JP2015086292A - Method for manufacturing foamed molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a foamed molding having improved mechanical strength.SOLUTION: The method for manufacturing a foamed molding includes melting and mixing 100 pts.wt. of an olefinic resin and 0.1 to 1 pts.wt. of polycarboxylic acid to obtain a mixture in melting state, mixing the mixture in melting state and liquid in supercritical state to obtain a foamable composition, then foaming molding by injecting the foamable composition into a mold. By such a method, a foamed molding containing fine foaming cells dispersed uniformly and excellent in mechanical strength and appearance can be manufactured.

Description

  The present invention relates to a method for producing a foam molded article using a fluid in a supercritical state.

  Olefin-based molded articles are excellent in light weight and moldability, and thus are used in various fields such as automobile parts and household appliance parts. In recent years, olefin-based resins have been used as foam molded articles from the viewpoint of further weight reduction of the molded articles.

  The production of a foamed molded article using an olefin-based resin is performed by injection molding from the viewpoint of productivity. In the injection molding method, an olefin-based resin is melt-kneaded in the presence of a foaming agent, and then injected into a mold and foamed to obtain a foam-molded product.

  In the foam molded product, in order to improve its mechanical strength and appearance, it is necessary that fine foam cells are uniformly dispersed. For this reason, attempts have been made to use a supercritical fluid as a foaming agent.

  For example, Patent Document 1 discloses a method for producing a foamed molded article in which a supercritical gas is infiltrated into a resin composition comprising 100 parts by weight of an olefin resin and 0.1 to 40 parts by weight of a layered silicate, and then degassed. It is disclosed.

JP 2002-348398 A

  However, in the method of Patent Document 1, it is difficult to finely disperse the supercritical gas in the olefin resin. Therefore, the foam cell formed by the supercritical gas is coarsened, and the mechanical strength of the foam molded article cannot be sufficiently improved.

  Therefore, this invention provides the manufacturing method of the foaming molding with improved mechanical strength.

  The method for producing a foamed molded article of the present invention is obtained by melting and kneading 100 parts by weight of an olefin resin and 0.1 to 1 part by weight of a polycarboxylic acid to obtain a molten mixture, which is supercritical with the above molten mixture. After obtaining a foamable composition by mixing with a fluid in a state, the foamable composition is injected into a mold and foam-molded.

  First, in FIGS. 1-3, the schematic diagram of the injection molding apparatus used suitably in order to implement the method of this invention is shown. The injection molding apparatus shown in FIGS. 1 to 3 includes an extruder 10, a supercritical fluid introduction apparatus 20, and a mold 30.

  The extruder 10 includes a heating cylinder 11 and a hopper 12 that is installed at the rear end of the heating cylinder 11 and feeds resin into the heating cylinder 11. A screw (not shown) is rotatably disposed in the heating cylinder 11 and can melt and knead the olefin resin and the polyvalent carboxylic acid.

  The supercritical fluid introduction device 20 includes a cylinder 21 filled with a fluid used as a raw material for a fluid in a supercritical state, a booster (not shown) that pressurizes the fluid, and a heater (not shown) that heats the fluid. ) And a pipe 23 connecting the cylinder 21 and the supercritical fluid generator 22. The supercritical fluid introduction device 20 is connected to the heating cylinder 11 via a pipe 23 on the downstream side in the extrusion direction from the hopper 12.

  A mold 30 is connected to the tip of the heating cylinder 11. The mold 30 includes a fixed mold 31, a movable mold 32, and a cavity 33 formed between the fixed mold 31 and the movable mold 32.

  Next, the manufacturing method of a foaming molding is demonstrated using the injection molding apparatus mentioned above.

  First, as shown in FIG. 1, an olefin-based resin and a polyvalent carboxylic acid are charged into a heating cylinder 11 from a hopper 12 of an extruder 10 and melted and kneaded in the heating cylinder 11 to obtain a molten mixture. Can do. At the time of melt-kneading the olefin resin and the polyvalent carboxylic acid, the polyvalent carboxylic acid can be thermally decomposed to generate a gas. As a result, fine bubbles containing the pyrolysis gas of polyvalent carboxylic acid are uniformly and finely dispersed in the molten mixture.

