JP2000037744A - Injection molding method for generating micro pores in wall thickness of plastic product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high appearance quality-product wherein a transferability is raised, unevenness in generating pores is removed, and stiffness is raised in a method for injection molding of a molded product having pores in a wall thickness. SOLUTION: When a resin is filled in a cavity 4 in which a molded product 8 is to be molded in injection molding, a movable sub-mold 3 is advanced to reduce a volume in the cavity 4. Just after forming a skin layer 10, the movable sub-mold 3 is retreated to restore a volume in the cavity 4 to a last volume of the molded product 8, and a pressure in the cavity 4 is reduced. Thereby, micro pores 9 can be generated uniformly in a wall thickness enclosed by the skin layer 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for producing fine pores in the thickness of a plastic product.

[0002]

2. Description of the Related Art In injection molding of plastic products, lightening and thinning of molded products are being promoted for reasons such as cost reduction of products. As a known technique for obtaining such a lightweight and thin molded product, a foam molding method for forming minute pores within the thickness of the molded product is known.

In this method, a resin to which a foaming agent is added is filled in a mold cavity and molded, whereby the foaming agent is foamed in the cavity to generate minute pores in the thickness of a molded product. This is a technique for obtaining a lightweight molded product. However, in this method, when the thickness of the molded product is small, the generation of pores is not sufficient, or a portion that does not foam is formed depending on the shape of the molded product, and the generation of pores is uneven inside the molded product. In addition, the appearance of the molded article obtained by this is not entirely smooth, and appearance defects similar to jetting or silver, which are called swirl marks, occur.

Further, in the case of the molding method using this foaming agent, a strain due to residual stress is generated in the molded product due to a pressure gradient generated when the resin is filled in the cavity, and the molded product is warped or formed. However, there is a problem that sufficient pores are not generated within the thickness of the steel. Such poor appearance of the foamed molded product is mainly used to reduce the filling amount of the resin in the mold cavity or to reduce the filling pressure and the holding pressure in order to increase the generation rate of pores, and to perform molding. This is a defect caused by gasification of the foaming agent on the surface of the molded article. In addition, the filling pressure of the molded product is higher in the resin pressure near the gate than in the flow end portion of the molded product, and this phenomenon appears particularly remarkably when the molded product has a small thickness, and reaches below the foaming gas pressure. Up to this point, there is a problem that unevenness occurs due to the internal pressure, and as a result, uneven foaming occurs in the entire molded article, thereby causing warpage.

[0005] As a method for improving the appearance defect of the foam molded article, there is a method called gas counter pressure. This is because, in order to suppress foaming on the surface of the molded article, an inert gas of about several kg / cm ² or the like is previously injected into the cavity, and foaming on the resin surface where the resin pressure decreases is suppressed. This is the method of applying the minimum pressure. However, although this method can prevent poor appearance due to foaming on the surface of the molded product, it does not uniformly foam the entire thickness of the molded product and cannot uniformly generate pores throughout the molded product. Also, the residual stress after filling cannot be reduced.

On the other hand, in order to improve the rigidity of the molded article, carbon fibers, glass fibers, beads, and the like are often added to the resin as fillers. Appear, and the appearance quality is significantly reduced. Further, the molded article formed in this way has a problem that warping and twisting are likely to occur due to the orientation of the filler, and the quality and reliability of the molded article are significantly impaired.

According to the present invention, the resin is filled in a state where the volume in the cavity is reduced in advance, the pressure in the cavity is increased by applying sufficient pressure to the resin in the cavity, and the volume in the cavity is increased immediately after the skin layer is formed. By depressurizing the inside, the fine pores are uniformly generated within the thickness of the molded product, achieving the purpose of weight reduction, further improving the appearance quality, and distorting,
It is an object of the present invention to provide an injection molding method for obtaining a molded article free from warpage or the like.

[0008]

In order to solve the above problems, according to the first aspect of the present invention, in the injection molding of a plastic product having minute pores in the wall thickness, the volume in the cavity is reduced in advance. The resin is filled in the cavity in a state in which the cavity layer is formed, and immediately after the skin layer is formed in the cavity, the volume in the cavity is returned to the volume for molding the final molded product, and the pressure in the cavity is reduced by reducing the pressure. It is characterized in that minute pores are generated within the thickness of the molded product.

