JP4579898B2 - Molding method and molding apparatus - Google Patents

Description

  The present invention relates to a molding method and a molding apparatus for molding a resin product having a thick-walled portion that is convex on the back surface side, and more particularly to an improvement in a technique for controlling the supply of molten resin into a cavity.

  The resin product has a convex thick portion as a reinforcing rib on the back side which is a non-design surface. In molding of such resin products, the heat capacity of these parts differs due to the difference in thickness between the thick part and the other parts. Therefore, in the thick part, sink marks due to shrinkage of the molten resin occur on the surface side, which is the design surface. Will occur. As a result, there is a problem in that a dent is formed on the surface side of the thick-walled portion and appearance quality is impaired. Therefore, a technique has been proposed in which an excessive amount of molten resin filled in the cavity of the mold is held and solidified in that state to replenish the shrinkage of the molten resin and prevent the occurrence of sink marks. (For example, patent document 1). In the technique of Patent Document 1, simultaneously with holding pressure of the molten resin, pressurized gas is injected into the cavity from the mold surface on the back surface side of the mold to press the molten resin against the mold surface on the front surface side.

  However, in the technique of Patent Document 1, when the resin holding pressure is not appropriate, the product surface is likely to be dented. In addition, since the pressurized gas is injected simultaneously with the resin holding pressure, the pressure of the injected pressurized gas must be set high, and it is necessary to use a pressure-resistant structure for the device used, resulting in an increase in the device price. . Furthermore, since a resin pressure holding step is required, productivity is reduced.

  Therefore, the present applicant supplies molten resin in an amount smaller than the cavity volume, and injects gas into the cavity without holding the molten resin, so that the molten resin can be removed from the mold surface on the back side of the mold. It has been proposed that the molten resin is brought into close contact with the mold surface on the surface side of the mold (see, for example, Japanese Patent Application No. 2005-369144).

  By the way, in the supply of the molten resin, it is necessary to accurately control the supply amount of the molten resin in order to suppress the occurrence of variations in product weight. There is a technique for controlling the supply amount of the molten resin, for example, by controlling the supply amount by setting the injection rate of the molten resin from each valve gate to the cavity and the supply setting time of the molten resin (for example, Patent Document 2). In the technology of Patent Document 2, the injection rate of the molten resin from each valve gate is controlled according to the measurement time by the timer from the supply start time, and all valve gates are measured when the measurement time by the timer exceeds the set time. The supply of the molten resin from is terminated.

  However, since the technique of Patent Document 2 does not perform feedback control in the supply of the molten resin, it cannot cope with the aging of an apparatus such as a screw used for injection of the molten resin through the supply port.

  Therefore, it is conceivable to arrange a pressure sensor for detecting the pressure value of the molten resin in the cavity and perform feedback control of the supply of the molten resin by the screw based on the detected pressure value by the pressure sensor. FIG. 12 is a cross-sectional view showing a schematic configuration of a cavity 1 in which a plurality of pressure sensors 3 are provided at flow end positions E, F, and G of a molten resin supplied from a plurality of valve gates 2. In the molten resin supply control by the pressure sensor 3, the pressure values of the molten resin at the flow end positions E, F, G are detected, and when all the detected pressure values exceed the pressure threshold value, The supply of molten resin has been completed at the same time.

  However, in this case, at each flow end position E, F, G, since the temperature drop of the molten resin reaching there is large, a temperature difference in the molten resin tends to occur every time the resin product is molded, and melting due to the temperature drop occurs. Variations occur in the degree of shrinkage of the resin and its viscosity. As a result, since the pressure value of the molten resin varies at each of the flow end positions E, F, and G, the supply amount of the molten resin cannot be accurately controlled, and there is a concern that the weight of the molded product may vary.

Japanese Patent Laid-Open No. 11-198165 JP 2005-297384 A

  Therefore, the present invention can cope with the aging of the apparatus, as well as the molding method capable of suppressing the occurrence of sink marks on the surface side of the resin product by accurately controlling the supply amount of the molten resin. And it aims at providing a forming device.

