JP7218990B2 - Injection molded product and its molding method - Google Patents

Description

The present invention relates to an injection-molded article and its molding method, and more particularly to an injection-molded article having a weld line and its molding method.

In injection molding, a weld portion (hereinafter also referred to as a weld line) is formed at a location where molten resin flowing in the mold joins. In the weld line, the adhesiveness of the resin is lower than in other areas, and the mechanical strength is lowered. In particular, when a tensile force acts in a direction perpendicular to the weld line formed in a straight line, the stress concentrates on the V-groove formed on the weld line on the surface of the injection molded product. Therefore, there is a problem that deformation, cracking, and the like are likely to occur.

In general, it is important not to form weld lines in areas where stress is concentrated in injection molded products, but it may be difficult to avoid the formation of weld lines depending on the shape of the product.

Therefore, techniques have been developed to improve the mechanical strength of the region where the weld line is formed.

For example, Patent Literature 1 describes a technique of forming a weld line 120 formed in an injection-molded product 110 not in a straight line but in a wavy shape, as shown in FIG. 10 .

FIG. 11 is a schematic diagram of an injection mold 130 for molding the conventional injection-molded product 110 shown in FIG. The mold 130 has a cavity 134 , a gate 132 for injecting resin into the cavity 134 , and a rotary pin 139 having a circular surface continuous with the cavity forming surface of the mold 130 . As indicated by the dashed line in FIG. 11, the rotating pin 139 is normally provided at the confluence position of the molten resin where the straight weld line 131 is generated, and is configured to be rotatable around the central axis by an actuator (not shown). (See hollow arrow in FIG. 11).

In this injection molding apparatus 150, molten resin is injected from the gate 132 into the cavity 134 while the rotation pin 139 is being rotated. As indicated by the black arrow in FIG. 11, the injected resin flows in two along the shape of the cavity 134, merges at the installation position of the rotating pin 139, and receives the rotating force of the rotating pin 139. A curved weld line 120 is formed by changing the flow velocity of the respective molten resins joining together. When the installation area of the rotating pin 156 is almost completely filled with the molten resin, the pressure causes the rotating pin 156 to stop rotating.

In the injection-molded product 110 thus completed, as shown in FIG. 10, the weld line 120 is linear in the extending direction Y of the weld line 120 (that is, when no rotational force is applied by the rotating pin 139). It is formed in a wave shape having unevenness in a direction X orthogonal to the direction in which the weld line 131 extends. The width dimension between the adjacent weld lines ₁₂₀ in the extending direction Y of the corrugated portion is the largest at the width dimension W1 on the side of the base 122a, and gradually decreases toward the side of the tip 122b.

JP-A-2002-86506

In the injection-molded product described in Patent Document 1, by making the weld line wavy, it is possible to increase the bonding area between the resins forming the weld line compared to a straight weld line. As a result, the bonding strength at the weld line can be increased, and the mechanical strength of the weld line formation region can be increased.

However, the resistance to tensile stress in the direction perpendicular to the extending direction of the weld line, which is particularly concerned about a decrease in strength in the weld line formation region, is still not sufficient, and further strength improvement is required. had been

The present invention has been made in view of the above problems, and an object of the present invention is to provide an injection-molded article having a weld line, in which the mechanical strength of the weld line forming region is excellent, and a method for molding the same. do.

In order to achieve the above object, the injection molded article according to the present invention is an injection molded article having a weld line, wherein the weld line is curved to be convex in a direction intersecting the extending direction of the weld line. It has at least one protruding line portion, and the width dimension between the weld lines in the extending direction of the protruding line portion is the largest in a region closer to the tip side than the base portion.

According to this configuration, since the weld line has a projecting line portion that is curved in a direction intersecting the extending direction of the weld line, the resins forming the weld line can be joined together. Strength can be increased. In addition, since the width dimension between the weld lines in the extension direction of the weld lines is the largest in the region on the tip side of the base portion, the projecting line portions extend in the direction perpendicular to the extension direction of the weld lines. When a tensile force acts, this region of maximum width exerts an anchoring effect, improving the resistance to tensile stress. As a result, an injection-molded product having excellent mechanical strength in the weld line forming region can be obtained.

Moreover, the injection-molded article according to the present invention is characterized in that, in the injection-molded article described above, a plurality of the projecting line portions are formed side by side in the extending direction.

