JP5348574B2 - Synthetic resin injection molded product and injection molding method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molded article which has a thin-wall center part where a center gate is arranged and a thick-wall part in the peripheral edge of the center part, and which has high grade appearance and excellent designability by suppressing the occurrence of a shrink mark in the article. <P>SOLUTION: There is provided the injection molded article made of a synthetic resin in which the center part is formed thin-walled and the peripheral edge of the center part is formed thick-walled. The injection molded article is molded by: injection-filling molten resin into a cavity through a plurality of pin gates arranged within a predetermined range in a part of a mold, the part corresponding to the center part of the molded article, thereby molding a primary molded article; and performing a secondary injection molding in which molten resin flows film-like at least on the front surface of the primary molded article. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

The present invention relates to a synthetic resin injection-molded article having a central portion formed thin and a thick portion at the periphery thereof, and an injection molding method thereof.

  Regarding a method for injection molding of a molded product having a thick part, Patent Document 1 discloses a so-called double molding method in which injection of molten resin is carried out in two steps for a molded product having a thin part and a thick part. Is described, and the dimensional accuracy and appearance of the molded product are improved by suppressing the occurrence of sink marks in the thick-walled portion.

  FIG. 8 is a perspective view of an injection-molded product 101 used as a member of a cosmetic container such as cream, FIG. 9 (a) is a longitudinal sectional view, and FIG. 8 (b) is a plan view. 107 is formed with a concave portion 108 which is a hemispherical housing portion coaxially with the rotational symmetry axis AX of the block body 107.

On the other hand, this molded product has a wall thickness in the vicinity of the corner portion 111 of nearly 20 mm, and an ordinary injection molding causes sink marks, resulting in a poor appearance. As shown in FIG.
In the double molding, firstly, a primary molded product 115 is molded by primary injection molding, and this primary molded product 115 is used as an insert material, and a secondary injection molding is performed in which a molten resin is flowed in a covering state on the surface, A covering portion 117 is formed.

Here, generally, the primary molded product 115 is injection-filled radially into the cavity via a center gate (pin gate) disposed at a position corresponding to the center of the bottom surface of the molded product 101 of the injection mold. Sinking occurs due to cooling shrinkage after molding, but by applying secondary injection molding to the surface with a thickness of about 2 mm, sinking is repaired and the appearance without unevenness due to sinking is good. A molded product can be obtained.

JP 2003-25377 A

  However, as in the case of the primary molded product 115 shown in FIG. 9B, when the thickness of the center of the bottom surface where the center gate mark 115t is located is thin, if the diameter of the center gate is too large, Problems such as the occurrence of cracks in the vicinity of the gate mark 115t occur, and according to conventional experience, the diameter of the center gate needs to be about 80% or less of the wall thickness at the position corresponding to the center gate.

As a result, the injection speed cannot be increased sufficiently despite the thick wall portion 103 at the peripheral portion, and the resin pressure at the thick wall portion 103 is insufficient. A prominent sink mark is generated at a portion indicated by an arrow in FIG. 9B in the vicinity, and there arises a problem that the appearance defect cannot be complemented by secondary injection molding.
Especially in applications such as packaging for cosmetics where packaging has a significant effect on its productability, designability may be given priority over moldability, and the product value may be impaired by slight appearance defects. As described above, there is a demand for improvement related to an injection molding method for a molded product which is a thick molded product as a whole but has a thin portion at the center.

An object of the present invention is to suppress the occurrence of sink marks in a molded product having a thin central portion where the center gate is disposed and having a thick portion at the periphery thereof, and has a high-quality appearance and has a good design. The object is to provide an excellent injection molded product.

The main structure of the injection-molded article of the present invention according to the means for solving the technical problem is
In a synthetic resin molded product in which the central part is formed thin and the peripheral edge of the central part is formed thick, the injection rate of the molten resin into the cavity of the mold corresponding to the central part of the molded product A molded product formed by primary injection molding in which a molten resin is injected and filled into a cavity through a pin gate arranged in a plurality so as to be able to be increased is used as a primary molded product,
With this primary molded product as an insert material, at least the front side of the primary molded product shall be molded by flowing a molten resin in a covering state and performing secondary injection molding,
It is in.

