JPH0752183A - Hollow injection molded piece, molding method thereof, and mold therefor - Google Patents

Abstract

PURPOSE:To let pressure fluid in with pressure also in a thick part positioned apart from a pressure fluid press-in section without providing rib-like inductive channel by forming a hollow also in a thin part integrated with the thick part having a hollow so as to let the hollows communicate with each other and letting one end of the hollow at the thin part communicate with the pressure fluid press-in section. CONSTITUTION:A hollow injection molded piece is equipped with a thick part 2 on, for example, one side of a thin part 3. At the thick part 2, a hollow part 1a for preventing sink mark is formed and a hollow part 1b is formed also nearly at the center of the thin part 3. One end of the hollow part 1b communicates with a pressure fluid press-in section 4 and the other end communicates with the hollow part 1a of the thick part 2. A mold cavity 5 for molding it forms the pressure fluid press-in section 4 on the opposite side of a thick part molding area 6 of a thin part molding area 7. On the surface of the mold cavity 5 in the thin part molding area 7, a heat insulating material 8 is provided at a position corresponding to a predetermined area A extending from the pressure fluid press-in section 4 to the thick part 2 so as to cool the melting resin later than the other area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow structure having a hollow portion formed by pressurizing a pressurized fluid into a molten resin injected into a mold cavity and discharging the pressurized fluid after cooling as necessary. The present invention relates to an injection-molded article, a method for molding the same, and a mold used for the same.

[0002]

2. Description of the Related Art Conventionally, it has been known to prevent a so-called sink mark generated in a thick portion of a molded article by pressurizing a pressurized fluid to form a hollow portion.

The pressurizing fluid is press-fitted from a pressurizing fluid nozzle built in an injection nozzle or a pressurizing fluid nozzle directly provided in a mold. The pressurizing fluid press-fitting part into the mold cavity is
When using the pressurized fluid nozzle built into the injection nozzle, it is the gate part.When using the pressurized fluid nozzle directly installed in the mold, open the pressurized fluid nozzle to the sprue or runner, or directly into the mold cavity. Depending on whether it is opened to the gate or the mold cavity, it will be the opening of the pressurized fluid nozzle to the mold cavity.

By the way, when the pressurizing fluid press-fitting portion cannot be located at a position close to the thick-walled portion where the hollow portion is to be formed due to the design of the mold, the pressurizing fluid press-fitting portion goes to the thick-walled portion. In order to easily guide the pressurized fluid, continuous rib-shaped guiding channels from the pressurized fluid press-fitting portion to the thick portion are provided.

Utilizing the fact that the pressurized fluid is easily guided along the thick-walled portion where the molten resin easily flows, the above-mentioned guide channel sends the pressurized fluid to the thick-walled portion distant from the pressurized fluid press-fitting position. To induce.

[0006]

However, there are the following problems in the induction of the pressurized fluid by the above-mentioned guide channel.

(1) An originally unnecessary rib-like portion is formed on the surface of the molded product from the pressurizing fluid press-fitting portion to the thick portion, which deteriorates the appearance of the obtained hollow molded product.

(2) In order to prevent the adverse effect on the appearance, the guide channel is formed on the back side of the molded product which is inconspicuous, but the surface condition on the surface side corresponding to the position of the guide channel. It tends to cause fine sink marks.

(3) The hollow portion formed by the pressurization of the pressurized fluid is apt to have a larger cross section at a thicker portion, and accordingly, the amount of the molten resin pushed away by the pressurized fluid is increased. Since the guide channel portion is a thick portion where the pressurized fluid is easily guided, the amount of molten resin that is pushed away by the pressurization of the pressurized fluid increases. Therefore, the thick portion to form the hollow portion serves as a reservoir for the molten resin that has been pushed away, and the hollow portion formed in the thick portion becomes smaller,
In the extreme case, the hollow portion is not formed, and it becomes difficult to sufficiently prevent sink marks in the thick portion.

(4) It is necessary to consume extra resin for forming a thick portion, which is an unnecessary induction channel. The present invention has been made in view of the above-mentioned conventional problems, and it is possible to reliably perform formation of a rib-shaped guide channel even on a thick portion located away from the pressurized fluid press-fitting portion. The purpose is to be able to direct a pressurized fluid.

