JP2004134515A - Electromagnetic wave shield component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave shield component holding good molding external appearance and fluidity during molding by expressing excellent electromagnetic wave shield performance, in the electromagnetic wave shield component composed of a molding of a conductive thermal plastic resin composition. <P>SOLUTION: The electromagnetic wave shield component includes (A) a thermal plastic resin, and (B) a minute carbon fiber of which the average fiber diameter is 200 nm or less, and of which the curvature is 5° or more, and molds the thermal plastic resin composition in which a rate of (B) the minute carbon fiber to the sum of (A) the thermal plastic resin and (B) the minute carbon fiber is 0.05-20 wt%. The volume resistivity (ρ<SB>VC</SB>) of the inside of the molding is 1×10<SP>3</SP>Ωcm or less, and a ratio (ρ<SB>VS</SB>)/(ρ<SB>VC</SB>) of volume resistivity (ρ<SB>VS</SB>) measured through the surface of the molding and the volume resistivity (ρ<SB>VC</SB>) of the inside of the molding is 100 or more. <P>COPYRIGHT: (C)2004,JPO

Description

【０１０４】
得られた各組成物のペレットを用いて、７５ＴＯＮ射出成型機にて図７に示す形状の１５０ｍｍ×１５０ｍｍのシートサンプル（厚みは各々表２〜４に示す通り。）３０を成形した。このときの射出圧力は、１８００ｋｇ／ｃｍ^２（１７６．５ＭＰａ）以下に設定し、組成物の流動性に応じて、所定の充填時間となるように圧力と速度を適正化しながら成形した。金型キャビティ末端から１０ｍｍ手前の位置で、射出圧力から保持圧力へ切り変えて成形した。保持圧力は８００ｋｇ／ｃｍ^２（７８．４ＭＰａ）以下で３秒間加えた。但し、射出圧力１８００ｋｇ／ｃｍ^２、保持圧力８００ｋｇ／ｃｍ^２でも充填できない場合は、“充填不良”として成形を中断した。成形条件（シリンダ温度、金型温度、射出率）は表２〜４に示す通りである。
【０１０５】
得られたシートサンプルについて、以下の評価を行った。
【０１０６】
（１）微細炭素繊維の繊維直径、長さ／径比、及び屈曲度
実施例１のシートサンプルから、樹脂の流動方向に沿って、かつサンプル表面に垂直に超薄切片を切り出し、透過型電子顕微鏡にて観察し、成形品内部の微細炭素繊維の繊維直径、長さ／径比、屈曲度をそれぞれ１０点測定し、平均値を算出した。結果を以下に示す。
【０１０７】
繊維直径＝１０．５ｎｍ
長さ／径比＝２２以上
屈曲度＝６７°
【０１０８】
なお、ここで、長さ／径比については、超薄切片を作製する際に、繊維の一部が切断されるために、正確な繊維長を測定することができないが、少なくとも本発明の望ましい範囲内であることを確認した。
【０１０９】
（２）　炭素繊維の繊維直径、及びアスペクト比
実施例３（組成物４）及び４（組成物５）のシートサンプルを、流れ方向に沿って破断した破断面を、光学顕微鏡にて観察して、炭素繊維の繊維直径及び長さを、それぞれ１０点ずつ測定して平均値を算出した。
【０１１０】

【０１１１】
なお、ここでアスペクト比については、破断面に露出した炭素繊維の一部が樹脂に隠れてしまうため、正確な繊維長を測定することができないが、少なくとも本発明の望ましい範囲内であることを確認した。
【０１１２】
（３）　黒鉛の粒子径、及びアスペクト比
予め混練前の黒鉛の粒子径を、光学顕微鏡にて１５０点測定して平均値を算出した結果、１６．３μｍであり、微細炭素繊維に対する径比は１５５２であった。
【０１１３】
実施例７のシートサンプルを、流れ方向に沿って、かつサンプル表面に垂直に破断した破断面を、電子顕微鏡にて観察して、黒鉛の厚さを２０点測定して平均値を算出し、上記の粒子径との比を求めてアスペクト比を算出した結果、３８であった。
【０１１４】
（４）　体積抵抗値及び表面抵抗値
▲１▼　図７のシートサンプル３０のＡ，Ｂ，Ｃの位置から幅１５ｍｍの短冊状に切り出したテストピースを、液体窒素中で冷却した後、約３０ｍｍ長さに破断して、図３（ｂ）に示すような幅Ｗ＝１５ｍｍ、長さＬ＝約３０ｍｍの破断試料２０を作製した（厚さは表２〜４に示す通り。）。
【０１１５】
▲２▼　破断試料２０の破断面２０Ａ，２０Ｂに、１５００Åの厚みで銀を蒸着して、図４（ａ）に示す如く、電極２１Ａ，２１Ｂを形成した。
【０１１６】
▲３▼　電極２１Ａ，２１Ｂ間の抵抗値を測定し、サンプルの幅Ｗ，長さＬ，厚さを実測して体積抵抗率（ρ_ＶＣ）を算出した。
【０１１７】
▲４▼　次に、図５（ａ）に示す如く、破断試料２０の表裏の板面の同位置に、１０ｍｍ×１０ｍｍの大きさで１５００Åの厚みで銀を蒸着して電極２２Ａ，２２Ｂを形成した。
【０１１８】
▲５▼　電極２２Ａ，２２Ｂ間の抵抗値を測定し、サンプルの厚さを実測して体積抵抗率（ρ_ＶＳ）を算出した。
【０１１９】
なお、抵抗値の測定には、以下の測定器を用いた。
【０１２０】

【０１２１】
図７のＡ，Ｂ，Ｃから切り出した試料のそれぞれの値の平均値を求め、結果を表２〜４に示した。
【０１２２】
（５）　電磁波シールド性
テクノサイエンスジャパン社製　ＫＥＣ法シールド測定装置を用いて、電界シールド効果を測定した（出力１１０ｄＢｕＶ）。８００ＭＨｚでのシールド効果を代表値とし、結果を表２〜４に示した。数値は小さいほど（マイナスの数値が大きいほど）電磁波シールド効果が高いことを表す。
【０１２３】
（６）　１０点平均粗さ（Ｒｚ）
表面外観の指標として、上記抵抗値測定部分のＲｚ（１０点平均粗さ）を下記表面粗さ計を用いて、下記条件にて測定し、結果を表２〜４に示した。
【０１２４】
東京精密社製　表面粗さ計「サーフコム４８０Ａ」
カットオフ波長：２．５ｍｍ
測定長：３ｍｍ
測定スピード：０．３ｍｍ／ｓｅｃ
【０１２５】
なお、１０点平均表面粗さ（Ｒｚ）とは、粗さ曲線の平均線から縦倍率の方向にカットオフ波長２．５ｍｍで測定した、最も高い山頂から５番目までの山頂の標高の絶対値の平均値と、最も低い谷底から５番目までの谷底の標高の絶対値の平均値との和より算出して求める。従って、Ｒｚの数値は、小さいほど平滑な表面で、外観に優れることを示す。ただし、極めて平滑な表面の場合、山及び谷が測定範囲内に５個以上存在しないと算出が不可能である。そのような場合には、最大山と最大谷の和、すなわちＲ_ｍａｘで置き換えることができる。
【０１２６】
なお、用いた成型機の金型表面は、Ｒ_ｍａｘ０．２μｍ以下であることを確認した。従って、Ｒｚ（又はＲ_ｍａｘ）がこれより大きいものは、表面の金型転写性が不良であり、外観が損なわれていることを意味する。
【０１２７】
（７）　光沢度
表面外観の指標として、光沢度を測定し、結果を表２〜４に示した。光沢度は、表面に光を当てた際の反射の程度を表す量で、屈折率１．５６７のガラス板表面の光沢度を１００としたときの相対値である。測定には、堀場製作所社製「グロスチェッカー　ＩＧ−３３０」を用い、反射角度６０°にて測定した。この数値が大きいほど、成形品表面の金型の転写性が良好となり、その結果、光沢に優れることを表す。
【０１２８】
（８）　成形性
上述の成形条件の範囲内で得られたシートサンプルについて、充填度合いを目視で観察し、流動性の指標として下記評価基準で評価し、結果を表２〜４に示した。
○…樹脂がキャビティに完全に充填した。
△…末端部に１０ｍｍ未満の未充填部分が生じた。
×…末端部に１０ｍｍ以上の未充填部分が生じた。
【０１２９】
（９）　ＥＳＤ防止性評価
これらの成形品のＥＳＤ防止特性として接触電流及び帯電電極を次の機器を用いて測定し、結果を表２〜４に示した。
【０１３０】
チャージプレートモニター；ヒューグエレクトロニクス社製
表面電位計；モンローエレクトロニクス社製　２４４Ａ
オシロスコープ；レクロイ社製　ＬＣ５８４Ａ
電流プローブ；テクトロニクス社製　ＣＴ１
【０１３１】
１．接触電流
過電流防止特性の評価として帯電したシートサンプル（図７）に、接地された電子部品が接触した場合に生じる接触電流について、電子部品を接地プローブで代用して以下の通り測定した。
▲１▼　チャージプレートモニター上に、シートサンプルを置いた。
▲２▼　チャージプレートモニターを使用して、プレート及びサンプルに１０００Ｖを３秒間充電させた後、接地から切り離して絶縁した。
▲３▼　３秒後に接地プローブをＡ〜Ｃに接触させて、プローブを流れる接触電流を測定した。この場合、接触電流はナノ秒オーダーの交流電流が流れ、次第に減衰するので、最も高い電流値を接触電流とした。
▲４▼　Ａ〜Ｄ部位を各３回繰り返して測定し、さらにＡ〜Ｃの全ての測定値（１２点）を平均した。
【０１３２】
２．帯電電位
帯電電位は次の通り測定した。
▲１▼　チャージプレートモニター上に、シートサンプル（図７）を置いた。
▲２▼　サンプル及びプレートが帯電ゼロで、かつ接地から絶縁された状態で、サンプルの上方よりコロナチャージによって、プレートモニターが１０００Ｖになるまで、帯電させた。
▲３▼　サンプルを載せているプレートを接地して、接地後３秒後のＡ〜Ｃ部の表面電位を測定した。
【０１３３】
【表２】

