JP2006181957A - Polypropylene-based resin expansion-molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably manufacture a polypropylene-based resin expansion-molded article with a desired expansion ratio while preventing air bubbles formed by a foaming agent from being dissipated by being broken during expansion blow molding. <P>SOLUTION: This polypropylene-based resin expansion-molded article is expansion-molded by adding the foaming agent to a compounded polypropylene-based resin which is composed of 30-70 wt% polypropylene with a long chain branching structure, and 70-30 wt% polypropylene for general purposes. In the polypropylene with the long chain branching structure, a melt tension is 100 mN or more. In the polypropylene for general purposes, a melt flow rate is 2.0 (g/10 min) or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polypropylene resin foam molded article produced by foam blow molding.

  In the foam blow molding method of a polypropylene resin foam molded article, foaming is performed by bubbles produced by a foaming agent kneaded in the polypropylene resin. However, general-purpose polypropylene has a narrow foaming temperature range, and if the temperature exceeds the foaming temperature, the viscosity and melt tension of the molten resin will decrease and bubbles due to the foaming agent will dissipate to the outside, resulting in insufficient foaming ratio. Depending on the case, there is a problem in that open-cell formation or bubble breakage may progress and foaming may become impossible.

  The method for producing a polypropylene resin foam disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-122488) described below has been made in view of the above problems.

  In the method disclosed in Patent Document 1, the melt tension exceeds 100 mN, the melt flow rate is 0.5 to 15 (g / 10 minutes), and the polypropylene resin is 20 to 70% by weight, and the melt tension is less than 30 mN. A base resin composed of 30 to 80% by weight of a polypropylene resin having a melt flow rate of 2 to 30 (g / 10 min), a foaming agent added to the base resin, kneaded and melted, and parison , And the parison is clamped with a blow mold, and then a pressurized fluid is introduced to produce a hollow polypropylene resin foam molded article.

However, in the above method disclosed in Patent Document 1, it is necessary to form a skin layer on the parison so that bubbles due to the foaming agent are not dissipated. For this purpose, the parison must be extruded with the resin temperature of the parison immediately after being extruded from the extrusion die being lower than 180 ° C. As a result, corrugated irregularities are generated on the wall surface of the polypropylene resin foam molding, resulting in poor appearance. Further, it takes time to lower the temperature of the molten resin of the parison, and there is a problem that productivity is low.
JP 2004-122488 A

  The present invention has been made in view of the above-described problems of the prior art, and even when the parison is extruded at a high temperature and high speed, the bubbles due to the foaming agent do not break and dissipate during foam blow molding. An object of the present invention is to make it possible to stably produce a polypropylene resin foam molded article having a desired expansion ratio.

  In order to achieve the above object, a polypropylene resin foam molded article according to the present invention is a compounded polypropylene resin comprising a polypropylene having a long-chain branched structure and a polypropylene having a melt flow rate of 2.0 (g / 10 min) or less. A hollow foamed molded article obtained by adding a foaming agent and foaming blow molding, wherein the blended polypropylene resin has a melt tension of 30 mN or more at 230 ° C and a melt flow rate of 2.7 (g / 10 min at 230 ° C). ) It is characterized by the following.

  In addition, a blended polypropylene resin comprising 30 to 70% by weight of polypropylene having a long chain branched structure and a melt tension of 100 to 100 mN and 70 to 30% by weight of polypropylene having a melt flow rate of 2.0 (g / 10 min) or less. The hollow body is foam blow molded by adding a foaming agent.

  Further, in the foamed molded product, the thickness ratio of the skin layer on the inner surface and the outer surface with respect to the wall thickness is 3% or more, respectively, the tensile elastic modulus (C) and the foaming ratio (B) of the foamed molded product, and the foaming The tensile elastic modulus (A) of the compounded polypropylene resin molded body used for the molded body preferably satisfies the relationship C> A / B.

  The foamed molded article may be a duct, a bottle, or a container having a bent portion that is bent three-dimensionally.

  Here, the long chain branched structure is a structure in which long chains of molecules are bonded at branch points, and improves the melt tension of polypropylene. The following (1) to (7) are methods for improving the melt tension.

