JP4817180B2 - Injection molding method for synthetic resin molded products - Google Patents

Description

  The present invention relates to an injection molding method for a synthetic resin molded product, and more particularly to a double injection molding method.

  For example, Patent Document 1 describes an invention relating to a cork stopper with a knob in which a knob member made of a synthetic resin and a cork stopper are fixedly assembled using an adhesive. Here, since the knob member is a considerably thick product as a whole, an injection molding method for suppressing the occurrence of sink marks on the surface or improving the gloss of the outer surface in applications where appearance is required. It is necessary to adopt.

Further, regarding a method of injection molding of a molded product having a thick portion, Patent Document 2 discloses that a molded product having a thin wall portion and a thick wall portion is injected with molten resin as primary injection molding and secondary injection molding. A so-called double injection molding method, which is carried out in batches, is described, and the dimensional accuracy and appearance of the thick-walled portion are improved.
JP 2003-226341 A JP 2003-25377 A

  The present invention eliminates the need for post-processing such as drilling, cutting of the sprue runner, or gate mark processing after the primary and secondary injection molding of the double injection molding method. Thus, an object of the present invention is to provide an injection-molded product having a high-quality appearance at a low cost.

Of the present invention for solving the above technical problem, the method of the first invention is:
In the injection molding method for synthetic resin molded products,
A pin gate is disposed on one of the cavity mold and the core mold that form the cavity, and a core pin that passes through the cavity coaxially with the pin gate is disposed on the other. First injection molding is performed using a mold in which an annular channel is formed at the tip of the pin gate by entering a predetermined distance inside,
In this primary injection molding, injection molding of a primary molded product in which a molten resin is injected and filled into a cavity through an annular channel and a through hole penetrating from an inner surface to an outer surface is formed by a core pin,
Next, using the primary molded product as an insert material, the secondary injection molding is performed by flowing molten resin in a covering state from the inner surface opening end of the through hole through the through hole to cover at least the outer surface of the primary molded product. ,
It is in.

The synthetic resin filled in the mold by the mold used in the primary injection molding of the first invention is a primary molded product part formed in the cavity and a sprue runner part formed by a sprue runner. Are connected by an annular portion formed by an annular channel.

Here, by appropriately setting the difference in the diameter between the pin gate tip and the core pin tip, and the approach distance of the core pin tip into the pin gate, a notch-like shape is formed at the connection between the annular portion and the primary molded product. By forming the portion having, it is possible to reliably achieve the cutting at the gate when the molded product is released, and the core pin penetrating the cavity from the inner surface to the outer surface without post-processing in the primary molded product A through-hole penetrating through can be formed.
In some cases, a slightly jagged portion may be formed at the periphery of the end of the through hole when cutting at the gate at the time of mold release, but the resin in this portion melts during the second injection molding, so even if it is transparent Even in the case of a molded product having the above, the appearance is not impaired.

  Then, this primary molded product is used as an insert material, and the opening end of the inner surface of the through hole is brought into close contact with the pin gate of the mold used for the secondary injection molding, and the primary end is passed through the through hole from the opening end. Since the secondary injection molding is performed by flowing the molten resin in a coated state on at least the outer surface of the molded product, the gate mark does not remain on the outer surface where appearance is required. No post-processing for surface finishing is required, and the product cost can be reduced.

  Even if the primary molded product is molded to be relatively thick and sink marks occur on the outer surface, in secondary injection molding using this primary molded product as an insert material, the molten resin is a sink mark of this primary molded product. Therefore, the surface of the secondary molded product can be made flat without sink.

  In addition, since the molding part in the secondary injection molding (hereinafter referred to as the secondary molding part) can be made relatively thin and the thickness can be made uniform as a whole, the resin is sufficient and uniform throughout the entire area. Pressure can be reduced, shrinkage of the molded product in the cooling and solidification process of secondary injection molding is small and uniform, cooling and solidification proceeds in close contact with the mold surface, and appearance is required It is possible to obtain a molded article having a good surface gloss of the portion to be formed.

In the first aspect of the invention , the outer side surface refers to a surface portion that is visible or easily visible from the outside in a state in which the product is used, that is, a surface portion that particularly requires appearance, and the inner side surface is not visible from the outside. Or a surface portion that is difficult to see, that is, a surface portion that is not particularly required for appearance.

The method of the second invention is that, in the method of the first invention , the approach distance of the tip portion of the core pin into the pin gate is 0.1 mm or more.

In the design of the mold used for the injection molding of the present invention, the basic shape of the annular channel formed at the tip of the pin gate is a channel width determined by the difference in diameter between the pin gate and the tip of the core pin. a is channel length determined by the penetration distance into the interior of the pin gate of the tip portion of the core pin.