Further, in the invention according to claim 2,
The invention according to claim 1 is characterized in that molding is performed using a resin to which a foaming agent has been added.

Further, in the invention according to claim 3,
The invention according to claim 1 is characterized in that molding is performed using a resin to which an organic / inorganic filler is added.

Further, in the invention described in claim 4,
The invention according to claim 1 is characterized in that molding is performed using a resin to which a foaming material and a filler are added.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The injection molding method according to the present invention makes it possible to produce fine pores evenly in the thickness of a molded product, and at the same time, to enhance the transferability so that it can be used as an external part. It is possible to provide a plastic molded product with low distortion and no warpage. That is, according to the present invention, a movable portion capable of reducing the volume in the cavity is provided in advance in a part of the cavity, and when filling the resin, the movable portion is driven to reduce the volume in the cavity. Is reduced. Then, the resin is filled, and immediately after the skin layer is formed, the movable portion is retracted to return the volume (pressure) in the cavity to the final molded product position, so that the volume in the cavity is filled with the resin. It is something that expands.

At this time, inside the cavity, there is a skin layer formed on the cavity wall surface between the fixed side and the movable side, and a molten resin layer surrounded by the skin layer. The internal pressure of the bed decreases rapidly. As a result, the skin layer transfers and forms the mold surface, while fine pores are generated in the molten resin layer.
As a result, a molded article having fine pores between the high transfer skin layer and the wall thickness can be obtained. At this time, if the resin contains a foaming material, the generation rate of pores can be increased.

Further, since the pressure is reduced after the formation of the skin layer and pores are generated, swirl marks due to the foaming agent are not generated on the surface of the skin layer, and a high quality appearance is obtained. Also, since the cavity pressure is extremely low,
Residual stress caused by uneven filling pressure of the resin is also eliminated, and a molded product with extremely low distortion, no warpage, and high transfer can be obtained.

According to the present invention, at the time of filling the resin, a movable portion which operates to reduce the volume in the cavity is provided to fill the resin, and after the filling is completed, the movable portion is formed immediately after the skin layer is formed. It is necessary to move the movable part to the final molded article position about 1.0 second after the filling is completed, and more preferably, to increase the volume in the cavity. In addition, if necessary, the compressed resin of the sprue portion and the runner portion may flow into the cavity via the gate after the filling is completed, and in order to prevent this, a shut-off mechanism that operates after the filling is completed by the gate. The sprue portion or the runner portion may be provided in the sprue portion or the runner portion.

[0016]

Embodiment 1 An embodiment of the present invention will be described in detail with reference to the mold sectional views of FIGS. 1 (a), 1 (b) and 1 (c). First,
As shown in FIG. 1 (a), the fixed side main mold 1, the movable side main mold 2, and the movable side sub-type (movable part) 3 of the mold have a smaller thickness (a smaller volume) than the required molded product shape. (Small) cavity 4 is formed.

Next, as shown in FIG. 1B, a resin 7 is filled into the cavity 4 through a sprue 5 and a runner 6, and the cavity 4 is filled with the resin 7. At this time, the cavity surface of the mold is sufficiently transferred into the cavity 4 by the pressure at the time of filling.

Next, as shown in FIG. 1C, immediately after the skin layer 10 is formed, the movable part sub-mold 3 is retracted to the final shape position of the molded product requiring the sub-mold 3, and the volume in the cavity 4 is enlarged. Let it. As a result, the pressure in the cavity 4 is reduced, and fine pores 9 are generated in the molded product portion.

A more specific embodiment will be described in detail with reference to FIG. FIG. 2A is a diagram schematically illustrating a cross section of a mold and a molded product. The cavity 4 has a thickness of 1.
0 mm, length 300 mm, width 30 mm. In addition, the average value (Ra) of the mold surface roughness of the cavity 4 is 0.1 mm.
30 μm. The temperature of the mold having the cavity 4 is heated to 60 ° C., and a polypropylene resin (MK811 manufactured by Showa Denko KK) and a molding machine (Toshiba Machine IS-350) are used.
EW) for injection molding. The molding condition was a resin temperature of 225 ° C., and the filling time in the cavity 4 was 0.4.
Seconds. Movable part sub mold 3 0.4 seconds after completion of resin filling
Was moved by 1.0 mm. After moving the movable part sub-mold 3, the resin is cooled while being fixed, and the mold is opened to form the molded product 8.
Was taken out. The molded article 8 was left at room temperature 22 ° C. for 2 days, and evaluated.