The molding method of the present invention is a method of molding a resin product having a thick wall portion convex on the back side by supplying a molten resin in an amount smaller than the cavity volume of the mold, First step of supplying molten resin into the cavity through a plurality of supply ports of the cavity, and injecting gas into the cavity from the mold surface of the mold on the back side of the product, so that the molten resin and the mold on the back side A second step of forming a gap between the mold surface and the molten resin in close contact with the mold surface of the mold on the surface side of the product, while maintaining the form of the molten resin set by the second step A third step of solidifying the molten resin, setting a pressure threshold for the molten resin for each supply port, and for each supply port between the start of the first step and the end of the second step, Melting near no feed port Pressure value and detects the pressure value of the fat is terminated the supply of molten resin when exceeding the pressure threshold, the supply amount of the molten resin in the first step, 3-20% less value for the volume of the cavity And a set pressure value corresponding to the supply amount of the molten resin optimized for each supply port for molding a resin product is used as the pressure threshold value of each supply port .

  In the molding method of the present invention, in the second step, by injecting gas into the cavity from the mold surface of the mold on the back side of the product, the molten resin supplied in the first step and the mold on the back side of the product A gap is formed between the mold surface of the mold and the molten resin is brought into close contact with the mold surface of the mold on the surface side of the product, so that the back surface side of the molten resin is between the mold surface of the mold on the back surface side. Solidification is slowed down by the heat insulating action of the voids formed, and solidification is started from the molten resin in close contact with the mold surface of the mold on the surface side. Thereby, the molten resin is attracted to the mold surface of the mold on the front surface side, and sink marks are generated on the back surface side of the molten resin. Then, as the cooling proceeds, solidification of the molten resin on the back surface side is started, but at this time, the surface side of the molten resin is already solidified, so that it is not affected by shrinkage due to solidification on the back surface side of the molten resin. As a result, sink marks do not occur on the surface side of the resin product.

  Here, since the molten resin in the vicinity of each supply port that is not the flow end is a resin immediately after being supplied, the temperature of the molten resin is small. As a result, there is no difference in the degree of shrinkage and viscosity of the molten resin due to the temperature drop every time the resin product is molded, so that there is no variation in the pressure value of the molten resin. In the molding method of the present invention, the pressure value of the molten resin in the vicinity of each supply port is detected, and the feedback control of the supply amount of the molten resin is performed based on the detected pressure value. The supply amount can be controlled with high accuracy. In addition, since the feedback control of the supply amount of the molten resin is performed for each supply port in which the pressure threshold value of the molten resin is set, the supply amount of the molten resin can be controlled with higher accuracy. Therefore, even when the present invention is applied to an apparatus that does not perform a feedback control of the molten resin supply rate or an apparatus that is not stable, such as an aging apparatus, it is possible to suppress the occurrence of variations in the weight of the resin product.

  In particular, when the holding pressure does not contribute to the supply amount into the cavity (for example, when the holding pressure applied to the molten resin as the secondary pressure is low when the gas is injected in the second step or when no holding pressure is applied), the molten resin Therefore, the molding method of the present invention is particularly effective. In addition, when pressure is not applied to the molten resin, the pressure of the gas can be lowered, so that it is not necessary to use a pressure-resistant structure for the device used, and the cost of the mold and the device can be reduced. In other words, it is only necessary to use an air supply source on the factory infrastructure, for example, which has a relatively low pressure, so that there is no need to use a pressure compressor in the apparatus. Further, in this case, since the resin pressure holding step is not necessary, productivity can be improved.

  Moreover, the recessed part for shape | molding a thick part can be provided in the metal mold | die surface in the back surface side of a product, and a 2nd process can perform gas injection | pouring from the bottom face of the said recessed part, and its vicinity. In this aspect, since the gas can be concentrated in the thick portion and its vicinity, the thick portion can be separated from the mold more efficiently.

The molding apparatus of the present invention is an apparatus to which the molding method of the present invention is applied. That is, the molding apparatus of the present invention is an apparatus that molds a resin product having a thick portion convex on the back side by supplying a molten resin in an amount smaller than the cavity volume of the mold, Supply means for supplying molten resin into the cavity through a plurality of supply ports of the mold cavity, and by injecting gas into the cavity from the mold surface of the mold on the back side of the product, the molten resin and the mold on the back side A gas injection means for forming a gap between the mold surface and the molten resin in close contact with the mold surface on the surface side of the product, and a supply that is installed near each supply port and is not a fluid end A pressure detection means for detecting the pressure value of the molten resin in the vicinity of the mouth, and a control means for controlling the supply of the molten resin, a pressure threshold value of the molten resin is set for each pressure detection means, For each supply means, when the pressure value detected by the pressure detection means exceeds the pressure threshold, the supply of the molten resin from the supply port is terminated, and the solidification of the molten resin is performed by the molten resin set by the gas injection means. The molten resin supply amount in the first step is set to a value 3 to 20% less than the volume of the cavity, and a resin product is molded as the pressure threshold value of each supply port. Therefore, a set pressure value corresponding to the supply amount of the molten resin optimized for each supply port is used . In the molding apparatus of the present invention, a recess for molding the thick portion is formed on the mold surface of the mold on the back side of the product, and an opening into which gas is injected near the bottom and the recess of the recess Is preferably formed. Further, it is preferable that a pressure threshold corresponding to each pressure detecting means is set in the control means so that the molten resin supplied into the mold cavity is smaller than the cavity volume of the mold. It is. In the molding apparatus of the present invention, the same actions and effects as those of the molding method of the present invention can be obtained.

