JP2009255349A - Gas pressure injection molding method and injection molded body molded by this method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas pressure injection molding method for obtaining an injection molded body having no sink on a design surface, flat and smooth surface, and high-quality appearance, and an injection molded body molded by the method. <P>SOLUTION: The gas pressure injection molding method includes a step of pressing a pressurized gas between a back surface (non-design surface) of the injection molded body and a mold cavity corresponding thereto after injecting a thermoplastic resin in the mold cavity as a molten resin, and pressing the surface (design surface) of the injection molded body to the mold cavity surface (design side mold surface) corresponding thereto. The method includes (a) a step of raising the temperature of the mold cavity surface to a temperature 0-30°C higher than the glass transition temperature of the thermoplastic resin before injecting the molten resin into the mold cavity surface, and (b) a step of cooling the injection molded body by lowering the temperature of the mold cavity surface 20°C or lower than the glass transition temperature of the thermoplastic resin. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas pressure injection molding method for obtaining an injection molded body having a design surface, a smooth surface and a high quality appearance, and an injection molded body molded by the method.

Conventionally, sink marks that occur on the surface (hereinafter also referred to as a design surface) of a molded body having bosses and ribs on the back surface (hereinafter also referred to as a non-design surface) are prevented, and the surface appearance is improved. A method to make it is being studied. For example, in Patent Document 1, after the molten resin is injected after setting the temperature of the mold cavity surface to a temperature slightly lower than the Vicat softening point of the resin to be molded, the non-design surface of the molded body and the corresponding mold Gas pressure injection molding method to prevent sink marks that occur on the design surface due to resin shrinkage and to obtain a molded product with excellent appearance by cooling the molded product while injecting pressurized gas between the mold cavity surfaces Is disclosed. Further, in Patent Document 2, injection molding is performed by setting the temperature of the mold cavity surface by high frequency induction heating before molding to a temperature at which the elastic modulus of the resin is reduced to 1/3 or less at room temperature, and cooling. In the same way as described above, a gas pressure injection molding method is disclosed in which a pressurized gas is pressed between a non-design surface of a molded body and a mold cavity to obtain a molded body having no sink and excellent appearance. Yes.
As another method for obtaining a molded article having a high-quality appearance, Patent Document 3 discloses that a heating medium (for example, water vapor) and a cooling medium (for example, water) are selectively allowed to flow through a mold cavity cooling hole. Discloses a method for controlling the temperature of the mold cavity in the molding process. Specifically, the temperature of the mold cavity surface is raised to a temperature 0-100 ° C. higher than the resin deflection temperature before injection molding and injected, and after molding, a temperature 10 ° C.-100 ° C. lower than the deflection temperature under load. And a method of taking out a molded body by cooling, that is, a method of injection molding by raising and lowering the mold cavity temperature in the molding step.

JP-A-11-314241 Japanese Patent Laid-Open No. 06-254924 Japanese Patent Laid-Open No. 10-100196

However, in the method disclosed in Patent Document 1, although the sink mark on the design surface is improved, the temperature of the mold cavity surface is low, and it has a high-quality appearance that completely solves weld lines, jetting, flow marks, and the like. It is difficult to obtain a molded body. In the method disclosed in Patent Document 2, an inductor is used to heat the mold cavity by induction heating. However, it is difficult to design the shape of the inductor coil to achieve uniform heating, and uneven heating of the mold cavity can be avoided. Absent. In addition, application to a molded body having a complicated shape, for example, a case-shaped molded body having a deep depth, has a problem that it is difficult in principle for the reasons described above. Furthermore, since only the mold surface on the design surface side is heated, the resin orientation strain remaining on the surface of the molded body of the design surface and the non-design surface is different, and the occurrence of warpage cannot be suppressed depending on the shape of the molded body.
In the method disclosed in Patent Document 3, molding having a high-quality appearance is performed only when the temperature of the mold cavity surface is set to be equal to or higher than the glass transition temperature of the resin (approximately 20 ° C. higher than the deflection temperature under load of the resin). The body is obtained, but the problem of sink marks on the bosses and ribs has not been improved. In addition, by using a gas assist molding method in combination, that is, by inserting a high-pressure gas into a portion that tends to cause sink marks such as bosses and ribs, sink marks can be partially suppressed. It is effective only for the part of the molded body containing gas, and is not technically sufficient.

