JP4347942B2 - Polypropylene resin foam particles for molding - Google Patents

Description

【００１０】
（但し上記（１）式中、Ｐｗ は発泡粒子１個当たりの平均重量（ｍｇ）、Ｅｒ は発泡粒子の嵩発泡倍率（倍）、Ｄは発泡粒子の気泡径（ｍｍ）、Ａは基材樹脂の密度（ｇ／ｃｍ³）を示す。）
【００１１】
本発明の発泡粒子は、示差走査熱量測定において得られるＤＳＣ曲線に、発泡粒子の基材樹脂の融解熱に相当する固有ピークよりも高温側に高温ピークが現れ、該高温ピークの熱量が１０Ｊ／ｇ以上、１５Ｊ／ｇ未満であるものが好ましい。
【００１２】
【発明の実施の形態】
本発明の発泡粒子の基材樹脂は無架橋プロピレン系ランダム共重合体であり、プロピレンと共重合される他のコモノマーとしては、エチレン、１−ブテン、１−ペテン、１−ヘキセン等のプロピレン以外のα−オレフィン等が挙げられる。上記プロピレン系ランダム共重合体は、プロピレン−エチレンランダム共重合体、プロピレン−ブテンランダム共重合体等の２元共重合体であっても、プロピレン−エチレン−ブテンランダム共重合体等の３元共重合体であっても良い。共重合体中におけるプロピレン以外のコモノマー成分の割合は、０．０５〜１５重量％、特に０．１〜１０重量％が好ましい。コモノマー成分の割合が０．０５重量％に満たない場合には、発泡成型体の耐寒性等の物性が低下し、１５重量％を超えると共重合体の融点を１４０℃以上とすることが困難となり、この結果、発泡成型体の耐熱性や、圧縮強さ等の機械的物性が低下する虞れがある。
【００１３】
本発明の発泡粒子は、基材樹脂の融点が１４０℃以上であることが必要であるが、発泡粒子を成型する際の生産性や設備コスト等を考慮すると、プロピレン系樹脂ランダム共重合体の融点は１６０℃以下であることが好ましく、特に１４１〜１５５℃であることが好ましい。更に、発泡粒子の基材樹脂であるプロピレン系ランダム共重合体は、発泡成型体の耐熱性及び発泡粒子製造時の発泡効率を考慮すると、メルトフローレイトが０．５〜１２ｇ／１０分のものが好ましく、特に４〜１０ｇ／１０分のものが好ましい。尚、メルトフローレイトはＪＩＳ Ｋ７２１０の試験条件１４で測定された値である。
【００１４】
本発明の発泡粒子は、前記（１）式で示されるＣＮＩの値が２．００以上、３．８０未満のものである。（１）式において、発泡粒子１個当たりの平均重量：Ｐｗは、無作為に選んだ発泡粒子１０個の総重量を測定し、その総重量を発泡粒子の個数（即ち、１０）で除して求めた値である。また発泡粒子の気泡径：Ｄは発泡粒子内に存在する気泡の平均径である。具体的には、無作為に選んだ発泡粒子を略中心部で切断し、その切断面を顕微鏡に写し出した画面上又は顕微鏡写真上にて、任意の気泡壁から別の任意の気泡壁までの任意の長さ：Ｌの直線上に存在する気泡数：Ｎを数え、下記（２）式により各発泡粒子の平均気泡径：Ｄ´を求める。但し、該直線の始点は任意の気泡壁とし、終点は別の任意の気泡壁とし、始点と終点との間には少なくとも１０個の気泡が存在するようにする。
【００１５】
【数３】
Ｄ´＝１．６２×（Ｌ÷Ｎ） ・・・・（２）
【００１６】
以上の操作を計３個の発泡粒子に対して行い、発泡粒子３個分の平均気泡径：Ｄ´を相加平均することにより発泡粒子の気泡径：Ｄを算出する。
【００１７】
上記（１）式における発泡粒子の嵩発泡倍率：Ｅrは後述の測定に基づく発泡粒子の見掛け発泡倍率に１．６を乗じた値が便宜上採用される。また基材樹脂の密度：Ａは本発明では便宜上、０．９ｇ／ｃｍ³とする。
【００１８】
本発明の発泡粒子は、上記ＣＮＩの値が２．００以上、３．８０未満であるとともに発泡粒子を空気で加圧処理して付与した粒子内空気圧が、２３℃の大気圧下において１．２ｋｇｆ／ｃｍ^２（Ｇ）から０．８ｋｇｆ／ｃｍ^２（Ｇ）（圧力の単位：ｋｇｆ／ｃｍ^２の後の“（Ｇ）”は、ゲージ圧を意味する。）に減衰する時間（以下、単に内圧減衰時間と呼ぶ。）が８０分以上のものである。発泡粒子の内圧減衰時間を測定するためには、まず発泡粒子を空気で加圧処理して発泡粒子内に空気を浸透させて高い内圧を付与し、付与した内圧が１．２ｋｇｆ／ｃｍ^２（Ｇ）から０．８ｋｇｆ／ｃｍ^２（Ｇ）まで減衰する時間を測定する。具体的には以下の方法により測定される。
【００１９】
まず、発泡粒子は通過させないが空気は自由に通過できるサイズの針穴を多数穿設した７０ｍｍ×１００ｍｍ程度のポリエチレン製袋の中に複数個の発泡粒子を収容する。次に、この発泡粒子入り袋を２３℃に保持しながら密閉容器内にて空気で加圧することにより２〜３ｋｇｆ／ｃｍ²(G)の空気内圧を発泡粒子に付与する。ついで、その袋を密閉容器内から２３℃の大気圧下の恒温室に取り出し、直ちに秤に乗せて重量を読み取る（最初に重量を読み取った時間を基準時間とする。）。その袋を秤に乗せたままとし、基準時間から２時間後までは５分おきに重量を読み取り、基準時間から２時間後より基準時間から４８時間後までは３０分おきに重量を読み取る。発泡粒子内の加圧空気は時間の経過とともに気泡膜を透過して外部に抜け出すため発泡粒子の重量はそれに伴って減少し、基準時間から４８時間後では平衡に達しているため実質的にその重量は安定している。上記４８時間後の重量測定を終えてから直ちに同恒温室内にて袋から発泡粒子の全てを取り出して袋の重量を読み取る。上記のいずれにおいても重量は０．０００１ｇまで読み取るものとする。得られたデータより発泡粒子重量（ｇ）を縦軸とし、時間（分）を横軸にして発泡粒子重量−時間曲線を作成する。尚、縦軸の発泡粒子重量は、発泡粒子入り袋の重量からポリエチレン製袋の重量を差し引いた値である。
【００２０】
得られた発泡粒子重量−時間曲線より、発泡粒子の空気内圧が１．２ｋｇｆ／ｃｍ²(G)に相当する粒子重量となった時間：ｔ_1.2（分）から、空気内圧が０．８ｋｇｆ／ｃｍ²(G)に相当する重量となるまでの時間：ｔ_0.8（分）を読み取る。このようにして得られたｔ_0.8（分）−ｔ_1.2（分）が、本発明で言う「内圧減衰時間」である。尚、発泡粒子の空気内圧：Ｐ（ｋｇｆ／ｃｍ²(G)）は、下記（３）式より算出される。
【００２１】
【数４】
Ｐ＝（Ｗ÷Ｍ）×Ｒ×Ｔ×Ｑ÷Ｖ ・・・・（３）
【００２２】
上記（３）式は気体の状態式を変形したものであり、（３）式中の各記号は以下の通りである。
【００２３】
Ｗは増加空気重量（ｇ）であり、各時間における発泡粒子重量と基準時間から４８時間後の発泡粒子重量：Ｓ（ｇ）との差を意味する。Ｍは空気の分子量であり、ここでは２８．８（ｇ）の定数を採用する。Ｒは気体定数であり、ここでは０．０８２（ａｔｍ・ｌ/Ｋ・ｍｏｌ）の定数を採用する。Ｔは絶対温度を意味し、２３℃の雰囲気が採用されいてるので、ここでは２９６（°Ｋ）の定数である。Ｑは圧力をａｔｍ単位からｋｇｆ／ｃｍ²単位に換算するための係数であり、ここでは１．０３３２（ｋｇｆ／ｃｍ²／ａｔｍ)を採用する。Ｖは発泡粒子の見掛け体積から発泡粒子中に占める基材樹脂の体積を差し引いた体積（ｌ）を意味する。尚、上記基準時間から４８時間後に袋から取り出された発泡粒子の全量を直ちに２３℃の水１００ｃｍ³が収容されたメスシリンダー内の水に水没させたときの目盛りから、発泡粒子の体積：Ｙ（ｃｍ³）を算出し、これをリットル（ｌ）単位に換算してこれを発泡粒子の見掛け体積（ｌ）とする。また発泡粒子中に占める基材樹脂の体積は、上記体積：Ｙ（ｃｍ³）を発泡粒子の見掛け発泡倍率（倍）で除してその値をリットル（ｌ）単位に換算することで求められる。発泡粒子の見掛け発泡倍率は、基材樹脂密度：Ａ（０．９ｇ／ｃｍ³）を発泡粒子の見掛け密度（ｇ／ｃｍ³）で除すことにより求められる。また発泡粒子の見掛け密度（ｇ／ｃｍ³）は上記発泡粒子重量：Ｓ（ｇ）を体積：Ｙ（ｃｍ³）で除すことにより求められる。
