JPH0716868A - Method and apparatus for molding resin - Google Patents

Abstract

PURPOSE:To lessen a pressure loss and to enable execution of injection molding under a low pressure by a method wherein a prescribed quantity of molten resin is stored and the stored molten resin is injected into and made to flow in a molding part by using the pressure of the fluid and molded therein. CONSTITUTION:A resin passage of a nozzle 25 is closed by a shut-off valve 26, while a resin passage 19 is closed by a three-way valve 20, and a breathing mechanism 27 communicates with a resin inlet 15 through a selector device 22, a gas passage 23 and the three-way valve 20 and reduces a pressure in a storage chamber 14. When the resin passage 19 is opened by the three-way valve 20, molten resin 28 flows into the storage chamber 14 by a prescribed quantity with the rotating motion of a screw 12. Then, the resin passage 19 is closed by the three-way valve 20, while a nitrogen gas supply source 21 is connected with the resin inlet 15 through the selector device 22 and the gas passage 23 and a nitrogen gas of high pressure is introduced into the storage chamber 14. By opening the shut-off valve 26 of the nozzle 25, the molten resin 28 in the storage chamber 14 is injected under the pressure of the nitrogen gas into a cavity 8 from a resin outlet 16 through the nozzle 15 and filled up therein.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin molding method and a molding apparatus used for the method.

[0002]

2. Description of the Related Art In the case of injection molding a resin, a step of plasticizing and melting the resin and a step of injecting and filling the melted resin into a cavity of a mold are required. In order to make the two processes efficient, generally, an "in-line screw" mechanism is often adopted, and the configuration is as shown in FIG. 3, which will be described below with reference to FIG.

In FIG. 3, 31 is a mold which is separated along a parting line 32 into a fixed mold 33 and a movable mold 34. The movable mold 34 is connected to a hydraulic ram 37 for opening and closing the mold. The movable die 34 reciprocates to form a cavity 38 between the movable die 34 and the fixed die 33. Reference numeral 39 is a cylinder in which a screw 40 is disposed inside and a nozzle 41 is attached to the tip end, 42 is a heater disposed around the cylinder 39, and 43 is a hopper that stores resin pellets to be supplied to the cylinder 39. , 44 are screws 4
A motor for rotating 0, a deceleration mechanism 45 for decelerating the rotation of the motor 44 and transmitting it to the screw 40, a hydraulic injection cylinder 46 for reciprocating the screw 40 in the front-rear direction, and 47 mounted on the front end of the screw 40. It is a check ring for preventing backflow.

Next, the operation will be described. In the plasticizing / melting process, the cylinder 3 is fed from the hopper 43.
The solid resin pellets supplied to the inside 9 are plasticized by the frictional heat generated by the shearing frictional force with the screw 40 rotated by the drive of the motor 44 and the heat conduction from the heater 42 to become fluid. .

Next, the molten resin is transported forward of the cylinder 39 by pushing open the check ring 47 by the pushing force of the rotating screw 40, and the reciprocating screw 40 is transported forward of the molten resin 48. It retracts due to its own internal pressure and is stored in the front end portion of the molten resin cylinder 39 in an amount necessary for molding.

Then, in the injection molding process, the molten resin 48 accumulated at the front end portion of the cylinder 39 is injected into the cavity 38 of the mold 31 from the nozzle 41 by the screw 40 moving forward by the hydraulic pressure of the injection cylinder 46. Is filled.

When the screw 40 moves forward,
The check ring 47 is closed to prevent the molten resin from flowing back.

Thereafter, the mold 31 is cooled by cooling water to obtain a resin molded product corresponding to the shape of the cavity 38.

[0009]

When a resin is injection-molded by a conventional molding apparatus, the molten resin is transported forward by the rotational movement of the screw in the cylinder, and at the same time, a predetermined amount of the molten resin is nozzled by the reciprocating movement of the screw. Was injection-filled into the cavity and molded.

In this case, however, since the screw requires extremely complicated motions of rotation and reciprocation, a large power is required as a driving source of the screw, and further, when the molten resin flows to the cavity, it is generated. The pressure loss is large, and as a result, it is difficult to downsize the molding apparatus, and there is a problem in terms of energy saving.