According to this configuration, the bonding strength between the resins forming the weld lines and the anchoring effect of the projecting line portions when tensile stress acts can be further enhanced by the plurality of projecting line portions.

Further, the injection-molded article according to the present invention is characterized in that, in the injection-molded article described above, the projecting line portion is formed in a tapered shape in which the width dimension increases from the base portion toward the tip end side. and

According to this configuration, the anchoring effect of the projecting line portion can be enhanced, and the resistance to tensile stress can be further improved.

Moreover, the injection-molded article according to the present invention is characterized in that, in the injection-molded article described above, the weld line forming the projecting line portion is curved.

According to this configuration, it is possible to increase the bonding strength at the weld line by increasing the bonding area between the resins forming the weld line.

Further, a method for molding an injection-molded article according to the present invention is the above-described method for molding an injection-molded article, in which, with the mold for injection molding opened, the inside of the cavity forming part of the mold is In the area where the molten resin injected into the cavity joins installing a partition member capable of partitioning the flow path; injecting molten resin into the cavity of the clamped mold; dividing the partition by the molten resin that joins at the installation position of the partition member and fusing the member.

According to this configuration, in the injection molding, when the mold for injection molding is opened, the area where the molten resin joins, that is, the area where the weld line is formed, has a curved shape that is substantially the same as the projecting line portion. By setting a partition member having a wall portion, clamping the molds in this state, and injecting the molten resin, a merging surface of the molten resin is formed along the shape of the partition member. In addition, since the partition member is made of a thermoplastic resin having a melting point that is the same as or close to that of the injected molten resin, the molten resin melts and joins together when the molten resin contacts. As a result, it is possible to form a resin joint surface along the shape of the partition member, that is, a weld line having a projecting line portion.

According to the injection molded article and the molding method thereof according to the present invention, the mechanical strength of the weld line formation region in the injection molded article can be improved.

1 is a perspective view of a portion of an injection-molded product according to a first embodiment of the present invention, where a weld line is formed; FIG. Schematic of an injection mold. The perspective view of a partition member. FIG. 2 is a cross-sectional view of a main part of an injection mold; The figure explaining the manufacturing process of an injection molded product. The figure explaining the manufacturing process of an injection molded product. FIG. 10 is an enlarged cross-sectional view of a main part showing a modification of the injection mold; The perspective view of the part in which the weld line of the injection molded product of 2nd Embodiment was formed. FIG. 11 is a perspective view showing yet another embodiment of an injection molded article; FIG. 2 is a perspective view of a portion of a conventional injection molded product where a weld line is formed; Schematic diagram of a conventional injection mold.

(First embodiment)
An injection-molded product 10 according to a first embodiment of the present invention will be described below with reference to FIGS. 1 to 6. FIG. The injection molded product 10 is molded by injection molding of resin, and has a weld line 20 formed at a portion where molten resin joins during injection molding.

FIG. 1 is a perspective view of a portion of an injection molded product 10 where a weld line 20 is formed. The weld line 20 has a protruding line portion 22 that is curved in a direction intersecting the extending direction Y of the weld line 20 (the direction from one end 20a to the other end 20b of the weld line 20). The projecting line portion 22 in the illustrated example is formed so as to be curved in a substantially trapezoidal shape in a direction X perpendicular to the extending direction Y (hereinafter also simply referred to as the orthogonal direction X). Also, in this weld line 20, a plurality of projecting line portions 22-1, 22-2, 22-3, 22-4, and 22-5 are formed side by side in the extending direction Y. As shown in FIG. In this embodiment, the extending direction Y of the weld line 20 and the orthogonal direction X are orthogonal to the thickness direction of the plate-shaped injection molded product 10 .

One protruding line portion 22 extends in a tapered shape from a base portion 22a (the side open in the orthogonal direction X) toward the protruding tip 22b side such that the width dimension W in the extending direction Y increases. It has a first side portion 23a, a second side portion 23b, and a top side portion 23c connecting the tips of the first and second side line portions 23a and 23b. The top side portion 23c extends substantially parallel to the extension direction Y. As shown in FIG. The projecting line portion 22 has the largest width dimension W at the top side portion 23c.

