JP2013035149A - Injection molding method of synthetic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding method of a synthetic resin, which uses a molding die with uncomplicated structure and prevents the occurrence of weld mark, thereby preventing deterioration in appearance and strength or the occurrence of stress cracking of the product, and which provides the product tinted with metallic color tone, little affected by the weld mark thereby free from deterioration in the appearance.SOLUTION: The synthetic resin 15 to be injection-molded is injected into a cavity of the die and the occurrence of the weld mark is prevented by pressing and compressing a molten synthetic resin part in a position where the weld mark is caused by the collision of a plurality of the flows of the molten synthetic resin in the die and fusing the plurality of the flows of the molten synthetic resin 15.

Description

  The present invention relates to a synthetic resin injection molding method, and more particularly, to a synthetic resin injection molding method containing metallic particles.

  Synthetic resin molded products used in home appliances and automobiles are mass-produced by an injection molding method, and some are used by improving the appearance by spray painting. However, a coating method without painting is desired because of high coating costs and environmental pollution caused by organic solvents.

  Therefore, by changing the compounding ratio of metal material particles and colorants and molding conditions, or by performing injection molding by improving the mold, molded products with a metallic appearance can be prevented. The manufacturing method of this is proposed. For example, the following patent documents 1-3 are mentioned.

  In the invention disclosed in Patent Document 1, the ratio of aluminum flakes and thermoplastic resin is changed, and aluminum flakes are kneaded in a relatively large proportion, so that the frequency of contact between aluminum during kneading is increased, and aluminum flakes and The present invention relates to a method for producing a molded article having a metallic appearance by reducing deformation and damage of aluminum flakes by reducing contact with a hard thermoplastic resin such as polycarbonate. In Patent Literature 2, aluminum powder, interference pearl mica, and thermoplastic resin are blended at a predetermined ratio, and further, by adding a coloring material, the same flip-flop metallic feeling as a coated product (the hue changes depending on the direction of the line of sight) This is related to the production of a molded article having a visible appearance.

  In Patent Document 3, a mixture of magnetic metal flakes in injection molded resin is injected into a cavity of a mold, and the magnetic force of a magnet embedded in a magnet embedding part provided across a portion where a weld mark is generated is obtained. The magnetic metal flakes are alternately attracted and moved in the melted resin so as to cross the portion where the weld mark is generated by alternately generating, and the flow of the resin at the weld mark generating portion is alternately changed. This prevents the occurrence of weld marks and prevents the appearance, strength, and stress cracking of the product from occurring, and also reduces the influence of the weld marks on products that produce metallic colors, thereby impairing the appearance. There is something that can be done.

JP 2004-188745 A JP 2006-9034 A Japanese Patent Laid-Open No. 10-95026

  However, in the above-described prior art, the ratio between the aluminum flakes and the thermoplastic resin is changed, and the aluminum flakes are kneaded at a relatively large ratio, or the aluminum powder, the interference pearl mica and the thermoplastic resin are blended at a predetermined ratio. There is a problem that various elaborate injection molding preparation steps are required, such as blending a coloring material, using a specially prepared magnetic metal flake, and providing a magnet in a mold. Further, as shown in FIG. 1 of the related art, there is an explanatory view showing a flow of resin in which a weld mark is generated in a plan view. Referring to FIG. 1, in a disc-shaped synthetic resin molded article 10 having a plurality of holes 11, when molten resin is injected from a gate 12, the flow of the resin is indicated by an arrow A around a mold that forms the holes 11. As shown, the resin flow is divided into two, and the flow of the resin divided into two collides with each other as shown by an arrow A, so that a so-called linear weld mark 13 is formed. It is generally known that when two or more flows of resin collide without being fused with each other, a linear weld mark 13 is generated at the collision portion. The weld mark 13 impairs the appearance of the product. In particular, the metallic resin molded product is defective due to color unevenness. Further, the strength in the direction perpendicular to the weld mark 13 is considerably lower than that of the portion where no weld mark is generated, and stress cracking is likely to occur. For this reason, it is necessary to prevent the weld mark 13 from being generated as much as possible in the injection molded product.

  The present invention has been made in view of such problems, and the structure of the molding die is not complicated, the occurrence of weld marks is prevented, and the appearance, strength, and stress cracking of the product are prevented from occurring. In the products that produce metallic colors, the influence of weld marks is reduced so that the appearance is not impaired, and the amount of metal flakes used for producing metallic colors mixed in the resin is small, and Another object of the present invention is to provide a method for molding a metallic resin using extremely ordinary metal flakes (for example, aluminum flakes) that are not expensive and have special properties.

