JP4386526B2 - Airbag storage cover - Google Patents

Description

（ｂ）ポリイソシアネート
（ｃ）ポリイソシアネートと反応しうる活性水素を２個有する鎖延長剤
【００１８】
本発明のポリウレタンエラストマーの（ａ）成分し使用されるポリカーボネートジオールは、Ｓｃｈｅｌｌ著、Ｐｏｌｍｅｒ Ｒｅｖｉｅｗ 第９巻、第９〜２０ページ（１９６４年）に記載された種々の方法により脂肪族および／または脂環式ジオールから合成される。
【００２０】
本発明のエアバッグカバーに好適なポリカーボネートジオールとしては、１，４−ブタンジオールまたは１，５−ペンタンジオールのいずれか一方と、１，６−ヘキサンジオールから合成される共重合ポリカーボネートジオールが、得られるエアバッグカバーの低温特性に優れるので好ましい。ポリマー中の繰り返し単位である、１，４−ブタンジオールまたは１，５−ペンタンジオールのいずれか一方と、１，６−ヘキサンジオールの割合は、１０／９０〜９０／１０、好ましくは、２０／８０〜８０／２０、さらに好ましくは３０／７０〜７０／３０である。
【００２１】
本発明に用いられるポリカーボネートジオールの平均分子量の範囲は、通常数平均分子量で５００〜５０００であり、好ましくは、１０００〜３０００、さらに好ましくは１５００〜２５００のものが使用され、そのポリマー末端は、実質的にすべてヒドロキシル基であることが望ましい。
【００２２】
本発明においては、先に示したジオールの他に、１分子に３個以上のヒドロキシル基を持つ化合物、例えば、トリメチロールエタン、トリメチロールプロパン、ヘキサントリオール、ペンタエリスリトール、等の少量を用いる事により多官能化したポリカーボネートを用いたポリウレタンも含まれる。
【００２３】
次に、本発明のポリウレタンエラストマーの（ｂ）成分に使用されるポリイソシアネートとしては、例えば２，４−トリレンジイソシアネート、２，６−トリレンジイソシアネート、及びその混合物（ＴＤＩ）、ジフェニルメタン−４，４’−ジイソシアネート（ＭＤＩ）、ナフタレン−１，５−ジイソシアネート（ＮＤＩ）、３，３’−ジメチル−４，４’−ビフェニレンジイソシアネート、粗製ＴＤＩ、ポリメチレンポリフェニルイソシアネート、粗製ＭＤＩ等の公知の芳香族ジイソシアネート；キシリレンジイソシアネート（ＸＤＩ）、フェニレンジイソシアネート等の公知の芳香脂環族ジイソシアネート；４，４’−メチレンビスシクロヘキシルジイソシアネート（水添ＭＤＩ）、ヘキサメチレンジイソシアネート（ＨＭＤＩ）、イソホロンジイソシアネート（ＩＰＤＩ）、シクロヘキサンジイソシアネート（水添ＸＤＩ）等の公知の脂肪族ジイソシアネート、及びこれらのイソシアネート類のイソシアヌレート化変性品、カルボジイミド化変性品、ビウレット化変性品等である。
【００２４】
又、本発明のポリウレタンエラストマーの共重合成分（ｃ）として必要により用いられる適当な鎖延長剤としては、ポリウレタン業界における、常用の鎖延長剤が包含される。岩田敬治監修最近ポリウレタン応用技術ＣＭＣ１９８５年第２５〜２７ページ記載の、公知の水、低分子ポリオール、ポリアミン等が含まれる。本発明に用いられる脂肪族ポリカーボネートと共に、本発明の効果を損なわない範囲で、ポリウレタンの用途に応じて、公知のポリオールを併用してもよい。公知のポリオールとして、今井嘉夫、ポリウレタンフオーム高分子刊行会１９８７年第１２〜２３ページに記載の公知のポリエステル、ポリエーテルカーボネート等のポリオールがある。
【００２５】
具体的には、低分子ポリオールとしては通常分子量が３００以下のジオールが用いられる。例えば、エチレングリコール、１，３−プロピレンジオール、１，４−ブタンジオール、ペンタメチレングリコール、ヘキサメチレングリコール、ネオペンチルグリコール、デカメチレングリコール等の脂肪族ジオールが挙げられる。
【００２６】
また、１，１−シクロヘキサンジメタノール、１，４−シクロヘキサンジメタノール、トリシクロデカンジメタノール等の脂環式ジオール、キシリレングリコール、ビス（ｐ−ヒドロキシ）ジフェニル、ビス（ｐ−ヒドロキシフェニル）プロパン、２，２−ビス［４−（２−ヒドロキシエトキシ）フェニル］プロパン、ビス［４（２−ヒドロキシ）フェニル］スルホン、１，１−ビス［４−（２−ヒドロキシエトキシ）フェニル］シクロヘキサン等、が挙げられる。好適には、エチレングリコール、１，４−ブタンジオールが用いられる。
【００２７】
本発明のポリウレタンエラストマーを製造する方法としては、ポリウレタン業界で公知のウレタン化反応の技術が用いられる。例えば、該ポリオールと有機ポリイソシアネートを常温から２００℃で反応させることにより、ＮＣＯ末端のポリウレタンプレポリマーが生成する。
【００２８】
又、該ポリオールとポリイソシアネート及び必要に応じて鎖延長剤を用いて、熱可塑性のポリウレタンエラストマーを製造する事が出来る。これらの製造に於いては三級アミンや錫、チタンなどの有機金属塩等に代表される公知の重合触媒「例えば、吉田敬治著（ポリウレタン樹脂）日本工業新聞社刊第２３−３２頁（１９６９年）に記載」を用いる事も可能である。又、これらの反応を溶媒を用いておこなってもよく、好ましい溶剤として、ジメチルホルムアミド、ジエチルホルムアミド、ジメチルアセトアミド、ジメチルスルホキシド、テトラヒドロフラン、メチルイソブチルケトン、ジオキサン、シクロヘキサノン、ベンゼン、トルエン、エチルセルソルブ等がある。
【００２９】
又、本発明のポリウレタンエラストマー製造に当り、イソシアネート基に反応する活性水素を一つだけ含有する化合物、例えばエチルアルコール、プロピルアルコール等の一価アルコール、及びジエチルアミン、ジｎプロピルアミン等の二級アミン等を末端停止剤として使用することができる。
【００３０】
本発明の、ポリカーボネートポリオールを使用したポリウレタンエラストマーは、他のポリウレタンエラストマーに比べて、柔軟性、弾性回復に優れるばかりではなく、加水分解性が極めて良好であるため、常時手に触れるエアバッグカバーに使用した場合、耐汗性が優れるのため好適である。
【００３１】
本発明のポリウレタンエラストマーのショアＤ硬さは好ましくは２０〜７０、さらに好ましくは２５〜５０の範囲であり、ソフトセグメント量は適宜選択される。ショアＤ硬さが２０未満では、高温での展開性能、耐スクラッチ性が劣るので好ましくない。また、ショアＤ硬さが７０を越えると、得られるエアバッグカバーの低温展開性能、ソフト感が不足するので好ましくない。
【００３２】
また、本発明のポリウレタンエラストマーのメルトフローレート（２３０℃、２．１６ｋｇ加重の値、以下ＭＦＲと略記）は０．５〜１００ｇ／１０分、好ましくは５〜５０ｇ／１０分、さらに好ましくは１０〜３０ｇ／１０分である。ＭＦＲが０．５ｇ／１０分未満では、射出成形性に劣り、ショートショットとなってしまうので好ましくない。また、ＭＦＲが１００ｇ／１０分を越えると、機械物性（破断強度、破断伸び等）や摩耗性、等に劣るばかりではなく、展開性能も悪化するので好ましくない。
【００３３】
本発明に用いられる添加剤としては少なくとも酸化防止剤、光安定剤及び熱安定剤が用いられることが望ましい。これらの酸化防止剤としては燐酸、亜燐酸、の脂肪族、芳香族又はアルキル基置換芳香族エステルや次亜燐酸誘導体、フェニルホスホン酸、フェニルホスフィン酸、ジフェニルホスホン酸、ポリホスホネート、ジアルキルペンタエリスリトールジホスファイト、ジアルキルビスフェノールＡジホスファイト等のリン化合物；フェノール系誘導体特にヒンダードフェノール化合物、チオエーテル系、ジチオ酸塩系、メルカプトベンズイミダゾール系、チオカルバニリド系、チオジプロピオン酸エステル等のイオウを含む化合物；スズマレート、ジブチルスズモノオキシド等のスズ系化合物を用いることができる。
【００３４】
