JP2003053771A - Method for manufacturing resin molded article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To monolithically mold a resin molded article having a thick-walled part relatively large in thickness and a thin-walled part relatively reduced in thickness with good dimensional accuracy. SOLUTION: The resin molded article is manufactured through a first process for molding the outline shape of the thick-walled part of the resin molded article 1, a second process for taking the outline shape molded article 1 obtained in the first process out of a mold and cooling the same until the shrinkage after molding advances sufficiently to stabilize the dimensional shape of the molded article and a third process for positioning the outline shape molded article obtained in the second process in an injection mold as an insert and injecting a molten resin in the mold to mold the thick-walled part 2 having a predetermined shape and the thin-walled part 3 integrated with the thick-walled part 2 by covering the surface of the outline shape molded article 1.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a resin molded product having a thick portion and a thin portion.

[0002]

2. Description of the Related Art When a resin molded article having a thick portion is injection-molded, a large injection molding machine having a large injection capacity is used in order to improve the filling property of the resin into the molding space for molding the thick portion. Used. Further, since the thick portion has a large shrinkage after molding, in order to obtain a molded product having a predetermined size and shape, the mold design is performed with the shrinkage in mind.

However, when injection molding a molded product in which a thick portion having a relatively large thickness and a thin portion having a relatively small thickness are integrally formed, the shrinkage after molding is large in the thick portion and thin. Since the portion is small, the deformation of the thin portion, which is originally small in contraction, is likely to be large under the influence of the shrinkage of the thick portion. Therefore, it has been practiced to separately form the thick portion and the thin portion and integrate them by screwing or bonding to form a predetermined shape.

[0004]

The problem to be solved by the present invention is, as described above, not to rely on screw fastening or adhesion, but to a thick part having a relatively large thickness and a relatively thin thickness. It is to integrally mold a resin molded product having a thin portion with high dimensional accuracy.

[0005]

In order to solve the above-mentioned problems, the manufacturing method according to the present invention includes the following first step to third step, in which a relatively thick wall portion and a relatively thick wall portion are provided. It is characterized in that a resin molded product having a thin portion having a small thickness is integrally molded. The first step is to mold the general shape of the thick part of the resin molded product. In the second step, the general shape molded product obtained in the first step is taken out from the molding die and cooled. At this time, the general shape molded product is sufficiently contracted after molding, and thereafter the shape and dimension are stable. Then, in the third step, the general shape molded product obtained in the second step is positioned as an insert in an injection molding die, and molten resin is injected into the mold to cover the surface of the general shape molded product with a predetermined shape. The thick wall portion and the thin wall portion integrated with the thick wall portion are molded. The term "covering the surface of the roughly shaped product" means covering the entire surface or a part of the surface of the roughly shaped product.

According to the above-mentioned manufacturing method of the present invention, the third step is the molding for covering the surface of the roughly shaped molded product mainly to arrange the thick wall portion into a predetermined shape, and the thin wall portion is carried out at the same time. And the molding of substantially thin wall. Therefore, the dimensional shrinkage of the molded product taken out from the mold through the third step is small, and accurate molding can be performed. Moreover, since the dimensional shape of the general shape molded product is already stable in the third step, it functions extremely effectively as a reinforcing material,
This contributes to suppressing shrinkage after molding of the resin molded product molded in the third step and maintaining the dimensional shape.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 2, a resin molded product including a block-shaped thick portion 2 and a cross-shaped thin portion 3 is integrally molded. First, in the first step, the rough shape of the thick portion 3 is formed. FIG. 1 shows a molded product 1 of this general shape. The dimensional shape of the general shape molded product 1 is set so that a part or the whole thereof is smaller than the thick portion 2 having a predetermined size. In the second step, the general shape molded product 1 is taken out from the mold and cooled. Here, the general shape molded product 1 sufficiently causes shrinkage after molding, and the subsequent dimensional shape is stable.
Since the dimensional shrinkage of the thick-walled molded product after molding is large, it is meaningless to improve the dimensional accuracy of the rough-shaped molded product 1, and it is sufficient to literally mold the rough-shaped portion 2 into the rough shape. The molding of the general shape molded product 1 is performed by an appropriate molding means such as injection molding or compression molding.

In the third step, the general shape molded product 1 having a stable size and shape in the second step is positioned as an insert in the injection molding die, and the molten resin is injected into the die. In this step, the molten resin is filled in the mold so as to cover the surface of the molded product 1 having the general shape. As a result, the thick portion 2 having a predetermined shape is formed. At the same time, the thin portion 3 is formed integrally with the thick portion 2. Since the resin layer covering the surface of the molded product 1 having a general shape has a small thickness like the thin portion 3, the dimensional shrinkage after molding in the third step is small. In addition, since the dimensional shape of the general shape molded article 1 is already stable in the third step, it functions extremely effectively as a reinforcing material. Since the general shape molded product 1 can hold the dimensional shape while suppressing the shrinkage of the resin molded product molded in the third step after molding, molding with good dimensional accuracy can be performed.
In the molding in the third step, in addition to the general shape molded product 1, a metal insert or the like is positioned and arranged as necessary.

The resin to be molded is polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylerene-ethylene terephthalate (PBT-PET copolymer resin), polyether ether ketone (PEEK resin), polyphenylene sulfide (PPS). ), Polyetherimide (PEI), 6 nylon (PA6), 6-6 nylon (PA66), polycarbonate (PC), and the like. These are used alone or as a mixture. Further, for the purpose of improving heat resistance and dimensional stability, inorganic fillers such as glass fiber, glass beads, and talc may be appropriately added to these resins.