  In view of the above circumstances, the problem to be solved by the present invention is a gas pressure injection molding method and method for obtaining an injection molded body having a smooth surface and a high quality appearance without sinking on the design surface. It is to provide an injection-molded body molded by the above method.

  Therefore, as a result of intensive studies to solve the above problems, the present inventor injected the thermoplastic resin into the mold cavity as a molten resin, and then corresponds to the back surface (non-design surface) of the injection molded body. Gas injection including the step of press-fitting a pressurized gas between the mold cavity surfaces (non-design side mold surfaces) and pressing the surface of the injection molded body (design surface) against the corresponding mold cavity surface (design side mold surface) (A) Before injecting molten resin into a mold cavity, the temperature of the mold cavity surface is raised to a temperature higher by 0 to 30 ° C. than the glass transition temperature of the thermoplastic resin. And (b) after completion of injection of the molten resin, cooling the injection molded body by lowering the temperature of the mold cavity surface to a temperature that is 20 ° C. lower than the glass transition temperature of the thermoplastic resin; By injection molding method including No sink marks on the entire Takumi surface, smooth surface, and a molded article having an appearance of high quality has led to the completion of the present invention found that stably obtained.

That is, the present invention is as follows.
[1]
After injecting the thermoplastic resin into the mold cavity as a molten resin, pressurize the pressurized gas between the back surface (non-design surface) of the injection molded body and the corresponding mold cavity surface (non-design side mold surface). A gas pressure injection molding method including a step of pressing a surface (design surface) of an injection molded body against a corresponding mold cavity surface (design side mold surface),
(A) before injecting the molten resin into the mold cavity, raising the temperature of the mold cavity surface to a temperature 0-30 ° C. higher than the glass transition temperature of the thermoplastic resin;
(B) after completion of injection of the molten resin, cooling the injection molded body by lowering the temperature of the mold cavity surface to a temperature lower by 20 ° C. or more than the glass transition temperature of the thermoplastic resin;
Including injection molding.
[2]
The injection molding method according to [1] above, wherein the thermoplastic resin is an amorphous thermoplastic resin.
[3]
An injection molded article molded by the injection molding method according to the above [1] or [2].

By the gas pressure injection molding method of the present invention, it is possible to obtain a molded product having a design appearance, a smooth surface, and a high quality appearance free from weld lines, flow marks and the like.
The gas pressure injection molding method of the present invention includes filler reinforcing fillers such as glass fibers, carbon fibers, and glass flakes, filler reinforcing resins added with other fillers, chemical foaming agents, and foaming resins added with physical foaming agents. It can be applied to other injection molding. Even when the injection molding method of the present invention is applied to these resins, there is no sink on the design surface, the surface of the filler is floated, the surface is smooth without swirl marks, and there are no weld lines, flow marks, etc. A molded product having a high-quality appearance can be stably obtained.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  First, an apparatus used for the gas pressure injection molding method of the present embodiment (hereinafter also simply referred to as the molding method of the present embodiment) will be described. In the following FIGS. 1-3, an example of the metal mold | die used with the shaping | molding method of this Embodiment is shown. 1 to 3, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 shows an example of a mold and a mold temperature controller used in the molding method of the present embodiment. As shown in FIG. 1, the mold 1 includes a fixed mold 1a and a movable mold 1b, and an ejector pin 6 that projects an injection-molded body after the injection molding is arranged is disposed on the movable mold 1b. The mold 1 also has mold cavity temperature adjusting cooling holes 8a and 8b, and the heating medium and the cooling medium controlled by the mold temperature controller 11 selectively flow, so that the mold cavity surface in the molding process is The temperature is adjusted.

  The mold temperature controller 11 includes a heating medium supply source 12 that supplies a heating medium (for example, water vapor) to raise the temperature of the mold cavity surface, and a temperature (cooling) of the mold cavity surface. It has the cooling medium supply source 13 which supplies a cooling medium (for example, water), and the control apparatus which controls operation | movement of a heating medium supply source and a cooling medium supply source.

  The portions constituting the mold cavity surfaces 2a and 2b have a nested structure in order to improve the heat efficiency of the heating and cooling medium, and the nested structure is thermally insulated from the mold body through the heat insulating layers 5a and 5b. Is preferred. In addition, the mold cavity temperature adjusting cooling holes 8a and 8b are also preferably installed as close to the mold cavity surface as possible from the viewpoint of efficiently raising and lowering the mold cavity surface.