これらは単独で用いても２種以上組み合わせて用いても構わない。これら安定剤の添加量はポリエーテルエステルブロック共重合体１００重量部に対し、０．０１〜５重量部、好ましくは０．１〜３重量部、さらに好ましくは０．２〜２重量部が望ましい。通常、酸化防止剤は一次、二次、三次老化防止剤に分けることが出来る。特に一次老化防止剤としてのヒンダードフェノール化合物としてはＩｒｇａｎｏｘ１０１０（商品名：チバガイギー社製）、Ｉｒｇａｎｏｘ１５２０（商品名：チバガイギー社製）等が好ましい。二次老化防止剤としての燐系化合物はＰＥＰ−３６、ＰＥＰ−２４Ｇ、ＨＰ−１０（いずれも商品名：旭電化（株）製）Ｉｒｇａｆｏｓ１６８（商品名：チバガイギー社製）が好ましい。さらに三次老化防止剤としての硫黄化合物としてはジラウリルチオプロピオネート（ＤＬＴＰ）、ジステアリルチオプロピオネート（ＤＳＴＰ）等のチオエーテル化合物が好ましい。
【００３５】
また紫外線吸収剤・光安定剤としてはベンゾトリアゾール系、ベンゾフェノン系化合物等が挙げられる。光安定剤としてはヒンダードアミン化合物のようなラジカル捕捉型光安定剤が好適に用いられる。
【００３６】
また必要に応じて得られる組成物に可塑剤の添加を行なっても良い。かかる可塑剤の例としてジオクチルフタレート、ジブチルフタレート、ジエチルフタレート、ブチルベンジルフタレート、ジ−２−エチルヘキシルフタレート、ジイソデシルフタレート、ジウンデシルフタレート、ジイソノニルフタレート等のフタル酸エステル類：トリクレジルホスフェート、トリエチルホスフェート、トリブチルホスフェート、トリ−２−エチルヘキシルホスフェート、トリメチルヘキシルホスフェート、トリス−クロロエチルホスフェート、トリス−ジクロロプロピルホスフェート等の燐酸エステル類：トリメリット酸オクチルエステル、トリメリット酸イソデシルエステル、トリメリット酸エステル類、ジペンタエリスリトールエステル類、ジオクチルアジペート、ジメチルアジペート、ジ−２−エチルヘキシルアゼレート、ジオクチルアゼレート、ジオクチルセバケート、ジ−２−エチルヘキシルセバケート、メチルアセチルリシノケート等の脂肪酸エステル類：ピロメリット酸オクチルエステル等のピロメリット酸エステル：エポキシ化大豆油、エポキシ化アマニ油、エポキシ化脂肪酸アルキルエステル等のエポキシ系可塑剤：アジピン酸エーテルエステル、ポリエーテル等のポリエーテル系可塑剤：液状ＮＢＲ、液状アクリルゴム、液状ポリブタジエン等の液状ゴム：プロセスオイル等を挙げることが出来る。
【００３７】
これら可塑剤は単独、あるいは２種以上組み合わせて使用することが出来る。可塑剤の添加量は要求される硬度、物性に応じて適宜選択されるが、組成物１００重量部当り１〜５０重量部が好ましい。
【００３８】
また、物性を損なわない範囲でカオリン、シリカ、マイカ、二酸化チタン、アルミナ、炭酸カルシウム、珪酸カルシウム、クレー、カオリン、ケイソウ土、アスベスト、硫酸バリウム、硫酸アルミニウム、硫酸カルシウム、塩基性炭酸マグネシウム、二硫化モリブデン、グラファイト、ガラス繊維、炭素繊維等の充填剤や補強材：ステアリン酸亜鉛やステアリン酸ビスアマイドのような滑剤ないしは離型剤：着色のためのカーボンブラック、群青、チタンホワイト、亜鉛華、べんがら、紺青、アゾ顔料、ニトロ顔料、レーキ顔料、フタロシアニン顔料等の染顔料：オクタブロモジフェニル、テトラブロモビスフェノールポリカーボネート等の難燃化剤：発泡剤：エポキシ化合物やイソシアネート化合物等の増粘剤：シリコーンオイルやシリコーン樹脂等、公知の各種添加剤を用いることが出来る。
【００３９】
本発明のエアバック装置の収納カバーを構成する熱可塑性エラストマー組成物は、各種押出機、バンバリーミキサー、ニーダー、ロール、さらにこれらを組み合わせたもの等により、溶融混練後、造粒することにより容易にペレットの形態で得られる。この熱可塑性エラストマー組成物を一般の熱可塑性樹脂や熱可塑性エラストマーの成形に使用される汎用の単純な射出成形機で成形することにより高い生産性で収納カバーを得ることが出来る。
【００４０】
次に、図に従って、本発明の収納カバーの構造を具体的に説明する。図１は本発明による運転席用エアバッグ装置の収納カバーの一例を示す斜視図である。図５は本発明による助手席用エアバッグ装置の収納カバーの一例を示す斜視図である。図８は本発明による助手席用エアバッグ装置の収納カバーの他の例を示す図６と同様の断面を示す模式図である。図９は図８に示す収納カバーの図７と同様の断面を示す模式図である。
【００４１】
収納カバーの天面は、図１に示すようなＨ字状、図５に示すようなコの字状、その他Ｘ字状、放射状、円弧状、Ｕ字状等に設定できる。また、収納カバーの側壁は、図８、９に示すように設定することが出来る。脆弱な構造の破断予定部分は、収納カバーの設定された破断予定線に沿った部分にＶ字状溝、Ｕ字状溝、コの字状溝、その他の断面形状の溝を設けたり他の部分の肉厚より薄くしたり、スリットや切込みを断続的に設けることにより実現できる。また、収納カバー表面をシボ加工することにより表面の耐傷付性をさらに改善することが出来る。
【００４２】
【実施例】
以下に実施例、比較例に基づき本発明を更に詳しく説明するが、本発明はこれにより限定されるものではない。
＜評価方法＞
はじめに実施例及び比較例において用いられた物性評価項目と、その評価方法について以下に説明する。
【００４３】
〔メルトフローレート（ＭＦＲ）〕
各熱可塑性エラストマー組成物のペレット約５ｇを、真空乾燥器にて７０℃で約１２時間真空乾燥させた後、直ちに、直径２．０９０ｍｍ、長さ８ｍｍのオリフィスにより、荷重２．１６ｋｇ、測定温度２３０℃のＬ条件でＭＦＲを測定した。
【００４４】
〔融点〕
各熱可塑性エラストマー組成物約１０ｍｇを、ＳＥＩＫＯ電子工業社製の示差熱量計（ＤＳＣ−２００）にかけ、昇温速度１０℃／分の条件で、窒素雰囲気下（１０ｃｃ／分）、標準物質との温度差ΔＴの変化を調べて、得られた温度−温度差（ΔＴ）曲線から吸熱ピークのトップの温度を融点とした。
【００４５】
〔表面硬度〕
ショアＤ硬度を２５℃で測定した。
〔曲げ弾性率（ＭＰａ）〕
ＪＩＳ Ｋ７２０３に従って、長さ１２５ｍｍ×幅１２．５ｍｍ×長さ３ｍｍの射出成形試験片を用い、曲げ速度２ｍｍ／分の条件で、−５０℃、−４０℃、−２５℃、０℃、２３℃、１００℃の各温度において曲げ弾性率を測定した。
【００４６】
〔破断強度（ＭＰａ）、破断伸び（％）〕
ＪＩＳ Ｋ６３０１に従って、長さ２０ｍｍ×幅３ｍｍ×厚さ２ｍｍの射出成形試験片を用い、２５℃で、ヘッドスピード２０ｍｍ／分の条件で引張試験を行うことにより測定した。
【００４７】
〔表面耐傷付性〕
荷重を３４０ｇとして鉛筆硬度（９Ｂ〜９Ｈ）にて評価した。
〔耐汗性〕
射出試験片を人工汗液（人工汗液組成；ＮａＣｌ７ｇ、メチルアルコール５００ｃｃ、尿素１ｇ、乳酸４ｇ、蒸留水５００ｃｃ）に常温にて３０日間浸漬した。試験片を取り出し、磨耗試験を行った後の外観（ＪＩＳ Ｋ７２０４磨耗輪による試験後の外観）を３等級で評価した。
３；磨耗輪による傷が全く認められない
２；磨耗輪による傷がわずかに認められる
１；磨耗輪による傷が明らかに認められる
【００４８】
〔収納カバーの展開性能〕
鉄製の取付金具（リテーナー）にエアバッグと収納カバーを取り付け、更にガス発生器を取り付けてエアバッグ装置を組み立てる。次にこのエアバッグ装置を展開温度（−４０℃、室温あるいは９０℃）の空気恒温槽に入れ、内温が安定してから更に２時間放置した後エアバッグを取り出し、架台に取付け通電し展開する（空気恒温槽からエアーバッグ装置を取り出してから一分以内に通電する。）。収納カバーが破断片を発生することなく破断予定部分で開裂しエアバッグが展開すれば収納カバーの展開性は良好とする。
脂肪族コポリカーボネートジオールの合成方法を下記に参考例として示す。
【００４９】
参考例１
デイクソンパッキン３φを充填した直径１０ｍｍ、長さ３００ｍｍの蒸留塔及び温度計、攪拌機付きの３リットルフラスコに、エチレンカーボネート（ＥＣ）９７０ｇ（１１モル）、１，６−ヘキサンジオール（ＨＤＬ）６５０ｇ（５．５モル）、１，５−ペンタンンジオール（ＰＤＬ）５７０ｇ（５．５モル）を加え２０ｔｏｒｒの減圧下に加熱攪拌し、内温が１５０℃になるようにコントロールした。蒸留塔の塔頂より共沸組成のＥＣとエチレングリコール（以下ＥＧと略す）を溜出させながら２０時間反応を行った。次に蒸留塔を取り外して、減圧度を７ｔｏｒｒにして、未反応のＥＣとジオールを回収した。未反応物の溜出の終了後に内温を１９０℃にし、その温度を保ったままジオールを溜出させることにより自己縮合反応を行い分子量を上昇させた。４時間後、ＧＰＣ分析により分子量２０００のポリマーを得た。収量は７４０ｇであり水酸基価は５６ｍｇＫＯＨ／ｇであった。このポリマーをｐｃ−ａと略す。
