JPH09220728A - Resin molded product and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more certainly prevent the sink of a resin molded product and to reduce the number of control processes by using first and third molds holding a primary molded object to mold the residual part of a thick-walled part and a thin-walled part from other resin material. SOLUTION: A lower mold 21 and a mold 22 for an elastic part are used to primarily mold an elastic part 14 from a proper elastomer material. Next, the elastic part 14 of the primary molded object is left in the lower mold 21 to replace the mold 22 for the elastic part with a mold 23 for a flat plate part and, when a proper resin material for secondary molding is injected into a cavity, the elastomer of the primary molded object is compressed by injection pressure. Next, the molds 21, 23 are cooled by the cooling mechanisms provided to the interiors of them to cool and solidify the resin material 25. At this time, the resin material is cooled from the contact part with the mold to begin to solidify.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a resin molded product which makes it possible to prevent sink marks of a resin molded product by using an elastomer, and a new type resin molded product produced by this method.

[0002]

2. Description of the Related Art Conventionally, in a resin molded product having a thick part and a part having different thicknesses such as a boss part and a rib part, the surface of the thick part and the part having uneven thickness is generally called a sink mark. The problem is that dents occur.

A sinking mechanism will be schematically described with reference to FIG. When molding the resin molded product 1 having the rib portion 3, the resin filled in the mold is first cooled by a cooling mechanism (not shown) provided in the mold as shown in FIG. It gradually cools from the portion in contact with the surface of the mold (not shown) and begins to solidify. In this figure, the shaded portion represents a solidified layer of resin, and the inner portion not shaded represents a molten portion of the resin. As shown in FIGS. 1 (b) and 1 (c) in sequence, when the solidification progresses to the inside, the portion where the flat plate portion 2 and the rib portion 3 of the resin molded product 1 intersect is more resinous than other flat plate portions. Since the amount of heat is large and the heat capacity of that portion is large, the molten portion remains only at the intersection. When cooling further progresses and all the molten parts are solidified, volume contraction of the resin occurs, and due to the force at that time, the upper part (opposite side of the rib) which is relatively thin in the rib part is downward (direction of the rib). 1D, it is depressed and causes a defect called a sink shown by 5 in FIG. 1 (d).

Since sink marks seen in resin molded products are not desirable in appearance, various measures have been taken conventionally to prevent the occurrence of sink marks. Among these, as recent ones, JP-A-4-1013 and JP-A-6-2858.
As described in Japanese Patent Publication No. 96-96, an elastic body is set in a mold, and the elastic body compressed by the injection pressure of the resin gradually returns to its original size as the volume of the resin contracts due to cooling and solidification of the resin. There is a technology for compensating for the lack of volume of a resin molded product while restoring it, thereby preventing sink marks in the molded product.

Further, in Japanese Patent Laid-Open No. 5-278039, the temperature inside the mold is partially changed, and especially inside the mold so that the temperature of the back surface (the surface which is not the design surface) of the molded product becomes high. There is described a technique in which a sink having a low thermal conductivity is arranged on the back surface of the molded product to thereby form a molten portion (uncured portion) of the resin toward the back surface of the molded product, thereby positively forming a sink mark on the back surface side. .

[0006]

In the method of setting the elastic body in the mold as described in JP-A-4-1013 and JP-A-6-285896, the elastic body is separately manufactured. In addition to the necessity, the elastic body arranged in the mold, which is repeatedly exposed to high heat and high pressure, requires maintenance and replacement due to durability problems, and therefore management is troublesome. Further, in the method of arranging the insert having a small thermal conductivity in the mold as described in JP-A-5-278039, the temperature of the insert is low at the beginning of molding and then gradually increases, so that the temperature Without careful management, the occurrence of sink marks cannot be completely suppressed, and this temperature management is difficult.

It is an object of the present invention to provide a method for producing a resin molded product, which makes it possible to prevent sink marks of the resin molded product more reliably and to reduce management man-hours therefor. Another object of the present invention is to provide a resin molded product having no sink mark.

[0008]

The method for producing a resin molded product according to the present invention uses a first mold and a second mold when molding a resin molded product having a thick portion and a thin portion. The primary molded body that becomes a part of the thick wall portion is molded from an elastomer material, and the remaining portion of the thick wall portion and the thin wall portion are formed by using the first mold and the third mold that hold the primary molded product. It is characterized in that the part is molded from another resin material.