  Examples of olefin resins include ethylene resins and propylene resins. Of these, propylene-based resins are preferable. According to the propylene-based resin, it is possible to produce a foamed molded article having excellent mechanical strength.

  Examples of the propylene-based resin include a propylene homopolymer and a propylene-α-olefin copolymer. These propylene resins may be used alone or in combination of two or more.

  In the propylene-α-olefin copolymer, the α-olefin copolymerized with propylene is a component other than propylene, such as ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, Examples include 1-hexene, 1-octene, 1-nonene, and 1-decene. Of these, ethylene is preferable. Further, the propylene-α-olefin copolymer may be either a block copolymer or a random copolymer.

  The content of the propylene component in the propylene-based resin is preferably 50% by weight or more, more preferably 55 to 95% by weight, and particularly preferably 60 to 90% by weight. By setting the content of the propylene component to 50% by weight or more, the mechanical strength of the foamed molded product can be improved.

  The polyvalent carboxylic acid may be a compound having two or more carboxyl groups. Specifically, citric acid, tartaric acid, malic acid, succinic acid, oxalic acid, adipic acid, malonic acid, phthalic acid, sebacic acid, maleic acid, fumaric acid, malonic acid, itaconic acid, glutaric acid (pentanedioic acid) , Gluconic acid, glutaconic acid, and pentenedioic acid. Above all. Succinic acid, tartaric acid, malic acid, and citric acid are preferred. According to these polyvalent carboxylic acids, the fluid in the supercritical state can be finely dispersed in the molten mixture. In addition, polyvalent carboxylic acid may use only 1 type, or may use 2 or more types together.

  When melt-kneading the olefin resin and the polyvalent carboxylic acid, the blending ratio of the polyvalent carboxylic acid is limited to 0.1 to 1 part by weight with respect to 100 parts by weight of the olefin resin. 0.5 parts by weight is preferred. If the blending ratio of the polyvalent carboxylic acid is too low, the supercritical fluid may not be sufficiently finely dispersed in the molten mixture. Moreover, when there are too many compounding ratios of polyhydric carboxylic acid, there exists a possibility that the mechanical strength of a foaming molding may fall.

  When melt-kneading the olefin resin and polyvalent carboxylic acid, other components may be melt-kneaded in addition to these. Examples of other components include crystal nucleating agents, lubricants, fillers (for example, talc, calcium carbonate, and glass fiber), antioxidants, pigments, and colorants.

  When the olefin resin and the polyvalent carboxylic acid are melt-kneaded, the melt-kneading temperature is preferably 190 to 230 ° C, more preferably 200 to 220 ° C. By setting the melt kneading temperature within the above range, the polyvalent carboxylic acid can be thermally decomposed while suppressing the thermal decomposition of the olefin resin.

  Next, the cylinder 21 is opened, and the fluid filled in the cylinder 21 is heated by the supercritical fluid generator 22 to a temperature equal to or higher than the temperature at the critical point and pressurized at a pressure equal to or higher than the pressure at the critical point. A supercritical fluid is obtained. By introducing the supercritical fluid into the heating cylinder 11 through the pipe 23, the foamed composition is obtained by mixing the molten mixture and the supercritical fluid in the heating cylinder 11.

  In the molten mixture, as described above, fine bubbles containing a pyrolysis gas of polyvalent carboxylic acid are uniformly finely dispersed. As a result, there are many interfaces between the fine bubbles and the molten olefin resin, and the fluid in the supercritical state is easily taken into such interfaces. Therefore, by mixing the mixture in the molten state and the fluid in the supercritical state, the fluid in the supercritical state can be uniformly finely dispersed from the fine bubbles that are uniformly finely dispersed as the starting point (bubble nuclei). .