【００２４】
尚、以上の測定においては、発泡粒子重量：Ｓが０．５０００〜１０．００００ｇで、且つ体積：Ｙが５０〜９０ｃｍ³となる量の複数個の発泡粒子が使用される。
【００２５】
上記内圧減衰時間が８０分未満の発泡粒子は、発泡粒子を金型内等で成型して得た、成型直後の発泡成型体に生じる収縮を回復するのに長い時間を要したり、或いは収縮が回復しないものが含まれる割合が高くなり、成型体の不良率が高くなる。このような観点から、上記内圧減衰時間は、８５分以上であることが好ましく、特に９０分以上であることが好ましい。
【００２６】
上記ＣＮＩ値が３．８０以上になると成型時に必要な成型用飽和水蒸気の圧力が高くなってしまい、本発明の目的が達成できない。尚、ＣＮＩ値を３．６０以下にすれば、成型時に必要な成型用飽和水蒸気の圧力をより低下させることが可能となるため好ましいが、ＣＮＩ値があまり小さくなりすぎると、機械的圧縮等により発泡粒子が連続気泡状態になり易く、また養生後の成型体表面に皺が入り易くなる、等の問題が起こり得るので、ＣＮＩの下限値は２．００である。従って、ＣＮＩの値は３．６０〜２．００であることが好ましい。尚、上記ＣＮＩの値は、発泡粒子１個当たりに含まれる気泡数が多くなるほど大きな値を示し、その気泡数が少なくなるほど小さな値を示すことになる。
【００２７】
発泡粒子は小さいものの方が成型時の飽和水蒸気圧を小さくできる利点があり、一方、発泡粒子が小さすぎると発泡効率が悪くなるため、本発明の発泡粒子の１個当たりの平均重量は０．２〜１．１ｍｇである。発泡粒子１個当たりの平均重量が４．０ｍｇを超える場合、成型時に高い圧力の飽和水蒸気が必要となり、また得られた発泡成型体の断熱性が低下したり機械的な圧縮を受けると気泡が破泡しやすくなる等の虞れがある。
【００２８】
また本発明の発泡粒子は、発泡粒子の示差走査熱量測定において得られるＤＳＣ曲線に、発泡粒子の基材樹脂の融解熱に相当する固有ピークよりも高温側に高温ピークが現れ、該高温ピークの熱量が１０Ｊ／ｇ以上、１５Ｊ／ｇ未満であるものが好ましい。高温ピークの熱量が１０Ｊ／ｇ未満の場合、発泡成型体の圧縮強度、エネルギー吸収量等が低下する一方、成型後に加熱養生しても成型体に生じた収縮が回復されにくい傾向にあり、また高温ピークの融解熱量が１５Ｊ／ｇ以上の場合には、発泡粒子を成型する際の内圧付与のための処理時間が長く必要となる虞れがある。本発明において上記高温ピークの熱量が、特に１１〜１４Ｊ／ｇのものが好ましい。
【００２９】
上記高温ピークの熱量とは、発泡粒子２〜４ｍｇを、示差走査熱量計によって室温から２２０℃まで１０℃／分で昇温した時に得られるＤＳＣ曲線（図１に示す。）に現れる、基材樹脂に固有の固有ピークａが現れる温度よりも高温側に現れる高温ピークｂの熱量で、該高温ピークｂの面積に相当するものであり、例えば次のようにして求めることができる。即ち、まずＤＳＣ曲線上の８０℃に相当する点αと、発泡粒子の融解終了温度Ｔ_E に相当するＤＳＣ曲線上の点βとを結ぶ直線（α−β）を引く。次に固有ピークａと高温ピークｂとの間の谷部に当たるＤＳＣ曲線上の点γからグラフの縦軸と平行な直線を引き、前記直線（α−β）と交わる点をδとする。高温ピークｂの面積は、ＤＳＣ曲線の高温ピークｂの部分の曲線と、線分（δ−β）と、線分（γ−δ）とによって囲まれる部分（図１において斜線を付した部分）の面積である。
【００３０】
この高温ピークｂは、上記のようにして測定した第１回目のＤＳＣ曲線には現れるが、第１回目のＤＳＣ曲線を得た後、２２０℃から１０℃／分で一旦、４０℃付近まで降温し、再び１０℃／分で２２０℃まで昇温した時に得られる第２回目のＤＳＣ曲線には現れず、第２回目のＤＳＣ曲線には基材樹脂に固有の固有ピークａのみが現れる。
【００３１】
発泡粒子の嵩発泡倍率が低いものからは、低発泡の成型体しか得ることができないが、発泡粒子の嵩発泡倍率が高いものからは、低発泡の成型体も高発泡の成型体も容易に得ることができる。このような観点から、本発明の発泡粒子の嵩発泡倍率は４０倍以上である。一方、発泡粒子の嵩発泡倍率があまりにも高くなりすぎると気泡が破泡しやすくなるので、嵩発泡倍率は８０倍以下である。
【００３２】
本発明の発泡粒子の製造には、例えばプロピレン系樹脂粒子を発泡剤と共に密閉容器内で水等の分散媒に分散させ、加熱して樹脂粒子を軟化させるとともに樹脂粒子に発泡剤を含浸させた後、樹脂粒子の軟化温度以上の温度で容器内より低圧下に樹脂粒子を放出して発泡させる、公知の発泡方法を適用することができる。この際、予め樹脂粒子１個当たりの平均重量と目的とする発泡粒子の嵩発泡倍率を決めれば、後は発泡粒子の気泡径を調節することでＣＮＩ値が３．８０未満の発泡粒子を製造することができる。発泡粒子の気泡径の調節は、主として無機粉体等の気泡調節剤の使用によって行われるが、発泡温度や発泡剤の種類及び使用量等でも気泡径が変化する。よって、目的の気泡径を得るには予備実験をして条件を設定する必要がある。また、得られる発泡粒子に対して、上記内圧減衰時間が８０分以上となる性質を付与するには、発泡粒子のＤＳＣ曲線における高温ピークの熱量が８Ｊ／ｇ以上、好ましくは１０Ｊ／ｇ以上となるような条件で発泡粒子を製造すれば良い。上記高温ピークを有する発泡粒子は、上記公知の発泡方法において樹脂粒子を密閉容器内で分散媒に分散させて加熱する際に、樹脂粒子の融解終了温度：Ｔｅ以上に昇温することなく、樹脂粒子の〔融点：Ｔｍ−１５℃〕以上、融解終了温度：Ｔｅ未満の範囲内の任意の温度：Ｔａで止めて、その温度：Ｔａで十分な時間（好ましくは１０〜６０分程度）保持し、その後、〔融点：Ｔｍ−５℃〕〜〔融解終了温度：Ｔｅ＋５℃〕の範囲の任意の温度：Ｔｂに調節し、その温度：Ｔｂで止めて、必要であれば当該温度で更に十分な時間（好ましくは１０〜６０分程度）保持してから、樹脂粒子を容器内から放出して発泡させる方法により得ることができる。
【００３３】
また発泡粒子の上記高温ピークの熱量の大小は、主として、発泡粒子を製造する際の樹脂粒子に対する上記温度：Ｔａと該温度：Ｔａにおける保持時間、及び上記温度：Ｔｂと該温度：Ｔｂにおける保持時間並びに昇温速度に依存する。発泡粒子の上記高温ピークの熱量は、温度：Ｔａ又はＴｂが上記温度範囲内において低い程、保持時間が長い程、更に昇温速度が遅い程、大きくなる傾向を示す。通常、昇温速度は０．５〜５℃／分が採用される。これらの点を考慮して予備実験を繰り返せば、所望の高温ピーク熱量を示す発泡粒子の製造条件は容易に知ることができる。
【００３４】