The basic idea of the above configuration is that, in the primary molded product, a plurality of pin gates are arranged at predetermined positions of the cavity mold corresponding to the central portion formed in the thin shape of the molded product, and arranged at these predetermined positions. The total cross-sectional area of the gate, which is the inflow path of the resin into the cavity, while the function of a center gate that causes the molten resin to flow radially from the center of the molded product to the periphery by the plurality of pin gates In order to eliminate the restriction on the diameter of the center gate disposed in the thin portion.
That is, the molten resin can be flowed radially from the central portion of the cavity at a sufficiently high injection speed, and the thick wall portion on the periphery can be filled in a short time. Occurrence can be suppressed.

  Then, using this primary molded product as an insert material, at least the front side surface of the primary molded product is made to flow through the molten resin in a covering state from the position corresponding to the central portion of the primary molded product via the center gate, and then subjected to secondary injection molding. By performing the molding, even if a slight appearance defect such as shrinkage remains in the primary molded product, the secondary injection molding can compensate for this defective portion, and has a higher quality appearance. A molded article can be provided.

  Here, the number of pin gates in the primary molded article, the range of the arrangement area, and the arrangement position are the rotational axis symmetry of the molded article, the wall thickness distribution, the anisotropy of the flow distance to the flow end, and the sink or weld. This is a design item that can be determined in consideration of the degree of occurrence of the mark.

  In the description of the main configuration, the front side surface of the primary molded product refers to a surface portion that is visible or easily visible from the outside in a state where the product is used, that is, a surface portion that particularly requires appearance.

  Another configuration of the present invention is that a plurality of pin gates are arranged in a range in which the distance between any two pin gates in the primary molded product is within 20 mm in the main configuration.

The above configuration shows a specific reference for the positions where a plurality of pin gates are arranged.
Here, if the distance between any two pin gates is too large, the weld marks become conspicuous at the part where the resin flowing into the cavity from these two gates merges and collides, and the appearance of the molded product However, when the distance between the pin gates is within 20 mm, more preferably within 15 mm, the molten resin merges and collides at a higher temperature so that the weld mark of the primary molded product is inconspicuous. It can be in the undetectable range.

  Still another configuration of the present invention resides in that, in the main configuration, the diameter of each pin gate in the primary molded product is 80% or less of the thickness of the molded product at a position where each pin gate opposes.

  The above configuration presents a standard for determining the diameter of each pin gate of the primary molded product. By setting it to 80% or less of the thickness of the molded product at a position facing each pin gate, the vicinity of the gate mark of the primary molded product It is possible to effectively prevent cracks from occurring.

  Still another configuration of the present invention resides in that, in the main configuration described above, the primary molded product has a shape having rotational axis symmetry, and the pin gate is disposed at an axially symmetric position with respect to the symmetry axis.

  In the above configuration, the shape of the primary molded product is specified as having rotational axis symmetry. In such a molded product having rotational axis symmetry, a pin gate is appropriately arranged at a position axially symmetric with respect to the symmetrical axis. By providing, the primary molded product can be a molded product in which the generation of sink marks is suppressed more effectively.

Still another configuration of the present invention is the above-described configuration having rotational axis symmetry, wherein the primary molded product is formed into a regular quadrangular prism block body, and a hemispherical concave portion coaxially with respect to the rotational symmetry axis of the block body. As a formed product,
This is because four pin gates are arranged at a position equidistant from the center on the line connecting the center of the center and the corners at the thin center.

  The above configuration is an example in which the shape of the molded product is further specified. In consideration of the corner portion which is the largest thick portion and has a long flow distance, the portion corresponding to the line connecting the center of the bottom surface and each corner portion is 4. By providing a single pin gate, it is possible to effectively suppress the occurrence of sink marks near the corners.

