JPH10278083A - Screw for injection molding machine of liquid silicone rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent worn powder and flash of a molding and to improve a metering accuracy by providing a valve chamber having a valve in contact with a valve seat of a rear part urged by a coiled spring at a central channel from a confluent part of a plurality of oblique channels combined at a periphery of a central axis inclined from a material inhibiting inside base to a central axis and a central channel. SOLUTION: Liquid silicone rubber 62 is slushed, accumulated and enhanced at its pressure in an oblique channel 54 by the rotation of a screw, and a ball valve 58 is moved to an end of a screw head 52. The rubber 62 is invaded from a gap between a valve seat 56 and the valve 58 into a valve chamber 57, slushed to a resin bank 50 via a central channel 55, accumulated, and enhanced at its compression force in the bank 50. The head 52 is returned back by its reaction. The rotation of the screw is stopped by a limit switch to complete a metering step. The valve 58 is urged to the seat 56 by a coiled spring 59 to prevent backflow of the rubber 62. Accordingly, there is no fear of generating and mixing frictional powder, and accurate metering and injecting can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a screw for an injection molding machine for liquid silicone rubber.

[0002]

2. Description of the Related Art Conventionally, silicone rubber molded products have been obtained by molding a millable silicone rubber using a mold, but recently, injection molding technology of liquid silicone rubber has been developed. Accordingly, a molded product can be obtained simply and easily as in the case of injection molding of a thermoplastic resin.

[0003] In general, in injection molding of a thermoplastic resin, a thermally softened resin is injected into a mold, cooled and solidified into a predetermined shape, and then the mold is opened to take out a molded product.

At this time, since the volume of the resin injected into the mold decreases as the resin cools, so-called sink marks are generated. In injection molding of a thermoplastic resin, a sufficient injection pressure is applied until the resin is cooled and solidified. The addition of (cushion molding) has been performed to prevent the occurrence of sink marks.

On the other hand, in the injection molding of liquid silicone rubber, a normal temperature liquid silicone rubber capable of being heat-crosslinked is injected into a mold heated to about 130 to 200 ° C.
A molded article is obtained by rapidly heating in a mold to cause a crosslinking reaction and curing.

At this time, as the liquid silicone rubber injected into the mold is heated from room temperature to the temperature of the mold, the pressure generated due to the expansion of the volume of the liquid silicone rubber and the injection pressure are combined, so that the injection pressure in the cavity is reduced. The pressure increases rapidly. And when the amount of liquid silicone rubber injected into the mold is larger than the volume in the cavity of the mold,
Due to lack of mold closing pressure per unit area due to thermal expansion, burrs may occur or the shape and dimensions of molded products may be inaccurate, so the amount of rubber injected must be accurately measured (cut off) Molding).

FIG. 7 shows a system using a screw-in-line type injection molding machine used for injection molding of a conventional liquid silicone rubber.

When performing injection molding of liquid silicone rubber by this system, first, the liquid silicone rubber 2 is supplied into the cylinder 3 by the operation of the pump 1 and the driving means 4
The screw 5 is retracted while rotating, and the liquid silicone rubber 2 is kneaded in the cylinder 3 while being kneaded.
Is moved in the direction of the front end.

As the liquid silicone rubber 2 moves toward the tip of the screw 5, as shown in FIG.
A check ring 7, which is incorporated between the rear end surface of the screw 5 and the sealing portion 6 of the screw 5 behind the rear end surface, moves in the distal direction, and moves in the distal direction. The rear end surface and the front end surface of the check ring 7 abut.

The inner wall of the cylinder 3 and the outer diameter of the check ring 7 are fitted so that the check ring 7 can move freely in and out of the cylinder 3, but the resin does not leak from the fitting portion. Is set closely.

The liquid silicone rubber 2 has a gap formed between the outer diameter of the screw 5 and the inner diameter of the check ring 7,
Through a plurality of concave portions 8 formed in the axial direction of the tip portion of the screw 5, and flows into a resin pool 9 formed by the tip surface of the screw 5 and the inner wall of the cylinder 3.

