JP6880395B2 - Manufacturing method of injection molded product - Google Patents

Description

The present invention relates to a method for producing an injection molded product.

As shown in Patent Document 1, a lower grill of an automobile has a configuration including a plurality of plate portions extending in parallel and a frame portion for connecting them to each other. Such a lower grill may be formed by injection molding.

The injection molding is performed by filling the cavity of the split mold having a cavity having the same shape as the desired injection molded body with the resin in a molten state and then solidifying the resin. The cavity is provided with a plate cavity corresponding to the plate of the injection molded product, and the resin is usually flowed from both ends of the plate cavity toward the center along the longitudinal direction of the plate cavity. The inside of the part cavity is filled with resin.

Japanese Unexamined Patent Publication No. 2016-03522

As the resin is filled into the plate cavity, the gas in the plate cavity is usually discharged through the parting line of the split die, but depending on the flow of the resin, the gas is not properly discharged and the plate is not discharged properly. Gas may be sandwiched by the resin from both ends of the cavity and remain in the plate cavity (gas residue is generated). Deterioration of appearance quality such as gas residue, resin deterioration due to compression of gas and high temperature, and gas traces being formed on the injection molded product is likely to occur.

The present invention has been made in view of such circumstances, and provides a method for producing an injection-molded article, which can suppress the generation of gas residue and improve the appearance quality of the injection-molded article.

According to the present invention, there is a method for manufacturing an injection-molded article including a plurality of plate portions extending in parallel and a frame portion for connecting them to each other, and the injection-molded article is divided into a pair of parts divided by a parting line. It is formed by solidifying the resin after filling the cavity in the mold with the resin in a molten state, and the cavity is provided with a plate portion cavity corresponding to the plate portion, and the resin is filled when the resin is filled. Is flowed from both ends of the plate cavity toward the center along the longitudinal direction of the plate cavity, and in the plate cavity, the gas existing in the plate cavity before filling with the resin is said. Provided is a method for producing an injection-molded article, which is configured to form a flow velocity distribution of the resin so as to be guided toward the parting line as the resin is filled.

As a result of diligent studies on the cause of gas residue, the present inventor has found that, in the prior art, the thickness of the plate cavity is substantially constant in the width direction (direction perpendicular to the longitudinal direction) of the plate cavity. Therefore, the flow velocity of the resin becomes almost constant in the width direction of the plate cavity, and as a result, the resin is prevented from being pushed out toward the parting line by a slight fluctuation in the molding conditions. It was discovered that gas may remain in the flow.

Then, based on this finding, the plate cavity so as to form a flow velocity distribution of the resin so that the gas existing in the plate cavity before the resin filling is guided toward the parting line with the resin filling. It was found that the gas in the plate cavity can be surely guided toward the parting line by configuring the above, and thereby the generation of the remaining gas can be suppressed, leading to the completion of the present invention. It was.

Hereinafter, various embodiments of the present invention will be illustrated. The embodiments shown below can be combined with each other.
Preferably, the plate cavity is provided with a pair of parting lines, and the plate cavity is configured such that the flow velocity of the resin increases as the distance from one of the parting lines increases.
Preferably, the plate cavity has one side edge and the other side edge that is the opposite side edge, and the parting line is provided at a position adjacent to the one side edge, and the plate cavity is provided. Is that the thickness of the other side edge side is larger than the thickness of the one side edge side in the cross section perpendicular to the longitudinal direction of the plate portion cavity.
Preferably, the cavity comprises a frame cavity corresponding to the frame, the frame cavity comprises a pair of short side cavities and a pair of long side cavities, the short side cavity and the length. The side cavities are connected to each other to form the frame cavity, and both ends of the plate cavity are connected to the short side cavity.
Preferably, a pillar cavity for connecting the plurality of plate cavities is provided between the pair of short side cavities, and both ends of the pillar cavity are connected to the long side cavity.
Preferably, the frame cavity is provided with a groove over the entire circumference.
Preferably, the split die is provided with a gate for allowing the resin to flow into the cavity, and the gate is provided in the same plane as the plate cavity.
Preferably, the cavity comprises a frame cavity corresponding to the frame and the gate is connected to the frame cavity.

It is a perspective view of the injection molded article 1 of one Embodiment of this invention. It is a perspective view which looked at the injection molded article 1 of FIG. 1 from another angle. FIG. 3A is a cross-sectional view taken along the line AA in FIG. 2, and FIG. 3B is an end view of the plate portion 2. It is a perspective view which shows the split dies 21 and 22 used for injection molding of an injection molded body 1. It is a perspective view which shows the shape of the cavity 11 which is composed of the division molds 21 and 22. It is sectional drawing in the same cross section as FIG. 3A in the state which the divided molds 21 and 22 are closed. 7A is an enlarged view of the region A in FIG. 6, and FIG. 7B is a perspective view of the plate cavity 12. FIG. 8A is a cross-sectional view of the plate cavity 12 passing through the center in the thickness direction, and FIG. 8B is an enlarged view of a region B in FIG. 8A. It is a perspective view of the plate part cavity 12 of the prior art.