The second invention shows the design criteria relating to the flow path length. If the flow path length is too short, an annular flow path cannot be formed sufficiently, and the uniform fluidity of the molten resin is impaired. In addition, since the gate cutting property is also impaired, it is preferable that the approach distance of the tip of the core pin into the pin gate is 0.1 mm or more.

  Here, if the flow path length is too long, the flow path resistance increases and the injection speed decreases, but the upper limit of the flow path length can be appropriately set in consideration of the melt viscosity of the synthetic resin to be used. it can.

The method of the third invention is that, in the first or second invention , the difference in diameter between the pin gate and the core pin is in the range of 0.1 to 1.0 mm.

The method of the third invention shows the design criteria related to the channel width of the annular channel described above. If the channel width is too narrow, the channel resistance becomes large, and if it is too wide, the gate cutting property is obtained. Is damaged.
Therefore, by making the difference in diameter between the pin gate and the core pin in the range of 0.1 to 1.0 mm, more preferably in the range of 0.2 to 0.6 mm, that is, the flow path width is 0.05 to 0.5 mm. By making the range, more preferably in the range of 0.1 to 0.3 mm, it is possible to ensure a good cutting performance of the gate at the time of mold release in a range in which an increase in flow resistance due to the annular channel is suppressed. .

According to a fourth aspect of the present invention , in the first, second, or third aspect of the invention , a notch-like shape is formed at a connecting portion between the primary molded product portion and the annular portion formed in the annular flow path.

According to the fourth invention , the cutting performance at the gate at the time of mold release can be improved.

According to a fifth aspect of the present invention , in the fourth aspect of the invention , the tip end portion of the pin gate is formed in a reduced diameter shape toward the open end.

5th invention is one method of forming a notch shape in the connection part of a primary molded product part and an annular part, and is a notch shape in the shape of a circumference connected to a primary molded product of the outer peripheral surface of an annular part. The shape can be formed.

The method of the sixth invention is that, in the first , second , third , fourth or fifth invention , the core pin has a reduced diameter from the base end portion toward the tip end portion.

According to the sixth aspect of the invention, it is possible to easily perform die cutting related to the core pin of the primary molded product, and it is possible to more smoothly achieve injection filling of the molten resin via the through hole in the secondary injection molding.

According to a seventh aspect of the present invention , in the first, second, third , fourth , fifth or sixth aspect , the primary molded product is a cylindrical product with a top, and penetrates from the inner side surface of the top wall to the outer side surface. Forming a through hole.

The seventh invention is a specific example of the shape of the primary molded product, including the secondary injection molding, and has a high quality including a thick-walled, large-thickness fluctuation, and further made of a transparent resin. A top-cylindrical molded product having an appearance and excellent design can be provided.

The present invention is a method having the above-described configuration, and has the following effects.
In the first invention , by injecting the molten resin through the annular channel formed at the tip of the pin gate, cutting at the gate can be reliably achieved at the time of mold release, The core pin penetrating the cavity can form a through hole penetrating from the inner surface to the outer surface without post-processing in the primary molded product.

  Also, the secondary injection molding is performed by using the primary molded product as an insert material and flowing molten resin in a covering state from the opening end of the inner side surface of the through hole through the through hole to cover at least the outer side surface of the primary molded product. Therefore, the gate trace does not remain on the outer surface where the appearance is required, and the post-processing for removing the gate trace and finishing the surface becomes unnecessary, and the product cost can be reduced.

In the second aspect of the invention , by making the approach distance of the tip portion of the core pin into the pin gate within a range of 0.1 mm or more, uniform fluidity and good cutting performance of the gate at the time of mold release are secured. can do.

In the third invention , the flow resistance is increased by the annular channel by setting the channel width in the range of 0.05 to 0.5 mm, more preferably in the range of 0.1 to 0.3 mm. In the suppressed range, it is possible to ensure good cutting performance of the gate at the time of mold release.

In the fourth aspect of the invention , it is possible to improve the cutting performance at the gate by forming a notch-shaped shape at the connecting portion between the primary molded product and the annular portion formed in the annular channel. it can.

In the fifth invention , it is one method of forming a notch-shaped shape in the connecting portion between the primary molded product and the annular portion, and the circumferential portion is connected to the primary molded product on the outer peripheral surface of the annular portion. A notch shape can be formed.

In the sixth invention , it is possible to facilitate the die-cutting of the core pin of the primary molded product, and more smoothly achieve the injection filling of the molten resin via the through hole in the secondary injection molding. be able to.