  According to the molding method or the molding apparatus of the present invention, even when applied to an apparatus that does not perform feedback control of the molten resin supply rate or an apparatus that is not stable, such as an aging apparatus, the volume variation of the resin product In other words, the effect of reducing the occurrence of sink marks on the surface side of the resin product can be obtained.

(1) Configuration of Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional side view showing a partial configuration of a molding apparatus 1 according to an embodiment of the present invention. FIG. 2 is a schematic sectional view showing the cavity C of FIG. FIG. 3 is a side view illustrating the configuration of the molding apparatus 1.

  The molding apparatus 1 includes a mold 10 including a fixed mold 11 and a movable mold 12. A cavity C is formed between the fixed mold 11 and the movable mold 12. The cavity surface (front surface mold surface) of the fixed mold 11 corresponds to the design surface of the resin product, and the cavity surface (mold surface on the back surface side) of the movable mold 12 corresponds to the non-design surface of the resin product. The cavity surface of the movable mold 12 is formed with a plurality of recesses 13 for forming reinforcing ribs (thick parts) that form the convex shape of the resin product. A gas injection passage 14 for injecting gas into the cavity C is formed in the movable mold 12. The gas injection passage 14 opens to the cavity surface of the movable mold 12 through the openings 14A and 14B.

  In the openings 14A and 14B, a material intrusion preventing member such as a sintered vent (not shown) for preventing the molten resin from entering the gas injection passage 14 is disposed. That is, the material intrusion prevention member has a function of allowing the injected gas to pass through and injecting into the cavity C and preventing the molten resin from entering the cavity C. The openings 14 </ b> A and 14 </ b> B are preferably opened in the concave portion 13 in the cavity surface of the movable mold 12 and a flat portion in the vicinity thereof. The gas injection is performed, for example, by the gas injection unit 15 using factory air. In this aspect, since factory air is used, no special equipment for gas supply is required, so that the cost of the apparatus can be reduced. The injected gas does not need to be kept in the mold 10 and may be discharged to the outside from the mating surface of the fixed mold 11 and the movable mold 12. In this aspect, since it is not necessary to seal the injected gas, the manufacturing cost can be reduced.

A plurality of resin supply portions 20 (20 _{-1 to} 20 _-3 , supply means) for supplying molten resin to the cavity C are installed on the side surface portion of the mold 10. The resin supply unit 20 includes a cylinder 21, a valve gate pin 22, a hydraulic cylinder 23, a valve gate 24 (supply port), a gate drive unit 25, and a resin supply control unit 26 (control means). As an actuator for moving the valve gate pin 22 back and forth, a driving means using an electromagnetic action may be used. The cylinder 21 has a substantially cylindrical shape having a conical portion at the tip, and molten resin is injected into the cylinder 21 from an injection device including a screw (not shown) that moves forward and backward through a resin injection port 21A. The valve gate pin 22 is provided inside the cylinder 21 so as to be movable along its axis. The valve gate pin 22 is driven by the hydraulic cylinder 23 to inject molten resin inside the cylinder 21 into the cavity C through the valve gate 24. The opening / closing operation of the valve gate 24 is driven by the gate drive unit 25. The resin supply control unit 26 controls the hydraulic cylinder 23 and the gate drive unit 25.