[0011]

For this reason, according to the invention of claim 1, as shown in FIGS. 1 and 2, a thin portion 3 integrated with a thick portion 2 having a hollow portion 1a is formed. The hollow portion 1b is formed, one end of the hollow portion 1b of the thin portion 3 is communicated with the pressurized fluid press-fitting portion 4 for forming the hollow portions 1a, 1b, and the other end of the thin portion 3 is formed of the thick portion 2. This is a hollow injection-molded product that is communicated with the hollow portion 1a.

Further, in the invention of claim 2, FIG. 1 and FIG.
As shown in FIG. 3, a hollow molding die in which a thin-walled molding region 7 is arranged between a pressurized fluid press-fitting portion 4 into a mold cavity 5 and a thick-walled molding region 6 to which a pressurized fluid is to be introduced. In the blow molding method used, the molten resin injected into the thin portion molding region 7 in a predetermined region A extending from the pressurized fluid press-fitting portion 4 side to the thick portion molding region 6 This is a hollow injection molding method in which the cooling is delayed from the cooling of the molten resin in the other region B in the thin portion forming region 7.

Further, in the invention of claim 3, as shown in FIGS. 1 and 7, the pressurizing fluid press-fitting portion 4 into the mold cavity 5 and the thick-walled portion molding region 6 to which the pressurizing fluid is to be guided. In the hollow molding die in which the thin-walled molding region 7 is located between the two, a predetermined amount extending from the pressurizing fluid press-fitting portion 4 side to the thick-walled molding region 6 on the mold cavity surface of the thin-walled molding region 7. The hollow injection molding die is provided with a heat insulating material 8 for insulating the area A.

The present invention will be further described.

1 and 2 show a first example of a hollow injection-molded product according to the invention of claim 1, wherein this hollow injection-molded product is provided on one side of a thin portion 3 having a thin plate shape. The thick portion 2 having a rectangular cross section is formed so as to be continuous over the one side.

Here, the thick portion 2 is a portion thick enough to cause a clear sink when the hollow portion 1a is not formed, for example, a reinforcing rib portion or a boss portion. Further, the thin portion 3 is a thin portion that does not cause a clear sink without forming the hollow portion 1b, and is not limited to a flat plate portion as shown in FIG. It may have a curved plate shape. Further, the thickness is not limited to the case where the entire area has the same thickness, and the wall thickness may vary to some extent.

A hollow portion 1a is formed in the thick portion 2 in order to prevent sink marks in the thick portion 2. In addition, a hollow portion 1b is also formed substantially in the center of the thin portion 3.

The hollow portion 1b formed in the thin portion 3 has one end communicating with the pressurized fluid press-fitting portion 4 for forming the hollow portions 1a, 1b, and the other end having the hollow portion 1a of the thick portion 2a. Is in communication with. The pressurized fluid press-fitting portion 4 is usually left as a small hole in the hollow injection molded product.

The hollow portion 1b of the thin portion 3 is formed to guide the pressurized fluid press-fitted from the pressurized fluid press-fitting position 4 to the thick portion 2, and the portion where the hollow portion 1b is formed. Is approximately equal to the thickness of the adjacent thin portion 3 where the hollow portion 1b is not formed. That is, in this hollow injection-molded product, the hollow portion 1b is formed without providing the thin portion 3 with a thick portion such as a rib-shaped guide channel as in the prior art.

The hollow portion 1b of the thin portion 3 shown in the figure is one, but when the thick portion 2 is long, for example, the hollow portion 1b is branched into a plurality of thick portions, respectively. It can be made to communicate with the two hollow portions 1a. In addition, a plurality of pressurizing fluid press-fitting portions 4 are provided for one thick portion 2.
Alternatively, a plurality of hollow portions 1b extending from the thin wall portion 3 may be formed.

FIGS. 3 and 4 show a second example of the hollow injection-molded product according to the invention of claim 1, wherein this hollow injection-molded product is located near one side of the thin portion 3 having a thin plate shape. The cylindrical thick portion 2 is formed at two places.

A hollow portion 1a is formed in each thick-walled portion 2, and a hollow portion 1b branched into a V-shape is formed in the thin-walled portion 3. One end of the hollow portion 1b is connected to the pressurizing fluid press-fitting portion 4 on one side, and the other end is connected to the hollow portion 1a of each thick portion 2 on the branch side.

In this embodiment, a hollow portion 1b branched from the pressurizing fluid press-fitting portion 4 is formed in the thin-walled portion 3 so that the pressurizing fluid can be directly guided to the thick-walled portion 2 from the pressurizing fluid press-fitting portion 4. However, the hollow portion 1b is not branched and is formed only on one of the left and right thick portions 2, and another hollow portion (not shown) that connects the left and right thick portions 2 is formed. It can also be formed in the thin portion 3.