In the seventh aspect of the present invention , there is a top cylindrical molded product having a high-quality appearance and excellent design, including a thick-walled, large-thickness variation, and further made of a transparent resin. Can be provided.

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a molded product formed by an embodiment of the molding method of the present invention, which will be described later, FIG. 1 is a perspective view, and FIG. 2 is a longitudinal sectional view taken along the line AA in FIG. is there.
This molded product 1 has a cylindrical shape with a transparent resin, and has an outer diameter of 67 mm, a height of 35 mm, and a thickness of the side wall 2 of 4 mm. Moreover, as shown in FIG. 1 and FIG. 2 (a), the top wall 3 is gently curved to have a recess 4, and its thickness is in the range of 4 to 6 mm.

As can be seen from FIG. 2 (a), this molded product 1 is a double injection molded product, and the outer surface of the top wall 13 and the side wall 12 of the top cylindrical shaped molded product 11 is formed as a secondary molded part 15f. 6 is the state of exterior packaging.
Further, a through hole 16 is formed at the center position of the top wall 13 of the primary molded product 11 and is filled with the secondary molded portion 6. In addition, the primary molded product 11 has a recess 14 and the thickness of the top wall 13 varies in the range of 2 to 4 mm, while the secondary molded portion 6 has a uniform thickness of approximately 2 mm as a whole. It is.

The molded product 1 is a thick molded product having a maximum thickness of 6 mm at the top wall 3 and the thickness of the top wall 3 varies from 4 to 6 mm. There is no unevenness, and even if light is reflected on the surface of the molded product 1, the unevenness is so smooth that it cannot be detected, and the gentle curvature of the top wall 3 can be formed without any distortion. This is a molded product having a high-quality appearance without a gate mark on the wall 3.
Further, although it is made of a transparent resin, the through-hole 16 of the primary molded product 11 or the ring-shaped gate trace is disappeared in appearance by the secondary injection molding.

  Next, FIGS. 3 to 7 are for explaining an embodiment of the molding method of the present invention. 3 to 6 illustrate the primary injection molding process for molding the primary molded article 11 in FIG. 2A, and FIG. 3 is a longitudinal section of an example of a mold used for this injection molding. It is a schematic explanatory drawing shown.

This mold 21 basically forms a cavity 24 into which molten resin is injected and filled by a cavity mold 22 and a core mold 23. A pin gate 25 is disposed on the core mold 23 side, and a cavity is formed. A core pin 26 penetrating the cavity 24 coaxially with the pin gate 25 is disposed on the mold 22 side.
The core pin 26 has the same diameter at the tip portion of 0.2 mm, but the diameter is reduced from the base end portion to the tip end portion except for the tip portion.

4 is an enlarged longitudinal sectional view showing the vicinity of the gate of the mold 21 of FIG. 3, and FIG. 5 is a plan sectional view taken along the line BB in FIG. The structure near the gate will be described.
The distal end of the pin gate 25 has a shape that decreases toward the opening end. The diameter d1 of the opening end is 1.3 mm, the distal end diameter d2 of the core pin 26 is 0.9 mm, and the distal end of the core pin 26 is inside the pin gate 25. Is set to enter 0.2 mm. Thereby, an annular channel 27 having a flow width W at the opening end of 0.2 mm and a flow length L of 0.2 mm is formed at the tip of the pin gate 25.

  In the primary injection molding using the mold 21, the molten resin is injected and filled into the cavity 24 through the annular channel 27. Here, FIG. 6 is an explanatory view showing the synthetic resin portion taken out from the mold 21 shown in FIG. 4. As shown in FIG. 6, the primary molded product 11 portion and the sprue runner in the mold 21 are shown. The part 19 is in a state of being connected by an annular part 17 formed in the annular channel 27.

  And the front-end | tip of the pin gate 25 is made into a reduced diameter shape, the notch part 18 is formed in the periphery at the connection part of the primary molded article 11 part and the annular part 17, and the thickness in this notch part 18 part is about 0.2 mm. By forming a thin wall, the gate can be smoothly cut from the notch portion 18 at the time of mold release, and the through hole 16 penetrating from the inner side surface 15b to the outer side surface 15f is formed without performing post-processing. The molded product 11 can be molded.

Next, FIG. 7 is a schematic explanatory view showing a state in which the primary molded article 11 that has been subjected to primary injection molding is set as an insert material in the cavity 34 of the mold 31 for secondary injection molding.
In this second injection molding, the molten resin flowing from the pin gate 35 is injected from the opening end of the molded product inner side surface 15b of the through hole 16 through the through hole 16 into the cavity 34 in a covering state on the outer surface 15 of the primary molded product 11. Filled.

