JPH0755511B2 - Ultra high molecular weight polyethylene injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is excellent in impact resistance, wear resistance, self-lubricating property, chemical resistance and the like, and is capable of performing highly accurate molding. Therefore, the present invention relates to an injection molding method of ultra-high molecular weight polyethylene, which is being widely used for various machine parts, household products, etc., and particularly, in this injection molding method, a molten resin is injected into a mold cavity at a high shear rate. It is indispensable to inject with a high shear rate imparting mechanism on the injection molding machine side to increase the degree of freedom of molding and to manufacture a die at low cost. Injection molding method.

(Prior Art) Regarding the injection molding method of ultra high molecular weight polyethylene, conventionally, as shown in Japanese Patent Publication No. 57-30067, it is possible to inject a resin in a flash flow state injected at a high shear rate into a mold cavity. Stated. Generally, the shear rate is represented by γ = 4Q / πR ³ . However, γ: shear rate (sec ^-1 ), Q: injection rate (cc / sec), R: inlet radius (cm)
And To give a high shear rate in the above equation, Q
It is necessary to increase R or decrease R, but Q
The maximum value of is determined by the maximum injection capacity of the injection molding machine, and in the injection molding method of ultrahigh molecular weight polyethylene, R is usually adjusted to achieve a high shear rate. For example, in an injection molding machine with a mold clamping force of 50 tons that is generally commercially available, the injection rate is around 100 cc / sec. Therefore, the injection rate is 50000 sec ^-1 or more as described in JP-B-57-30067. In order to obtain the shear rate of, R must be 0.137 cm or less. That is, a portion for obtaining a high shear rate as described above must be provided in the resin flow path, and this portion is usually the gate portion 21a or runner portion 2 of the fixed mold 21 as shown in FIG.
It is installed in 1b. FIG. 4 is a diagram showing a three-piece mold, which is composed of an intermediate mold 24 between a fixed mold 21 and a movable mold 23. When the gate 21a is made smaller, the sprue runner 21b is taken out. It is necessary to make a work on the intermediate mold 24 for use. In addition, 25 is a molded product.

(Problems to be Solved by the Invention) In the above-mentioned conventional technique, when a portion for obtaining a high shear rate is installed in a mold, the mold has already been engraved and there is no degree of freedom. When the injection rate Q changes, the molten resin has to be shot, and R must be set to a predetermined value by trial and error, which requires a great number of steps. Also,
Japanese Examined Patent Publication No. 57-
As described in 30067, after the action of the injected molten resin being flushed into a fine cotton candy shape and the action of the fine resin being evenly distributed in the cubity, It is important that the high-molecular-weight polyethylene 26 is fusion-bonded and integrated over the entire mold cavity, and compression-molded in order to obtain a hard molded product having no void inside. In order to perform such compression molding, as shown in FIG. 5, the piston 22 is moved to the right to compress the ultra-high molecular weight polyethylene 26 in the mold cavity. The phenomenon in which the ultrahigh molecular weight polyethylene 26 in the cavity flows backward to the screw 28 side of the heating cylinder 27 of the injection molding machine, and a sufficient compression force cannot be applied to the molded product. For this purpose the gate part 21a
A method of mechanically shutting off the mold may be considered, but when this method is adopted in the mold, there is a problem that the mold becomes complicated and the manufacturing cost increases due to an increase in size.

(Means for Solving the Problems) The present invention has been made to solve the problems in the above-mentioned conventional techniques, and the resin is controlled by the opening degree of the rotary valve attached to the tip of the nozzle of the injection molding machine and the moving speed of the screw. The shear rate applied to the mold cavity is selected and adjusted, cotton-like resin is supplied into the mold cavity, and the rotary valve is fully closed immediately after the predetermined stroke of the screw is injected. The object was achieved by an injection molding method of ultra-high molecular weight polyethylene, which is characterized by compressing.

(Operation) At the tip of the nozzle of the injection molding machine, a rotary valve controlled by a throttle opening setting device that can be set independently of the resin injection speed setting value is provided. The shear rate of the molecular weight polyethylene is determined by the injection speed set value (Q) and the rotary valve opening set value (R; the hydraulic equivalent circle radius R giving the shear rate is variable depending on the throttle opening). As described above, the ultra-high molecular weight polyethylene which has been given a high shear rate in the rotary valve section forms a flash flow state as described in Japanese Patent Publication No. 57-30067 and is filled in the cavity of the mold. After the mold cavity is filled with a predetermined injection amount in the flash flow state, the rotary valve is fully closed and, at the same time, the mold cavity is compressed. Since the state of the resin filled in the mold cavity is cotton-like, it is difficult to measure in the cavity before compression, but the shear rate given to ultra high molecular weight polyethylene in the screw is 10 to 10 ² sec ^-1 ,
In this state, the ultra-high molecular weight polyethylene is in a molten and highly viscous state and is not a cotton-like flash flow, so the predetermined amount of resin to be filled into the mold cavity can be easily and accurately measured by the stroke of the screw. You can

