JP2011126186A - Resin molding process and injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a resin product of a thin wall and good quality without altering physical properties or characteristics of the resin used for molding. <P>SOLUTION: A molten resin LQ injected from a nozzle 202 of injection device 201 passes a channel 305 formed in a fixed mold 301 and flows into a cavity SP between the fixed mold 301 and a movable mold 302. Temperature of one mold, either the fixed mold 301 or the movable mold 302, is set to a temperature (first temperature) which is not higher than flow stop temperature or glass transition point of the molten resin LQ. Temperature of the other mold, either the fixed mold 301 or the movable mold 302, is set to a resin cooling temperature (second temperature) which is low enough to solidify the molten resin LQ and lower than the first temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a resin molding method for obtaining a thin resin molded product, and an injection molding apparatus suitable for the resin molding method.

  Conventionally, molten resin is poured into a gap (hereinafter sometimes referred to as “cavity”) between a fixed mold (female mold) and a movable mold (male mold) in a mold used for resin injection molding, and the resin is filled. Molding of parts is performed. Here, a thinner and lighter resin product is produced as the cavity is narrowed. However, in this case, the molten resin poured into the cavity is cooled and solidified before reaching every corner of the cavity. Therefore, various attempts have been made to spread the molten resin to every corner of the cavity.

  As a first example, a material having excellent fluidity when dissolved in a resin used for molding is used (for example, Patent Document 1).

  As a second example, carbon dioxide is dissolved in a resin to improve the fluidity of the resin (for example, Patent Document 2).

JP 2009-062526 A JP 2003-165135 A

  However, in the first example, the types of resins that can be used are limited. On the other hand, in the case of the second example, carbon dioxide bubbles are generated before the molten resin is cooled, and the surface of the molded resin part is not smoothed.

  An object of the present invention is to obtain a thin, high-quality resin product by performing molding without changing the physical properties and characteristics of the resin used for molding.

  The injection molding method of the present invention is a resin molding method for injecting molten resin into a cavity formed between a fixed mold and a movable mold, and molding either of the fixed mold and the movable mold. The temperature of one of the molds is set to a flow stop temperature at which the molten resin starts to solidify or a first temperature equal to or lower than the glass transition point, and the temperature of the other mold of the fixed mold and the movable mold is set to the first temperature. A first step of setting a second temperature lower than the first temperature; and a second step performed after the first step and injecting a molten resin into the cavity and molding the second cavity.

  The injection molding apparatus of the present invention has an injection port, an injection device for injecting molten resin from the injection port, a fixed mold having a flow path through which the molten resin injected from the injection port passes, and the fixing A closed position in which a cavity into which the molten resin injected into the flow path abuts against the mold flows is formed between the fixed mold and an open position in which the cavity is separated from the fixed mold and opened. The temperature of any one of the movable mold movable between the fixed mold and the movable mold is set to a flow stop temperature at which the molten resin starts to solidify or a first temperature lower than the glass transition point. And a temperature adjusting device for setting the temperature of one of the stationary mold and the movable mold to a second temperature lower than the first temperature.

  According to the present invention, the solidification of the molten resin is delayed by heating one mold, and the molten resin spreads to every corner of the cavity. Therefore, molding can be performed without changing the physical properties and characteristics of the resin used for molding. Even thin-walled high-quality resin products can be obtained. In addition, since the resin is thin in the cavity, the amount of heat in the resin in the cavity is small, and the other mold temperature is low, so that a thin molded product can be produced in a sufficient molding cycle even if the temperature setting of the temperature adjusting device is constant during molding.

It is a schematic diagram of an injection molding apparatus. It is explanatory drawing which shows the change of the molten resin in the cavity by the resin molding using an injection molding apparatus. It is explanatory drawing which shows the change of the molten resin in the cavity by the resin molding using an injection molding apparatus.

  One embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram of an injection molding apparatus 101. The injection molding apparatus 101 includes an injection apparatus 201, a fixed mold 301, a movable mold 302, and a temperature adjustment apparatus 401.

  The injection device 201 has a cylinder 203 that forms an injection port 202 at the tip. A band-shaped heater (not shown) is wound around the cylinder 203 and is heated by this heater. A screw 205 is inserted into the cylinder 203. A linear scale 208 for detecting the position of the screw 205 is attached to the screw 205. A hopper 204 is attached to the cylinder 203. From this hopper 204, a solid pellet-shaped resin SQ as a material is supplied into the cylinder 203. The resin SQ is transported in the direction toward the injection port 202 by the rotation of the screw 205 by the drive of the screw driving device 206, and is melted by the frictional heat with the cylinder 203 and the heat of the heater to become a liquid molten resin LQ. The molten resin LQ sent to the tip of the screw 205 retracts the screw 205 with the pressure. When the screw driving device 206 detects that the position of the screw 205 has reached the holding pressure switching position or an arbitrary position set by the user, an amount of the molten resin LQ necessary for molding the molded product is transferred to the tip of the screw 205 and the cylinder 203. The screw 205 is stopped, the screw 205 is advanced, and the molten resin LQ is injected into the cavity SP.

