JP2005028731A - Manufacturing method of resin molded product having boss part and mold for use therein - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a resin molded product having a boss part capable of simultaneously preventing the sink and flash of the resin molded product without forming the bottomed opening part of the boss part as a thick-walled part, and a mold for use therein. <P>SOLUTION: This mold 20 has an upper mold 21 and a lower mold 22, and a tubular pin 23 and an inside pin 24 are arranged to the thick-walled part corresponding to the boss part of the upper mold 21. A gap 25 is formed between the tubular pin 23 and the inside pin 24 and a compressed gas is supplied from the gap 25 to prevent the sink of the resin molded product 30. Further, the tubular pin 23 and the inside pin 24 are arranged so that the leading ends of them are positionally aligned and, in the forming range in the height direction of the boss part 31, the inner diameter of the tubular pin 23 is made constant and the outer diameter of the inside pin 24 is made constant. Therefore, the thickness of the gap 25 is made constant in this range. By this constitution, the formation of flash to the resin molded product 30 is prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for molding a resin molded product having a boss portion and a mold used therefor.
[0002]
[Prior art]
When a resin molded product having a boss portion is molded by an injection molding method, sink marks are likely to occur in a partially thick portion such as the boss portion. Therefore, there is a problem that the appearance of the molded product is deteriorated or the dimensional accuracy is deteriorated. For example, when a resin molded product having a boss portion having a bottomed opening on the projecting surface is injection-molded, sink marks are likely to occur on the opposite side of the bottom surface of the boss portion from the bottom opening. Therefore, compressed gas is supplied to the bottom surface of the bottomed opening to prevent sink marks (for example, Japanese Patent Laid-Open No. 10-086169).
[0003]
The technique disclosed in the above publication will be specifically described with reference to FIG. A resin molded product is molded by injecting molten resin into a cavity 6 formed in a mold 10 having a lower mold 2 and an upper mold 1. In particular, the upper die 1 of the mold 10 has a shape corresponding to the boss portion of the resin molded product, and a thick portion for forming the boss portion is formed between the lower die 2 and the upper die 1. And the tubular pin 3 and the inner side pin 4 are arrange | positioned at this thick part, The bottomed opening part of a boss | hub part is formed with this tubular pin 3. As shown in FIG. Further, the tip 4 a of the inner pin 4 is provided at a position where the tip 4 a is withdrawn from the tip 3 a of the tubular pin 3. Further, a gap 5 is formed between the tubular pin 3 and the inner pin 4, and compressed gas is supplied from the gap 5 into the cavity 6 corresponding to the boss portion. In this way, by supplying the compressed gas from the gap 5 between the tubular pin 3 and the inner pin 2, it is possible to prevent the occurrence of sink marks on the side opposite to the bottom surface of the bottomed opening of the boss portion. . Furthermore, in the technique described in the above publication, the tip of the inner pin 4 is provided at a position where the tip of the inner pin 4 is withdrawn from the tip of the tubular pin 4, and by forming a thick portion on the bottom surface of the bottomed opening of the boss portion, It is possible to prevent the base portion of the boss portion from becoming thin and the strength from being lowered.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-086169
[Problems to be solved by the invention]
However, as disclosed in the above-mentioned Patent Document 1, when a method of forming a thick part on the bottom surface of the bottomed opening of the boss part is adopted, an extra portion is formed in the resin molded product, and the material The amount of use increases. Further, in order to form a thick part sufficient to suppress sink marks, it is necessary to obtain an optimum value of the thickness of the thick part. It is hard to avoid loss.
[0006]
Furthermore, the tip of the inner pin 4 disposed inside the tubular pin 3 forms a gap 5 with the tubular pin 3, but the gap 5 is formed between the tubular pin 3 and the inner pin 4. Only the tip portion 7 of the inner pin 4 is present, and the diameter of the inner pin 4 is reduced in other portions, and the gap 5 between the inner pin 4 and the tubular pin 3 is set large. For this reason, when the molten resin is injected into the mold, the molten resin enters the gap 5 between the tubular pin 3 and the inner pin 4 and burrs are likely to occur in the resin molded product.