  The molded body formed by the mold 1 has a non-design surface having thick ribs 3 and a design surface that is the opposite surface, and the non-design surface is a mold cavity surface 2b (non-surface) on the movable mold 1b side. The design surface is molded with the mold cavity surface 2a (design side mold surface) on the fixed mold 1a side. Here, the design surface may be formed by the mold cavity surface 2b on the movable mold 1b side, and the non-design surface may be formed by the mold cavity surface 2b of the fixed mold 1a. The thick rib 3 may be a thick boss.

  A gas injection path 9 is formed in the movable mold 1b, and gas is supplied from the pressurized gas source to the gas injection path 9. Further, the movable mold 1b is provided with a pressurized gas press-fitting pin 4 having a tip facing the mold cavity 2. As shown in FIGS. 2 (a) and 2 (b), the press-fit pin 4 has a shape in which the cross-section of the tip is a part of a circle, and a clearance c is formed between the press-fit pin 4 and the movable die 1b. Has been. The clearance does not allow the molten resin to flow back and enter, but the pressurized gas can pass through. Specifically, a clearance of 0.01 to 0.05 mm is provided. Pressurized gas supplied from the pressurization source passes through the clearance between the press-fit pin 4 and the movable mold 1 b and is press-fitted into the mold cavity 2. In order to prevent gas backflow leakage, the press-fit pin 4 is provided with a sealing material 7a. As the sealing material 7a, it is preferable to use a heat-resistant O-ring made of nitrile-butadiene rubber or the like. FIG. 3 shows an example of the structure of the pressurized gas press-fit pin 4. Further, in order to prevent leakage of gas press-fitted into the mold cavity 2, a seal material 7b is also provided in the clearance between the ejector pin 6 and the movable mold 1b.

  Further, if the sealing performance of the parting surface of the mold 1 is high, air in the mold cavity 2 before injection of the molten resin, gas generated from the molten resin, a part of the pressurized gas, etc. stay on the design surface side. The sink on the design surface side corresponding to the thick rib 3 may not be sufficiently improved. In order to prevent this, a degassing vent groove 10 (a slit that is large enough to allow gas to pass through, although molten resin cannot enter) is provided on the parting surfaces of the fixed mold 1a and the movable mold 1b. It is preferable to keep it open to the atmosphere.

[Gas pressure injection molding method]
Next, the gas pressure injection molding method of this embodiment implemented using the above apparatus will be described using symbols in the drawings.

  In the gas pressure injection molding method of the present embodiment, a thermoplastic resin is injected into the mold cavity as a molten resin, and then the back surface (non-design surface) of the injection-molded product and the corresponding mold cavity surface (non-design) A gas pressure injection molding method including a step of pressing a pressurized gas between side mold surfaces) and pressing a surface of the injection molded body (design surface) against a corresponding mold cavity surface (design side mold surface). (A) before injecting the molten resin into the mold cavity, raising the temperature of the mold cavity surface to a temperature 0-30 ° C. higher than the glass transition temperature of the thermoplastic resin; And a step of cooling the injection-molded product by lowering the temperature of the mold cavity surface to a temperature lower by 20 ° C. or more than the glass transition temperature of the thermoplastic resin after the injection of the molten resin.

  In the molding method of the present embodiment, the resin viscosity immediately after injection is obtained by injecting the molten resin in a state where the temperature of the mold cavity surface is raised to a temperature 0 to 30 ° C. higher than the glass transition temperature of the thermoplastic resin. Of the gas pressure to be pressed from the non-design surface for preventing sink of the design surface in the gas press-fitting step described later. Therefore, compared to the conventional gas pressure injection molding method that molds at a mold cavity temperature lower than the Vicat softening point of the resin, the design surface has a lower gas pressure, no sink, smooth surface, and excellent appearance. Can be obtained.

  Step (a) is a step of raising the temperature of the mold cavity surface to a temperature higher by 0 to 30 ° C. than the glass transition temperature of the thermoplastic resin before injecting the molten resin into the mold cavity.