In the resin molding apparatus, assuming a static sealing state in which molten resin does not flow out from the tip of the nozzle, the static Pascal principle is established, so that the injection cylinder diameter is D _i , Assuming that the screw diameter is D _S , the hydraulic pressure introduced into the injection cylinder is P _i , and the molten resin pressure at the screw tip is P _S , then P _S = P _i × (D _i / D _s ) ² (1) .

In the recent molding apparatus, the maximum molten resin pressure P _s max obtained when the hydraulic pressure P _i is increased to the maximum pressure P _i max of the injection cylinder is 200 M.
It is designed to appear even if it exceeds P _a .

However, in normal molding, injection molding is usually performed at a pressure lower than the maximum molten resin pressure P _s max. If the pressure at that time is the required molten resin pressure P _s act, that pressure is When the mechanical friction loss due to bearings is ignored, the molten resin flowing in the injection process has the physical properties of liquid and causes pressure loss. Is decided so as to be in balance with the total pressure loss when flowing.

The pressure loss is now Δ in the screw portion.
Pscr, when the nozzle portion DerutaPnoz, the cavity portion and _{ΔPcav, P s act ≧ ΔPscr +} ΔPnoz + ΔPcav (2) next, in a total ordinary injection molding pressure loss in each section, a large and very 100MP _a more In most cases, the required molten resin pressure P _s act needs to be extremely large.

On the other hand, the required molten resin pressure P _s act is P _s act = P _i act × (D _i / D _s ) ² (3) from the above equation (1), so the required molten resin pressure P _s act In order to increase the value of (D _i / D _s ) is constant, the required hydraulic pressure P
_i act must be large.

Therefore, if the required hydraulic pressure is increased,
Inevitably, the molding apparatus becomes large in size, and a large amount of energy is required to generate a large hydraulic pressure, which is a problem.

Further, assuming that the physical properties of the molten resin are a viscous Newtonian fluid having a viscosity μ, and its flow path is simplified to be a cylindrical flow with a radius R and a flow path length L, the molten resin The pressure loss ΔP due to the flow of is ΔP = 8 · μ · L · V / R ² (4). However, it is assumed that the flow velocity V is constant and is a steady flow.

In the injection step, when the molten resin existing at the tip of the cylinder is pushed out from the nozzle by the forward movement of the screw and injected and filled in the cavity of the mold, the driving source for moving the screw forward is the hydraulic pressure introduced into the injection cylinder. And, as can be seen from FIG. 3, the injection cylinder 46
Is at the far end of the flow end of the molten resin, that is, the position farthest from the cavity 38 of the mold 31, and the flow path length L of the equation (4) becomes a very large value when the molding apparatus becomes large.

Therefore, when a sufficient pressure is applied to the flow end in injection molding, the pressure loss ΔP also increases when the flow path length L is large, so that the hydraulic pressure introduced into the injection cylinder is _a very large pressure exceeding 10 MPa. There was also a problem that was necessary.

In the present invention, the pressure loss is reduced by making the molten resin flow to the molding portion by utilizing the pressure of the fluid.
It is an object of the present invention to provide a resin molding method and a resin molding apparatus that can perform injection molding at a low pressure.

[0021]

In order to achieve the above object, in the resin molding method of the present invention, the resin is plasticized
It has a step of melting, a step of storing a predetermined amount of the molten resin, and a step of injecting a predetermined amount of the stored resin into the molding portion of the mold by the pressure of the fluid.

The pressure of the fluid for injecting a predetermined amount of the stored resin into the molding portion of the mold is a gas inert to the resin, or a liquid such as an inert gas, air, or water. Can also be used at a pressure of.

In order to achieve the above object, in the resin molding apparatus of the present invention, a portion for plasticizing / melting the resin, a portion for storing a predetermined amount of the molten resin, and a predetermined amount of the stored resin And a part for molding the resin injected by the pressure of the fluid.

A portion for storing a predetermined amount of the melted resin can be provided at a portion for plasticizing / melting the resin, a portion for molding the resin, or between these portions.

Further, a resin storage chamber is provided at a portion for storing a predetermined amount of the molten resin, and a resin inflow portion and a resin outflow portion are provided in this storage chamber, and these inflow / outflow portions are opened. The inner surface of the storage chamber is preferably formed in a curved shape.

Further, the inner surface of the resin storage chamber provided in a portion for storing a predetermined amount of the melted resin is preferably coated with a resin that is non-adhesive to the resin, for example, a Teflon coating or a ceramic coating such as TiN. It is effective.

[0027]

When resin molding is performed by the resin molding method and the resin molding apparatus configured as described above, the drive source for flowing the melted resin to the molding portion of the mold uses the pressure of the fluid. Therefore, the pressure applied to the molten resin has a small pressure loss, is well transmitted to the flow end, and evenly pressurizes each part of the resin, so that the above-mentioned required molten resin pressure is reduced, and as a result, the required fluid pressure is reduced. Even if it is set small, it works so that a smooth resin flow can be obtained.

Since the fluid layer can penetrate into the inside of the molten resin layer, the flow distance becomes substantially small and the pressure loss becomes small. Therefore, the required molten resin pressure can be set small. Also works so as to obtain a good resin flow, and so-called loose low-pressure molding becomes possible.

Further, when the fluid layer is made to penetrate into the molding portion of the mold, the injection driving source comes closer to the flow end, the substantial flow distance is further reduced, and the pressure loss is also reduced. Acts to allow even lower pressures. In addition, when the fluid layer reaches near the flow end, the pressure holding effect is enhanced and the transferability is also enhanced, and the cavity is formed by removing the fluid after molding or leaving it as it is. If it does so, it will become a hollow molded article, and it will be effective in terms of saving the amount of resin.

On the inner surface of the chamber where the molten resin is stored,
By forming a curved surface portion or coating the entire inner surface with a resin and a non-adhesive coating, the flow of resin in the room and the transmission of pressure are improved, and it acts to further reduce pressure loss. You can also

[0031]

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

In FIG. 1, 1 is a parting line 2
Is a mold which is separated into a fixed mold 3 and a movable mold 4 along the movable mold 4, and the movable mold 4 is connected to a mold clamping hydraulic ram 7 through a movable side fixed plate 6 and reciprocates to move to and from the fixed mold 3. A cavity 8 for molding the resin is formed therebetween. Reference numeral 9 is a cylinder for plasticizing and welding resin, 10 is a heater arranged around the cylinder 9, 11 is a hopper for supplying solid phase resin pellets into the cylinder 9, and 12 is a screw arranged in the cylinder 9. The resin pellets 29 are plasticized by being rotated by the driving device 13 including a motor deceleration mechanism. Reference numeral 14 is a storage chamber for the molten resin 28, and the resin inlet 1
5 and a resin outlet 16 are provided, and the resin inlet 1 is provided on the inner surface.
5, curved surface portions 17 and 18 having the outlet 16 as an apex are respectively formed, and the shape of the portion is made into a conical shape. The inner surface of the storage chamber 14 is covered with a film made of Teflon. Reference numeral 19 is a resin flow path connecting the cylinder 9 and the resin inlet 15 of the storage chamber 14, and 20 is a three-way valve provided in the resin flow path 19, which shuts off the resin flow path 19 to connect the cylinder 9 and the storage chamber 14. Between the gas inflow valve, which is connected to the supply source 21 of high-pressure gas, for example, nitrogen gas, and which connects the gas flow path 23 having the switching device 22 with the resin inflow port 15. It has both functions and features. 24 is a heater arranged around the storage chamber 14,
25 is a nozzle that connects the storage chamber 14 and the cavity 8 of the mold 1, 26 is a shut-off valve provided in the nozzle 25,
It has a function of opening and closing the resin passage of the nozzle 25. Two
Reference numeral 7 is a degassing mechanism that communicates with the gas flow path 23 via the switching device 22, 28 is a molten resin, and 29 is a resin pellet.