  In addition to the primary molded product having the shape described above, the occurrence of sink marks in the primary molded product can be more effectively suppressed by appropriately arranging the pin gate according to the shape of the molded product as described above. it can.

  Here, in the injection molded product described in claims 1 to 5 described above, sink marks of the thick molded product are effectively suppressed by a plurality of pin gates arranged in the mold, and these molded products remain as they are. Can be used as a final product, but when a higher quality appearance is required depending on the field of use, it can be effectively used as a primary molded product that becomes the core of a so-called double-molded injection molded product, The sixth aspect of the present invention relates to an injection molded product by this double molding.

Next, the molding method of the present invention is:
It is an injection molding method for a molded product made of a synthetic resin in which a central part is formed thin, and a peripheral part of the central part is formed thick,
Using a mold that forms a cavity with a cavity mold and a core mold, a plurality of molds are arranged in the cavity mold corresponding to the center of the molded product so that the injection speed of the molten resin into the cavity can be increased. The primary molded product (15) is injection molded by injection filling molten resin into the cavity through the pin gate.
The primary molded product (15) is used as an insert material, and at least the front side surface (15f) of the primary molded product (15) is subjected to secondary injection molding by flowing molten resin in a covering state,
It is in.

The basic idea of the above molding method is that in a primary molded product, a plurality of pin gates are arranged at predetermined positions of a cavity mold corresponding to the central portion formed in a thin shape of the molded product, and arranged at these predetermined positions. The cross-sectional area of the gate, which is the inflow path of the resin into the cavity, is exhibited while functioning as a center gate that causes the molten resin to flow radially from the center to the periphery of the molded product by a plurality of pin gates provided. It is intended to eliminate the restriction on the diameter of the center gate disposed in the thin wall part as a total,
The molten resin is allowed to flow radially from the center of the cavity at a sufficiently high injection speed, so that the resin can be filled in the thick part of the periphery in a short time, and sinking occurs in the thick part of the primary molded product. It becomes possible to suppress.

The present invention is the configuration and method described above, and has the following effects.
In the injection molded product having the main configuration of the present invention,
Even if the primary molded product is a molded product with a thin central part, the molten resin is caused to flow radially from the vicinity of the center of the cavity at a sufficiently high injection speed, and the thick wall portion at the periphery is filled in a short time. Can effectively suppress the occurrence of sink marks in the thick part of the primary molded product,
Further, by using the primary molded product in which the occurrence of sink marks is suppressed in this way and further subjecting the surface thereof to secondary injection molding, a molded product having a high-quality appearance can be provided.

  Further, by arranging a plurality of pin gates within a range in which the distance between any two pin gates in the primary molded product is within 20 mm, more preferably within 15 mm, the molten resin has a higher temperature. Therefore, it is possible to make the weld mark of the primary molded product inconspicuous and further undetectable.

  Moreover, in the primary molded product, the occurrence of cracks in the vicinity of the gate trace of the primary molded product can be effectively prevented by setting the thickness to 80% or less of the thickness of the molded product at the position facing each pin gate.

  Further, in the primary molded product having rotational axis symmetry, it is possible to make the primary molded product in which the occurrence of sink marks is more effectively suppressed by appropriately arranging a pin gate at a position axially symmetric with respect to the symmetry axis. it can.

  Further, in a primary molded product in which a hemispherical concave portion serving as a storage portion is formed coaxially with respect to the rotational symmetry axis of the block body in a regular square columnar block body, the line connecting the center of the bottom surface and each corner portion By providing four pin gates in the portion corresponding to, the occurrence of sink marks in the thick portion near the corner can be more effectively suppressed.