  In the molding method of the present embodiment, the temperature of the mold cavity surface before injection molding is raised to a temperature that is 0 to 30 ° C., preferably 10 to 20 ° C. higher than the glass transition temperature of the thermoplastic resin. is important. When the temperature of the mold cavity surface before injection is lower than the glass transition temperature of the thermoplastic resin, the effect of the gas pressure pressed from the non-design surface in the gas press-in process described later is small, and the sink on the design surface is not sufficiently suppressed. There is a fear. Further, since it becomes difficult to completely prevent weld lines, flow marks, etc., the appearance tends to deteriorate. Conversely, if the temperature of the mold cavity surface before injection exceeds 30 ° C. higher than the glass transition temperature of the thermoplastic resin, heat loss unnecessary for heating and cooling the mold occurs, and the mold cavity surface The cooling time of the product tends to be long and the productivity of the molded product tends to be reduced. The temperature of the mold cavity surface before injection is particularly preferably raised to a temperature 10 to 20 ° C. higher than the glass transition temperature of the thermoplastic resin from the viewpoint of efficiently obtaining a molded article having a good appearance.

  The temperature control of the mold cavity surface is performed by a mold temperature controller 11 including a heating medium supply source 12 and a cooling medium supply source 13. In this step, a heating medium (for example, water vapor) is passed through the mold cavity cooling holes 8a and 8b to raise the temperature of the mold cavity surfaces 2a and 2b.

  After raising the temperature of the mold cavity surface (after step (a)), a thermoplastic resin is injected into the mold cavity 2 as a molten resin. The injection amount of the molten resin is preferably an amount sufficient to fill the volume of the mold cavity 2. Further, when injecting the molten resin, it is preferable that a sufficient holding pressure is applied in the cavity. By sufficiently applying the injection holding pressure, the adhesion between the resin and the mold cavity surfaces 2a and 2b is increased, and the pressure holding property of the gas layer described later tends to be improved.

  Immediately after the injection of the molten resin, preferably before applying a holding pressure, a pressurized gas is injected through the clearance between the gas injection pin 4 and the movable mold 1b (gas injection step). As a result, a gas layer made of pressurized gas is formed in the gap between the molten resin injected into the mold cavity 2 and the mold cavity surface 2b. The sealing material 7b provided in the clearance between the ejector pin 6 and the movable die 1b helps to maintain the pressure of the gas layer.

  This gas layer formed on the projecting side (non-design surface side) of the thick rib 3 of the molded body has a mold cavity on the opposite surface, that is, the design surface side of the molded body while the molten resin is cooled and solidified. Press continuously against surface 2a. At this time, as shown in FIG. 4, the base of the rib 3 is squeezed by the pressure of the pressurized gas, whereby the molten resin in the vicinity of the rib 3 flows, and the design surface corresponding to the rib 3 further becomes the mold cavity surface. 2a. This can prevent the design surface from sinking due to the volume contraction of the rib 3. FIG. 5 shows an example of a molded body molded by a normal molding method in which no pressurized gas is injected. The design surface on the opposite side corresponding to the thick rib 3 is sinked due to the shrinkage of the thick rib 3 in the cooling process, and the appearance is poor.

  In general, the effect of preventing sink marks in the gas pressure injection molding method largely depends on the thickness of the resin solidified layer on the surface of the rib 3 of the molded body and the resin viscosity inside the rib 3 at the time of pressurizing the pressurized gas. In the molding method of the present embodiment, the temperature of the mold cavity surface is raised to a temperature 0 to 30 ° C. higher than the glass transition temperature of the thermoplastic resin, and the molten resin is injected, so that the rib 3 immediately after the injection is finished. The resin solidified layer on the surface becomes thin and soft, and the resin viscosity inside the rib 3 is kept sufficiently low. Therefore, compared with the conventional method of molding at a mold cavity temperature that is 20 ° C. or more lower than the glass transition temperature of the resin, it is possible to obtain a good sink prevention effect at a lower gas pressure.

  After the pressurization of the pressurized gas, the pressure of the gas layer formed on the non-design surface side of the molded body is maintained to some extent, but the pressure decreases with time. The magnitude of the pressure in the gas layer and the pressure drop speed affect the occurrence of appearance sink marks and the appearance. As a matter of course, if the high pressure gas layer can be maintained for a long time, the sinking prevention effect is enhanced. Therefore, like the mold 1 shown in FIG. 1, it is preferable to use a highly airtight mold in which the sealing materials 7a and 7b are installed in the movable mold 1b so that the pressurized gas does not leak.