【０１３４】
【表３】

【０１３５】
【表４】

【０１３６】
実施例１０，比較例１３
ポリカーボネート樹脂組成物１を使用して、押し出しシートサンプルを成形した。成形機はφ６５ｍｍ（Ｌ／Ｄ２８）の押し出し機に、７５０ｍｍ巾のＴダイを取り付けて、２．０ｍｍ厚みのシートを得た。成形条件は表５に示す通りとした。
【０１３７】
得られた成形品を１２０ｍｍ×１２０ｍｍに切り出して、実施例１と同様に評価を行い、結果を表５に示した。
【０１３８】
【表５】

【０１３９】
以上の結果から次のことがわかる。
【０１４０】
実施例１及び比較例１〜２に示すように、同一の材料組成であっても、抵抗値が本発明の範囲外の比較例１及び２は、電磁波シールド性や流動性に劣っており、一方、成形条件を適正化して抵抗値が本発明の範囲内にコントロールされた実施例１であれば、電磁波シールド性と成形性及び外観（光沢）を高度のレベルで兼ね備えた成形品が得られた。
【０１４１】
実施例２及び比較例３においても、同様の結果となった。比較例３は、実施例１に較べて、微細炭素繊維の添加量が多いにも関わらず、電磁波シールド性が劣った。言い換えれば、導電性を本発明の範囲にコントロールすることによって、微細炭素繊維の少ない添加量で優れた電磁波シールド性を得ることができることが分かる。
【０１４２】
また、比較例４においては、電磁波シールド性は優れるものの、体積抵抗率の比ρ_ＶＳ／ρ_ＶＣが本発明の範囲よりも小さく（即ち、表面付近の微細炭素繊維の絡み合いが十分に減少していない）、成形性や外観が著しく劣る。
【０１４３】
微細炭素繊維に炭素繊維を併用した実施例４〜７、比較例５〜６においても同様である。
【０１４４】
また、炭素繊維のみを添加した比較例７〜９は、表面と内部の炭素繊維の絡み合いを極端に変化させることができないために、抵抗値を本発明の範囲内にコントロールすることができず、その結果、電磁波シールド性と、外観を両立した成形品は得られなかった。なお、微細炭素繊維と鱗片状黒鉛を併用した組成物を用いた実施例７は、光沢は低いものの、Ｒｚが炭素繊維を添加した成形品に比べて、良好で、ムラのない均一な成形品が得られた。
【０１４５】
また、成分Ａの熱可塑性樹脂をポリカーボネート樹脂からポリブチレンテレフタレートに変えた実施例９及び比較例１２、成形方法を射出成形から押し出し成形に変えた実施例１０及び比較例１３についても、電磁波シールド性に明確な差がある。
【０１４６】
また、実施例の中でも、成形品の表面を介して測定した体積抵抗率（ρ_ＶＳ）が１×１０^４Ω以上１×１０^１２Ω未満であるものは、接触電流が少なく、かつ帯電量も少ない、優れたＥＳＤ防止性を兼ね備える。
【０１４７】
【発明の効果】
以上詳述した通り、本発明によれば、導電性熱可塑性樹脂組成物の成形品よりなる電磁波シールド部品であって、少ない微細炭素繊維の添加量で優れた電磁波シールド性能を発現し、かつ良好な成形品外観と成形時流動性を保持した電磁波シールド部品が提供される。
【図面の簡単な説明】
【図１】成形品の表面及び内部の微細炭素繊維の分散状態を示す模式図である。
【図２】微細炭素繊維による導電性ネットワークを説明する模式図である。
【図３】図３（ａ）は抵抗値測定用サンプルの切り出し位置を示す成形品の斜視図であり、図３（ｂ）は切り出した破断試料を示す斜視図である。
【図４】図４（ａ）は成形品の内部の体積抵抗率（ρ_ＶＣ）の測定方法を示す破断試料の断面図であり、図４（ｂ）はこのときの抵抗値の等価回路図である。
【図５】図５（ａ）は成形品の表面を介して測定した体積抵抗率（ρ_ＶＳ）の測定方法を示す破断試料の断面図であり、図５（ｂ）はこのときの抵抗値の等価回路図である。
【図６】本発明に係る微細炭素繊維の屈曲度の測定方法の説明図である。
【図７】実施例及び比較例で作製したシートサンプルの平面図である。
【符号の説明】
１　マトリックス樹脂
２　微細炭素繊維
１０　成形品
１０Ａ　高抵抗層
１０Ｂ　低抵抗層
２０　破断試料
２１Ａ，２１Ｂ，２２Ａ，２２Ｂ　電極
３０　シートサンプル[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electromagnetic wave shielding component that is effective as a casing having electromagnetic wave shielding performance in the field of electronic devices such as personal computers, mobile phones, other high-frequency communication devices and medical electronic devices. In particular, the volume resistivity measured through the surface of the molded article is 1 × 10 ⁴ Ω or more 1 × 10 ¹² The electromagnetic wave shielding component of the present invention controlled to less than Ω is useful as an ESD damage prevention case or tray having an electromagnetic wave shielding property around an electronic device such as a hard disk, a magnetic head, an IC, and an LCD, and a jig for manufacturing. is there.
[0002]
[Prior art]
Conventionally, as a measure against electromagnetic wave shielding in the field of electronic devices such as personal computers, mobile phones, other high-frequency communication devices and medical electronic devices, a metal such as copper or nickel is used as an electromagnetic wave shielding layer inside a resin molded housing. It has been practiced to provide layers by plating. However, this method has a problem that the number of manufacturing steps for the plating process is increased, and as a result, the cost is increased.
[0003]
On the other hand, a conductive molded product obtained by molding a conductive thermoplastic resin composition in which a conductive resin such as a metal fiber or a carbon fiber is filled in a thermoplastic resin is also used as an electromagnetic wave shielding component. However, in order to obtain a sufficient electromagnetic wave shielding property by such a conductive thermoplastic resin composition, it is necessary to add a large amount of conductive fiber, and for a large amount of conductive fiber to be added, the obtained molded article is required. The fibers are more likely to emerge on the surface of the resin, thereby impairing the appearance; and the fluidity of the conductive thermoplastic resin composition is reduced, thus causing problems such as impairing the moldability. In particular, when a non-crystalline resin material such as a polycarbonate resin or an ABS resin is selected as the base resin, the resulting molded product is excellent in warpage and dimensional accuracy, but greatly deteriorates in appearance due to conductive fibers. Such a decrease in appearance and fluidity is a serious problem, especially in thin housings such as recent computers and portable electronic devices. In order to maintain the appearance and the fluidity, it is desirable that the amount of the conductive fiber added is small, but in this case, the electromagnetic wave shielding performance cannot be exhibited.
[0004]
On the other hand, it has also been proposed to add electromagnetic wave shielding properties by adding fine carbon fibers such as carbon nanotubes to a thermoplastic resin (Japanese Patent Application Laid-Open No. Hei 8-508534). In order to obtain electromagnetic wave shielding properties, it is necessary to add a large amount of fine carbon fibers, which results in an increase in cost, and also has problems such as a decrease in fluidity, appearance, and mechanical strength.
[0005]
In a process of manufacturing a high-density electronic device such as an IC or a magnetic head, the device is damaged not only by an excessive transient current flowing into the device due to electrostatic discharge (ESD) but also by a transient electromagnetic wave generated by the discharge. It is said that.
[0006]
On the other hand, in precision control instruments such as aircraft, automobiles, and medical equipment, malfunctions due to transient electromagnetic waves due to the above-mentioned discharge also become a problem.
[0007]
Electromagnetic wave shielding components in such a field need not only electromagnetic wave shielding performance but also ESD prevention properties such as antistatic and transient current prevention.
[0008]
Highly conductive materials such as metal materials have good electromagnetic wave shielding properties, but the surface conductivity is too high. Cause outbreak. Further, a transient current wave is generated by the discharge, which induces an unnecessary current in a nearby electronic device, thereby destroying the device or causing a malfunction of the device.
[0009]
[Patent Document 1]
Japanese Patent Publication No. Hei 8-508534
[0010]
[Problems to be solved by the invention]
The present invention is directed to an electromagnetic wave shielding part comprising a molded article of a conductive thermoplastic resin composition, the electromagnetic wave shielding part exhibiting excellent electromagnetic wave shielding performance, and maintaining a good appearance of the molded article and fluidity during molding. The purpose is to provide.
[0011]
[Means for Solving the Problems]
The electromagnetic wave shielding component of the present invention comprises (A) a thermoplastic resin and (B) fine carbon fibers having an average fiber diameter of 200 nm or less and a degree of bending of 5 ° or more, wherein (A) the thermoplastic resin and (B) An electromagnetic wave shielding component comprising a molded product obtained by molding a thermoplastic resin composition in which the proportion of (B) the fine carbon fiber to the total of the fine carbon fiber is 0.05 to 20% by weight, wherein the molded product Internal volume resistivity (ρ _VC ) Is 1 × 10 ³ Ω · cm or less and the volume resistivity (ρ) measured through the surface of the molded article. _VS ) And the volume resistivity inside the molded article (ρ _VC ) And the ratio (ρ _VS ) / (Ρ _VC ) Is 100 or more.
[0012]
The present inventors have studied to obtain a molded article having excellent appearance and fluidity during molding and good electromagnetic wave shielding properties, and have obtained the following findings.
[0013]
That is, the thermoplastic resin composition to which fine carbon fibers are added has a remarkable increase in melt viscosity in a low shear rate region, and tends to lead to poor appearance such as a flow mark due to a decrease in fluidity. On the other hand, in the high shear rate region, since the fine carbon fibers are oriented, the melt viscosity is lowered, and the fluidity and appearance are improved, but the contact of the fine carbon fibers becomes insufficient, and the conductivity is reduced. As a result, the electromagnetic wave shielding property is impaired.
[0014]
On the other hand, if a large amount of fine carbon fiber is added, the conductivity can be improved even under a high shear rate, but this not only leads to an increase in cost but also impairs the appearance and fluidity.
[0015]
Further, as a result of further study based on the above findings, the following (1) and (2) are realized, and the electromagnetic wave shielding characteristics can be obtained by the conductivity of the inner layer without impairing the appearance and fluidity of the surface layer. It was found that good electromagnetic wave shielding parts could be obtained.
[0016]
{Circle around (1)} As shown in FIG. 1, the fine carbon fibers 2 near the surface of the molded article 10 are oriented along the flow direction, and instead of sacrificing conductivity, the flowability is not impaired and the surface is smooth and good. Maintain a good appearance. In this case, the vicinity of the surface of the molded product 10 becomes the high resistance layer 10A having low conductivity, and the electromagnetic wave shielding property is not provided.
{Circle around (2)} On the other hand, inside the molded article 10, the fine carbon fibers 2 are sufficiently entangled to form a conductive network and impart conductivity. Therefore, the inside of the molded product becomes the low resistance layer 10B, and exhibits the electromagnetic wave shielding property.
[0017]
In order to realize the above (1) and (2), the dispersion state of the fine carbon fibers is extremely changed between the surface and the inside of the molded article, whereby the resistance value between the surface and the inside of the molded article is changed. It needs to be very different.
[0018]
By the way, the fine carbon fibers used in the present invention have the property of being entangled with each other. When molded through a solidification process, the fine carbon fibers 2 are oriented in the matrix resin 1 due to the shearing force generated at the time of flow, as shown in FIG. It becomes insufficient and the conductivity becomes low.
[0019]
The fine carbon fibers 2 oriented in the matrix resin 1 are shown in FIGS. 2B and 2C while the temperature of the matrix resin 1 is high (the melt viscosity is low) at the beginning of the cooling and solidifying process. As described above, the orientation is relaxed, and a conductive network is formed. As a result, the conductivity is improved. This phenomenon is verified by reheating a molded article having low conductivity (high resistance value) formed under the condition that the fine carbon fibers 2 are extremely oriented, thereby improving the conductivity of the heated portion. Is done. This phenomenon occurs not only in a molding process in which a resin is completely melted and flows therethrough, as in injection molding and extrusion molding, but also in a molding method in which a semi-molten sheet is stretched and molded, as in vacuum molding. Similarly, the conductivity (resistance value) fluctuates due to the orientation of the fine carbon fibers in the drawing process and the relaxation of the orientation in the cooling process.
[0020]
Utilizing such a mechanism, the fine carbon fibers near the surface of the molded article are sufficiently oriented to maintain the appearance and fluidity, while the fine carbon fibers inside the molded article form a high degree of entanglement. Thereby, the electromagnetic wave shielding component of the present invention can be obtained.
[0021]
However, if the flow velocity of the resin is excessively increased in order to promote the orientation of the fine carbon fibers on the surface of the molded article, the internal entanglement is insufficient, and the electromagnetic wave shielding property is extremely reduced. The thickness of housing parts such as computers and mobile phones is generally 0.5 to 2.5 mm. In such thin molded products, the inside of the molded product is rapidly cooled, so that the electromagnetic wave shielding characteristics are not improved. Easy to lose. Therefore, in the present invention, the melt viscosity of the resin, the flow rate of the resin, the cooling rate, etc., so that the difference between the orientation of the fine carbon fibers on the surface of the molded article and the entanglement of the fine carbon fibers inside the molded article changes extremely. It needs to be adequately optimized.