【００５０】
参考例２、３
ジオールとして１，４−ブタンジオール（ＢＤＬ）、１，５−ペンタンジオール、１，６−ヘキサンジオールを用い、表１に示した各量とした以外は、参考例１と同様な方法で脂肪族コポリカーボネートジオール（ｐｃ−ｂ、ｐｃ−ｃ）を得た。各々の分子量を表１に示す。
【００５１】
【表１】

【００５２】
実施例および比較例にて使用した原材料、および評価方法は以下のとおりである。
１．ポリウレタンエラストマー（以下ＴＰＵと略記）成分
（１）ＴＰＵ−１：
参考例１で得たｐｃ−ａ２００ｇ、ヘキサメチレンジイソシアネート６７．２ｇを攪拌装置、温度計、冷却管の付いた反応器に仕込み、１００℃で４時間反応し末端ＮＣＯのプレポリマーを得た。該プレポリマーに鎖延長剤の１，４−ブタンジオール３０ｇ、触媒としてジブチルスズジラウリレート０．００６ｇを加えてニーダー内蔵のラボ用万能押出機（（株）笠松化工研究所製ＬＡＢＯ用万能押出機ＫＲ−３５型）で１４０℃で６０分反応後、得られたポリウレタンエラストマー１００重量部に対し、カーボンブラックマスターペレット（ロイヤルブラックＲＢ９００５）を１重量部、Ｉｒｇａｎｏｘ１０１０を０．１重量部、ジラウリルチオプロピオネート（ＤＬＴＰ、吉富製薬（株）製）を０．１５重量部、及びＴＩＮＵＶＩＮ３２７（チバガイギー社製）を０．１重量部それぞれ加え、押出し機にてペレットとした。ウレタンエラストマーのショアＤ硬さは３９、ＭＦＲは２４であった。
【００５３】
（２）ＴＰＵ−２：
ポリカーボネートジオールとしてｐｃ−ｂを用いた以外は、ＴＰＵ−１の合成方法と同様に重合しウレタンエラストマーを得た。得られたウレタンエラストマーのショアＤ硬さは４２、ＭＦＲは２０であった。
【００５４】
（３）ＴＰＵ−３：
ポリカーボネートジオールとしてｐｃ−ｃを用いた以外は、ＴＰＵ−１の合成方法と同様に重合しウレタンエラストマーを得た。得られたウレタンエラストマーのショアＤ硬さは４３、ＭＦＲは２８であった。
【００５５】
（４）ＴＰＵ−４：
ポリカーボネートジオールの替わりに、ポリカプロラクトンポリオール（ダイセル製、プラクセル２２０、分子量２，０００）を用いた以外は、ＴＰＵ−１の合成方法と同様の方法で合成した。得られたウレタンエラストマーのショアＤ硬さは４５、ＭＦＲは２７であった。
【００５６】
（５）ＴＰＵ−５：
ミラクトラン Ｅ１９０（日本ミラクトラン社製、ＭＤＩ／アジペート系ＴＰＵ）、ショアＤ硬さ４５、ＭＦＲ；２８
【００５７】
実施例１
ＴＰＵ−１を用い上記物性を測定した。結果を表２に示した。次に、ＴＰＵ−１を用い、射出成形し、複数の運転席用エアーバッグ装置の収納カバーを得た。成形サイクルは８０秒であり、得られた収納カバーを使って組み立てたエアバッグ装置の−４０℃、常温、９０℃での展開性能をまとめて表２に示す。
【００５８】
実施例１の収納カバーの形状を図１〜図４を参照して以下具体的に説明する。図１は本発明による運転席用エアバッグ装置の収納カバーの一例を示す斜視図である。図２は図１のＩＩ−ＩＩ線による収納カバーの断面を示す模式図である。図３は図２の収納カバーのＶ字状溝の拡大断面を示す模式図である。図４は図２の収納カバーのＵ字状溝の拡大断面を示す模式図である。
【００５９】
図１に示すように、収納カバーはリテーナー（図字せず）に取り付けるためのボルト穴を有するフランジ５を周囲に有し、一方が開き、内側にエアバッグを収納できる空間８を有して箱状に形成されており、天面２に脆弱な構造の破断予定部分３が図１の点線で示すようにＨ字状に配設され、天面２の二個所に図１の一点鎖線で示すようにヒンジ部４が配設されている。
【００６０】
破断予定部分３は図２及び図３に示すように天面２の裏側の破断形状がＶ字状のＶ溝６により形成されている。ヒンジ部４は図２、図４に示すように天面２の裏側の断面形状がＵ字状のＵ溝７により形成されている。エアバッグ（図字せず）が膨張すると収納カバー１は破断予定部分３で破断し、二つの扉２ａ、２ｂがそれぞれヒンジ部４を軸に展開し、エアバッグが放出され膨張する。
【００６１】
破断予定部分３の寸法はＨ字の縦の二本の棒に相当する部分が１２ｃｍ、横の棒に相当する部分が１５ｃｍであり、破断予定部分の肉厚が０．５ｍｍ、ヒンジ部の肉厚が１．９ｍｍ、その他の部分は３ｍｍである。また、実施例１の収納カバーは最大型締力１５０ｋｇ／ｃｍ²、最大射出圧力６０ｋｇ／ｃｍ²の汎用型射出成形機に上記収納カバー用金型を取付け、運転温度２００〜２３０℃で成形した。また、実施例１では内容積６０リットルのエアバッグを使用し、ガス発生量が約１モルであるガス発生器１個を使用した。
【００６２】
実施例２、３
ＴＰＵ−２、ＴＰＵ−３を用い、実施例１と同様に物性評価およびエアバッグの評価を実施した。結果を表２に示した。
【００６３】
【表２】

【００６４】
実施例４
ＴＰＵ−１を用い、射出成形して複数の助手席用エアバッグ装置の収納カバーを得た。成形サイクルは６５秒であった。得られた収納カバーを使って組み立てたエアバッグ装置の−４０℃、常温、９０℃での展開性はいずれも良好であった。
【００６５】
図５は本発明による助手席用エアバッグ装置の収納カバーの一例を示す斜視図である。図６は図５のＶＩ−ＶＩ線による収納カバーの断面を示す模式図である。図７は図５のＶＩＩ−ＶＩＩ線による収納カバーの断面を示す模式図である。なお、この実施例９の収納カバーの形状を図５、図６及び図７に示す。即ち、収納カバー１１は天板１２と四枚の側壁１８とからなる。天板１２は側壁１８の外側まで庇状に張り出しており、側壁は下端外周につば１５がつけられている。収納カバー１１は側壁１８に配置されている穴１９を使ってリテーナー（図字せず）に取り付けることが出来、リテーナーにはガス発生器（図字せず）が取り付けられる。
【００６６】
収納カバーの天板１２、側壁１８、リテーナー、ガス発生器で形成される空間にエアバッグ（図字せず）を収納することが出来る。脆弱な構造の破断予定部分１３、１３’が図５、図６、図７に示すように天面１２の側壁１８より内側に配設され、ヒンジ部１４が図５、図６に示すように配設されている。破断予定部分１３、１３’は図５、６に示すように配設されている。
【００６７】
破断予定部分１３、１３’は図６、図７に示すように天板１２の裏側の断面形状がＶ字状のＶ溝１６、１６’により形成されている。ヒンジ部１４は図６に示すように天板１２の裏側の断面形状がＵ字状のＵ溝１７により形成されている。
【００６８】
エアーバッグが膨張すると収納カバー１１は破断予定部分１３、１３’で破断し、破断予定部１３、１３’とヒンジ部で囲まれる部分１２ａがヒンジ部１４を軸として展開し、エアバッグが放出され膨張することになっている。収納カバー１１の寸法は、（イ）天板１２の長辺３４ｃｍ、短辺１４ｃｍ、厚さ３ｍｍ、（ロ）側壁１８の長辺約２８ｃｍ、短辺約１０ｃｍ、高さ約６．８ｃｍ、厚さ約３ｍｍ、（ハ）破断予定部の肉厚０．５ｍｍ、（ニ）ヒンジ部の肉厚１．９ｍｍである。
【００６９】
また、実施例４の収納カバーは最大型締力２１５ｋｇ／ｃｍ²、最大射出圧力６０ｋｇ／ｃｍ²の汎用型射出成形機に上記収納カバー用金型を取付け、運転温度２００〜２３０℃で成形した。また、実施例４では内容積１２０リットルのエアバッグを使用し、ガス発生量が約１モルであるガス発生器２個を使用した。
【００７０】
比較例１、２
ＴＰＵとしてＴＰＵ−４、ＴＰＵ−５を用いた以外は実施例１と同様に評価を行った。結果を表３に示した。
【００７１】
【表３】

【００７２】
【発明の効果】
以上説明したように、本発明は、特定の熱可塑性エラストマー組成物を射出成形法により成形することを採用し、脆弱な構造の破断予定部分を配設したことにより、耐久性に優れ、優れた感触を有し、広い温度範囲で確実に展開できるばかりではなく、高生産性、塗装レスが可能となり、低コストが実現されるエアバッグ収納カバーを実現した。