  The rate of pressure drop of the gas layer varies greatly depending on the airtightness of the mold 1, the type of resin used, molding conditions, and the like. In the molding method of the present embodiment, the resin and the mold cavity surfaces 2a and 2b are injected by injecting the molten resin in a state where the temperature of the mold cavity surface is 0 to 30 ° C. higher than the glass transition temperature of the thermoplastic resin. Since the adhesion to the gas layer becomes higher, the pressure retention of the gas layer becomes better. Therefore, it is possible to prevent the sink of the design surface even with a gas pressure that is less than half that of the conventional method of molding at a mold cavity temperature that is 20 ° C. lower than the glass transition temperature of the resin.

  The pressure of the pressurized gas varies depending on the type of resin, the shape of the thick rib 3 of the molded body, the plate thickness, and the like, but is usually 1 to 15 MPa, preferably 3 to 10 MPa. The timing for pressurizing the pressurized gas into the mold cavity 2 is preferably immediately after the molten resin is sufficiently filled in the mold cavity 2. Further, in order to prevent leakage of the pressurized gas, it is effective to press the molded body against the design surface side with the pressurized gas and simultaneously apply resin holding pressure to replenish the resin. The pressurized gas that can be used in the molding method of the present embodiment is not particularly limited, and nitrogen, air, carbon dioxide gas, and the like can be used. Among them, it is preferable to use an inert gas such as nitrogen.

  Step (b) is a step of cooling the injection molded body by lowering the temperature of the mold cavity surface to a temperature lower by 20 ° C. or more than the glass transition temperature of the thermoplastic resin after the injection of the molten resin.

  After injecting the molten resin, the supply of the heating medium is stopped, the cooling medium is promptly flowed from the cooling medium supply source 13 to the mold cavity cooling holes 8a and 8b, and the mold cavity surfaces 2a and 2b are passed through the glass transition temperature of the thermoplastic resin. Then, the temperature is lowered to a temperature lower by 20 ° C. or more, preferably 30 ° C. or more, and the molded body is sufficiently cooled, and then the molded body is taken out from the mold.

  Here, the temperature of the mold cavity surface in step (b) is defined as a temperature that is 20 ° C. or more lower than the glass transition temperature of the thermoplastic resin because the deflection temperature under load of most of the non-crystalline resin is the glass transition temperature. This is because it is about 20 ° C. lower than the temperature, and if the molded body is taken out of the mold at a temperature lower than this, deformation due to insufficient cooling of the molded body can be suppressed.

  Further, after the molded body is taken out from the mold, supply of the cooling medium from the cooling medium supply source 13 to the mold cavity cooling holes 8a and 8b is stopped, and the heating medium is transferred from the heating medium supply source 12 to the mold cavity cooling hole. The temperature of the mold cavity surface 2a and 2b is started to flow through 8a and 8b, and the temperature of the mold cavity surface is raised to a temperature 0 ° C to 30 ° C higher than the glass transition temperature of the thermoplastic resin, The molding method of the present embodiment can be carried out continuously.

  The thermoplastic resin injected into the mold cavity as a molten resin is not particularly limited, but is preferably an amorphous thermoplastic resin (hereinafter also referred to as an amorphous resin). Amorphous resins tend to be more effective in preventing sinking due to pressurized gas because they do not undergo a sudden change in viscosity until the resin solidification point (glass transition temperature) during the cooling process after resin injection, and maintain a rubber elastic state. It is in. On the other hand, when the resin reaches a temperature below the melting temperature (more precisely, the recrystallization temperature) during the cooling process, the surface of the molded body suddenly becomes hard due to crystallization, and sudden shrinkage is caused accordingly. Because it begins, it may be substantially difficult to prevent sinking with pressurized gas.

  Examples of the amorphous thermoplastic resin include rubber-reinforced styrene resins such as polystyrene (PS) and high impact polystyrene (HIPS), styrene-acrylonitrile copolymer (SAN resin), acrylonitrile-butyl acrylate rubber-styrene. Copolymer (AAS resin), for example, ABS resin such as acrylonitrile-butadiene-styrene copolymer, acrylonitrile-methylmethacryl-butadiene-styrene copolymer, PC resin such as polycarbonate (PC resin), PC / ABS, Examples thereof include acrylic resins such as polymethyl methacrylate (PMMA resin), modified polyferylene nylene ether (modified PPE resin), and the like. The thermoplastic resin may be a polymer alloy. For example, the above-mentioned PC / ABS resin, a modified PPE resin modified with styrene, a PMMA / ABS resin, a PC / PS resin, or the like is preferably used.