Next, the operation will be described. First, the resin passage of the nozzle 25 is closed by the shut-off valve 26, the resin passage 19 is closed by the three-way valve 20, and the degassing mechanism 27 is operated by the switching device 22 and the gas. Channel 23, three-way valve 2
The inside of the storage chamber 14 is depressurized by communicating with the resin inflow port 15 via 0.

On the other hand, in the cylinder 9, the screw 12
The resin pellet 29 is plasticized and melted by the rotating motion of the screw and the heating of the heater 10, and the screw 1 that rotates at the same time
2 is transported to the front part of the cylinder 9.

Next, when the resin flow passage 19 is opened by the three-way valve 20, the molten resin 28 flows into the storage chamber 14 by a predetermined amount due to the rotational movement of the screw 12. In this case, since the inner surface of the storage chamber 14 is covered with the Teflon film and the curved surface portion 17 is formed in the vicinity of the resin inlet port 15,
The molten resin 28 flows into the storage chamber 14 extremely smoothly.

Next, the resin passage 19 is closed by the three-way valve 20, and the nitrogen gas supply source 21 is switched to the switching device 22,
If the high pressure nitrogen gas is introduced into the storage chamber 14 and the shutoff valve 26 of the nozzle 25 is opened by connecting the resin inlet 15 via the gas flow path 23, the molten resin 28 in the storage chamber 14 will be removed. From the resin outlet 16 through the nozzle 25, the cavity 8 is injected and filled with nitrogen gas pressure. Also in this case, the inner surface of the storage chamber 14 is covered with a Teflon film, and the presence of the curved surfaces 17 and 18 makes it extremely effective to introduce high-pressure gas into the storage chamber 14 and to flow the molten resin 28 into the cavity 8. proceed.

A schematic view of the flow state of the molten resin 28 with reference to FIG. 2 shows that the high-pressure gas layer 30 slightly penetrates into the reservoir chamber 14 as shown in FIG. Partially flows into the cavity 8.
In the middle injection stage, as shown in (b), the high pressure gas layer 3
0 presses the molten resin 28 in the storage chamber 14 and causes most of the molten resin 28 to flow into the cavity 8. When the injection is completed, as shown in (c), the storage chamber 1
The molten resin 28 in 4 is entirely injected and flowed into the cavity 8 due to the gas pressure, and is filled in the cavity 8. At the same time, the high-pressure gas layer 30 enters the molten resin 28 in the cavity 8.

Therefore, since the high-pressure gas layer 30 which is the driving source for injection reaches the vicinity of the flow end 31 of the molten resin 28, the substantial flow distance becomes short, and the gas pressure is also present. Therefore, the pressure loss also becomes small, and as a result, the gas pressure required for injection can be efficiently injection-molded even at _a low pressure of ₁ to 20 MPa.

Further, since the high-pressure gas layer 30 penetrates into the cavity 8 and presses the molten resin 28, the pressure-holding effect is enhanced, the transferability is enhanced, and the obtained molded product becomes a hollow body. It also has the effect of reducing the amount of resin.

When the amount of molten resin flowing into the storage chamber 14 is a predetermined amount required for molding, the high pressure gas layer 30 can enter the cavity 8.
Although a molded product of the hollow body as described above is obtained, the chamber volume is set such that a predetermined amount of molten resin that is equal to or more than the amount of resin required for molding can flow into the storage chamber 14, or the amount of high-pressure gas introduced is appropriate. Alternatively, if the high-pressure gas layer 30 is prevented from entering the cavity 8, a molded product that is not a hollow body can be obtained.

The amount of high-pressure gas to be introduced is determined by the volume of the cavity, the porosity of the hollow body, the injection speed, the resin viscosity and the like.

[0042] Now, when using the ABS resin as the resin was injection molded casing of the molded article thicker with nitrogen gas 10MP _a as a high pressure gas, the pressure of the high pressure gas 4MP _a,
The amount of high-pressure gas was 3 liters in the standard state, and a good injection molded product was obtained, but when the same molded product was obtained by the conventional "in-line screw" system, the injection pressure was 120.
When MP _a is required and high pressure gas is used, molding can be performed with a low injection pressure.

