JP7257256B2 - INJECTION MOLDING APPARATUS AND INJECTION MOLDING METHOD - Google Patents

Description

TECHNICAL FIELD The present invention relates to an injection molding apparatus and an injection molding method for injection molding a flat plate molded product with an arbitrary mold clamping force smaller than the maximum mold clamping force when clamping a mold.

Generally, in a mold clamping device of an injection molding machine, if high-pressure mold clamping is performed with a maximum mold clamping force, mold clamping can be performed safely without causing defects such as burrs. However, on the other hand, since an excessive mold clamping force is applied to the mold, it causes early deterioration of the mold and an unnecessary increase in energy consumption. It becomes necessary to treat stains and pains on the surface, and to repair them. Therefore, if the mold can be clamped with an appropriate minimum mold clamping force, excessive clamping force applied to the mold can be avoided. It is possible to reduce production costs and avoid interruptions in production.

In Patent Document 1, the problem is to accurately set the appropriate minimum mold clamping force that does not cause burr defects, and to obtain a wider range of information related to changes in the mold due to resin filling. The clamping force (100[%], 80[%], 70[%] . The relative position of the movable platen with respect to the fixed platen in the injection process is detected by a mold position sensor attached to the outer surface of the fixed platen that supports the fixed mold and the movable platen that supports the movable mold, and at least the position of the mold is detected. Disclosed is a mold clamping force setting method that sets, as an appropriate mold clamping force, a mold clamping force that is increased by a predetermined amount with respect to the mold clamping force when the change occurs when a change occurs that satisfies a predetermined condition. was done.
Japanese Patent Application Laid-Open No. 2010-111005

However, even if the mold clamping force setting method of Patent Document 1 is effective when molding products with different shapes and sizes, there is a trial molding process, and products with the same shape and size can be produced efficiently. There was a problem that it was not easy to do and productivity was low.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an injection molding apparatus and an injection molding method for a flat plate molded product that can efficiently manufacture high-quality flat plate molded products while suppressing the pressure inside the mold.

That is, the injection molding apparatus of the present invention is an injection molding apparatus for manufacturing a flat plate molded product made of resin using a mold for injection molding, wherein the mold corresponds to the shape of the flat plate molded product. A fixed template having a substantially rectangular cavity surface and provided with a plurality of gates communicating with the cavity surface is provided. and each group is arranged in a common filled resin flow passage.

Here, the term "arranged in a staggered manner" means that when a plurality of rows of gates are arranged in parallel, the pitches of the plurality of gates in adjacent rows are staggered. This is an arrangement in which when a gate is projected in a direction perpendicular to the direction in which the row extends, it does not match the projected images of the gates adjacent to the row.
In other words, "arranged in a zigzag pattern" means that when attention is paid to the gates arranged in the p-th column, the gates arranged in the p+1-th column, and the gates arranged in the p+2-th column, these This refers to an arrangement in which three gates are not arranged in a straight line but staggered.

Further, the injection molding method of the present invention is an injection molding method performed by using the injection molding apparatus of the present invention, in which resin is injected from a plurality of gates of one group for simultaneous resin filling on one side of the mold. Then, resin is sequentially injected from the gates of another group toward the other side of the mold, and before the injection of resin from the gates of the one group is stopped, the gates of the other group are injected. Injection of resin from the plurality of gates is started, and after injection of resin from the plurality of gates of the other group is started, injection of resin from the plurality of gates of the one group is stopped. .

Further, the injection molding method of the present invention is an injection molding method performed by using the injection molding apparatus of the present invention, wherein resin is injected from a plurality of gates of one group, which are simultaneously filled with resin at substantially the center of the mold. is started, and then injection of resin is started from a plurality of the gates of a pair of groups on both sides of one group in which resin is filled simultaneously in the central part, Before the injection of resin from the plurality of gates of one group which is simultaneously filled with resin is stopped, the injection of resin is started from the plurality of gates of the pair of groups which are simultaneously filled with resin, and the pair of gates are simultaneously filled with resin. After starting injection of resin from the plurality of gates of the group, injection of resin from the plurality of gates of one group, which simultaneously fills the substantially central portion of the mold with resin, is stopped.