  In the molding method of the present embodiment, for example, when an amorphous ABS resin having a glass transition temperature of 110 ° C. (for example, acrylonitrile-butadiene-styrene copolymer) is used as the thermoplastic resin, the step (a) The temperature of the mold cavity surface before the resin injection is preferably 120 to 130 ° C., and the temperature of the mold cavity surface in the cooling step after the resin injection in the step (b) is preferably 50 ° C. or less.

  The thermoplastic resin used in the molding method of the present embodiment may contain various additives. For example, elastomers, plasticizers, foaming agents, stabilizers, antistatic agents, ultraviolet absorbers, flame retardants, colorants, mold release agents and fibrous reinforcing agents such as glass fibers, potassium titanate whiskers, zinc oxide whiskers, Can optionally contain fillers such as glass beads, glass flakes, mica, calcium carbonate, talc and the like.

  When filler-reinforced resin added with fillers such as glass fiber, carbon fiber, glass flakes, and other fillers is molded by the usual molding method, the float of the filler on the surface of the molded body is inevitable and the surface is smooth. Moreover, it is difficult to obtain a molded body having an excellent appearance. However, according to the molding method of the present embodiment, the temperature of the mold cavity surface is raised to a temperature 0 to 30 ° C. higher than the glass transition temperature of the thermoplastic resin before injecting the molten resin. Because the resin is injected into the mold cavity, the resin in contact with the mold cavity surface is sufficiently soft, and the resin pressure due to the injection pressure suppresses the floating of the filler on the surface of the molded body, and the mold cavity surface is transferred well. It is possible to obtain a molded body having a smooth surface and a high quality appearance.

  In general, when foaming resin is injection-molded, surface roughness that occurs on the surface of the molded product due to the blowing of foaming gas in the process of molten resin flowing in the mold cavity, so-called swirl marks, occurs on the surface of the molded product. However, also in this case, according to the molding method of the present embodiment, a molded body having a smooth surface and a high quality appearance can be obtained by the same mechanism as described above. In the case of injection molding of foamable resin, the inside of the mold cavity is previously pressurized with nitrogen or compressed air before injection in order to prevent the gas from being blown when the molten resin flows through the mold cavity. Is preferred.

Examples and comparative examples that specifically describe the present embodiment will be exemplified below, but the present embodiment is not limited to the following examples unless it exceeds the gist.
The molding conditions in the examples and the evaluation method of the injection-molded body are as follows.
(1) Molding conditions Injection molding machine: SG220 manufactured by Sumitomo Heavy Industries, Ltd.
Resin injection secondary pressure (holding pressure): 80% of injection primary pressure
Control of mold cavity temperature: Use high-pressure steam for temperature rise and water for temperature drop Pressurized gas injection conditions Gas used: Nitrogen Gas pressure: 5 MPa
Gas injection timing, time: 5 sec immediately after injection
Gas pressure release: 40 seconds after the end of injection (2) Sink depth of molded product: Maximum value of design surface (H portion) corresponding to rib shown in FIG.
Device name: “SURFTEST500” manufactured by Mitutoyo
Detector: Diamond needle contact sensor (conical 90 °)
Tip radius of curvature: 5 μm
(Measurement condition)
Scanning speed: 2mm / sec
Scanning distance: 4mm
(3) 60 ° glossiness of molded product: ASTM D523-67
Measuring machine: Digital variable angle gloss type “UGV-5K” manufactured by Suga Test Instruments Co., Ltd.

  FIG. 6 shows a perspective view of an injection molded body obtained in the following examples and comparative examples. The injection-molded body has a size of 300 mm × 200 mm × 30 mm, a plate thickness of 2.5 mm, and a rib with a thickness of 2.0 mm on the non-design part (back surface).