[0022]
In the present invention, the volume resistivity (ρ) inside the molded article is determined by the entanglement of the fine carbon fibers inside the molded article. _VC ) Is 1 × 10 ³ Since the conductivity is as excellent as Ω · cm or less, excellent electromagnetic wave shielding properties can be obtained.
[0023]
Also, the volume resistivity measured through the surface of the molded article (ρ _VS ) And the volume resistivity inside the molded product (ρ _VC ) And the ratio (ρ _VS ) / (Ρ _VC ) Is 100 or more, the volume resistivity on the surface of the molded article is significantly larger than the volume resistivity inside the molded article. This is because a high-resistance layer in which fine carbon fibers are oriented is formed on the surface of the molded article. Such an oriented layer is excellent in fluidity and surface appearance.
[0024]
In addition, the volume resistivity (ρ _VC ) Is a volume resistivity measured by providing an electrode inside the molded article without passing through the surface of the molded article, as described later. That is, for example, a fractured sample (width W, length L, thickness t) 20 as shown in FIG. 3B is cut out from the flat plate portion 10a of the molded product 10 as shown in FIG. As shown in FIG. 4A, the electrodes 21A and 21B are formed on the fractured surfaces 20A and 20B of the fractured sample 20, and the resistance between the electrodes 21A and 21B is measured. In the fractured sample 20, the surface layer has a resistance value R due to the orientation of the fine carbon fibers. _S , And the inside has a resistance value R _C , The surface resistance R _S Is the internal resistance R _C , The resistance R measured in the parallel equivalent circuit shown in FIG. _VC Is the resistance value R of the internal low resistance layer _C Is almost equivalent to Actually, it is considered that the resistance value is gradually inclined from the surface of the molded article to the inside, but in any case, the resistance value R _VC Is dominated by the internal low resistance layer.
[0025]
Further, as shown in FIG. 5A, when electrodes 22A and 22B are formed on both surfaces of the fractured sample 20 and the resistance between the electrodes 22A and 22B is measured, the resistance R measured through the surfaces is measured. _VS Is the resistance R of the high-resistance layer on one surface, as shown in FIG. _S And the resistance value R of the internal low resistance layer _C And the resistance value R of the high resistance layer on the other surface _S And the resistance value of the series equivalent circuit composed of the above, that is, it corresponds to the sum of these resistance values. Therefore, the resistance value R _VS Is the high resistance value R near the surface _S Is almost equivalent to
[0026]
From the measured resistance value, the volume resistivity is
Volume resistivity = (measured value of resistance value) x electrode area / distance between electrodes
Therefore, the volume resistivity inside the molded product (ρ _VC ) And the volume resistivity measured through the surface of the part (ρ _VS ) Can be obtained as follows.
[0027]
Volume resistivity inside the molded product (ρ _VC ) = (W × t) / L × (R _VC ) Volume resistivity measured through the surface of the molded article (ρ _VS ) = A / t × (R _VS )
(However, A is the area of the electrodes 22A and 22B)
[0028]
Volume resistivity inside the molded product (ρ _VC ), The volume resistivity measured through the surface of the molded article (ρ _VS ) Ratio (ρ _VS ) / (Ρ _VC ) Is 100 or more, which means that the resistance R of the high resistance layer on the surface of the molded product is _S Is the R of the internal low resistance layer _C In other words, fine carbon fibers are entangled inside to form a conductive network, and high conductivity is obtained, and good electromagnetic wave shielding properties are obtained. It is oriented and shows low conductivity but good fluidity and excellent surface smoothness.
[0029]
In the present invention, 30 parts by weight or less of conductive fibers having an average fiber diameter of 0.5 to 20 μm is blended with respect to 100 parts by weight of the total of (A) the thermoplastic resin and (B) the fine carbon fibers. In addition, the electromagnetic wave shielding property can be further improved without significantly impairing the appearance and fluidity. Further, by blending 30 parts by weight or less of a flaky conductive filler having an average particle diameter of 0.5 to 100 μm with respect to a total of 100 parts by weight of the thermoplastic resin (A) and the fine carbon fiber (B), Electromagnetic wave shielding properties can be improved without impairing the appearance.
[0030]
The thermoplastic resin composition constituting the electromagnetic wave shielding component of the present invention has a shear rate of 50 (sec). ^-1 ) Melt viscosity (η ₅₀ ) And a shear rate of 5000 (sec) ^-1 ) Melt viscosity (η ₅₀₀₀ ) And the ratio (η ₅₀ ) / (Η ₅₀₀₀ ) Is from 3 to 20 to improve the fluidity and appearance of the surface layer having a high shear rate, and to easily obtain an electromagnetic wave shielding component having a good balance of the electromagnetic wave shielding properties of the inner layer having a relatively low shear rate. Is preferred.
[0031]
That is, the volume resistivity ratio (ρ) within the range of the present invention described above. _VS ) / (Ρ _VC As described above, it is necessary to extremely change the dispersion structure of the fine carbon fibers near and inside the molded product as described above. To achieve this, shearing of the melt viscosity of the thermoplastic resin composition is required. It is desirable that the speed dependency is large.
[0032]
Generally, for example, when molding an injection-molded article, the shear rate becomes higher near the surface. On the other hand, in the thermoplastic resin composition according to the present invention, the melt viscosity of the resin composition decreases due to the orientation of the entangled fine carbon fibers. This is because as the shear rate increases, the fine carbon fibers are oriented and entanglement is reduced. Therefore, the large dependence of the melt viscosity on the shear rate leads to a large difference in the degree of orientation of the fine carbon fibers between the vicinity of the surface and the inside.
[0033]
Therefore, the melt viscosity ratio (η ₅₀ ) / (Η ₅₀₀₀ ) Is preferably 3 or more. However, this melt viscosity ratio (η ₅₀ ) / (Η ₅₀₀₀ ) Is excessively large, poor transfer of the mold shape in a portion where the flow velocity is low, sink marks, flow marks, and the like are generated. ₅₀ ) / (Η ₅₀₀₀ ) Is preferably 20 or less.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the electromagnetic wave shielding component of the present invention will be described in detail.
[0035]
First, the components of the thermoplastic resin composition which is the molding material of the electromagnetic wave shielding component of the present invention will be described.
[0036]
<Components>
(A) Thermoplastic resin
Examples of the thermoplastic resin (A) include ABS resin, AS resin, polycarbonate, polyarylate, polyphenylsulfone, polyethersulfone, polyetherimide, polyoxymethylene, polystyrene, alicyclic polyolefin, and polyethylene. And thermoplastic resins such as polypropylene, polymethylpentene, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyamide, and polyetheretherketone. One or more of these can be appropriately selected and used from the characteristics such as mechanical strength and moldability according to the use of the electromagnetic wave shielding component.
[0037]
Among the thermoplastic resins described above, examples of the non-crystalline thermoplastic resin include ABS resin, AS resin, polycarbonate, polyarylate, polyphenylsulfone, polyethersulfone, polyetherimide, modified polyoxymethylene, polystyrene, and fat. Cyclic polyolefins and the like can be mentioned, while crystalline thermoplastic resins include polyethylene, polypropylene, polymethylpentene, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyamide and the like.
[0038]
Among such thermoplastic resins, non-crystalline thermoplastic resins are desirable in terms of dimensional accuracy, warpage, and the like. For example, ABS resins, AS resins, polystyrene, polycarbonate, polyarylate, polyphenylsulfone, polyetherimide, and fats Desirable are cyclic polyolefins and the like. Above all, an ABS resin and a polycarbonate resin are preferable because they have a good balance between cost and performance.
[0039]
(B) Fine carbon fiber
The fine carbon fiber of the component (B) used in the present invention has an average fiber diameter of 200 nm or less, and is generally produced by a vapor growth method. As the fine carbon fibers, for example, carbon fibrils described in JP-T-8-508534 are used.
[0040]
That is, the carbon fibrils have a graphite outer layer that is deposited substantially concentrically with the cylindrical axis of the fibrils, and the fiber central axis is not linear, but has a undulating and serpentine tubular configuration. .
[0041]
The average fiber diameter of the carbon fibrils is 200 nm or less, preferably 100 nm or less, more preferably 20 nm or less. The fiber diameter of carbon fibrils depends on the method of producing carbon fibrils and has a slight distribution. The average fiber diameter referred to here is an average value measured at 10 points by microscopic observation.
[0042]
If the average fiber diameter of the carbon fibrils is larger than 200 nm, the contact between the fibrils in the matrix resin becomes insufficient, so that a large amount of addition is required to develop conductivity, or the fineness between the surface layer and the inner layer is reduced. It becomes difficult to control the dispersion state of the carbon fibers.
[0043]
The average fiber diameter of the carbon fibrils is preferably 0.1 nm, particularly preferably 0.5 nm or more. If the average fiber diameter is smaller than this, production is extremely difficult.
[0044]
The carbon fibrils preferably have a length-to-diameter ratio (length / diameter ratio, ie, aspect ratio) of 5 or more, and particularly those having a length / diameter ratio of 20 or more, because a conductive network is easily formed. It is desirable because excellent conductivity can be obtained with a small amount of addition. A more preferred length / diameter ratio of carbon fibrils is 1000 or more. In addition, the fiber diameter and fiber length (and aspect ratio) of the carbon fibrils are average values of ten actually measured values when observed with a transmission electron microscope.
[0045]
The wall thickness (wall thickness of the tubular body) of the carbon fibrils having a fine tubular shape is usually about 3.5 to 75 nm. This usually corresponds to about 0.1 to 0.4 times the outer diameter of the fibril.
[0046]
When at least a portion of the carbon fibrils is in the form of aggregates, the resin composition as a raw material does not contain fibril aggregates having a diameter of about 50 μm, particularly 10 μm or more as measured on an area basis. However, it is desirable in that the amount of addition for obtaining the predetermined conductivity is small, and the mechanical properties of the obtained molded product are not reduced.
[0047]
Furthermore, in the present invention, the fine carbon fibers such as carbon fibrils, having a meandering fiber shape, increase the entanglement between the fibers, and can obtain conductivity with a small amount of addition, and at the same time, the effect of the present invention can be obtained. Desirable in terms of large.
[0048]
