by clamping a mold by taking out a heating member after confronting faces of a movable mold and stationary mold have been heated by means of the heating member. CONSTITUTION:A mold clamping action of both molds 10, 20 is performed during operation extending from a state where both of the molds 10, 20 are heated at an appropriate temperature to that directly before joining of parting faces of a stationary mold 10 and movable mold 20 together and once stopped. Under this state a heating member 30 is inserted between faces 16, 25 confronting with each other. When the confronting faces of the molds 10, 20 are heated by the heating member 30, the confronting faces are changed to a state where a temperature of the confronting faces turned higher than that of the inside of the mold. After the confronting faces have been turned into this state, the mold clamping action is completed by removing the heating member 30 from a space between the confronting faces 16, 25 of the molds 10, 20. Molten thermoplastics is injected through a nozzle 3 while a temperature of the confronting faces is higher than those of the insides of both the molds 10, 10. The injected plastics is filled up by flowing smooth without being cooled suddenly.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an injection molding method, for example, a method for injection molding materials such as resins that melt easily but also harden quickly.

Traditionally, molds are divided into a fixed mold and a movable mold, and the facing surfaces of each divided mold are in direct contact with the atmosphere and have a higher temperature than other parts of the mold. decreases (see Figure 7)
Therefore, during molding, the resin flow flowing along this opposing surface slows down and hardens quickly, resulting in weld lines and flow marks on the product, which deteriorates the quality of the product. Therefore, in order to solve this problem, a passage for passing hot air or heated steam was provided near the opposing surfaces in the mold.
Immediately before injection, as described above, a heating medium is passed through to heat the opposing surfaces including the parting surface, but hot air is also sent into the cavity space of the clamped mold just before injection. However, the former has the problem that the mold structure is complex and expensive, and the temperature control becomes complicated as not only the opposing surface is heated but also the inside of the mold, while the latter causes uneven temperature if the cavity is large. At the same time, the hot air must be passed through the hot air inlet and the resin must be prevented from leaking, making the mold structure complicated and expensive.

Purpose Therefore, this invention heats the facing surfaces of a movable mold and a fixed mold with a heating member, and then takes out the heating member and clamps the mold to perform injection molding, thereby eliminating weld lines, flow marks, etc. on the surface of the product. The purpose is to provide an injection molding method that can improve the quality of the products.

EXAMPLE Hereinafter, an example of an apparatus for carrying out the injection molding method of the present invention will be described with reference to FIGS. 1 to 6.

In the figure, reference numeral 1 denotes a fixed plate, and the fixed plate 1 is provided with a hole 5 into which a nozzle 3 is inserted. A movable platen 7 faces the fixed platen 1 and moves forward and backward as shown by arrows. A fixed mold 10 is fixed to the fixed platen 1, and a movable mold 20 is fixed to the movable platen 7. The fixed mold 10 is formed with a nozzle touch 11 for receiving the nozzle 3, a sprue 12 following the nozzle touch 11, a runner 13, and a cavity 14 at the end of the runner 13 to form the shape of the product. On the other hand, movable mold 2
0, the sprue 12. of the fixed mold 10 when the mold is clamped.
A sprue 21, a runner 22, and a cavity 23 are formed which are integral with the runner 13 and cavity 14, respectively.

Furthermore, both molds io and zo are provided with oil temperature control pipes 15 and 24 for controlling the temperature of the molds. Fixed mold 10
and a facing surface 16 that faces the movable mold 20 when the mold is clamped;
25 has cavities 14.23. Runner 13.22
and both molds 10.20 each other than sprue 12.21
There is a parting surface 17.26 which contacts and seals.

As can be seen when the molds 10 and 20 are clamped, in this example they are two molds for a biconvex lens.

A heating member 30 is sandwiched between the mold 10 and the mold 20 in FIG. ing. In this example, the heating member 36 has a flat plate shape as shown in FIG. 3, but depending on the shape of the product, like the heating member 40 shown in FIG. It may also be formed by Also, the fifth
As shown in the figure, the heating member 50 may be in the form of a sheet or film. In the case of the heating member 40 as shown in FIG. 4, the entire opposing surface 16.25 can be heated more uniformly.

Next, a molding method using the injection molding apparatus having such a configuration will be described.

In the mold open state as shown in FIG. The mold clamping operation is carried out until just before the .26 comes together, and then stopped. In this state, the opposing surfaces 16 of both molds 10.20
．． a heating member 30 that heats the opposing surface 16.25 between 25 and 25;
Insert 40.50 as shown in Figure 1. heating member 30,
The gap between 40.50 and the parting surface 17.26 is 0.
The thickness is preferably about 1 to 10 mn. And heating member 30,
When the facing surface of the mold 10.20 is heated at a temperature of 40° 50°C (100 to 200°C, approximately 0.5 to 10 seconds, depending on the mold temperature), the state shown in Fig. 7 changes to the facing face shown in Fig. 6. The temperature changes to become higher than the temperature inside the mold. After reaching this state, the heating members 30, 40, 50 are removed from between the opposed surfaces 16.degree. 25 of the molds 10, 20, and the mold clamping operation is completed. The molten thermoplastic is injected from the nozzle 3 while this opposing surface is hotter than the inside of both molds 10.20. The molten thermoplastic from nozzle 3 passes from nozzle touch 11 through sprue 12.21 to runner 13.2.
2 and fills the cavity 14.23.

During this time, the opposing surfaces 16 and 25 of both molds 10 and 20, especially the surfaces of the runners 13 and 22 and cavities 14 and 23, are heated to high temperatures, so the injected plastic moves along these surfaces more rapidly than before. It flows smoothly and fills without being cooled. Therefore, weld lines are not formed where two flows collide, or flow lines with noticeable flows are not formed, and the quality of the product can be guaranteed. After filling, the mold is kept under pressure and cooled, then the mold is opened and the product is taken out.

Effects As explained above, according to this invention, injection molding is performed using a heating member that heats only the facing surface, rather than heating the entire mold, so that the flow of molten thermoplastic plastic is reduced. It is possible to provide an injection molding method that produces high quality products that are free from molding defects such as weld lines and flow marks. Furthermore, since this method does not heat the entire mold and only heats the opposing surface, the heating time does not take very long, and since the heat capacity is small, cooling does not take much time, so the molding cycle can be made faster than other heating processes. It can be made shorter by comparison.

[Brief explanation of drawings]

Figures 1 to 6 show an embodiment of an injection molding apparatus for carrying out the injection molding method of the present invention, and Figure 1 shows the injection molding apparatus in a state where the opposing surface is heated with a heating member. FIG. 2 is a front view of the main parts of the injection molding apparatus in the mold open state, FIGS. 3, 4, and 5 are perspective views showing an example of the heating member, and FIG. FIG. 7 is a diagram showing the temperature state of the mold when the conventional heating member is not used. 10... Fixed mold 13.22... Runner 14.23... Cavity 16.25...
Opposing surface 17.26...Parting surface 20...Movable mold 30, 40, 50...Heating member Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 6 -〇 1 Fig. 5 Figure 7

Claims (1)

[Claims] The mold clamping operation is stopped just before the parting surfaces of the movable mold and the fixed mold come together, and a heating member for heating the opposing surfaces is inserted between the opposing surfaces of the two molds to heat the opposing surfaces. After removing the heating member from between the opposing surfaces and completing mold clamping, inject and fill the molten thermoplastic while the opposing surfaces are at a higher temperature than the insides of the two molds, and after cooling, open the molds and perform molding. An injection molding method characterized by: