JP5649695B2 - Thermoplastic resin injection molding method - Google Patents

Description

  The present invention relates to a thermoplastic resin injection molding method. More specifically, the present invention relates to an injection molding method in which a gas is dissolved in a molten resin to reduce the viscosity of the molten resin, and the mold surface is highly transferred to the surface of a molded product.

  In general, in injection molding, a mold is kept at a temperature lower than the glass transition temperature of the molding resin, and a molten resin is filled in the mold, pressure-holding, and cooling to obtain a molded product.

  Specifically, first, in the resin filling step, the molten resin in contact with the mold surface by the fountain flow at the tip of the fluidized resin is cooled by a mold having a glass transition temperature lower than that to form a high-viscosity layer called a skin layer. Thereafter, in the resin pressure-holding step, the skin layer is pressed against the surface of the mold to transfer the mold surface to the surface of the molded product, and the molded product is obtained by holding and cooling. Therefore, in order to highly transfer the mold surface to the surface of the molded product, it is necessary to keep the viscosity of the skin layer small before the resin pressure holding step.

  For this reason, in the prior art, a method of keeping the viscosity of the skin layer small by keeping the mold lower than the glass transition temperature of the molding resin and the highest temperature in the range has been adopted. However, in this method, since the mold temperature is high, heat transfer from the molten resin to the mold is small, and there is a problem that the productivity of the molded product is lowered due to a long resin cooling step.

  In the conventional technique, a heating medium such as a heater is installed in the mold, and the mold temperature is kept higher than the glass transition temperature until the resin pressure holding step. By doing so, the viscosity of the skin layer is reduced and the mold surface is highly transferred to the resin surface, and in the subsequent resin cooling step, the mold temperature is lowered below the glass transition temperature to solidify the molten resin, and molding I was getting goods. However, this method requires a time for raising and cooling the mold temperature, resulting in a problem that the molding cycle is long and productivity is lowered.

  As a method of highly transferring the mold surface to the molded product surface while solving the above problems, Patent Document 1 discloses that a gas body having a solubility of at least twice that of air in the mold resin is placed in the mold cavity. An injection molding method for filling and then filling with molten resin is disclosed. In this way, by dissolving the gas body on the resin surface and lowering the solidification temperature of the molding resin, it is said that there is an effect of reducing the viscosity of the skin layer and highly transferring the mold surface to the molded product surface. .

  Further, in Patent Document 2, carbon dioxide is used as a gas body to be dissolved in the molten resin, carbon dioxide is dissolved in advance in the molten resin, carbon dioxide is further filled in the mold cavity, and then the mold cavity is filled. Discloses an injection molding method in which a molten resin is filled. In this way, the gas body is dissolved in the resin to lower the solidification temperature of the molding resin, thereby reducing the viscosity of the skin layer and highly transferring the mold surface to the molded product surface.

  Patent Document 3 discloses an injection molding method in which, after filling a molding resin into a cavity, the resin filling is stopped once, carbon dioxide is injected between the molding resin and the cavity surface, and then the pressure holding process is performed. It is disclosed. As such, by dissolving the gas body on the resin surface and lowering the solidification temperature of the molding resin, the viscosity of the skin layer is reduced and the mold surface is highly transferred to the molded product surface. Yes.

JP 09-236763 A Japanese Patent Laid-Open No. 10-538386 JP 2006-335011 A

  However, the injection molding methods described in Patent Document 1 and Patent Document 2 have the following problems. That is, when a shutoff nozzle having a needle valve that mechanically opens and closes the resin path at the nozzle tip is used, the molten resin stays in the vicinity of the needle valve, and the molten resin carbonizes due to an increase in the thermal history of the staying resin. . When the carbonized resin is carried into the mold by the molten resin, it becomes a cause of molding defects as resin dust particularly in an optical element using a transparent material.

  The above problem can be avoided by using an open nozzle having a resin path opened at the tip of the nozzle. However, the use of an open nozzle causes another problem as follows. First, as shown in FIG. 6, in the step of filling and pressurizing the gas body 13 into the mold cavity 3, the gate 4, the runner 5, and the sprue 6 via the pipe 11, The molten resin 10 in the plasticizing device 19 of the injection molding device is pressurized by the gas body 13. At this time, the gas body 13 is locally and excessively dissolved in the molten resin 10 at the interface 14 where the gas body 13 and the molten resin 10 are in contact with each other. Therefore, molding defects such as foaming of the molten resin 10 in the subsequent filling step and instability of the resin flow due to local decrease in resin viscosity, and instability of the resin pressure in the mold associated therewith, occur.