Here, even if the primary molded article 11 has irregularities due to sink marks due to molding shrinkage, the irregularities are complemented by the secondary injection molding described above, and there is no irregularities due to sink marks as a whole. It is possible to provide a molded product having a high-quality appearance in which the gentle curvature of the top wall 3 is formed without any distortion.
In addition, ring-shaped gate marks remain on the periphery of the through-holes 16 of the primary molded product 11, but the resin in the vicinity including the through-holes 16 melts during the second injection molding, and these marks disappear. Even if it is a transparent molded product, the trace can be made invisible.

As mentioned above, although the embodiment and the effect were demonstrated about the shaping | molding method of this invention along the Example, the method of this invention is not limited to the Example demonstrated above. For example, the shape of the molded product is not limited to a crested cylindrical body, and can be generally applied to a molded product having a thick portion, or a molded product in which the appearance is particularly important.
In practice, the mold used for injection molding is configured by combining various members such as an operating mechanism, a die-cutting mechanism, a cooling mechanism, a sprue bushing, and a nesting, but it relates to the mold in the description of the above embodiment. The drawings are shown as schematic illustrations and show a very basic structure.

  As described above, the injection molding method of the present invention can provide a molded product having a good appearance including a thick-walled molded product at low cost without using post-processing, and particularly requires a high-quality appearance. It is expected that it can be widely deployed in various applications.

It is a perspective view which shows an example of the molded article by the shaping | molding method of this invention. 1A is a longitudinal sectional view taken along line AA in FIG. 1, and FIG. 1B is a plan view. It is a schematic explanatory drawing which shows longitudinally an example of the metal mold | die used for the shaping | molding method of this invention. It is a longitudinal cross-sectional view which expands and shows the gate vicinity of the metal mold | die of FIG. It is a plane sectional view shown along the BB line in FIG. It is explanatory drawing which takes out and shows the synthetic resin part with which the inside of the metal mold | die of FIG. 4 is filled. It is a schematic explanatory drawing which cuts and shows the state which set the primary molded product in the cavity of the metal mold | die for secondary injection molding.

DESCRIPTION OF SYMBOLS 1; Molded product 2; Side wall 3; Top wall 4; Recessed part 6; Secondary molded part 11; Primary molded part 12; Side wall 13; Top wall 14; Recessed part 15f: Outer side surface 15b; Ring part 18; Notch part 19; Sprue runner part 21; (Primary injection molding) mold 22; Cavity mold 23; Core mold 24; Cavity 25; Pin gate 26; Core pin 27; Secondary injection molding) Mold 32; Cavity mold 33; Core mold 34; Cavity 35; Pin gate d1, d2; Diameter W; Flow width L;

Claims (4)

A pin gate (25) is disposed on one of the cavity mold (22) and the core mold (23) forming the cavity (24), and the cavity (24) is coaxially formed with the pin gate (25) on the other. Arrange the core pin (26) to penetrate,
In the clamped state, the tip of the core pin (26) is allowed to enter a predetermined distance into the pin gate (25) to form an annular channel (27) at the tip of the pin gate (25),
The approach distance to the inside of the pin gate (25) at the tip of the core pin (26) is 0.1 mm or more,
A die (21) in which the difference in diameter between the pin gate (25) and the core pin (26) is in a range of 0.1 to 1.0 mm, and the core pin (26) is reduced in diameter from the base end portion toward the tip end portion. The first injection molding is performed using
In the primary injection molding, molten resin is injected and filled into the cavity (24) via the annular channel (27), and the core pin (26) is used to change the inner surface (15b) to the outer surface (15f). The primary molded product (11) formed with a through hole (16) penetrating into the injection molding,
Next, using the primary molded product (11) as an insert material, from the opening end of the inner surface (15b) of the through hole (16) through the through hole (16), at least the outer surface of the primary molded product (11) An injection molding method, wherein the second injection molding is performed by flowing a molten resin in a coating form (15f). Injection molding method of claim 1 wherein forming a notch shape to the connecting portion of the primary molded article (11) annular section formed in part an annular channel (27) (17). 3. The injection molding method according to claim 2, wherein the pin gate (25) is formed to have a reduced diameter with the tip end portion facing the open end. The primary molded product (1) is a cylindrical product with a top, and a through hole (16) penetrating from the inner side surface (15b) at the center of the top wall (13) to the outer side surface (15f) is formed . 4. The injection molding method according to 2 or 3 .

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