The resins used in the first step and the third step are preferably the same series of resins. In this case, in the third step, since the molten resin injected into the mold fits to the surface of the general shape molded product 1, the general shape molded product 1 and the injected resin can be well integrated. More preferably, a resin that can be molded at a temperature lower than the molding temperature in the third step is selected as the resin used in the first step, and the molding in the first step may be performed at a lower temperature than the molding in the third step.
By doing so, the crystallization of the resin is suppressed (the resin crystal particles are small) in the general shape molded product 1 that has undergone the second step. Therefore, in the third step, the general shape molding is performed by the heat of the injected resin. The surface of the article 1 is easily melted, and the injected resin and the general shape article 1 are well integrated.
Since the molding temperature of the third step is higher than the molding temperature of the first step, the crystallization of the resin proceeds (the crystal particles of the resin increase), and the heat resistance of the manufactured resin molded article also increases. The combination of the resin forming the general shape molded product 1 and the resin injected in the third step is, for example, P of a low melting point grade.
PS and high melting point grade PPS. However, PPS
Can change the molding temperature even with the same grade.
It is possible to set the molding temperature of the step (mold temperature) to about 90 ° C and the molding temperature of the third step (mold temperature) to about 150 ° C. In addition, the combination of the resin used in the first step and the resin used in the third step is a combination of PBT and PPS.

Further, in order to improve the integration of the injected resin and the general shape molded article 1, an undercut-shaped recess 4 is formed on the surface of the general shape molded article 1 and / or the general shape molded article. It is preferable to form a through hole 5 penetrating 1 (see FIG. 1). Since the molten resin injected in the third step flows into the concave portion 4 and fills the concave portion 4, a resin layer covering the surface of the general shape molded article 1 to form the rough shape molded article 1 and the thick portion 2 is formed. The mechanical connection of is strengthened. Through hole 5
The resin that has flowed into and filled this also exerts a rivet function to strengthen the mechanical connection. In the third step, if one of the opposite surfaces of the roughly shaped molded article is not covered with the injected resin layer, the opening of the through hole 5 on that surface is enlarged to form a step, and The filled resin is used as the head of the rivet to exert the rivet function.

[0012]

EXAMPLES PPS was selected as the resin, and a 100 ton injection molding machine was used to mold a roughly shaped molded product 1 having the shape shown in FIG. 1 (mold temperature 90 ° C.). Take this out of the mold,
It was left at room temperature and cooled sufficiently. Next, the general shape molded product 1 is positioned in another mold, and a 200 ton injection molding machine is used to inject a molten resin (PPS similar to that in the first step) to mold the resin into the predetermined shape shown in FIG. The product was molded (mold temperature 150 ° C.). The thickness of the resin layer covering the surface of the molded article 1 for forming the thick portion 2 is 3 mm on average. The thin portion 3 has a thickness of 3 mm. The dimensional shrinkage of the resin molded product molded in this way is 1.5 / 1000.
Met. Deformation of warpage and twist of the thin part 3 (maximum amount of lift from the surface when placed on a flat surface) is 0.3
It was mm.

For comparison, the same PPS as in Example 1 was used, and a 300 ton injection molding machine was used to mold the resin molded product having the predetermined shape shown in FIG. 2 in one step (mold temperature 15).
0 ° C). Although there was no problem with the resin filling property, the dimensional shrinkage of the resin molded product was 3.5 / 1000. Thin part 3
The warp and twist deformation was 2 mm.

[0014]

As described above, according to the method of the present invention, a resin molded product having a thick portion having a relatively large thickness and a thin portion having a relatively small thickness can be obtained with high dimensional accuracy. , Sled
It is possible to suppress twisting and integrally mold. Even if there is some resin filling shortage in the molding of the roughly shaped molded product in the first step, the shortage can be compensated for by the molding in the third step, and there is no problem. It is also possible to manufacture using a small injection molding machine.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a perspective view of a schematic shaped molded product molded in a first step.

FIG. 2 is a perspective view of a resin molded product having a thick portion and a thin portion manufactured according to the embodiment of the present invention.

[Explanation of symbols]

1 is a general shape molded product 2 is a thick part 3 is the thin portion 4 is a recess 5 is a through hole

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazutake Fujisawa             Shinjin, 3-chome, Shodaita-cho, Hirakata-shi, Osaka             Toto Latex Co., Ltd. (72) Inventor Hiroshi Ueda             Shinjin, 3-chome, Shodaita-cho, Hirakata-shi, Osaka             Toto Latex Co., Ltd. F-term (reference) 4F206 AA24 AA28 AA29 AA34 AD05                       AM35 JA07 JB12

Claims (3)

[Claims] 1. A method for producing a resin molded product having a relatively thick thick portion and a relatively thin thin portion, the first step of molding a schematic shape of the thick portion, Second step of taking out and cooling the roughly shaped molded product obtained in the first step from the molding die, positioning the roughly shaped molded product as an insert in an injection molding die, and injecting a molten resin into the die to obtain a roughly shaped A method for producing a resin molded product, comprising: a third step of molding a thick part having a predetermined shape covering the surface of the molded product and a thin part integrated with the thick part. 2. The resins used in the first step and the third step are the same type of resin, and the resin used in the first step is a resin that can be molded at a lower temperature than the third step, and the first step is the third step. The method for producing a resin molded product according to claim 1, wherein the resin molded product is molded at a lower temperature. 3. The resin according to claim 1, wherein the general shape molded product molded in the first step is provided with a recess and / or a through hole into which the molten resin molded in the third process flows. Manufacturing method of molded products.