【図面の簡単な説明】
【図１】本発明による運転席用エアバッグ装置の収納カバーの一例を示す斜視図である。
【図２】図１のＩＩ−ＩＩ線による収納カバーの断面を示す模式図である。
【図３】図２の収納カバーのＶ字状溝の拡大断面を示す模式図である。
【図４】図２の収納カバーのＵ字状溝の拡大断面を示す模式図である。
【図５】本発明による助手席用エアーバッグ装置の収納カバーの一例を示す斜視図である。
【図６】図５のＶＩ−ＶＩ線による収納カバーの断面を示す模式図である。
【図７】図５のＶＩＩ−ＶＩＩ線による収納カバーの断面を示す模式図である。
【図８】本発明による助手席用エアバッグ装置の収納 カバーの他の例を示す図６と同様の断面を示す模式図である。
【図９】図８に示す収納カバーの図７と同様の断面を示す模式図である。
【符号の説明】
１、１１、２１・・・収納カバー
２・・・天面
２ａ・・・扉
３、１３、１３’、２３、２３’・・・破断予定部分
４、１４、２４・・・ヒンジ部
５・・・フランジ
６、１６、１６’、２６、２６’・・・Ｖ溝
７、７’、１７、２７・・・Ｕ溝
８・・・空間
９・・・穴
１２、２２・・・天板
１２ａ・・・天板の開口部
１８・・・側板
１９・・・穴[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a storage cover for an air bag device designed to protect a passenger from a secondary collision with a control device, an instrument panel or the like by restraining an occupant on the seat side when a high-speed moving body such as an automobile collides. About.
[0002]
[Prior art]
In principle, the airbag system includes a collision detection device and an airbag device that detect a collision of a high-speed moving body. The latter airbag device is an airbag, a gas generator that generates gas for inflating the airbag, A storage cover for storing the airbag and the gas generator, and a fixture (retainer) for attaching the gas generator and the storage cover.
[0003]
The airbag device is attached to the front of the occupant in the high-speed moving body. When the collision detection device is activated due to a collision accident or the like, gas is instantaneously generated from the gas generator, and is surrounded by the gas generator, the storage cover, and the fixture. The airbag that is folded and stored in the space formed is filled with gas, the storage cover is expanded by the pressure of the gas filled in the airbag, and the airbag is occupant from the opening obtained by the deployment. By releasing and inflating instantaneously toward the front of the vehicle, the occupant is restrained to the seat side, and as a result, the occupant can be prevented from colliding with the control device, the instrument panel, etc.
[0004]
Therefore, the storage cover of the airbag device, when a collision accident occurs and the gas generator is activated, reliably deploys the debris that may hurt the occupant without splashing and releases the bag instantaneously. It must be. As a storage cover for such an air bag apparatus, Japanese Patent Laid-Open No. 50-127336, Japanese Patent Laid-Open No. 55-110463, Japanese Patent Laid-Open No. 52-116537, Japanese Patent Laid-Open No. 1-202550, or Japanese Patent Laid-Open No. 5-038996. Various proposals have been made in publications and the like.
[0005]
JP-A-50-127336 and JP-A-511011043 are made of a urethane resin or an elastic material, and a reinforcing material such as a fiber net or a metal net is embedded in a portion other than a portion to be broken. A storage cover with a structured structure has been proposed. In these proposals, since the resin material used is fragile, it is necessary to adopt a structure in which a reinforcing material is embedded in order to prevent debris scattering when the airbag device is operated. It takes time to set, and it is difficult to obtain a molded product in which a reinforcing material is embedded at a predetermined position with high accuracy. Furthermore, in the case of urethane resin by reaction injection molding, the reaction proceeds sufficiently in the mold. Time has to be taken and has the disadvantages of low production rate and low production yield.
