JPH09234760A - Resin molded product having boss or rib, injection molding apparatus and injection molding method thereof - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To eliminate a warp or distortion of a molded product having a boss or a rib and having a structure capable of preventing a sink from being generated in a resin molded product which is likely to cause a sink. Provided are an injection molding device and an injection molding method capable of performing highly accurate molding. SOLUTION: (1) In a resin molded product having a boss or a rib, a protrusion and a narrowed portion are provided around the boss or rib on the back surface side of the molded product. (2) In an injection molding device equipped with a means for injecting compressed gas into a mold, a compressed fluid injection port is provided on a mold cavity surface in the vicinity of a boss or rib on the back surface side of a molded product,
In addition, a concave portion and a convex portion are provided on the mold cavity surface around them. (3) Using the above injection molding apparatus, in a state where the molten resin filled in the mold cavity is being cooled and solidified,
Injection molding is performed by injecting compressed gas into the back surface side of the molded product in the cavity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molded product having a boss or a rib made of a thermoplastic resin, an injection molding apparatus and an injection molding method therefor, and manufacturing interior and exterior parts of automobiles, furniture, chairs, building materials, etc. Available when you do.

[0002]

2. Description of the Related Art Since a resin molded product obtained by injection molding has a unique molding shrinkage, a recessed portion on the surface of the molded product is caused by shrinkage of a portion such as a central portion of a boss or a rib or a thick wall portion where cooling is delayed, There was a so-called sink mark. In order to prevent this, in the conventional injection molding, it was done to prevent sink marks by applying excessive holding pressure to the resin injected into the mold cavity, but it is difficult to completely eliminate sink marks, rather than the boss. -There was a problem that warp deformation occurs due to excessive holding pressure applied to the surfaces other than the ribs and thick parts.

On the other hand, as a method for preventing sink marks without applying such an excessive holding pressure, Japanese Patent Laid-Open No. 50-75247.
There is known an injection molding method as disclosed in Japanese Patent Laid-Open No. 59-220337 and Japanese Patent Laid-Open No. 59-220337, in which a compressed fluid such as compressed air is pressed into the cavity to press the resin against the inner surface of the cavity to prevent sink marks.

[0004]

However, in Japanese Patent Application Laid-Open No. 50-75247, a valve rod is provided in a guide hole formed in a core, and pressure fluid (air) is injected from a gap portion opened and closed by advancing and retracting the valve rod. Therefore, a valve rod for injecting a pressure fluid and a control device for controlling its advance / retreat are required, which complicates the mold structure and increases the control factors during injection molding, which makes control difficult. is there.

On the other hand, in Japanese Unexamined Patent Publication No. 59-220337, a porous member having a plurality of through holes is embedded in a mold, and compressed air is sent through the through holes by an air control means. There is a problem in that it is difficult to perform a process for embedding in the surface, a method for fixing a porous member that can withstand the press-fitting pressure of compressed air, and the like, and it is necessary to manufacture the mold with high accuracy, which makes the manufacturing difficult. Moreover, since high-pressure compressed air is pressed into the surface of the molten resin, there is a risk of explosion of the compressed air due to expansion and heat. Furthermore, the compressed air press-fitted from the through holes of the porous member does not stay in the through holes of the porous member and escapes to the periphery thereof, so that there is a problem that the pressure holding effect of the compressed air is small.

The present invention relates to a molded product having bosses or ribs, which is likely to cause sink marks on the outer surface, and has a structure capable of preventing sink marks, an injection molding apparatus used for producing the molded product, and warpage or distortion of the molded product. It is an object of the present invention to provide an injection molding method that can eliminate the above and can perform molding with high precision.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, it was found that the following means can solve the problem. (1) A resin molded product having bosses or ribs, characterized in that it has a protrusion on the periphery of the boss or rib on the back surface side of the molded product. (2) The resin molded product according to (1) above, which further has a narrowed portion in the vicinity of the protrusion on the back surface side. (3) A device for producing a resin molded product having a boss or a rib by injection molding, which has means for injecting a compressed gas into a mold and corresponds to the boss or rib on the back surface side of the molded product. A compressed gas injection port is provided in the vicinity of the mold cavity surface, and the wall of the filling resin prevents diffusion of the compressed gas around the part corresponding to the boss or rib on the mold cavity surface and around the compressed gas injection port. An injection molding device for a resin molded product, which is provided with a concave portion for. (4) The injection molding apparatus for a resin molded product according to the above (3), wherein a convex portion is provided adjacent to the concave portion on the surface of the mold cavity and around the concave portion. (5) In the injection molding method using the injection molding apparatus according to the above (3) or (4), in a state where the molten resin filled in the mold cavity is cooling and solidifying, An injection molding method for a resin molded product, which comprises injecting a compressed gas into the back surface side.