  The fixed mold 301 has a concave surface 303 having a molded product shape, and a parting (PL) surface 303 a is formed around the concave surface 303. A flow path 305 that penetrates from the concave surface 303 to the back surface 304 is formed in the fixed mold 301. The injection port 202 of the injection device 201 is connected to the end of the flow path 305 that opens to the back surface 304 side of the fixed mold 301, and molten resin LQ injected from the injection port 202 is injected into the concave surface 303. Is done.

  The movable mold 302 has a convex surface 306 that enters the concave surface 303 of the fixed mold 301. In the movable mold 302, a parting (PL) surface 306 a that abuts the parting (PL) surface 303 a of the fixed mold 301 is formed around the convex surface 306. Such a movable mold 302 has a parting (PL) surface 306 a in contact with the parting (PL) surface 303 a of the fixed mold 301, so A cavity SP is formed. The cavity SP communicates with the flow path 305. In addition, the movable mold 302 is movable between a closed position 302C where the cavity SP is formed between the movable mold 302 and the fixed mold 301 and an open position 302O which is separated from the fixed mold 301. The movable mold 302 is positioned at either the closed position 302C or the open position 302O by driving the opening / closing drive unit 307.

  The temperature adjustment device 401 includes a cooling unit 402, a heating unit 403, and a control circuit 404 as a control unit. The cooling unit 402 adjusts the temperature of the movable mold 302 to maintain the resin cooling temperature (second temperature) that is sufficiently low for the molten resin LQ to solidify. In addition, the heating unit 403 adjusts the temperature of the fixed mold 301 and maintains the temperature (first temperature) below the flow stop temperature of the molten resin LQ or near the glass transition point. The flow stop temperature or glass transition point is a temperature at which the molten resin LQ starts to solidify and is higher than the resin cooling temperature.

  Incidentally, since the molded product of the molten resin LQ molded in the cavity SP is thin, the amount of heat stored in the molten resin LQ injected into the cavity SP is small in the first place. The injected molten resin LQ is in contact with the movable mold 302, and heat escapes from the movable mold 302 and is cooled. Here, as another embodiment, the control circuit 404 receives an electric signal from the linear scale 208 and determines whether or not the screw 205 is displaced and the molten resin LQ is injected into the cavity SP. When the determination is made, the heating unit 403 is stopped, the cooling unit 402 is driven to cool the fixed mold 301, and the temperature of the fixed mold 301 is brought close to the resin cooling temperature to further increase the molten resin LQ in the cavity SP. It may be cooled quickly.

  In addition, the temperature of the fixed mold 301 decreases with time, and further decreases when the movable mold 302 is positioned at the open position 302O in order to take out the molded product. Therefore, as yet another embodiment, a temperature sensor (not shown) is attached to the fixed mold 301, and the temperature of the fixed mold 301 is set to a predetermined temperature (for example, flow) by an electric signal from the temperature sensor. When it is determined that the temperature is equal to or lower than the stop temperature (or the glass transition point) and the resin cooling temperature), the heating unit 403 is driven to set the temperature of the fixed mold 301 near the flow stop temperature (or glass transition point). You may make it raise to.

  In such an injection molding apparatus 101, the temperature adjusting device 401 sets the temperature of the fixed mold 301 to a temperature lower than or equal to the flow stop temperature (or glass transition point) and the temperature of the movable mold 302 to the resin cooling temperature. To do. In this state, when the molten resin LQ is injected from the injection port 202 of the injection device 201, the molten resin LQ enters the cavity SP via the flow path 305. When the molten resin LQ that has entered the cavity SP contacts the convex surface 306 of the movable mold 302, the molten resin LQ is cooled by the movable mold 302 and solidification starts. For this reason, along the surface of the convex surface 306, the skin layer SL (refer FIG.2 and FIG.3) of molten resin LQ appears. On the other hand, of the molten resin LQ that has entered the cavity SP, the portion on the concave surface 303 side of the fixed mold 301 is harder to solidify than the convex surface 306 of the movable mold 302. This is because the temperature of the fixed mold 301 is close to the flow stop temperature of the molten resin LQ or the glass transition point. As a result, the molten resin LQ that has entered the cavity SP through the flow path 305 travels along the surface of the skin layer SL, reaches the outer edge of the skin layer SL, and reaches every corner of the cavity SP. Therefore, according to the injection molding apparatus 101 of the present embodiment, it is possible to obtain a thin, high-quality resin product by performing molding without changing the physical properties and characteristics of the molten resin LQ used for molding.

  Furthermore, when the fixed mold 301 is cooled after the cavity SP is filled with the molten resin LQ, the molten resin LQ can be solidified in a shorter time, and the time required for resin molding can be shortened.

  In addition, when a temperature sensor (not shown) is attached to the fixed mold 301 and the fixed mold 301 whose temperature has been lowered is heated again, the time required to obtain the next molded product is shortened. The production efficiency of the molded product increases.

