JP3658097B2 - Resin molded body with magnetic body and method of manufacturing screw drive device - Google Patents

Description

（式中、Ｘは直結または炭素数 1〜 10 の炭化水素基、六フッ素化されたイソプロピリデン基、カルボニル基、チオ基およびスルホン基からなる群より選ばれた基を表わし、Ｒ₁ 〜Ｒ₄ は水素、低級アルキル基（炭素数 1〜5 ）、低級アルコキシ基（炭素数 1〜5 ）、塩素または臭素を表わし、互いに同じであっても異なっていてもよい。Ｙは炭素数 2以上の脂肪族基、環式脂肪族基、単環式芳香族基、縮合多環式芳香族基、芳香族基が直接または架橋基により相互に連結された非縮合多環式芳香族基からなる群から選ばれた 4価の基を表わす。）
【００２０】
（Ｉ）式で示される熱可塑性ポリイミド樹脂は、たとえば、下記（ＩＩ）式で示される芳香族エーテルジアミンと 1種以上の芳香族テトラカルボン酸二無水物の反応によって得られるポリアミド酸を脱水環化して得られる。
【化２】

（式中、Ｘは直結または炭素数 1〜 10 の炭化水素基、六フッ素化されたイソプロピリデン基、カルボニル基、チオ基およびスルホン基からなる群より選ばれた基を表わし、Ｒ₁ 〜Ｒ₄ は水素、低級アルキル基（炭素数 1〜5 ）、低級アルコキシ基（炭素数 1〜5 ）、塩素または臭素を表わし、互いに同じであっても異なっていてもよい。）
【００２１】
このような熱可塑性ポリイミド樹脂のうち、市販品としては（Ｉ）式におけるＲ₁ 〜Ｒ₄ が全て水素である三井東圧化学社製の商品名オーラム（ＡＵＲＵＭ）などを挙げることができる。その化学式を（ＩＩＩ）式に示す。
【化３】

このようなポリイミド系樹脂は、イミド基もしくは芳香族環の少なくとも 1種類以上を有する点で、機械的強度が高く、また、エーテル結合を適度に有するため、成形時に望ましい溶融粘度となるため生産性効率の優れた射出成形が可能となるため好ましいものと言える。
【００２２】
熱可塑性ポリイミド樹脂組成物に配合される黒鉛の形態は薄片状、鱗片状、球状、棒状等その形状は問わないが、低摩擦係数、耐摩耗性などの摺動特性を重視するのであれば、球状のものが好ましく、一方、摺動特性と生産性、価格等とで、平均して総合的に優れるものを選ぶのであれば、薄片状、鱗片状であっても十分である。このような黒鉛としては、たとえば、ピッチ、コークス、タール、フラン系樹脂、ポリアクリロニトリル系樹脂、エポキシ系樹脂、フェノール系樹脂等を原料として、約 800〜3000℃、原料によっては、約 1200 〜 2300 ℃の高温熱処理温度で焼成したものであればよい。熱処理温度が低すぎると、黒鉛の固定炭素量が十分に高くならず、一方、熱処理温度が高すぎると、黒鉛の昇華等などが発生して黒鉛の熱分解が急激に進行したり、また、そのような高温にするためのエネルギー効率等の点で無駄が生じたりするため好ましくない。
【００２３】
このような黒鉛の平均粒径は、 5〜50μm 、好ましくは 5〜25μm のものが望ましい。平均粒径が大きすぎると、樹脂組成物中での分散不良の原因となり、摺動特性も満足できない。平均粒径が小さすぎると、凝集の原因となり、結果としてやはり分散不良となる。このような理由から、黒鉛の平均粒径は 5〜15μm であることがより好ましい。
【００２４】
また、フッ素系樹脂としては、耐熱性、摺動性、射出金型からの離型性等に優れた四フッ化エチレン樹脂（ＰＴＦＥ）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体（ＰＦＡ）、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（ＦＥＰ）などのパーフルオロ系フッ素樹脂が好ましく、とくに四フッ化エチレン樹脂（ＰＴＦＥ）が好ましい。
【００２５】
パーフルオロ系フッ素樹脂は、骨格である炭素の周囲を全てフッ素で囲まれたもの、もしくは微量の酸素を介して全てフッ素で取り囲まれているために安定しており、低摩擦係数、非粘着性、耐熱性、耐薬品性などの点で優れている。このような、フッ素系樹脂をナット樹脂組成物中に所定量配合することで、ナットに摺動性が付与され、たとえば射出成形からのナット部材のねじり抜き取り性が容易にもなり、また、少ない駆動力でナット２を回転、駆動することもでき、これにより筒状磁性体５たとえば回転子、固定子６をも小型化することができる。このように、ナット２もしくはねじ軸３のような摺動部材にフッ素系重合体を添加したり、また、塗布したりすることによって、効率よくねじを駆動、回転させることができる。
【００２６】
上述のナットを形成する合成樹脂の溶融粘度よりも低い溶融粘度を有する合成樹脂で、固着樹脂層に使用できる合成樹脂の例としては、たとえば、ナットに前述の熱可塑性ポリイミド樹脂組成物を用いた場合は、６１２ナイロン、６１０ナイロン、４６ナイロン、６６ナイロン、１１ナイロン、１２ナイロン、３ナイロン、６ナイロン、芳香族ナイロン、共重合ナイロンなどのポリアミド系樹脂、ビスフェノールＡとエピクロルヒドリンから製造されるフェノキシ樹脂、内部可塑化ポリエステル樹脂などを用いることができる。
【００２７】
脆性材料からなる焼結体である筒状磁性体５たとえば回転子と、通常合成樹脂からなるナット２とを固着し一体化することのできる材料として、ナットを形成する合成樹脂の溶融粘度よりも低い溶融粘度を有する合成樹脂であることが好ましい。
なぜなら、固着樹脂１６の溶融粘度がナット２の溶融粘度より低い合成樹脂であると、ナット２と回転子を射出成形によって固着層となる合成樹脂で一体化するときに、ナット２を形成する成形圧力より、低い成形圧力で射出することが可能なためである。ナット２の成形圧力より低い圧力で固着樹脂１６となる合成樹脂を射出成形すれば、固着層で一体に形成されたナット２に寸法変化は生じず、回転子が破損することはないからである。
【００２８】
具体的に固着樹脂について説明すると、このような固着樹脂は、たとえば、ＪＩＳ Ｋ ７２１０に基ずく試験法、もしくは、これに準ずる測定法等により粘度を測定することもできるが、この方法に準じた射出成形時のシリンダーまたはノズルの温度において測定した粘度であってもよく、測定方法はいずれであってもよい。たとえば、溶融樹脂の剪断速度が10² 〜10⁴ sec^-1、好ましくは10³ 〜10⁴ sec^-1のときに、溶融粘度が 50 〜200 Pa・s 、好ましくは、 100〜150 Pa・s のように比較的溶融粘度の低い樹脂材であれば、射出成形時に、大きな充填圧力をかけなくても、金型のキャビティ内へ樹脂が充填されやすい。
【００２９】
このため、脆性な回転子と剛性のある樹脂製ナット２とを射出圧力をたとえば、 100〜1300kgf/cm² （ 1〜13kgf/mm² ）、好ましくは 100〜800 kgf/cm² （ 1〜8 kgf/mm² ）、より好ましくは 100〜500 kgf/cm² （ 1〜5 kgf/mm² ）に設定し、保圧をたとえば、 100〜500 kgf/cm² （ 1〜5 kgf/mm² ）、好ましくは 100〜 300kgf/cm² （ 1〜3 kgf/mm² ）に設定して射出により固着しても回転子は破損されにくいことが考えられる。
なお、ナット２部材、筒状磁性体５たとえば回転子部材ともに共通して、前述の圧力が低すぎると、ボイド、ひけ等の発生原因となり、圧力が高すぎると、バリやクラッキング、クレージング等の発生原因となることが考えられる。
さらに、上記各々の圧力を回転子の引っ張り強度、もしくは圧縮強度よりも低い圧力下において射出成形することがより望ましいと考えられる。このようにして溶融粘度の低い固着用樹脂材にて回転子の機械的強度よりも低い圧力下において、固着樹脂層を射出により形成することにより、脆弱な回転子は成形圧力によって破損することなく、効率よく、一体成形体を形成することができるようになる。
【００３０】
そのような固着樹脂材の一例としてポリアミド系樹脂で具体的に説明する。ポリアミド系樹脂は、分子構造中において、主鎖にアミド結合（−ＮＨＣＯ−）を含む線状重合体であり結晶性樹脂である。そのため、機械的特性に優れ、耐衝撃性もまたよい。そして−ＮＨＣＯ−により親水性を有するので吸水性はあるが、これにより耐衝撃性、柔軟性は増加する。そのような特性であるため、比較的脆性材料の回転子と剛直な樹脂材からなるナット２等を射出成形法によって固着しても、回転子にはクラックなどの破損は発生しずらいと考えられる。このような理由から、たとえば、標準品などで、伸びが 1〜 300％の固着樹脂、好ましくは 3〜200 ％のポリアミド樹脂が好ましいと考えられる。伸び率が小さすぎると、柔軟性に期待できず、大きすぎると機械的強度、剛性が低下する。
【００３１】
またこのようなアミド結合（−ＮＨＣＯ−）を主鎖に有する樹脂は吸水性があるので、寸法精度もそれと共に変化する。そのため、吸水率は少ないほうが、回転子とナット２とを長期間安定して固着固定する上で有利であり、たとえば標準品で吸水率が 0.1〜1 ％、好ましくは 0.1〜0.5 ％（ 24 時間）であるものが好適である。
なお、前述の伸びは、たとえば、ＡＳＴＭ Ｄ６３８、前述の吸水率は、たとえば、ＡＳＴＭ Ｄ５７０により測定できるが、そのような測定方法に限定されるものではなく、いずれの測定法であってもよい。また、このような重合体によりなる成形体の表面硬度は比較的大きく、耐摩耗性があり、また、低摩耗係数で自己潤滑性も有するので、摺動特性も有しており、滑り軸受材などとしての摺動材としてもまた好適である。なお、摺動特性を向上させるため、固着樹脂材 100重量部あたり、前述のポリイミド系樹脂へ所定量添加する理由と同様に 1〜50重量部のフッ素系重合体や、また機械的強度を向上させる目的として、 1〜100 重量部、好ましくは 10 〜 50 重量部のガラス繊維等の強化繊維類等の少なくとも 1種類以上の充填材を固着樹脂組成物に添加、配合してもよい。
【００３２】
ここで、強化繊維類の形態は、繊維径 0.1〜50μm 、繊維長 0.001〜10mm、好ましくは繊維径 1〜25μm 、繊維長 0.01 〜1 mmであればよい。繊維径、繊維長が細すぎたり、短すぎたりすると機械的強度が向上されにくく、一方、繊維径、繊維長が太すぎたり、長すぎたりすると相手摺動材の摩耗の進行が早くなると考えられるため好ましくない。
【００３３】
以上の内容を満足するポリアミド系重合体として、たとえば式（ＩＶ）に示されるようなポリアミド６１２樹脂などを例示することができる。
【化４】