As shown in FIG. 3, when the warpage a of the obtained molded product 8 was measured, it was 0.1 mm. Further, in the cross section of the molded product 8, fine pores 9 with no variation could be formed both at the gate portion and at the end of the molded product 8. The average value of the surface roughness of the molded product 8 is 0.3
The transfer rate to the die surface (here, the transfer rate was (molded article roughness / mold surface roughness) × 100) was 96.7%. The density of the molded article 8 is 0.60 g /
cm ³ . It should be noted that the warpage a shown in FIG. 3 is exaggerated in the amount of warpage as compared with the actual warp dimension on the drawing.

[0021]

Comparative Example 1 Using the same mold, resin and molding machine as in Example 1, the movable part sub-mold 3 was moved 1.0 mm in advance before filling the resin, the cavity thickness was set to 2.0 mm, and after filling, Injection molding was performed under the same conditions as in Example 1 except that the movement was not performed.

When the warpage a of the obtained molded product was measured, it was 1.0 mm. Further, the surface roughness of the molded product is 0.1.
The transfer rate to the mold surface was 31%. No pores were found in the cross section of the molded product. The density of the molded product was 0.93 g / cm ³ .

[0023]

Example 2 In Example 1, the polypropylene resin (MK811 manufactured by Showa Denko KK) used had a weight of 100.
Using the same mold and molding machine as in Example 1 except that the resin to which the azodicarponamide-based foaming agent (Polyslen EE-506, trade name, manufactured by Eiwa Chemical Industry Co., Ltd.) was added in a weight of 4 was used. Injection molding was performed.

As a result, the warpage a of the obtained molded article 8 was measured (0.1 mm. In addition, fine pores 9 having no variation were formed at both the gate and the end of the molded article. The density of the obtained molded product 8 was about 0.49 g / cm ³ , and the average value of the surface roughness of the molded product 8 was 0.31 μm. The transfer rate for this was 96.7%.

[0025]

Comparative Example 2 Using the same mold, resin, and molding machine as in Example 2, the movable part sub-mold 3 was moved 1.0 mm in advance before filling the resin, the cavity thickness was set to 2.0 mm, and after filling. Injection molding was performed under the same conditions as in Example 2 except that the movement was not performed.

As a result, the warpage a of the obtained molded product was measured and found to be 1.0 mm. Further, fine irregularities were generated on the surface of the molded product 8 by swirl marks. As a result, the average value of the surface of the molded product was 0.95 μm, and the transfer rate to the mold surface was 31%. . Further, uniform pores were not formed in the cross section of the molded product, and as a result, the density of the molded product was about 0.83 g / cm ³ .

[0027]

Example 3 In Example 1, a resin to be used was a polyamide resin containing 30% of carbon filler (TLP1021 manufactured by Toray Industries, Inc.), and injection filling was performed. The molding condition is a resin temperature of 285 ° C., and the filling time into the cavity 4 is 0.4 seconds. Injection molding was performed using the same mold and molding machine as in Example 1 except that the movable part sub-mold 3 was moved 1.0 mm after 0.4 seconds of resin filling.

As a result, the warpage a of the obtained molded product 8 was 0.1 mm. Also, fine pores 9 could be formed in the cross section of the molded product 8. The surface roughness of the molded product 8 was 0.32 μm, and the transfer rate to the die surface was 93.7%. The density of the molded product 8 is 0.6
It was 9 g / cm ³ .

[0029]

Comparative Example 3 Using the same mold, resin, and molding machine as in Example 3, the movable sub-mold 3 was moved 1.0 mm in advance before filling the resin, the cavity thickness was set to 2.0 mm, and after filling. Injection molding was performed under the same conditions as in Example 3 except that the movement was not performed.