尚、以上で説明した温度範囲は、発泡剤として無機ガス系発泡剤を使用した場合の適切な温度範囲である。従って、発泡剤が有機揮発性発泡剤に変更された場合には、その種類や使用量に応じてその適切な温度範囲は上記温度範囲よりもそれぞれ低温側にシフトすることになる。
【００３５】
また上記融点：Ｔｍとは、樹脂粒子２〜４ｍｇを試料として用いて前述の如き発泡粒子のＤＳＣ曲線を得るのと同様の方法で樹脂粒子に対して示差走査熱量測定を行い、これによって得られた２回目のＤＳＣ曲線（その一例を図２に示す。）に現れる固有ピークａの頂点の温度であり、融解終了温度：Ｔｅとは、該固有ピークａの裾が高温側でベースライン（α−β）の位置に戻ったときの温度を言う。
【００３６】
上記方法において用いる発泡剤としては、有機揮発性発泡剤や無機ガス系発泡剤、或いはこれらの混合物等を用いることができる。揮発性発泡剤としてはプロパン、ブタン、ヘキサン、ヘプタン等の脂肪族炭化水素類、シクロブタン、シクロヘキサン等の環式脂肪族炭化水素類、クロロフロロメタン、トリフロロメタン、１，１−ジフロロエタン、１，２，２，２−テトラフロロエタン、メチルクロライド、エチルクロライド、メチレンクロライド等のハロゲン化炭化水素等が挙げられ、これらは２種以上を混合して用いることができる。また無機ガス系発泡剤としては、窒素、二酸化炭素、アルゴン、空気等が挙げられ、これらは２種以上を混合して用いることができる。揮発性発泡剤と無機ガス系発泡剤とを混合して用いる場合、上記した揮発性発泡剤と無機ガス系発泡剤より任意に選択した化合物を組み合わせて用いることができる。上記発泡剤のうち、特にオゾン層破壊の虞れがなく、安価な無機ガス系発泡剤が好ましく、なかでも窒素、空気、二酸化炭素が好ましい。
【００３７】
発泡剤の使用量は、得ようとする発泡粒子の発泡倍率に応じ、また基材樹脂の種類、発泡剤の種類等を考慮して決定するが、通常、樹脂１００重量部当たり、揮発性発泡剤で５〜５０重量部、無機ガス系発泡剤で０．５〜３０重量部程度を用いることが好ましい。
【００３８】
発泡粒子製造に際して樹脂粒子を分散させる分散媒としては、上記した水に限らず、樹脂粒子を溶解させない溶媒であれば使用することができる。水以外の分散媒としては、例えばエチレングリコール、グリセリン、メタノール、エタノール等が挙げられるが、通常は水を用いることが好ましい。また樹脂粒子を分散媒に分散させるに際し、必要に応じて分散剤を分散媒に添加することができる。分散剤としては、微粒状の酸化アルミニウム、酸化チタン、塩基性炭酸マグネシウム、塩基性炭酸亜鉛、炭酸カルシウム、カオリン、マイカ、クレー等が挙げられる。これら分散剤は通常、樹脂粒子１００重量部当たりに対し、０．２〜２重量部程度使用される。
【００３９】
樹脂粒子としては、前記したプロピレン系ランダム共重合体よりなるものが用いられるが、本発明の所期の効果を損なわない範囲内において、プロピレン系ランダム共重合体に、他のプロピレン系樹脂（例えばプロピレン系ブロック共重合体等）や、高密度ポリエチレン、中密度ポリエチレン、低密度ポリエチレン、直鎖状低密度ポリエチレン、直鎖状超低密度ポリエチレン、エチレン−酢酸ビニル共重合体、エチレン−アクリル酸共重合体、エチレン−メタクリル酸共重合体等のエチレン系樹脂、或いはポリスチレン、スチレン−無水マレイン酸共重合体等のスチレン系樹脂、他の樹脂を配合して用いることができる。
【００４０】
また上記樹脂の他に、エチレン−プロピレンゴム、エチレン−１−ブテンゴム、プロピレン−１−ブテンゴム、スチレン−ブタジエンゴムやその水添物、イソプレンゴム、ネオプレンゴム、ニトリルゴム、或いはスチレン−ブタジエンブロック共重合体エラストマーやその水添物等のエラストマーを添加することもできる。上記プロピレン系ランダム共重合体以外の樹脂やエラストマー等を配合する場合、これらプロピレン系ランダム共重合体以外の樹脂やエラストマーの添加量は、合計で１０重量％程度以下となるようにすることが好ましい。
【００４１】
更にまた樹脂粒子中には、各種添加剤を添加することができる。このような添加剤としては、例えば酸化防止剤、紫外線吸収剤、帯電防止剤、難燃剤、金属不活性剤、顔料、染料、結晶核剤、或いはホウ酸亜鉛、タルク、炭酸カルシウム、ホウ砂、水酸化アルミニウム等の無機粉体等が挙げられる。これらの添加剤は合計で樹脂粒子１００重量部当たり、２０重量部以下、特に５重量部以下添加することが好ましい。
【００４２】
尚、上記した方法によって得られたポリプロピレン系樹脂発泡粒子は、大気圧下で熟成した後、加圧空気下で加圧処理して内圧を付与し、その後、水蒸気や熱風を用いて加熱する（この工程を以下、二段発泡と言う。）ことによって、より高発泡倍率の発泡粒子とすることが可能である。
【００４３】
発泡成型体は、発泡粒子を必要に応じて気泡内圧を高めてから、加熱及び冷却が可能であって且つ開閉し密閉できる型内に充填し、水蒸気圧１．５〜６．０ｋｇｆ／ｃｍ²(G)のスチームを供給して型内で発泡粒子同士を加熱して膨張させて融着させ、次いで冷却して型内から取り出すバッチ式成型法を採用して製造することができる。また、発泡成型体は発泡粒子を、必要に応じて気泡内圧を高めてから、通路内の上下に沿って連続的に移動するベルト間に連続的に供給し、水蒸気加熱領域を通過する際に発泡粒子同士を膨張融着させ、その後冷却領域を通過させて冷却し、次いで得られた成型体を通路内から取り出し、適宜長さに順次切断する連続式成型法（例えば特開平９−１０４０２６号、特開平９−１０４０２７号及び特開平１０−１８０８８８号等に記載される成型方法）により製造することもできる。尚、発泡粒子の気泡内圧を高めるには、密閉容器に発泡粒子を入れ、該容器内に加圧空気を供給した状態で適当な時間放置して発泡粒子内に加圧空気を浸透させればよい。
【００４４】
以上のようにして製造される発泡成型体は、ＡＳＴＭ−Ｄ２８５６−７０の手順Ｃに基づく連続気泡率が４０％以下であることが好ましく、３０％以下であることがより好ましく、２５％以下であることが最も好ましい。連続気泡率が小さい成型体ほど、機械的強度に優れる。
【００４５】
【実施例】
以下、実施例を挙げて本発明を更に詳細に説明する。
実施例１〜２、参考例１、比較例１〜３
プロピレン−エチレンランダム共重合体（融点１４６℃、エチレン成分２．３重量％、ＪＩＳ Ｋ７２１０の条件１４で測定されたメルトフローレイト１０ｇ／１０分）１００重量部当たりに対し、表１に示す量のホウ酸亜鉛（富田製薬株式会社製のホウ酸亜鉛２３３５）を押出機内で添加して両者を押出機内で溶融混練し、ストランド状に押出して急冷した後、ペレタイザーにて切断し、ミニペレット（樹脂粒子）を製造した。
【００４６】