Hereinafter, embodiments of the present invention will be described. The various features shown in the embodiments shown below can be combined with each other. In addition, the invention is independently established for each feature.

1. 1. Injection Molded Body As shown in FIGS. 1 to 3B, the injection molded body 1 of the embodiment of the present invention is a lower grill of an automobile and is formed by injection molding. The injection-molded article 1 includes a plurality of plate portions 2 extending in parallel and a frame portion 3 for connecting them to each other. The frame portion 3 has a rectangular shape with rounded corners, includes a pair of short side portions 3a and a pair of long side portions 3b, and the short side portions 3a and the long side portions 3b are connected to each other to form the frame portion 3. It is configured. Both ends of each plate portion 2 are connected to the short side portion 3a. Between the pair of short side portions 3a, a plurality of pillar portions 5 for connecting the plurality of plate portions 2 are provided. Both ends of each pillar portion 5 are connected to the long side portion 3b. The plurality of plate portions 2 and the plurality of pillar portions 5 are arranged in a grid pattern. Therefore, the injection-molded article 1 of the present embodiment is configured by providing a lattice composed of a plurality of plate portions 2 and a plurality of pillar portions 5 in the frame portion 3. The frame portion 3 is provided with a groove 4 over the entire circumference.

As shown in FIG. 3B, the plate portion 2 has one side edge 2f and the other side edge 2r which is the opposite side edge. The injection molded body 1 is installed in an automobile with one side edge 2f side facing the front side (design side) of the automobile. In the plate portion 2, the thickness Tf on the one side edge 2f side is thicker than the thickness Tr on the other side edge 2r side. Tr / Tf is, for example, 0.2 to 0.95, preferably 0.5 to 0.9. Specifically, this value is, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, where It may be in the range between any two of the illustrated values. Since the plate portion 2 has such a shape, gas residue is less likely to be generated during the production of the injection molded product 1. Details will be described later.

The width W of the plate portion 2 is preferably larger than the thickness Tf, and the value of Tf / W is, for example, 0.05 to 0.5, preferably 0.1 to 0.3. Specifically, this value is, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, and is within the range between any two of the numerical values exemplified here. It may be.

2. Method for Manufacturing an Injection Molded Body As shown in FIG. 4, the injection molded body 1 is manufactured by injection molding using a pair of split dies 21 and 22. The split dies 21 and 22 are provided with recesses 21a and 22a, and as shown in FIG. 6, when the split dies 21 and 22 are closed, the cavities 11 are formed by the recesses 21a and 22a. The contact surface of the split dies 21 and 22 is the parting line PL. The split mold 21 is provided with a gate 16 that communicates with the recess 21a. The injection-molded article 1 is formed by filling the cavity 11 with a molten resin through a gate 16 and then solidifying the resin.

As shown in FIG. 5, the cavity 11 has the same shape as the injection molded body 1. That is, the cavity 11 includes a plurality of plate cavities 12 extending in parallel and a frame cavity 13 for connecting them to each other. The plate cavity 12 and the frame cavity 13 correspond to the plate 2 and the frame 3, respectively.

The frame cavity 13 has a rectangular shape with rounded corners, includes a pair of short side cavities 13a and a pair of long side cavities 13b, and the short side cavities 13a and the long side cavities 13b are connected to each other. The frame portion cavity 13 is configured. Both ends of each plate cavity 12 are connected to the short side cavity 13a. Between the pair of short side cavities 13a, a plurality of column cavities 15 for connecting the plurality of plate cavities 12 are provided. Both ends of each pillar cavity 15 are connected to the long side cavity 13b. The plurality of plate cavities 12 and the plurality of pillar cavities 15 are arranged in a grid pattern. Therefore, the cavity 11 of the present embodiment is configured by providing a grid composed of a plurality of plate cavities 12 and a plurality of pillar cavities 15 in the frame cavity 13. The frame portion 3 is provided with a groove 14 over the entire circumference. A gate 16 communicates with the short side cavity 13a.

As shown in FIG. 7A, the split mold 21 has a shape corresponding to one side edge 12f and the upper surface 12t of the plate cavity 12, and the split mold 22 has the other side edge 12r and the lower surface of the plate cavity 12. It has a shape corresponding to 12b, and the divided dies 21 and 22 are combined to form the plate cavity 12. The upper surface 12t is parallel to the opening / closing direction S of the split dies 21 and 22. The lower surface 12b is inclined so that the distance from the upper surface 12t increases as the distance from the other side edge 12r increases. As described above, since the plate portion cavity 12 does not have a portion having a reverse taper, the die-cutting of the injection molded body 1 is facilitated.