As a result, the warpage a of the molded product was 1.2 mm. No pores were formed in the cross section of the molded product. The surface roughness of the molded product was 1.66 μm, and the transfer rate to the mold surface was 18%. Further, the surface of the molded product was found to be embossed by the filler. The density of the molded article is l. It was 44 g / cm ³ . The density of the molded product was 1.25 g / cm ³ .

[0031]

Example 4 In Example 1, a resin used was a 30% carbon filler resin and 100 parts of a polyamide resin (TLP1021 manufactured by Toray Industries, Inc.) and 100 parts of a bicarbonate foaming material (Serpon TSC-, trade name of Eiwa Chemical Co., Ltd.). 4
4) Injection molding was performed using the same mold and molding machine as in the example except that 3 parts were used.

As a result, the warpage a of the molded product 8 is equal to 0. lmm
Met. Further, in the cross section of the molded product 8, fine pores 9 could be formed. Further, the density of the obtained molded article 8 was about 0.60 g / cm ³ . The surface roughness of the molded product 8 was 0.32 μm, and the transfer rate to the mold surface was 93.7%.

[0033]

Comparative Example 4 Using the same mold, resin, and molding machine as in Example 4, the movable part sub-mold 4 was moved 1.0 mm in advance before filling the resin, the cavity thickness was set to 2.0 mm, and after filling. Injection molding was performed under the same conditions as in Example 4 except that the movement was not performed.

As a result, the warpage a of the molded product was 1.2 mm
Met. Mainly, the surface roughness of the molded product is l. 85 μm
And the transfer rate to the mold surface was 16%.
Further, on the surface of the molded product, the rising of the filler and swirl marks were observed. Also, uniform pores are not formed in the cross section of the molded product, and as a result, the density of the molded product is 1.2.
It was 0 g / cm ³ .

[0035]

[Table 1]

[0036]

According to the present invention, when filling the resin, the volume in the cavity is reduced, and immediately after the skin layer is formed, the volume in the cavity is returned to the final molding volume and injection molding is performed. Thereby, minute pores can be generated evenly between the skin layers of the molded article. As a result,
High transfer, no swirl marks, distortion, warpage, etc.
High quality molded products can be obtained. As a result, the molded article molded by the method of the present invention can be used as an external part, and has the effect of increasing the rigidity as compared with the conventional molding method using a foaming agent.

[Brief description of the drawings]

1A and 1B are cross-sectional views of a mold according to the present invention, wherein FIG. 1A is a cross-sectional view of a cavity before resin filling, FIG. 1B is a cross-sectional view of the cavity immediately after resin filling, and FIG. FIG. 4 is a cross-sectional view of the cavity after the movement.

FIG. 2A is a cross-sectional view of a cavity immediately after resin filling in an example, and FIG. 2B is a cross-sectional view of a cavity immediately after resin filling in a comparative example after moving a movable part sub-type in the example.

FIG. 3 is a schematic diagram at the time of measuring a molded product warpage.

[Explanation of symbols]

 1 Fixed-side main mold 2 Movable-side main mold 3 Movable-side sub-type 4 Cavity 5 Sprue 6 Runner 7 Resin 8 Molded product 9 Pores 10 Skin layer

Continued on the front page F term (reference) 4F202 AA11 AA29 AB02 AB11 AB16 AB19 AG20 CA11 CB01 CB30 CK19 CK52 4F206 AA11 AA29 AB02 AB11 AB16 AB19 AG20 JA07 JB30 JM05 JN22 JN25 JQ81

Claims (4)

[Claims] In an injection molding of a plastic product having minute pores in a thickness, a resin is filled in a cavity in a state where the volume in the cavity is reduced in advance.
Next, immediately after the skin layer is formed in the cavity, the volume in the cavity is returned to the volume for molding the final molded product, and the inside of the cavity is decompressed, so that minute pores are formed in the thickness of the molded product. Injection molding method to produce 2. The injection molding method according to claim 1, wherein the molding is performed using a resin to which a foaming agent is added. 3. The injection molding method according to claim 1, wherein the molding is performed using a resin to which an organic / inorganic filler is added. 4. The injection molding method according to claim 1, wherein the molding is performed using a resin to which a foaming material and a filler are added.