[0007]
The present invention has been made in view of the above-described problem, and can prevent a sink and a burr of a resin molded product at the same time without making the bottomed opening of the boss part a thick wall part. It is an object of the present invention to provide a method for producing a resin molded product having a portion and a mold used therefor.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a method for producing a resin molded product having a boss portion according to the present invention is a method of manufacturing a resin molded product having a boss portion having a bottomed opening on a projecting surface and having a shape corresponding to the boss portion. A method of injecting molten resin forming the resin molded product into a mold and molding the mold, wherein the mold is disposed in a tubular pin disposed in the bottomed opening portion of the boss portion and a tube of the tubular pin. And when the molten resin is injected into the mold, compressed gas is supplied to the bottomed opening of the boss portion from the gap between the tubular pin and the inner pin. In the method of manufacturing a resin molded product that presses the bottom surface of the bottomed opening portion of the boss portion, the tubular pin and the inner pin are arranged such that one end side facing the bottom surface of the bottomed opening portion of the boss portion is aligned. And the inner pin Wherein the thickness of the gap between the tubular pin is constant in a range from the bottom opening bottom surface of the boss portion to the protruding surface of the boss portion.
[0009]
Furthermore, the mold of the present invention for solving the above-mentioned problems is a mold used when injection molding a resin molded product having a boss portion having a bottomed opening on a projecting surface, the boss The bottomed opening of the boss portion from a tubular pin disposed so as to fit in the bottomed opening of the portion, an inner pin disposed in a tube of the tubular pin, and a gap between the tubular pin and the inner pin In the mold having a supply means for supplying compressed gas to the bottom surface of the part, the tubular pin and the inner pin are arranged such that one end side facing the bottom surface of the bottomed opening of the boss part is aligned. And the thickness of the gap between the inner pin and the tubular pin is constant in the range from the bottom surface of the bottomed opening of the boss portion to the protruding surface of the boss portion. .
[0010]
In the present specification, the “projection surface of the boss part” means not the side peripheral surface or the inner peripheral surface of the boss part but the surface of the tip on the side where the boss part projects. In addition, “the bottom surface of the bottomed opening of the boss portion” refers to the bottom surface of the bottomed opening portion formed on the boss portion from the protruding surface side. In addition, the “range from the bottom surface of the bottomed opening of the boss portion to the protruding surface of the boss portion” simply means that the height of the boss portion is based on the bottom surface of the bottomed opening of the boss portion. It is a range.
[0011]
Patent Document 1 shown in the related art discloses a case in which the positions of the tip portions of the tubular pin 3 and the inner pin 4 are aligned as a comparative example. According to Patent Document 1, when the tips of the tubular pin 3 and the inner pin 4 are aligned, the supplied compressed gas leaks into the general surface from the bottom surface of the bottomed opening of the boss portion and It is described that, as the strength decreases, a slight depression is formed on the surface of the resin molded product. However, since such a problem greatly depends on the gas pressure when supplying the compressed gas, it is considered that the strength of the resin molded product and the formation of the dent can be solved by adjusting the pressure of the compressed gas. It is done. However, in the technique disclosed in Patent Document 1, since the gap between the inner pin and the tubular pin is set wide in a portion other than the tip portion of the inner pin, the pressure loss of the molten resin when passing through the gap As a result, the molten resin is presumed to easily enter the gap when the molten resin is injected into the mold.
[0012]
Therefore, as a result of diligent study, the present inventors have used a tubular pin and an inner pin as a mold to be used in a method for producing a resin molded product having a boss portion that prevents the sink of the resin molded product by compressed gas. One end side (front end side) facing the bottom of the bottomed opening of the boss of the resin molded product is aligned and the boss protrudes from the bottom of the bottomed opening of the boss of the resin molded product It has been found that the use of a pin having a constant thickness between the inner pin and the tubular pin in the range up to the surface can simultaneously prevent sink marks and burrs of the resin molded product.