The resin molded product of the present invention has a thick portion and a thin portion, a portion of the thick portion is made of an elastomer material, and the remaining portion of the thick portion and the thin portion are other resin materials. It is characterized by being molded from.

The "thick part" in the present invention refers to a part thicker than other parts of the molded product, such as those bosses and ribs in a resin molded product having a boss and a rib. . Further, the "thin portion" refers to a portion of the resin molded product other than such a thick portion. However, the term "thick part" here refers to a part of the molded product that includes not only the thicker part than the other parts of the molded product in the strict sense, but also the thin part around it. It should be understood.

[0011]

2 (a) is a perspective view showing an example of a resin molded product of the present invention, and FIG. 2 (b) is a sectional view thereof. The illustrated resin molded product 10 includes a flat plate portion 11 that is a thin portion and a boss portion 12 that is a thick portion. The flat plate portion 11 is injection-molded using a thermoplastic resin. The boss portion 12 is composed of a boss base portion 13 continuously formed with the flat plate portion 11, and an elastic portion 14 surrounding the outer periphery of the boss base portion 13 and formed of an elastomer integrally with the boss base portion 13. This molded product 10
In this way, the elastic portion 14 formed by the two-color molding and the primary molding is integrated with the other secondary molding portion (the flat plate portion 11 and the boss base portion 13).

Next, the method of the present invention will be described with reference to FIGS. 3 to 5 by taking the case of manufacturing the resin molded product 10 as an example. FIG. 3 schematically shows a mold used in this method, and FIG. 3A shows a lower mold 21 of the first mold,
FIG. 3B shows the elastic part mold 22 of the second mold, and FIG. 3C shows the flat plate part mold 23 of the third mold.

When the resin molded product 10 is manufactured by using these molds, first, as shown in FIG. 4 (a), a lower mold 21 and a mold 22 for the elastic portion are used to form an appropriate elastomer. The elastic portion 14 is primarily formed from the material. Next, the elastic part mold 22 is replaced with the flat plate part mold 23, leaving the elastic part 14 of the primary molded body in the lower mold 21, and as shown in FIG. When a suitable resin material 25 is injected into the cavity, the injection pressure causes the elastomer of the elastic portion 14 of the primary molded body to be compressed as shown by the arrow in the figure.

Next, the molds 21 and 23 are cooled by a cooling mechanism (not shown) provided inside them to cool and solidify the resin material 25. At this time, as shown in FIG. 4 (c), the resin is cooled from the portion in contact with the mold and begins to solidify. At this time, the portion of the resin 25 in contact with the elastic portion 14 of the elastomer has not yet started to solidify due to the heat insulating action of this elastomer material (because the thermal conductivity is lower than that of the mold material). In the figure, the shaded portion indicates the solidified resin portion. Further, although the volume shrinkage occurs due to the cooling and solidification of the resin material 25, the volume shrinkage does not occur in the boss portion as a whole because the elastomer material compressed at the time of injection returns to the original shape.

After a while, when the solidification progresses to the inside of the resin material 25, as shown in FIG. 5 (a), the melted portion 26 remains only in the vicinity of the elastomer, and the entire solidified state is obtained. The reason why the melted portion 26 remains only in the vicinity of the elastomer material is that a large amount of resin is present in this portion as compared with other portions, and heat is insulated by the elastomer and cooling is delayed. At this time, the surface side (upper side in the figure) of the molded product has been solidified with a considerable thickness.