また、以上のようなポリアミド６１２樹脂としては、デュポン社製商品名、ザイテルＦＥ５３８２等を挙げることができる。
【００３４】
固着樹脂の層厚は、回転子とナットとを回転子の破損などを生じることなく一体成形することのできる厚さであればよい。その厚さは、たとえば 0.3〜5mm 、好ましくは 0.5〜3mm であればよい。層厚が薄すぎると、固着、接着性に期待できず、厚すぎるとねじ駆動装置を小型化できない。
【００３５】
本発明に係るねじ駆動装置の製造方法にあっては、上述のナットのねじ山の表面あるいはねじ軸の表面に摩擦係数の小さいコーティング層を被覆することにより、摺動抵抗を小さく、かつ安定した摺動特性が得られる。好適なコーティング層としては、ポリフルオロアルキル重合体（ＰＦＡＥ）やフルオロポリエーテル重合体などの含フッ素重合体が好ましい。
ここで、ポリフルオロアルキル重合体とは、たとえば、ＣＦ₃ （ＣＦ₂ ）₇ −、Ｈ（ＣＦ₂ ）₆ −、ＣＦ₂ Ｃl （ＣＦ₂ ）₁₁−、（ＣＦ₃ ）₂ ＣＦ（ＣＦ₂ ）₇ −、ＣＦ₂ Ｃl （ＣＦ₃ ）ＣＦ（ＣＦ₂ ）₇ −などのポリフルオロアルキル基を有する重合体であり、フルオロポリエーテル重合体は、一般式、−Ｃ_x Ｆ_2x−Ｏ−（x は 1〜4 の整数）で示される単位を主要構造単位とし、数平均分子量が 1000 〜50000 の重合体である。このような含フッ素重合体は軸受材料に対して親和性の高い官能基、たとえばエポキシ基、アミノ基、カルボキシル基、水酸基、メルカプト基、イソシアネート基、スルフォン基、エステル基等を含有しているものが好ましい。
【００３６】
具体的には、以下の式（Ｖ）に示すように、末端にイソシアネート基を有するパーフルオロ系ポリエーテル重合体（ＰＦＰＥ）がナット２などの基材と付着性に優れ、また、前述のフッ素系樹脂の添加と同様に、基材付着後のフルオロポリエーテル重合体の非粘着性や摺動特性に優れており、またこのような被覆層の形成は容易でもあり、摺動性、価格などに平均して総合的に優れるため好ましい。
【化５】