[0013]
As described above, the inner pin and the tubular pin are arranged with the one end side facing the bottom of the bottomed opening of the boss of the resin molded product aligned to improve the strength of the bottom of the bottomed opening of the boss For this purpose, it is not necessary to form a thick part, and it is not necessary to obtain an optimum value of the thickness of the thick part. Furthermore, since the thickness of the gap between the inner pin and the tubular pin is constant in the range from the bottom of the bottomed opening of the boss portion of the resin molded product to the protruding surface of the boss portion, the molten resin is applied to the mold. When injected, a large pressure loss impedes the penetration of the molten resin into the gap. Moreover, in the technique shown in Patent Document 1, it is necessary to process the shape of the inner pin so that only the tip portion has a large diameter, and there is a problem that the processing is troublesome. Since the inner week surface of the pin and the outer peripheral surface of the inner pin may be formed with a constant diameter, there is an advantage that the inner pin can be easily processed.
[0014]
Furthermore, the present inventors can reduce the sink of the resin molded product by adjusting the ratio of the outer diameter of the tubular pin and the outer diameter of the inner pin when the tips of the tubular pin and the inner pin are aligned. It has been found that it is possible to prevent the formation of dents in the resin molded product. Specifically, when the outer diameter of the tubular pin is R and the outer diameter of the inner pin is r, the value of R / r is preferably 2.15 to 2.24, and more preferably 2.19. It should be ~ 2.23. In particular, when the tubular pin and the inner pin are arranged so that R / r = 2.23, the resin molded product can be prevented from sinking even if compressed gas is supplied, and the resin molded product has a dent. The formation can be suppressed.
[0015]
In this way, it is possible to prevent sink marks and dents formed in the resin molded product even when the tips of the tubular pin and the inner pin are aligned and set the optimum value for the thickness of the thick part It is more advantageous to arrange the tips of the tubular pin and the inner pin at the same position in that it does not need to be performed or an extra resin for forming the thick portion is not required. Furthermore, when the tips of the tubular pin and the inner pin are arranged at the same position, the molten resin can easily enter the gap between the tubular pin and the inner pin. Since it is constant in the range from the bottom surface of the bottomed opening of the part to the protruding surface of the boss part, it is possible to suppress the intrusion of the molten resin into the gap, resulting in the formation of burrs on the resin molded product. It can be suppressed.
[0016]
Furthermore, in the method for producing a resin molded product having a boss portion according to the present invention, the molten resin may be mainly composed of polypropylene. In the present invention, the “main body” refers to a substance having the highest content (for example, by mass%) in a target substance. When adopting a resin mainly composed of polypropylene as the molten resin, polypropylene has good fluidity, so if the molten resin is irradiated into the mold, burrs are likely to occur in the resin molded product, and the effects of the present invention are more effective. It becomes remarkable.
[0017]
Furthermore, the injection pressure of the compressed gas is preferably 2 MPa to 4 MPa. In order to prevent the occurrence of sink marks and burrs on the resin molded product, the method and the mold of the present invention are still effective, but even in that case, the compressed gas injection pressure is adjusted to an effective range. There is a need to. If the pressure of the compressed gas is less than 2 MPa, the occurrence of sink marks on the resin molded product cannot be sufficiently suppressed. On the other hand, if the injection pressure exceeds 4 MPa, the injection pressure is too large and the resin molded product is compressed. It becomes a factor by which the hollow resulting from gas is formed.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an example of a mold according to the present invention, and outlines a method for producing a resin molded product having a boss according to the present invention. FIG. 2 shows an example of a resin molded product that can be produced by the mold and method of the present invention. In the case of this embodiment, the resin molded product is a toilet seat made of polypropylene, and FIG. 2 shows an enlarged boss portion formed on the toilet seat. As shown in FIG. 2, a boss portion 31 having a bottomed opening 33 is formed in the base portion 32 of the resin molded product 30. The boss 31 has a cylindrical shape, and the bottomed opening 33 is a cylindrical space.