As shown in FIG. 5 (b), when the cooling and solidification are completed, the last molten portion 26 (see FIG.
Due to the volume contraction of (a), a contraction force is generated toward the center of the fusion zone, but since a considerably thick solidified layer is formed on the upper side and left and right sides of the fusion zone, it should be directed from the bottom to the center. Will be applied intensively. Due to this force, the elastic portion 14 of the elastomer is pulled upward, which prevents the sinking of the flat plate portion having the boss portion. A state in which the elastic portion 14 is pulled upward is schematically shown in FIG. 6, and arrows in the figure represent forces acting to pull the elastic portion 14 upward. (Usually, the force acts toward the center of the fusion zone,
When all of its circumference is covered with a thick solidified layer and is strong enough to resist the force, the central part becomes an empty place with no material, and a phenomenon called a void occurs, which reduces the product strength. Cause. )

Examples of the elastomer material which can be used for the primary molding in the present invention include styrene elastomers and olefin elastomers, but usable elastomer materials are not limited to these. In addition, as a resin material that can be used for secondary molding, ABS (acrylonitrile-butadiene-styrene copolymer), PP (polypropylene), P
A thermoplastic resin material such as E (polyethylene) can be used, but the usable resin material is not limited to these.

The present invention can also combine the advantages of two-color molding. For example, in the case of the resin molded article 10 described above, since the boss portion 12 has an elastomer up to the tip thereof, this portion can be used as a seal portion or a cushion material, or as a screw stopper.

[0019]

As described above, according to the present invention,
Since the primary molding of the elastomer for a part of the thick part and the secondary molding of the resin material for the other parts were performed in two-color molding, the elastomer of the primary molded body was compressed by the secondary injection pressure. The volumetric shrinkage due to cooling and solidification of the next molding material is compensated by the restoration of the compressed elastomer, and the heat insulating effect of the elastomer hardens the surface side first to strengthen it, and the low elastic modulus of the elastomer makes the elastomer By expanding and compensating for volume contraction to prevent buckling of the surface layer, it is possible to reliably prevent the occurrence of sink marks. Further, since the elastomer of the elastic portion having a heat insulating function is formed every molding and becomes a part of the molded product and is not repeatedly used, there is no fear of deterioration and maintenance is unnecessary. Furthermore, since the primary molded product is immediately used as a heat insulating material, the temperature is stable, and the product does not vary from product to product, and management is easy.

[Brief description of drawings]

FIG. 1 is a diagram schematically illustrating a sinking mechanism, (a) is a diagram showing a state at the start of cooling / solidification of a molding material, and (b) is a diagram showing cooling / solidification progressing. It is a figure which shows a state, (c) is a figure which shows the state which most of the molding material solidified, (d) is a figure which shows the place where cooling and solidification were completed.

FIG. 2 is a diagram illustrating a resin molded product of the present invention,
(A) is a perspective view of a resin molded product, (b) is a sectional view taken along the line I-I of (a).

FIG. 3 is a diagram illustrating a mold used in the present invention,
(A) is a figure which shows a lower metal mold | die, (b) is a metal mold | die for elastic parts, (c) is a metal mold | die for flat plate parts.

FIG. 4 is a diagram for explaining the first half of the method of the present invention,
(A) is a figure which shows primary molding of an elastic part, (b) shows injection of a secondary molding material, (c) shows the start of cooling and solidification of a secondary molding material.

FIG. 5 is a diagram illustrating the latter half of the method of the present invention,
FIG. 7A is a diagram showing a state in the middle of cooling / solidification, and FIG. 7B is a diagram showing a state of completion of cooling / solidification.

FIG. 6 is a diagram showing a part of a boss portion for explaining a force acting on the elastic portion after the resin material is completely cooled and solidified.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Resin molded product 2 ... Flat plate part 3 ... Rib part 5 ... Sink 10 ... Resin molded product 11 ... Flat plate part 12 ... Boss part 13 ... Boss base 14 ... Elastic part 21 ... Lower mold 22 ... Elastic part mold 23 ... Mold for flat plate part 25 ... Resin material 26 ... Melting part

Claims (4)

[Claims] 1. When molding a resin molded product having a thick portion and a thin portion, a primary molded body that is a part of the thick portion is formed by using a first mold and a second mold as an elastomer. Molded from material,
Manufacture of a resin molded product characterized by molding the remaining part of the thick part and the thin part from another resin material using the first mold and the third mold to which the primary molded body is fastened. Method. 2. The thick portion is a boss portion or a rib portion,
The method of claim 1. 3. A thick wall portion and a thin wall portion, a part of the thick wall portion is made of an elastomer material, and a remaining portion of the thick wall portion and the thin wall portion are molded from another resin material. Resin molded product characterized by. 4. The thick portion is a boss portion or a rib portion.
The resin molded product according to claim 1.