FIGS. 5 and 6 show a third example of the hollow injection molded product according to the invention of claim 1, and this hollow injection molded product has a thin portion 3 having a thin plate-like shape facing each other. A thick portion 2 having a rectangular cross section is formed on each of the two sides so as to extend over each of the sides. That is, the two thick portions 2 are positioned with the thin portion 3 interposed therebetween.

A hollow portion 1a is formed in each thick portion 2, and a hollow portion 1b connecting the hollow portions 1a of both thick portions 2 is formed in the thin portion 3. The hollow portion 1a of one thick portion 2 (the thick portion 2 on the front side in the drawing) is directly connected to the pressurized fluid press-fitting portion 4 located in the thick portion 2 and is formed in the thin portion 3. One end of the hollow portion 1b is connected to the pressurized fluid press-fitting portion 4 via the hollow portion 1a of the thick portion 2 on the front side in the figure.

Next, a hollow injection molding method and a hollow injection molding die according to the present invention will be described with reference to FIGS. 7 and 1.

FIG. 7 shows a mold cavity 5 for molding the hollow injection-molded article shown in FIG.
Is a thick-walled part molding region, and 7 is a thin-walled part molding region.

The thick portion molding region 6 is a region for molding the thick portion 2 in the hollow injection molded product shown in FIG. 1, and the thin portion molding region 7 is also in the hollow injection molded product shown in FIG. This is a region for molding the thin portion 3.

The pressurizing fluid is press-fitted into the mold cavity 5 from the side end of the thin-walled molding region 7 opposite to the thick-walled molding region 6 side. It is Part 4.

On the surface of the mold cavity 5 in the thin-walled molding region 7, a position corresponding to a predetermined region A (see FIG. 1) extending from the pressurized fluid press-fitting portion 4 side to the thick-walled portion 2 is shown in FIG. Insulation 8 is provided as shown.

The heat insulating material 8 may have a lower thermal conductivity than the material constituting the mold and can withstand the temperature at the time of injection of the molten resin. For example, polyimide, epoxy resin, silicone resin, tetrafluoroethylene resin, Ceramic or the like can be used.

Hollow injection molding according to the present invention is performed as follows.

First, a predetermined amount of molten resin is injected into the mold cavity 5, and then a pressurized fluid is injected.

As the resin to be used, general thermoplastic resins used in general injection molding and extrusion molding can be used, but thermosetting resins can also be used. Further, various additives, fillers, fillers and the like can be added and used as necessary.

The pressurized fluid is a gaseous or liquid fluid at room temperature and atmospheric pressure that does not react or mix with the molten resin used for molding at the temperature and pressure of injection molding. For example, nitrogen gas, carbon dioxide gas, air, helium gas,
Glycerin, liquid paraffin, molten resin, etc., but an inert gas such as nitrogen gas is preferable. The pressure of the pressurized fluid is generally about 10 to 500 kg / cm ² .

The pressurizing fluid is injected at a timing after injection (full shot) of a sufficient amount of molten resin to fill the mold cavity 5 or an amount of molten resin insufficient to fill the mold cavity 5. Injection (short shot)
After.

In the case of full shot, as the molten resin cools and shrinks, the pressurized fluid is pressed in according to the amount of shrinkage. For short shots,
The pressurized fluid is pressed in according to the unfilled volume of the molten resin and the shrinkage amount of the resin.

In the case of a short shot, it is preferable to pressurize the pressurized fluid after filling 90% or more of the volume of the mold cavity 5 with the molten resin. If the unfilled volume is too large, it becomes difficult to form the hollow portion 1b at the predetermined position of the thin portion 3. In the case of a short shot, it is possible to pressurize the pressurized fluid while continuing the injection of the molten resin.

By the way, the heat insulating material 8 provided in the mold cavity 5 cools the molten resin filled in the area (predetermined area A in FIG. 1) where the heat insulating material 8 is provided in the thin portion forming area 7. Is delayed from the molten resin filled in another area (another area B in FIG. 1).
Therefore, the cooling of the molten resin in the predetermined region A extending from the pressurized fluid press-fitting portion 4 side to the thick portion molding region 6 is delayed from the cooling of the molten resin in the other region B in the thin portion forming region 7. It will be.