FIG. 4 is a plan view for explaining the positions of gates formed on the cavity surface according to the first embodiment of the present invention; FIG. 4 is an explanatory diagram relating to the position of the gate formed on the cavity surface according to the first embodiment of the present invention, (a) an explanatory schematic diagram of the gate position, and (b) an enlarged explanatory schematic diagram of the gate position. 3A and 3B are other explanatory diagrams related to the position of the gate formed on the cavity surface according to the first embodiment of the present invention, (a) an explanatory schematic diagram of the gate position, and (b) an enlarged explanatory schematic diagram of the gate position. FIG. 4 is an explanatory diagram showing the timing of injecting resin in Example 1 of the present invention; FIG. 5 is an explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 1 of the present invention; FIG. 10 is another explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 1 of the present invention. FIG. 5 is another explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 1 of the present invention. Still another explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 1 of the present invention. FIG. 5 is an explanatory diagram showing the timing of injecting resin in Example 2 of the present invention. FIG. 5 is an explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 2 of the present invention; FIG. 10 is another explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 2 of the present invention. FIG. 9 is another explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 2 of the present invention. Still another explanatory view showing analysis results of the injection molding die according to the present invention during the resin filling process in Example 2 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An injection mold according to an embodiment of an injection molding apparatus of the present invention and a method for manufacturing a flat plate molded article made of resin using the mold will be described below with reference to the drawings. First, the arrangement of the gates of the injection mold used in this embodiment will be described.

The mold 1 for injection molding of this embodiment shown in FIG. 1 has a cavity 2 having a substantially rectangular shape and one side of which has a trapezoidal shape. placed. The pitch between the direct gates 3 is set to 200 mm.
The depth of the cavity substantially matches the thickness of the resulting flat plate product.

As shown in FIG. 1, the direct gates G1 to G38 are arranged in a staggered manner, and when a plurality of rows of gates are arranged in parallel, the pitches of the gates in adjacent rows are shifted. . That is, when the plurality of gates G1 to G5 in the columns G1 to G5 are projected in a direction orthogonal to the direction in which the columns extend, the plurality of gates G6 in the columns G6 to G11 adjacent to the columns G1 to G5 are projected. ∼G11 are arranged inconsistently.
That is, when focusing on the gates G12 to G16 arranged in the p-th column, the gates G17 to G22 arranged in the p+1-th column, and the gates G23-G27 arranged in the p+2-th column, these three columns Gates G12, G17 and G23 are not arranged in a straight line but are staggered.

By arranging them in a zigzag manner in this way, it is possible to minimize gas puddles 4 between the resins injected from the respective gates G1 to G38 as shown in FIGS. 2(a) and 2(b).

On the other hand, as shown in FIGS. 3(a) and 3(b), each of the gates G1 to G38 is positioned at the intersection point of a lattice formed by a vertical line A extending in the vertical direction of the cavity surface and a horizontal line B extending in the horizontal direction. In the case where a plurality of gates G1 to G38 are provided at position P and are formed at approximately equal intervals along the vertical and horizontal directions of the cavity surface, each gate G1 to G38 emits A gas puddle 4 between resins becomes large, and the resin charging efficiency is poor.

Further, in the injection mold 1 of the present embodiment, any three adjacent gates among the plurality of gates G1 to G38 communicating with the surface of the cavity 2 are arranged at the vertex positions of an equilateral triangle.

In the injection mold 1 according to the embodiment of the present invention, the distance between adjacent gates among the staggered direct gates G1 to G38 is shorter than the flow length of the resin injected from one gate. set as The resin flow length is calculated by analysis from the resin injection pressure from the gate, the viscosity and temperature of the injected resin, and the plate thickness of the molded product.