(Examples 1 and 2 and Comparative Examples 1 to 4)
1 was molded using the thermoplastic resin and molding conditions shown in Table 1 to obtain a molded body shown in FIG. In all Examples and Comparative Examples, immediately after injection of the molten resin, pressurized gas was injected from three locations (A in FIG. 6) surrounded by the ribs on the non-design surface. The depth of sink marks on the design surface (H part in FIG. 6) of the obtained molded body was measured using the measuring instrument and conditions described above, and used as a measure of surface smoothness. Further, the 60 ° gloss (glossiness) of the design surface of the molded body was measured and used as a measure of the beauty of the surface appearance. The measurement results are shown in Table 1.

As is clear from the results in Table 1, the molten resin was injected in a state where the temperature of the mold cavity surface was raised to a temperature 10 ° C. higher than the glass transition temperature of the resin. The molded bodies of Examples 1 and 2 formed by lowering (cooling) the temperature to a temperature lower by 50 ° C. than the glass transition temperature of the resin have a small design surface sink (shrink depth is shallow), and the surface. It was smooth and had a high 60 ° glossiness and a high quality appearance.
On the other hand, the molded bodies of Comparative Examples 1 and 2 in which gas pressure injection molding was performed in a state where the temperature of the mold cavity surface was kept constant at a temperature lower by 50 ° C. than the glass transition temperature of the resin were the same as those of Examples 1 and 2. Compared to the molded body, the design surface sink was large and the 60 ° gloss was also low. In particular, Example 2 and Comparative Example 2 used a filler-reinforced resin, and thus there was a large difference in sink depth and 60 ° gloss.
Also, without performing the gas pressurization process, the mold cavity surface temperature is 10 ° C higher than the glass transition temperature at the time of resin injection, and 50 ° C lower than the glass transition temperature of the resin at the time of cooling. Although the molded articles of Comparative Examples 3 and 4 that were molded had a 60 ° glossiness comparable to that of Examples 1 and 2, the sink depth was significantly larger than that of Examples 1 and 2.

  The molded body (with ribs) obtained by the gas pressure injection molding method of the present invention has no sink, has a smooth surface, and has an excellent appearance. In particular, an OA device that requires a beautiful appearance. The present invention has industrial applicability as a housing, a front cover or a housing of a flat panel display.

An example of a mold and a mold temperature controller used in the gas pressure injection molding method of the present embodiment is shown. An example of the form of the clearance of the front-end | tip of the pressurization gas press-fit pin of the metal mold | die used with the gas pressurization injection molding method of this Embodiment is shown. An example of the shape of the pressurization gas press-fit pin of the metal mold | die used with the gas pressurization injection molding method of this Embodiment is shown. The one aspect | mode of the molded object at the time of press-fitting pressurized gas to the rib part of a non-design surface is shown. The one aspect | mode of the molded object when not press-fitting pressurized gas to the rib part of a non-design surface is shown. An example of the injection-molded body of the present embodiment is shown.

Explanation of symbols

1: Mold 1a: Fixed mold 1b: Movable mold 2: Mold cavity 2a: Design side mold cavity surface 2b: Non-design side mold cavity surface 3: Thick ribs 4: Pressurized gas press-fit pins 5a, 5b: Thermal insulation layer 6: Ejector pin 7a, 7b: Sealing material 8a, 8b: Mold cavity cooling hole 9: Gas injection path 10: Vent groove on parting surface 11: Mold temperature controller 12: Heating medium supply source 13: Cooling Medium supply source c: Notch groove A: Pressurized gas pressure inlet H part: Sink mark of molded body on opposite surface of rib

Claims (3)

After injecting the thermoplastic resin into the mold cavity as a molten resin, pressurize the pressurized gas between the back surface (non-design surface) of the injection molded body and the corresponding mold cavity surface (non-design side mold surface). A gas pressure injection molding method including a step of pressing a surface (design surface) of an injection molded body against a corresponding mold cavity surface (design side mold surface),
(A) before injecting the molten resin into the mold cavity, raising the temperature of the mold cavity surface to a temperature 0-30 ° C. higher than the glass transition temperature of the thermoplastic resin;
(B) after completion of injection of the molten resin, cooling the injection molded body by lowering the temperature of the mold cavity surface to a temperature lower by 20 ° C. or more than the glass transition temperature of the thermoplastic resin;
Including injection molding.   The injection molding method according to claim 1, wherein the thermoplastic resin is an amorphous thermoplastic resin.   An injection molded article molded by the injection molding method according to claim 1 or 2.