In order to obtain such entanglement, the present invention uses fine carbon fibers having a degree of bending of 5 ° or more, preferably 20 ° or more, and more preferably 40 ° or more.
[0049]
The degree of bending of the fine carbon fiber is determined by, for example, removing the resin component of the electromagnetic wave shielding component of the present invention by a solvent or ion sputtering to expose the fine carbon fiber, or an ultra-thin section cut out from a molded product by an electron microscope. It can be measured by observation. In this case, the measurement is performed on the fine carbon fibers in the surface layer within 50 μm from the surface of the molded article.
[0050]
As shown in FIG. 6, the degree of flexure is determined by observing a fine carbon fiber 2 such as carbon fibril with a microscope, measuring 5 times the fiber diameter (fiber diameter (d portion in FIG. 6)) on the same fiber, 2) A random point A and B are selected apart from each other by a method such as measuring along the fiber with _A , L _B And draw the tangent L _A , L _B The outer angle (the angle indicated by α in FIG. 6) of the point Q where X intersects is measured. The average value of 10 points is taken, and this is defined as the degree of bending.
[0051]
This angle is 0 ° if the fiber is straight, 180 ° if it is a semicircle, and 360 ° if it draws a circle.
[0052]
If the degree of bending α obtained by performing such a measurement is 5 ° or more, preferably 20 ° or more, and more preferably 40 ° or more, it is easy to form a network by entanglement of the fine carbon fibers. It is preferable in terms of imparting conductivity and electromagnetic wave shielding properties.
[0053]
In the present invention, it is important that the average fiber diameter of the fine carbon fiber is 200 nm or more and the degree of bending is 5 ° or more. If the fine carbon fiber does not satisfy these conditions, the effects of the present invention cannot be obtained. That is, if the average fiber diameter of the fine carbon fibers exceeds 200 nm, even if the degree of bending is 5 ° or more, the fine carbon fibers are hard to be oriented due to shearing due to the rigidity of the fibers. Does not decrease, causing a decrease in fluidity and poor appearance. In addition, even if the average fiber diameter is 200 nm or less, if the degree of bending is less than 5 °, the entanglement of the fine carbon fibers is less likely to occur, and as a result, the conductivity of the inner layer is not improved, and the electromagnetic wave shielding performance is reduced. Spoil.
[0054]
In particular, when the carbon fibers are fine carbon fibers having an average fiber diameter of 50 nm or less and a degree of bending of 20 ° or more, the effect of the present invention is large.
[0055]
Note that ordinary carbon fibers (pitch-based, PAN-based) are rigid and linear fibers having a fiber diameter of about 7 to 13 μm, and have a degree of bending of less than 5 °. With such straight fibers, no entanglement occurs, and it is difficult to form a network structure.
[0056]
In the present invention, as the fine carbon fiber, a commercially available product, for example, a carbon nanotube of Hyperion Catalysis International Inc. can be used.
[0057]
The fine carbon fiber used in the present invention may be subjected to a thermoplastic resin as the component (A) or various surface treatments or treatments with a dispersant. As the treating agent in this case, for example, a coupling agent such as a silane coupling agent, a titanate coupling agent, an aluminum coupling agent, or a block or graft copolymer of a nonpolar segment and a polar segment can be used. .
[0058]
In the present invention, the content of the fine carbon fibers in the thermoplastic resin composition is 0.05 to 20% by weight based on the total of the thermoplastic resin (A) and the fine carbon fibers (B). Preferably it is 1 to 15% by weight, more preferably 2 to 10% by weight. If the content of the fine carbon fiber is less than this range, it is not possible to obtain sufficient conductivity and electromagnetic wave shielding properties for the obtained electromagnetic wave shielding component, and if the content of the fine carbon fiber is more than this range, the fluidity is reduced. And the resulting molded article may have poor appearance.
[0059]
(C) Conductive fiber
Examples of the conductive fiber include metal fibers such as aluminum, silver, copper, zinc, nickel, stainless steel, brass, and titanium, pitch-based carbon fibers, PAN-based carbon fibers, carbon-based fibers such as graphite whiskers, zinc oxide, and tin oxide. Metal oxide fibers such as indium oxide may be used. In the case where the metal oxide fiber has conductivity due to the generation of surplus electrons due to the presence of lattice defects, a metal oxide having a conductivity increased by adding a dopant may be used. For example, aluminum is used for zinc oxide, antimony is used for tin oxide, tin is used for indium oxide, and the like. Further, a composite conductive fiber in which a carbon fiber or the like is coated with a metal or a coating layer of carbon, metal, or conductive tin oxide is formed on the surface of a potassium titanate whisker can also be used. One of these conductive fibers may be used alone, or two or more thereof may be used in combination.
[0060]
Among these conductive fibers, carbon fibers (pitch-based or PAN-based) are preferable in that they are excellent in the effect of improving the conductivity of the molded article. In particular, a carbon fiber whose surface is coated with a metal such as nickel is desirable.
[0061]
The average fiber diameter of the conductive fibers is preferably from 0.5 to 20 μm, and more preferably from 5 to 15 μm, at an average value measured at 10 points by microscopic observation, in that the effect of improving the conductivity is great.
[0062]
The aspect ratio (fiber length / fiber diameter) of the conductive fibers in the state of being dispersed in the molded product is 3 or more, preferably 5 or more, more preferably 10 to 1000 as an average value measured at 10 points by microscopic observation. This is preferable because the conductivity is improved.
[0063]
Inside the molded article, the conductivity is improved as the entanglement between the conductive fiber and the fine carbon fiber is denser. For that purpose, by the conductive network by the entanglement of the fine carbon fiber, while the conductive fiber is entangled, the electrical contact becomes good when the conductive fiber is connected, but for the network by the entanglement of the fine carbon fiber, If the conductive fibers are not large enough, this network has little effect of entanglement of the conductive fibers. Therefore, in order to sufficiently obtain this effect, the ratio (Dc / Db) of the average fiber diameter (Dc) of the conductive fibers to the average fiber diameter (Db) of the fine carbon fibers is 100 to 5000, preferably 600 to 5000. It is desirable that
[0064]
By adding such conductive fibers having an average fiber diameter of 0.5 to 20 μm to the thermoplastic resin composition used in the present invention, the electromagnetic wave shielding properties of the electromagnetic wave shielding component obtained without impairing the appearance and fluidity are further improved. Can be done.
[0065]
That is, in the surface layer, the conductive fibers and the fine carbon fibers are oriented, and instead of lowering the conductivity, the fluidity and appearance are improved, while in the inner layer, the orientation of the fine carbon fibers is sufficiently relaxed. By doing so, the conductive fibers are electrically connected with the fine carbon fibers to form a highly conductive network. As a result, the internal conductivity is improved, and excellent electromagnetic wave shielding properties are exhibited.
[0066]
The amount of such conductive fibers is preferably 30 parts by weight or less, particularly preferably 3 to 20 parts by weight, based on 100 parts by weight of the total of (A) the thermoplastic resin and (B) the fine carbon fibers. is there. If the amount of the conductive fiber is small, the effect of improving the conductivity due to the compounding of the conductive fiber cannot be sufficiently obtained, but if the amount is more than the above range, the fluidity and appearance are impaired.
[0067]
(D) Scale-like conductive filler
As the flaky conductive filler, one or two or more flaky metal fillers such as graphite, Ni flake, and stainless flake can be used. Among them, graphite is preferred because of its excellent balance of appearance, cost and conductivity. As the graphite, natural flaky graphite or artificial graphite manufactured in a flaky shape using petroleum coke or pitch coke as a main raw material can be used.
[0068]
The average particle size of the flaky conductive filler is 0.5 to 200 μm, preferably 1 to 100 μm, and more preferably 5 to 70 μm. The average particle size of the flaky conductive filler is an average value measured at least 20 points in a plane direction of the flaky conductive filler with an electron microscope. If the average particle diameter of the flaky conductive filler is smaller than the above range, the effect of improving the conductivity is small, and if it is large, the fluidity is impaired or the weld strength is reduced.
[0069]
In addition, the aspect ratio (particle diameter / thickness in the plane direction) of the flaky conductive filler has an average value of 5 or more, preferably 10 to 1000, as measured by microscopic observation, whereby the conductivity is improved. This is preferred.
[0070]
As in the case of the above-described conductive fibers, the tighter the entanglement between the flaky conductive filler and the fine carbon fibers, the higher the conductivity inside the molded article. In view of this entanglement, the ratio (Dd / Db) between the average particle diameter (Dd) of the flaky conductive filler and the average fiber diameter (Db) of the fine carbon fibers is 100 to 5000, preferably 600 to 5000. This is preferable because the network of fine carbon fibers has a large effect of entangling the flaky conductive filler and is excellent in conductivity.
[0071]
When the flaky conductive filler having an average particle diameter of 0.5 to 100 μm is added to the thermoplastic resin composition used in the present invention, the electromagnetic wave shielding properties of the electromagnetic wave shielding component can be improved without impairing the appearance. .
[0072]
That is, the flaky conductive filler enhances the conductivity by the same effect as the conductive fiber, and can improve the electromagnetic wave shielding property, and in the surface layer of the molded product, the plane of the flaky conductive filler is formed. Since it is oriented parallel to the surface of the product, unevenness due to the flaky conductive filler is reduced, and the appearance is hardly deteriorated.
[0073]
The amount of such a flaky conductive filler is preferably 30 parts by weight or less, particularly preferably 3 to 20 parts by weight, based on 100 parts by weight of the total of (A) the thermoplastic resin and (B) the fine carbon fibers. Department. When the blending amount of the flaky conductive filler is small, the effect of improving the conductivity due to the blending of the flaky conductive filler cannot be sufficiently obtained, but when the amount is larger than the above range, the fluidity and appearance are impaired. .
[0074]
When the thermoplastic resin composition according to the present invention contains both the above (D) scaly conductive filler and the above (C) conductive fiber, the total amount of these is (A) the thermoplastic resin. It is preferably 30 parts by weight or less, and particularly preferably 3 to 20 parts by weight, based on 100 parts by weight in total of (B) and the fine carbon fiber.
[0075]
(E) Additional components
In the thermoplastic resin composition according to the present invention, in addition to the above components (A) to (D), if necessary, additional components can be blended within a range not to impair the above performance.
[0076]