In addition, the gates to be opened are set so that the injection pressure does not exceed the mold clamping force of the molding machine when some of the direct gates G1 to G38 are opened simultaneously.
For example, in the injection mold 1 shown in Fig. 1, G1 to 5 are grouped as one group, and G6 to 11 are grouped as the second group. It becomes necessary to reduce the number of gates to be used and group the number of open gates to 3 points.
In such a case, for example, G1 to 3 or G1, 2, 6 are the first group, and G4, 5, 11 or G3, 7, 8 are the second group, and the opening is advanced, and the opening gate meanders. You can also make it so that it goes on. Such a degree of freedom in selection of injection gates that are open is an advantage obtained as a result of the staggered arrangement of the direct gates G1 to G38, which can minimize gas stagnation 4 between resins.

In relation to the above, when some of the direct gates G1 to G38 are opened simultaneously, the valve controller can set the upper limit of the number of simultaneous opening points.

Next, an example will be described in which a flat plate molded product made of resin was actually manufactured using the injection mold according to the above embodiment. In each of the following examples, PP-GF30 was used as the resin to produce a product having a product volume of 4658 cm ³ and a product projected area of 19085 cm ² . Analysis conditions were set to 220° C. resin temperature, 50° C. mold temperature, 4.7 seconds injection time, 190 seconds holding pressure time, 40 MPa holding pressure, and 20 seconds cooling time. A molding machine with a mold clamping force of 2000 tons was used using a hot runner direct gate.
[Example 1]
FIG. 4 shows timings for injecting resin from gates G1 to G38 in this embodiment.
First, the mold for injection molding is clamped with a mold clamping force of 2100 tons. The resin filling pressure was 787 kg/cm ² . The total resin filling time was 5.2 seconds, the resin temperature was 217°C and the tip temperature of the resin stream was 223°C. The required injection pressure was 1150 kg/cm ² .
First, the gates G34 to G38 were opened and the resin was injected for 1.8 seconds. Next, 1.6 seconds after the start of resin injection from gates G34 to G38, gates G28 to G33 were opened with gates G34 to G38 open, and resin was injected for 0.7 seconds. During this time, the injection of resin from gates G34 to G38 was stopped 1.8 seconds after the start of resin injection from gates G34 to G38.

Next, 2.1 seconds after the start of resin injection from gates G34 to G38, gates G23 to G27 were opened with gates G28 to G33 open, and resin was injected for 0.7 seconds. During this time, 2.3 seconds after the start of resin injection from gates G34 to G38, that is, at 0.7 seconds after the start of resin injection from gates G28 to G33, resin injection from gates G28 to G33 was stopped.

Next, 2.7 seconds after the start of resin injection from gates G34 to G38, gates G17 to G22 were opened with gates G23 to G27 open, and resin was injected for 0.7 seconds. During this time, 2.8 seconds after the start of resin injection from gates G34 to G38, that is, at 0.7 seconds after the start of resin injection from gates G23 to G27, resin injection from gates G23 to G27 was stopped.

Next, 3.3 seconds after the start of resin injection from gates G34 to G38, gates G12 to G16 were opened with gates G17 to G22 open, and resin was injected for 0.7 seconds. During this time, 3.4 seconds after the start of resin injection from gates G34 to G38, that is, at 0.7 seconds after the start of resin injection from gates G17 to G22, resin injection from gates G17 to G22 was stopped.

Next, 3.9 seconds after the start of resin injection from gates G34 to G38, gates G6 to G11 were opened with gates G12 to G16 open, and resin was injected for 0.7 seconds. During this time, 4.0 seconds after the start of resin injection from gates G34 to G38, that is, at 0.7 seconds after the start of resin injection from gates G12 to G16, resin injection from gates G12 to G16 was stopped.

