JPS61143109A - Method of injection molding thermoplastic - Google Patents

Abstract

PURPOSE:To elevate a mold surface quickly so as to avoid quenching positively, by inserting a heat element between opened molds so that the mold surface that is required to be heated highly may be heated selectively. CONSTITUTION:By operating a transferring apparatus 20, a heat element 19 is inserted between opened molds 5, 9, and an electric current is passed to a heater 21. Thus, a mold surface A where a highly heated condition is required is heated directly to a certain temperature using a temperature detector 24. When the electric current to the heater 21 is stopped, a clamping apparatus 3 is actuated to clamp the molds 5, 9, and injection operation is effected by a plasticizing apparatus 12, so that a certain amount of a melted resin can be injected to fill the mold cavity before the mold surface A heated by the heater 21 cools.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for injection molding thermoplastic plastics.

(Prior art and its problems) As shown in FIG. 1, the temperature control of the surface of the mold for forming a molded product is carried out using the mold mounting plate 7. This is done only by indirectly heating or cooling the entire metal molds 5, 9, which are lumps of metal, by forcedly circulating a heat medium adjusted to an appropriate temperature through the medium passages 6, 10 provided in the molds 5, 9. Even if the heat medium flowing through the medium passages 6 and 10 is switched from a low temperature (or high temperature) medium to a high temperature (or low temperature) medium in synchronization with the molding process, the mold surface temperature changes extremely slowly and does not reach the predetermined temperature. It takes time to become. This prevents the resin injected and filled into the mold cavity 16 from contacting the mold surface A and cooling and solidifying during the injection filling process, and also prevents the holding pressure applied to the resin at the final stage of the injection filling process. If the mold surface A is kept at a high temperature so as to be reliably controlled, it will take time to cool the molded product in the cooling process, resulting in an extremely long cycle time.

Therefore, in the past, the molds 5 and 9 were required to be cooled in order to promote the cooling and assimilation of the resin in the mold cavity 16 in order to shorten the cycle time, and the cooling of the resin progressed during injection and filling. It was considered unavoidable.

However, in this conventional method, the resin surface is rapidly cooled by contact with the mold surface A during the injection filling process, leaving distortion in the cooling layer, and if the cooling of the resin progresses too much, the holding pressure cannot be reliably controlled. The problem of molding defects could not be avoided.

(Purpose of the Invention) The present invention was made to solve the above-mentioned problems in the conventional method, and while the mold should be cooled in the same manner as in the conventional method, the resin surface that should be prevented from being rapidly cooled can be surely cooled down quickly. The aim is to avoid this and achieve stable injection molding.

(Structure of the Invention) The present invention involves inserting a heat element between the molds in an open state prior to the injection filling process, and selectively heating the mold surface that requires particularly high temperature with the heat element. 0 (Example) An example of an injection molding machine embodying the present invention will be described below with reference to Figures 4 to 4.

In the figure, 1 is a fixed platen connected to a back plate 4 of a mold clamping device 3 via tie bars 2, and a fixed mold 5 is connected to the fixed platen 1 via a mold mounting plate 7 having a built-in medium passage 6. It is installed.

A movable platen 8 is slidably fitted to the tie bar 2 by a mold clamping device 3, and a movable mold 9 is attached to the movable platen 8 via a mold mounting plate 11 having a built-in medium passage 10. There is.

2 is a plasticizing device equipped with an injection nozzle 13, in which the raw resin supplied from the hopper 4 into the plasticizing cylinder 5 is melted while being kneaded by a screw (not shown), and the tip of the plasticizing cylinder 5 is melted by the metering retreat of the screw. After the molten resin is stored in the mold, a certain amount of the molten resin can be injected from the injection nozzle 13 through the sprue bush 17 into the cavity 16 formed by the molds 5 and 9 by advancing the screw.

I8 is an ejector pin used for ejecting the molded product.

Reference numeral 19 denotes a heat element, which is disposed on the upper part of the fixed platen 1 and the back plate 4, or on the side of the injection molding machine, so that it can be taken in and out between the molds 5 and 9 when the mold is opened in the transfer device 2o. .

When this heat element 19 is inserted between the molds 5 and 9, it is connected to a mold surface heating heater 21 corresponding to the mold surface A that requires a particularly high temperature in order to avoid rapid cooling of the resin, and A monitoring heater 22 corresponding to the mold surface B used for monitoring heating is embedded in a plate 23 made of an insulator such as quartz glass. On the other hand, a surface temperature detector arm such as a thermocouple is incorporated in the monitoring mold surface B.