[0008]

Embodiments of the present invention will be described below. The present invention mainly targets a molded product in which various bosses or ribs molded by an injection molding method are installed. The resin molded product having the boss or rib of the present invention is shown in FIG.
As shown in FIGS. 4 to 4, a protrusion 20 is provided around the boss or rib on the back surface side of the molded product 90, and a narrowed portion 21 is preferably provided further adjacent to the protrusion 20. To do. In the protrusion 20, when the molten resin filled in the mold cavity is cooling and solidifying, the compressed gas injected near the boss or rib on the back surface side of the molded product in the cavity does not leak to the periphery. It functions as a barrier. As a result, the compressed gas injected can be held near the boss or rib where sink marks are likely to occur, and the desired holding pressure can be maintained until the molten resin cools and solidifies. Moreover, when the molten resin is pressed against the mold cavity surface by the compressed gas, the narrowed portion 21 plays a role of blocking the molten resin in the vicinity of the protrusion 20 so as not to move further away from the boss or rib. Thus, the pressure holding effect is further improved. Since the molded product of the present invention is designed in such a structure, it is a molded product in which sink marks are reliably prevented.

The height of the protrusions 20 may be usually set in the range of 2 to 10 mm in consideration of the ability to retain compressed gas. The shape is not particularly limited, but a cross section having a triangular shape, a trapezoidal shape, a rectangular shape, or the like is preferable. The wall thickness t of the molded product of the narrowed portion 21 is usually 1 mm or more, and the ratio to the peripheral wall thickness is preferably 45 to 95%.
The range is more preferably 50 to 80%. If it is less than 45%, welds may occur, and if it exceeds 95%, a trace of compressed gas may remain. The shape of the narrowed portion 21 is not particularly limited, but a cross section having a triangular shape, a trapezoidal shape, a rectangular shape, or the like is preferable. In addition, the boss or rib may have a thickened portion formed at its base. This means that the back surface side of the molded product 90 is depressed by the amount that the sink mark on the front surface side is prevented. However, if the thickened portion is formed, the sinker lacking portion is replenished by the thickened portion, resulting in insufficient strength. It is speculated that this can be prevented.

The injection molding apparatus for resin molded products having bosses or ribs according to the present invention is provided with means for injecting compressed gas into the mold, and as shown in FIGS. Is provided with a compressed gas injection port 10 in the vicinity of the mold cavity surface corresponding to, and a portion of the mold cavity surface corresponding to the boss or rib and the periphery surrounding the compressed gas injection port are provided with a compressed resin gas injection wall. A concave portion 92 for preventing diffusion is provided, and preferably, a convex portion 94 is further provided adjacent to the concave portion of the mold cavity surface and surrounding the concave portion. This recess is a protrusion on the molded product,
The convex portion corresponds to the narrowed portion.

As means for injecting the compressed gas into the mold, for example, the clearance at the cavity side tip portion (portion opened to the cavity surface) of the ejection pin for releasing the molded product is 1/100 to 8 /. Is set to 100 mm,
Examples include those in which compressed gas is supplied into the cavity through this clearance, and those in which the porous member 40 is provided at the inlet of the injection port opened on the cavity surface and compressed gas is supplied into the cavity. The compressed gas inlet is provided in the mold cavity surface near the position corresponding to the boss or rib on the back surface side of the molded product. The distance may be appropriately selected depending on the shape of the molded product and the like.

The recess 92 forming the projection 20 of the molded product is
It holds compressed gas in the vicinity of them during molding so that the desired holding pressure can be maintained until the molten resin cools and solidifies, and the boss or rib and the above-mentioned compressed gas inlet are completely In addition to the case where the concave portion 92 is provided so as to be surrounded by, there is a gap in part (the concave portion 92 is interrupted)
In some cases, the recess 92 may be partially provided depending on the shape of the molded product. Particularly, as shown in FIG. 3, when the gas injection port 10 is provided only on one side of the rib 91, the rib 91 also functions as a barrier against the compressed gas, like the protrusion of the molded product. It is also possible to omit providing the concave portion so as to overlap the cavity surface in the vicinity thereof. The depth and shape of the recess correspond to the height and shape of the protrusion of the molded product, and the cross section is preferably triangular, trapezoidal, rectangular, or the like.

Further, the convex portion 94 of the mold cavity surface forming the narrowed portion 21 of the molded product is a melt that should form a barrier when the molten resin is pressed against the mold cavity surface by the compressed gas as described above. The resin serves to block the resin from moving to the remote side of the boss or rib, and is provided on the mold cavity surface at a position remote from the recess 92 and adjacent to the recess 92 as viewed from the boss or rib. . As described above, the gas injection port 10 is provided only on one side of the rib 91.
Since it is provided, when it is omitted to provide a concave portion overlapping the cavity surface in the vicinity thereof, the convex portion 94 of that portion is formed from the rib 91 as viewed from the gas inlet 10 as shown in FIG. It is provided on the mold cavity surface on the remote side and adjacent to the rib 91.