Next, 4.5 seconds after the start of resin injection from gates G34 to G38, gates G1 to G5 were opened with gates G6 to G11 open, and resin was injected. During this time, 4.6 seconds after the start of resin injection from gates G34 to G38, that is, 0.7 seconds after the start of resin injection from gates G6 to G11, resin injection from gates G6 to G11 was stopped.

In the above embodiment, resin injection is started from gates G34 to G38 on the right side in FIG. The timing of resin injection was shifted in the order of , and the resin was injected. Moreover, since the plurality of gates are arranged in a zigzag pattern, the amount of air trapped in the cavity can be minimized, thereby preventing appearance defects such as burning caused by the air trapped. Therefore, it is possible to manufacture a high-quality flat plate molded product. In addition, since the plurality of gates are staggered and evenly arranged in this way, the pressure inside the mold can be suppressed to a low level without a partial increase in pressure in the cavity. Therefore, it was possible to suppress the pressure inside the mold to a low level and efficiently manufacture a high-quality flat plate product.

Further, according to this embodiment, since the plurality of gates are arranged in a zigzag pattern and evenly on the cavity surface 10, the pressure inside the mold is approximately the same at any position in the cavity. Therefore, since the pressure inside the mold can be kept low, a mold clamping device with a small mold clamping force can be used, and space can be saved.

In addition, resin injection is started from gates G34 to G38 on the right side in FIG. Since the resin is injected in one direction from one side to the other side with the timing of . As a result, the resulting flat plate molded product does not have appearance defects such as burning caused by air pockets, so that a high quality flat plate molded product can be efficiently manufactured.

5 to 8 show analysis results of the injection molding die 1 during the resin filling process in Example 1. FIG.
FIG. 5 shows the weld line 5 of the mold 1 for injection molding. By opening the gates G34 to G38 of the first row and filling with resin, a weld 5 is generated in the portion where the molten resin joins between the gates of the first row. The resin reaches gates G28 to G33 arranged in a zigzag pattern in the second row before the resin is filled between the weld 5 generated in the first row and the gate position. By opening the gates G28 to G33 of the second row at this timing, an analysis result was obtained in which welds did not occur between the gates G28 to G33 of the second row. Furthermore, when the resin filled from the gates G28 to G33 of the second row reaches the position of the gates G23 to G27 of the third row, the gates G23 to G27 of the third row are opened to No weld occurs between the three rows of gates G23 to G27. Thereafter, by repeating this process, the inside of the mold 1 is filled with the resin.
When focusing on an arbitrary single gate, the resin injected from the gates G1 to G38 arranged in a staggered manner and filled into the cavity is injected into the cavity concentrically with that gate as the center. As a result, it is known that the resin filling the cavity flows in an arc around each of the gates G1 to G38. In addition, the distance between adjacent gates is shorter than the flow length of the resin injected from one gate, and since the gates G1 to G38 are arranged so as to be almost the same, the resin filling speed is It is possible to easily set the molding conditions only by controlling the time to open the gate under the condition that the conditions are not changed in .

FIG. 6 shows the pressure distribution during V/P switching. The mold 1 is filled with resin by opening the gates from the gates G34 to G38 in the first row to the gate group in the last row in order. The mold clamping force is analyzed by using the resin pressure in the mold 1 obtained by analysis at the timing of opening each gate and the integral value of the projected area of the injection resin flow area from the gate group where resin is injected at the same time. can be calculated. While confirming the mold clamping force calculated by this analysis, the distance between the gates and the number of gates to be opened in the mold design are determined so as not to exceed the capacity of the injection molding machine. Here, it was set so as not to exceed the maximum clamping force of 2100 tons. Finally, by checking the VP switching pressure, it was confirmed that the flow ends of the resin coming out of each gate in the last row reached the end of the product almost simultaneously.

FIG. 7 shows the pressure distribution of the injection mold 1 at the filling time of 5.184 seconds. FIG. 7 shows the time it takes for the resin to reach each location in the mold, and the flow pattern of the resin until it is completely filled can be confirmed. 5. It can be confirmed that the filling was completed in 184 seconds and the resin flowed in order from one side of the molded product.

