JPS5845944B2 - Injection molding method for crosslinkable polymer materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in methods for injection molding crosslinkable polymeric materials.

The term "polymer material" as used herein refers to rubbers and synthetic resins, and "crosslinking" includes not only crosslinking of synthetic resins but also Calosulfur of rubber.

Conventionally, in injection molding of crosslinkable polymer materials, the molding material is plasticized in a screw extruder, and then the plasticized material extruded from the extruder is passed through a passage connecting the extruder and the cavity, in which case each injection amount is The cutting edge is heated to a constant temperature, and the heated material is press-fitted into the cavity to perform crosslinking.

In this method, the time required for cross-linking of the molding material that is extruded from the extruder and press-fitted into the cavity is equal to the time required to press-fit the molding material into the cavity;
This corresponds to the sum of the time required for crosslinking of the molding material that was last press-fitted into the cavity, but if the molding material that reached the cavity last is crosslinked, the time after reaching the cavity is at least longer than the time required for press-fitting. , and wasting this waiting time is not effective from the standpoint of shortening the molding cycle.

In addition, since the molding material is forced into the cavity after leaving the extruder, it is heated to a nearly constant temperature in the passage.
There is a shift in the timing of starting crosslinking between the material press-fitted first and the material press-fitted last into the cavity due to the press-fitting time difference, which is also unfavorable in terms of the quality of the molded product.

The present invention provides an improved injection molding method for a crosslinkable polymeric material. Specifically, in a method for injection molding a crosslinkable polymeric material that involves a crosslinking reaction during molding,
The molding material to be press-fitted into the cavity is rapidly heated at the cutting tip while being transferred to the cavity, and the heating temperature is gradually increased from the beginning to the end of the transfer of the molding material, so that the cavity is filled with the molding material. After that, the entire cycle of the molding material is crosslinked almost simultaneously and molded.

This will be explained in detail below based on the attached drawings.

FIG. 1 shows an example of an apparatus for carrying out the present invention, in which 1 is a ring 2 having a molding material inlet 4 and a heated fluid passage 5 in the pipe, and a ring 2 provided inside the ring 2 for kneading and transferring the material. The extruder is composed of a rotating screw 3, and the base of the screw 3 is connected to a hydraulically operated piston (not shown) so that it can reciprocate.

The molding material plasticized by the extruder 1 is stored in a cylinder in front of the retracted screw, from which material outside the molding cycle is extruded to the tubular heater 11.

The tubular heater 11 is composed of a multi-tube type made up of relatively small diameter tubes, and generates Joule heat by applying a voltage from the outside through the connection pieces 15 and 16, thereby causing the passage inside the tubes to be heated. It is designed to heat the molding material passing through it.

In the figure, 12 is a nozzle, 13 is a mounting board for the tubular heater 11,
14 is the bag nut.

As shown in FIG. 2, the tip of the tubular heater 11 is crimped and connected to the mold protrusion 6 through a nozzle 12, for example, by spherical contact, so that the two can be separated as necessary. You can.

The molding material leaving the tubular heater 11 is then sent to a mold for crosslinking molding.

The mold consists of a fixed mold 6 and a movable mold 7 with a cavity 8 inside.
is molded, and heaters 9 and 10 are built into the fixed plates 9 and 10 of both molds, respectively, and the temperature of the mold is maintained approximately equal to the crosslinking temperature of the molding material by the heaters. There is.

The above has described the outline of the process from the extruder for the crosslinked molding material to the mold.Next, we will discuss the special temperature control of the molding material in the tubular heater, which is a feature of this invention. A means for gradually increasing the heating temperature of the material for one cycle passing through the pipe from the beginning to the end of the material transfer into the pipe will be explained.

Means for heating the molding material using the tubular heater can be roughly divided into two: supplying the required power to the tubular heater and automatically controlling the supplied power.

Hereinafter, a specific example of these will be explained in detail with reference to FIG. 3, which shows an electrical system diagram.

In the figure, 17.18 is a limit switch, 19.2
0 is a bar for moving the limit switch.

The limit switch 17 moves on the bar 19 and is activated when the tip of the screw shaft 3 hits the mounting board 13 of the tubular heater 11. On the other hand, the limit switch 18 moves on the bar 19. It is set to operate at a position of, for example, about 4 degrees from the position toward the base of the screw shaft 3.

An operating protrusion 21 is fixed to the base of the screw shaft 3, and this protrusion moves forward and backward together with the screw shaft to operate the respective contacts of the limit switches 17 and 18.