  In the vicinity of each valve gate 24, a pressure sensor 30 (pressure detection means) for detecting the pressure value of the molten resin is provided. The pressure sensor 30 is, for example, a piezoelectric element. In order for the pressure sensor 30 to detect the surface pressure of the cavity surface, the pressure detection surface of the pressure sensor 30 is disposed so as to be flush with the cavity surface of either the fixed mold 11 or the movable mold 12. Is preferred. Alternatively, the pressure detection surface of the pressure sensor 30 may be disposed so as to protrude somewhat from the cavity surface of either the fixed mold 11 or the movable mold 12. Further, the pressure sensor 30 may be disposed on the cavity surface of either the fixed mold 11 or the movable mold 12 in consideration of its function, but in consideration of the influence on the appearance quality of the resin product, the pressure sensor 30 It is preferable to arrange on the cavity surface.

  In the pressure sensor 30, a pressure threshold for controlling the molten resin supply is set for each valve gate 24 corresponding to the pressure sensor 30 and stored in the resin supply control unit 26. When the pressure value detected by the pressure sensor 30 corresponding thereto is equal to or less than the pressure threshold value, each resin supply control unit 26 moves a screw (not shown) in the injection progress direction with the valve gate 24 open. The molten resin from 24 is supplied. On the other hand, each of the resin supply control units 26 controls the hydraulic cylinder 23 and the gate drive unit 25 when the detected pressure value exceeds the pressure threshold value, and closes the valve gate 24 to close the valve gate 24 with the valve gate pin 22. Is instantaneously moved to end the supply of the molten resin from the valve gate 24.

The pressure threshold value is a set pressure value corresponding to the molten resin supply amount optimized for each resin supply unit 20 in order to mold a desired resin product. Specifically, when the supply of the molten resin by all the resin supply units 20 is completed by the control of the supply of the molten resin for each resin supply unit 20, a desired amount of melting is performed at the flow end positions H to M in FIG. The set pressure value is such that the resin has reached. In this embodiment, the pressure threshold P ₁ of the upper pressure sensor 30 in FIG. _2, the pressure threshold P ₂ of the pressure sensor 30 in the lower left side of FIG. _2, the pressure threshold P ₃ of the pressure sensor 30 of the lower right side of FIG. 2 Is set.

As described above, the feedback control by the resin supply unit 20 is performed for each valve gate 24 in which the pressure thresholds P _{1 to} P ₃ of the molten resin are set. The total amount of molten resin supplied to the cavity C is set to an amount smaller than the volume of the cavity C. Specifically, when the unfilled ratio of the molten resin is less than 3%, a portion where the molten resin is completely filled is generated in a part of the cavity C, so that there is no space for the molten resin to move to the fixed mold 11 side. On the other hand, if the unfilled ratio of the molten resin exceeds 20%, the absolute amount of the molten resin is insufficient, so that it is difficult to maintain the shape as a resin product. For this reason, it is optimal that the total amount of molten resin supplied is 11% less than the volume of the cavity C. Good.

  In addition, the molding apparatus 1 includes a temperature control unit 40 that controls the temperature of the mold 10. The temperature control unit 40 controls the temperature of the movable mold 12 by supplying hot water to the movable mold 12 and the fixed mold hot water supply section 41 that controls the temperature of the fixed mold 11 by supplying warm water to the fixed mold 11. A movable hot water supply unit 42 is provided.

  In setting the temperature of the mold 10, it is preferable that the temperature of the fixed mold 11 is higher than the temperature of the movable mold 12. For example, in the fixed mold 11, the temperature of the central part is set to 80 to 90 ° C, and the temperature of the peripheral part is set to 80 to 95 ° C. In the movable mold 12, the temperature of the central part is set to 70 to 80 ° C, and the temperature of the peripheral part is set to 60 to 85 ° C. In this aspect, solidification of the molten resin immediately after gas injection by the gas injection part 15 can be prevented.

The temperatures of the fixed mold 11 and the movable mold 12 of the mold 10 are preferably set as follows according to the type of resin used (see FIG. 13 (c)). In this embodiment, since the molten resin is in close contact with the fixed mold 11 and solidifies faster than the movable mold 12 side, sink marks are concentrated on the movable mold 12 side and do not occur on the fixed mold 11 side.
(A) Temperature range of fixed mold 11 In the case of crystalline resin (crystallization temperature +50) ° C. to (crystallization temperature −50) ° C.
In case of non-crystalline resin (glass transition temperature + 50) ° C. to (glass transition temperature−50) ° C.
(B) Temperature range of movable mold 12 In the case of crystalline resin (fixed mold temperature −10) ° C. to (fixed mold temperature −50) ° C.
In case of non-crystalline resin (fixed mold temperature -10) ° C-(fixed mold temperature -50) ° C