In the injection molding method of the present invention, in the injection molding of the primary molded product, the sectional area of the gate, which is the inflow path of the resin into the cavity, is increased as a whole, and the center gate disposed at the portion facing the thin wall portion It is intended to eliminate the restriction on the diameter, and the molten resin can be flowed radially from the central part of the cavity at a sufficiently high injection speed, so that the thick wall part at the periphery can be filled with the resin in a short time. The occurrence of sink marks in the thick part of the primary molded product can be effectively suppressed.

It is a perspective view which shows an example of the primary molded product used for the molded product of this invention. It is (a) longitudinal cross-sectional view and (b) top view of the primary molded product of FIG. It is a longitudinal cross-sectional view shown along the diagonal direction of the primary molded product of FIG. It is the schematic of the metal mold | die used for injection-molding the primary molded article of FIG. 1, (a) is a longitudinal cross-sectional view of the state which clamped the cavity metal mold | die and the core metal mold | die, (b) is a cavity metal mold | die. FIG. It is a perspective view which shows one Example of the molded article of this invention. It is (a) longitudinal cross-sectional view and (b) top view of the molded article of FIG. It is a schematic explanatory drawing of the secondary injection molding process of the molded article of FIG. It is a perspective view which shows an example of the conventional thick molded product. It is (a) longitudinal cross-sectional view and (b) top view of the molded article shown in FIG.

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are diagrams for explaining an example of a primary molded product 15 used in an injection molded product of the present invention. FIG. 1 is a perspective view, FIG. 2 (a) is a longitudinal sectional view, and FIG. ) Is a plan view, and FIG. 3 is a longitudinal sectional view taken along a diagonal line.
This primary molded product 15 is a transparent molded product made of styrene acrylonitrile resin, in which a hemispherical concave portion 8 is formed coaxially with respect to the rotational symmetry axis AX of the short regular square columnar block 7 as a housing portion. The central portion of the bottom surface 9 that is the central portion of the molded product is a thin portion 2 that is formed to be thin, and has a thick portion 3 that is formed thick on the periphery thereof.

The dimensions of the primary molded product 15 are such that each side of the regular square is 53 mm, the height is 22 mm, the opening diameter of the recess 8 is 47 mm, the depth is 20.5 mm, and the center of the bottom surface 9 corresponding to the position of the axis of symmetry AX The thickness t1 of C is 1.5 mm, and the thickness t2 of the corner 11 is 18 mm (see FIG. 3). Then, as shown in the bottom view of FIG. 2 (b), on the line connecting the center C of the bottom wall 9 and each corner portion 11, the mold 21 (described later) is disposed at an equal distance (6 mm) from the center C. There is a pin gate mark 5 corresponding to the four pin gates 25 having a diameter of 0.8 mm.
Each corner 11 has a shape rounded off with a radius of curvature R of 4 mm (see FIG. 3).

4 is a schematic view of a mold 21 used for injection molding the primary molded article 15 of FIG. 1, and FIG. 4 (a) shows a state in which the cavity mold 22 and the core mold 23 are clamped. FIG. 4B is a bottom view of the cavity mold 22.
Conventionally, in a molded product having a shape as shown in FIG. 1, it is usual to arrange one pin gate as a center gate at the center position of the cavity mold 22, but in the cavity mold 22 shown in FIG. The pin gate 25 is arranged at a position equidistant from the center (6 mm) on the line connecting the center Cm and the corner. (See Fig. 4 (b))
Here, the thickness of the molded product 1 at each pin gate 25 position is 2 mm, and the diameter of each pin gate 25 is 0.8 mm which is 80% or less of the wall thickness.
Then, the molten resin flows radially into the cavity 24 of the mold 21 through the four pin gates 25 and is filled, and the primary molded product 15 is injection-molded.

  The primary molded product 15 of FIG. 1 injection-molded by the mold 21 shown in FIG. 4 has a thin portion with a minimum thickness of 1.5 mm at the central portion, and the maximum thickness at the corner portion 11 of the periphery. In spite of a thick molded product having a large wall thickness variation having an 18 mm thick portion, the occurrence of sink marks was sufficiently suppressed, and the product could be used as a product as it was.