Similar to the concave portion 92, the convex portion 94 has a gap (a convex portion 94 is interrupted) in a part other than the case where it is provided so as to completely surround the boss or rib and the gas injection port.
In some cases, or depending on the shape of the molded product, the convex portion 94 may be partially provided. The height and shape of the convex portion correspond to the groove depth and shape of the drawn portion of the molded product, and the cross section is preferably triangular, trapezoidal, rectangular, or the like. As the compressed gas in the present invention, compressed air can be applied because it has a relatively low pressure, but compressed nitrogen gas is suitable in terms of safety and the like. The gas pressure may be selected within the range of 0.1 to 10 MPa.

The injection molding method of the present invention uses the above-mentioned injection molding apparatus, and in the state where the molten resin filled in the mold cavity is being cooled and solidified, the back surface of the molded article in the cavity is It is characterized in that a compressed gas is injected into the side. Hereinafter, the molding procedure will be described with reference to the schematic configuration diagram shown in FIG. (1) Using the injection molding machine 1, the resin plasticized and melted under the proper conditions for the resin properties to be used, as in normal injection molding,
The mold cavity 8 is filled. The resin pressure applied to the gas inlet increases as the molten resin is filled, but the gas inlet is not clogged because the pin clearance prevents the resin from flowing. (2) When a predetermined amount of molten resin is filled, the compressed gas supplied from the gas supply device 12 is injected into the mold through the injection port of the mold. Initially, the compressed gas is injected at a low pressure (typically 0.2 to 3 MPa) for a predetermined time (typically 0.2 to 3 seconds), and then at a high pressure (typically 3.5 to 10 MPa). ) For a predetermined time (as a typical value,
It is advisable to control such that the injection is performed for 2 seconds or more. Alternatively, the control may be performed in multiple stages.

Since the molten resin is still in a molten state at the stage of being cooled and solidified, even a low-pressure compressed gas is easily injected into the gap between the inner surface of the mold and the back surface side of the molded product in contact therewith, and the molded product. A space is formed between 90 and the mold 5. Next, when a high-pressure compressed gas is injected, the space is filled with the compressed gas and a sufficient holding pressure is applied to the molded article 90,
The front surface side of the molded product 90 is pressed against the inner surface of the cavity 8 of the mold 4. At this time, as shown in FIGS. 1 to 4, the compressed gas injected between the recessed grooves 19 (between the injection portion and the ribs or bosses of the molded product) and between the recessed portions (between the injection part and the protrusions of the molded product) is confined. As a result, the holding pressure is maintained at the rib or boss portion where sink marks are likely to occur. The convex portion 94 adjacent to the concave portion of the mold cavity surface prevents the molten resin from moving to the remote side of the boss or rib when the molten resin is pressed against the mold cavity surface by the compressed gas as described above. Since it is closed to the end, it becomes more effective to maintain the holding pressure, and a molded product with very few sink marks can be obtained.

Further, since the compressed gas injected in the initial stage is at a low pressure as described above, when the solidified layer on the resin surface in the initial stage of cooling is in a thin state, the solidified layer is broken by the pressure of the compressed gas and gas Does not hide inside the resin, and it is possible to manufacture a high-quality molded product free from problems such as reduction in strength. (3) When the molten resin is cooled and solidified, the cavity is degassed, the mold is opened, and the ejection pin is ejected to take out the molded product 90. The above molding cycle is repeated to sequentially manufacture molded products.

The present invention can be applied not only to molded products in which bosses or ribs are variously installed, but also to clips having partial thick-walled portions or those having no thick-walled portions. As an injection molding machine that can be used in the present invention, a molding machine having general specifications can be adopted as long as it can control the function of the mold.

Examples of resins that can be used include thermoplastic resins such as polyethylene, polypropylene, ABS, polycarbonate, and polyamide, or elastomers such as ethylene / α-olefin copolymer elastomers, talc, mica, and carbonic acid in addition to these thermoplastic resins. Examples thereof include those to which an inorganic filler such as calcium, glass fiber or carbon fiber is added. In most cases, polypropylene resin is used.

[0020]

EXAMPLES The present invention will be described below with reference to specific examples. [Embodiment 1] When a molded product made of a flat plate 90 having a single rib 91 as shown in FIGS. 1 and 4 is injection-molded, a structure having a projection and a narrowed portion on its outer peripheral portion is adopted.

The dimensions of the molded product are 250 mm in both length and width.
Then, the general thickness (d) other than the rib 91 is 2.5 mm,
The rib base thickness (e) is set to 2 mm. Protrusion 2
0 is located 30 mm apart along the rib and its height is 2 mm. Further, the narrowed portion 21 is installed along the rib on the outer periphery adjacent to the protrusion 20 at a narrowed ratio of 50% [(thickened portion thickness / general wall thickness) × 100 (%)]. Note that the ribs 91,
The thickness and the like of the plane plate 90 are illustrated to be larger than the actual size.