続いて、オートクレーブ内に上記ミニペレット１００重量部、分散媒として水３００重量部、分散剤としてカオリン０．３重量部、界面活性剤としてドデシルベンゼンスルホン酸ナトリウム０．００６重量部、及び発泡剤として表１に示す量の二酸化炭素（ドライアイス）を充填して密閉した後、オートクレーブ内容物を攪拌しつつ、２℃／分の昇温速度で表１に示す温度（Ｔａ）まで加熱し、同温度温度（Ｔａ）で表１に示す時間保持し、次いで１℃／分の昇温速度で表１に示す温度（Ｔｂ）まで加熱し、同温度（Ｔｂ）で表１に示す時間保持した後、オートクレーブ底部に取り付けられたバルブを開放し、オートクレーブ内容物を大気圧下に放出して発泡粒子（一段発泡粒子）を得た。尚、この際、オートクレーブ内に高圧の空気を導入しつつ放出を行った。得られた一段発泡粒子を常温、大気圧下で２４時間放置した後、嵩発泡倍率を測定し、次いで常温の加圧空気を使用して表１に示す空気内圧を発泡粒子に付与した後、０．６ｋｇｆ／ｃｍ²(G) の飽和水蒸気を吹きつけて高発泡の発泡粒子（二段発泡粒子）を得た。得られた二段発泡粒子を、常温、大気圧下で２４時間放置してから該二段発泡粒子の平均重量（ｍｇ）、嵩発泡倍率（倍）、高温ピークの融解熱量（Ｊ／ｇ)、平均気泡径（ｍｍ）及び内圧減衰時間（分）を測定した。更に、これらのデータに基づいてＣＮＩ値を計算により求めた。これらの結果を表２に示す。
【００４７】
続いて、二段発泡粒子に対し、常温の加圧空気を使用して１．２ｋｇｆ／ｃｍ²(G) の空気内圧を発泡粒子に付与した後、直ちに３００ｍｍ×３００ｍｍ×６０ｍｍの内寸法を持つ金型に充填し、次いで本加熱時の飽和水蒸気よりも０．８〜０．４ｋｇｆ／ｃｍ²(G) 低い圧力の飽和水蒸気を使用して予備加熱した後、表２に示す圧力の飽和水蒸気（表２中では「最低飽和水蒸気圧」と表示）を型内に導入して本加熱を行った。得られた成型体は、大気圧下、６０℃で２４時間養生した。尚、「最低飽和水蒸気圧」とは、外観が良好（成型体表面のボイドが少ない）で、収縮が小さく（金型内容積１００％に対する養生後の成型体の体積が９０％以上である）、且つ発泡粒子間の融着度合いの高い（得られた成型体より厚さ１０ｍｍ×幅３０ｍｍ×長さ１００ｍｍとなるように切断して得られた試験片を、引張試験機にて５００ｍｍ／分の速度で引張って破断させて破断面を観察し、このときの破断面の材料破壊の割合が６０％以上）成型体を得るのに必要な最低飽和水蒸気圧を意味する。
【００４８】
【表１】

【００４９】
【表２】

【００５０】
参考例２
実施例１と同じ操作を繰り返して一段発泡粒子を製造した。得られた一段発泡粒子を常温、大気圧下で２４時間放置してから該一段発泡粒子の平均重量（ｍｇ）、嵩発泡倍率（倍）、高温ピークの融解熱量（Ｊ／ｇ)、平均気泡径（ｍｍ）及び内圧減衰時間（分）を測定した。更に、これらのデータに基づいてＣＮＩ値を計算により求めた。これらの結果を表２に示す。
【００５１】
続いて、その一段発泡粒子に対し、常温の加圧空気を使用して０．８ｋｇｆ／ｃｍ²(G) の空気内圧を付与した後、直ちに３００ｍｍ×３００ｍｍ×６０ｍｍの内寸法を持つ金型に充填し、次いで本加熱時の飽和水蒸気よりも０．８〜０．４ｋｇｆ／ｃｍ²(G) 低い圧力の飽和水蒸気を使用して予備加熱した後、表２に示す「最低飽和水蒸気圧」を型内に導入して本加熱を行った。得られた成型体は、大気圧下、６０℃で２４時間養生した。
【００５２】
【発明の効果】
以上説明したように本発明の発泡粒子は、１４０℃以上という高融点の無架橋プロピレン系ランダム共重合体を基材樹脂とする発泡粒子であるため、機械的物性に優れた発泡成型体を得ることができる。しかも、本発明の発泡粒子は基材樹脂の融点が高いにもかかわらず、従来の同融点の無架橋プロピレン系ランダム共重合体を基材とする発泡粒子に比べ、低い圧力の水蒸気によって加熱しても発泡粒子間の融着性に優れ、粒子間の空隙の少ない、又は空隙のない外観良好な発泡成型体を得ることができる。更に本発明の発泡粒子は低圧水蒸気による成型が可能であるから、従来の同融点の無架橋プロピレン系樹脂発泡粒子に比べ、発泡粒子の成型用水蒸気にかかるエネルギーコストの低減化を図ることができ、また成型サイクルも短くすることができるため生産性の向上を図ることができる等の効果を有する。
【図面の簡単な説明】
【図１】本発明の成型用ポリプロピレン系樹脂発泡粒子の、第１回目のＤＳＣ曲線のチャートの一例を示す図である。
【図２】ポリプロピレン系樹脂粒子の第２回目のＤＳＣ曲線のチャートの一例を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a foamed polypropylene resin particle for molding.
[0002]
[Prior art]
Polypropylene-based resin foams are widely used as packaging materials, building materials, heat insulating materials and the like because they are excellent in properties such as mechanical strength and buffering properties. As a method for producing a polypropylene resin foam, methods such as an extrusion molding method and an in-mold molding method are known.
[0003]
Of these, the extrusion molding method is a suitable method for continuously obtaining long foams, but this method can produce plate-like foams, columnar foams, or the direction of extrusion on these surfaces. It is difficult to obtain a foam having a complicated shape because the cross-sectional shape perpendicular to the extrusion direction is always the same long foam, such as a shape having ridges extending along the direction. On the other hand, the in-mold molding method is a method in which polypropylene resin foamed particles are filled in a mold, and the foamed particles are fused by steam heating to obtain a mold-shaped foam molded product. As long as the body can be released from the mold, a molded body having an arbitrary shape can be obtained depending on the shape of the inner surface of the mold. For this reason, the in-mold molding method is widely used for producing foamed molded products having various shapes.