Since the flow path of the raw material in the nozzle 10 incorporated at the tip of the cylinder 3 is normally shut off by opening and closing means (not shown), as the liquid silicone rubber 2 accumulates, the liquid silicone in the resin reservoir 9 The compression force of the rubber 2 increases, and the screw 5 is gradually pushed back by the reaction force.

When the screw 5 retreats to a predetermined position, the operation of the driving means 4 is controlled by the limit switch 11 shown in FIG. 7, and the retraction is stopped simultaneously with the stop of the rotation of the screw 5. As a result, a predetermined amount (one shot) of the liquid silicone rubber 2 is stored in the resin reservoir 9, and the plasticization (metering) process is completed.

Next, the nozzle 1 is opened and closed by opening / closing means (not shown).
The liquid silicone rubber 2 stored in the resin reservoir 9 at the tip end surface of the screw 5 by the operation of the injection cylinder 12 is opened by the operation of the injection cylinder 12 through the nozzle 10.
It is pushed into 3.

At this time, as shown in FIG. 9, the non-return ring 7 moves rearward due to the reaction force received from the liquid silicone rubber 2 in the resin pool 9, and the rear end face of the non-return ring 7 is 6 to prevent the liquid silicone rubber 2 from flowing backward.

Thereafter, the preheated mold 1
After the liquid silicone rubber 2 is kept in the inside 3 for a certain period of time and sufficiently cured by a crosslinking reaction, the mold 13 is opened to take out a molded product, and one cycle of molding is completed.

[0017]

However, in the conventional screw in-line type injection molding machine as described above,
At the time of metering and injection, the front and rear end faces of the check ring 7, which is a valve for preventing the backflow of the raw material resin, collide with the rear end face of the tip portion of the screw 5 and the seal portion 6, and at this time, abrasion powder generated due to contact between the two. There is a problem that the liquid silicone rubber is mixed into the liquid silicone rubber 2.

In particular, at the time of injection, the check ring 7 is rapidly moved rearward due to the reaction force of the injection pressure, so that a strong impact force collides with the seal portion 6 and causes abrasion powder to be generated. Further, after receiving a reaction force from the liquid silicone rubber 2 in the resin pool 9 at the time of injection, the check ring 7 is pushed back to prevent a backflow of the raw material resin.
A time lag occurs between the moment when a predetermined amount of resin is transferred to the resin reservoir 9 and the measurement is completed, and the moment when the check ring 7 and the seal portion 6 of the screw 5 abut to seal the resin reservoir 9, and accurate measurement cannot be performed. There was a problem.

Further, since the check ring 7 located at the tip of the screw 5 operates only by the pressure change of the liquid silicone rubber 2 due to the rotation of the screw 5, the viscosity of the liquid silicone rubber 2 and the operating speed of the screw 5 Susceptible to external disturbances, such as incomplete operation of the valve,
There has been a problem that accurate weighing cannot be performed as described above due to non-operation.

In the molding of liquid silicone rubber, the thermal expansion coefficient specific to liquid silicone rubber is large, the flowability is good,
Due to properties such as high compressibility, it is difficult to measure with the conventional injection molding machine as described above, and burrs and short shots are liable to occur on molded products.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and a valve for preventing backflow of a raw material resin which has been operated only by a change in pressure of the raw material resin at the time of measurement or injection is measured. Later, by changing to a structure with a new backflow prevention mechanism that closes immediately by the spring force of the coil spring, the generation of wear powder caused by contact between the valve and other parts when opening and closing the valve is prevented, and the weighing accuracy is greatly improved. The main purpose is to prevent the occurrence of burrs and short shots in molded products.

[0022]

SUMMARY OF THE INVENTION A screw for a liquid silicone rubber injection molding machine according to the present invention is disposed in a cylinder, and rotates around a central axis to transfer a material between the cylinder and the tip in a tip direction. In the screw, a bulging material blocking portion is formed at a tip portion, and a plurality of inclined flow paths inclined from a plurality of locations on an inner base portion of the material blocking portion toward the central axis and joined around the central axis. Forming an internal resin flow path consisting of a central flow path from the junction of the flow paths to the tip along the central axis, and further forming a valve chamber having a valve seat at the rear in the central flow path; It is characterized in that a valve abutting on the valve seat is urged by a coil spring and disposed in the chamber.