In the weld line 20 of the present embodiment, five protruding line portions 22-1 to 22-5 are formed side by side so that the convex directions alternate. The sides match. Specifically, each of the first and second side portions 23a and 23b of the protruding line portion 22-2 that is convex on one side (the right side in FIG. 1) of the orthogonal direction X is adjacent to and orthogonal to this. The first side edge portion 23a of the projecting line portion 22-1 and the second side edge portion 23b of the projecting line portion 22-3, which are convex in the other side of the direction X (the left side in FIG. 1), and the side edge share the department. Note that the number of projecting line portions 22 is not limited to five, and may be one or more.

In the injection-molded product 10, the weld line 20 has the projecting line portion 22, so that the joint area between the resins forming the weld line 20 can be increased and the joint strength can be increased.

In addition, in the projecting line portion 22, the width dimension W between the weld lines in the extending direction Y is the largest in the region closer to the tip 22b than the base portion 22a. When a tensile force acts on X, the area on the side of the tip 22b with a larger width dimension W bites into the back of the base part 22a with a smaller width dimension W than this, and is in a state of thrusting, exhibiting a resistance to the tensile force ( so-called anchor effect). As a result, the resistance to tensile stress in the direction orthogonal to the extending direction of the weld line can be improved, and the mechanical strength of the weld line formation region can be increased. In addition, by having a plurality of such projecting line portions 22, the anchor effect can be further enhanced and the mechanical strength can be improved.

In addition, when a tensile force in the orthogonal direction X acts on each protruding line portion 22, the first side portion 23a and the second side portion 23b extending in a tapered shape exert a yield strength, so that a high anchoring force is obtained. effect can be obtained.

Next, a method for molding the injection-molded product 10 described above will be described. FIG. 2 is a schematic diagram of an injection mold 30 for molding the injection molded product 10. As shown in FIG.

The mold 30 has a fixed side mold and a movable side mold that can approach and separate from the fixed side mold. In FIG. 2, the cross section of the stationary side mold is shown, and the description of the movable side mold is omitted. The mold 30 has a gate 32 through which molten resin is injected and a cavity 34 communicating with the gate 32 . 2 indicates the direction in which the molten resin injected from the gate 32 flows.

A partition member 50 made of a thermoplastic resin is installed in the cavity 34 of the mold 30 during injection molding. The partition member 50 is attached to the cavity forming portion of the mold 30 in a state where the mold 30 is opened.

FIG. 3 is a perspective view of the partition member 50. FIG. The partition member 50 is formed in a wall shape capable of partitioning the flow path in the cavity 34 , and has a curved wall portion that is substantially the same as the projecting line portion 22 of the weld line 20 .

The partition member 50 of the present embodiment is formed in a wall shape having substantially the same shape as the weld line 20, and has a plurality of protruding walls corresponding to the plurality of protruding line portions 22-1 to 22-5 of the weld line 20. It has parts 52-1 to 52-5. Specifically, one projecting wall portion 52 includes a first side wall portion 53a and a second side wall portion 53a corresponding to the first side portion 23a, the second side portion 23b, and the top side portion 23c, respectively. It has a portion 53b and a top wall portion 53c.

Next, a method of molding the injection-molded product 10 using the mold 30 and the partition member 50 described above will be described.

First, with the mold 30 opened, the partition member 50 is installed in the cavity forming portion 36 of the mold 30 (partition member installation step). The partition member 50 is installed in a region where a weld line is formed (that is, a region where the injected molten resin joins). In this embodiment, as shown in FIG. 4 , both ends 50 a and 50 b of the partition member 50 are fitted into grooves 38 a and 38 b formed in the cavity forming portion 36 of the mold 30 .

After installing the partition member 50, the mold is clamped and molten resin is injected into the cavity 34 from the gate 32 (molten resin injection step). The injected molten resin branches along the shape of the cavity 34 of the mold 30 and flows to the area where the partition member 50 is installed, as indicated by the arrows in FIG.

As shown in FIG. 5 , the split molten resin 18 flows so as to join at the installation position of the partition member 50 , and the periphery of the partition member 50 is filled with this molten resin 18 . The partition member 50 is melted by the heat of the molten resin 18 in contact with its peripheral surface, and the wall portion disappears. A weld line 20 is formed along the shape of the member 50 (weld line forming step).

Next, the molded product is cooled in the mold 30, and after the molded product is hardened, the mold 30 is opened and the injection molded product 10 is taken out. The burrs generated by the grooves 38a and 38b are removed after taking out from the mold 30. As shown in FIG.