  On the other hand, there is a possibility that sink marks will occur on both sides as follows, outside the temperature range of the above aspect. That is, when only the temperature of the movable mold 12 exceeds the specified range, a part of the molten resin cannot be peeled off from the movable mold 12 and there is a risk that sink marks will occur on both sides (see FIG. 13 (d)). ). If only the temperature of the fixed mold 11 exceeds the specified range, the solidified layer on the fixed mold 11 side is thin and the strength against volume shrinkage cannot be obtained, so there is a risk that sink marks will occur on both sides ( (See FIG. 13 (e)). When only the temperature of the movable mold 12 does not reach the specified range, the solidification on the movable mold 12 side is accelerated, so that the solidified layer on the movable mold 12 side becomes thick, and there is a risk that sink marks will occur on both sides (see FIG. 13 (b)). If only the temperature of the fixed mold 11 does not reach the specified range, the molten resin cannot adhere to the fixed mold 11 and there is a risk of sink marks on both sides (see FIG. 13A).

(2) Operation | movement of embodiment Next, the method to shape | mold a resin product using the shaping | molding apparatus 1 is demonstrated with reference mainly to FIG. FIG. 4 is a diagram illustrating a time chart of a molding method according to an embodiment of the present invention. FIGS. 5-9 is a schematic sectional side view showing each process of the shaping | molding method which concerns on one Embodiment of this invention. FIG. 10 is a side sectional view showing a partial configuration of a resin product molded by the molding method according to one embodiment of the present invention. FIG. 11 is a perspective view illustrating the overall configuration of the resin product in FIG. 10. 4 to 9, the gas injection passage 14 and the openings 14A and 14B are not shown in order to avoid complication of the drawings.

  First, the fixed mold 11 and the movable mold 12 of the mold 10 are closed, and a cavity C is formed between the fixed mold 11 and the movable mold 12 (step S101). At this time, it is preferable that the temperature of the fixed mold 11 and the movable mold 12 is appropriately set to a temperature corresponding to the type of resin used by using the temperature control unit 40. Subsequently, the valve gates 24 of the plurality of resin supply units 20 are opened (step S102), and as shown in FIG. 5, the supply of the molten resin 50 is started by the valve gate pins 22 through the valve gates 24 inside the cavities C ( Step S103, first step).

  Here, each pressure sensor 30 detects the pressure value of the molten resin 50 in the vicinity of the corresponding valve gate 24, and each resin supply control unit 26 determines whether or not the detected pressure value exceeds the pressure threshold value. Determination is made (step S104). For example, when the pressure value of the molten resin 50 near the valve gate 24 is equal to or lower than the pressure threshold value, the resin supply control unit 26 determines in step S104 that the pressure value detected by the pressure sensor 30 is equal to or lower than the pressure threshold value. The supply of the molten resin 50 from the valve gate 24 corresponding to the pressure sensor 30 that has detected the value is continued (step S102). On the other hand, when the pressure value of the molten resin 50 in the vicinity of the valve gate 24 exceeds the pressure threshold value, the resin supply control unit 26 determines in step S104 that the pressure value detected by the pressure sensor 30 exceeds the pressure threshold value, and the pressure By closing the valve gate 24 of the resin supply unit 20 corresponding to the pressure sensor 30 that has detected the pressure value exceeding the threshold value and stopping the movement of the valve gate pin 22, the supply of the molten resin 50 from there is finished ( Step S105). Such feedback control in steps S102 to S105 is executed for each resin supply unit 20.

Specifically, the upper resin supply section 20 _-1 in Fig. 2, the when the detected pressure value by the pressure sensor 30 is a pressure threshold P ₁ below performs the supply of the molten resin 50, the detected pressure value is the pressure threshold P ₁ When the value exceeds the value, the supply of the molten resin 50 is terminated. The resin supply section 20 _-2 lower left side of FIG. 2 performs supply of the molten resin 50 when the detected pressure value by the pressure sensor 30 is the threshold value P ₂ or less, the melt when the detected pressure value exceeds the pressure threshold P ₂ The supply of the resin 50 is finished. In the lower right side of the resin supply section 20 _-3 of FIG. 2 performs supply of the molten resin 50 when the detected pressure value by the pressure sensor 30 is the threshold value P ₃ or less, the melt when the detected pressure value exceeds the threshold value P ₃ The supply of the resin 50 is finished.

