JP3086308B2 - Sandwich molding method for plastic molded products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sandwich molding a plastic molded article, and more particularly, to a method for molding a plastic molded article capable of ensuring a sandwich state even at a terminal portion or a projecting portion of the molded product.

[0002]

2. Description of the Related Art There are many plastic molded products having portions requiring various performances such as surface rigidity and hardness, such as mounting portions for tightening and fixing, at terminal portions or projecting portions. For this reason, conventionally, a soft resin material,
It has been widely practiced to inject a hard resin material continuously through the same sprue to form a skin layer and a core layer by using a molding method for forming a skin layer and a core layer, that is, a so-called sandwich molding method. However, in the usual sandwich molding method, the cavity is filled with the soft resin material injected and injected earlier at the end portion or the protruding portion of the molded product, and the hard resin material injected later cannot enter as a core layer, and the sandwich is not formed. There is a problem that it is difficult to form a state. In order to solve such a problem, as shown in FIG. 5, a core pin (not shown) for forming a through hole is provided in a cavity 2 having a shape of a molded product, and a hollow portion is formed outside the product portion. 9 and the small flow path 5, a molding method in which the hard resin material B has room for extruding the soft resin material A (Japanese Patent Laid-Open No. 2-206517), FIG.
As shown in the figure, a cavity 9 for forming an attachment portion is continuously provided in the cavity 2 having the shape of a molded product,
A mold having a slide core 3 provided with a core pin 33 for forming a through-hole, which can be closed in the middle of the hollow portion, and in which the mounting portion is substantially composed of only the hard resin material B. Method (JP-A-2-206518)
Etc. have been proposed.

[0003]

However, the performances required of the plastic molded product are not limited to the strength of the terminal portion and the projecting portion of the molded product such as the mounting portion. That is, in many cases, it is desired to form a reliable sandwiched state even at the terminal portion or the protruding portion of the molded product due to a demand for appearance, touch, crack prevention and the like. On the other hand, in the molding method in which the core layer is caused to flow while pushing the skin layer previously injected by the constituent resin, if a uniform and stable skin layer is to be secured on the surface of the molded product, There is a limit in reaching the core layer to the end of the molded article, and as a result, a sandwich state cannot be sufficiently secured at the end of the molded article. In addition, in the above-described molding method, since the mounting portion of the terminal portion or the protruding portion is substantially made of only a hard resin material, problems such as cracks, breaks, and the like are likely to occur on the fastening seat side of the mounting portion. .

The present invention has been made in view of the above viewpoints, and ensures a sandwich state even at a terminal portion or a protruding portion of a molded product, and provides a plastic molded product having strength, appearance, touch, crack prevention, and the like. An object of the present invention is to provide a sandwich molding method excellent in required various properties.

[0005]

According to the sandwich molding method of the present invention, an injection mold is clamped, a soft resin material is injected and injected through a sprue, and then a hard resin material is injected and injected. By arranging the hard resin material in the soft resin material, in a method of molding a plastic molded product having a sandwich structure comprising a skin layer of the soft resin material and a core layer of the hard resin material on at least a part of the molded product, A cavity is provided adjacent to a cavity corresponding to a terminal portion or a protruding portion of a plastic molded product intended for a sandwich structure, and a small channel is formed by moving the cavity, and the cavity and the cavity are formed through the small channel. Using a mold having a slide core capable of making the part continuous, in a state where the small flow path is initially closed by the slide core, the soft resin Fee, injection amount, excluding the hard resin material corresponding amount to be injected into the cavity, then a hard resin material is injected injected into the soft resin material,
The cavity is substantially filled with the hard resin material and the soft resin material, and thereafter, the slide core is moved to form a small channel, and the cavity and the cavity are made continuous through the small channel, Further, the hard resin material or the soft resin material that almost fills the inside of the cavity is injected and injected into the cavity, and the soft resin material near the cavity is extruded into the cavity, and near the cavity, The present invention is characterized in that the hard resin material is further pushed to the cavity side so that the hard resin material is also disposed at the end of the plastic molded product or at the tip end of the protrusion.