[0019]
When the resin molded product 30 as shown in FIG. 2 is manufactured, as shown in FIG. 1, molten resin to be a resin molded product is injected into a mold 20 having a cavity 26 having a shape corresponding to the shape of the resin molded product 30. Can be obtained. The mold 20 includes an upper mold 21 and a lower mold 22. The upper die 21 is formed with a cylindrical thick portion so as to correspond to the boss portion 31 of the resin molded product 30, and the tubular pin 23 is arranged so as to be inserted into the thick portion. The tubular pin 23 has a diameter corresponding to the inner diameter of the boss portion 31 of the resin molded product 30 formed by injection molding, and the upper mold so as to correspond to the length of the boss portion 31 from the protruding surface 35 of the boss portion 31. It protrudes from 21 and is arrange | positioned. Further, an inner pin 24 is disposed in the tube of the tubular pin 23. The distal ends of the tubular pin 23 and the inner pin 24 are arranged at the same position. In other words, the inner pin 24 is not positioned to be retracted or protruded from the tip of the tubular pin 23. Further, a gap 25 is formed between the tubular pin 23 and the inner pin 24 so that compressed gas from a supply means (not shown) can be supplied. The gap 25 has a thickness from the protruding surface 35 side of the boss portion 31 (corresponding to the upper end surface 26a of the cavity 26) to the bottomed opening bottom surface 34 side of the boss portion 31 (tubular pin 23 and inner pin 24). In the range corresponding to the front end surface 26b of the head). Specifically, the inner diameter of the tubular pin 23 is constant within the above range, the outer diameter of the inner pin 24 is constant within the above range, and the thickness of the gap 25 is constant. In the case of this embodiment, the lower mold 22 has a shape corresponding to the surface opposite to the side on which the boss portion 31 of the resin molded product 30 is formed.
[0020]
In the present embodiment, the thickness of the gap 25 formed between the tubular pin 23 and the inner pin 24 is 10 to 50 μm. If the thickness of the gap 25 is 10 μm or less, a larger injection pressure is required to supply sufficient compressed gas to prevent the resin molded product 30 from sinking due to pressure loss in the gap 25. It is not preferable. On the other hand, if the thickness of the gap 25 is 50 μm or more, it is not preferable because the molten resin easily enters the gap 25.
[0021]
In order to prevent the occurrence of sink marks and burrs on the resin molded product 30, it is effective to adjust the ratio between the outer diameter (R) of the tubular pin 23 and the outer diameter (r) of the inner pin 24. Specifically, the value of R / r is preferably in the range of 2.15 to 2.24, and more preferably in the range of 2.19 to 2.23. In particular, R / r = 2.23 is preferable.
[0022]
Hereinafter, a procedure for molding a resin molded product by an injection molding method using the above-described mold 20 will be described. First, molten resin to be a resin molded product 30 is injected and filled into the cavity 26 of the mold 20 arranged as shown in FIG. In the present embodiment, polypropylene is used as the molten resin, but other thermoplastic resins such as polyethylene, ABS, polycarbonate, and polyamide can be used.
