JP2004300260A - Method for producing polypropylene resin foam molding and foam molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a foam molding of a polypropylene resin, by which productivity is slightly reduced and occurrence of silver streak is controlled. <P>SOLUTION: The method for producing the foam molding of a propylene resin comprises mixing 100 parts wt. of a resin composition composed of 70-93 wt.% of a propylene-based polymer (A) having 5-150 (g/10 minutes) melt flow rate (MFR) measured at 230°C under 2.16 kg load and 7-30 wt.% of a straight-chain low-density polyethylene (B) having 0.91-0.945 (g/cm<SP>3</SP>) density and 1-50 (g/10 minutes) melt flow rate (MFR) measured at 190°C under 2.16 kg load with 0.1-0.5 part wt. of inorganic chemical blowing agent (C) to prepare a foam resin composition and subjecting the foam resin composition to foam molding using a mold for injection molding having 1.0 mmt-5.0 mmt average cavity clearance (t). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２５】
（２）直鎖状低密度ポリエチレン（Ｂ）
コモノマー；４−メチル−１−ペンテン
コモノマー含量：１３モル％
融点：１１５℃
密度：０．９１５（ｇ／ｃｍ^３）
ＭＦＲ：１５（ｇ／１０分）（１９０℃、２．１６ｋｇ荷重）
オルゼン剛性：２３０（ＭＰａ）
【００２６】
実施例１〜３および比較例１〜４
プロピレン系重合体（Ａ）としてのプロピレン・エチレンブロック共重合体（Ａ−１）と直鎖状低密度ポリエチレン（Ｂ）を表２に記載した配合割合（重量％）で混合し、押出機を用いてペレット化した（樹脂組成物１００重量部）。
それをさらに炭酸水素ナトリウム１５重量％、クエン酸１５重量％及び低密度ポリエチレン５０重量％とから構成された発泡剤マスターバッチ１．０重量部を加えてドライブレンドした（発泡性ポリプロピレン樹脂組成物ペレット）。
【００２７】
発泡性ポリプロピレン樹脂組成物ペレットを用い次に示す条件で射出成形して発泡成形品を得た。
なお、射出充填工程は発泡性樹脂組成物を連続して射出する方法をとり角板型（４０ｃｍ×２０ｃｍ）にて、成形した。
得られた成形体の表面外観評価結果を表２に示す。
【００２８】
なお、成形条件は次の通りであった。
射出成形機：宇部興産機械（株） ＭＤ３５０Ｓ−ＩＩＩ型
成形品サイズ：縦４０ｃｍ、横２０ｃｍ、厚さ２．５ｍｍの平板
ゲート構造：成形品中央１点ダイレクトゲート
射出温度：２００℃
射出圧力：１５０Ｍｐａ
射出時間：１．４秒（射出開始から原料の全量を射出し終了までの時間）
成形型表面温度：５０℃
【００２９】
実施例４〜９および比較例５〜１０
プロピレン系重合体（Ａ）としてのプロピレン・エチレンブロック共重合体（Ａ−１）を８０重量％と直鎖状ポリエチレン（Ｂ）を２０重量％で混合し、押出機を用いてペレット化した（樹脂組成物１００重量部）。
それをさらに炭酸水素ナトリウム１５重量％、クエン酸１５重量％及び低密度ポリエチレン５０重量％とから構成された発泡剤マスターバッチ１．０〜３．０重量部を加えてドライブレンドした（発泡性ポリプロピレン樹脂組成物ペレット）。
【００３０】
発泡性ポリプロピレン樹脂組成物ペレットを用い次に示す条件で射出成形して発泡成形品を得た。
なお、射出充填工程は発泡性樹脂組成物を連続して射出する方法をとり角板型（４０ｃｍ×２０ｃｍ）にて、成形した。
得られた成形体の発泡倍率、表面外観評価結果を表３に示す。
【００３１】
なお、成形条件は次の通りであった。
射出成形機：宇部興産機械（株） ＭＤ３５０Ｓ−ＩＩＩ型
成形品サイズ：縦４０ｃｍ、横２０ｃｍ、厚さ２．５ｍｍの平板
ゲート構造：成形品中央１点ダイレクトゲート
射出温度：２００℃
射出圧力：１５０Ｍｐａ
成形型表面温度：５０℃
【００３２】
【表２】