Such additional components include, for example, inorganic fibrous reinforcing materials such as glass fiber, silica fiber, silica / alumina fiber, potassium titanate fiber, and aluminum borate fiber; and organic materials such as aramid fiber, polyimide fiber, and fluororesin fiber. Inorganic fillers such as fibrous reinforcement, talc, calcium carbonate, mica, glass beads, glass powder, glass balloons, solid lubricants such as fluororesin powder, molybdenum disulfide, plasticizers such as paraffin oil, antioxidants, Various types such as heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizers, lubricants, compatibilizers, antifogging agents, antiblocking agents, slip agents, dispersants, coloring agents, antibacterial agents, fluorescent brighteners, etc. Additives can be mentioned.
[0077]
Further, the thermoplastic resin composition according to the present invention may contain a particulate or other conductive filler other than the above (C) conductive fibers and (D) flaky conductive filler. Examples of such a conductive filler include particles such as aluminum, copper, nickel and stainless steel, carbon black (such as furnace black and acetylene black), and carbon-based fillers such as spherical carbon produced from mesophase pitch. No.
[0078]
Hereinafter, a method for producing the electromagnetic wave shielding component of the present invention by molding such a thermoplastic resin composition will be described.
[0079]
<Production method>
The thermoplastic resin composition according to the present invention can be produced by a usual thermoplastic resin processing method. For example, (A) a thermoplastic resin and (B) fine carbon fibers, and if necessary, (C) conductive fibers and / or (D) flaky conductive fillers, and if necessary, (E) ) After all of the added components are previously mixed, the mixture can be produced by melt-kneading with a Banbury mixer, a roll, a Brabender, a single-screw kneading extruder, a twin-screw kneading extruder, a kneader, or the like.
[0080]
Further, the electromagnetic wave shielding component of the present invention can be manufactured by molding such a thermoplastic resin composition using various melt molding methods. Specific examples of the molding method include compression molding, extrusion molding, vacuum molding, blow molding, and injection molding. Among these molding methods, remarkable effects can be obtained particularly in the injection molding method and the vacuum molding method.
[0081]
When the thermoplastic resin composition according to the present invention is manufactured, a masterbatch in which a high concentration of the component (B) is added to a part of the component (A) is manufactured in advance, and the masterbatch is then referred to as (A). )) It may be diluted with the component.
[0082]
Hereinafter, the melt viscosity of the thermoplastic resin composition according to the present invention and the volume resistivity of the electromagnetic wave shielding component of the present invention will be described.
[0083]
<Melt viscosity of thermoplastic resin composition>
As mentioned above, the volume resistivity ratio (ρ _VS ) / (Ρ _VC In order to realize (3), it is necessary to extremely change the dispersion structure of the fine carbon fibers near and inside the surface of the molded article. For that purpose, it is desirable that the shear viscosity dependence of the melt viscosity of the thermoplastic resin composition is large, and poor transfer of the mold shape at a portion where the flow velocity is small, without sink marks or flow marks, etc. In order to make the degree of orientation of the fine carbon fibers largely different between the vicinity of the surface and the inside, the thermoplastic resin composition constituting the electromagnetic wave shielding component of the present invention has a shear rate of 50 (sec). ^-1 ) Melt viscosity (η ₅₀ ) And a shear rate of 5000 (sec) ^-1 ) Melt viscosity (η ₅₀₀₀ ) And the ratio (η ₅₀ ) / (Η ₅₀₀₀ ) Is preferably 3 or more and 20 or less.
[0084]
In particular, when a polycarbonate resin is used as the component (A), the thermoplastic resin composition according to the present invention has a shear rate of 5000 (sec.) At 300 ° C. ^-1 ) Is not more than 300 (Pa · s) and the melt viscosity ratio (η ₅₀ ) / (Η ₅₀₀₀ ) Is desirably 3.5 or more and 18 or less.
[0085]
<Volume resistivity of molded product>
In order to obtain a good electromagnetic wave shielding component by imparting electromagnetic wave shielding properties to the inner layer without impairing the appearance and fluidity of the surface of the molded product, the electromagnetic wave shielding component of the present invention employs the volume resistivity inside the molded product ( ρ _VC ) Is 1 × 10 ³ Ω · cm or less and the volume resistivity (ρ) measured through the surface of the molded article _VS ) And the volume resistivity (ρ _VC ) And the ratio (ρ _VS ) / (Ρ _VC ) Is 100 or more.
[0086]
The electromagnetic wave shielding component of the present invention has a volume resistivity (ρ) inside the molded product due to the entanglement of the fine carbon fibers inside the molded product. _VC ) Is 1 × 10 ³ Since the conductivity is as excellent as Ω · cm or less, excellent electromagnetic wave shielding properties can be obtained. The volume resistivity inside this molded product (ρ _VC ) Is preferably 1 × 10 ^-3 ~ 1 × 10 ² Ω · cm.
[0087]
Also, the volume resistivity measured through the surface of the molded article (ρ _VS ) And the volume resistivity inside the molded product (ρ _VC ) And the ratio (ρ _VS ) / (Ρ _VC ) Is 100 or more, the volume resistivity on the surface of the molded article is significantly larger than the volume resistivity inside the molded article. This is because a high-resistance layer in which fine carbon fibers are oriented is formed on the surface of the molded article. Such an oriented layer is excellent in fluidity and surface appearance. This volume resistivity ratio (ρ _VS ) / (Ρ _VC ) Is preferably 500 or more, more preferably 1000 or more. In particular, the volume resistivity measured through the surface of the molded article (ρ _VS ) Is 1 × 10 ⁵ When it is Ω · cm or more, the appearance is good, and it is preferable. Preferred volume resistivity (ρ _VS ) Is 1 × 10 ⁵ ~ 1 × 10 ¹⁰ Ω · cm.
[0088]
In particular, within the scope of the present invention, the volume resistivity (ρ) measured through the surface of the molded article _VS ) Is 1 × 10 ⁴ More than 1 × 10 ¹² When the resistance is less than Ω, the ESD protection property is good, and as a result, the electromagnetic wave shielding property by the high conductive layer inside the molded article and the antistatic property and the overcurrent preventing property on the molded article surface are obtained. Volume resistivity measured through the surface of the molded article (ρ _VS ) Is, in particular, 1 × 10 ⁴ More than 1 × 10 ¹¹ Less than Ω, preferably 1 × 10 ⁴ More than 1 × 10 ¹⁰ Less than Ω, more preferably 1 × 10 ⁵ More than 1 × 10 ¹⁰ Less than Ω is desirable in that the antistatic property and the transient current preventing property are improved.
[0089]
Further, it is preferable that a relatively large-sized conductive filler such as carbon fiber or graphite is not added because of excellent transient current prevention.
[0090]
An example of the method for measuring the volume resistivity according to the present invention is as follows.
[0091]
Volume resistivity inside the molded product (ρ _VC In order to measure (1), it is necessary to form an electrode inside the molded article and perform the measurement. For this purpose, for example, the measurement may be performed in the following procedure.
[0092]
(I) As shown in FIG. 3, the molded product 10 is broken such that two fractured surfaces are opposed to each other. At this time, when the molded article sample is cooled to a low temperature (preferably cooled in liquid nitrogen (-147 ° C.)) and fractured, the dispersion state of the fine carbon fibers and the conductive fibers is maintained, and the resistance value is accurately adjusted. It is desirable because it can be measured.
[0093]
(Ii) As shown in FIG. 4A, electrodes 21A and 21B are formed on the fractured surfaces 20A and 20B of the fractured sample 20 by applying a conductive paste or depositing a metal. The electrodes need to be made of a material that is sufficiently higher (lower in resistance, preferably lower by at least one order of magnitude) than the conductivity of the sample 20. Therefore, it is preferable to form an electrode by depositing a metal such as silver.
[0094]
(Iii) A resistance value between the fractured surfaces (between the electrodes 21A and 21B) of the fractured sample 20 is measured, and a volume resistance value is calculated by the following formula.
(Ρ _VC ) = A / L × (R _VC )
Here, A: electrode area (= sample thickness t × width W)
L: distance between electrodes (= sample length L)
R _VC ;measured value
[0095]
Also, the volume resistivity measured through the surface of the molded article (ρ _VS 5), electrodes 22A and 22B are provided facing the back and front surfaces of the fractured sample 20, as shown in FIG. Volume resistivity (ρ _VS ) Has a relatively high value, so that the electrode may be provided with a conductive paste or may be directly measured with a conductive rubber or metal probe. However, from the viewpoint that a contact area between the sample surface and the electrode can be sufficiently secured, it is desirable to form the electrode by depositing silver or the like. Volume resistivity (ρ _VS ) Is similarly calculated from the above formula, but in this case, the distance between the electrodes corresponds to the molded product thickness t.
[0096]
<How to fasten with other parts>
When fastening the electromagnetic wave shielding component of the present invention to another metal product, for example, when inserting and fixing a bottle or screw, a lownet or the like in a prepared hole of a molded product, by heating pins and screws, etc., It is desirable to use heating insertion, which is performed by softening the resin at the contact portion.
[0097]
This is because the softening of the resin in the contact portion causes the aggregation of the fine carbon fibers inside the molded product, and as a result, the electrical contact with the pins and the screws is improved. As a result, the conductivity between the electromagnetic wave shielding component of the present invention and other metal components fastened via pins or screws is improved, and it is possible to make the electric potential equipotential. And improvement of ESD protection.
[0098]
In this case, as a heating method, heater heating, ultrasonic heating, or the like can be used.
[0099]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0100]
In addition, the compounding raw materials used in the examples and comparative examples are as follows.
Polycarbonate resin: manufactured by Mitsubishi Engineering-Plastics Corporation "Novalex 7022"
Polybutylene terephthalate resin: "Novadur 5010" manufactured by Mitsubishi Engineering-Plastics Corporation
Carbon fiber 1: trade name "HTA-C6-SRS" manufactured by Toho Rayon Co., Ltd. (cut fiber length 6 mm)
Carbon fiber 2: Toho Rayon Co., Ltd. product name "HTA-MC-C6-U" (nickel-coated carbon fiber, cut fiber length 6 mm)
Fine carbon fiber: Carbon nanotube manufactured by Hyperion Catalysis International
Graphite: Product name “CP / B” (scale graphite) manufactured by Nippon Graphite Co., Ltd.
[0101]
Examples 1 to 9 and Comparative Examples 1 to 12
Each material was mixed with the components shown in Table 1, and the barrel temperature was set to 300 using a twin-screw extruder (“PCM45” manufactured by Ikegai Iron & Steel Co., Ltd., L / D = 32 (L: screw length, D: screw diameter)). The mixture was melt-kneaded at 160 ° C. and a screw rotation speed of 160 rpm to obtain pellets of the conductive polycarbonate resin composition.
[0102]
The compounding and kneading of the fine carbon fibers was carried out by preparing a masterbatch in which 15% by weight of the fine carbon fibers were added to the polycarbonate resin in advance, and diluting this with the remaining components to a predetermined compounding amount.
[0103]
[Table 1]