As the injection molding machine, IS-2 manufactured by Toshiba Machine Co., Ltd.
00 (mold clamping pressure: 200 ton) and a mold having a shape corresponding to the molded product (as shown in FIG. 1, it has a concave portion corresponding to the protrusion of the molded product and a convex portion corresponding to the narrowed portion. (Provided) is used to mold at a resin molding temperature of 200 ° C. and a mold temperature of 30 ° C. As compressed gas,
Nitrogen gas of 5 MPa was used.

The resin used has an MFR (melt flow ratio) of 10 g / 10 min (230 ° C., 2.16 k).
gf) block PP (polypropylene). The sink state of the flat surface portion was detected using a surface roughness meter (Surfcoder SE-30D manufactured by Kosaka Laboratory). As a result, the amount of sink marks was 1 μm or less, and the appearance was also good.

[Example 2] The same procedure as in Example 1 was carried out except that the above-mentioned aperture ratio was changed to 75%. As a result, the amount of sink marks was 1 μm or less, and the appearance was also good. [Example 3] The same operation as in Example 1 was carried out except that the above-mentioned aperture ratio was 90%. As a result, the amount of sink marks was 1 μm or less, and the appearance was also good.

[Example 4] The same procedure as in Example 1 was carried out except that the above-mentioned aperture ratio was 40%. The amount of sink marks was 1 μm or less. Welding was observed in the narrowed part. [Example 5] The same procedure as in Example 1 was carried out except that the above-mentioned aperture ratio was 100% (no aperture). Sink amount is 1 μm
It was below. On the back side, there was evidence that gas seemed to have dipped into the molded product.

[0026]

EFFECTS OF THE INVENTION The resin molded product having a boss or rib of the present invention is one in which a protrusion and, if necessary, a narrowed portion are provided around the boss or rib on the back surface side of the molded product, which corresponds to that. Molded in a cavity with a shaped mold and an injection molding device having a means for injecting compressed gas into the mold, while the molten resin filled in the mold cavity is cooling and solidifying. The compressed gas injected into the back surface side of the product is confined by the concave portions of the mold, and the convex portions further effectively hold the rib or boss portion, so that the occurrence of sink marks can be sufficiently prevented. In addition, in order to prevent sink marks by injecting compressed gas, it is not necessary to apply an excessive holding pressure to the molten resin injected into the cavity,
It is possible to perform injection molding at a relatively low pressure, eliminate warpage and distortion of the molded product, and mold with high precision.

According to the present invention, there is no need for a valve rod and a device for controlling the advance / retreat of the valve rod, and the die structure can be simplified, so that the die can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a mold and a molded product (with ribs) according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a mold and a molded product (with a boss) according to an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a mold and a molded product (having a porous member at an inlet) according to an embodiment of the present invention.

4A is a schematic plan view of a molded article according to an embodiment of the present invention, FIG. 4B is a schematic sectional view taken along line AA ′, and FIG. 4C is a schematic sectional view taken along line BB ′.

FIG. 5 is a schematic configuration diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1 ... Injection molding machine 4, 5 ... Mold 8 ... Cavity 10 ... Injection port 12 ... Gas supply device 19 ... Mold concave groove (corresponding to rib etc.) 20 .. -Projection 21 ... Drawing part (t is the thickness of the drawing part) 90 ... Molded product 91 ... Rib 92 ... Recess 93 ... Boss 94 ... Convex part

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Claims (5)

[Claims] 1. A resin molded product having a boss or a rib, wherein the resin molded product has a protrusion on the back surface side of the molded product, the protrusion surrounding the boss or the rib. 2. The resin molded product according to claim 1, further comprising a narrowed portion adjacent to the protrusion on the back surface side and around the protrusion. 3. An apparatus for producing a resin molded product having a boss or a rib by injection molding, comprising means for injecting a compressed gas into a mold, wherein the boss or rib on the back surface side of the molded product is A compressed gas injection port is provided on the corresponding mold cavity surface, and the compressed gas is diffused by the wall of the filling resin around the part corresponding to the boss or rib on the mold cavity surface and the periphery surrounding the compressed gas injection port. An injection molding device for a resin molded product, which is provided with a recess for preventing it. 4. The injection molding device for a resin molded article according to claim 3, wherein a convex portion is provided adjacent to the concave portion of the mold cavity surface and around the concave portion. 5. The injection molding method using the injection molding device according to claim 3, wherein the molten resin filled in the mold cavity is being cooled and solidified,
An injection molding method for a resin molded product, which comprises injecting compressed gas into the back surface side of the molded product in the cavity.