According to the above embodiment, the screw 12
Need only have the functions of plasticizing and melting the resin and the function of transporting the molten resin, and does not require the function of injecting the molten resin into the molding part of the mold as in the past. Therefore, the reciprocating motion is unnecessary by only the rotary motion, and as a result, the screw mechanism can be simplified and the molding apparatus itself can be downsized. Further, the screw 12 does not need to have the conventional check ring 47, and the problem such as resin burning which is likely to occur at the check ring portion can be solved.

Furthermore, since the injection molding uses the pressure of the gas, the pressure is transmitted to the flow end in the cavity without loss, so that the required molten resin pressure can be reduced, and as a result, the low pressure molding becomes possible. .

In the above embodiment, the storage chamber 14 is described as being arranged between the cylinder 9 and the mold 1, but it can be arranged inside the cylinder 9. If it is provided at the so-called loose resin transport portion, it can also have a function of measuring the amount of molten resin required for molding. The storage chamber 14 is a mold 1
It can also be installed inside, and in this case it can also be provided with the function of preventing the generation of runners by providing it in the manifold portion of the so-called hot runner mold.

[0046]

Since the present invention is constructed as described above, it has the following effects.

A predetermined amount of the melted resin is stored, and the stored molten resin is injected and flowed into the molding section by utilizing the pressure of the fluid, so that the loss of pressure is reached to the flow end of the molding section. Is small, and the pressure can be evenly transmitted, and a good molded product can be obtained.

Since no mechanical motion is used to drive the injection pressure, the molding apparatus can be simplified.

Further, since the pressure loss is small, the required molten resin pressure can be reduced, and so-called low pressure molding can be performed.
As a result, low distortion molding and high transfer molding can be performed.
Since the pressure resistance of the mold can be small, the cost of the mold can be reduced.
Also effective for downsizing of molding equipment.

Further, the required molten resin pressure can be further reduced by setting the volume of the reservoir, the amount of fluid, the pressure of fluid, etc. so that the fluid can penetrate into the molding portion at the end of injection. In addition, it is possible to obtain a hollow molded article having good transferability and reduced resin amount.

Furthermore, if a curved surface is formed on the inner surface of the chamber for storing the molten resin or a non-adhesive coating with the resin is applied, the flow of the molten resin and the transmission of fluid pressure can be made smoother. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory diagram of a resin molding apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing a flow state of a molten resin in an example of the present invention.

FIG. 3 is a cross-sectional explanatory view of a conventional resin molding device.

[Explanation of symbols]

 1 Mold 8 Cavity 9 Cylinder 12 Screw 14 Reservoir 15 Resin Inlet 16 Resin Outlet 17, 18 Curved Surface 21 Gas Supply Source 25 Nozzle 28 Molten Resin

Claims (6)

[Claims] 1. A step of plasticizing and melting a resin, a step of storing a predetermined amount of the melted resin, and a step of injecting a predetermined amount of the stored resin into a mold molding portion by the pressure of a fluid. A resin molding method comprising: 2. A predetermined amount of the stored resin is injected into a mold molding section by the pressure of gas or liquid.
The resin molding method described. 3. A portion for plasticizing and melting a resin, a portion for storing a predetermined amount of the melted resin, a portion for supplying a fluid pressure to the stored predetermined amount of resin, and an injection by the fluid pressure. And a part for molding the molded resin. 4. A part for plasticizing and melting a resin, a part for molding a resin, or a part between these parts,
The resin molding apparatus according to claim 3, wherein a portion for storing a predetermined amount of the melted resin is provided. 5. A resin storage chamber is provided at a portion for storing a predetermined amount of melted resin, and a resin inflow portion and a resin outflow portion are respectively provided in the storage chamber.
The resin molding apparatus according to claim 3, wherein a curved surface portion is formed on the inner surface of the storage chamber where the outflow portion opens. 6. The resin molding apparatus according to claim 5, wherein an inner surface of the resin storage chamber is coated with a molten resin and a non-adhesive coating.