[0004]
In the in-mold molding method, when the expanded particles filled in the mold are heated, it is necessary that the expanded particles expand to fill the gaps between the particles and to ensure that the particles are fused. For this reason, it is necessary to impart foaming ability to the foamed particles filled in the mold so that the foamed particles can be expanded by heating. Therefore, the foaming ability is given by compressing and filling the volume before filling the foamed particles into the mold, or the foamed particle internal pressure is reduced by pressurizing with air before filling the foamed particles into the mold. A method of imparting foaming ability by increasing is employed.
[0005]
Among the above methods, the in-mold molding method using expanded particles having an increased internal pressure is more suitable as a method for obtaining a foamed molded article having a higher expansion ratio than the in-mold molding method using compressed expanded particles. is there.
[0006]
[Problems to be solved by the invention]
Incidentally, in recent years, with the spread of polypropylene resin foams, foams with higher mechanical properties such as compressive strength have been demanded. In order to meet such demands, higher melting point polypropylene resins have come to be used as the base resin for the expanded particles. However, when molding using non-crosslinked polypropylene resin foam particles, which is preferable in terms of reusability, the higher the melting point of the base resin, the higher the melting point of the base resin, as long as the resin type and expansion ratio are the same. Unless the pressure (steam temperature) of the saturated water vapor for molding is increased, it is not possible to obtain an excellent molded body having excellent fusion properties between the foamed particles and few gaps between the particles. Therefore, high-melting point non-crosslinked polypropylene resin foamed particles need to be molded using saturated steam at a higher pressure. As a result, the energy cost increases and the molding cycle becomes longer and the productivity also decreases. There was a problem.
[0007]
The present invention has been made in view of the above points, and is based on an uncrosslinked polypropylene resin having the same melting point, although it is a foamed particle having a high melting point uncrosslinked polypropylene random copolymer of 140 ° C. or higher as a base resin. Provided is a polypropylene resin foam particle for molding, which can obtain an excellent foam molded article equivalent to the conventional foamed material even when heated using lower-pressure saturated water vapor than conventional foam particles used as a resin material For the purpose.
[0008]
[Means for Solving the Problems]
  That is, the polypropylene resin foam particles for molding of the present invention are polypropylene resin foam particles having a base resin of an uncrosslinked polypropylene random copolymer having a melting point of 140 ° C. or higher, and the bulk foaming ratio of the foam particles 40 to 80 times(However, those with a bulk density of 20 g / L or more are excluded)The average weight is 0.2 to 1.1 mg, and the air pressure in the particles applied by pressurizing the foamed particles with air is 1.2 kgf / cm at an atmospheric pressure of 23 ° C.²(G) to 0.8 kgf / cm²The time for decay to (G) is 80 minutes or more, and the CNI represented by the following formula (1) is 2.00 or more and less than 3.80.
Or, a polypropylene resin foamed particle having a non-crosslinked polypropylene random copolymer having a melting point of 140 ° C. or higher as a base resin, the foamed particle (however, a foamed particle foamed only with an organic volatile foaming agent) The bulk foaming ratio is 40 to 80 times, the average weight is 0.2 to 1.1 mg, and the intra-particle air pressure applied by pressurizing the foamed particles with air is 23 ° C. under atmospheric pressure. 1.2kgf / cm ² (G) to 0.8 kgf / cm ² The time for decay to (G) is 80 minutes or more, and the CNI represented by the following formula (1) is 2.00 or more and less than 3.80.
[0009]
[Equation 3]

[0010]
(In the above formula (1), Pw is the average weight (mg) per expanded particle, Er is the bulk expansion ratio (times) of the expanded particle, D is the bubble diameter (mm) of the expanded particle, and A is the substrate. Resin density (g / cm^Three). )
[0011]
  Expanded particles of the present inventionShowIn the DSC curve obtained in the differential scanning calorimetry, a high temperature peak appears on the higher temperature side than the intrinsic peak corresponding to the heat of fusion of the base resin of the expanded particles, and the heat amount of the high temperature peak is 10 J / g or more and less than 15 J / g. Is preferredYes.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The base resin of the expanded particles of the present invention is a non-crosslinked propylene random copolymer, and other comonomer copolymerized with propylene is other than propylene such as ethylene, 1-butene, 1-petene and 1-hexene. [Alpha] -olefin and the like. The propylene random copolymer may be a binary copolymer such as a propylene-ethylene random copolymer or a propylene-butene random copolymer, or a ternary copolymer such as a propylene-ethylene-butene random copolymer. It may be a polymer. The proportion of the comonomer component other than propylene in the copolymer is preferably 0.05 to 15% by weight, particularly preferably 0.1 to 10% by weight. When the proportion of the comonomer component is less than 0.05% by weight, physical properties such as cold resistance of the foamed molded product are lowered, and when it exceeds 15% by weight, it is difficult to make the copolymer melting point 140 ° C. or higher. As a result, the heat resistance of the foamed molded product and the mechanical properties such as compressive strength may be reduced.
[0013]
The foamed particles of the present invention require that the base resin has a melting point of 140 ° C. or higher, but considering the productivity and equipment cost when molding the foamed particles, the propylene-based resin random copolymer The melting point is preferably 160 ° C. or lower, and particularly preferably 141 to 155 ° C. Furthermore, the propylene-based random copolymer that is the base resin of the expanded particles has a melt flow rate of 0.5 to 12 g / 10 min in consideration of the heat resistance of the expanded molded body and the expansion efficiency at the time of manufacturing the expanded particles. In particular, those having 4 to 10 g / 10 min are preferred. The melt flow rate is a value measured under test condition 14 of JIS K7210.
[0014]
  The expanded particle of the present invention has a CNI value represented by the above formula (1).2.00 or more,3. Less than 80. In the formula (1), the average weight per expanded particle: Pw is the total weight of 10 randomly selected expanded particles, and the total weight is divided by the number of expanded particles (ie, 10). This is the value obtained. Further, the bubble diameter D of the expanded particles is an average diameter of the bubbles existing in the expanded particles. Specifically, randomly selected foam particles are cut at a substantially central part, and the cut surface is projected on a microscope or on a micrograph, from any bubble wall to any other bubble wall. Arbitrary length: The number of bubbles existing on a straight line of L: N is counted, and the average bubble diameter: D ′ of each foamed particle is obtained by the following equation (2). However, the start point of the straight line is an arbitrary bubble wall, the end point is another arbitrary bubble wall, and at least 10 bubbles exist between the start point and the end point.
[0015]
[Equation 3]
D ′ = 1.62 × (L ÷ N) (2)
[0016]
The above operation is performed on a total of three expanded particles, and the average cell diameter D ′ of the three expanded particles is arithmetically averaged to calculate the cell diameter D of the expanded particles.
[0017]
The bulk expansion ratio of the expanded particles in the above formula (1): Er is a value obtained by multiplying the apparent expansion ratio of the expanded particles based on the measurement described later by 1.6 for convenience. The density of the base resin: A is 0.9 g / cm for convenience in the present invention.^ThreeAnd
[0018]
  The expanded particle of the present invention has the above CNI value.2.00 or more,The air pressure inside the particles, which was less than 3.80 and applied by pressurizing the foamed particles with air, was 1.2 kgf / cm at an atmospheric pressure of 23 ° C.²(G) to 0.8 kgf / cm²(G) (Unit of pressure: kgf / cm²“(G)” after the signifies a gauge pressure. ) Decay time (hereinafter simply referred to as internal pressure decay time) is 80 minutes or more. In order to measure the internal pressure decay time of the expanded particles, first, the expanded particles are pressurized with air to infiltrate the air into the expanded particles to give a high internal pressure, and the applied internal pressure is 1.2 kgf / cm.²(G) to 0.8 kgf / cm²Measure the decay time to (G). Specifically, it is measured by the following method.