  When the supply of the molten resin 50 by all the resin supply units 20 is completed by controlling the supply amount of the molten resin 50 for each resin supply unit 20, a desired amount of the molten resin 50 is supplied into the cavity C, A desired amount of molten resin 50 has reached the flow end positions H to N shown in FIG. The total amount of molten resin 50 supplied to the cavity C at this time is set to an amount smaller than the volume of the cavity C.

  Subsequently, the gas injection unit 15 injects gas into the cavity C from the openings 14A and 14B of the movable mold 12 through the gas injection path 14 (step S106, second step). Thereby, as shown in FIG. 6, the molten resin 50 supplied into the cavity C is peeled off from the cavity surface of the movable mold 12 and is in close contact with the cavity surface of the fixed mold 11. In particular, as shown in FIG. 7, in this embodiment, the amount of molten resin 50 supplied inside the cavity C is smaller than the volume of the cavity C as described above. By reliably peeling the movable mold 12 from the cavity surface, the air gap 13A is reliably formed between the molten resin 50 and the cavity surface of the movable mold 12, and the fixed mold 11 and the movable mold 12 as described above. Therefore, the fixed mold 11 is reliably adhered to the cavity surface.

  The gas injection pressure into the cavity C is preferably 0.1 to 0.6 MPa. When the gas injection pressure is less than 0.1 MPa, the mold release from the movable mold 12 of the molten resin 50 becomes incomplete, and sink marks h are likely to occur at locations where the ribs R are present on the surface of the product W. On the other hand, when the injection pressure exceeds 0.6 MPa, the gas is caught in the cavity surface of the fixed mold 11 and the surface of the product W is swelled. In addition, you may perform the gas injection | pouring by the gas injection | pouring part 15 before completion | finish of supply of molten resin. In addition, the delay time from the supply start time of the molten resin 50 to the start of gas injection is preferably 0 to 5 seconds, and the gas injection time is preferably 2 to 40 seconds.

  Next, in a state where the form of the molten resin 50 inside the cavity C is maintained, cold water is supplied from the temperature control unit 40 to the fixed mold 11 and the movable mold 12 to start cooling the molten resin 50 (step S107, third process) ). Then, as shown in FIG. 8, on the surface side of the molten resin 50 that is in close contact with the cavity surface of the fixed mold 11, solidification starts from the cavity surface side of the fixed mold 11. With the formation of the solidified layer 50 a on the cavity surface side of the fixed mold 11, the molten resin 50 is attracted to the fixed mold 11 side, and the back surface of the molten resin peeled off from the cavity surface side of the movable mold 12 has a sink mark. h begins to occur. On the other hand, the back surface side of the molten resin 50 is peeled off from the mold surface of the movable mold 12 by gas injection. And since the space | gap 13A is formed between the back surface side of the molten resin 50, and the cavity surface of the movable mold | type 12, the back surface side of the molten resin 50 is rather than the surface side of the molten resin 50 by the heat insulation effect | action of the space | gap 13A. The progress of cooling is delayed, and the formation of a solidified layer has not yet started.

  As the cooling proceeds, a solidified layer 50b is formed on the back side of the molten resin 50 as shown in FIG. In this case, since the solidified layer 50a is already formed on the surface side of the molten resin 50, the surface side is not pulled by the shrinkage on the back surface side of the molten resin 50, and sink marks h are not formed on the solidified layer 50a on the surface side. Does not occur. Next, the mold 10 is opened (step S108), and the resin product W is taken out (step S109). In the resin product W, sink marks h are concentrated on the back surface side and are generated from the flat plate portion F to the rib R, but are not generated on the front surface side, so that no dent is generated there. As a specific example of the resin product W, as shown in FIG. 11, for example, a cover 100 used for a moped scooter can be cited. On the back side of the cover 50, a plurality of ribs R are formed in a lattice shape.