[0023]
After the filling of the molten resin into the cavity 26 is started, the compressed gas is supplied from the gap 25 to the bottom surface 34 of the bottomed opening 33 of the boss portion when the filling is completed or in the vicinity thereof. As the compressed gas, dry air, nitrogen gas, or the like can be used, but it is particularly preferable to use nitrogen gas in consideration of reactivity with the molten resin. Thereby, the base 32 of the boss part 31 is pressed against the lower mold 22 by the compressed gas, and sink marks generated at the base 32 of the boss part 31 can be prevented. The injection pressure of the compressed gas can be in the range of 2 MPa to 4 MPa. If the injection pressure of the compressed gas is less than 2 MPa, sink marks cannot be sufficiently prevented. On the other hand, if the injection pressure of the compressed gas exceeds 4 MPa, the injection pressure is too large and the resin molded product 30 is indented. Is easily formed. The timing for supplying the compressed gas is determined in advance, and the compressed gas is supplied after a preset time from the start of injection of the molten resin. This can be realized by setting an optimal injection timing of the compressed gas in advance in the timer of the injection molding apparatus. The injection timing of the compressed gas can be generally 10 to 20 seconds after the start of injection of the molten resin.
[0024]
Thereafter, the molten resin is cooled and solidified by holding the compressed gas for a certain period of time. Here, since the compressed gas is continuously supplied until the molten resin is cooled and solidified, the sink of the resin molded product can be prevented. Furthermore, since the molten resin does not easily enter the gap 25 by the configuration of the present invention, the formation of burrs on the resin molded product can be suppressed. The holding time of the compressed gas can be generally 30 to 50 seconds.
[0025]
In the present embodiment as described above, by supplying the compressed gas, it is possible to prevent sinking on the surface of the boss portion 31 opposite to the bottomed opening bottom surface 34 and to prevent the boss portion 31 from being present. Since no thick portion is provided in the bottom opening 33, there is no time loss in setting the optimum value of the thickness of the thick portion. Furthermore, since the thickness of the gap 25 for supplying the compressed gas is constant in the formation region of the boss portion 31 in the height direction of the boss portion 31, it is difficult for the molten resin to enter the gap 25. As a result, it is possible to prevent burrs from being formed on the resin molded product.
[0026]
【Example】
Hereinafter, specific examples of the present invention will be described. The resin molded product is a toilet toilet seat made of polypropylene, and a boss portion is formed on the surface opposite to the seat surface of the tip portion. The outer diameter of the boss is 7 mm, and the inner diameter is 3.35 mm. The height of the boss is 12 mm from the bottom of the bottomed opening of the boss.
[0027]
On the other hand, the tubular pin forming the bottomed opening of the boss part has an outer diameter of 3.35 mm, which is the same as the inner diameter of the boss part, and an inner diameter of 1.52 mm. Further, the outer diameter of the inner pin arranged in the tube of the tubular pin is 1.5 mm. A gap is formed between the tubular pin and the inner pin, and the thickness of the gap is 20 μm. Therefore, the relationship between the outer diameter (diameter: R) of the tubular pin and the outer diameter (diameter: r) of the inner pin is R / r = 2.23.
[0028]
As molding conditions for the resin molded product, the temperature of the molten resin is 195 ° C., the temperature of the mold is 50 ° C., the injection time is 13 seconds, and the cooling time is 40 seconds. The compressed gas injection conditions are as follows: the compressed gas injection pressure is 3 MPa; the compressed gas injection timing is 11 seconds after the start of filling with the molten resin; and the compressed gas holding time is 40 seconds. When the molten resin is cooled and solidified, the pressure is released and the mold is opened and taken out from the resin molded product mold.
[0029]
As described above, in the formed resin molded product, a surface opposite to the bottom surface of the bottomed opening portion of the boss portion was observed, and formation of burrs on the bottom surface of the bottomed opening portion of the boss portion was observed. As a result, no sink marks occurred on the surface of the boss portion opposite to the bottom surface of the bottomed opening, and no burr occurred on the bottom surface of the bottomed opening of the boss portion.