Generally, the shape of the valve is preferably spherical or conical, and the spherical or conical portion is used in contact with the valve seat.

In general, a tip portion having a material blocking portion, an internal resin flow path and a valve chamber is detachably fixed to a screw body, and this portion is separately processed.

Further, the distal end portion is configured to be dividable by a screw structure or the like at a position including the valve chamber, and the distal end portion is separated when it is necessary to expose the inside during cleaning or otherwise.

In the screw for a liquid silicone rubber injection molding machine according to the present invention, the coil spring presses the valve against the valve seat in the valve chamber, so that the backflow of the liquid silicone rubber is prevented.

At the start of the measurement, the resin receives a force greater than the resilience of the coil spring in the direction away from the valve seat due to the flow of the resin, so that the resin is transferred forward.

In particular, in the screw of the present invention, the resin flow path is quickly closed by the coil spring at the same time as the transfer of the resin is stopped, so that the resin is accurately measured, and there is no possibility that burrs are generated on the molded product.

The contact portion as the backflow prevention mechanism is only one portion of the valve and the valve seat, and since the valve is already closed at the time of injection, the valve and the valve seat do not collide with a strong impact force. .

[0030]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing an injection molding system used in an embodiment of the present invention.

This injection molding system comprises a screw-in-line type injection molding machine 21, a storage tank 23 for storing a liquid silicone rubber (liquid A) 22 containing a platinum catalyst,
A storage tank 25 for storing a liquid silicone rubber (liquid B) 24 containing a delay material, and a liquid silicone rubber A liquid 22,
Pumps 26 and 27 for sucking liquid B 24, and constant ratio measuring plungers 3 for supplying liquid silicone rubbers 22 and 24 from cocks 28 and 29 to injection molding machine 21 at the same ratio.
0 and a mold 31 for molding the raw rubber (mixture of the A liquid and the B liquid) into a predetermined shape.

The liquid silicone, which is the raw material rubber of the molded product, is first separated into two liquids, liquid A 22 and liquid B 24, and is stored at 25 ° C. or lower by a cooling device (not shown). . The composition of the A liquid 22 and the B liquid 24 shown in the following composition table is such that the time during which the injection molding from the mixing of the A liquid 22 and the B liquid 24 to the spontaneous curing is 3 days at room temperature. It is designed to be of the order.

(Component Table) Liquid A: silicone polymer, filler, platinum catalyst, pigment Liquid B: silicone polymer, filler, crosslinker, retarder, pigment The injection molding machine 21 has a supply pipe 41 as shown in FIG. ,
A liquid 22 of liquid silicone rubber supplied from 42;
Screw 44 for kneading liquid B 24 in cylinder 43
A cooling unit 45 for cooling the cylinder 43 to 25 ° C. or lower, a driving unit 46 for rotating the screw 44, a limit switch 47 for controlling the rotation of the screw 44 and the back and forth movement, Nozzle 48 blocking the flow path of the raw rubber by opening / closing means (not shown)
And a nozzle cylinder 49 capable of moving the nozzle 48 between the mold 31 and the tip of the cylinder 43 so as to be able to move forward and backward. Injection cylinder 5
1 and a screw head 52 incorporated at the tip of the screw 44.

The screw head 52 has a substantially conical tip at the tip as shown in FIG.
The rear end is a screw that is detachable from the tip of the screw 44. At the rear, there is a bulged material blocking portion 53, which is inclined from the inner base of the material blocking portion 53 to the tip side, and joins the rotation axis of the screw 44 to the inclined flow passage 54 and from the junction of the inclined flow passage 54. A central flow path 55 extending to the tip along the rotation axis and a valve chamber 57 having a valve seat 56 at the rear of the central flow path 55 are formed.
6, a steel ball valve 58 is arranged to be urged by a coil spring 59.

The substantially conical conical portion 60 having the central flow passage 55 and the valve portion 61 having the valve chamber 57 and the inclined flow passage 54 are separate parts that can be divided. The coil spring 5
The load 9 may be a relatively low load as long as the ball valve 58 can be moved without being affected by disturbance such as viscous resistance of the raw rubber.