  The injection molding method described in Patent Document 3 has the following problems. That is, since carbon dioxide is introduced between the mold cavity and the surface of the molded product, it is necessary to reduce the pressure of the molding resin in the mold cavity, and the control becomes very complicated. In addition, after filling the molding resin into the cavity, the resin filling is stopped once, and carbon dioxide is injected between the molding resin and the cavity surface. Dissolve in resin. Therefore, when the resin pressure in the mold becomes unstable or when the mold surface is transferred to the molding resin surface, a local transfer distribution occurs in the transfer surface. Also, when molding multiple molded products at the same time using branched runners, it is necessary to equalize the cavity filling amount of the pre-holding molding resin between each cavity and precisely control the pressurization time and pressure of the supplied carbon dioxide. become. Therefore, since complicated control is required as compared with normal injection molding, the difference in the dimensional accuracy of the molded product for each cavity increases.

  The present invention has been made in view of the above problems. Then, in the injection molding method that fills the mold with molten thermoplastic resin using an open nozzle, the molded product dimensions are transferred while the gas dissolution into the molded resin is stabilized and the mold surface is highly transferred to the molded product surface. The purpose is to stabilize the accuracy. Furthermore, according to the present invention, it is also possible to reduce the transfer between a plurality of cavities and variations in dimensional accuracy of a molded product.

The optical element manufacturing method of the present invention uses an open nozzle with a resin path open at the tip of a nozzle to supply molten thermoplastic resin to a mold, and the supplied resin is sprinkled with sprues, runners, and gates. An optical element manufacturing method for forming an optical element through a resin filling step of filling a plurality of cavities via the gas filling step, wherein a gas containing carbon dioxide or hydrocarbon is supplied to the mold during the resin filling step. The gas pressure of the gas supplied to the mold is set to 0.1 MPa or more and 15 MPa or less by the time when the resin flow front is in the sprue or the runner.

  According to the present invention, in injection molding of a thermoplastic resin, the viscosity of the molten resin can be lowered by dissolving a gas in the molten resin, and the mold surface can be highly transferred to the surface of the molded product. In addition, according to the present invention, by performing gas injection into the mold in the molten resin filling step, it is possible to prevent excessive dissolution of the gas into the molten resin, Variations in dimensional accuracy of molded products can be reduced. Furthermore, according to the present invention, in a molded product having a plurality of cavities separated by runners, variations in the transfer, appearance of the molded product, and dimensional accuracy among the cavities can be reduced.

It is a figure explaining the step at the time of completion of gas injection in the injection molding method of the present invention. It is the schematic of the injection molding apparatus of this invention. It is a figure explaining the step before molten resin injection in the injection molding method of the present invention. It is a figure explaining the step at the time of the gas injection start in the injection molding method of the present invention. It is a figure explaining the step of holding pressure in the injection molding method of the present invention. It is a figure explaining the state which injected the gas inside the cavity before the injection in the conventional injection molding method. It is a figure explaining the resin flow direction in the interface of resin and a carbon dioxide in the resin flow process in a metal mold | die sprue. It is a figure explaining the gas flow path which looked at the movable side metal mold | die from the parting surface. It is a figure explaining the gas channel which looked at the stationary side metal mold | die from the parting surface.

  Hereinafter, an injection molding method for filling a mold with the thermoplastic resin of the present invention will be described in detail with reference to the drawings.

  First, the outline of the present invention will be described. In the apparatus and method of the present invention, unlike the prior art, in the molten resin flow front, by injecting a gas containing hydrocarbons into the mold cavity, gate, runner and sprue and increasing the pressure in the molten resin filling process. The gas is dissolved in the molten resin. Therefore, by increasing the gas dissolution amount of the molten resin as the gas pressure in the mold increases, it is possible to stabilize the flow of the resin without locally dissolving the molten resin. In addition, when used for molded products with multiple cavities separated by the runner, the gas injection into the mold is started and the pressure is increased from the start of resin filling to the completion of sprue filling, so that Thus, the gas pressure can be kept uniform between the cavities. Therefore, it is possible to maintain uniform transfer of the mold surface to the surface of the molded product, appearance, and dimensional accuracy between a plurality of cavities.

  Here, as the gas containing hydrocarbon, carbon dioxide, methane, ethane, propane and the like are preferable. Since these are inert gases, it is possible to ensure safety during molding.