Since the pressurized fluid is press-fitted through a portion where it easily flows, it is an area in the thin portion molding area 7 where the heat insulating material 8 is provided, in which the cooling is delayed (predetermined area A). Will be guided into the molten resin in the thick-walled portion molding region 6 through the molten resin. Then, the pressurized fluid is guided through the predetermined region A in the thin portion molding region 7 to form the hollow portion 1b, and the pressurized fluid reaches the thick portion molding region 6 to form the hollow portion 1a. Become.

The heat insulating material 8 is provided from the side of the pressurizing fluid press-fitting portion 4 over the thick-walled portion molding region 6, but the pressurizing fluid press-fitting portion 4 is provided.
Also, even if it is not provided up to a position in contact with the thick-walled portion forming region 6, it is sufficient if it is provided up to the vicinity thereof. Further, the heat insulating material 8 can be provided not only on one mold side as shown in FIG. 7 but also on the other facing mold side to sandwich the thin portion molding region 7.

Instead of attaching the heat insulating material 8, a heat transfer material may be provided in an area other than the area where the heat insulating material 8 is provided.
That is, the cooling of the molten resin in the area where the heat transfer material is provided can be relatively delayed to delay the cooling of the molten resin in the area where the heat transfer material is not provided, that is, the predetermined area A described above. . In addition, the installation of this heat transfer material,
It can also be used together with the installation of the heat insulating material 8.

As the heat transfer material, any material may be used as long as it has a higher thermal conductivity than the mold constituent material and can withstand the temperature at the time of injection of the molten resin. For example, when the mold constituent material is carbon steel, aluminum or molybdenum. , Tungsten, magnesium, beryllium, copper, silver and the like and alloys thereof can be used.

Further, instead of attaching the heat insulating material 8, a partial heating means for heating the same area as the installation area of the heat insulating material 8 is provided, or conversely, a region other than the area provided with the heat insulating material 8 is provided. Partial cooling means for cooling the region may be provided, or both may be used together.

As the partial heating means, the mold cavity 5 is used.
Examples of the medium include a heating medium pipe for partially heating the surface of the and a high frequency dielectric heating device. Further, as the partial cooling means, a cooling medium pipe for partially cooling the surface of the mold cavity 5 can be mentioned. When these partial heating means and partial cooling means are used, it is preferable that the surface of the mold cavity 5 to be heated or cooled by the means is composed of the heat transfer material.

After pressurizing the pressurized fluid, after a predetermined holding time and completion of cooling, the pressurized fluid in the hollow portions 1a and 1b (see FIG. 1) may be discharged to take out the molded product.

[0047]

【Example】

Example 1 Using a hollow injection molding apparatus as shown in FIG. 8, a hollow injection molded product having a shape as shown in FIG. 5 was molded. As described above, the molded product has a thin plate-shaped thin portion 3 in the center and a thick portion 2 having a rectangular cross section at both sides, but as shown in FIG. 8, the thin portion 3 in FIG. As a result of injecting the molten resin and pressurizing the pressurized fluid from the central portion on the lower surface side, the pressurized fluid press-fitting portion 4 is formed at the central portion on the lower surface side of the thin portion 2 in FIG. 5, not at the position shown in FIG. It was

In FIG. 8, 8 is a heat insulating material of epoxy resin, and its installation position value is set to a predetermined area A shown in FIG.
Further, in FIG. 8, 9 is a pressurized fluid nozzle, 10 is an injection nozzle, and as shown in the drawing, the pressurized fluid was injected by the pressurized fluid nozzle 9 incorporated in the injection nozzle 10. Therefore, the pressurized fluid press-fitting position 4 is the gate portion.

The molding conditions are as follows.

Resin used: polystyrene (Asahi Kasei Kogyo's "# 400" colored black with carbon) Molding temperature: 220 ° C Injection time of molten resin: 1.74 sec (full shot) Pressurized fluid used: nitrogen gas Pressurized fluid press-in delay time (time from completion of injection until start of pressurization): 2 sec Pressurized fluid press-fit and hold time: 15 sec Cooling time: 30 sec

In the obtained hollow injection-molded article, the hollow portion 1a having a sufficient size was formed also in the thick portion 2, and no sink mark was observed in the thick portion 2.

The heat-insulating material 8 of the obtained hollow injection molded product
The back surface side of the portion corresponding to No. 1 had a completely uniform surface state, and no traces were found due to the installation of the heat insulating material 8 and the formation of the hollow portion 1b in the thin portion 3.

