JP2005313328A - Manufacturing method of resin molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a resin molded product constituted so as to mold the resin molded product by an injection molding machine having an injection unit not having a valve mechanism in order not only to prevent the complication of equipment but also to solve an increase in cost. <P>SOLUTION: In a gas counter pressure molding method for injecting a plasticized foamable resin in a mold cavity pressurized by gas to obtain the resin molded product having a foamed structure therein and having a smooth surface, a high pressure gas of 4.9-9.8 MPa is injected in a mold and the depressurization of the gas is performed simultaneously with or after the completion of injection. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a foam molded product by a gas counter pressure molding method, in particular, a foam molded product having an uneven thickness portion is molded by a normal injection molding machine, and the surface layer is smooth and non-foamed, and the internal layer The present invention relates to a method for producing a resin molded product composed of a foam layer.

  Conventionally, in the production of foamed molded products, in order to prevent sink marks, warpage, etc. of molded products, a thermoplastic resin containing a foaming agent is injected into a mold cavity under atmospheric pressure in an amount smaller than its volume, A method of filling voids by foaming resin is known as a short shot method. However, this molded product has a foamed pattern (swirl mark) on the surface, and a defect in appearance remains. On the other hand, the method of injecting a resin containing a foaming agent into a mold cavity pressurized with a gas body, which is also called a gas counter pressure method, can obtain a molded product in which no foamed resin is seen on the surface. Known as a method. This is plasticized and kneaded under the back pressure necessary to suppress foaming of the foamed resin, and the resin is injected into a mold that is held in the gas body above the foaming pressure. This is because it is equivalent to a molded product made of resin.

However, as in Patent Document 1, in the prior art, the gas body pressure in the mold gap is about 0.98 MPa or more. For this reason, it is necessary to increase the confidentiality of the mold in order to maintain the pressure in the mold cavity. Generally, a method of inserting an O-ring, gasket sheet, etc. into the mold dividing surface, sliding part, etc. is adopted. It has been. In addition, an injection unit of an injection molding machine is required to have a valve mechanism such as a needle nozzle, a slide nozzle, and a mechanical opening / closing nozzle so that back pressure can be applied. For this reason, gas counter pressure molding is complicated for injection molding machines, and the mold also requires special processing to improve confidentiality, so it is not suitable for those with complicated dividing surfaces or those with nested structures. The molding method was applied.
Japanese Patent Publication No. 1-21322

The present inventors have solved the disadvantages of the prior art so that they can be molded by an injection molding machine having an injection unit that does not have a valve mechanism in order to solve the complexity and cost increase of equipment, which is a disadvantage of the prior art. The purpose is to obtain.

The invention according to claim 1, which solves the above problem, injects a plasticized foamable resin into a mold cavity pressurized by gas, and has a resin molded product having a foamed structure inside and a smooth surface. In the obtained gas counter pressure molding method, a high-pressure gas of 4.9 to 9.8 MPa is injected into a mold, and the depressurization of the gas is performed simultaneously with or after the injection is completed.

  The invention according to claim 1 is a gas counter in which a plasticized foamable resin is injected into a mold cavity pressurized by a gas to obtain a resin molded product having a foamed structure and a smooth surface. In the pressure molding method, a high-pressure gas of 4.9 to 9.8 MPa is injected into the mold, and the depressurization of the gas is performed simultaneously with or after the injection is completed. Even if a gas leak occurs from the ejector pin, a pressure higher than the foaming pressure is applied to the mold until the resin injection is completed, so there is no foaming until the injection is completed. The flow pattern does not occur. Further, gas leakage always occurs from the protruding pin, and the gas leakage path acts more effectively as a gas venting effect in the mold.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a molding die apparatus according to the present invention. In FIG. 1, a conventional O-ring or the like is not inserted into the protruding pin 5 and is fitted only to the mold dividing surface 9, and a “thin press kit” (not shown) is used for pressure control in the mold. The “sympress kit” is an apparatus that can achieve a maximum pressure of 19.6 to 29.4 MPa by compressing an introduction pressure of 2.0 to 2.9 MPa from a nitrogen cylinder. In a mold in which only the mold dividing surface 9 is sealed and the plurality of protruding pins 5 are not sealed, gas leakage occurs even by pressurization from the “thin press kit”.