[0006]
In particular, the number of automobiles produced reaches 10 million units per year, and it is fatal that the production speed and production yield are low. Japanese Patent Application Laid-Open No. 52-116537 discloses an embrittlement temperature of −50 ° C. or less and a bending rigidity of 1,000 to 3,000 kg / cm.²A storage cover has been proposed which is made of a thermoplastic elastomer and has a fragile structure at a portion to be broken. According to this proposal, the productivity is improved because the structure is not embedded with a reinforcing material, but the bending rigidity of the material is 1,000 to 3,000 kg / cm.²Therefore, the performance in the low temperature region is not sufficient, and when it is deployed at a low temperature, it may break at a portion other than the planned breakage portion, which may cause the cover to scatter and injure the occupant.
[0007]
In JP-A-1-202550, a surface layer made of a soft resin having a JIS K6301-A hardness of 30 to 70 and a core layer made of a hard resin having elasticity are integrally formed, and a slit for cover cleavage is formed in the core layer. There has been proposed a storage cover having a structure provided with. The proposed storage cover gives the occupant a moderately soft feel, but the two-layer molding of the core layer and the surface layer is essential, which requires a complicated and expensive molding machine with two injection mechanisms. There are major drawbacks.
[0008]
Japanese Patent Application Laid-Open No. 5-038996 discloses a hydrogenated styrene-conjugated diene block copolymer, a rubber plasticizer, an olefin resin, which has a recess for storing an air bag inside and has a fragile structure to be broken. And a storage cover for an air bag device, which is an injection-molded body of a thermoplastic elastomer composition having a JISK6301A type hardness of 60 to 85. The proposed storage cover gives the occupant a moderately soft feel and high productivity, but the bending rigidity at low temperatures is relatively large, and in some cases it may become brittle at low temperatures and lose certainty in deployment performance. is there. Furthermore, the scratch resistance of the surface is not always good, and a hard urethane coating is required, which is not necessarily advantageous in terms of cost.
[0009]
[Problems to be solved by the invention]
The first requirement that the storage cover of the airbag apparatus should have is to deploy it securely and to have safety. That is, when the airbag apparatus is operated, the storage cover must be deployed without scattering debris that may hurt the occupant, and the bag must be released instantaneously.
[0010]
The second is adaptability over a wide temperature range. In the case of automobiles, the temperature of the storage cover is often -40 ° C to 90 ° C depending on the region, season, and condition of use, but it should not become fragile and lose its certainty at low temperatures or be softly deformed at high temperatures. . The third is durability against heat and light. In the case of an automobile, the storage cover is often used by being attached to a part irradiated with sunlight incident through the windshield.
[0011]
The fourth is high productivity and low production costs. This requirement is particularly important in mass produced automotive airbag devices. In particular, in order to reduce the material cost, it is important to reduce the thickness of the cover. For this purpose, a material having a certain degree of rigidity tends to be desired. The fifth is touch. Those having a large effect of giving a moderately soft feel when the occupant touches the storage cover, and thus bringing about psychological comfort important for safe driving are preferable. The sixth is an appearance problem, which is the difficulty of scratching the surface.
[0012]
That is, the object of the present invention is to provide a storage cover that has safety certainty, adaptability in a wide temperature range, durability, and a favorable feel, can realize high productivity and low cost (thinning), and is hard to damage the surface. It is to provide.
[0013]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have injected a specific polyurethane elastomer having a concave portion for storing an air bag inside and a rupture-scheduled portion having a fragile structure and a Shore D hardness of 20 to 70. The present invention has been completed by finding out that the storage cover obtained by molding in order to solve the above problems.
[0014]
  That is, the present invention is a storage cover for an airbag device comprising an injection molded body of a thermoplastic elastomer having an airbag storage recess on the inside and a rupture-scheduled portion having a fragile structure. A storage cover for an airbag device, which is a polyurethane elastomer having a Shore D hardness of 20 to 70, which is obtained by copolymerizing the components (a), (b) and (c).
(A) It consists of repeating units of the following formulas (2) and (3), and the ratio of (2) and (3) is (2) / (3) = 10/90 to 90/10 (molar ratio). Yes, a polycarbonate diol having a hydroxyl group as a terminal group (where n is the number of carbons in the formula (2))4Or an integer of 5Either one ofRepresents).
[Chemical 1]

(B) Polyisocyanate
(C) Chain extender having two active hydrogens capable of reacting with polyisocyanate
[0018]
  The polycarbonate diol used as the component (a) of the polyurethane elastomer of the present invention can be obtained by various methods described in Schell, Polmer Review, Vol. 9, pages 9 to 20 (1964). Synthesized from cyclic diolsThe
[0020]
BookThe polycarbonate diol suitable for the airbag cover of the invention includes 1,4-butanedioRumaOr 1,5-pentanediolEither one ofA copolymer polycarbonate diol synthesized from 1,6-hexanediol is preferable because the resulting airbag cover has excellent low-temperature characteristics. 1,4-butanedioe, a repeating unit in the polymerRumaOr 1,5-pentanediolEither one ofThe ratio of 1,6-hexanediol is 10/90 to 90/10, preferably 20/80 to 80/20, and more preferably 30/70 to 70/30.
[0021]
The range of the average molecular weight of the polycarbonate diol used in the present invention is usually 500 to 5000 in terms of number average molecular weight, preferably 1000 to 3000, more preferably 1500 to 2500, and the polymer terminal is substantially Therefore, it is desirable that all be hydroxyl groups.
[0022]
In the present invention, in addition to the above-mentioned diol, by using a small amount of a compound having three or more hydroxyl groups per molecule, for example, trimethylolethane, trimethylolpropane, hexanetriol, pentaerythritol, etc. Polyurethanes using polyfunctionalized polycarbonates are also included.
[0023]
Next, as the polyisocyanate used for the component (b) of the polyurethane elastomer of the present invention, for example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, and a mixture thereof (TDI), diphenylmethane-4, Known aromas such as 4'-diisocyanate (MDI), naphthalene-1,5-diisocyanate (NDI), 3,3'-dimethyl-4,4'-biphenylene diisocyanate, crude TDI, polymethylene polyphenyl isocyanate, crude MDI Known aromatic alicyclic diisocyanates such as xylylene diisocyanate (XDI) and phenylene diisocyanate; 4,4′-methylenebiscyclohexyl diisocyanate (hydrogenated MDI), hexamethylene diisocyanate (HMDI), Isophorone diisocyanate (IPDI), cyclohexane diisocyanate known aliphatic diisocyanate (hydrogenated XDI), etc., and isocyanurate-modified products of these isocyanates, carbodiimide-modified products, a biuretization modified products.
[0024]
In addition, examples of suitable chain extenders used as necessary as a copolymerization component (c) of the polyurethane elastomer of the present invention include conventional chain extenders in the polyurethane industry. Supervised by Keiji Iwata Recent polyurethane application technology CMC 1985, pages 25-27, known water, low molecular polyols, polyamines and the like are included. Along with the aliphatic polycarbonate used in the present invention, a known polyol may be used in combination in accordance with the use of the polyurethane as long as the effects of the present invention are not impaired. Known polyols include polyols such as known polyesters and polyether carbonates described in Yoshio Imai, pages 12 to 23, 1987, Polyurethane Foam Polymer Publications.
[0025]
Specifically, a diol having a molecular weight of 300 or less is usually used as the low molecular polyol. Examples thereof include aliphatic diols such as ethylene glycol, 1,3-propylene diol, 1,4-butane diol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, decamethylene glycol and the like.