FIG. 8 shows the temperature at the tip of the filled resin. When checking the resin flow pattern, the resin pressure at the gate portion of the p+1th row is low at the timing immediately before the gate of the p+1th row is opened. Since the melted resin in the runner is in a connected continuous channel, the resin pressure in the runner at the gate portion of the p-th row, through which the resin has flowed until then, decreases when the gate of the p+1-th row is opened. As a result, the flow rate of resin from the pth row gate is reduced. When the flow rate of the resin decreases in this manner, the flow velocity at the tip of the flow until then decreases, and the resin temperature at that portion rapidly decreases. When the resin temperature drops like that, the fluidity of the resin decreases, making it impossible to fill in an arc around each gate. Product strength failure occurs. Therefore, it is necessary to ensure that the temperature is above a certain level so that the resin can flow with fluidity when the flow tip reaches a place where the flow velocity decreases. Here, it was confirmed that the resin has fluidity and can flow at 200°C or higher.

[Example 2]
Next, another embodiment of the method for manufacturing a flat plate molded article made of resin according to the present invention will be described.
The mold for injection molding was clamped with a mold clamping force of 2800 tons using a mold clamping device (not shown) in the same manner as in Example 1. The resin filling pressure was 688 kg/cm ² . The total resin fill time was 6.2 seconds, the resin temperature was 186°C, and the tip temperature of the resin stream was 221°C. The required injection pressure was 1000 kg/cm ² .

FIG. 9 shows timings for injecting resin from gates G1 to G38 in this embodiment. First, gates G17 to G22 in the approximate center of the mold were opened to inject resin for 1.8 seconds.
Next, 1.7 seconds after the start of resin injection from the gates G17 to G22, the gates G12 to G16, which are a pair of gates G17 to G22 on both sides of the gates G17 to G22, are simultaneously filled with resin while the gates G17 to G22 are open. Then, the gates G23 to G27 were opened and the resin was injected for 1.3 seconds. During this time, the injection of resin from gates G17 to G22 was stopped 1.8 seconds after the start of resin injection from gates G17 to G22.

Next, 2.9 seconds after the start of resin injection from gates G17 to G22, gates G12 to G16 and gates G23 to G27 are opened, gates G6 to G11 and gates G28 to G33 are opened, and 1.1 The resin was injected for seconds. During this time, 3.0 seconds after the start of resin injection from gates G17 to G22, that is, at the time of 1.3 seconds after the start of resin injection from gates G12 to G16 and gates G23 to G27, gates G12 to G16 and gates G23 to Resin injection from G27 was stopped.

Next, 3.9 seconds after the start of resin injection from gates G17 to G22, open gates G1 to G5 and gates G34 to G8 with gates G6 to G11 and gates G28 to G33 open to inject resin. bottom. During that time, 4.0 seconds after the start of resin injection from gates G17 to G22, that is, at 1.1 seconds after the start of resin injection from gates G6 to G11 and gates G28 to G33, gates G6 to G11 and gates G28 to Resin injection from G33 was stopped.

The injection mold used in Example 2 includes a fixed mold plate and a movable mold plate in the same manner as in Example 1 described above, and a cavity 2 is formed by a gap between the fixed mold plate and the movable mold plate. , and the depth of the cavity 2 substantially matches the thickness of the obtained flat plate molded product.