According to the first aspect of the present invention for solving the above-mentioned problems, a synthetic resin to be injection-molded is injected into a cavity of a mold, and injection molding is performed in a portion where a weld mark is generated. In order to form a protruding part on the back side of the molded product, a pressing member that is positioned in a state in which a protruding part gap is provided continuously to the cavity is placed behind the molten synthetic resin supplied into the cavity. The pressing member is pressed and moved before the molten synthetic resin is solidified, and the molten synthetic resin is pressed and moved into the cavity while reducing the volume of the projecting portion gap. The synthetic resin injection is characterized in that the pressing surface is moved to a position that is flush with the back surface of the molded product 10 and is compressed by compression so that the flows of the plurality of molten synthetic resins in the mold are fused together. Molding method .
According to the second aspect of the present invention, a mixture of synthetic resin to be injection-molded and metal flakes is injected into a cavity of a mold, and injection molding is performed at a portion where a weld mark is generated. In order to form a protruding part on the back side of the molded product, a pressing member that is positioned in a state in which a protruding part gap is provided continuously to the cavity is placed behind the molten synthetic resin supplied into the cavity. The pressing member is pressed and moved before the molten synthetic resin is solidified, and the molten synthetic resin is pressed and moved into the cavity while reducing the volume of the projecting portion gap. Of the metallic synthetic resin, wherein the pressing surface of the metallic synthetic resin is moved to a position where it is flush with the back surface of the molded product 10 and is compressed so that the flows of the plurality of molten synthetic resins in the mold are fused together. Shoot It is a molding method.

  According to the present invention, two or more molten synthetic resin flows collide with each other and are fed into a cavity formed with a protrusion on the back side of a product to be injection-molded at a position where a weld mark is generated. The pressing member that is in contact with the back surface of the molten synthetic resin is pressed and moved before the molten synthetic resin is solidified, and is moved to a position where the pressing surface of the pressing member is flush with the back surface of the product. The pressure is compressed so that a plurality of flows of the resin are fused together, so that the generation of weld marks is prevented and the pressing surface of the pressing member is flush with the back surface of the product. Since the thickness of the molded product does not change, the reflected light from the back side inner surface of the light entering the synthetic resin molded product is uniform and does not cause color unevenness. And in the case of a metallic synthetic resin, the disordered orientation of the metal flakes in a molten synthetic resin can be adjusted, and the color irregularity of an external appearance can be eliminated.

It is explanatory drawing which showed the flow of the resin which a weld mark generate | occur | produced with the top view. In the conventional weld mark generation | occurrence | production part, it is a schematic diagram of the orientation state of the metal flake within the thickness T of a resin product. FIG. 3A is a cross-sectional view of a molding apparatus according to the present invention, and FIG. 3A is a diagram of a state in which an upper mold and a lower mold are clamped and molten synthetic resin is injected into a cavity. FIG. 3B is a state diagram in which the upper mold and the lower mold are opened. FIG. 4 is a schematic diagram (partially broken) of the orientation state of the metal flakes within the thickness T of the synthetic resin product in the weld mark generating portion of the present invention. In particular, in FIG. It is a schematic diagram just before a pressing member drives in the arrow B direction in the state which collided and the orientation of metal flakes is disordered. In FIG.4 (b), a press member is made to protrude in the cavity which becomes the back surface side of the synthetic resin molded product by which injection molding is carried out, and several flows of the molten synthetic resin in a metal mold are pressed. FIG. 3 is a schematic view of a state in which the metal flakes are fused and aligned.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 3 is a cross-sectional view of the molding apparatus 20 according to the present invention. FIG. 3A shows a state in which the upper mold 21 and the lower mold 30 are clamped and the molten synthetic resin 15 is injected into the cavity 34. It is a drawing of. FIG. 3B is a state diagram in which the upper mold 21 and the lower mold 30 are opened. The molding apparatus 20 includes an upper mold 21 having a predetermined mold surface 22 to be the surface 10a of the molded product, and a lower mold surface 31 corresponding to the mold surface 22 of the upper mold 21 to be the back surface 10b of the molded product. A mold 30 is provided. The upper die 21 can be moved up and down with respect to the lower die 30 by a hydraulic cylinder, a toggle mechanism or the like (not shown).