（式中、ｍ、ｎは整数を表わす。）
このようなものとして、モンテフルロス社製商品名：フォンブリンＺ−ＤＩＳＯＣ（数平均分子量約 2000 ）などを挙げることができる。
【００３７】
このような、含フッ素重合体を高フッ化有機溶媒に 0.1〜10重量％、効果的な薄層や、また液の歩留まり性、また価格等を考慮すれば 1〜5 重量％の濃度になるように希釈してナット２、もしくはねじ軸３のような、少なくとも一方の摺動部材に塗布する。塗布方法は、塗布液の歩留まりがよく効率的な浸漬塗布法（ディッピング）や、塗膜の厚みを精度よく形成できる霧化塗布法（スプレー）などを適宜選択することができる。
塗布後、自然乾燥もしくは生産性効率をあげるため、乾燥と薄層や基材の熱処理とを兼ねて、たとえば、50〜 350℃、好ましくは、50〜 280℃の温度で、 1〜 24 時間、好ましくは 1〜6 時間程度の加熱処理を施してもよい。このようにして、形成される塗布層の厚さは 0.001〜 30 μm 、好ましくは、0.01〜 10 μm の厚さであればよい。層の厚さが薄すぎると良好な摺動特性を長期間維持することが困難となり、厚すぎると、ナット２とねじ軸３との隙間寸法精度の管理が困難となり、円滑なねじの回転動作となりにくい。
【００３８】
そしてまた、ねじ軸３は、鋼表面に錆等による腐食の防止、若しくは腐食を抑える点から非磁性のステンレス鋼、アルミニウム合金鋼等の非鉄金属系非磁性鋼で形成することが好ましい。非磁性鋼であると、磁性化されにくいので、回転子などの磁石類の影響を受けにくい。これは、磁性化されていないことによりＳ極、Ｎ極がなく回転子５のＳ極、Ｎ極との互いの吸引力や反発力の影響がないため、ねじが停止しているときでも磁気力による不要な回転動の発生防止にもつながる。また、ねじ回転時にステッピング的な回転とならずトルク変動が少なく、滑らかな一定回転の回転動作となるため、非磁性鋼が好ましい。
【００３９】
そしてまた、本発明のねじ部形状は、図２に示すように、ナット２のねじ山の断面は半円径の形状で、これに対するねじ軸３のねじ谷１０は、ナット２のねじ山に対して、対称に傾斜する二つの傾斜面で形成される。本発明に係るねじは、図２に示されるようなすべりねじであって、ねじ山９とねじ谷１０がねじの進行方向に二点で線接触するようなねじに限らず、たとえば、ミニチュアねじ、メートル並目ねじ、メートル細目ねじ、ユニファイ並目ねじ、ユニファイ細目ねじ、２９度台形ねじ、３０度台形ねじ（メートル台形ねじ）等の台形ねじや、また、丸形ねじ、テイ型ねじ、ノコ型ねじ、三角ねじ、角ねじなどの角形ねじであったり、また、一条ねじ、もしくは複数条の数条ねじであってもよく、あらゆるねじ形状に適用することができる。
【００４０】
【実施例】
実施例および比較例で使用した材料を一括して以下に示す。
（１）回転子：ネオジウムー鉄系焼結磁石（引張り強度 7.6kgf/mm² 、圧縮強度 11 kgf/mm² ）
（２）ナット：熱可塑性ポリイミド樹脂（三井東圧化学社製商品名、オーラム＃４５０、射出成形温度約 400〜430 ℃、 420℃における溶融粘度 300〜500 Pa・s 、射出圧力 1500 kgf/cm² 、保圧 1500 から 800kgf/cm² の間で調整） 65 重量％に、黒鉛 20 重量％、フッ素系樹脂 3重量％、フェノール系樹脂硬化物 12 重量部からなる熱可塑性ポリイミド樹脂組成物
（３）ナット被覆層：フルオロポリエーテル重合体、モンテフルロス社製商品名、フォンブリンＺ一ＤＩＳＯＣ
（４）固着樹脂層：６１２ナイロン樹脂、デュポン社製商品名、ザイテルＦＥ５３８２（ガラス繊維 33 重量％混入）、射出成形温度約 230〜290 ℃、 250℃における溶融粘度 70 〜180 Pa・s 、固着層の厚さ約 0.4〜1 mm。
（５）ねじ軸：非磁性ステンレス鋼
上述の材料を用いてねじ駆動装置を作製した。なお、比較例１は固着樹脂にナットと同一の熱可塑性ポリイミド樹脂を用いる以外は実施例１と同一の方法で、また、比較例２は図４に示す従来方法によりねじ駆動装置を作製した。
【００４１】
ねじ駆動装置に用いられる磁性体付き樹脂成形体の作製方法を図１を援用して説明する。
射出成形金型１１、１２を準備し、一方の成形型１２のキャビティ１４を開放した状態で、そのキャビティ１４に筒状磁性体５となるネオジウムー鉄系焼結磁石およびナット２となる熱可塑性ポリイミド樹脂組成物からなる樹脂体を筒状の空隙部を有して挿入したのち、他方の型１１を衝合した（図１（ｂ））。
つぎに、スプルー１５を通じて固着樹脂１６を圧送してナット２の外周面と筒状磁性体５の内壁面との間の筒状空間に注入・充填した（図１（ｃ））。
射出成形条件は、射出圧力が 200kgf/cm² 、保圧は 200から 100kgf/cm² の間で調整し、また型温度が 70 ℃、樹脂温度が 280℃に設定した。
その後、注入・充填された固着樹脂１６を硬化後、一方の型１１から他方の型１２を離脱させてその一方の型１２のキャビティ１４を開口させ、エジェクトピンにより磁性体付き樹脂成形体２７を離型させた。
得られた磁性体付き樹脂成形体を固定子が取り付けられたケースに組み込みねじ駆動装置を得た。
【００４２】
得られたねじ駆動装置について、以下の評価試験を行った。
実施例および比較例の評価項目および評価方法を以下に示す。なお、本測定に使用した試験体は各ｎ＝５で行った。
（１）ナットの寸法の変化：射出成形によってナットのねじ山の寸法変形がどのくらい変化したかを測定する。
（２）回転子の破損率：射出成形後、回転子にクラックが入っているか否かを顕微鏡で観察し、クラックが入っている確率を調査する。
（３）回転子の寸法変化：射出成形後、クラックの入らなかった回転子の外径寸法に変化があるか否かを測定する。
評価結果を表１に示す。
【００４３】
【表１】