Activation of this contact means that the contacts of the circuit (normally closed circuit) in which current always flows inside the limit switch are separated and the current changes so that it cannot be restored.

In the figure, 22 is a snap switch for injection instruction, 23 is a timer that can arbitrarily adjust the delay time of injection instruction, 24 is a drive device that provides injection output to the screw shaft, 25 is a power source,
26 is a power switch, 27 is a magnet switch, 28
29 is a slide transformer, 29 is a step-down transformer, and 30 is a control device.

In order to issue an injection command, first, the injection command current emitted from the snap switch 22 enters the limit switches 17 and 18, passes through each of the above-mentioned normally closed circuits, and one reaches the timer 23, and the delay time set by this timer, for example, 05 seconds. The injection command is transmitted to the injection drive device 24 with a delay of 10 minutes.

As a result, the injection by the screw shaft 3 is actually started 05 seconds later than the injection instruction.

and after the start of injection - material outside the molding cycle is injected;
The tip of the screw shaft 3 is the mounting board 13 for the tubular heater 1
When it reaches the position where it hits, the limit switch 17 is activated, the injection instruction current is cut off, and the injection 1 drive device 24 is stopped.

Next, the current passing through the limit switch 18 on the west side enters the electromagnetic coil of the magnet switch 27 that leads the power source 25 to the slide transformer 28, energizes and closes the electromagnetic coil, and sends it to the tubular heater 11 for heating the blade tip. send electricity.

The tip of the screw shaft 3 is a mounting board 13 for the heater.
When the limit switch 18 is activated to open the magnet switch 27, for example, when the position reaches the fourth position, the limit switch 18 is activated.

The current signal that excites this electromagnetic coil is simultaneously transmitted to the control device 3.
0, this control device operates the step-down transformer 29 and/or the slide transformer 28 to automatically control the amount of power supplied to the tubular heater 1 according to time.

Figure 4 is for explaining the above automatic control in detail.
The step-down transformer 29 shown in FIG.
In this figure, 31 is a movable iron piece, 32 is a hydraulic linter, and 32 is a shaft.

The cylinder shaft 32 is movable in and out in the direction of the fingertip a, and moves a movable iron piece 31 fixed to the tip thereof, thereby adjusting the leakage magnetic flux, that is, the leakage reactance, of the magnetic leakage transformer 31, and the secondary side, that is, the tubular heater 11. Increase or decrease the amount of electricity supplied to

FIG. 5 shows a hydraulic system for hydraulically adjusting the movement in and out of the movable iron piece 31 to make the amount of electric power match the target value, in which 33 is an oil pump, 34 is a pressure reducing valve, 35 is a flow rate control valve, 36 is a directional control valve.

Now, if we assume that the injection time of the extruder 1 is 10 seconds, the material for one molding cycle that is heated while passing through the tube of the tubular heater 11 and press-fitted into the cavity 8 will be at that temperature. The temperature at which crosslinking occurs in a short time, say 13 seconds, at the start of injection, for example, 180°C, and the temperature at which crosslinking occurs in a short time, say, 3 seconds, at the end of injection, say 2.
If the material is raised with a nearly linear gradient at 0.00C or more, the entire material within the cavity will be crosslinked at the same time within 3 seconds after the injection is completed.

Therefore, it is safe to increase the thermal output as time passes from the start of injection of material for -4 cycles to the end 1 as long as the above conditions are satisfied.

For this purpose, the magnetic switch 2 detects the start of injection.
A current signal that excites the electromagnetic coil 7 is simultaneously sent to the directional control valve 36, thereby injecting a certain amount of oil at a certain pressure into the hydraulic cylinder 32, and moving the movable iron piece 31 fixed to the printer shaft 32 from its fixed position. The leakage magnetic flux of the magnetic leakage transformer 31 is reduced by moving away from the center of the magnetic flux in the outward direction at a constant speed, thereby increasing the induced voltage on the secondary side, and increasing the amount of electric power supplied to the tubular heater 11. increase the heat output of

Next, when the end of injection is detected, a current signal is sent to the opposite directional control valve of the directional control valve 36, and the movable iron piece 31 is returned to its original position through hydraulic pressure in the opposite direction.

Although it is not difficult to numerically calculate and control the almost linear output power inlet that supplies the amount of electric power to the tubular heater 11, in actual work, it is difficult to observe the molded product, the flow rate control valve, etc. Desired optimum conditions can be easily achieved by increasing or decreasing the rate of change by adjusting 35, or by increasing or decreasing the output position by changing the fixed position of the movable iron piece 31 or the brush 37 of the slide transformer 37 shown in FIG. 6, which will be described later. It is possible to find out.