Example 2 In place of providing the heat insulating material 8 in the first embodiment, the embodiment is carried out except that a die provided with an aluminum heat transfer material is used in a region other than the region provided with the heat insulating material 8. The same hollow injection-molded article was molded in the same manner as in Example 1.

As a result, a good hollow injection-molded article similar to that of Example 1 was obtained.

Comparative Example 1 Instead of providing the heat insulating material 8 in Example 1, a rib-shaped guide channel extending from the pressurizing fluid press-fitting portion 4 to the thick portion 2 is provided, and a hollow as shown in FIG. 9 is provided. An injection-molded product was molded. In FIG. 9, 11 is a guide channel part.

In the obtained hollow injection-molded article, the hollow portion 1a of the thick portion 2 was smaller than the hollow portion 1a in Example 1, and the thin portion 2 was slightly sinked.

On the back surface side of the guide channel portion 11 of the obtained hollow injection molded product, a slight difference in surface roughness, glossiness and sharpness from the adjacent region was recognized, and the guide channel portion 11 was formed. Traces of things have occurred.

Examples 3 and 4 and Comparative Example 2 The resin used was ABS resin ("AT30" manufactured by Asahi Kasei Kogyo KK).
Then, the same molding was performed as in Examples 1 and 2 and Comparative Example 1 except that the molding temperature was 240 ° C. The obtained hollow injection molded articles were the same as those in Examples 1 and 2 and Comparative Example 1, respectively.

[0059]

The present invention is as described above and has the following effects.

(1) Since it is not necessary to form the rib-shaped guide channel 11 on the surface of the molded product from the pressurizing fluid press-fitting portion 4 to the thick portion 2, a hollow molded product having a good appearance can be obtained.

(2) No trace of the installation or formation of the hollow portion 1b appears on the back surface of the heat insulating material 8 on the installation side, and the surface condition of the obtained hollow injection molded product is improved.

(3) The hollow portion 1 having a sufficient size for the thick wall portion 2
Since a can be formed, the thick portion 2 is surely prevented from sinking.

(4) Since it is not necessary to consume extra resin for forming the thick portion of the guide channel 11, the amount of resin consumed can be saved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first example of a hollow injection-molded article according to the invention of claim 1.

2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a perspective view showing a second example of the hollow injection-molded article according to the invention of claim 1.

4 is a sectional view taken along the line IV-IV in FIG.

FIG. 5 is a perspective view showing a third example of the hollow injection-molded article according to the invention of claim 1.

6 is a sectional view taken along line VI-VI in FIG.

7 is a diagram showing a mold cavity for molding the hollow injection-molded article shown in FIG. 1. FIG.

FIG. 8 is an explanatory diagram of the hollow injection molding apparatus used in Example 1.

9 is a perspective view of a hollow injection-molded article molded in Comparative Example 1. FIG.

[Explanation of symbols]

 A predetermined region in thin-walled part molding region B region other than predetermined region in thin-walled part molding region 1a, 1b hollow part 2 thick part 3 thin part 4 pressurizing fluid press-fitting part 5 mold cavity 6 thick part molding region 7 thin part Molding area 8 Heat insulating material 9 Pressurized fluid nozzle 10 Injection nozzle 11 Induction channel section

Claims (3)

[Claims] 1. A hollow portion is formed in a thin portion integrally with a thick portion in which the hollow portion is formed, and one end of the hollow portion of the thin portion has a pressurized fluid press-fitting portion for forming the hollow portion. The hollow injection-molded article is characterized in that the other end is communicated with the hollow portion of the thick portion. 2. A hollow molding method using a hollow molding die in which a thin-walled molding region is arranged between a pressurizing fluid press-fitting position into a mold cavity and a thick-walled molding region to which the pressurized fluid is to be guided. In the molten resin injected into the thin portion molding region, cooling of the molten resin in a predetermined region extending from the pressurized fluid press-fitting portion side to the thick portion molding region is performed in the thin portion forming region. The hollow injection molding method is characterized by delaying the cooling of the molten resin in other regions. . 3. A hollow molding die in which a thin-walled molding region is located between a pressurizing fluid press-fitting position into a mold cavity and a thick-walled molding region to which the pressurized fluid is to be guided. A hollow injection molding die, wherein a heat insulating material for insulating a predetermined area extending from the pressurizing fluid press-fitting portion side to the thick portion molding area is provided on a die cavity surface of the area.