  In the present embodiment, since the molten resin 50 in the vicinity of each valve gate 24 that is not the flow end is a resin immediately after being supplied, the temperature drop of the molten resin 50 is small. Thereby, in each shaping | molding of the resin product W, since the difference in the shrinkage degree and viscosity of the molten resin 50 by a temperature fall does not arise, the dispersion | variation in the pressure value of the molten resin 50 does not arise. Since the pressure value of the molten resin 50 in the vicinity of each valve gate 24 is detected and the feedback control of the supply amount of the molten resin 50 is performed based on the detected pressure value, the supply of the molten resin 50 is performed. The amount can be controlled with high accuracy. In addition, since the feedback control of the supply amount of the molten resin 50 is performed for each valve gate 24 in which the pressure threshold value of the molten resin 50 is set, the supply amount of the molten resin 50 can be controlled with higher accuracy. Therefore, even when applied to an apparatus that does not perform the feedback control of the molten resin supply rate or an apparatus that is not stable, such as an aging apparatus, it is possible to suppress the occurrence of variations in the volume of the resin product W, In short, the effect of reducing the occurrence of sink marks on the surface side of the resin product W can be obtained.

  In particular, when the holding pressure does not contribute to the supply amount into the cavity (for example, when the holding pressure applied to the molten resin as the secondary pressure at the time of gas injection in step S106 is low or when no holding pressure is applied), the molten resin 50 The present embodiment is particularly effective because the amount of supply can be controlled with higher accuracy. In addition, when no pressure is applied to the molten resin 50, the pressure of the gas can be reduced, so that it is not necessary to use a pressure-resistant structure for the device used, and the cost of the mold 10 and the device 1 can be reduced. Can do. Further, in this case, since the resin pressure holding step is not necessary, productivity can be improved. In addition, since the gas can be concentrated on the rib R and the vicinity thereof at the time of gas injection in step S106, the mold release of the rib R can be performed more efficiently.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to specific examples.

<Example>
In the embodiment, as shown in FIG. 2, a cavity C in which a pressure sensor 30 is arranged in the vicinity of each valve gate 24 is used, and molten resin is supplied from each valve gate 24 according to the flow shown in FIG. Molded. In the molten resin supply control by the pressure sensor 30, for each valve gate 24, the pressure value of the molten resin in the vicinity thereof is detected and the supply of the molten resin is terminated when the pressure value exceeds the pressure threshold. The pressure threshold value of each pressure sensor 30 is a value optimized so as to obtain a desired shape and weight of the resin product.

  In the example, the total supply amount of the molten resin at the end of the resin supply was set to 277 g, and the resin product was molded 100 times. As a result, as shown in Table 1, the maximum weight of the resin product was 278.1 g, the minimum weight was 274.7 g, and the variation in the weight of the resin product was 3.4 g.

<Comparative example>
In the comparative example, as shown in FIG. 12, the molten resin is supplied from each valve gate 2 using the cavity 1 in which the pressure sensor 3 is arranged at the flow end positions E, F, and G of the molten resin, and the resin product is molded. . In the supply control of the molten resin by the pressure sensor 3, the pressure values of the molten resin at the flow end positions E, F, G are detected, and the molten resin from all the valve gates 2 when all the pressure values exceed the pressure threshold value. Supply has been terminated at the same time. The pressure threshold value of each pressure sensor 3 is a value optimized so as to obtain a desired shape and weight of the resin product.

  In the comparative example, the total amount of molten resin supplied at the end of the resin supply was set to 264 g, and the resin product was molded 100 times. In the comparative example, the shape of the cavity 1 was the same as that of the cavity C of Example 1, and the resin product was molded in the same process and conditions as in the example except for the supply control of the molten resin. As a result, as shown in Table 1, the maximum weight of the resin product was 270 g, the minimum weight was 258 g, and the variation in the weight of the resin product was 12 g.

  As described above, in the embodiment, the pressure sensor is arranged in the vicinity of each valve gate and the supply control of the molten resin is performed for each valve gate, so that the supply amount of the molten resin can be accurately controlled. Thus, it was confirmed that variation in the weight of the resin product can be suppressed, and in other words, the effect of reducing the occurrence of sink marks on the surface side of the resin product can be obtained.