The "slide core" forms a small flow path on the slide core by retreating, and makes the cavity and the adjacent cavity part continuous through the small flow path. On the other hand, the small flow path is closed by the advance, and the cavity and the cavity are cut off. The size and shape of the slide core are not particularly limited as long as it has such a function, and examples thereof include a columnar slide core having a concave portion on the core upper surface or a prismatic slide core having a step on the core upper surface. Thus, a hollow portion more than the slide of the core can be formed. The depth of the "small flow path" formed by the retraction of the slide core is preferably 1 to 2 mm as shown in the second invention of the present application. If it is less than 1 mm, it is difficult for the soft resin material to flow from the small flow channel into the above-mentioned hollow portion, and it may be difficult to achieve the object of the present invention. On the other hand, 2m
If it exceeds m, the soft resin material becomes too easy to flow, and accordingly the hard resin material reaches the inside of the hollow portion, and it becomes difficult to cut off the portion filled in the hollow portion after molding or the cutting thereof. This is because a stripe pattern of a soft resin and a hard resin appears on the surface, which may not be preferable in appearance.

Further, as described above, the "injection amount of the soft resin material" is set to "the amount excluding the equivalent amount of the hard resin material" (that is, in the state of the short shot). This is because there is no room for injecting a necessary amount of the hard resin material by injecting. Means for stopping the slide core at the forward and backward positions are as follows:
Regardless of the particular type, for example, a hydraulic type, a spring type or the like can be used. Note that the “tip side” of the terminal portion or the like of the plastic molded product on which the “hard resin material” is disposed does not include the surface portion (the foremost portion) of the terminal portion of the molded product. This is because if the hard resin material is disposed up to the surface portion, the hard resin material is exposed at the portion and the sandwiched state is not obtained.

Here, the “soft resin material” includes:
For example, a resin obtained by blending EPDM with polypropylene, a soft PVC resin, an EVA (ethylene / vinyl acetate) resin, an SEBS (styrene / ethylene / butadiene / styrene) resin, and an SBS (styrene / butadiene / styrene)
(Styrene) resin. Examples of the “hard resin material” include, for example, AS resin, ABS
Resin, hard PVC resin, polypropylene resin containing filler such as talc, and the like can be given. In addition, materials other than resin such as glass fiber can be mixed into these resin materials according to the purpose of use of the molded product.

[0009]

The operation of the present invention will be specifically described below with reference to FIGS. FIG. 1 is a longitudinal sectional view of a molding die 1 for manufacturing a mudguard for an automobile. The molding die 1 includes a fixed side portion 11 and a movable side portion 12. Further, the movable side portion 12 is connected to a cavity (hereinafter, referred to as “main body forming cavity”) 21 that forms a molded article main body and forms a projection (hereinafter, referred to as “projecting portion forming cavity”). 22 and a slide core slideway 4 which is connected to the protrusion forming cavity 22 and slides the slide core. A protrusion 311 is provided on the protrusion forming cavity 22 side of the upper wall surface of the base 31 of the slide core, and a step 312 is provided on the opposite side, whereby the protrusion forming cavity 2 is provided in the movable mold 12.
2, a cavity 6 is formed. The protrusion 311 of the slide core serves as a small channel forming portion, and the step 312 serves as a surface on which the cavity 6 is formed.

Here, first, the slide core 3 is advanced (raised), and the small flow path forming portion 311 of the slide core 3 is brought into contact with the upper wall portion 41 of the slide core slide path 4 so that the small flow path is formed. To close. Next, the cavity 2 of the mold 1
The soft resin material A is injected and injected through the sprue-7. However, the injection of the soft resin material A is performed in a short shot state (a state in which the soft resin material A is not completely filled in the cavity 2). Further, while extruding the unsolidified portion of the soft resin material A previously injected into the cavity 2, the hard resin material B is injected and injected until the cavity is finally filled. However, in this case, as shown in FIG. 2, most of the protruding portion forming cavity 22 is filled with the soft resin material A injected and injected earlier, and the tip of the hard resin material B injected later is It is stopped near the entrance of the part forming cavity 22.

Next, when the interior of the cavity 2 is almost filled with the soft resin material A and the hard resin material B, the slide core 3 is retracted (downward) as shown in FIG.
Is formed to make the cavity 22 and the cavity 6 continuous. At the same time, the soft resin material A or the hard resin material B is injected into the cavity 2 through the sprue 7 and the cavities of the small flow path portion and the gap between the step portion 312 and the upper wall portion 41 of the slideway are formed. The formed cavity 6 is filled. As a result, the unsolidified portion of the soft resin material A that has been stagnant in the protrusion forming cavity 22 is extruded into the cavity 6, and accordingly, the hard resin stopped near the entrance of the protrusion forming cavity 22. Similarly, the leading portion of the resin material B moves so as to be pushed to the tip side of the protrusion forming cavity 22. At this time, the combined capacity of the cavity 6 and the small flow path 5 is changed from the capacity of the soft material to be extruded at the tip side of the projection forming cavity 22 in the state of FIG. The capacity is adjusted in advance to a value obtained by subtracting the amount of the soft material enough to constitute the surface on the side, so that even the hard material is not extruded into the cavity 6. Thereby, the soft material A is formed in the cavity 6.
And the hard material B is not extruded into the cavity 6. As described above, in the present invention, the sandwich state can be reliably ensured even at the end portion of the molded product.