If the distance between the pin gates 25 is too large, the weld mark becomes conspicuous at the portion where the molten resin flowing from each pin gate 25 merges and collides, but in this embodiment, the distance between each pin gate 25 is 12 mm at the maximum. There was no problem with the appearance of the weld mark.
In preliminary experiments, the distance between the pin gates 25 is 20 mm or less, preferably 15 mm or less.

  Here, the first feature of the design method of the present invention related to shape design and mold design for suppressing the occurrence of sink marks in molding a molded product having a shape such as the primary molded product 15 is as follows. Four pin gates 25 are arranged in a region having a diameter of 12 mm corresponding to the vicinity of the center C of the bottom surface 9 of the molded product 1, and the molten resin is fed from the center C of the primary molded product 15 toward the periphery by these pin gates 25. While exhibiting the center gate function of flowing radially, the cross-sectional area of the resin inflow path into the cavity 24 is increased as a whole, the restriction on the diameter of the center gate is eliminated, and the injection speed is increased sufficiently. It is in the point which made it possible.

In addition, regarding the shape design and mold design, the following points are taken into consideration.
(1) The plurality of pin gates 25 are arranged symmetrically in consideration of the symmetry of the primary molded product 15, the thickness distribution, and the like. In this embodiment, the pin gate 25 is arranged at a position corresponding to the line connecting the center, the C and the corner portion 11 in consideration of the long flow distance in the corner portion 11 and the large thickness.
(2) The distance between the pin gates 25 is set within a predetermined range in consideration of the generation of weld marks. In this embodiment, four pin gates 25 are disposed within a diameter of 12 mm.
(3) The corner 11 is rounded. If the radius of curvature R is too small, the sink on the inside of the corner portion 11 (the portion indicated by the white arrow in FIG. 2B and FIG. 3) becomes large. Therefore, in this embodiment, the radius of curvature R is set to 4 mm.

  When the primary molded product 15 having the shape shown in FIG. 1 is molded with a mold having a center gate having a diameter of 0.75 mm (a dimension corresponding to half the thickness of the center C), the injection speed is sufficiently increased. Therefore, the resin pressure at the thick part is insufficient, and a large sink is generated particularly near the corner part. (Refer to the molded product 101 in FIGS.

Next, FIG. 5 and FIG. 6 are for explaining an embodiment of the injection molded product of the present invention. FIG. 5 is a perspective view, FIG. 6 (a) is a longitudinal sectional view, and FIG. It is a bottom view.
This molded product is the same as the primary molded product 15 in which the primary molded product 15 of FIG. 1 is used as an insert as shown in FIG. 7 and the front side surface 15f of the primary molded product 15 is covered through the center gate 26. This is a so-called double-molded injection-molded product in which secondary injection molding is performed by melting and flowing resin (see the arrow in FIG. 7).

  In the molded product 1 of this example, the front side surface 15f from the bottom surface to the side surface of the primary molded product 15 in which the occurrence of sink marks was originally suppressed is covered with a thickness of about 2 mm by secondary molding. As a result, the unevenness due to slight sink marks remaining in the primary molded product 15 is finished to be completely flat, and a molded product exhibiting a high-quality appearance that does not sense distortion due to reflection of light has been obtained.

The coating thickness by the secondary injection molding should be as uniform as possible in order to eliminate the occurrence of sink marks due to the secondary injection molding itself. In this respect, the radius of curvature R of the corner portion 11 of the primary molded product 15 needs to be reduced. However, as described above, if the radius of curvature R is too small, sink marks will occur inside the corner portion 11. In consideration of this balance, the radius of curvature is set to 4 mm in the first molded product 15 shown in FIG.
In particular, in the molded product 1 such as the present embodiment in which the shape of the hemispherical concave portion 8 made of a transparent resin is visible from the outside and exhibits the design effect, the occurrence of sink marks in the molded product is also sufficient. It is necessary to design with consideration.