【００４４】
表１から明らかなとおり、実施例１はナットの寸法変化が非常に小さく、回転子の破損がなく、かつ回転子の寸法変化も非常に小さかった。これに対して、固着樹脂層にナットと同じ材料を使用した比較例１および従来技術で製造した比較例２は回転子が破損した。
【００４５】
【発明の効果】
本発明に係る磁性体付き樹脂成形体の製造方法は、筒状磁性体と樹脂体との空隙部に、その樹脂体の溶融粘度より低い溶融粘度を有する固着樹脂を充填し硬化する工程を有するので、筒状磁性体を破損することなく磁性体付き樹脂成形体を製造することができる。さらに、前工程や後工程を必要としないためコストの上昇を抑えることができる等、生産性に優れている。
【００４６】
本発明に係るねじ駆動装置の製造方法は、ナットの外周に取付けられるモータの回転子が固着樹脂を充填し硬化する工程を有するので、回転子を破損することなくねじ駆動装置を製造することができる。また、高精度なねじ山を保つことができる。さらに、前工程や後工程を必要としないためコストの上昇を抑えることができる等、生産性に優れている。
【図面の簡単な説明】
【図１】磁性体付き樹脂成形体の製造工程を示す図である。
【図２】ねじ駆動装置の断面図である。
【図３】従来のねじ駆動装置の断面図である。
【図４】従来の磁性体付き樹脂成形体の製造工程を示す図である。
【符号の説明】
２……ナット、５……筒状磁性体、１１、１２……成形型、１３……コアピン、１４……キャビティ、１５……スプルー、１６……固着樹脂、２７……磁性体付き樹脂成形体。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a resin-molded body with a magnetic body, and more particularly to a method of manufacturing a screw drive device using a nut with a cylindrical magnetic body made of a brittle material.
[0002]
[Prior art]
FIG. 3 shows a screw drive device that shows a cross-sectional view of a screw drive device that converts a rotational motion into a linear motion between a nut and a screw shaft constituting a motor (Japanese Utility Model Laid-Open No. 5-96605). In FIG. 3, 1 is a case, 2 is a resin nut, a cylindrical magnetic body 5 is integrally attached to the outer peripheral surface of the nut 2, and a stator 6 is attached to the inner peripheral surface of the case 1. Both constitute a motor 4 that rotationally drives the nut 2. Radial bearing surfaces 7 and 7 are formed on the outer peripheral surfaces of both ends of the nut 2 so as to be in contact with the inner surface of the case 1. In addition, thrust bearing surfaces 8 and 8 are formed on both end surfaces of the step provided in the central portion of the nut 2 so as to be in sliding contact with the inner end surface of the case 1. A thread 9 is formed on the inner diameter of the nut 2, and a thread valley 10 of the screw shaft 3 is screwed into the thread 9.
[0003]
Conventionally, the nut with a cylindrical magnetic body in such a screw drive device has been manufactured by the method shown in FIG.
Here, as shown in FIG. 4A, the main part of the apparatus for producing a resin-molded body with a magnetic body comprises two injection molds 11 and 12 (hereinafter simply referred to as molds). By colliding the two, a cavity 14 adapted to the outer shape of the resin molded body with magnetic material is formed, and a sprue 15 for supplying molten resin to the cavity 14 communicates with the cavity 14 to form a mold. Is provided.
When manufacturing a resin molded body with a magnetic body, first, as shown in FIG. 4B, with the cavity 14 of one mold 12 opened, the cylindrical magnetic body 5 serving as a rotor or the like in the cavity 14. After fitting, the other mold 11 is brought into contact.
Next, as shown in FIG. 4C, in this state, the molten resin 26 is pumped through the sprue 15 to be injected and filled into the hollow interior of the cylindrical magnetic body 5 in the cavity 14. By curing the resin 26, a resin-molded body 27 with a magnetic body in which the resin 26 is integrally molded in the hollow interior of the cylindrical magnetic body 5 as shown in FIG. 4 (d) can be obtained.
[0004]
[Problems to be solved by the invention]
Incidentally, the magnetic body is generally a sintered body made of a brittle material, and some of the composition materials have a large Young's modulus. When manufacturing a resin-molded body with a magnetic body using a magnetic body having a large Young's modulus, there are the following problems.
That is, when the resin molded body is integrally formed by injection molding inside the hollow of the magnetic body, tensile stress is generated in the circumferential direction of the magnetic body due to the injection pressure of the molten resin. On the other hand, in order to easily insert the magnetic body into the mold cavity, it is necessary to slide the outer peripheral surface of the magnetic body and the inner wall surface of the cavity, and there is a gap between the outer peripheral surface of the magnetic body and the inner wall surface of the cavity. It is necessary to form (clearance). As a result, if there is an unacceptable gap due to the aforementioned interaction, that is, the tensile properties of the magnetic material, the magnetic material may be damaged.
[0005]
The present invention has been made to cope with such problems, and provides a method for manufacturing a resin-molded body with a magnetic body and a screw driving device that can prevent damage to the magnetic body by simple means. With the goal.
[0006]
[Means for Solving the Problems]
The method for producing a resin-molded body with a magnetic body according to the present invention includes a step of placing a cylindrical magnetic body in a cavity of a molding die, and a resin body is inserted with a void in the hollow portion of the cylindrical magnetic body. And a step of filling the void portion with a fixing resin having a melt viscosity lower than the melt viscosity of the resin body and curing.
Further, the third step is characterized in that the fixing resin is filled and cured at a molding pressure lower than the mechanical strength of the cylindrical magnetic body.
Further, the filling and curing of the fixing resin is characterized by an injection molding method.
[0007]
A method for manufacturing a screw drive device according to the present invention includes: A step of providing a motor rotor made of a brittle material on the outer periphery of the nut, a step of screwing the nut with a screw shaft, and a step of rotatably mounting the nut in a case to which the motor stator is attached A step of providing a motor rotor on the outer periphery of the nut, the step of disposing the cylindrical magnetic body in the cavity of the mold, and the hollow portion of the cylindrical magnetic body. With voids Plastic nut And the process of inserting and arranging in the gap Plastic nut And a step of filling and curing a fixing resin having a melt viscosity lower than the melt viscosity. Further, the step of filling and curing the above-described fixing resin is a step of filling and curing the fixing resin with a molding pressure lower than the mechanical strength of the cylindrical magnetic body. Further, the filling and curing of the fixing resin is characterized by an injection molding method. here, Plastic nut The melt viscosity is a viscosity measured at the temperature of a cylinder or nozzle at the time of injection molding, and the measuring method is not particularly limited. Further, the mechanical strength of the cylindrical magnetic body refers to a strength that resists the filling pressure of the fixing resin.
[0008]
The method of manufacturing a resin-molded body with a magnetic body and a screw driving device according to the present invention is such that even if there is a gap between the cavity inner wall surface of the mold and the rotor, the rotor may be damaged or on the surface. Since there is no damage and it is not necessary to set the molding pressure low in the injection molding of the nut, a highly accurate thread can be formed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing a resin-molded body with a magnetic body according to the present invention, the molding method can be used without particular limitation, such as cast molding, reaction molding, injection molding, etc., but sprue, runner, etc. can be recovered and reused, An injection molding method that can efficiently produce the product is preferred. The manufacturing process of the resin-molded body with a magnetic body will be described with reference to FIG.
[0010]
First, as shown in FIG. 1 (a), the main part of the manufacturing apparatus is composed of two molds 11 and 12, and a cavity 14 adapted to the outer shape of the resin-molded body with a magnetic body is formed by abutting both. The core pin 13 is formed in the central portion of the cavity 14 and serves as a shaft hole of the molded body. A sprue 15 for supplying molten resin to the cavity 14 communicates with the cavity 14. The mold can be used without particular limitation, such as a rubber mold, a resin mold, a mold, etc., but a mold having good durability is preferable, and an injection mold excellent in productivity is more preferable.