[0019]
First, a plurality of foam particles are accommodated in a polyethylene bag of about 70 mm × 100 mm in which a large number of needle holes of a size that allows air to pass freely but not allow air to pass therethrough. Next, pressurizing with air in an airtight container while keeping the foamed particle bag at 23 ° C.²The air pressure of (G) is applied to the expanded particles. Next, the bag is taken out from the sealed container into a thermostatic chamber at 23 ° C. under atmospheric pressure, and immediately placed on a balance to read the weight (the time when the weight is first read is set as a reference time). The bag is left on the scale, and the weight is read every 5 minutes from 2 hours after the reference time, and the weight is read every 30 minutes from 2 hours after the reference time to 48 hours after the reference time. Since the pressurized air in the expanded particles permeates the bubble membrane and escapes to the outside as time passes, the weight of the expanded particles decreases accordingly, and the equilibrium is reached 48 hours after the reference time. The weight is stable. Immediately after the weight measurement after 48 hours is completed, all the expanded particles are taken out from the bag in the same temperature chamber and the weight of the bag is read. In any of the above, the weight is read up to 0.0001 g. From the obtained data, a foamed particle weight-time curve is prepared with the expanded particle weight (g) as the vertical axis and the time (minutes) as the horizontal axis. In addition, the expanded particle weight of a vertical axis | shaft is the value which deducted the weight of the polyethylene bag from the weight of the bag containing a expanded particle.
[0020]
From the obtained foam particle weight-time curve, the air pressure of the foam particles is 1.2 kgf / cm.²Time when the particle weight corresponding to (G) was reached: t_1.2(Min), the air pressure is 0.8 kgf / cm²Time until the weight corresponding to (G) is reached: t_0.8Read (minutes). T obtained in this way_0.8(Minutes) -t_1.2(Minute) is the “internal pressure decay time” referred to in the present invention. Incidentally, the air pressure of the expanded particles: P (kgf / cm²(G)) is calculated from the following equation (3).
[0021]
[Expression 4]
P = (W ÷ M) × R × T × Q ÷ V (3)
[0022]
The above equation (3) is a modification of the gas state equation, and each symbol in the equation (3) is as follows.
[0023]
W is an increased air weight (g), which means the difference between the expanded particle weight at each time and the expanded particle weight after 48 hours from the reference time: S (g). M is the molecular weight of air, and a constant of 28.8 (g) is adopted here. R is a gas constant, and here, a constant of 0.082 (atm · l / K · mol) is adopted. T means an absolute temperature, and since an atmosphere of 23 ° C. is adopted, it is a constant of 296 (° K) here. Q is the pressure from atm to kgf / cm²This is a coefficient for conversion to a unit. Here, 1.0332 (kgf / cm²/ Atm). V means the volume (l) obtained by subtracting the volume of the base resin in the expanded particles from the apparent volume of the expanded particles. The total amount of the expanded particles taken out from the bag 48 hours after the reference time was immediately added to 100 cm of water at 23 ° C.^ThreeFrom the scale when submerged in the water in the graduated cylinder containing the volume of the expanded particles: Y (cm^Three) Is calculated and converted into units of liters (l), which is used as the apparent volume (l) of the expanded particles. The volume of the base resin in the expanded particles is the above volume: Y (cm^Three) Is divided by the apparent expansion ratio (times) of the expanded particles, and the value is calculated in liter (l) units. The apparent expansion ratio of the expanded particles is the base resin density: A (0.9 g / cm^Three) Is the apparent density (g / cm) of the expanded particles^Three). The apparent density of the expanded particles (g / cm^Three) Is the above expanded particle weight: S (g), volume: Y (cm^Three).
[0024]
In the above measurement, the foamed particle weight: S is 0.5000 to 10.0000 g, and the volume Y is 50 to 90 cm.^ThreeAn amount of a plurality of expanded particles is used.
[0025]
The foamed particles having an internal pressure decay time of less than 80 minutes require a long time to recover the shrinkage generated in the foamed molded product immediately after molding, obtained by molding the foamed particles in a mold or the like. However, the ratio of those that do not recover increases, and the defect rate of the molded body increases. From such a viewpoint, the internal pressure decay time is preferably 85 minutes or more, and particularly preferably 90 minutes or more.
[0026]
  If the CNI value is 3.80 or more, the pressure of the saturated water vapor for molding required at the time of molding becomes high, and the object of the present invention cannot be achieved. If the CNI value is 3.60 or less, the pressure of the saturated water vapor for molding required at the time of molding can be further reduced. However, if the CNI value is too small, mechanical compression or the like may occur. Since the foamed particles are likely to be in an open cell state and wrinkles are likely to enter the surface of the molded body after curing, the lower limit of CNI is 2.00.Is. Therefore, the value of CNI is preferably 3.60 to 2.00. The CNI value indicates a larger value as the number of bubbles contained per expanded particle increases, and decreases as the number of bubbles decreases.
[0027]
  The smaller foamed particles have the advantage of reducing the saturated water vapor pressure during molding, while the foaming efficiency becomes worse if the foamed particles are too small.Of the present inventionAverage weight per foamed particleIs 0. 2 to 1.1 mgTheWhen the average weight per foamed particle exceeds 4.0 mg, saturated water vapor at a high pressure is required at the time of molding, and when the heat insulation property of the obtained foamed molded product is lowered or subjected to mechanical compression, bubbles are formed. There is a possibility that bubbles break easily.
[0028]
In the expanded particles of the present invention, a high temperature peak appears on the DSC curve obtained by differential scanning calorimetry of the expanded particles on the higher temperature side than the intrinsic peak corresponding to the heat of fusion of the base resin of the expanded particles. The heat quantity is preferably 10 J / g or more and less than 15 J / g. When the amount of heat at the high temperature peak is less than 10 J / g, the compressive strength, energy absorption amount, etc. of the foamed molded product are lowered, while shrinkage generated in the molded product tends to be difficult to recover even after heat curing after molding. When the heat of fusion at the high temperature peak is 15 J / g or more, there is a possibility that a long processing time is required for applying the internal pressure when molding the expanded particles. In the present invention, the heat amount of the high temperature peak is particularly preferably 11 to 14 J / g.
[0029]
The calorific value of the high temperature peak is a base material that appears in a DSC curve (shown in FIG. 1) obtained by heating 2 to 4 mg of expanded particles from room temperature to 220 ° C. at a rate of 10 ° C./min by a differential scanning calorimeter. The amount of heat of the high temperature peak b that appears on the higher temperature side than the temperature at which the intrinsic peak a unique to the resin appears, corresponds to the area of the high temperature peak b, and can be determined, for example, as follows. That is, first, the point α corresponding to 80 ° C. on the DSC curve and the melting end temperature T of the expanded particles_EA straight line (α−β) connecting the point β on the DSC curve corresponding to is drawn. Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the intrinsic peak a and the high temperature peak b, and the point intersecting with the straight line (α−β) is defined as δ. The area of the high temperature peak b is the portion surrounded by the curve of the high temperature peak b portion of the DSC curve, the line segment (δ−β), and the line segment (γ−δ) (the portion hatched in FIG. 1). Area.
[0030]
This high temperature peak b appears in the first DSC curve measured as described above, but after obtaining the first DSC curve, the temperature is once decreased from 220 ° C. to 10 ° C. to around 40 ° C. However, it does not appear in the second DSC curve obtained when the temperature is raised again to 220 ° C. at 10 ° C./min, and only the intrinsic peak a unique to the base resin appears in the second DSC curve.
[0031]
  DepartureFrom foam particles with a low bulk foaming ratio, only low foam moldings can be obtained, but from foam particles with high bulk foaming ratios, both low foam moldings and high foam moldings are easy. Obtainable. From such a viewpoint, the bulk expansion ratio of the expanded particles of the present inventionIs 40 times or moreIs. On the other hand, if the bulk foaming ratio of the foamed particles is too high, the bubbles tend to break, so the bulk foaming ratioIs 80 times or lessIt is.