【００３３】
【表３】

【００３４】
【発明の効果】
本発明によれば、生産性の低下が少なく、シルバーストリークの発生を抑制し得るポリプロピレン樹脂発泡体の製造方法を提供することが可能となる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a molded article of a polypropylene resin foamed resin.
[0002]
[Prior art]
Polypropylene resin is widely used as a molding material because of its excellent physical properties and moldability. Also, its ease of recycling is increasing its recognition as an environmentally friendly material. Are expanding.
[0003]
In the field of application of automotive interior parts, polypropylene resin foam moldings have been attracting attention from the viewpoint of weight reduction, in addition to the fact that polypropylene resins have excellent physical properties such as low specific gravity, high rigidity, and high melting point.
As a method for producing a polypropylene resin foam molded article, a molding method called a full shot method in which a resin that has been fully filled and injected into a cavity is foamed by an amount corresponding to a volume shrinkage when the resin is solidified is known.
However, when attempting to manufacture a large molded product by the full shot method, there is a problem that silver streaks called silver streaks occur around the gate and at the end of the molded product.
[0004]
It is known that it is effective to use a resin having a high melt flow rate in order to stabilize the foam cells, so that a propylene-ethylene block copolymer having a high melt flow rate has a density of 0. There has been proposed a method of producing a polypropylene resin foam by injection molding an ethylene-1-octene random copolymer of 0.86 to 0.88 (g / cm ³ ) and a foaming agent (see Patent Document 1). ), Although the resin foam produced by the method suppresses the generation of silver streaks, there is a problem that the ethylene-1-octene random copolymer is agglomerated and the productivity is greatly reduced.
Therefore, it has been desired to develop a method for producing a polypropylene resin foam molded article which can reduce the productivity and suppress the occurrence of silver streaks.
[0005]
[Patent Document 1]
JP-A-2002-11748
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a foamed polypropylene resin article which can suppress the occurrence of silver streaks with little decrease in productivity.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to find a method for producing a polypropylene resin foam molded article that can solve the above-described problems, and as a result, have found that a propylene-based polymer has a density of 0.910 to 0.945 ( g / cm ³ ) with a linear low-density polyethylene using an injection mold to foam-mold a polypropylene resin foam in which the generation of silver streaks is suppressed. The invention has been completed.
That is, the present invention provides a propylene-based polymer (A) having a melt flow rate (MFR) of 5 to 150 (g / 10 minutes) measured at 230 ° C. under a load of 2.16 kg, 70 to 93% by weight, and a density of 0. Linear low-density polyethylene (B) 7 having a melt flow rate (MFR) of 1 to 50 (g / 10 minutes) measured at 0.99 to 0.945 (g / cm ³ ), 190 ° C. and a load of 2.16 kg; A foamed resin composition is prepared by blending 0.1 to 0.5 parts by weight of an inorganic chemical foaming agent (C) with 100 parts by weight of a resin composition consisting of 30% by weight to 30% by weight. The present invention provides a method for producing a polypropylene resin foam molded article, which is characterized in that foam molding is performed using an injection mold having a length of 1.0 mmt to 5.0 mmt.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Examples of the propylene-based polymer (A) used in the present invention include (1) a homopolymer of propylene, and (2) a copolymer of propylene with an α-olefin as a main component.
The copolymer with an α-olefin containing propylene as a main component is a copolymer of propylene with at least one selected from the group consisting of ethylene and α-olefins having 4 to 12 carbon atoms. It is preferable that the copolymer contains at least 50% by weight of a derived repeating unit (hereinafter may be referred to as “propylene unit”) based on 100% by weight of the copolymer.
The flexibility and impact resistance of the copolymer can be controlled by selecting the amount of the repeating unit derived from ethylene or an α-olefin having 4 to 12 carbon atoms in the copolymer.
Examples of the α-olefin include 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like. When the copolymer has two or more kinds of repeating units other than the propylene unit, the total amount of the repeating units other than the propylene unit is preferably 35% by weight or less. Specific examples of preferred polypropylene resins include (i) a homopolymer of propylene, (ii) a random copolymer of propylene and ethylene, (iii) a random copolymer of propylene and an α-olefin, and (iv) propylene. Examples include a random copolymer of ethylene and an α-olefin, and (v) a block copolymer of propylene and ethylene. These homopolymers or copolymers may be used alone or in combination of two or more.
[0009]
The propylene-based polymer (A) needs to have a melt flow rate (MFR) measured at 230 ° C. under a load of 2.16 kg of 5 to 150 (g / 10 min), and 50 to 120 (g / min). 10 minutes). When the MFR is in this range, good injection moldability is exhibited.
If the MFR is less than 5 (g / 10 minutes), the pressure loss in the mold cavity is large, and silver strike is likely to occur due to foam breaking. If the MFR exceeds 150 (g / 10 minutes), Impact strength decreases.
[0010]
The linear low-density polyethylene (B) used in the present invention is preferably a random copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms.
Examples of the α-olefin having 4 to 10 carbon atoms include butene-1, 4-methyl-1-pentene, hexene-1, and octene-1. Among these, 4-methyl-1-pentene and hexene-1 are preferred.
The α-olefin contained in the linear low-density polyethylene (B) may be one type or two or more types.