[0011]
First, after the cavity 14 of one mold 12 is opened, a resin body such as the cylindrical magnetic body 5 and the nut 2 is inserted into the cavity 14 with a cylindrical gap, and FIG. The other mold 11 is abutted as shown in FIG. A sprue 15 is formed in the other mold 11 so as to communicate with the cavity 14.
In this state, as shown in FIG. 1 (c), the fixing resin 16 is pumped through the sprue 15 and injected into the cylindrical space between the outer peripheral surface of the resin body such as the nut 2 and the inner wall surface of the cylindrical magnetic body 5. Fill.
Then, after the injected and filled fixing resin 16 is cured, the other mold 12 is detached from one mold 11 and the cavity 14 of the one mold 12 is opened, and an appropriate means such as an eject pin is used for FIG. The resin molded body 27 with magnetic material shown in d) is released. In this way, even if a tensile stress or the like is generated in the circumferential direction of the cylindrical magnetic body 5, the magnetic body 5 is damaged because the stress falls within an allowable range due to the tensile characteristics of the cylindrical magnetic body 5. There is no. As a result, even the magnetic body 5 having a large Young's modulus can be used.
Here, the screw drive device can be obtained by incorporating the cylindrical magnetic body 5 into the case 1 to which the stator 6 is attached, with the motor rotor and the resin body as the nut 2. An example of such a screw drive device is shown in FIG.
[0012]
In the screw driving device shown in FIG. 2, the cylindrical magnetic body 5, for example, between the rotor and the nut 2, may have a means for preventing rotation of the rotor, preventing it from coming off, or omitted. Good. By having means such as a rotation stopper and a stopper, the nut 2 and the rotor 5 are more firmly fixed, and even a small member can be fixed without taking up space. On the other hand, if the fixing resin layer is sufficiently fixed and adhesive, means for preventing rotation and retaining may be omitted. In this case, for example, even if pressure is applied to the rotor at the time of injection molding, the rotor can be prevented from being damaged starting from the uneven portion, and the mechanical strength of the rotor is not reduced. Such a shape is also advantageous.
[0013]
Examples of magnetic materials suitable for the present invention include rare earth magnets such as neodymium-iron sintered magnets, ferrite magnets made of rare earth / cobalt magnets, ferrite powders or hard ferrites, and bonded magnets thereof. , Neodymium-iron (Nd-Fe), neodymium-iron-boron (Nd-Fe-B), samarium-cobalt (Sm-Co), samarium-iron-nitrogen (Sm-Fe-) N-based), samarium-iron-cobalt-nitrogen-based (Sm-Fe-Co-N-based), etc., all of which are made of brittle materials. Their physical properties include a tensile strength of 5-10kgf / mm ² About 7 to 8 kgf / mm on average ² Degree, compressive strength about 5-15kgf / mm ² About 8 to 13 kgf / mm on average ² Degree.
[0014]
Examples of resin bodies such as nuts include, for example, polyamide resins such as thermoplastic polyimide resins, polyamideimide resins, and aromatic polyamide resins, polyetherimide resins, and aromatic polyetheretherketone resins. Aromatic polyetherketone resins such as resins, polyethersulfone resins, polyarylene sulfide resins such as polyphenylene sulfide resins, polycyanoaryl ether resins, polyester resins such as aromatic polyester resins, polyolefin resins Thermoplastic resins such as injection-moldable molten fluororesins, thermosetting polyimide resins, epoxy resins, phenolic resins and allyl unsaturated polyester resins, and various synthetic resins List resin compositions containing compounding agents Can. The aromatic resin may be a wholly aromatic resin.
[0015]
Among these resin compositions, the thermoplastic polyimide resin composition is particularly preferable because of its excellent heat resistance, mechanical strength, wear resistance, and sliding properties. Other resins can also be used. For example, at least one resin selected from the above-mentioned resin group such as thermoplastic polyimide resin and having excellent mechanical strength 50 to 90% by weight, and if necessary, graphitize phenolic or non-phenolic resin raw materials 100 parts by weight of a resin composition consisting of about 50 to 10% by weight of graphite having a fixed carbon content of 97% or more and 100% or less, and if necessary, about 1 to 20 parts by weight of a fluororesin, Moreover, what blended about 5-30 weight part of powdery phenol resin hardened | cured material is suitable.
[0016]
If the fixed carbon content of graphite is less than 97%, satisfactory results cannot be obtained in both wear resistance and shrinkage ratio of the molded product before and after the crystallization treatment. Also, if the blending amount of graphite exceeds about 50% by weight, the melt viscosity of the resin composition becomes high and injection molding becomes difficult, and if it is less than about 10% by weight, the effect of improving the wear resistance cannot be sufficiently obtained. Furthermore, when the amount of the fluorine-based resin is less than about 5 parts by weight, sufficient sliding characteristics are not imparted to the thermoplastic polyimide resin composition, and when it exceeds about 20 parts by weight, the mechanical properties of the thermoplastic polyimide resin main body are increased. Strength is impaired. In addition, if the blended amount of the phenolic resin cured product is less than about 5 parts by weight, the effect of wear resistance cannot be obtained, and if it exceeds about 30 parts by weight, the melt viscosity of the composition becomes high and injection molding becomes difficult. In addition, the wear coefficient cannot be reduced. The same applies to not only the thermoplastic polyimide resin but also at least one resin selected from the above-mentioned synthetic resin group and having excellent mechanical strength.
[0017]
Such a nut 2 member has a high melt viscosity and an injection pressure of, for example, 500 to 2500 kgf / cm. ² (5-25kgf / mm ² ) Depending on the composition of additives, etc., 800-2000kgf / cm ² (8 ~ 20kgf / mm ² ) 1000-1600kgf / cm depending on the type of composition ² (10-16kgf / mm ² ), Holding pressure (injection holding pressure) 500-1000kgf / cm ² (5-10kgf / mm ² ) 700-1000kgf / cm depending on the type of composition ² (7-10kgf / mm ² ) Under high injection pressure conditions. By molding such a high-viscosity composition under high pressure, it is possible to make a screw molded body with excellent mechanical strength and dimensional accuracy and with less voids, so there is no wear or breakage of the thread portion. Plastic nut Can be obtained.
[0018]
The thermoplastic polyimide resin used here is moderate by adding energy such as heat to the repeating unit of the molecular structure while the imide group having excellent thermal characteristics and mechanical strength surrounds the aromatic group. An imide resin with a structure having multiple ether bond parts that exhibit excellent melting characteristics, and has two ether bond parts in the repeating unit to satisfy mechanical properties, rigidity, heat resistance, and injection moldability A polyimide resin is preferred. For example, reaction of aromatic ether diamines and aromatic ether diisocyanates with one or more acid anhydrides such as pyromellitic acid anhydride, benzophenone tetracarboxylic acid anhydride, biphenyl tetracarboxylic acid anhydride or derivatives thereof Can be mentioned.
[0019]
Specifically, an example of a polymer having an imide group and an aromatic group is shown in the formula (I).
[Chemical 1]