  The mold surface 31 of the lower mold 30 includes a mold surface 31 that becomes the back surface 10b of the disk-shaped synthetic resin molded product 10 to be injection molded. The lower mold 30 is provided with an injection passage 33 for injecting the molten synthetic resin 15 and a gate 32 (corresponding to the gate 12), and the flow of the molten synthetic resin 15 injected from the gate 32 is as follows. The upper pin 21 is divided into two parts by the projecting pins 23, and the two melt synthetic resin 15 flows around the projecting pins 23 collide with each other to generate weld marks 13. On the back surface side, in the injection molding process, the molten synthetic resin 15 temporarily flows to form a protruding portion 36. The projecting portion 36 is provided with an accommodation recess 35 in the lower mold 30 in contact with the lower surface of the position of the weld mark 13 generated at a position in contact with the four holes 11 of the molded article 10, and a hydraulic cylinder is provided in the accommodation recess 35. The pressure member main body 38 is fixed to the tip of the piston rod 39 of this hydraulic cylinder device, and the pressure member main body 38 and the piston rod 39 are formed integrally with the pressure member 37. Is slidably controlled and positioned in the housing recess 35 by the hydraulic cylinder device 40.

  Referring to FIG. 3B, the pressing member 37 is normally positioned by the hydraulic cylinder device 40 in a state where the protruding portion gap 36 is secured. The upper die 21 is lowered by a hydraulic cylinder, a toggle mechanism or the like (not shown), the upper die 21 and the lower die 30 are clamped, and the molten synthetic resin 15 is injected into the cavity 34 including the projecting portion gap 36. A state is reached (see FIG. 3A). In the injection molding process in this state, at the position where the flow of the two molten synthetic resins that wrap around the projecting pin 23 collides with each other to generate a weld mark, the protruding shape by the molten synthetic resin 15 is temporarily provided. A portion 36 is formed.

  Before the molten synthetic resin 15 in the cavity 34 including the protrusion 36 is solidified, the operation of the hydraulic cylinder device 40 causes the pressing surface of the pressing member 37 to protrude to a position flush with the back surface of the molded product 10. The molten synthetic resin 15 is pressed and moved into the cavity 34 while the volume of the gap 36 is reduced, and the molten synthetic resin portion at the position where the weld mark is generated is pressed and compressed to fuse the two molten resins. In addition to preventing the occurrence of the weld mark 13, in the case of a metallic synthetic resin, the disordered orientation of the metal flakes 16 in the molten synthetic resin 15 is adjusted (see FIGS. 4 (a) and 4 (b)). By the way, although it is easy to understand in the description here, the flow of two molten synthetic resins 15 is used, but in reality, the flow of two or more molten synthetic resins 15 may be used. Furthermore, if the surface of the disk-shaped synthetic resin molded product 10 is 10a and the back surface is 10b, the light entering from the front surface 10a of the molded product 10 does not change the thickness T of the molded product 10, so the back surface 10b The reflected light from the inner surface side of the film is uniform and does not cause color unevenness and the like, and it is convenient to improve the yield by ensuring good quality without any defects in appearance.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and it is needless to say that various modifications can be made without departing from the scope of the present invention.

  This technology is useful for the automobile industry, home appliance industry, housing industry, etc. using injection molding resin.

10 Disc-shaped synthetic resin molded product
10a Surface of molded product 10b Back surface of molded product 11 Hole 12, 32 Gate 13 Weld mark 15 Molten synthetic resin 16 Metal flake 20 Molding device 21 Upper mold 22 Mold surface 23 Projection pin 30 Lower mold 31 Mold surface 33 Injection passage 34 Cavity 35 Housing recess 36 Protruding part gap 36a Protruding part 37 Pressing member 40 Hydraulic cylinder device.

Claims (2)

The synthetic resin to be injection-molded is injected into the cavity of the mold, and in the portion where the weld mark is generated, it is connected to the cavity to form a protrusion on the back side of the molded product that is injection-molded in the injection molding process. A pressing member that is positioned in a state in which a gap for the protruding portion to be provided is secured is brought into contact with the back of the molten synthetic resin supplied into the cavity, and the pressing member is pressed before the molten synthetic resin is solidified. The molten synthetic resin is pressed and moved into the cavity while reducing the volume of the protruding portion gap, and moved to a position where the pressing surface of the pressing member is flush with the back surface of the molded product 10. Then, a synthetic resin injection molding method characterized by pressing and compressing so that a plurality of flows in the mold are fused together. A mixture of synthetic resin for injection molding and metal flakes is injected into the cavity of the mold, and a protrusion is formed on the back side of the molded product that is injection-molded at the part where the weld mark occurs. For this purpose, a pressing member that is positioned in a state in which a gap for the projecting portion provided continuously with the cavity is secured is brought into contact with the back of the molten synthetic resin supplied into the cavity, and the molten synthetic resin is solidified. The pressing member is pressed and moved in advance, and the molten synthetic resin is pressed and moved into the cavity while reducing the volume of the protruding portion gap, and the pressing surface of the pressing member is the back surface and the surface of the molded product 10. A method of injection molding of a metallic synthetic resin, wherein the injection molding method is characterized in that the metal synthetic resin is moved to a single position and pressed and compressed so that a plurality of flows in the mold are fused together.