[0104]
Using the obtained pellets of each composition, a 150 mm × 150 mm sheet sample (thickness is as shown in Tables 2 to 4) 30 having the shape shown in FIG. 7 was formed by a 75TON injection molding machine. The injection pressure at this time is 1800 kg / cm ² (176.5 MPa) or less, and molding was performed while optimizing the pressure and speed so as to obtain a predetermined filling time according to the fluidity of the composition. At a position 10 mm before the end of the mold cavity, the injection pressure was changed to the holding pressure to perform molding. Holding pressure is 800kg / cm ² (78.4 MPa) or less for 3 seconds. However, injection pressure 1800kg / cm ² , Holding pressure 800 kg / cm ² However, when filling was not possible, molding was interrupted as "poor filling". The molding conditions (cylinder temperature, mold temperature, injection rate) are as shown in Tables 2 to 4.
[0105]
The following evaluation was performed about the obtained sheet sample.
[0106]
(1) Fiber diameter, length / diameter ratio, and degree of bending of fine carbon fiber
From the sheet sample of Example 1, an ultra-thin section was cut out along the resin flow direction and perpendicular to the sample surface, observed with a transmission electron microscope, and the fiber diameter and length of the fine carbon fiber inside the molded product / Diameter ratio and bending degree were measured at 10 points each, and the average value was calculated. The results are shown below.
[0107]
Fiber diameter = 10.5nm
Length / diameter ratio = 22 or more
Flexion degree = 67 °
[0108]
Here, regarding the length / diameter ratio, when fabricating an ultra-thin section, since a part of the fiber is cut, an accurate fiber length cannot be measured. It was confirmed that it was within the range.
[0109]
(2) Fiber diameter and aspect ratio of carbon fiber
The cross-sections of the sheet samples of Examples 3 (composition 4) and 4 (composition 5) broken along the flow direction were observed with an optical microscope to determine the fiber diameter and length of the carbon fibers, respectively. The average value was calculated by measuring 10 points at a time.
[0110]