10 to 13 show analysis results of the injection molding die 1 during the resin filling process in Example 2. FIG.
FIG. 10 shows the weld line 6 of the mold 1 for injection molding. With the gates G17 to G22 in the approximate center of the mold as the first row, by opening the gates G17 to G22 and filling the resin, a weld 6 is generated at the part where the molten resin joins between the gates in the first row. . The resin reaches a pair of gates G12 to G16 and gates G23 to G27 arranged in a zigzag pattern in the second row until resin is filled between the weld 6 generated in the first row and the gate position. By opening gates G12 to G16 and gates G23 to G27 of each second row at this timing, an analysis result was obtained in which welds did not occur between gates G12 to G16 and gates G23 to G27 of each second row. . Furthermore, when the resin filled from the gates G12 to G16 and the gates G23 to G27 of the second row reaches the positions of the pair of the gates G6 to G11 and the gates G28 to G33 of the third row, the gate G6 of each third row -G11 and gates G28 to G33, welds do not occur between the gates G6 to G11 and the gates G28 to G33 in the third row as in the second row. Thereafter, by repeating this process, the inside of the mold 1 is filled with the resin.
The gates G1 to G38 arranged in a zigzag manner in this manner allow the resin being filled to flow in an arc centering on each of the gates G1 to G38. Since the gates G1 to G38 are arranged so that the flow length of the resin injected from the gate is shorter than the flow length of the resin injected from the gate of , and the gates G1 to G38 are arranged so that the resin filling speed is not changed during filling, the gate opening time It is possible to easily set molding conditions only by controlling . In addition, a weld occurs between the gates G17 to G22 of the first gate group, but even if the gates are the same, fine adjustment of the gate position should be performed using flow analysis based on the gate at the vertex of the equilateral triangle. Therefore, it is possible to easily avoid welds in areas where appearance and product strength are required by changing the molding conditions.

FIG. 11 shows the pressure distribution during V/P switching. The mold 1 is filled with resin by opening the gates from G17 to G22 in the first row to the gate group in the last row. The mold clamping force is analyzed by using the resin pressure in the mold 1 obtained by analysis at the timing of opening each gate and the integral value of the projected area of the injection resin flow area from the gate group where resin is injected at the same time. can be calculated. While confirming the mold clamping force calculated by this analysis, determine the distance between gates and the number of gates to be opened in mold design so as not to exceed the capacity of the injection molding machine. Here, it was set so as not to exceed the maximum clamping force of 2100 tons. Finally, by checking the VP switching pressure, it was confirmed that the flow ends of the resin coming out of each gate in the last row reached the end of the product almost simultaneously. These pressure distributions during filling are checked, and each gate position is adjusted using the analysis results, if necessary, so that the mold clamping force during filling does not exceed the predetermined limit of the molding machine.

FIG. 12 shows the pressure distribution of the injection mold 1 at the filling time of 6.180 seconds. FIG. 12 shows the time it takes for the resin to reach each location in the mold, and the pattern of the resin flow until the resin is completely filled can be confirmed. 6. It can be confirmed that the filling was completed in 180 seconds, and the resin flowed in order from the center of the molded product toward both sides.

FIG. 13 shows the temperature at the tip of the filled resin. Checking the flow pattern of the resin, just before opening the p+1-th row gate, the pressure at the p+1-th row gate is low, and the resin melt is in the connected continuous flow path, so the resin does not flow until then. In addition, the resin pressure at the gate portion of the p-th row is lowered. As a result, the flow rate of resin from the pth row gate is reduced. When the flow rate of the resin decreases in this manner, the flow velocity at the tip of the flow until then decreases, and the resin temperature at that portion rapidly decreases. When the resin temperature drops like that, the fluidity of the resin decreases, making it impossible to fill in an arc around each gate. Product strength failure occurs. Therefore, it is necessary to ensure that the temperature is above a certain level so that the resin can flow with fluidity when the flow tip reaches a place where the flow velocity decreases. Here, it was confirmed that the resin has fluidity and can flow at 200°C or higher.
In Example 2, moving the weld line to the center of the product increases the mold clamping force and increases the time it takes for the resin to fill the mold, but it is possible to obtain a product with a different weld position without changing the gate position. is.
On the other hand, in the case of the second embodiment, it is also possible to shape by adjusting the gate positions and gate groups using the gate position analysis results of the first embodiment.