(1) A method of mixing high-molecular-weight high-density polyethylene having a high melt tension (Japanese Patent Publication No. 6-55868).
(2) A method of mixing high-density polyethylene having a high melt tension produced by a chromium-based catalyst (JP-A-8-92438).
(3) A method of mixing low density polyethylene produced by a general high pressure radical polymerization method.
(4) A method of increasing melt tension by irradiating light to general polypropylene.
(5) A method of increasing ment tension by irradiating light to general polypropylene in the presence of a crosslinking agent or peroxide.
(6) A method of practicing a radically polymerizable monomer such as styrene on general polypropylene.
(7) There is a method of copolymerizing propylene and polyene (JP-A-5-194778, JP-A-5-19479). In this invention, what has (4) and (5) was used by having a long-chain branch structure.

  The tensile modulus is the ratio of the tensile stress within the tensile proportional limit and the corresponding strain, and in the absence of a tensile stress / strain curve, it depends on the slope of the tangent at the deformation starting point.

  The test piece was No. 2 of JIS K-7113, and the test method was performed at a tensile speed of 50 mm / min according to JIS K-7113.

  The test piece in the measurement of the tensile modulus of the blended polypropylene resin was 100 to 500 g of a foam cut out from the product, cut finely, re-extruded with an extruder, and made an unfoamed sheet of 50 mm × 150 mm thickness 2 mm. JIS K-7113 No. 2 test piece was prepared and measured by the method described above.

  Since this invention is comprised as mentioned above, there exists an effect as described below.

  The parison can be extruded at a high temperature, and the molding adjustment time can be shortened. In addition, bubbles due to the foaming agent are not dissipated, and a high-quality polypropylene resin foam molded article having a desired foaming ratio can be stably produced.

  In the method for producing a polypropylene resin foam molded article disclosed in Patent Document 1 described above, an extrusion die is used to form a skin layer on the outer peripheral surface of the extruded parison so that bubbles due to the foaming agent are not dissipated. It is necessary to set the set temperature of the extrusion die or the like so as to extrude the parison so that the molten resin temperature of the parison immediately after extrusion is less than 180 ° C. As a result, a cooling time for lowering the molten resin temperature to less than 180 ° C. is necessary, so that the molding adjustment time becomes long. On the other hand, when the high temperature molding is performed without lowering the temperature of the molten resin of the parison, the skin layer is not formed, the bubbles due to the foaming agent are broken, and the surface roughness of the wall surface of the foamed molded product becomes conspicuous.

  Therefore, when repeated experiments were performed, a general-purpose polypropylene having a melt flow rate (MFR) of 1.8 (g / 10 min) or less and a foaming polypropylene having a long-chain branched structure and a melt tension of 100 mN or more were mixed. The knowledge that a skin layer was formed on the parison even when high-temperature molding (180 ° C. or higher) was obtained when the blended polypropylene resin was used.

  Here, melt flow rate (MFR) is measured at a test temperature of 230 ° C. and a test load of 2.16 kg according to JIS K-7210 (1997).

  The melt tension is a melt tension tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.), with a preheating temperature of 230 ° C. and an extrusion speed of 5.7 mm / min, and a strand is extruded from an orifice having a diameter of 2.095 mm and a length of 8 mm. This shows the tension when the strand is wound around a roller having a diameter of 50 mm at a winding speed of 100 rpm.

  The present invention is based on the above knowledge, and has a melt tension of 30 to 70% by weight with a long chain branched structure and a melt tension of 100 mN or more, and a melt flow rate (MFR) of 1.8 (g / 10 min). ) A polypropylene resin foam molded article obtained by adding a foaming agent to a blended polypropylene resin composed of 70 to 30% by weight of the following general-purpose polypropylene and subjected to foam blow molding.

  As a foaming agent used in the present invention, either a physical foaming agent or a chemical foaming agent may be used.

  Physical foaming agents include inorganic physical foaming agents such as air, carbon dioxide, nitrogen gas, and water, and organic physical foaming agents such as butane, pentane, hexane, dichloromethane, dichloroethane, and in some cases, carbon dioxide, nitrogen, etc. The supercritical fluid can be used.

  As the chemical foaming agent, a superdegradable chemical foaming agent such as sodium bicarbonate, sodium citrate, or an azo compound can be used.