In FIGS. 7A to 7B, of the parting lines PL between the split dies 21 and 22, the parts above and below the plate cavity 12 are designated as parting lines PL1 and PL2, respectively. The parting line PL1 is provided at a position adjacent to the other side edge 12r, and the parting line PL2 is provided at a position adjacent to the one side edge 12f. The parting lines PL1 and PL2 correspond to a pair of parting lines in the claims.

As shown in FIG. 7A, in the plate portion cavity 12, the thickness Tf on the one side edge 12f side is thicker than the thickness Tr on the other side edge 12r side. Tr / Tf is, for example, 0.2 to 0.95, preferably 0.5 to 0.9. Specifically, this value is, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, where It may be in the range between any two of the illustrated values.

The width W of the plate cavity 12 is preferably larger than the thickness Tf, and the value of Tf / W is, for example, 0.05 to 0.5, preferably 0.1 to 0.3. Specifically, this value is, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, and is within the range between any two of the numerical values exemplified here. It may be.

As shown in FIG. 7B, a molten resin is flowed from both ends of the plate cavity 12 toward the center along the longitudinal direction of the plate cavity 12, thereby causing the plate cavity 12 to flow. Is filled with resin. When there is no resin in the plate cavity 12, gas G exists in the plate cavity 12, and the gas G is discharged from the plate cavity 12 through the parting line PL as the resin is filled. is required.

The resin R1 flows in the direction of arrow X1 from one end side of the plate cavity 12, and the resin R2 flows in the direction of arrow X2 from the other end side of the plate cavity 12. In the present embodiment, the thickness Tf on the one side edge 12f side of the plate cavity 12 is thicker than the thickness Tr on the other side edge 12r side, so that the resins R1 and R2 are made of the one side edge 12f. The flow velocity on the side is larger than the flow velocity on the other side edge 12r side. Therefore, as shown in FIG. 7B, the tip surfaces f1 and f2 of the resins R1 and R2 are in a state of being inclined from the surface perpendicular to the longitudinal direction of the plate cavity 12. Therefore, the tip surfaces f1 and f2 first come into contact with each other at the contact point CP on the one side edge 12f side, and then the contact surfaces of the tip surfaces f1 and f2 come into contact with each other from the one side edge 12f side toward the other side edge 12r side. spread.

When the contact surfaces of the tip surfaces f1 and f2 expand, the gas G in the plate cavity 12 is guided to the other side edge 12r side as shown by an arrow Y. Since the parting line PL1 is provided at a position adjacent to the other side edge 12r, the gas G is discharged to the outside of the plate cavity 12 through the parting line PL1. Therefore, according to the present embodiment, the gas remaining in the plate cavity 12 is suppressed, so that the deterioration of the resin and the formation of gas marks on the injection molded body 1 are suppressed, and the appearance quality is improved. Is improved. Further, since the other side edge 12r is not on the design side, even if deterioration of the resin or traces of gas are formed on the injection molded body 1, it is not noticeable.

Further, when the entire tip surfaces f1 and f2 are in contact at the same time, the traces (welds) of the contact surfaces are easily noticeable, but in the present embodiment, the contact surfaces of the tip surfaces f1 and f2 are from the one side edge 12f side to the other side edge 12r. As it spreads toward the side, the weld is less noticeable.

The angle α of the tip surface f1 with respect to the longitudinal direction of the plate cavity 12 is preferably 45 to 85 degrees, preferably 60 to 80 degrees. Specifically, the angle α is, for example, 45, 50, 55, 60, 65, 70, 75, 80, 85 degrees, and may be within the range between any two of the numerical values exemplified here. ..

As shown in the prior art of FIG. 9, when the thickness of the plate cavity 12 is substantially constant in the width direction of the plate cavity 12, the flow velocity of the resin flowing through the plate cavity 12 is also substantially constant. In this case, if the flow velocities of the resins R1 and R2 at the side edges 12f and 12r of the plate cavity 12 increase for some reason, the gas G is guided to the center of the plate cavity 12 in the width direction and is sandwiched by the resins R1 and R2. And be trapped. In such a state, the resin is likely to be deteriorated or gas marks are likely to be formed on the injection molded product 1, and the appearance quality is deteriorated. According to this embodiment, the occurrence of such a problem is suppressed.