Analysis results for each of the above examples will be described below.
Example 1 is filled from the right side. Example 2 is filled from the center.
The filling pressure could be lowered by 12% in Example 2.
The mold clamping force was able to be lowered by 25% in Example 1.
In the opening method of Example 2, the flow length in the lateral direction is long at the second gate from the center, and the gate is open for a long time, increasing the mold clamping force.
On the other hand, as for the warp, the amount of deformation of the outer periphery was small in Example 1.
The amount of cross-sectional deformation was smaller in Example 2.
As a result of each of the above examples, it can be said that the amount of deformation becomes smaller as the number of gates is increased. In addition, if it is flowed in the longitudinal direction, the amount of deformation in the cross section increases.

INDUSTRIAL APPLICABILITY The method for manufacturing a flat plate molded product of the present invention is suitable for manufacturing a flat plate molded product using a mold, and can be applied to manufacturing a flat plate molded product.

1... Injection mold, 2... Cavity, 3... Direct gate (G1 to G38), 4... Gas pool, 5, 6... Weld line.

Claims (8)

An injection molding apparatus for manufacturing a flat plate molded product made of resin using a mold for injection molding, wherein the mold has a substantially rectangular cavity surface corresponding to the shape of the flat plate molded product. , a fixed mold plate provided with a plurality of gates communicating with the cavity surface, the plurality of gates being arranged in a zigzag pattern and divided into a plurality of groups of a plurality of gates for simultaneous resin filling. , each group is arranged in a common filled resin flow path, and any three gates adjacent to each other among a plurality of gates communicating with the cavity surface are arranged at the apexes of an equilateral triangle. Injection molding equipment for flat plate molded products. 2. Injection of a flat molded product according to claim 1, wherein the distance between adjacent gates among the plurality of gates communicating with the cavity surface is set to be shorter than the flow length of the resin injected from one gate. molding equipment. 3. The injection molding apparatus for a flat molded product according to claim 2, wherein the resin flow length is calculated by analysis from the resin injection pressure from the gate, the viscosity and temperature of the injected resin, and the plate thickness of the molded product. 2. An injection molding method using the injection molding apparatus according to claim 1, wherein injection of resin is started from a group of a plurality of gates that are simultaneously filled with resin on one side of the mold, Resin is sequentially injected from the plurality of gates of another group toward the other side of the mold, and the plurality of gates of the other group before stopping the injection of resin from the plurality of gates of the one group. starting injection of resin from, and stopping injection of resin from the plurality of gates of the one group after starting injection of resin from the plurality of gates of the other group. injection molding method. 2. An injection molding method using the injection molding apparatus according to claim 1, wherein injection of resin is started from a plurality of the gates of one group, which are simultaneously filled with resin, substantially in the center of the mold. After that, injection of resin is started from a plurality of the gates of a pair of groups on both sides of one group in which resin is simultaneously filled in the central portion, and resin is simultaneously filled in approximately the center portion of the mold. Before resin injection from the plurality of gates of one group is stopped, resin injection is started from the plurality of gates of the pair of simultaneously resin-filled groups, and the plurality of gates of the pair of simultaneously resin-filled groups is started. A method of injection molding a flat plate molded product, characterized in that, after starting injection of resin from the gates, injection of resin from a plurality of the gates of one group, which simultaneously fills a substantially central portion of the mold with resin, is stopped. . 6. The method of injection molding a flat molded product according to claim 4 or 5, wherein the molding conditions are set by controlling the gate opening time while keeping the resin filling speed constant. 7. The injection molding method for a flat plate molded product according to claim 4, wherein the plurality of gates in one group which are filled with resin at the same time are set so that the injection pressure does not exceed the mold clamping force of the molding machine. The required mold clamping force is calculated by analysis using the resin pressure in the mold obtained by analysis and the integral value of the projected area of the flow area of the injection resin from the gate group where the resin is injected at the same time. The method for injection molding a flat molded article according to any one of claims 4 to 7.

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