  In the present invention, the fluid in the supercritical state means a fluid in a state where the temperature is equal to or higher than the temperature at the critical point (critical temperature Tc) and the pressure is equal to or higher than the pressure at the critical point (critical pressure Pc). As the fluid used for the supercritical fluid, carbon dioxide, nitrogen, helium, air, oxygen, hydrogen, and the like are used. Of these, nitrogen and carbon dioxide are preferable. These fluids are used as a supercritical state. When the fluid is in a supercritical state, it is easily taken into the interface and finely dispersed. In addition, the supercritical fluid may be used alone or in combination of two or more.

  For example, when obtaining nitrogen in a supercritical state, it is preferable to heat nitrogen to a temperature equal to or higher than the critical temperature Tc of nitrogen, particularly 10 to 50 ° C., and pressurize at a pressure equal to or higher than the critical pressure Pc of nitrogen, particularly 5 to 15 MPa. .

  When mixing the mixture in the molten state and the fluid in the supercritical state, the mixture in the molten state and the fluid in the supercritical state are heated at a temperature equal to or higher than the temperature at the critical point of the fluid (critical temperature Tc). It is preferable to mix while pressurizing at a pressure equal to or higher than the pressure at the point (critical pressure Pc). For example, when supercritical nitrogen is used, the molten mixture and supercritical nitrogen are heated to a nitrogen critical temperature Tc or higher, particularly 190 to 230 ° C., and nitrogen critical pressure Pc or higher, particularly 5 It is preferable to mix while pressurizing at a pressure of ˜15 MPa. Thereby, the state in which the fluid in the supercritical state is uniformly dispersed can be maintained even in the foamable resin composition.

  Then, after the molten mixture and the supercritical fluid are mixed with a screw in the heating cylinder 11 to obtain a foamable resin composition, the foamable resin composition is put into the cavity 33 of the mold 30 with a screw. Eject. Subsequently, as shown in FIG. 2, the inside of the cavity 33 is decompressed by retracting the movable mold 32 and increasing the internal volume of the cavity 33. As a result, the fluid changes from the supercritical state to the gas state, and the volume expands, whereby the foamed molded product can be obtained by foaming the molten mixture. Thereafter, the foam molded body can be taken out from the cavity 33 by cooling and solidifying in the cavity 33.

  In the foamable resin composition, as described above, since the fluid in the supercritical state is uniformly finely dispersed, such a foamable resin composition is injected into the cavity 33 of the mold 30 to perform foam molding. By doing so, it is possible to obtain a foamed molded product in which fine foamed cells are uniformly dispersed. Such a foam-molded article is excellent in mechanical strength such as bending elastic gradient and impact strength by including fine foam cells uniformly dispersed. Moreover, even if a foamed molded article having a high expansion ratio is produced, it is possible to suppress a decrease in mechanical strength and maintain excellent mechanical strength. Further, since the fine foam cells are uniformly dispersed, the appearance deterioration due to the occurrence of irregularities is highly suppressed, and a foamed molded article having excellent appearance characteristics can be obtained. Therefore, according to the method of the present invention, it is possible to produce a foamed molded article that is excellent in lightness, mechanical strength, and appearance.

  Such a foam-molded product can be used for various applications. Applications include, for example, automotive interior parts such as door trims, pillar trims, various box lids, instrument panels, and sun visors, exterior parts such as tire houses, under covers, side protection moldings, bumpers, soft facias, mudguards, and motorcycles. Examples include parts in various products such as sheets, furniture, building materials, home appliances, and electronic devices, as well as transport containers and cushioning materials. Especially, since the foaming molding of this invention is excellent in lightweight property, mechanical strength, and an external appearance property, it is preferable to be used as a motor vehicle interior component.

  According to the method of the present invention, a foamed molded article having improved mechanical strength can be produced.

The schematic diagram of the injection molding apparatus used suitably for the method of this invention is shown. The schematic diagram of the injection molding apparatus of the state which foamed the foamable resin composition in the cavity 33 of the metal mold | die 30 is shown.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

(Examples 1-3 and 5 and Comparative Examples 1-2)
Using the injection molding apparatus shown in FIG. 1, a foam molded article was produced as follows. First, the propylene-based resin (propylene-ethylene block copolymer, propylene component content 70% by weight, trade name “BC08F” manufactured by Nippon Polypro Co., Ltd.), malic acid, citric acid, and succinic acid are shown in Table 1, respectively. The blended amount was supplied into the heating cylinder 11 through the hopper 12 of the extruder 10 and melted and kneaded at 220 ° C. to obtain a molten mixture.