The linear low-density polyethylene (B) is preferably an ethylene-4-methyl-1-pentene random copolymer.
[0011]
The density of the linear low-density polyethylene (B) is required to be 0.910~0.945g / cm ^3, it is preferable that 0.915~0.925g / cm ^3. When the density is in this range, compatibility with the propylene-based polymer (A) is good, and characteristics excellent in balance between rigidity and impact strength can be obtained. If the density is less than 0.910 g / cm ³ , the rigidity of the obtained foamed polypropylene resin article is reduced. If the density exceeds 0.945 g / cm ³ , the impact strength will decrease.
[0012]
The linear low-density polyethylene (B) needs to have a melt flow rate (MFR) measured at 190 ° C. under a load of 2.16 kg of 1 to 50 (g / 10 minutes), and 10 to 40 (g / 10 minutes). g / 10 minutes). If it is less than 1 (g / 10 minutes), silver streaks tend to occur at the flow end, and if it exceeds 50 (g / 10 minutes), the impact strength is reduced.
The linear low-density polyethylene (B) has an effect of suppressing generation of silver streaks and improving impact strength.
[0013]
It is preferred that the resin composition comprising the propylene-based polymer (A) and the linear low-density polyethylene (B) does not contain ultrahigh molecular weight polypropylene.
Here, the ultrahigh molecular weight polypropylene refers to a polypropylene having an isotactic pentad fraction of 97% or more.
The resin composition needs to be composed of 70 to 93% by weight of the propylene-based polymer (A) and 7 to 30% by weight of the linear low-density polyethylene (B). It is preferably composed of 88% by weight and 12 to 25% by weight of a linear low density polyethylene (B), and 80 to 85% by weight of a propylene polymer (A) and 15 to 20% of a linear low density polyethylene (B). More preferably, it is composed of the weight%.
[0014]
Examples of the inorganic chemical blowing agent (C) used in the present invention include sodium hydrogen carbonate alone and a combination system of sodium hydrogen carbonate and an organic chemical blowing agent such as citric acid.
Among them, a combined system of sodium hydrogen carbonate and citric acid is preferably used.
The inorganic chemical foaming agent (C) needs to be 0.1 to 0.5 part by weight, and preferably 0.2 to 0.45 part by weight, based on 100 parts by weight of the resin composition. More preferably, it is 0.25 to 0.35 parts by weight.
If the amount of the inorganic chemical foaming agent (C) is less than 0.1 part by weight, foaming tends to be insufficient, and if it exceeds 0.5 part by weight, silver strike tends to occur.
[0015]
A foamed resin composition can be obtained by blending an inorganic chemical blowing agent (C) with a resin composition comprising a propylene-based polymer (A) and a linear low-density polyethylene (B). Examples of the compounding method of the foaming agent (C) include direct addition of an inorganic chemical foaming agent and addition of a foaming agent master batch.
[0016]
The polypropylene resin foam molded article can be obtained by subjecting the above foamed resin composition to foam molding using an injection mold having an average cavity clearance (t) of 1.0 mmt to 5.0 mmt.
The average cavity clearance (t) of the injection molding gold used needs to be 1.0 mmt to 5.0 mmt, preferably 1.5 mmt to 4.0 mmt, and more preferably 2.0 mmt to 3.0 mmt. More preferably, it is 0 mmt. If the average cavity clearance (t) is less than 1.0 mmt, the foaming becomes insufficient, and if it exceeds 5.0 mmt, silver strike tends to occur.
In the present invention, foam molding is performed using an injection mold.
Here, the injection temperature is usually 180 to 230 ° C, and preferably 190 to 220 ° C.
The injection time is usually 3.0 seconds or less, and preferably 2 seconds or less.
[0017]
The polypropylene resin foam molding of the present invention can be suitably used as interior and exterior parts of automobiles such as door trims, pillar garnishes, and side moldings since the occurrence of silver streaks is suppressed.
[0018]
【Example】
Hereinafter, the present invention will be described based on examples, but it goes without saying that the present invention is not limited to the examples.
[0019]
In addition, the physical properties of the compositions and molded articles obtained in the examples and comparative examples were evaluated by the following methods.
(1) MFR: Measured at 230 ° C., 190 ° C. under a load of 2.16 kg in accordance with ASTM D1238.
(2) Melting point (Tm): Measured using a differential scanning calorimeter DSC (Perkin Elmer) according to ASTM D3417.
[0020]
(3) Foaming ratio: The unfoamed product (dc0) measured by the underwater displacement method was divided by the specific gravity (dc1) of the foamed product, and the value was taken as (dc0 / dc1), and the value was taken as the foaming ratio. In addition, the expansion ratio was measured in a state including the skin layer.
[0021]
(4) High-speed penetrating impact strength: using a high-rate impact tester manufactured by Rheometrics, under the conditions of 23 ° C., under conditions of a striker tip diameter of 1/2 inch, a receiving ring diameter of 2 inches, and an impact speed of 3 m / s. A test was performed to determine the penetration energy (J).
[0022]
(5) Appearance: The surface of the foamed product was visually observed and judged according to the following criteria.
[Silver streak]
：: Not observed on the product surface at all, and has the same appearance as unfoamed.
：: Very slight in a part of the product, but almost no problem.
Δ: Slightly observed in a part of the product.
X: Many are seen on the entire surface.
[0023]
The physical properties of the propylene / ethylene block copolymer (A-1) and the linear low-density polyethylene (B) as the propylene-based polymer (A) used in the examples were as follows.
(1) Propylene / ethylene block copolymer (A-1)
[0024]
[Table 1]