[0111]
In addition, as for the aspect ratio, since a part of the carbon fiber exposed on the fracture surface is hidden by the resin, it is not possible to accurately measure the fiber length, but it is at least within a desirable range of the present invention. confirmed.
[0112]
(3) Graphite particle size and aspect ratio
As a result of previously measuring the particle diameter of graphite before kneading at 150 points using an optical microscope and calculating the average value, it was 16.3 μm, and the diameter ratio to fine carbon fibers was 1552.
[0113]
The sheet sample of Example 7, along the flow direction, and the fracture surface that was broken perpendicular to the sample surface was observed with an electron microscope, the thickness of graphite was measured at 20 points, and the average value was calculated. As a result of calculating the aspect ratio by calculating the ratio to the above particle diameter, it was 38.
[0114]
(4) Volume resistance and surface resistance
{Circle around (1)} A test piece cut into a strip having a width of 15 mm from the positions A, B, and C of the sheet sample 30 in FIG. 7 was cooled in liquid nitrogen, and then broken into a length of about 30 mm. A fractured sample 20 having a width W = 15 mm and a length L = about 30 mm as shown in b) was prepared (the thickness is as shown in Tables 2 to 4).
[0115]
{Circle over (2)} Silver was deposited on the fractured surfaces 20A and 20B of the fractured sample 20 to a thickness of 1500 ° to form electrodes 21A and 21B as shown in FIG.
[0116]
{Circle around (3)} The resistance value between the electrodes 21A and 21B is measured, and the width W, length L, and thickness of the sample are measured to measure the volume resistivity (ρ _VC ) Was calculated.
[0117]
{Circle over (4)} Next, as shown in FIG. 5 (a), silver is deposited to a size of 10 mm × 10 mm and a thickness of 1500 ° to form electrodes 22A and 22B at the same position on the front and back plate surfaces of the fractured sample 20. did.
[0118]
(5) The resistance between the electrodes 22A and 22B is measured, the thickness of the sample is measured, and the volume resistivity (ρ _VS ) Was calculated.
[0119]
The following measuring instruments were used for measuring the resistance value.
[0120]