  Next, the nitrogen gas filled in the cylinder 21 was heated to a temperature of 20 ° C. by the supercritical fluid generator 22 and was pressurized at a pressure of 12 MPa to obtain a supercritical state. Nitrogen in a supercritical state was transferred through the pipe 23 and then supplied into the heating cylinder 11 at a gas flow rate of 0.25 kg / hr, a gas injection pressure of 12 MPa, and an injection time of 8 seconds. Thereafter, the supercritical nitrogen and the molten mixture were mixed while heating at 220 ° C. During the mixing, the supercritical nitrogen and molten mixture were compressed by rotating the screw and pressurized at a pressure of 14 MPa. Thereby, a foamable resin composition was obtained.

  On the other hand, the fixed mold 31 and the movable mold 32 were heated to 50 ° C., and the fixed mold 31 and the movable mold 32 were clamped to form a cavity 33 with a gap of 0.9 mm. The foamable resin composition was injected into the cavity 33 under the conditions of an injection pressure of 150 MPa, an injection time of 1 second, a holding pressure of 40 Mpa, and a holding pressure time of 0.2 seconds. After injection, the movable mold 32 is retracted 1.8 mm to reduce the pressure in the cavity, thereby changing the nitrogen from the supercritical state to the gas state, thereby foaming the foamable resin composition to obtain a foamed molded product. It was. Thereafter, the foam molded body was cooled and taken out from the cavity 33. The foamed molded product was flat and had a thickness of 2.7 mm.

Example 4
Except for changing the amount of malic acid to 1.0 part by weight and changing the gas flow rate to 0.5 kg / hr when supplying supercritical nitrogen into the heating cylinder 11, as in Example 1, A foamed molded product was obtained.

(Evaluation)
About the foaming molding produced above, the bending elastic gradient and the low temperature falling ball impact strength were measured. The results are shown in Table 1.

(Bending elastic gradient)
By cutting the foam molded body, a flat rectangular test piece having a width of 50 mm and a length of 150 mm was obtained. About the test piece, the bending elastic gradient was computed based on JISK7171. Specifically, the test speed is 50 mm / min, the distance between the fulcrums is 100 mm, and a load (N) is applied to the central portion between the fulcrums in the thickness direction of the test piece to bend the test piece. At this time, a load-deflection curve was measured, a tangent line was drawn at a portion where the gradient of the curve was the largest, and a bending elastic gradient (N / cm) was calculated from the tangent line.

(Low temperature falling ball impact strength)
By cutting the foam molded article, a flat rectangular test piece having a width of 130 mm and a length of 300 mm was obtained. Next, under a temperature environment of −30 ° C., a 500 g iron ball was dropped vertically from a predetermined height onto the center of the test piece, and the maximum height of the iron ball that the test piece did not break (m ). Then, the low temperature falling ball impact strength [J (kgf · m)] was calculated by multiplying the maximum height of the steel ball by the weight of the iron ball.

DESCRIPTION OF SYMBOLS 10 Extruder 11 Heating cylinder 12 Hopper 20 Supercritical fluid introduction apparatus 21 Cylinder 22 Supercritical fluid generator 23 Piping 30 Mold 31 Fixed mold 32 Movable mold 33 Cavity

Claims (2)

  A melted mixture is obtained by melt-kneading 100 parts by weight of an olefin-based resin and 0.1 to 1 part by weight of a polyvalent carboxylic acid, and foamability is obtained by mixing the molten mixture with a fluid in a supercritical state. A method for producing a foamed molded article, comprising: obtaining the composition, and then injecting the foamable composition into a mold to perform foam molding.   The method for producing a foamed molded article according to claim 1, wherein the fluid in the supercritical state contains at least one of nitrogen in the supercritical state and carbon dioxide in the supercritical state.

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