As shown in FIG. 6, the extension direction Y of the weld line 20 of the injection-molded product 10 of the present embodiment merges when injection molding is performed without installing the partition member 50 in the mold 30. It substantially coincides with the direction in which the linear weld line 29 formed by the melted resin extends.

As described above, in the molding method of the present embodiment, the partition member 50 is installed in the region where the molten resin joins with the mold 30 opened, and the mold 30 is clamped in this state to allow the molten resin to flow. By injecting, the weld line 20 along the shape of the partition member 50 can be easily formed. In addition, the partition member 50 may be configured to be installed in the movable side mold instead of the fixed side mold.

Next, a modified example of the injection mold 30 will be described. FIG. 7 is an enlarged cross-sectional view of a main part showing a modification of the injection mold 30. As shown in FIG.

In this mold 30, the partition member 50 is fixed in the cavity 34 by a positioning mechanism provided in the mold 30 instead of the grooves 38a and 38b. This positioning mechanism has a pin holding member 42 inserted into a hole 39 formed in the cavity forming surface of the mold 30 and a pin member 40 attached to the tip of the pin holding member 42 . The pin holding member 42 is moved within the hole 39 by a moving mechanism (not shown), whereby the pin member 40 is projected into the cavity 34 as shown in FIG. As shown in (b), it is movable to a retracted position to retract outside the cavity 34 . The opening of the hole 39 on the cavity 34 side is closed with a cover member 46 having a through hole through which the pin member 40 can pass. A plurality of positioning mechanisms having such pin members 40 can be provided on the mold 30 as required.

In the mold 30 of the modified example, after the mold 30 is opened, the partition member 50 is fixed by the pin member 40 at the projecting position. FIG. 7A shows a state in which the pin member 40 is inserted into a hole formed in one end 50b of the partition member 50 to fix the position of the end 50b. The other end 50a of the partition member 50 is also fixed by the pin member 40 in the same manner.

After that, the mold 30 is clamped and the molten resin 18 is injected into the cavity 34 . After the molten resin 18 has flowed to the installation position of the partition member 50 , the pin member 40 is moved to the retracted position (see FIG. 6B), and the partition member 50 is melted by the molten resin 18 . As a result, as shown in FIG. 6(b), a weld line 20 along the shape of the partition member 50 is formed in the injection molded product 10. Next, as shown in FIG.

Although FIG. 7A shows an example in which the pin members 40 are inserted into holes formed in the partition member 50 and fixed, the peripheral surface of the partition member 50 is not limited to this. The position of the partition member 50 may be fixed by supporting it.

As yet another example of molding the injection-molded product 10 having the projecting line portion 22, the partition member 50 is made of a metal material that does not melt with the molten resin 18, and when the molten resin 18 fills the periphery of the partition member 50, A configuration can be employed in which the partition member 50 is retracted to the outside of the cavity 34 together.

(Second embodiment)
Next, a second embodiment of the injection molded product 10 will be described with reference to FIG. In addition, in FIG. 8, the same reference numerals are assigned to the same elements as in the above-described first embodiment, and detailed description thereof will be omitted.

In this injection molded product 10, a weld line 20 is formed in a curved shape. Specifically, the weld line 20 has a plurality of protruding line portions 22-1 to 22-5, and each protruding line portion 22 has a curved first side portion 23a and a curved second side portion 23b. and a curved top side portion 23c connecting these tips.

In each projecting line portion 22, the width dimension W between the weld lines 20 in the extending direction Y is formed so as to be the largest in the area closer to the tip 22b than the base portion 22a. In _FIG . ₈ , with respect to the width dimension W1 of the base portion 22a, the region closer to the tip 22b has the maximum width dimension W2.

In injection molding, when forming such a curved weld line 20, a wall portion having substantially the same shape as the weld line 20, that is, a curved projecting line portion 22-1 is formed in the mold 30. A partition member having a curved protruding wall portion having substantially the same shape as 22-5 is installed, and then the mold is clamped to inject molten resin 18, and the partition member made of thermoplastic resin is formed by the molten resin 18. It can be easily formed by melting. Further, by forming the wall portion of the partition member into a curved shape, the injected molten resin 18 can be easily filled around the partition member without gaps.