[0026]
In addition, alicyclic diols such as 1,1-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, xylylene glycol, bis (p-hydroxy) diphenyl, bis (p-hydroxyphenyl) propane 2,2-bis [4- (2-hydroxyethoxy) phenyl] propane, bis [4 (2-hydroxy) phenyl] sulfone, 1,1-bis [4- (2-hydroxyethoxy) phenyl] cyclohexane, etc. Is mentioned. Preferably, ethylene glycol and 1,4-butanediol are used.
[0027]
As a method for producing the polyurethane elastomer of the present invention, a urethanization reaction technique known in the polyurethane industry is used. For example, an NCO-terminated polyurethane prepolymer is produced by reacting the polyol and organic polyisocyanate at room temperature to 200 ° C.
[0028]
Also, a thermoplastic polyurethane elastomer can be produced using the polyol, polyisocyanate and, if necessary, a chain extender. In these productions, known polymerization catalysts represented by organic metal salts such as tertiary amines, tin and titanium [for example, Keiji Yoshida (Polyurethane resin), Nihon Kogyo Shimbun, pp. 23-32 (1969) It is also possible to use “describe in year)”. These reactions may be carried out using a solvent. Preferred solvents include dimethylformamide, diethylformamide, dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, methylisobutylketone, dioxane, cyclohexanone, benzene, toluene, ethyl cellosolve, etc. is there.
[0029]
In the production of the polyurethane elastomer of the present invention, a compound containing only one active hydrogen that reacts with an isocyanate group, for example, a monohydric alcohol such as ethyl alcohol or propyl alcohol, and a secondary amine such as diethylamine or di-n-propylamine Etc. can be used as end terminators.
[0030]
The polyurethane elastomer using the polycarbonate polyol of the present invention is not only excellent in flexibility and elastic recovery compared with other polyurethane elastomers, but also has extremely good hydrolyzability, so that it can be used as an air bag cover that is always touched by the hand. When used, it is suitable because it has excellent sweat resistance.
[0031]
The Shore D hardness of the polyurethane elastomer of the present invention is preferably in the range of 20 to 70, more preferably 25 to 50, and the soft segment amount is appropriately selected. A Shore D hardness of less than 20 is not preferable because the development performance at high temperatures and scratch resistance are poor. On the other hand, when the Shore D hardness exceeds 70, the low-temperature deployment performance and soft feeling of the obtained airbag cover are insufficient, which is not preferable.
[0032]
The melt flow rate (230 ° C., 2.16 kg load value, hereinafter abbreviated as MFR) of the polyurethane elastomer of the present invention is 0.5 to 100 g / 10 minutes, preferably 5 to 50 g / 10 minutes, more preferably 10 ~ 30 g / 10 min. If the MFR is less than 0.5 g / 10 min, the injection moldability is inferior and short shots are not preferable. On the other hand, if the MFR exceeds 100 g / 10 min, not only the mechanical properties (breaking strength, breaking elongation, etc.) and wear properties are inferior, but also the unfolding performance is deteriorated.
[0033]
As the additive used in the present invention, at least an antioxidant, a light stabilizer and a heat stabilizer are preferably used. These antioxidants include phosphoric acid, phosphorous acid, aliphatic, aromatic or alkyl group-substituted aromatic esters and hypophosphorous acid derivatives, phenylphosphonic acid, phenylphosphinic acid, diphenylphosphonic acid, polyphosphonates, dialkylpentaerythritol diesters. Phosphites, phosphorus compounds such as dialkylbisphenol A diphosphites; phenol derivatives, particularly hindered phenol compounds, thioethers, dithioates, mercaptobenzimidazoles, thiocarbanilides, thiodipropionates, and other sulfur-containing compounds; Tin compounds such as dibutyltin monoxide can be used.
[0034]
These may be used alone or in combination of two or more. The addition amount of these stabilizers is 0.01 to 5 parts by weight, preferably 0.1 to 3 parts by weight, more preferably 0.2 to 2 parts by weight with respect to 100 parts by weight of the polyetherester block copolymer. . In general, antioxidants can be divided into primary, secondary and tertiary antioxidants. In particular, Irganox 1010 (trade name: manufactured by Ciba Geigy), Irganox 1520 (trade name: manufactured by Ciba Geigy) and the like are preferable as the hindered phenol compound as the primary antiaging agent. The phosphorus-based compound as the secondary anti-aging agent is preferably PEP-36, PEP-24G, HP-10 (all trade names: manufactured by Asahi Denka Co., Ltd.) Irgafos 168 (trade name: manufactured by Ciba Geigy). Furthermore, as a sulfur compound as a tertiary antiaging agent, thioether compounds such as dilauryl thiopropionate (DLTP) and distearyl thiopropionate (DSTP) are preferable.
[0035]
Examples of the ultraviolet absorber / light stabilizer include benzotriazole compounds and benzophenone compounds. As the light stabilizer, a radical scavenging light stabilizer such as a hindered amine compound is preferably used.
[0036]
Moreover, you may add a plasticizer to the composition obtained as needed. Examples of such plasticizers include phthalates such as dioctyl phthalate, dibutyl phthalate, diethyl phthalate, butyl benzyl phthalate, di-2-ethylhexyl phthalate, diisodecyl phthalate, diundecyl phthalate, diisononyl phthalate: tricresyl phosphate, triethyl phosphate, Phosphate esters such as tributyl phosphate, tri-2-ethylhexyl phosphate, trimethylhexyl phosphate, tris-chloroethyl phosphate, tris-dichloropropyl phosphate: trimellitic acid octyl ester, trimellitic acid isodecyl ester, trimellitic acid esters, Dipentaerythritol esters, dioctyl adipate, dimethyl adipate, di-2-ethylhexylase Acid, dioctyl azelate, dioctyl sebacate, di-2-ethylhexyl sebacate, methyl acetyl lysinate, etc .: pyromellitic esters such as pyromellitic octyl ester: epoxidized soybean oil, epoxidized linseed Examples include oils, epoxy plasticizers such as epoxidized fatty acid alkyl esters: polyether plasticizers such as adipic acid ether esters and polyethers, liquid rubbers such as liquid NBR, liquid acrylic rubber, and liquid polybutadiene: process oils and the like. I can do it.
[0037]
These plasticizers can be used alone or in combination of two or more. The amount of the plasticizer added is appropriately selected according to the required hardness and physical properties, but is preferably 1 to 50 parts by weight per 100 parts by weight of the composition.
[0038]
In addition, kaolin, silica, mica, titanium dioxide, alumina, calcium carbonate, calcium silicate, clay, kaolin, diatomaceous earth, asbestos, barium sulfate, aluminum sulfate, calcium sulfate, basic magnesium carbonate, disulfide as long as the physical properties are not impaired. Fillers and reinforcements such as molybdenum, graphite, glass fiber, carbon fiber: Lubricants or mold release agents such as zinc stearate and bisamide stearate: carbon black for coloring, ultramarine, titanium white, zinc white, red pepper, Dye pigments such as bitumen, azo pigments, nitro pigments, lake pigments, phthalocyanine pigments: flame retardants such as octabromodiphenyl and tetrabromobisphenol polycarbonate: foaming agents: thickeners such as epoxy compounds and isocyanate compounds: silicone oils Silico Down resins can be used various known additives.
[0039]
The thermoplastic elastomer composition constituting the storage cover of the airbag apparatus of the present invention can be easily obtained by granulation after melt-kneading with various extruders, Banbury mixers, kneaders, rolls, and combinations thereof. Obtained in the form of pellets. A storage cover can be obtained with high productivity by molding this thermoplastic elastomer composition with a general-purpose simple injection molding machine used for molding general thermoplastic resins and thermoplastic elastomers.
[0040]
Next, the structure of the storage cover of the present invention will be specifically described with reference to the drawings. FIG. 1 is a perspective view showing an example of a storage cover of an airbag device for a driver's seat according to the present invention. FIG. 5 is a perspective view showing an example of a storage cover of a passenger seat airbag device according to the present invention. FIG. 8 is a schematic view showing a cross section similar to FIG. 6 showing another example of the storage cover of the airbag device for the passenger seat according to the present invention. FIG. 9 is a schematic view showing a cross section similar to FIG. 7 of the storage cover shown in FIG.