It is a schematic sectional side view showing the partial structure of the shaping | molding apparatus which concerns on one Embodiment of this invention. It is a schematic sectional drawing showing the cavity of FIG. It is a side view showing the structure of the shaping | molding apparatus which concerns on one Embodiment of this invention. It is a figure showing the time chart of the shaping | molding method which concerns on one Embodiment of this invention. It is a schematic sectional side view showing the process of the shaping | molding method which concerns on one Embodiment of this invention. FIG. 6 is a schematic cross-sectional side view illustrating a process of the molding method following FIG. 5. FIG. 7 is a schematic side cross-sectional view illustrating a process of the molding method following FIG. 6. It is a schematic sectional side view showing the process of the shaping | molding method following FIG. It is a schematic sectional side view showing the process of the shaping | molding method following FIG. It is a sectional side view showing the partial structure of the resin product shape | molded by the shaping | molding method which concerns on one Embodiment of this invention. It is a perspective view showing an example of the resin product by which the shaping | molding method which concerns on one Embodiment of this invention was carried out. It is a schematic sectional drawing showing the cavity of a shaping | molding apparatus. It is a figure for demonstrating the various shaping | molding states by the preset temperature of a metal mold | die.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Molding apparatus, 10 ... Mold, 13 ... Recess, 14A, 14B ... Opening, 15 ... Gas injection part (gas injection means), 20 ... Resin supply part (supply means), 24 ... Valve gate (supply port) , 26 ... Resin supply control section (control means), 30 ... Pressure sensor (pressure detection means), 50 ... Molten resin, 100 ... Cover (resin product), C ... Cavity, R ... Rib (thick part), W ... Resin products,

Claims (7)

In a molding method of molding a resin product having a thick part convex on the back side by supplying a molten resin in an amount smaller than the cavity volume of the mold,
A first step of supplying the molten resin into the cavity through a plurality of supply ports of the cavity of the mold;
By injecting gas into the cavity from the mold surface of the mold on the back surface side of the product, a gap is formed between the molten resin and the mold surface of the mold on the back surface side. A second step of bringing the molten resin into close contact with the mold surface of the mold on the surface side;
A third step of solidifying the molten resin in a state where the shape of the molten resin set by the second step is maintained,
For each supply port, set a pressure threshold of the molten resin,
Between the start of the first step and the end of the second step, the pressure value of the molten resin in the vicinity of the supply port that is not the flow end is detected for each supply port and the pressure value is the pressure. When the threshold value is exceeded, the supply of the molten resin is terminated ,
The supply amount of the molten resin in the first step is set to a value 3 to 20% less than the volume of the cavity,
A molding method characterized in that a set pressure value corresponding to the supply amount of molten resin optimized for each supply port for molding the resin product is used as the pressure threshold value of each supply port . In the mold surface of the mold on the back side of the product, a recess for molding the thick part is provided,
2. The molding method according to claim 1, wherein in the second step, the gas is injected from a bottom surface of the concave portion and the vicinity thereof. The mold includes a movable mold having the mold surface on the back side of the product, and a fixed mold having the mold surface on the surface side of the product,
  3. The molding method according to claim 1, wherein the temperature of the fixed mold is set higher than the temperature of the movable mold in the cavity to which the molten resin is supplied in the first step.   The molding method according to claim 1, wherein the gas injection pressure into the cavity in the second step is set to 0.1 to 0.6 MPa. In a molding apparatus that molds a resin product having a thick-walled portion convex on the back side by supplying a molten resin in an amount smaller than the cavity volume of the mold,
Supply means for supplying the molten resin into the cavity through a plurality of supply ports of the cavity of the mold;
By injecting gas into the cavity from the mold surface of the mold on the back surface side of the product, a gap is formed between the molten resin and the mold surface of the mold on the back surface side. Gas injection means for bringing the molten resin into close contact with the mold surface of the mold on the surface side;
A pressure detecting means that is installed in the vicinity of each of the supply ports and detects the pressure value of the molten resin in the vicinity of the supply port that is not the flow end;
Control means for controlling the supply of the molten resin,
For each pressure detection means, a pressure threshold value of the molten resin is set,
The control means, for each supply means, terminates the supply of the molten resin from the supply port when the pressure value detected by the pressure detection means exceeds the pressure threshold,
Solidification of the molten resin is performed in a state of holding the shape of the molten resin set by the gas injection means ,
The supply amount of the molten resin in the first step is set to a value 3 to 20% less than the volume of the cavity,
A molding apparatus using a set pressure value corresponding to a supply amount of a molten resin optimized for each supply port in order to mold the resin product, as the pressure threshold value of each supply port . On the mold surface of the mold on the back side of the product, a recess for forming the thick part is formed,
The molding apparatus according to claim 5 , wherein an opening into which the gas is injected is formed in a bottom surface of the recess and in the vicinity of the recess. In the control means, a pressure threshold value corresponding to each pressure detecting means is set so that the molten resin supplied into the mold cavity has a smaller amount than the cavity volume of the mold. The molding apparatus according to claim 5 .

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