  However, if a high-pressure gas of 4.9 to 9.8 MPa is injected into the mold immediately before resin injection, the resin injection is completed even if gas leakage from a plurality of protruding pins 5 occurs. It is possible to keep the pressure inside the mold at least 0.98 MPa for a second.

  Further, as an incidental effect, a gas leak occurs as shown in FIG. 2 from the unsealed projecting pin 5 at the time of resin injection, but this gas leakage path simultaneously contributes to the degassing effect of the foaming gas. This effectively acts on the degassing effect of the tip of the boss by the sleeve structure which is a kind of the pin 5.

  Here, if the high-pressure gas injected into the mold falls below 4.9 MPa, the pressure inside the mold cannot be maintained at 0.98 MPa or more, foaming occurs during resin injection, and swirl marks are generated on the product surface. End up. On the other hand, when the high-pressure gas injected into the mold exceeds 9.8 MPa, the mold opens, causing burrs.

As the resin used in the present invention, thermoplastic resins can be widely used. For example, polypropylene (PP), polystyrene (PS), acrylic nitrile-styrene copolymer (AS), acrylonitrile-butadiene-styrene copolymer (ABS). Etc. As the foaming agent, those used in general foam molding can be widely used, and examples thereof include azodicarbonamide (ADCA), dinitropentamethylenetetramine (DPT), 4,4′-oxybisbenzenesulfonylhydrazide (OBSH), and the like. .

  The amount of the blowing agent added to the resin is desirably 0.25 to 1.5 wt%. The foaming agent is decomposed by heat to form bubbles in the resin. On the other hand, the molding time is, for example, 1 cycle, 1 to 2 minutes. When the amount of the foaming agent (pellet) exceeds 1.5 wt%, excessive foaming occurs within the molding time in the injection cylinder, and bubbles are likely to be generated on the surface, so that an appearance improvement effect in a low gas pressure range cannot be obtained. On the other hand, if the amount is less than 0.25 wt%, bubbles are observed inside, but the amount is insufficient, so that sink and warp cannot be prevented. As for the expansion ratio, it is sufficient that the foam can be expanded to the extent that the internal shrinkage distortion when the molded product is hardened, and may be in a general range, that is, 1.0 (no foam) to 1.2.

  In the present invention, the gas pressure of the gas counter pressure needs to be in the range of 4.9 to 9.8 MPa. In order to set the gas pressure of the gas counter pressure to 4.9 to 9.8 MPa, the pressure of 2.0 to 2.9 MPa introduced from the nitrogen cylinder is compressed by using a thin press kit, so that the maximum pressure is 19.6 to 29 MPa. The pressure is set to 4 MPa. Then, a high pressure gas of 4.9 to 9.8 MPa is injected from the gas counter pressure immediately before resin injection. By doing so, even if gas leakage from a plurality of protruding pins occurs, a high-pressure gas of 4.9 to 9.8 MPa is injected from the gas counter pressure immediately before resin injection. By doing so, even if gas leakage from a plurality of protruding pins occurs, the pressure in the mold can be kept at least 0.98 MPa for 3 to 20 seconds after the resin injection is completed.

1 is a schematic view of a molding die apparatus according to the present invention. It is the A section enlarged view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold production apparatus 5 Molding pin 7 Cavity 9 Mold division surface 11 Thin press kit 13 Mold division surface seal

Claims (1)

In a gas counter pressure molding method in which a plasticized foamable resin is injected into a mold cavity pressurized with gas to obtain a resin molded product having a foamed structure inside and a smooth surface, 4. A method for producing a resin molded product, comprising injecting a high-pressure gas of 4.9 to 9.8 MPa, and performing gas depressurization simultaneously with or after completion of injection.

Images