(Wherein X represents a group selected from the group consisting of a direct bond or a hydrocarbon group having 1 to 10 carbon atoms, a hexafluorinated isopropylidene group, a carbonyl group, a thio group and a sulfone group; ₁ ~ R _Four Represents hydrogen, a lower alkyl group (1 to 5 carbon atoms), a lower alkoxy group (1 to 5 carbon atoms), chlorine or bromine, which may be the same as or different from each other. Y is an aliphatic group having 2 or more carbon atoms, a cycloaliphatic group, a monocyclic aromatic group, a condensed polycyclic aromatic group, or a non-condensed polycyclic ring in which aromatic groups are connected to each other directly or via a bridging group Represents a tetravalent group selected from the group consisting of the formula aromatic groups. )
[0020]
For example, the thermoplastic polyimide resin represented by the formula (I) is obtained by dehydrating a polyamic acid obtained by the reaction of an aromatic ether diamine represented by the following formula (II) with one or more aromatic tetracarboxylic dianhydrides. To obtain.
[Chemical formula 2]

(Wherein X represents a group selected from the group consisting of a direct bond or a hydrocarbon group having 1 to 10 carbon atoms, a hexafluorinated isopropylidene group, a carbonyl group, a thio group and a sulfone group; ₁ ~ R _Four Represents hydrogen, a lower alkyl group (1 to 5 carbon atoms), a lower alkoxy group (1 to 5 carbon atoms), chlorine or bromine, which may be the same as or different from each other. )
[0021]
Among such thermoplastic polyimide resins, as a commercial product, R in the formula (I) ₁ ~ R _Four A trade name Aurum manufactured by Mitsui Toatsu Chemicals Co., Ltd., which is all hydrogen. Its chemical formula is shown in formula (III).
[Chemical 3]

Such a polyimide resin has high mechanical strength because it has at least one kind of imide group or aromatic ring, and has an appropriate ether bond, so that it has a desirable melt viscosity at the time of molding. It can be said that it is preferable because injection molding with excellent efficiency is possible.
[0022]
The shape of the graphite compounded in the thermoplastic polyimide resin composition may be any shape such as flakes, scales, spheres, rods, etc., but if importance is attached to sliding characteristics such as low friction coefficient and wear resistance, Spherical ones are preferred. On the other hand, if a material with excellent sliding properties, productivity, price, etc. is selected on average, a flake shape or a scale shape is sufficient. As such graphite, for example, pitch, coke, tar, furan resin, polyacrylonitrile resin, epoxy resin, phenol resin, etc. are used as raw materials, about 800-3000 ° C., and depending on the raw materials, about 1200-2300 Any material fired at a high temperature heat treatment temperature of 0 ° C. may be used. If the heat treatment temperature is too low, the amount of fixed carbon in the graphite will not be sufficiently high, while if the heat treatment temperature is too high, graphite sublimation will occur and the pyrolysis of the graphite will proceed rapidly, It is not preferable because waste is caused in terms of energy efficiency for achieving such a high temperature.
[0023]
The average particle size of such graphite is 5 to 50 μm, preferably 5 to 25 μm. When the average particle size is too large, it causes a dispersion failure in the resin composition, and the sliding characteristics cannot be satisfied. If the average particle size is too small, it will cause aggregation, resulting in poor dispersion. For these reasons, the average particle size of graphite is more preferably 5 to 15 μm.
[0024]
In addition, as fluororesins, tetrafluoroethylene resin (PTFE) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), which are excellent in heat resistance, slidability, release properties from injection molds, etc. Perfluoro fluororesins such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are preferable, and tetrafluoroethylene resin (PTFE) is particularly preferable.
[0025]
Perfluoro-based fluororesins are stable because they are all surrounded by fluorine around the skeleton carbon or surrounded by fluorine via a small amount of oxygen, and have a low coefficient of friction and non-adhesiveness. Excellent in heat resistance and chemical resistance. By blending a predetermined amount of such a fluororesin into the nut resin composition, the nut is provided with slidability, and for example, the nut member can be easily pulled out from injection molding, and there is little. The nut 2 can also be rotated and driven by a driving force, whereby the cylindrical magnetic body 5 such as the rotor and the stator 6 can be reduced in size. Thus, the screw can be efficiently driven and rotated by adding or applying the fluoropolymer to the sliding member such as the nut 2 or the screw shaft 3.
[0026]
As an example of a synthetic resin having a melt viscosity lower than that of the synthetic resin forming the nut described above and usable for the fixing resin layer, for example, the above-described thermoplastic polyimide resin composition is used for the nut. In this case, polyamide resin such as 612 nylon, 610 nylon, 46 nylon, 66 nylon, 11 nylon, 12 nylon, 3 nylon, 6 nylon, aromatic nylon, copolymer nylon, phenoxy resin produced from bisphenol A and epichlorohydrin An internal plasticized polyester resin or the like can be used.
[0027]
As a material capable of fixing and integrating a cylindrical magnetic body 5 which is a sintered body made of a brittle material, such as a rotor, and a nut 2 usually made of a synthetic resin, it is more than the melt viscosity of the synthetic resin forming the nut. A synthetic resin having a low melt viscosity is preferred.
This is because when the fixing resin 16 is a synthetic resin whose melt viscosity is lower than the melt viscosity of the nut 2, the nut 2 is molded when the nut 2 and the rotor are integrated with the synthetic resin that becomes the fixing layer by injection molding. This is because it is possible to inject at a molding pressure lower than the pressure. This is because if the synthetic resin that becomes the fixing resin 16 is injection-molded at a pressure lower than the molding pressure of the nut 2, the dimensional change does not occur in the nut 2 formed integrally with the fixing layer, and the rotor is not damaged. .
[0028]
Specifically, the fixing resin will be described. The viscosity of such a fixing resin can be measured by, for example, a test method based on JIS K 7210 or a measurement method according to this method. The viscosity may be measured at the temperature of the cylinder or nozzle at the time of injection molding, and any measurement method may be used. For example, the shear rate of molten resin is 10 ² ~Ten ^Four sec ^-1 , Preferably 10 ^Three ~Ten ^Four sec ^-1 In this case, a resin material having a relatively low melt viscosity, such as a melt viscosity of 50 to 200 Pa · s, preferably 100 to 150 Pa · s, does not require a large filling pressure during injection molding. The resin is easily filled into the mold cavity.
[0029]
For this reason, the brittle rotor and the rigid resin nut 2 are injected at an injection pressure of, for example, 100 to 1300 kgf / cm. ² (1-13kgf / mm ² ), Preferably 100-800 kgf / cm ² (1-8 kgf / mm ² ), More preferably 100-500 kgf / cm ² (1-5 kgf / mm ² ), And holding pressure is, for example, 100-500 kgf / cm ² (1-5 kgf / mm ² ), Preferably 100-300kgf / cm ² (1-3 kgf / mm ² It is conceivable that the rotor is not easily damaged even if it is fixed by injection.
It should be noted that both the nut 2 member and the cylindrical magnetic body 5 such as the rotor member are common. If the pressure is too low, voids, sink marks, etc. may occur. If the pressure is too high, burrs, cracking, crazing, etc. It may be the cause of the occurrence.
Further, it may be more desirable to perform injection molding under the pressures lower than the tensile strength or compressive strength of the rotor. Thus, by forming the fixing resin layer by injection under a pressure lower than the mechanical strength of the rotor with the fixing resin material having a low melt viscosity, the fragile rotor is not damaged by the molding pressure. Thus, an integrally molded body can be formed efficiently.
[0030]
As an example of such a fixing resin material, a polyamide resin will be specifically described. The polyamide-based resin is a linear polymer and a crystalline resin including an amide bond (—NHCO—) in the main chain in the molecular structure. Therefore, it has excellent mechanical properties and good impact resistance. And since it has hydrophilicity by -NHCO-, there is water absorption, but this increases impact resistance and flexibility. Because of such characteristics, even if the rotor made of a relatively brittle material and the nut 2 made of a rigid resin material are fixed by an injection molding method, the rotor is unlikely to be damaged such as cracks. . For this reason, it is considered that, for example, a standard resin or the like is preferably a fixing resin having an elongation of 1 to 300%, preferably a polyamide resin of 3 to 200%. If the elongation is too small, flexibility cannot be expected, and if it is too large, the mechanical strength and rigidity are lowered.
[0031]
In addition, since a resin having such an amide bond (—NHCO—) in the main chain has water absorption, the dimensional accuracy also changes with it. For this reason, a smaller water absorption rate is advantageous in stably fixing and fixing the rotor and the nut 2 for a long period of time. For example, a standard product has a water absorption rate of 0.1 to 1%, preferably 0.1 to 0.5% (24 hours ) Is preferred.
In addition, although the above-mentioned elongation can be measured by ASTM D638, for example, and the above-mentioned water absorption can be measured by ASTM D570, for example, it is not limited to such a measuring method, and any measuring method may be used. In addition, the molded body made of such a polymer has a relatively large surface hardness, wear resistance, and has a low wear coefficient and self-lubricating property. It is also suitable as a sliding material. In addition, in order to improve the sliding characteristics, 1 to 50 parts by weight of the fluoropolymer and the mechanical strength are improved in the same way as the reason for adding a predetermined amount to the polyimide resin per 100 parts by weight of the fixing resin material. In order to achieve this, 1 to 100 parts by weight, preferably 10 to 50 parts by weight of at least one filler such as reinforcing fibers such as glass fibers may be added to and mixed with the fixing resin composition.
[0032]
Here, the form of the reinforcing fibers may be a fiber diameter of 0.1 to 50 μm and a fiber length of 0.001 to 10 mm, preferably a fiber diameter of 1 to 25 μm and a fiber length of 0.01 to 1 mm. If the fiber diameter or fiber length is too thin or too short, it is difficult to improve the mechanical strength. On the other hand, if the fiber diameter or fiber length is too thick or too long, the wear of the mating sliding material will be accelerated. This is not preferable.
[0033]
As the polyamide polymer satisfying the above contents, for example, a polyamide 612 resin represented by the formula (IV) can be exemplified.
[Formula 4]