[0032]
In the production of the foamed particles of the present invention, for example, propylene-based resin particles are dispersed in a dispersion medium such as water in a closed container together with a foaming agent, and the resin particles are softened by heating and the resin particles are impregnated with the foaming agent. Thereafter, a known foaming method in which the resin particles are released and foamed at a temperature equal to or higher than the softening temperature of the resin particles under a low pressure from the inside of the container can be applied. At this time, if the average weight per resin particle and the bulk foaming ratio of the target foamed particle are determined in advance, then the foamed particle having a CNI value of less than 3.80 is manufactured by adjusting the cell diameter of the foamed particle. can do. The bubble diameter of the foamed particles is mainly adjusted by using a bubble regulator such as inorganic powder. However, the bubble diameter also changes depending on the foaming temperature, the type and amount of the foaming agent, and the like. Therefore, in order to obtain the target bubble diameter, it is necessary to set conditions by conducting a preliminary experiment. In addition, in order to give the foamed particles the property that the internal pressure decay time is 80 minutes or more, the amount of heat at the high temperature peak in the DSC curve of the foamed particles is 8 J / g or more, preferably 10 J / g or more. What is necessary is just to manufacture expanded particles on such conditions. The foamed particles having the high temperature peak can be obtained by heating the resin particles in the above-mentioned known foaming method by dispersing them in a dispersion medium in a dispersion medium and heating them without raising the melting end temperature of the resin particles to Te or higher. More than [melting point: Tm−15 ° C.] of the particle, melting end temperature: any temperature within the range of less than Te: stop at Ta, and hold at temperature: Ta for a sufficient time (preferably about 10 to 60 minutes) Thereafter, the temperature is adjusted to an arbitrary temperature: Tb in the range of [melting point: Tm−5 ° C.] to [melting end temperature: Te + 5 ° C.], and the temperature is stopped at Tb. After holding for a time (preferably about 10 to 60 minutes), it can be obtained by a method in which resin particles are discharged from the container and foamed.
[0033]
The amount of heat at the high temperature peak of the expanded particles is mainly determined by the temperature: Ta and the retention time at the temperature: Ta and the retention at the temperature: Tb and the temperature: Tb with respect to the resin particles when the expanded particles are produced. Depends on time and heating rate. The amount of heat at the high temperature peak of the expanded particles tends to increase as the temperature: Ta or Tb is lower in the temperature range, the holding time is longer, and the heating rate is slower. Usually, the temperature rising rate is 0.5 to 5 ° C./min. If the preliminary experiment is repeated in consideration of these points, the production conditions of the expanded particles exhibiting a desired high temperature peak heat quantity can be easily known.
[0034]
In addition, the temperature range demonstrated above is a suitable temperature range at the time of using an inorganic gas type | system | group foaming agent as a foaming agent. Therefore, when the foaming agent is changed to an organic volatile foaming agent, the appropriate temperature range is shifted to the lower temperature side than the above temperature range depending on the type and amount of use.
[0035]
The melting point: Tm is obtained by performing differential scanning calorimetry on the resin particles in the same manner as the DSC curve of the expanded particles as described above using 2 to 4 mg of resin particles as a sample. Is the temperature of the apex of the intrinsic peak a appearing in the second DSC curve (an example is shown in FIG. 2), and the melting end temperature: Te is the baseline (α The temperature when returning to the position of -β).
[0036]
As the foaming agent used in the above method, an organic volatile foaming agent, an inorganic gas-based foaming agent, or a mixture thereof can be used. Volatile blowing agents include aliphatic hydrocarbons such as propane, butane, hexane and heptane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, 1, Examples include halogenated hydrocarbons such as 2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride. These may be used in a mixture of two or more. Moreover, as an inorganic gas type | system | group foaming agent, nitrogen, a carbon dioxide, argon, air etc. are mentioned, These can mix and use 2 or more types. When mixing and using a volatile foaming agent and an inorganic gas type | system | group foaming agent, the compound arbitrarily selected from the above-mentioned volatile foaming agent and an inorganic gas type | system | group foaming agent can be used in combination. Of the above-mentioned foaming agents, there is no fear of destruction of the ozone layer, and inexpensive inorganic gas-based foaming agents are preferable, and nitrogen, air, and carbon dioxide are particularly preferable.
[0037]
The amount of the foaming agent used is determined according to the expansion ratio of the foamed particles to be obtained and considering the type of base resin, the type of foaming agent, etc. It is preferable to use 5 to 50 parts by weight of the agent and about 0.5 to 30 parts by weight of the inorganic gas-based foaming agent.
[0038]
The dispersion medium for dispersing the resin particles in the production of the expanded particles is not limited to the above-described water, and any solvent that does not dissolve the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like, but it is usually preferable to use water. Further, when dispersing the resin particles in the dispersion medium, a dispersant can be added to the dispersion medium as necessary. Examples of the dispersant include finely divided aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, kaolin, mica, and clay. These dispersants are usually used in an amount of about 0.2 to 2 parts by weight per 100 parts by weight of the resin particles.
[0039]
As the resin particles, those composed of the above-mentioned propylene-based random copolymer are used, but within the range that does not impair the desired effect of the present invention, the propylene-based random copolymer may be mixed with other propylene-based resins (for example, Propylene block copolymer, etc.), high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer A polymer, an ethylene resin such as an ethylene-methacrylic acid copolymer, or a styrene resin such as polystyrene or a styrene-maleic anhydride copolymer, or another resin can be used.
[0040]
Besides the above resins, ethylene-propylene rubber, ethylene-1-butene rubber, propylene-1-butene rubber, styrene-butadiene rubber and hydrogenated products thereof, isoprene rubber, neoprene rubber, nitrile rubber, or styrene-butadiene block copolymer An elastomer such as a combined elastomer or a hydrogenated product thereof can also be added. When a resin or elastomer other than the propylene random copolymer is blended, the amount of resin or elastomer other than the propylene random copolymer is preferably about 10% by weight or less in total. .
[0041]
Furthermore, various additives can be added to the resin particles. Examples of such additives include antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, metal deactivators, pigments, dyes, crystal nucleating agents, or zinc borate, talc, calcium carbonate, borax, Examples thereof include inorganic powders such as aluminum hydroxide. These additives are preferably added in a total amount of 20 parts by weight or less, particularly 5 parts by weight or less per 100 parts by weight of the resin particles.
[0042]
The expanded polypropylene resin particles obtained by the above-described method are subjected to pressure treatment under pressurized air after being aged under atmospheric pressure to give an internal pressure, and then heated using water vapor or hot air ( This process is hereinafter referred to as two-stage foaming), whereby foamed particles with a higher foaming ratio can be obtained.
[0043]
The foamed molded product is filled with a foamed particle in a mold that can be heated and cooled and opened and closed and sealed after increasing the internal pressure of the foam as necessary. The water vapor pressure is 1.5 to 6.0 kgf / cm.²It is possible to manufacture by adopting a batch molding method in which the steam of (G) is supplied and the expanded particles are heated and expanded in the mold to be fused and then cooled and taken out from the mold. In addition, the foamed molded article continuously supplies foamed particles between the belts that continuously move along the upper and lower sides in the passage after increasing the bubble internal pressure as necessary, and passes through the steam heating region. The foamed particles are expanded and fused together, and then cooled by passing through a cooling region, and then the obtained molded product is taken out from the passage and cut into appropriate lengths sequentially (for example, Japanese Patent Laid-Open No. 9-104026). And a molding method described in JP-A-9-104027 and JP-A-10-180888. In order to increase the bubble internal pressure of the foamed particles, the foamed particles are put into a sealed container, and the compressed air is allowed to permeate into the foamed particles by leaving the container in a state where pressurized air is supplied. Good.