25 is a control unit for controlling 19 and a transfer device ship, and 26 is a metal plate that circulates a heat medium through the medium passages 6 and 10 of the mold mounting plates 7 and 11 to adjust the temperature of the mold 5°9. A control section for controlling the mold temperature regulator, the mold clamping device 3, and the plasticizing device 12, and both control sections 25 and 26 are capable of sequentially controlling the operation of the injection molding machine, as will become clear from the following description. interconnected.

Next, a case in which the present invention is implemented using such an injection molding machine will be explained.

(1) When the operation is started, the transfer device 20 is activated and the heat element 19 is inserted between the open molds 5°9, and the heater 21 inside the heat element 19 is
is energized. This state is maintained during mold opening under control by a timer.

Therefore, the corresponding mold surface A, which requires a particularly high temperature, is directly heated by the heater 21 in the heat elm member 19, and the temperature is raised to a constant temperature by feedback control using the temperature detector 24.

(Depending on the time up of the stick timer, one element 1
9 exits from between the molds 5 and 9 to the outside, and the power supply to the heater 21 in the heat element 19 is cut off, but immediately after that, the mold clamping device 3 is activated to close the molds 5 and 9 and clamp the mold. is performed, and subsequently the injection operation is performed by the plasticizing device 12, so that a certain amount of molten resin is poured into the mold cavity 16 while the mold surface A heated by the heater 21 is not cooled down.
It will be injected and filled inside.

Therefore, although the molds 5 and 9 are adjusted to a constant low temperature by the mold temperature regulator, the mold surface A, which requires a particularly high temperature in order to avoid rapid cooling of the resin, is kept at a high temperature. The molten resin flows smoothly inside the mold cavity 16 without being rapidly cooled by the molds 5 and 9, and the holding pressure applied to the molten resin inside the mold cavity 16 at the final stage of the injection filling process also works reliably. Therefore, the molten resin is reliably filled into the mold cavity 16 in a stable state.

(3) The mold 5.9 is cooled by a mold temperature controller so that the temperature does not rise due to the heat retained by the molten resin in the mold cavity 16. Since the molds 5 and 9 are further cooled after the injection filling process, the molten resin in the mold cavity 16 is rapidly cooled.

Therefore, a molded article is formed in a short cooling process, and is then discharged from the injection molding machine through a mold opening process and a discharge process.

(→After the process of discharging the molded product, the heat niremen 19 is inserted between the molds 5°9 in the open state) and the above (η) is inserted.

The molding cycle of heating the mold surface A, mold clamping, injection/holding pressure, cooling, opening the mold, and discharging the molded product described in (2) and (3) is repeated.

(Effects of the Invention) As described above, according to the present invention, the timing of moving the heat element in and out of the mold and the timing of heat generation are linked to the operation of the molding machine, and the heat element is inserted into the mold prior to the injection filling process.
It is inserted between open molds, and the heat element selectively heats the surface of the mold that requires particularly high temperatures, allowing the temperature to rise reliably and quickly. It becomes possible to rapidly heat only the surface of the mold where it is desired to avoid rapid cooling of the injected and filled resin, which would be a problem in molding, while maintaining its rapid cooling function as an object to be cooled.

Therefore, the mold cavity can be reliably filled with molten resin in a stable state and then rapidly cooled, resulting in a high-quality, precise molded product.

[Brief explanation of the drawing]

FIG. 1 is a schematic front view of an injection molding machine for implementing the present invention;
Figure 2 is an enlarged cross-sectional view showing the mold of the same injection molding machine in the closed state, and Figures 3 and 4 are cross-sectional views and partially enlarged views showing the heating method of the same mold in the open state. be. l...Fixed platen, 2...Tie bar, 3...Mold clamping device, 4...Back plate, 5...Fixed mold, 6...Medium passage, 7...Mold installation Plate, 8...Movable platen,
9... Movable mold, 10... Medium passage, 11... Mold mounting plate, 12... Plasticizing device, 13... Injection nozzle, 16... Mold cavity 9... - Heat element, 20...Transfer device, 21...Mold surface heating heater, 22...Monitoring heater, 23...Pull,
Rate, 24...Temperature detector, 25. 26...control unit. 1, 3, and 18. 11

Claims (1)

[Claims] Injection molding of thermoplastic plastics, which is characterized by inserting a heat element between open molds prior to the injection filling process, and selectively heating the mold surface that requires particularly high temperature with the heat element. Method.