[0025]
(2) Linear low density polyethylene (B)
Comonomer; 4-methyl-1-pentene comonomer content: 13 mol%
Melting point: 115 ° C
Density: 0.915 (g / cm ³ )
MFR: 15 (g / 10 minutes) (190 ° C., 2.16 kg load)
Olsen rigidity: 230 (MPa)
[0026]
Examples 1-3 and Comparative Examples 1-4
The propylene / ethylene block copolymer (A-1) as the propylene-based polymer (A) and the linear low-density polyethylene (B) were mixed at the mixing ratio (% by weight) described in Table 2, and the extruder was used. And pelletized (100 parts by weight of the resin composition).
Further, 1.0 part by weight of a foaming agent master batch composed of 15% by weight of sodium hydrogen carbonate, 15% by weight of citric acid and 50% by weight of low-density polyethylene was added and dry-blended (foamable polypropylene resin composition pellets). ).
[0027]
Injection molding was performed using the foamable polypropylene resin composition pellets under the following conditions to obtain a foam molded article.
In the injection filling step, a method of continuously injecting the foamable resin composition was used, and the foamed resin composition was molded in a square plate type (40 cm × 20 cm).
Table 2 shows the results of evaluating the surface appearance of the obtained molded body.
[0028]
The molding conditions were as follows.
Injection molding machine: Ube Industries Machinery Co., Ltd. MD350S-III Molded product Size: 40cm long, 20cm wide, 2.5mm thick flat plate Gate structure: One point at the center of molded product Direct gate Injection temperature: 200 ° C
Injection pressure: 150Mpa
Injection time: 1.4 seconds (time from the start of injection to the end of injection of the entire amount of raw material)
Mold surface temperature: 50 ° C
[0029]
Examples 4 to 9 and Comparative Examples 5 to 10
80% by weight of the propylene / ethylene block copolymer (A-1) as the propylene-based polymer (A) and 20% by weight of the linear polyethylene (B) were mixed and pelletized using an extruder ( 100 parts by weight of a resin composition).
Further, 1.0 to 3.0 parts by weight of a foaming agent master batch composed of 15% by weight of sodium hydrogen carbonate, 15% by weight of citric acid and 50% by weight of low-density polyethylene was added and dry-blended (foamable polypropylene). Resin composition pellets).
[0030]
Injection molding was performed using the foamable polypropylene resin composition pellets under the following conditions to obtain a foam molded article.
In the injection filling step, a method of continuously injecting the foamable resin composition was used, and the foamed resin composition was molded in a square plate type (40 cm × 20 cm).
Table 3 shows the expansion ratio and surface appearance evaluation results of the obtained molded article.
[0031]
The molding conditions were as follows.
Injection molding machine: Ube Industries Machinery Co., Ltd. MD350S-III Molded product Size: 40cm long, 20cm wide, 2.5mm thick flat plate Gate structure: One point at the center of molded product Direct gate Injection temperature: 200 ° C
Injection pressure: 150Mpa
Mold surface temperature: 50 ° C
[0032]
[Table 2]

[0033]
[Table 3]

[0034]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the polypropylene resin foam which can suppress generation | occurrence | production of silver streak with little decrease in productivity.

Claims (2)

70-93% by weight of a propylene polymer (A) having a melt flow rate (MFR) of 5 to 150 (g / 10 minutes) measured at 230 ° C under a load of 2.16 kg, and a density of 0.91 to 0.945. (G / cm ³ ), a melt flow rate (MFR) measured at 190 ° C. under a load of 2.16 kg is 1 to 50 (g / 10 minutes), and is 7 to 30% by weight of linear low density polyethylene (B). With respect to 100 parts by weight of the resin composition, 0.1 to 0.5 parts by weight of the inorganic chemical blowing agent (C) is blended to prepare a foamed resin composition, and the average cavity clearance (t) is 1.0 mmt. A method for producing a foamed molded article of a polypropylene resin, wherein foaming is carried out using an injection molding die of up to 5.0 mmt. A foamed polypropylene resin article having an expansion ratio of 1.01 to 1.2, obtained by the production method according to claim 1.