In the injection-molded product 10 of the second embodiment, by forming the projecting line portion 22 in a curved shape, the weld line 20 is formed by increasing the joint area compared to when the projecting line portion 22 is configured by a straight line. can increase the bonding strength in In addition, when a tensile force acts in the orthogonal direction X in the region where the weld line ₂₀ is formed, the region of the maximum width dimension W2 on the tip 22b side exhibits an anchor effect, resulting in high resistance to tensile stress. Thereby, the mechanical strength of the weld line 20 can be improved.

Next, still another embodiment of the injection molded product 10 will be described with reference to FIGS. 9(a) and 9(b). In addition, in FIGS. 9A and 9B, the same reference numerals are assigned to the same elements as in the above-described first embodiment, and detailed description thereof will be omitted.

In the embodiment shown in FIG. 9( a ), a weld line 20 having a plurality of projecting line portions 22 is formed in the cylindrical region of the injection molded product 10 . Each projecting line portion 22-1 to 22-5 has a width dimension _W.sub.2 on the side of the tip 22b larger than the width dimension _W.sub.1 of the base portion 22a. Thus, the region where the weld line 20 is formed in the injection molded product 10 may be a curved plate-like portion. At least one projecting line portion 22 may be formed.

In another embodiment shown in FIG. 9(b), a weld line 20 is formed in a cylindrical region of an injection molded product 10, and the weld line 20 is composed of a plurality of projecting line portions 22 curved in a substantially heart shape. -1 to 22-5. Each projecting line portion 22-1 to 22-5 has a width dimension _W.sub.2 on the side of the tip 22b larger than the width dimension _W.sub.1 of the base portion 22a. At least one projecting line portion 22 may be formed.

In the injection-molded product 10 shown in FIGS. 9(a) and 9(b), a tensile force was applied in a direction perpendicular to the extending direction Y of the weld line 20 (that is, the circumferential direction of the cylindrical injection-molded product 10). At this time, the region on the tip side of the protruding line portion 22 exerts an anchor effect, so that the resistance to tensile stress can be improved.

9(a) and 9(b), the molding method of the injection-molded product 10 shown in each of FIGS. In other words, a partition member having a wall portion having substantially the same shape as the shape of the weld line 20 of each injection molded product 10 is installed in the mold, and the mold is clamped in this state. The partition member can be molded by injecting a molten resin using a squeegee and melting the partition member with the filled molten resin. When molding the injection-molded product 10 shown in FIG. 9B, it is possible to easily fill the molten resin along the wall portion of the partition member curved in a heart shape, as indicated by the dashed arrow.

The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the scope of the invention.

For example, the injection-molded article 10 may be a fiber-reinforced resin injection-molded article containing reinforcing fibers therein. In such a case, reinforcing fibers made of short fibers such as glass fibers and carbon fibers are placed in the cavity of the mold for injection molding, and the gaps between the reinforcing fibers are sewn in the area where the weld line is formed in the cavity. A partition member is installed to form the weld line. After that, the mold is clamped, molten resin is injected into the cavity, and the partition member is melted by the molten resin.

REFERENCE SIGNS LIST 10 injection molded product 20 weld line 22 projecting line portion 30 injection mold 50 partition member 52 projecting wall portion

Claims (5)

For injection molded products with weld lines,
The weld line has at least one projecting line portion that is convexly curved in a direction orthogonal to the extending direction of the weld line,
An injection-molded article, wherein the width dimension between the weld lines in the extending direction of the projecting line portion is the largest in a region closer to the tip than the base portion. 2. The injection-molded product according to claim 1, wherein a plurality of said projecting line portions are formed side by side in said extending direction. 3. The injection-molded product according to claim 1, wherein the projecting line portion is tapered such that the width increases from the base toward the tip. The injection molded article according to any one of claims 1 to 3, wherein the weld line forming the projecting line portion is curved. A method for molding an injection-molded article for forming the injection-molded article according to any one of claims 1 to 4,
When the mold for injection molding is opened, a thermoplastic resin having a melting point equal to or close to that of the resin is added to the cavity forming part of the mold where the molten resin injected into the cavity joins. A step of installing a partition member formed and having a curved wall portion that is substantially the same as the projecting line portion and capable of partitioning a flow path in the cavity;
a step of injecting a molten resin into the cavity of the clamped mold;
A method of molding an injection-molded product, comprising: melting the partition member with the molten resin that merges at the installation position of the partition member.

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