In the injection molding system using the screw of the embodiment of the present invention configured as described above, molding is performed as follows.

First, A liquid 22 and B liquid 24 of liquid silicone stored in storage tanks 23 and 25 pass through cocks 28 and 29 by operating pumps 26 and 27, respectively, The A liquid 22 and the B liquid 24 of the silicone are measured at the same ratio, and are supplied from the supply pipes 41 and 42 into the cylinder 43 of the injection molding machine 21 at a resin supply pressure of, for example, 40 kg / cm ² as shown in FIG. You.

The operation of the driving means 46 causes the screw 44
Retreats while rotating, liquid silicone A liquid 22, liquid B 2
4 is kneaded in the cylinder 43 while being transferred to the screw head 52 side as shown in FIG.

While the screw 44 continues to rotate, the liquid silicone rubber 62 flows into the inclined flow passage 54, and as the liquid silicone rubber 62 accumulates, the pressure of the liquid silicone rubber 62 in the inclined flow passage 54 gradually increases. hand,
As shown in FIG. 5, the ball valve 58 moves to the tip side of the screw head 52.

The movement of the ball valve 58 causes the liquid silicone rubber 62 to enter the valve chamber 57 from the gap between the valve seat 56 and the ball valve 58, and to flow through the central flow path 55 to the resin pool 5.
Flows to zero. At this time (at the time of measurement), the flow path of the liquid silicone rubber 62 in the nozzle 48 is closed by opening / closing means (not shown) provided in the nozzle 48.

Therefore, as the liquid silicone rubber 62 accumulates, the liquid silicone rubber 6
2, the screw head 52 is gradually pushed back along with the screw 44 by the reaction force.

Thereafter, for example, when the 15 cm screw 44 is retracted, the limit switch 47 operates to stop the rotation of the screw 44, and at the same time, the screw 44
Stops retreating and the weighing process ends, for example, 200cc
Is stored in the resin pool 50.

At this time, since the pressure received from the inclined flow passage 54 is lower than the load of the coil spring 59, the ball valve 58 is immediately moved by the resilience of the coil spring 59 to the valve seat 5.
6 to return to the same arrangement as before the start of the measurement shown in FIG. 4, and the backflow of the liquid silicone rubber 62 is prevented.

Next, the nozzle cylinder 49 shown in FIG.
The nozzle 48 is moved to, for example, the mold 31 heated to 150 ° C. by the operation described above, and subsequently, the flow path of the raw material in the nozzle 48 is opened by opening / closing means (not shown).

By the operation of the injection cylinder 51, the liquid silicone rubber 62 stored in the resin reservoir 50 is injected into the mold 31 at an injection pressure of 150 to 200 kg / cm ² by the movement of the screw head 52 and the screw 44, for example. .

After the injection, the flow path of the raw material in the nozzle 48 is closed by opening / closing means (not shown), and is retracted toward the cylinder 43 by the operation of the nozzle cylinder 49.

After that, the liquid silicone rubber 62 is
For example, the mold is put into the mold 1 for about 1 to 2 minutes, and after a crosslinking reaction occurs and is cured, the molded article is taken out from the mold 31 and one cycle of molding is completed as described above.

According to the injection molding system using the screw according to the embodiment of the present invention, the valve is naturally closed by the coil spring 59 set at a relatively low load when the supply pressure from the rear of the screw 44 decreases. Because of the mechanism, the ball valve 58 and the valve seat 56 do not come into contact with each other due to a strong impact due to a reaction force of the injection pressure or the like. Therefore, there is no possibility that abrasion powder is generated by the operation of the ball valve 58 and is mixed into the liquid silicone rubber 62.

Further, the ball valve 58 in the screw head 52 of the injection molding machine 21 is pressed against the valve seat 56 immediately after the measurement is completed by the resilience of the coil spring 59, so that the ball valve 58 is affected by disturbance. The ball valve 58 can be operated without fail and the valve can be closed, whereby the backflow of the liquid silicone rubber 62 from the resin reservoir 50 can be prevented.