  First, an injection molding apparatus used in the injection molding method of the present invention will be described. In the present embodiment, carbon dioxide is used as the gas containing hydrocarbons.

  FIG. 2 is an overall view of an injection molding apparatus used in the present invention. The apparatus includes a molding apparatus 18, a plasticizing apparatus 19, molds 1 and 2, and a high-pressure gas production and supply apparatus 20, and an open nozzle 7 is used for a resin path at the nozzle tip of the plasticizing apparatus. .

  As shown in FIG. 3, in the apparatus, the molding resin is introduced into the heated cylinder 8 through the hopper 17 of the plasticizing apparatus 19, and then the screw 9 in the cylinder 8 is rotated. Then, it is transported to the open nozzle 7 while melting. Next, an arbitrary volume of the molten resin is measured at the tip of the open nozzle 7, and the molten resin at the tip of the open nozzle 7 is supplied into the mold as the screw 9 moves. Here, the fixed-side mold 1 and the movable-side mold 2 are clamped by a molding apparatus 18 to form a cavity 3 on the joint surface. The mold cavity 3 circulates through the tip of the open nozzle 7 and the spru 6, runner 5, and gate 4 in the mold.

  The high-pressure gas production and supply device 20 pressurizes the carbon dioxide supplied from the high-pressure gas cylinder 21 and supplies it to the mold cavity 3 via the pipe 11. The pipe 11 can be arbitrarily opened and closed by a valve 15. At this time, the gas pressure is determined to be equal to or higher than the atmospheric pressure while confirming the transfer of the surface of the molded product. Here, the high-pressure gas production apparatus and the mold are required to have a seal structure for maintaining the gas pressure. Therefore, the gas pressure is preferably 15 MPa or less at which the rubber material of the seal member can hold the pressure. Further, the carbon dioxide 13 in the mold cavity 3 can be discharged out of the mold via the pipe 12. The pipe 12 can be arbitrarily opened and closed by a valve 16.

  Next, the injection molding method of the present invention will be described in detail with reference to the molding process diagrams shown in the order of FIG. 3, FIG. 4, FIG. 1, and FIG.

  First, as shown in FIG. 3, a desired amount of the molten resin 10 is measured in the cylinder 8 by the plasticizing device 19, and then the fixed mold 1 and the movable mold 2 are clamped by the molding apparatus 18.

  Next, as shown in FIG. 4, the screw 9 of the plasticizing device 19 is advanced to supply the molten resin 10 to the sprue 6 of the stationary mold 1.

  Next, as shown in FIG. 1, when the molten resin 10 reaches a desired position in the spru 6, the valve 15 is opened and the carbon dioxide 13 is supplied to the mold via the pipe 11. The carbon dioxide 13 passes through the flow path in the fixed mold and is injected into the cavity 3 from the groove 28 shown in FIG. 8 via the gas inlet 26 and the gas flow path 25 of FIG. Then, the molten resin 10 is pressurized through the gate 4, the runner 5 and the sprue 6. As shown in FIG. 7, the injected carbon dioxide 13 penetrates into the molten resin from the flow front that is an interface with the molten resin 10 to reduce the viscosity of the molten resin, and then along the flow of the molten resin. Reach the mold surface.

  Here, the groove 28 is required to have a groove depth of 10 μm or less through which the molten resin 10 cannot pass but the carbon dioxide 13 can pass. The groove 28 is preferably the final filling portion of the molten resin 10 because the cavity 3, the gate 4, the runner 5 and the sprue 6 that are not filled with the molten resin 10 need to be pressurized with the carbon dioxide 13. .

  The filling amount of the molten resin 10 into the sprue 6 when supplying the carbon dioxide 13 to the mold is such that a back flow of the molten resin 10 occurs due to the pressure of the carbon dioxide 13, and the carbon dioxide enters the open nozzle 7 of the plasticizing device 19. It is preferable that it is the quantity which 13 does not enter.

  In addition, the start time for injecting the carbon dioxide 13 into the mold cavity 3 is controlled by the position of the plasticizing screw of the optional plasticizing device 19 or the time after the start of the filling process of the molten resin 10, and a signal output from the molding device. Then, the valve 15 is opened.