FIG. 6 shows a slide transformer 37 in place of the slide transformer 28 shown in FIG. 3, which is coupled with a swing motor 38 that can reciprocate at any rotation angle within 360 degrees using hydraulic pressure as power. In the diagram, 37 is a brush, 38.3
8 is a hydraulic inlet/outlet, 39.39 is a primary side tap of the slide transformer, and 40.40 is a secondary side tap.

The rotating shaft of the brush 37 is concentrically connected to a swing motor 38, and during the swing rotation of the motor, the brush 37 is reciprocated from any fixed position to any fixed position in the song at any constant speed. This allows the secondary voltage to be sent to the step-down transformer 29 to be controlled.

The hydraulic pressure for operating the swing motor 38 may be provided by replacing the hydraulic cylinder 32 shown in FIG. 5 with the swing motor 38.

In addition, the means for controlling the force and heat of the molding material in the tubular heater is not limited to the method of the embodiment described above; for example, the swing motor 38 can be replaced by a super variable speed electric motor or a combination thereof.

In addition to the above-mentioned example, the above-mentioned automatic control that controls the amount of electric power can also be performed by electrically or electronically controlling the music.

Furthermore, although the above-mentioned automatic control assumes that the flow rate of the injection material for the -acid type cycle is always approximately constant, in reality, the flow rate cannot be said to be strictly constant;
At the start of injection, there is usually a flow velocity difference of one violet in the song.

Therefore, if such a one-violet difference in flow velocity is to be taken up as a problem and the above-mentioned automatic control is to be carried out with high accuracy, for example, a temperature measuring device should be installed near the outlet of the nostle 12 of the tubular heater 1. It is also possible to incorporate a sensor, use this sensor as a detection end, select an appropriate one from among the wide range of automatic control methods for the songs described above, and control the amount of electric power as the control target.

In addition to injection molding using the above-mentioned automatic control, instead of keeping the amount of power supplied to the tubular heater 1 constant, the flow rate of the molding material passing through the tube of the tubular heater is changed to increase the flow rate at the time it passes through the tube. Control can also be performed by adding the above-mentioned temperature difference to the material temperature.

In this case, as a means to change the flow rate of the molding material, for example, a flow control valve that adjusts the amount of oil sent from the storage chamber at the tip of the plasticizing cylinder to the cylinder that injects the molding material, can be automatically controlled in accordance with the above example. It's fine.

According to this invention, in injection molding of a crosslinkable polymer material that causes a thermal crosslinking reaction during molding, the crosslinking time of the molding material press-fitted into the cavity after injection into the cavity is several seconds regardless of the size of the molded product. Not only can the cavity be shortened, but also the entire material within the cavity is cross-linked at the same time, making it possible to obtain a molded product of better quality than conventional products.

It should be noted that the present invention and its implementation device are not limited to injection molding, but can also be used in song molding techniques, for example transfer molding (also called injection molding).

That is, it is possible to similarly speed up crosslinking by incorporating the force heating device (based on a resistance heating tube) of the apparatus according to the present invention into a part of the raw material passage connecting the raw material storage chamber of transfer molding and the molding cavity.

[Brief explanation of the drawing]

Fig. 1 is a partial sectional view of the device implementing the present invention, Fig. 2 is a partially enlarged sectional view of Fig. 1, Fig. 3 is an electrical system diagram of the device implementing the present invention, and Fig. 4 is the electricity supplied to the tubular heater. FIG. 5 is a perspective view of an example of an automatic quantity control device, FIG. 5 is a hydraulic system diagram for adjusting the automatic control device of FIG. 4, and FIG. 6 is a perspective view of a slide transformer. DESCRIPTION OF SYMBOLS 1... Extruder, 2... Plasticizing cylinder, 3... Rotating screw shaft, 6... Fixed mold, 7... Movable mold, 8... Cavity, 11... Tubular Heater, 24・
...Injection, driving device, 30...Temperature control device.

Claims (1)

[Claims] 1. In a method of injection molding a crosslinkable polymer material that involves a crosslinking reaction during molding, the molding material press-fitted into the cavity is rapidly heated during transfer to the cavity,
In addition, the thermal temperature at the cutting edge is gradually increased from the beginning to the end of the transfer of the molding material, and after the cavity is filled with the molding material, the entire cycle of the molding material is crosslinked almost simultaneously and molded. Characteristic injection molding method for crosslinkable polymer materials.