Moreover, as a polyamide 612 resin as mentioned above, the Du Pont brand name, Zytel FE5382, etc. can be mentioned.
[0034]
The layer thickness of the fixing resin may be a thickness that allows the rotor and the nut to be integrally formed without causing damage to the rotor. The thickness may be, for example, 0.3-5 mm, preferably 0.5-3 mm. If the layer thickness is too thin, it is not possible to expect adhesion and adhesion, and if it is too thick, the screw drive device cannot be miniaturized.
[0035]
In the method of manufacturing the screw drive device according to the present invention, the sliding resistance is reduced and stabilized by coating the surface of the screw thread of the nut or the surface of the screw shaft with a coating layer having a small friction coefficient. Sliding characteristics can be obtained. As a suitable coating layer, a fluorine-containing polymer such as a polyfluoroalkyl polymer (PFAE) or a fluoropolyether polymer is preferable.
Here, the polyfluoroalkyl polymer is, for example, CF _Three (CF ₂ ) ₇ -, H (CF ₂ ) ₆ -, CF ₂ Cl (CF ₂ ) ₁₁ -, (CF _Three ) ₂ CF (CF ₂ ) ₇ -, CF ₂ Cl (CF _Three ) CF (CF ₂ ) ₇ A polymer having a polyfluoroalkyl group such as-, and the fluoropolyether polymer has a general formula: -C _x F _2x A polymer having a unit represented by -O- (x is an integer of 1 to 4) as a main structural unit and a number average molecular weight of 1000 to 50000. Such fluorine-containing polymers contain functional groups having high affinity for bearing materials, such as epoxy groups, amino groups, carboxyl groups, hydroxyl groups, mercapto groups, isocyanate groups, sulfone groups, ester groups, etc. Is preferred.
[0036]
Specifically, as shown in the following formula (V), the perfluoro polyether polymer (PFPE) having an isocyanate group at the terminal is excellent in adhesion to a base material such as a nut 2 and the above-mentioned fluorine. As with the addition of resin, the non-adhesiveness and sliding properties of the fluoropolyether polymer after adhesion to the base material are excellent, and the formation of such a coating layer is easy. It is preferable because it is generally excellent on average.
[Chemical formula 5]