Therefore, the measurement accuracy can be improved, and short shots and burrs of the molded product can be prevented.

Further, the screw head 52 alone is screwed into the screw 44 and is a detachable and separate component, and the conical portion 60 and the valve portion 61 having the valve chamber 57 can be disassembled. In addition, maintenance is easy when the liquid silicone rubber 62 solidifies in a sludge shape in the internal resin flow path.

In this embodiment, the spherical ball valve 58 is used as a valve for preventing the backflow of the liquid silicone rubber. However, the conical valve 63 has a conical shape as shown in FIG.
However, the same effect can be obtained.

[0054]

According to the screw for an injection molding machine for liquid silicone rubber of the present invention, the valve for preventing backflow of the raw resin does not come into contact with other parts such as the valve seat with a strong impact force. There is no danger that abrasion powder will be generated by the opening and closing operations of the liquid and mixed into the liquid silicone rubber.

Also, as soon as the pressure received from the raw material resin behind the screw falls below the set load of the coil spring, a mechanism for closing the backflow prevention valve is provided. There is no time lag between the moment when the liquid is supplied and the measurement is completed and the moment when the valve is closed and the resin pool side is closed, so that accurate measurement and injection can be performed.

Further, since the check valve is operated by the resilience of the coil spring in addition to the pressure change of the raw resin, it is hardly affected by disturbances such as the viscosity of the raw resin and the operating speed of the screw. The valve can be reliably operated, and accurate metering and injection can be performed as described above.

Therefore, the use of the above-described mechanism for preventing the backflow of the raw material resin can improve the measurement accuracy, so that it is possible to suppress the occurrence of burrs and short-circuits in the finished molded product.

[Brief description of the drawings]

FIG. 1 is a diagram showing an injection molding system used in an embodiment of the present invention.

FIG. 2 is a sectional view of an injection molding machine used in an embodiment of the present invention.

FIG. 3 is a sectional view of a screw head used in an embodiment of the present invention.

FIG. 4 is a detailed view of a screw for an injection molding machine before the start of measurement in an embodiment of the present invention.

FIG. 5 is a detailed view of a screw for an injection molding machine at the start of measurement according to an embodiment of the present invention.

FIG. 6 is a detailed view showing another shape of a valve according to the present invention.

FIG. 7 is a view showing an injection molding system used for molding a conventional liquid silicone rubber.

FIG. 8 is a detailed view of a conventional screw for an injection molding machine at the start of metering.

FIG. 9 is a detailed view of a conventional screw for an injection molding machine immediately after injection.

[Explanation of symbols]

Reference numeral 21: injection molding machine, 43: cylinder, 44: screw, 52: screw head, 53: material blocking part, 54: inclined flow path, 55: central flow path, 56: valve seat, 57 ... valve chamber, 58 ... ball valve, 59 ... coil spring, 60 ... conical part, 61 ... valve part, 62 ...
Liquid silicone rubber, 63 ... conical valve.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazuhisa Urakawa 6-31 Roppongi, Minato-ku, Tokyo Toshiba Silicone Corporation

Claims (4)

[Claims] 1. A screw which is disposed in a cylinder, rotates around a central axis, and transfers a material between the cylinder and the tip in a tip direction. A plurality of inclined flow paths that incline toward the central axis from a plurality of locations on the inner base of the blocking portion and merge around the central axis, and a central flow path from the junction of the inclined flow paths to the tip along the central axis And a valve chamber having a valve seat at the rear in the central flow path, and a valve abutting on the valve seat is biased by a coil spring in the valve chamber. A screw for an injection molding machine for liquid silicone rubber, characterized in that: 2. The screw for an injection molding machine for liquid silicone rubber according to claim 1, wherein the shape of the valve is spherical or conical. 3. The injection of liquid silicone rubber according to claim 1, wherein a tip portion having the material blocking portion, the internal resin flow path and the valve chamber is detachably fixed to a screw body. Screw for molding machine. 4. A screw for a liquid silicone rubber injection molding machine according to claim 1, wherein said tip portion is configured to be dividable at a position including a valve chamber.