[0044]
The foamed molded article produced as described above preferably has an open cell ratio based on ASTM-D2856-70 Procedure C of 40% or less, more preferably 30% or less, and 25% or less. Most preferably it is. The smaller the open cell ratio, the better the mechanical strength.
[0045]
【Example】
  Hereinafter, the present invention will be described in more detail with reference to examples.
Example 12,Reference Example 1,Comparative Examples 1-3
  Propylene-ethylene random copolymer (melting point 146 ° C., ethylene component 2.3 wt%, melt flow rate 10 g / 10 min measured under condition 14 of JIS K7210) per 100 parts by weight of the amount shown in Table 1 Zinc borate (Zinc borate 2335 manufactured by Tomita Pharmaceutical Co., Ltd.) was added in the extruder, both were melt-kneaded in the extruder, extruded into strands, quenched, cut with a pelletizer, and mini-pellets (resin Particles).
[0046]
Subsequently, 100 parts by weight of the above-mentioned mini pellets in the autoclave, 300 parts by weight of water as a dispersion medium, 0.3 parts by weight of kaolin as a dispersant, 0.006 parts by weight of sodium dodecylbenzenesulfonate as a surfactant, and as a foaming agent After filling and sealing the amount of carbon dioxide (dry ice) shown in Table 1, the autoclave contents were heated to the temperature (Ta) shown in Table 1 at a rate of temperature increase of 2 ° C./min while stirring the autoclave. After holding at the temperature temperature (Ta) for the time shown in Table 1, then heating to the temperature (Tb) shown in Table 1 at a rate of temperature increase of 1 ° C./min, and holding at the same temperature (Tb) for the time shown in Table 1 The valve attached to the bottom of the autoclave was opened and the contents of the autoclave were released under atmospheric pressure to obtain expanded particles (single-stage expanded particles). At this time, discharging was performed while introducing high-pressure air into the autoclave. The resulting single-stage expanded particles were allowed to stand at room temperature and atmospheric pressure for 24 hours, then the bulk expansion ratio was measured, and then the air pressure shown in Table 1 was applied to the expanded particles using compressed air at room temperature. 0.6 kgf / cm²The saturated water vapor of (G) was sprayed to obtain highly expanded expanded particles (two-stage expanded particles). The obtained two-stage expanded particles are allowed to stand at room temperature and atmospheric pressure for 24 hours, and then the average weight (mg), bulk expansion ratio (times), and heat of fusion at high temperature peak (J / g). The average bubble diameter (mm) and the internal pressure decay time (minutes) were measured. Furthermore, the CNI value was obtained by calculation based on these data. These results are shown in Table 2.
[0047]
Subsequently, for the two-stage expanded particles, 1.2 kgf / cm using normal temperature pressurized air.²After applying the air pressure of (G) to the foamed particles, the mold is immediately filled into a mold having an inner dimension of 300 mm × 300 mm × 60 mm, and then 0.8 to 0.4 kgf / cm than the saturated water vapor during the main heating.²(G) After preheating using low-pressure saturated steam, introduce saturated steam (shown as “lowest saturated steam pressure” in Table 2) into the mold and perform the main heating. It was. The obtained molded body was cured at 60 ° C. under atmospheric pressure for 24 hours. “Minimum saturated water vapor pressure” means that the appearance is good (the void on the surface of the molded body is small) and the shrinkage is small (the volume of the molded body after curing is 90% or more with respect to the mold internal volume of 100%). In addition, a test piece obtained by cutting the foamed particles so as to have a thickness of 10 mm, a width of 30 mm, and a length of 100 mm from the obtained molded body with a tensile tester is 500 mm / min. This means the lowest saturated water vapor pressure necessary for obtaining a molded body).
[0048]
[Table 1]

[0049]
[Table 2]

[0050]
Reference example 2
  Example1The same operation as above was repeated to produce single-stage expanded particles. The obtained single-stage expanded particles are allowed to stand at room temperature and atmospheric pressure for 24 hours, and then the average weight (mg) of the single-stage expanded particles, bulk expansion ratio (times), heat of fusion at high temperature peak (J / g), average bubbles Diameter (mm) and internal pressure decay time (min) were measured. Furthermore, the CNI value was obtained by calculation based on these data. These results are shown in Table 2.
[0051]
Subsequently, 0.8 kgf / cm is applied to the one-stage expanded particles using normal temperature pressurized air.²(G) Immediately after applying the internal air pressure of (G), the mold having an internal dimension of 300 mm × 300 mm × 60 mm was filled, and then 0.8 to 0.4 kgf / cm than the saturated water vapor during the main heating.²(G) After preheating using low-pressure saturated steam, the “minimum saturated steam pressure” shown in Table 2 was introduced into the mold to perform main heating. The obtained molded body was cured at 60 ° C. under atmospheric pressure for 24 hours.
[0052]
【The invention's effect】
As described above, the foamed particles of the present invention are foamed particles using a non-crosslinked propylene random copolymer having a high melting point of 140 ° C. or higher as a base resin, so that a foamed molded article having excellent mechanical properties is obtained. be able to. In addition, the foamed particles of the present invention are heated by steam at a lower pressure than conventional foamed particles based on uncrosslinked propylene random copolymers having the same melting point, although the base resin has a high melting point. However, it is possible to obtain a foam-molded article that is excellent in fusibility between the expanded particles and has a good appearance with few voids between the particles or no voids. Furthermore, since the foamed particles of the present invention can be molded with low-pressure steam, the energy cost of steam for molding foamed particles can be reduced compared to conventional uncrosslinked propylene resin foamed particles with the same melting point. In addition, since the molding cycle can be shortened, the productivity can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a first DSC curve chart of a polypropylene-based resin foam particle for molding according to the present invention.
FIG. 2 is a diagram showing an example of a second DSC curve chart of polypropylene resin particles.

Claims (3)

Polypropylene resin foamed particles having a non-crosslinked polypropylene random copolymer having a melting point of 140 ° C. or higher as a base resin, and a bulk expansion ratio of the foamed particles of 40 to 80 times (however, a bulk density of 20 g / L or less) The average air weight is 0.2 to 1.1 mg, and the air pressure inside the particles applied by pressurizing the foamed particles with air is 1.2 kgf / cm ² (G ) To 0.8 kgf / cm ² (G) is 80 minutes or more, and CNI represented by the following formula (1) is 2.00 or more and less than 3.80 Polypropylene resin foam particles.

In the above formula (1), Pw is the average weight (mg) per expanded particle, Er is the bulk expansion ratio (times) of the expanded particle, D is the bubble diameter (mm) of the expanded particle, and A is the base resin. The density (g / cm ³ ) is shown. Polypropylene resin foam particles having a non-crosslinked polypropylene random copolymer having a melting point of 140 ° C. or higher as a base resin, the foam particles (however, excluding foam particles foamed only with an organic volatile foaming agent) The bulk foaming ratio is 40 to 80 times, the average weight is 0.2 to 1.1 mg, and the air pressure inside the particles applied by pressurizing the foamed particles with air is 1. 2kgf / cm ² (G) to 0.8 kgf / cm ² A polypropylene-based resin foamed particle for molding, wherein the decay time in (G) is 80 minutes or more, and the CNI represented by the following formula (1) is 2.00 or more and less than 3.80.

In the above formula (1), Pw is the average weight (mg) per expanded particle, Er is the bulk expansion ratio (times) of the expanded particle, D is the bubble diameter (mm) of the expanded particle, and A is the base resin. Density (g / cm ³ ). In the DSC curve obtained in the differential scanning calorimetry, a high temperature peak appears on the higher temperature side than the intrinsic peak corresponding to the heat of fusion of the base resin of the expanded particles, and the heat quantity of the high temperature peak is 10 J / g or more and less than 15 J / g. 3. The expanded polypropylene-based resin particle for molding according to claim 1 or 2 .

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