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a view showing an apparatus for carrying out an injection molding method for ultra high molecular weight polyethylene according to the present invention, wherein 1 is a screw fitted into a cylinder 2 of an injection molding machine, and 3 is a screw for pressing the screw 1. Cylinder for injecting ultra-high molecular weight polyethylene with a rotary valve 4 for giving a high shear rate to the ultra-high molecular weight polyethylene, and 5 an ultra-high molecular weight with a high shear rate given by the rotary valve 4. A nozzle for guiding polyethylene to the gate portion 6a of the fixed mold 6, a movable mold 7 for forming a mold cavity 9 together with the fixed mold 6 and the piston 8, and 10 a piston rod 3a of the injection cylinder 3. With respect to the screw position detector whose axial movement is fixed, 11 is the stroke setting device of the screw 3, and 12 is the set value of the stroke of the screw 3 and the actual value. Comparator for comparing measurements, 13
Is an injection speed setting device controlled by a signal from the comparator 12, and 14 is a hydraulic pressure source 15 by a signal from the injection speed setting device 13.
Injection rate control device for controlling the amount of hydraulic oil supplied from the injection cylinder 3 to the injection cylinder 3, 16 is a valve opening setting device controlled by a signal from the comparator 12, 17 is the valve opening setting device 16 A drive device for the rotary valve 4, which is controlled by the signal of the above, and a compression force setting 18 for giving a compression force to the ultra high molecular weight polyethylene in the mold cavity 9 by the signal from the valve opening setting device 16. And 19 is the compression force setting device
The hydraulic oil from the hydraulic power source 20 is supplied to the piston 8 based on the signal of 18
It is a compressing force control device for supplying the hydraulic oil chamber 8a to the compressing force to the ultra high molecular weight polyethylene in the mold cavity 9. Next, the operation will be described. First, in the injection process, according to the set values set in the injection speed setting device 13 and the valve opening setting device 16, the moving speed of the screw 1 (the injection rate Q is determined by this value) by the injection speed control device 14 and the valve driving device 17. Is determined) and the opening degree of the rotary valve 4 is determined, and the ultrahigh molecular weight polyethylene is transferred to the mold cavity 9 by a predetermined shear rate determined by these two values.
It is injected inside. The injection amount of the ultra high molecular weight polyethylene is determined by the amount of the screw 1 moving the value of the screw stroke setting device 11 which is set in advance. That is, after the start of injection, the screw position detector moves as the screw 1 moves.
10 detects the movement stroke, and the comparator 12 compares it with the value set in the screw stroke setting device 11.
When they match, the injection speed control device 14 issues a command indicating the movement of the screw 1, that is, a command to stop the injection and a command to completely close the rotary valve 4 to the valve drive device 17, and at the same time, the mold is pressed. When a compression start command is issued to the compression force control device 19 for compressing the cavity 9, the hydraulic force source 15a supplies the hydraulic force chamber 15a of the piston 8 to the compression force control device 1.
Since the hydraulic oil is supplied through 9 and the hydraulic oil in the hydraulic oil chamber 8b is returned to the tank 20, the piston 8 compresses the cotton-like ultra high molecular weight polyethylene in the mold cavity 9 and the timer period (not shown) Inside the compression continues. FIG. 2 is a diagram showing the operation timings of the injection speed control device 14, the valve drive device 17, and the compression force control device 19 in the device shown in FIG. The description of FIG. 2 is omitted because it has been described in FIG.

(Effects of the Invention) As described in detail above, according to the present invention, the following effects are obtained.

(1) The high shear rate application of ultra-high molecular weight polyethylene is freely adjusted and set by the opening degree of the rotary valve provided in the injection molding machine and the injection speed setting.

(2) Even if the sprue runner of the mold is processed in a certain state, the adjustment device for giving the shearing speed is installed on the injection molding machine side, so that the mold reworking correction is unnecessary.

(3) The amount of resin filled in the mold cavity can be accurately measured by the position (stroke) of the screw.

(4) By fully closing the rotary valve during the compression process, it is possible to prevent the resin from flowing back from the mold cavity to the injection molding machine side, so that the compression pressure can be set high and a good quality molded product can be obtained. it can.

(5) Since the gate of the molded product in the mold can be molded even if it is a direct gate, the gate can be enlarged, so that the mold can be manufactured at a low cost without using a complicated three-plate mold or the like. .

[Brief description of drawings]

FIG. 1 is a diagram showing an apparatus for carrying out the injection molding method for ultrahigh molecular weight polyethylene of the present invention, and FIG. 2 is an injection speed control device 14, a valve drive device 17 and a compression force in the device shown in FIG. FIG. 3 is a diagram showing the operation timing of the control device 19, and FIGS. 3 to 5 are diagrams showing a conventional technique. 1 …… Screw 2 …… Cylinder 3 …… Injection cylinder 4 …… Rotary valve 5 …… Nozzle 6 …… Fixed mold 7 …… Movable mold 8 …… Piston 9 …… Mold cavity 10 …… Screw position detection Device 11 …… Screw stroke setting device 12 …… Comparator 13 …… Injection speed setting device 14 …… Injection speed control device 15, 15a …… Hydraulic source 16 …… Valve position setting device 17 …… Valve drive device 18… … Compression force setting device 19 …… Compression force control device 20 …… Tank

Claims (1)

[Claims] 1. A cotton-like resin is supplied into a mold cavity by selecting and adjusting a shearing rate applied to the resin according to an opening of a rotary valve attached to a tip of a nozzle of an injection molding machine and a moving speed of a screw. An injection molding method of ultra-high molecular weight polyethylene characterized in that the rotary valve is fully closed immediately after injection of a predetermined stroke of the screw and the mold cavity is compressed at the same time.