  In this injection molding apparatus 101, the temperature of the movable mold 302 is set to a temperature lower than or equal to the flow stop temperature of the molten resin LQ or near the glass transition point (first temperature), and the temperature of the fixed mold 301 is set. The resin cooling temperature (second temperature) may be set. In this case, the molten resin LQ injected from the injection port 202 does not immediately solidify even when it touches the flow path 305 and the concave surface 303 of the fixed mold 301 and reaches the convex surface 306 of the movable mold 302. Then, the skin layer SL appears along the surface of the concave surface 303 of the fixed mold 301, and the molten resin LQ flows between the convex surface 306 of the movable mold 302 and the skin layer SL, and melts to every corner of the cavity SP. Resin LQ is distributed.

  Example 1 FIG. 2 is an explanatory diagram showing changes in the molten resin LQ in the cavity SP in resin molding using the injection molding apparatus 101. The inventor heated the polypropylene resin to 230 degrees Celsius, melted it, and filled the injection apparatus 201. Further, the inventor adjusted the temperature of the movable mold 302 to 40 degrees Celsius by adjusting the cooling unit 402 of the temperature adjusting device 401. The inventor also adjusted the temperature of the fixed mold 301 to 120 degrees Celsius by adjusting the heating unit 403 of the temperature adjustment device 401. The inventor then forms a cavity SP having an average thickness of 1.5 millimeters, a lateral width of 2.5 meters, and a height of 500 to 700 mm in order to form a resin bumper cover for an automobile, and a movable die 301 and a movable die. 302 was used for injection molding. At this time, the temperature of the fixed mold 301 remains 120 degrees Celsius.

  FIG. 2 shows a state of the molten resin LQ that is poured into the cavity SP and is solidified. The temperature of the part in contact with the movable mold 302 in the molten resin LQ was 40 degrees Celsius. Moreover, the temperature of the part which contact | connects the fixed metal mold | die 301 among molten resin LQ was 120 degreeC. The molten resin LQ in the cavity SP was divided into a skin layer SL on the movable mold 302 side and a flow portion LL on the fixed mold 301 side. As time passes, the skin layer SL moves to the fixed mold 301 side, and the skin layer SL becomes thicker. Finally, all the molten resin LQ poured into the cavity SP is solidified. did.

  Example 2 FIG. 3 is an explanatory diagram showing changes in the molten resin LQ in the cavity SP in resin molding using the injection molding apparatus 101. The inventor controlled the temperature adjusting device 401 so that the fixed mold 301 is changed from 120 degrees Celsius to 40 degrees Celsius after filling the cavity SP with the molten resin LQ in addition to the conditions in the first embodiment.

  In the stage before controlling the temperature adjusting device 401, as shown in FIG. 2, the portion on the movable mold 302 side of the molten resin LQ poured into the cavity SP and being solidified becomes the skin layer SL, and the fixed mold The portion on the 301 side is a flow portion LL. Thereafter, when the control of the temperature adjusting device 401 is started and the temperature of the fixed mold 301 is lowered from 120 degrees Celsius, a new skin layer SL2 is formed on a portion of the molten resin LQ that is in contact with the movable mold 302 as shown in FIG. With the passage of time, the skin layer SL and the skin layer SL2 moved so as to approach each other, and finally all the molten resin LQ poured into the cavity SP became the skin layer SL. The time required for the molten resin LQ to solidify in Example 2 was shorter than the time required for the molten resin LQ to solidify in Example 1.

DESCRIPTION OF SYMBOLS 101 Injection molding apparatus 201 Injection apparatus 202 Injection port 301 Fixed mold 302 Movable mold 302C Closed position 302O Open position 305 Flow path 401 Temperature adjusting apparatus 404 Control circuit (control part)
LQ molten resin

Claims (4)

A resin molding method in which a molten resin is injected into a cavity formed between a fixed mold and a movable mold and molded.
The temperature of one of the fixed mold and the movable mold is set to a flow stop temperature at which the molten resin starts to solidify or a first temperature lower than the glass transition point, and the fixed mold and the movable mold are set. A first step of setting the temperature of either one of the molds to a second temperature lower than the first temperature;
A second step, which is performed after the first step, and injects a molten resin into the cavity to be molded;
An injection molding method comprising: A third step that is performed after the second step and cools the one mold;
The injection molding method according to claim 1. An injection device having an injection port and injecting molten resin from the injection port;
A stationary mold having a flow path through which the molten resin injected from the injection port passes;
A closed position in which a cavity into which the molten resin injected into the flow path abuts the fixed mold flows is formed between the fixed mold, and an open position in which the cavity is opened away from the fixed mold. , Movable mold that can move between,
The temperature of one of the fixed mold and the movable mold is set to a flow stop temperature at which the molten resin starts to solidify or a first temperature lower than the glass transition point, and the fixed mold and the movable mold are set. A temperature adjusting device for setting the temperature of any one of the other molds to a second temperature lower than the first temperature;
An injection molding apparatus comprising: The temperature adjusting device cools the one mold after the injection device injects the molten resin.
The injection molding apparatus according to claim 3.

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