(In the formula, m and n represent integers.)
As such a thing, the product name: Fomblin Z-DISOC (number average molecular weight of about 2000) manufactured by Montefluros Co., Ltd. can be exemplified.
[0037]
In consideration of such a fluorine-containing polymer in a highly fluorinated organic solvent, 0.1 to 10% by weight, an effective thin layer, the yield of the liquid, and the price, the concentration is 1 to 5% by weight. It is diluted and applied to at least one sliding member such as the nut 2 or the screw shaft 3. As the coating method, an efficient dip coating method (dipping) with a good yield of the coating solution, or an atomization coating method (spray) that can form the thickness of the coating film with high accuracy can be appropriately selected.
After application, in order to increase the efficiency of natural drying or productivity, both drying and heat treatment of the thin layer and the substrate, for example, 50-350 ° C., preferably 50-280 ° C., 1-24 hours, Preferably, heat treatment for about 1 to 6 hours may be performed. The thickness of the coating layer thus formed may be 0.001 to 30 μm, preferably 0.01 to 10 μm. If the layer thickness is too thin, it will be difficult to maintain good sliding characteristics for a long period of time, and if it is too thick, it will be difficult to manage the gap dimensional accuracy between the nut 2 and the screw shaft 3, and smooth screw rotation will be achieved. It is hard to become.
[0038]
The screw shaft 3 is preferably formed of non-ferrous metal-based non-magnetic steel such as non-magnetic stainless steel or aluminum alloy steel from the viewpoint of preventing corrosion due to rust or suppressing corrosion on the steel surface. Non-magnetic steel is hard to be magnetized, and is not easily affected by magnets such as a rotor. This is because the magnets are not magnetized, so there is no S pole or N pole, and there is no influence of mutual attractive force or repulsive force with the S pole or N pole of the rotor 5, so even when the screw is stopped This also helps prevent unnecessary rotational movement caused by force. In addition, non-magnetic steel is preferable because it does not become stepping rotation during screw rotation, and torque fluctuation is small and the rotation operation is smooth and constant rotation.
[0039]
Further, as shown in FIG. 2, the threaded portion of the present invention has a semicircular cross section of the thread of the nut 2, and the thread valley 10 of the screw shaft 3 against the thread of the nut 2. On the other hand, it is formed of two inclined surfaces that are inclined symmetrically. The screw according to the present invention is a sliding screw as shown in FIG. 2 and is not limited to a screw in which the thread 9 and the thread valley 10 are in line contact at two points in the direction of travel of the screw. , Metric coarse screw, metric fine screw, unified coarse screw, unified fine screw, 29 degree trapezoidal screw, 30 degree trapezoidal screw (metric trapezoidal screw) and other trapezoidal screws, round screw, Tee type screw, saw It may be a square screw such as a die screw, a triangular screw, or a square screw, or may be a single screw or a plurality of multiple screws, and can be applied to any screw shape.
[0040]
【Example】
The materials used in the examples and comparative examples are collectively shown below.
(1) Rotor: Neodymium-iron sintered magnet (tensile strength 7.6kgf / mm ² , Compressive strength 11 kgf / mm ² )
(2) Nut: Thermoplastic polyimide resin (trade name, Aurum # 450, manufactured by Mitsui Toatsu Chemical Co., Ltd., injection molding temperature of about 400 to 430 ° C, melt viscosity at 420 ° C of 300 to 500 Pa · s, injection pressure of 1500 kgf / cm ² , Holding pressure 1500 to 800kgf / cm ² A thermoplastic polyimide resin composition comprising 65% by weight, graphite 20% by weight, fluororesin 3% by weight, phenolic resin cured product 12 parts by weight
(3) Nut coating layer: fluoropolyether polymer, trade name, manufactured by Montefluros, Fomblin Z-1 DISOC
(4) Adhesive resin layer: 612 nylon resin, DuPont brand name, Zytel FE 5382 (mixed by 33% by weight of glass fiber), injection molding temperature of about 230 to 290 ° C., melt viscosity at 250 ° C. 70 to 180 Pa · s, adhering Layer thickness about 0.4-1 mm.
(5) Screw shaft: Non-magnetic stainless steel
A screw driving device was manufactured using the above-described materials. In Comparative Example 1, a screw driving device was manufactured by the same method as in Example 1 except that the same thermoplastic polyimide resin as the nut was used as the fixing resin, and in Comparative Example 2, a conventional method shown in FIG.
[0041]
A method for producing a resin molded body with a magnetic material used in a screw drive device will be described with reference to FIG.
In the state where the injection molds 11 and 12 are prepared and the cavity 14 of one mold 12 is opened, the neodymium-iron sintered magnet that becomes the cylindrical magnetic body 5 and the thermoplastic polyimide that becomes the nut 2 are formed in the cavity 14. After inserting the resin body which consists of a resin composition with a cylindrical space | gap part, the other type | mold 11 was abutted (FIG.1 (b)).
Next, the fixing resin 16 was pumped through the sprue 15 to fill and fill the cylindrical space between the outer peripheral surface of the nut 2 and the inner wall surface of the cylindrical magnetic body 5 (FIG. 1C).
The injection molding condition is that the injection pressure is 200kgf / cm ² The holding pressure is 200 to 100kgf / cm ² The mold temperature was set to 70 ° C and the resin temperature was set to 280 ° C.
Thereafter, after the injected and filled fixing resin 16 is cured, the other mold 12 is detached from the one mold 11 to open the cavity 14 of the one mold 12, and the resin-molded body 27 with magnetic material is formed by an eject pin. The mold was released.
The obtained resin-molded body with a magnetic body was assembled in a case to which a stator was attached to obtain a screw driving device.
[0042]
The following evaluation tests were performed on the obtained screw driving device.
Evaluation items and evaluation methods of Examples and Comparative Examples are shown below. In addition, the test body used for this measurement was performed by each n = 5.
(1) Nut dimensional change: Measure how much the dimensional deformation of the nut thread has changed by injection molding.
(2) Damage rate of rotor: After injection molding, whether or not the rotor has cracks is observed with a microscope, and the probability of cracks is investigated.
(3) Dimensional change of rotor: After injection molding, it is measured whether or not there is a change in the outer diameter dimension of the rotor that did not crack.
The evaluation results are shown in Table 1.
[0043]
[Table 1]

[0044]
As is clear from Table 1, in Example 1, the dimensional change of the nut was very small, the rotor was not damaged, and the dimensional change of the rotor was very small. On the other hand, in Comparative Example 1 using the same material as the nut for the fixing resin layer and Comparative Example 2 manufactured by the conventional technique, the rotor was damaged.
[0045]
【The invention's effect】
The method for producing a resin-molded body with a magnetic body according to the present invention includes a step of filling a space between the cylindrical magnetic body and the resin body with a fixing resin having a melt viscosity lower than the melt viscosity of the resin body and curing the resin. Therefore, a resin-molded body with a magnetic body can be manufactured without damaging the cylindrical magnetic body. Furthermore, since a pre-process and a post-process are not required, an increase in cost can be suppressed and the productivity is excellent.
[0046]
The method for manufacturing a screw drive device according to the present invention includes a step in which a rotor of a motor attached to the outer periphery of a nut is filled and cured with a fixing resin, so that the screw drive device can be manufactured without damaging the rotor. it can. Moreover, a highly accurate thread can be maintained. Furthermore, since a pre-process and a post-process are not required, an increase in cost can be suppressed and the productivity is excellent.
[Brief description of the drawings]
FIG. 1 is a diagram showing a manufacturing process of a resin molded body with a magnetic body.
FIG. 2 is a cross-sectional view of a screw driving device.
FIG. 3 is a cross-sectional view of a conventional screw driving device.
FIG. 4 is a diagram showing a manufacturing process of a conventional resin molded body with a magnetic body.
[Explanation of symbols]
2 ... Nut, 5 ... Tubular magnetic body, 11, 12 ... Mold, 13 ... Core pin, 14 ... Cavity, 15 ... Sprue, 16 ... Fixed resin, 27 ... Resin molding with magnetic body body.

Claims (6)

Arranging the cylindrical magnetic body in the cavity of the mold;
A step of inserting and arranging a resin body having a void in the hollow portion of the cylindrical magnetic body;
And filling the void portion with a fixing resin having a melt viscosity lower than the melt viscosity of the resin body, followed by a step of curing. Arranging the cylindrical magnetic body in the cavity of the mold;
A step of inserting and arranging a resin body having a void in the hollow portion of the cylindrical magnetic body;
And a step of filling and curing the fixing resin at a molding pressure lower than the mechanical strength of the cylindrical magnetic body. 3. The method for producing a resin-molded body with a magnetic body according to claim 1, wherein the fixing resin is filled and cured by an injection molding method. A step of providing a motor rotor made of a brittle material on the outer periphery of the resin nut, and a step of screwing the resin nut with a screw shaft and incorporating the motor nut in a case to which the stator of the motor is attached. A manufacturing method of a screw drive device comprising:
The step of providing the rotor of the motor on the outer periphery of the resin nut includes the step of disposing a cylindrical magnetic body in the cavity of the mold, and the resin nut having a gap in the hollow portion of the cylindrical magnetic body. And a step of filling the void portion with a fixing resin having a melt viscosity lower than the melt viscosity of the resin nut and curing it. A screw driving device comprising: a step of providing a rotor of a motor made of a brittle material on the outer periphery of the nut; and a step of screwing the nut with a screw shaft and rotatably incorporating the nut in a case to which the motor stator is attached. A manufacturing method of
The step of providing the rotor of the motor on the outer periphery of the nut includes the step of disposing a cylindrical magnetic body in the cavity of the molding die, and the nut is inserted and disposed with a gap in the hollow portion of the cylindrical magnetic body. A method of manufacturing a screw drive device, comprising: a step; and a step of filling and curing a fixing resin at a molding pressure lower than the mechanical strength of the cylindrical magnetic body. 6. The method for manufacturing a screw drive device according to claim 4, wherein the fixing resin is filled and cured by an injection molding method.

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