  In addition, when the ratio of the polypropylene for foaming having a long chain branched structure and a melt tension of 100 mN or more is less than 30% by weight, the melt elongation of the parison is lowered and the moldability is remarkably deteriorated. On the other hand, if it exceeds 70% by weight, the overall melt flow rate is increased, and bubbles due to the foaming agent are easily dissipated. In order to prevent the bubbles from escaping, a cooling time for lowering the temperature of the molten resin of the parison is required, and as a result, the molding adjustment time becomes long. Furthermore, since the foaming polypropylene is more expensive than the general-purpose polypropylene, the cost of the final product is increased.

  FIG. 1 is a schematic perspective view of a foam duct according to an embodiment. The foam duct 1 has a center portion 1a and one bent portion 1b connected to one end side of the center portion 1a, and the other bent portion 1c connected to the other end side of the center portion 1a. It is a three-dimensionally bent cylindrical body that is integrally molded by blow molding.

  One bent portion 1b is bent in an arc shape with respect to the central portion 1a (bent toward the X-axis side in the drawing), and a cross-sectional shape in which a slightly higher step 2a from the central portion 1a is formed on the side opposite to the central portion The expanded bulging portion 2 is continuously provided. On the other hand, the other bent portion 1c connected to the other end side of the central portion 1a is bent in an L shape with respect to the central portion 1a (bent to the Z-axis side shown in the drawing, and then bent to the Y-axis side shown in the drawing). The connecting portion 3 is provided with a pair of protrusions 3a, 3b protruding from the outer surface at a distance from each other on the side opposite to the center.

  If the blow mold is a split mold having a cavity that regulates the outer surface of the foam duct 1 in a clamped state, burrs are generated in all parts of the parting line 5 of the foam duct 1. Either a total burr-type blow mold or a blow mold in which burrs are generated only at the parting line 5 in the bulging portion 2 and the closing portion 4 may be used.

  Using a foam blow molding machine (Nippon Steel Works P-50-L / D34) equipped with a screw extruder, a foam having a three-dimensionally bent portion similar to that shown in FIG. A duct sample was subjected to foam blow molding under the following molding conditions.

Molding conditions Outer diameter of parison: 120mm
Inner thickness of parison: 5mm
Wall thickness of the thinnest part of the foam duct 0.3mm
Foaming agent: 0.77% by weight of carbon dioxide (CO ₂ )

  Blended polypropylene resin: Polypropylene for foaming having a long chain branching structure and a melt tension of 100 mN or more (manufactured by Sun Allomer Co., Ltd., PF814 MFR: 3.0 (g / 10 min)), 50% by weight, general-purpose polypropylene [Japan Polypro Corporation, EC9 MFR: 0.5 (g / 10 min)] 50% by weight

  A foam duct sample was foamed and blow molded in the same manner as in Example 1 except that the compounded polypropylene resin was changed to general-purpose polypropylene [MFR: 1.2 (g / 10 min) BC8D manufactured by Nippon Polypro Co., Ltd.]. did.

  A foam duct sample was foamed and blow molded in the same manner as in Example 1 except that the compounded polypropylene resin was changed to general-purpose polypropylene [MFR: 1.5 (g / 10 min) EC7 manufactured by Nippon Polypro Co., Ltd.]. did.

  The foam duct sample was foamed and blow molded in the same manner as in Example 1 except that the compounded polypropylene resin was changed to general purpose polypropylene [MFR: 1.8 (g / 10 min) BC8 manufactured by Nippon Polypro Co., Ltd.]. did.

(Comparative Example 1)
A foam duct sample was foamed and blow molded in the same manner as in Example 1 except that the blended polypropylene resin was changed to general-purpose polypropylene [MFR: 2.3 (g / 10 min), FL6CK manufactured by Nippon Polypro Co., Ltd.]. did.

(Comparative Example 2)
The foam duct sample was subjected to foam blow molding in the same manner as in Example 1 except that the blended polypropylene resin was changed to general-purpose polypropylene [MFR: 2.7 (g / 10 min), Nippon Polypro Co., Ltd. BC6]. did.