[0030]
【The invention's effect】
As described above, in the method for producing a resin molded product having a boss portion according to the present invention, a resin molded product having a boss portion having a bottomed opening on a protruding surface is placed in a mold having a shape corresponding to the boss portion. A method in which a molten resin forming a resin molded product is injected and molded, and the mold has a tubular pin disposed in the bottomed opening of the boss portion and an inner pin disposed in the tube of the tubular pin When the molten resin is injected into the mold, compressed gas is supplied from the gap between the tubular pin and the inner pin to the bottomed opening of the boss, and the bottom of the bottomed opening of the boss is pressed. In the method for producing a resin molded product, the tubular pin and the inner pin are arranged such that one end side facing the bottom surface of the bottomed opening of the boss portion is aligned, and the thickness of the gap between the inner pin and the tubular pin is From the bottom of the bottomed opening of the boss to the protruding surface of the boss Since there is a constant in the range, without a bottom opening of the boss portion and the thick portion, it is possible to prevent the resin molded article sink marks and burrs at the same time.
[0031]
Furthermore, the mold of the present invention is a mold used when injection molding a resin molded product having a boss portion having a bottomed opening on the projecting surface, and is fitted into the bottomed opening of the boss. A tubular pin disposed so as to fit together, an inner pin disposed within the tube of the tubular pin, and a supply means for supplying compressed gas to the bottom surface of the bottomed opening of the boss portion from the gap between the tubular pin and the inner pin , The tubular pin and the inner pin are arranged such that one end side facing the bottom surface of the bottomed opening portion of the boss portion is aligned, and the boss portion protrudes from the bottom surface of the bottomed opening portion of the boss portion. Since the thickness of the gap between the inner pin and the tubular pin is constant in the range up to the surface, without making the bottomed opening of the boss part thick, Can be prevented at the same time.
[Brief description of the drawings]
FIG. 1 shows an example of a mold according to the present invention and a view for explaining a method for producing a resin molded product having a boss according to the present invention.
FIG. 2 is an enlarged view showing an example of a resin molded product molded according to the present invention.
FIG. 3 is a view for explaining a conventional method for producing a resin molded product having a boss portion together with a mold to be used.
[Explanation of symbols]
20 Mold 23 Tubular pin 24 Inner pin 25 Gap 30 Resin molded product 31 Boss part 32 Base part 33 Bottomed opening part 34 Bottomed opening part bottom face 35 Projection surface

Claims (4)

A method of molding a resin molded product having a boss portion having a bottomed opening on a projecting surface by injecting a molten resin forming the resin molded product into a mold having a shape corresponding to the boss portion, The mold has a tubular pin arranged in the bottomed opening of the boss part and an inner pin arranged in a tube of the tubular pin, and when the molten resin is injected into the mold In the method of manufacturing a resin molded product for supplying compressed gas to the bottomed opening of the boss portion from the gap between the tubular pin and the inner pin and pressing the bottom surface of the bottomed opening of the boss portion,
The tubular pin and the inner pin are arranged such that one end side of the boss portion facing the bottom surface of the bottomed opening is aligned, and the thickness of the gap between the inner pin and the tubular pin is the boss. A method for producing a resin molded product having a boss portion, characterized in that the surface is constant in a range from the bottom surface of the bottomed opening to the protruding surface of the boss portion. The method for producing a resin molded product having a boss portion according to claim 1, wherein the molten resin is mainly composed of polypropylene. The method for producing a resin molded product according to claim 2, wherein an injection pressure of the compressed gas is 2 MPa to 4 MPa. A mold used when injection molding a resin molded product having a boss portion having a bottomed opening on a protruding surface,
A tubular pin arranged to fit into the bottomed opening of the boss,
An inner pin disposed within the tube of the tubular pin;
In a mold having supply means for supplying compressed gas to a bottom surface of the bottomed opening of the boss portion from a gap between the tubular pin and the inner pin,
The tubular pin and the inner pin are arranged such that one end side facing the bottom surface of the bottomed opening portion of the boss portion is aligned, and the boss portion protrudes from the bottom surface of the bottomed opening portion of the boss portion. A method for producing a resin molded article having a boss portion, characterized in that a thickness of a gap between the inner pin and the tubular pin is constant in a range up to a surface.

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