[0041]
The top surface of the storage cover can be set to an H shape as shown in FIG. 1, a U shape as shown in FIG. 5, other X shapes, radial shapes, arc shapes, U shapes, or the like. The side wall of the storage cover can be set as shown in FIGS. The fragile structure of the fragile structure is provided with a V-shaped groove, U-shaped groove, U-shaped groove, or other cross-sectional shape groove along the predetermined rupture line of the storage cover. It can be realized by making it thinner than the thickness of the part or by providing slits and cuts intermittently. In addition, the scratch resistance of the surface can be further improved by applying a texture to the surface of the storage cover.
[0042]
【Example】
Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited thereto.
<Evaluation method>
First, physical property evaluation items used in Examples and Comparative Examples and evaluation methods thereof will be described below.
[0043]
[Melt flow rate (MFR)]
About 5 g of pellets of each thermoplastic elastomer composition were vacuum-dried at 70 ° C. for about 12 hours in a vacuum drier, and immediately, a load of 2.16 kg and a measurement temperature were measured by an orifice having a diameter of 2.090 mm and a length of 8 mm. MFR was measured under L conditions of 230 ° C.
[0044]
[Melting point]
About 10 mg of each thermoplastic elastomer composition was applied to a differential calorimeter (DSC-200) manufactured by SEIKO ELECTRONIC INDUSTRIAL CO., LTD. Under a nitrogen atmosphere (10 cc / min) under the condition of a heating rate of 10 ° C./min. The change in temperature difference ΔT was examined, and the temperature at the top of the endothermic peak was taken as the melting point from the obtained temperature-temperature difference (ΔT) curve.
[0045]
〔surface hardness〕
Shore D hardness was measured at 25 ° C.
[Flexural modulus (MPa)]
According to JIS K7203, using an injection-molded test piece having a length of 125 mm, a width of 12.5 mm, and a length of 3 mm, and at a bending speed of 2 mm / min, −50 ° C., −40 ° C., −25 ° C., 0 ° C., 23 ° C. The flexural modulus was measured at each temperature of 100 ° C.
[0046]
[Break strength (MPa), break elongation (%)]
According to JIS K6301, measurement was performed by performing a tensile test at 25 ° C. under a head speed of 20 mm / min using an injection-molded test piece having a length of 20 mm × width of 3 mm × thickness of 2 mm.
[0047]
[Surface resistance]
The load was set to 340 g, and the pencil hardness (9B to 9H) was evaluated.
[Sweat resistance]
The injection test piece was immersed in artificial sweat (artificial sweat composition: NaCl 7 g, methyl alcohol 500 cc, urea 1 g, lactic acid 4 g, distilled water 500 cc) at room temperature for 30 days. The appearance after the test piece was taken out and subjected to the wear test (appearance after the test with the JIS K7204 wear wheel) was evaluated with 3 grades.
3; No scratches caused by worn wheels
2; slight scratches due to wear rings are observed
1: Scratches due to wear rings are clearly observed
[0048]
[Deployment performance of storage cover]
Attach the airbag and storage cover to an iron mounting bracket (retainer), and then attach the gas generator to assemble the airbag device. Next, this airbag device is put in an air thermostat at a deployment temperature (−40 ° C., room temperature or 90 ° C.) and left for another 2 hours after the internal temperature stabilizes. (Electrically energize within one minute after removing the airbag device from the air temperature chamber). If the storage cover is opened at the portion to be broken without generating broken pieces and the airbag is deployed, the deployability of the storage cover is good.
A method for synthesizing an aliphatic copolycarbonate diol is shown below as a reference example.
[0049]
Reference example 1
To a 3 liter flask equipped with a 10 mm diameter and 300 mm long distillation tower and thermometer and a stirrer packed with Dixon packing 3φ, 970 g (11 mol) of ethylene carbonate (EC), 650 g of 1,6-hexanediol (HDL) ( 5.5 mol) and 570 g (5.5 mol) of 1,5-pentanediol (PDL) were added, and the mixture was heated and stirred under a reduced pressure of 20 torr, and the internal temperature was controlled to 150 ° C. The reaction was carried out for 20 hours while distilling EC and ethylene glycol (hereinafter abbreviated as EG) having an azeotropic composition from the top of the distillation column. Next, the distillation column was removed, and the degree of vacuum was changed to 7 torr to recover unreacted EC and diol. After the distillation of unreacted substances was completed, the internal temperature was set to 190 ° C., and the diol was distilled while maintaining the temperature, thereby carrying out a self-condensation reaction to increase the molecular weight. After 4 hours, a polymer having a molecular weight of 2000 was obtained by GPC analysis. The yield was 740 g, and the hydroxyl value was 56 mgKOH / g. This polymer is abbreviated as pc-a.
[0050]
Reference examples 2 and 3
Aliphatic in the same manner as in Reference Example 1 except that 1,4-butanediol (BDL), 1,5-pentanediol and 1,6-hexanediol were used as the diol, and the amounts shown in Table 1 were used. Copolycarbonate diol (pc-b, pc-c) was obtained. The respective molecular weights are shown in Table 1.
[0051]
[Table 1]

[0052]
The raw materials used in the examples and comparative examples and the evaluation methods are as follows.
1. Polyurethane elastomer (hereinafter abbreviated as TPU) component
(1) TPU-1:
200 g of pc-a and 67.2 g of hexamethylene diisocyanate obtained in Reference Example 1 were charged into a reactor equipped with a stirrer, a thermometer and a condenser, and reacted at 100 ° C. for 4 hours to obtain a prepolymer of terminal NCO. Adds 30g of 1,4-butanediol as a chain extender to the prepolymer and 0.006g of dibutyltin dilaurate as a catalyst, and incorporates a kneader built-in universal extruder (laboratory extruder for LABO manufactured by Kasamatsu Chemical Research Laboratory Co., Ltd.) KR-35 type) at 140 ° C. for 60 minutes, and after 100 parts by weight of the resulting polyurethane elastomer, 1 part by weight of carbon black master pellet (Royal Black RB9005), 0.1 part by weight of Irganox 1010, dilaurylthio 0.15 parts by weight of propionate (DLTP, manufactured by Yoshitomi Pharmaceutical Co., Ltd.) and 0.1 part by weight of TINUVIN 327 (manufactured by Ciba Geigy) were added, respectively, and pelletized with an extruder. The Shore D hardness of the urethane elastomer was 39, and the MFR was 24.
[0053]
(2) TPU-2:
Except for using pc-b as the polycarbonate diol, polymerization was performed in the same manner as in the synthesis method of TPU-1, to obtain a urethane elastomer. The resulting urethane elastomer had a Shore D hardness of 42 and an MFR of 20.
[0054]
(3) TPU-3:
Except for using pc-c as the polycarbonate diol, polymerization was performed in the same manner as in the synthesis method of TPU-1, to obtain a urethane elastomer. The resulting urethane elastomer had a Shore D hardness of 43 and an MFR of 28.
[0055]
(4) TPU-4:
It synthesize | combined by the method similar to the synthesis | combining method of TPU-1, except having used the polycaprolactone polyol (The product made from Daicel, Plaxel 220, molecular weight 2,000) instead of polycarbonate diol. The resulting urethane elastomer had a Shore D hardness of 45 and an MFR of 27.
[0056]
(5) TPU-5:
Miractolan E190 (Nippon Miractoran, MDI / adipate TPU), Shore D hardness 45, MFR; 28
[0057]
Example 1
The above physical properties were measured using TPU-1. The results are shown in Table 2. Next, TPU-1 was used for injection molding to obtain storage covers for a plurality of driver's seat airbag devices. The molding cycle is 80 seconds, and the deployment performance at −40 ° C., room temperature, and 90 ° C. of the airbag apparatus assembled using the obtained storage cover is shown in Table 2.