(Comparative Example 3)
A foam duct sample was foamed and blown in the same manner as in Example 1 except that the blended polypropylene resin was changed to general-purpose polypropylene [MFR: 9.0 (g / 10 min), J700GP manufactured by Idemitsu Petrochemical Co., Ltd.] Molded.

  About each sample of Examples 1-4 and Comparative Examples 1-3, the film thickness ratio of a skin layer, the presence or absence of the unevenness | corrugation of an inner surface, and the presence or absence (formability of shaping | molding) of the generation | occurrence | production of a pinhole were evaluated visually. The results are shown in Table 1.

※ａ 表中、一般ＰＰとＰＦ８１４との重量％割合は５０％、５０％である。
※ｂ 上表中実施例１、３に使用した一般ＰＰは押出し成形グレードである。
※ｃ 上表中実施例２、４、比較例２に使用した一般ＰＰは射出グレードである。

* A In the table, the percentage by weight of general PP and PF814 is 50% and 50%.
* B General PP used in Examples 1 and 3 in the above table is an extrusion molding grade.
* C General PP used in Examples 2 and 4 and Comparative Example 2 in the above table is an injection grade.

  As is apparent from Table 1, 30 to 70% by weight of polypropylene for foaming having a long chain branched structure and a melt tension of 100 mN or more, and 70 to 30% by weight of general-purpose polypropylene having a melt flow rate of 1.8 (g / min) or less. % Of the blended polypropylene resin mixed with the foaming agent, the skin layer is reliably formed without lowering the surface temperature of the parison, and the foamed body having a desired foaming ratio does not break the foam cell due to the foaming agent. Ducts can be manufactured.

  In addition, the foam duct has a skin layer thickness ratio of 3% or more on the inner surface and the outer surface with respect to the wall thickness, respectively, and the foam duct tensile elastic modulus (C), which is the tensile elastic modulus of the foam molded article, and the expansion ratio (B) and the unfoamed tensile elastic modulus (A), which is the tensile elastic modulus of the blended polypropylene resin molded body used for the foam duct, satisfy the relationship C> A / B.

  The polypropylene resin foam molded article according to the present invention is excellent in heat insulation, heat resistance, rigidity, etc., and has a bottle, a duct, a hollow double wall structure panel, a side wall or a bottom wall of a hollow double wall structure. And various uses. In particular, it is suitable for various ducts for automobiles that require heat resistance and light weight.

It is a model perspective view of the foam duct by one Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Foam duct 1a Center part 1b, 1c Bending part 2 Bulging part 3 Connection part 4 Closing part 5 Parting line

Claims (7)

A hollow foamed molded article obtained by adding a foaming agent to a blended polypropylene resin composed of a polypropylene having a long-chain branched structure and a polypropylene having a melt flow rate of 2.0 (g / 10 min) or less. And
A polypropylene resin foam molded article, wherein the blended polypropylene resin has a melt tension of 30 mN or more at 230 ° C. and a melt flow rate of 2.7 (g / 10 min) or less at 230 ° C.   Foamed into a blended polypropylene resin composed of 30 to 70% by weight of polypropylene having a long chain branching structure and a melt tension of 100 mN or more and 70 to 30% by weight of polypropylene having a melt flow rate of 2.0 (g / 10 min) or less. A polypropylene resin foam molded article, which is a hollow body molded by blow molding with an additive.   The foam molded body has a thickness ratio of the skin layer on the inner surface and the outer surface of the wall thickness of 3% or more, and the tensile elastic modulus (C) and expansion ratio (B) of the foam molded body, and the foam molded body. 3. The polypropylene resin foam molded article according to claim 1, wherein the tensile modulus (A) of the blended polypropylene resin molded article used in the step satisfies a relationship of C> A / B.   The polypropylene resin foam molded article according to any one of claims 1 to 3, wherein the foam molded article is a duct.   The polypropylene-based resin foam-molded article according to any one of claims 1 to 3, wherein the foam-molded article is a duct having a bent portion that is three-dimensionally bent.   The polypropylene resin foam molded article according to any one of claims 1 to 3, wherein the foam molded article is a bottle.   The polypropylene resin foam molded article according to any one of claims 1 to 3, wherein the foam molded article is a container.

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