[0012]

The present invention will be described below in detail with reference to examples. (1) Production of Test Product As shown in FIG. 4, a plastic molded product 8 produced in this example has a main body 81, a protruding portion 82, and a soft fin portion 83.
An automotive mudguard consisting of First, as shown in FIG. 1, a molding die 1 including a fixed side portion 11 and a movable side portion 12 was prepared. Here, the molding die 1 forms a cavity 2 in a clamped state, and the cavity 2
Is a cavity for forming a soft fin portion provided below the main body forming cavity 21, a projecting portion forming cavity 22, and a main body (hereinafter referred to as a "soft fin portion forming cavity").
To ) 23. Also, this body cavity 2
A sprue 7 for injecting the resin material into the cavity 2 and a slide core slideway 4 for the slide core 3 to slide at an end of the protruding portion forming cavity 22 are provided above the resin material 1. It is installed continuously.

Further, the slide core 3 comprises a base 31 for controlling the behavior of the resin material and a connecting rod 32 provided below the base. In addition, this base 31 has
As shown in FIG. 3, a projection 311 is provided on the side of the projection forming cavity on the upper wall surface, and a step 312 is formed on the opposite side. The step 312 forms a cavity 6 between the movable mold 12 and the upper wall 41 of the slideway 4 as shown in the drawing. As the slide core 3 advances (rises), the protrusion 311 contacts the upper wall portion 41 of the slide core sliding path to close the small flow path 5, and the protrusion 311 retreats (falls) to move the protrusion 311. The small flow path 5 is formed apart from the upper wall portion 41. Due to the formation of the small flow path 5, the volume of the hollow portion 6 formed between the step 312 of the core and the upper wall portion 41 of the core sliding path increases as the core descends. Connecting rod 32 provided below the slide core
Is a rod for linking the slide core 3 and a controller (not shown) for controlling the mounting position of the slide core by hydraulic pressure.

Using the above molding die 1, a test piece was prepared as follows. First, the slide core 3 is advanced (raised), the projection 311 is brought into contact with the upper wall 41 of the slide core slideway 4 to close the small flow path 5, and this state is secured by a controller (not shown). . Next, the soft resin material A (a polypropylene resin blended with EPDM, the same applies hereinafter) melted in a cavity 2 of the molding die 1 in a heating cylinder (not shown) is passed through a sprue 7 into a short shot state. Injection.

Further, the hard resin material B (polypropylene resin containing talc, the same applies hereinafter) melted in a heating cylinder (not shown) is introduced into the cavity 2 and the unsolidified portion of the soft resin material A previously injected is removed. While pushing, the hard resin material B is injected and injected until the cavity is finally filled. Then, the slide core 3 is moved backward (downward),
A small channel 5 and a cavity 6 were formed between the protrusion 311 and the slide core slideway 4. At the same time, only the soft resin material A or the hard resin material B was injected into the cavity 2 through the sprue 7 to fill the cavity 6. The height of the small flow path 5 formed by the retreat of the slide core 3 is 1 mm. Next, after holding pressure, cooling and solidifying, and releasing the mold, a portion of the soft resin material A which had entered the cavity and solidified was cut off and deburred to produce a plastic molded product as a test sample.

(2) Performance Evaluation Appearance Evaluation In this performance evaluation, the degree of formation of the sandwiched state at the protruding portion 82 of the test sample is visually evaluated.
The protruding portion 82 of the test article was cut with a knife so that its longitudinal section and transverse section were cut. Then, the state of each section was visually observed. According to this, the sandwich state is sufficiently ensured up to the end of the protruding portion 82.