  When the runner 5 is branched and a mold having a plurality of cavities 3 is used, as shown in FIG. 1, the flow front of the molten resin 10 when the carbon dioxide 13 reaches a pressure of 0.1 MPa to 15 MPa is obtained. , Preferably inside the sprue 6. The mold cavity 3 before filling with the molten resin 10 is confined with air and is at atmospheric pressure. Accordingly, the carbon dioxide pressure can be supplied into the mold at atmospheric pressure or higher and dissolved in the molten resin 10 to highly transfer the mold surface to the surface of the molded product. Further, when the gas pressure exceeds 15 MPa, a seal structure for holding the gas pressure in the mold corresponding to the gas pressure is required. In particular, when the mold temperature is set to a high temperature of 100 ° C. or higher, highly heat-resistant fluoro rubber is required as the gas seal member 29. However, since the pressure resistance is low, sealing becomes difficult when the gas pressure exceeds 15 MPa. .

  Here, the sprue 6 is located at an intermediate point between the open nozzle 7 and the molds 1 and 2 as shown in the drawings. Thereby, the pressure of the carbon dioxide 13 becomes equal between the plurality of cavities 3 through the runner 5 and the gate 4, and the molten resin 10 is uniformly distributed to the plurality of cavities 3 while receiving the flow resistance due to the pressure of the carbon dioxide 13. Can flow. Further, when the dimensional accuracy of the molded product required in the plurality of cavities 3 is acceptable, even if the flow front of the molten resin 10 is at the runner 5 when the carbon dioxide 13 reaches a pressure of 0.1 MPa to 15 MPa. Good. In this case, there is no local dissolution of carbon dioxide in the molten resin, although there are differences in dimensional accuracy and the transfer amount of the mold surface to the surface of the molded product between the cavities. Therefore, when transferring the mold surface to the molding resin surface, there is a local transfer distribution preventing effect in the transfer surface.

  Next, the filling process is completed by injecting the molten resin 10 while the pressure of the carbon dioxide 13 is maintained at a pressure of 0.1 MPa or more and 15 MPa or less by the high pressure gas production apparatus 20. Then, as shown in FIG. 5, a resin pressure holding step is performed. The pressure holding process is completed together with the gate seal, the valve 15 is closed, and the injection of carbon dioxide 10 is stopped. At the same time, the valve 16 is opened, and the carbon dioxide 13 in the mold is released through the gas discharge path and the pipe 12 shown in FIG.

  Thereafter, the molded product is sufficiently cooled in the resin cooling process, the mold clamping force of the molding device 18 is released, the fixed mold 1 and the movable mold 2 are separated, and the molded product from the parting line surface. Take out.

  The following are mentioned as a molded article manufactured by the method of this invention described above. That is, it is required to transfer the surface of a mold such as a spherical lens, an aspherical lens, a free-form surface lens, a Fresnel lens, a toric lens, an fθ lens, a prism, a mirror, and a light guide plate with high precision. It is an optical element.

DESCRIPTION OF SYMBOLS 1 Fixed side metal mold 2 Movable side metal mold 3 Cavity 4 Gate 5 Runner 6 Sprue 7 Open nozzle 8 Cylinder 9 Screw 10 Molten resin 11 Piping 1
12 Piping 2
13 Carbon dioxide 14 Molding resin and carbon dioxide interface 15 Valve 1
16 Valve 2
DESCRIPTION OF SYMBOLS 17 Hopper 18 Molding apparatus 19 Plasticizing apparatus 20 High pressure gas production supply apparatus 21 Carbon dioxide cylinder 22 Flow direction of resin 23 Interface of resin and mold 24 Interface of carbon dioxide and mold 25 Gas flow path 26 Gas injection path 27 Gas discharge Channel 28 Groove connecting gas channel and mold cavity 29 Gas seal member

Claims (4)

Using an open nozzle with the resin path at the nozzle tip open,
An optical element manufacturing method in which a molten thermoplastic resin is supplied to a mold, and an optical element is molded through a resin filling step of filling the supplied resin into a plurality of cavities via a sprue, a runner, and a gate. And
During the resin filling step, start supplying a gas containing carbon dioxide or hydrocarbon to the mold,
The method for producing an optical element, wherein the gas pressure of the gas supplied to the mold is set to 0.1 MPa or more and 15 MPa or less by the time when the flow front of the resin is in the sprue or the runner.   The supply of the gas to the mold is started by a position of a plasticizing screw for supplying the resin to the mold, or by a time after starting to supply the resin to the mold. Item 2. A method for producing an optical element according to Item 1.   The gas pressure of the gas is maintained at 0.1 MPa or more and 15 MPa or less until the filling of the cavity is completed after the gas pressure is set to 0.1 MPa or more and 15 MPa or less. The manufacturing method of the optical element of description.   The method for manufacturing an optical element according to claim 1, wherein the hydrocarbon is methane, ethane, or propane.