And the molded product 1 of a present Example is the content which has the mouth_tube | cylinder part 32, the outer casing-shaped plate piece 33 whose outer shape is a regular tetragon, and the accommodating part 34 as shown by the dashed-two dotted line in Fig.6 (a). The container member 31 can be fitted and used as a cosmetic container.
Further, since the molded product 1 is made of a transparent resin, it can be seen as if the hemisphere by the concave portion 8 is floating in the block body, and a high-grade product image can be given.

  As described above, the molded product of the present invention, the primary molded product to be used, the mold for injection molding of the primary molded product, and the injection molding method have been described according to the examples. However, the present invention is limited to these examples. It is not something. As described in the examples, the molded product of the present invention can obtain a high-quality appearance by double molding, but it is not only used for such packaging, but generally has a thin portion at the center. In a meat molded product, it is also possible to provide a precision molded product in which the occurrence of sink marks is highly suppressed.

As described above, the injection-molded product of the present invention has a highly suppressed occurrence of sink marks in the thick-walled portion, and has a high-quality appearance and excellent design by double molding. It is expected that it can be widely developed in the field of cosmetic containers and the like with high-quality packaging.

DESCRIPTION OF SYMBOLS 1; Molded article 2; Thin part 3; Thick part 5; Gate trace 7; Block body 8; Recess 9; Bottom face 11; Corner part 12; Pin gate trace 15; Primary molded article 15f; Mold 22; Cavity mold 23; Core mold 24; Cavity 25; Pin gate 26; Center gate 31; Inner container member 32; Mouth tube portion 33; Plate piece 34; Storage portion 101; Block body 108; Concave part 111; Corner part 115; Primary molded product 115t; Gate mark 117; Cover part AX; Axis of symmetry C; Center Cm; Center t1, t2; Wall thickness R;

Claims (6)

A synthetic resin molded product (1) having a thin central portion and a thick peripheral edge of the central portion, corresponding to the central portion of the molded product (1) of the mold (21) In the first injection molding, the molten resin is injected and filled into the cavity (24) via a plurality of pin gates (25) arranged to increase the injection speed of the molten resin into the cavity (24). The molded product is the primary molded product (15),
Injection molded product formed by performing secondary injection molding by flowing the molten resin in a covering state on at least the front side surface (15f) of the primary molded product (15) using the primary molded product (15) as an insert material .   The injection molded product according to claim 1, wherein in the primary molded product (15), a plurality of pin gates (25) are arranged in a range in which a distance between any two pin gates (25) is within 20 mm.   The injection-molded product according to claim 1 or 2, wherein the diameter of each pin gate (25) in the primary molded product (15) is 80% or less of the thickness of the molded product (1) at the position of each pin gate (25). .   The injection-molded article according to claim 1, 2 or 3, wherein the primary molded article (15) has a shape having rotational axis symmetry, and the pin gate (25) is arranged in an axially symmetric position with respect to the symmetry axis (AX). .   The primary molded product (15) is a regular quadrangular prism-shaped block (7) in which a hemispherical recess (8) is formed coaxially with the rotational symmetry axis (AX) of the block (7). In the thin central portion, four pin gates (25) are equidistant from the center (C) on the line connecting the center (C) of the central portion and each corner (11). The injection-molded product according to claim 4, wherein An injection molding method of a synthetic resin molded article (1) in which a central part is formed thin and a peripheral part of the central part is formed thick, and includes a cavity mold (22) and a core mold (23). Using the mold (21) constituting the cavity (24), the injection speed of the molten resin into the cavity (24) can be increased at the portion corresponding to the central part of the molded product of the cavity mold (22). The molten resin is injected and filled into the cavity (24) through a plurality of pin gates (25), and the primary molded product (15) is injection molded,
Injection using the primary molded article (15) as an insert material, and performing secondary injection molding by flowing molten resin in a covering state on at least the front side surface (15f) of the primary molded article (15) Molding method.

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