Mechanical Evaluation In this performance evaluation, the strength of the protruding portion 82 of the test sample was evaluated. First, a through hole (about 6 mmφ) for mounting is provided on the protruding portion 82 of the test sample by a drill (not shown).
There the mudguard fixing bolt (M5, pitch 0.
8) was inserted. Next, this mudguard fixing bolt is connected to an iron plate having a through hole of about 6 mmφ (thickness of about 1.2 mm).
mm), and a mudguard fixing nut (M5, pitch 0.8) was screwed from the tip of the mudguard fixing bolt. A washer (about 1 mm thick) is provided between the tightening seat and the mudguard fixing nut.
Is inserted.

Further, a torque wrench was attached to the mudguard fixing nut, and the mudguard fixing nut was tightened with a torque of 20 kgfmm. Then, after leaving this for 400 hours, the nut for fixing the mudguard was loosened, the test sample was attached to and detached from the iron plate, and the state of the mounting portion of the test sample, especially the state of the tightening seat was observed. Next, the same test was performed on the same test specimen as that used here except that the torque applied to the nut for fixing the mudguard was 25 kgfmm. Further, the same test was repeated on the same test article while increasing the torque applied to the mudguard fixing nut in increments of 5 kgfmm.

According to the above test, even when a large torque of 40 kgfmm was applied, no crack was generated in the protruding portion (mounting portion) of the test product, particularly in the portion of the tightening seat where strength was required. . Further, throughout the test product, when the mudguard fixing nut was tightened, the nut did not loosen. It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention according to the purpose and application. That is, the shape and size of the plastic molded product, the terminal or the protruding portion, the type of the hard resin material and the soft resin material to be used, the shape and size of the molding die, the thickness forming position, the setting of the intermediate position, etc. Instead, various selections are made according to the purpose of use of the plastic molded article.

[0020]

As described above, according to the sandwich molding method for a plastic molded article of the present invention, the sandwich at the end portion or the protruding portion of the molded article, which is relatively difficult to form by the ordinary molding method, is surely secured. I can do it. Therefore, strength, appearance, touch,
It is possible to manufacture a plastic molded product excellent in various characteristics required for the plastic molded product, such as crack prevention.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a mold for manufacturing a mudguard for an automobile in an embodiment.

FIG. 2 is an explanatory view showing a state in which a slide core is advanced in the molding die.

FIG. 3 is an explanatory view showing a state in which a slide core is retracted in the molding die.

FIG. 4 is a perspective view of an automobile mudguard manufactured in this embodiment.

FIG. 5 is an explanatory view showing a molded state of one end of an automobile mudguard according to a conventional example.

FIG. 6 is a longitudinal sectional view showing a molding state of an automobile mudguard according to another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold for manufacturing mudguard for automobile 11 Fixed side part 12 Movable side part 2 Cavity 21 Main body forming cavity 22 Projecting part forming cavity 23 Soft fin part forming cavity 3 Slide core 33 Core pin 4 Slide core sliding path 5 Small flow Road 6 Cavity 7 Sprue 8 Plastic molded article 81 Main body 82 Mounting part 83 Soft fin 9 Cavity A Soft resin material B Hard resin material.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/84 B29C 33/00-33/76

Claims (2)

(57) [Claims] Claims 1. An injection molding die is clamped, a soft resin material is injected and injected through a sprue, and then a hard resin material is injected and injected to dispose the hard resin material in the soft resin material. In a method of molding a plastic molded product having a sandwich structure comprising a skin layer of a soft resin material and a core layer of a hard resin material in a part of the molded product, the molded product corresponds to a terminal portion or a protruding portion of the plastic molded product intended for the sandwich structure. A cavity is provided adjacent to the cavity to be formed, and a small mold is formed by moving the mold, and a mold having a slide core capable of connecting the cavity and the cavity through the small passage is used. In a state where the small flow path is closed by the slide core, the amount of the soft resin material is the amount excluding the equivalent amount of the hard resin material to be injected into the cavity. Injecting, and then injecting a hard resin material into the soft resin material to substantially fill the cavity with the hard resin material and the soft resin material, and then moving the slide core to form a small channel. Then, the cavity and the cavity are made continuous through the small flow path, and the hard resin material or the soft resin material just enough to substantially fill the inside of the cavity is injected and injected into the cavity to form the cavity. By extruding a nearby soft resin material into the cavity, and by further pushing the hard resin material located near the cavity toward the cavity, the end of the plastic molded article or the tip side of the protruding portion is also pressed. A method for molding a plastic molded article having a sandwich structure, comprising disposing a hard resin material. 2. The method according to claim 1, wherein the height of the small flow path is 1 to 2 mm.