[0058]
The shape of the storage cover of Example 1 will be specifically described below with reference to FIGS. FIG. 1 is a perspective view showing an example of a storage cover of an airbag device for a driver's seat according to the present invention. FIG. 2 is a schematic view showing a cross section of the storage cover taken along line II-II in FIG. FIG. 3 is a schematic view showing an enlarged cross section of the V-shaped groove of the storage cover of FIG. FIG. 4 is a schematic view showing an enlarged cross section of the U-shaped groove of the storage cover of FIG.
[0059]
As shown in FIG. 1, the storage cover has a flange 5 having a bolt hole for attaching to a retainer (not shown) in the periphery, one side is open, and a space 8 in which an airbag can be stored is provided inside. 1 is formed in a box shape, and a portion 3 of the structure that is fragile to the top surface 2 is arranged in an H shape as shown by the dotted line in FIG. As shown, a hinge portion 4 is provided.
[0060]
As shown in FIGS. 2 and 3, the planned fracture portion 3 is formed by a V-shaped groove 6 having a V-shaped fracture on the back side of the top surface 2. As shown in FIGS. 2 and 4, the hinge portion 4 is formed by a U groove 7 having a U-shaped cross section on the back side of the top surface 2. When the airbag (not shown) is inflated, the storage cover 1 is broken at the planned breakage portion 3, the two doors 2a and 2b are deployed around the hinge portion 4, and the airbag is released and inflated.
[0061]
The dimension of the planned breakage part 3 is 12 cm for the part corresponding to the two vertical H-shaped bars, 15 cm for the part corresponding to the horizontal bar, the thickness of the part to be broken is 0.5 mm, and the thickness of the hinge part The thickness is 1.9 mm, and the other parts are 3 mm. The storage cover of Example 1 has a maximum clamping force of 150 kg / cm.²Maximum injection pressure 60kg / cm²The above-mentioned mold for storage cover was attached to a general-purpose injection molding machine and molded at an operating temperature of 200 to 230 ° C. In Example 1, an air bag having an internal volume of 60 liters was used, and one gas generator having a gas generation amount of about 1 mol was used.
[0062]
Examples 2 and 3
Using TPU-2 and TPU-3, physical property evaluation and airbag evaluation were performed in the same manner as in Example 1. The results are shown in Table 2.
[0063]
[Table 2]

[0064]
Example 4
Using TPU-1, injection storage was performed to obtain a plurality of passenger airbag covers. The molding cycle was 65 seconds. The deployability at −40 ° C., room temperature, and 90 ° C. of the airbag apparatus assembled using the obtained storage cover was good.
[0065]
FIG. 5 is a perspective view showing an example of a storage cover of a passenger seat airbag device according to the present invention. 6 is a schematic view showing a cross section of the storage cover taken along line VI-VI in FIG. FIG. 7 is a schematic view showing a cross section of the storage cover taken along line VII-VII in FIG. The shape of the storage cover of Example 9 is shown in FIGS. That is, the storage cover 11 includes a top plate 12 and four side walls 18. The top plate 12 extends in a bowl shape to the outside of the side wall 18, and the side wall is provided with a flange 15 on the outer periphery of the lower end. The storage cover 11 can be attached to a retainer (not shown) using a hole 19 arranged in the side wall 18, and a gas generator (not shown) is attached to the retainer.
[0066]
An airbag (not shown) can be stored in a space formed by the top plate 12, the side wall 18, the retainer, and the gas generator of the storage cover. As shown in FIGS. 5, 6, and 7, the fragile structure to be broken 13, 13 ′ is disposed inside the side wall 18 of the top surface 12, and the hinge portion 14 is as shown in FIGS. 5 and 6. It is arranged. The portions to be broken 13, 13 'are arranged as shown in FIGS.
[0067]
As shown in FIGS. 6 and 7, the breakable portions 13 and 13 ′ are formed by V grooves 16 and 16 ′ having a V-shaped cross section on the back side of the top plate 12. As shown in FIG. 6, the hinge portion 14 is formed by a U groove 17 having a U-shaped cross section on the back side of the top plate 12.
[0068]
When the airbag is inflated, the storage cover 11 is broken at the planned breaking portions 13 and 13 ', the portion 12a surrounded by the breaking portions 13 and 13' and the hinge portion is deployed with the hinge portion 14 as an axis, and the airbag is released. It is supposed to expand. The dimensions of the storage cover 11 are: (a) the long side 34 cm, the short side 14 cm, and the thickness 3 mm of the top plate 12; (b) the long side side 28 cm, the short side 10 cm, the height about 6.8 cm, and the thickness. The thickness is about 3 mm, (c) the thickness of the planned fracture portion is 0.5 mm, and (d) the thickness of the hinge portion is 1.9 mm.
[0069]
The storage cover of Example 4 has a maximum clamping force of 215 kg / cm.²Maximum injection pressure 60kg / cm²The above-mentioned mold for storage cover was attached to a general-purpose injection molding machine and molded at an operating temperature of 200 to 230 ° C. In Example 4, an air bag having an internal volume of 120 liters was used, and two gas generators having a gas generation amount of about 1 mol were used.
[0070]
Comparative Examples 1 and 2
Evaluation was performed in the same manner as in Example 1 except that TPU-4 and TPU-5 were used as TPUs. The results are shown in Table 3.
[0071]
[Table 3]

[0072]
【The invention's effect】
As described above, the present invention employs the molding of a specific thermoplastic elastomer composition by an injection molding method, and has an excellent durability due to the provision of a fragile structure to be broken. An air bag storage cover that has a touch and can be deployed reliably over a wide temperature range, as well as being highly productive and paint-free, realizing low cost.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of a storage cover of an airbag device for a driver's seat according to the present invention.
FIG. 2 is a schematic diagram showing a cross section of the storage cover taken along line II-II in FIG.
3 is a schematic view showing an enlarged cross section of a V-shaped groove of the storage cover of FIG. 2. FIG.
4 is a schematic view showing an enlarged cross section of a U-shaped groove of the storage cover of FIG. 2. FIG.
FIG. 5 is a perspective view showing an example of a storage cover of a passenger seat airbag device according to the present invention.
6 is a schematic view showing a cross section of the storage cover taken along line VI-VI in FIG. 5;
7 is a schematic view showing a cross section of the storage cover taken along line VII-VII in FIG. 5;
FIG. 8 is a schematic view showing a cross section similar to FIG. 6 showing another example of the storage cover of the airbag device for the passenger seat according to the present invention.
9 is a schematic view showing a cross section similar to FIG. 7 of the storage cover shown in FIG. 8;
[Explanation of symbols]
1, 11, 21 ... Storage cover
2 ... top
2a ... door
3, 13, 13 ', 23, 23'.
4, 14, 24 ... hinge part
5 ... Flange
6, 16, 16 ', 26, 26' ... V-groove
7,7 ', 17,27 ... U groove
8 ... space
9 ... hole
12, 22 ... top plate
12a ... Opening of top plate
18 ... side plate
19 ... hole

Claims (1)

A storage cover for an airbag apparatus comprising an injection molded body of a thermoplastic elastomer having a concave portion for storing an airbag inside and a rupture-scheduled portion having a fragile structure, wherein the thermoplastic elastomer is the following (a), ( A storage cover for an airbag device, which is a polyurethane elastomer having a Shore D hardness of 20 to 70, which is obtained by copolymerizing the components b) and (c).
(A) It consists of repeating units of the following formulas (2) and (3), and the ratio of (2) and (3) is (2) / (3) = 10/90 to 90/10 (molar ratio). There, polycarbonate diol terminal group is a hydroxyl group (however, represents a (2) wherein n is either the integer 5 was or 4 carbon atoms).

(B) Polyisocyanate (c) Chain extender having two active hydrogens capable of reacting with polyisocyanate

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