As shown in FIGS. 8A to 8B, the gate 16 for pouring the resin into the plate cavity 12 is provided in the short side cavity 13a of the frame cavity 13 in the same plane of each plate cavity 12. There is. When the gate 16 is provided at such a position, the resin flowing in from the gate 16 is displaced only in the in-plane direction of the plate cavity 12 so as to go around the groove 14, as shown by the arrow X in FIG. 8B. It is injected into the portion cavity 12. When the resin is displaced in the out-of-plane direction of the plate cavity 12, the loss of the injection pressure of the resin tends to be large, but in the present embodiment, the resin is displaced only in the in-plane direction of the plate cavity 12 and the plate portion. Since it is injected into the cavity 12, the loss of injection pressure is suppressed. Therefore, high pressure is applied to the resin also on the contact surfaces of the tip surfaces f1 and f2 of the resins R1 and R2, so that the weld becomes less noticeable.

In the present embodiment, the gate 16 is provided at a position biased toward the front side in the front-rear direction in the short side cavity 13a, but the position where the gate 16 is provided is not particularly limited, and the position is biased toward the rear side in the front-rear direction. Alternatively, it may be provided at the center in the front-rear direction.

The present invention can also be implemented in the following aspects.
In the above embodiment, due to the difference in the thickness of the plate cavity 12, the gas existing in the plate cavity 12 before filling the resin is guided toward the parting line PL1 as the resin is filled. Although the flow velocity distribution of the resin is formed, such a flow velocity distribution of the resin may be realized by another means. For example, a difference can be formed in the flow velocity of the resin by providing a difference in the temperature of the split dies 21 and 22, or by providing a difference in the surface roughness of the inner surface of the plate cavity 12.
-In the above embodiment, the gas is induced toward one of the pair of parting lines PL1 and PL2, but the resin that induces the gas toward both of the pair of parting lines PL1 and PL2. A flow velocity distribution may be formed. For example, by configuring the plate cavity 12 so that the flow velocity of the resin near the center in the width direction of the plate cavity 12 is large and the flow velocity of the resin decreases toward each of the parting lines PL1 and PL2. A smooth flow velocity distribution can be realized.

1: Injection molded body 2: Plate part 2f: One side edge 2r: Other side edge 3: Frame part 3a: Short side part 3b: Long side part 4: Groove 5: Pillar part 11: Cavity 12: Plate part cavity 12t: Top surface 12b: Bottom surface 12f: One side edge 12r: Other side edge 13: Frame cavity 13a: Short side cavity 13b: Long side cavity 14: Groove 15: Pillar cavity 16: Gate 21: Split mold 21a: Recession 22: Divided mold 22a: Recessed CP: Contact point G: Gas PL: Parting line PL1: Parting line PL2: Parting line S: Opening / closing direction f1: Tip surface f2: Tip surface

Claims (8)

A method for manufacturing an injection-molded article, which comprises a plurality of plate portions extending in parallel and a frame portion for connecting them to each other.
The injection molded product is formed by filling cavities in a pair of split dies divided by a parting line with a molten resin and then solidifying the resin.
The cavity includes a plate cavity corresponding to the plate.
When filling the resin, the resin is flowed from both ends of the plate cavity toward the center along the longitudinal direction of the plate cavity.
The plate cavity forms a flow velocity distribution of the resin so that the gas existing in the plate cavity is guided toward the parting line with the filling of the resin before the resin is filled. Consists of
The plate cavity has one side edge and the other side edge which is the opposite side edge.
The parting line has a portion provided at a position adjacent to said one side edge, that having a site that is provided at a position adjacent to the other side edge, the manufacturing method of the injection molded article. The plate cavity is configured such that the flow velocity of the resin increases as the distance from either the portion provided at a position adjacent to the one side edge or the portion provided at a position adjacent to the other side edge increases. The method according to claim 1. The method according to claim 1 or 2, wherein the plate cavity has a thickness on the one side edge side larger than the thickness on the other side edge side in a cross section perpendicular to the longitudinal direction of the plate cavity. The cavity includes a frame cavity corresponding to the frame.
The frame portion cavity includes a pair of short side cavities and a pair of long side cavities, and the short side cavities and the long side cavities are connected to each other to form the frame portion cavities.
The method according to any one of claims 1 to 3, wherein both ends of the plate cavity are connected to the short side cavity. 4. A pillar cavity is provided between the pair of short side cavities to connect the plurality of plate cavities, and both ends of the pillar cavity are connected to the long side cavity. The method described in. The method according to claim 4 or 5, wherein the frame cavity is provided with a groove over the entire circumference. The split mold includes a gate for allowing the resin to flow into the cavity.
The method according to any one of claims 1 to 6, wherein the gate is provided in the same plane as the plate cavity. The cavity includes a frame cavity corresponding to the frame.
The method of claim 7, wherein the gate is connected to the frame cavity.

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