[0121]
The average value of each value of the sample cut out from A, B, and C in FIG. 7 was obtained, and the results are shown in Tables 2 to 4.
[0122]
(5) Electromagnetic shielding
The electric field shielding effect was measured using a KEC method shield measuring device manufactured by Techno Science Japan (output: 110 dBuV). Tables 2 to 4 show the results with the shielding effect at 800 MHz as a representative value. The smaller the numerical value (the larger the negative value), the higher the electromagnetic wave shielding effect.
[0123]
(6) 10-point average roughness (Rz)
As an index of the surface appearance, Rz (10-point average roughness) of the above-mentioned resistance value measurement portion was measured using the following surface roughness meter under the following conditions, and the results are shown in Tables 2 to 4.
[0124]
SURFCOM 480A, a surface roughness meter manufactured by Tokyo Seimitsu Co., Ltd.
Cutoff wavelength: 2.5mm
Measurement length: 3mm
Measurement speed: 0.3mm / sec
[0125]
The 10-point average surface roughness (Rz) is the absolute value of the altitude of the highest peak to the fifth peak measured at a cutoff wavelength of 2.5 mm in the direction of the longitudinal magnification from the average line of the roughness curve. And the average of the absolute values of the altitudes of the valley floors from the lowest valley to the fifth valley bottom. Therefore, the smaller the value of Rz, the smoother the surface and the better the appearance. However, in the case of an extremely smooth surface, calculation is impossible unless there are five or more peaks and valleys within the measurement range. In such a case, the sum of the maximum peak and the maximum valley, ie, R _max Can be replaced by
[0126]
The mold surface of the molding machine used was R _max It was confirmed that the thickness was 0.2 μm or less. Therefore, Rz (or R _max ) Is larger than this means that the surface mold transferability is poor and the appearance is impaired.
[0127]
(7) Glossiness
Gloss was measured as an index of surface appearance, and the results are shown in Tables 2 to 4. The gloss is an amount representing the degree of reflection when light is applied to the surface, and is a relative value when the gloss of the surface of the glass plate having a refractive index of 1.567 is set to 100. The measurement was performed at a reflection angle of 60 ° using “Gloss Checker IG-330” manufactured by Horiba, Ltd. The larger the value, the better the transferability of the mold on the surface of the molded product, and as a result, the better the gloss.
[0128]
(8) Formability
With respect to the sheet samples obtained within the above-mentioned molding conditions, the degree of filling was visually observed, and evaluated based on the following evaluation criteria as a fluidity index. The results are shown in Tables 2 to 4.
…: The resin was completely filled in the cavity.
Δ: An unfilled portion of less than 10 mm was formed at the end.
X: An unfilled portion of 10 mm or more was formed at the end.
[0129]
(9) ESD protection evaluation
The contact current and the charging electrode were measured as the ESD protection characteristics of these molded products using the following equipment, and the results are shown in Tables 2 to 4.
[0130]
Charge plate monitor; manufactured by Hugh Electronics
Surface electrometer; 244A manufactured by Monroe Electronics
Oscilloscope; LC584A manufactured by LeCroy
Current probe; CT1 manufactured by Tektronix
[0131]
1. Contact current
As an evaluation of the overcurrent prevention characteristics, a contact current generated when a grounded electronic component was brought into contact with a charged sheet sample (FIG. 7) was measured as follows, using the electronic component instead of a grounding probe.
(1) The sheet sample was placed on the charge plate monitor.
{Circle around (2)} Using a charge plate monitor, the plate and the sample were charged at 1000 V for 3 seconds, then separated from the ground and insulated.
{Circle around (3)} Three seconds later, the ground probes were brought into contact with AC to measure the contact current flowing through the probes. In this case, the contact current is such that an alternating current of the order of nanoseconds flows and gradually attenuates.
{Circle around (4)} The A to D sites were measured three times each, and all the measured values (A to C) (12 points) were averaged.
[0132]
2. Charge potential
The charging potential was measured as follows.
(1) The sheet sample (FIG. 7) was placed on the charge plate monitor.
{Circle around (2)} In a state where the sample and the plate were zero-charged and insulated from the ground, the plate monitor was charged from above the sample by corona charging until the plate monitor became 1000V.
{Circle around (3)} The plate on which the sample was placed was grounded, and the surface potentials of portions A to C three seconds after the grounding were measured.
[0133]
[Table 2]

[0134]
[Table 3]

[0135]
[Table 4]

[0136]
Example 10 and Comparative Example 13
Using the polycarbonate resin composition 1, an extruded sheet sample was formed. As a molding machine, a T die having a width of 750 mm was attached to an extruder having a diameter of 65 mm (L / D28) to obtain a sheet having a thickness of 2.0 mm. The molding conditions were as shown in Table 5.
[0137]
The obtained molded product was cut out into a size of 120 mm × 120 mm, and evaluated in the same manner as in Example 1. The results are shown in Table 5.
[0138]
[Table 5]

[0139]
The following can be understood from the above results.
[0140]
As shown in Example 1 and Comparative Examples 1 and 2, even in the same material composition, Comparative Examples 1 and 2 having resistance values outside the range of the present invention are inferior in electromagnetic wave shielding properties and fluidity, On the other hand, in Example 1 in which the molding conditions were optimized and the resistance value was controlled within the range of the present invention, a molded product having both the electromagnetic wave shielding property, moldability and appearance (gloss) at a high level was obtained. Was.
[0141]
Similar results were obtained in Example 2 and Comparative Example 3. Comparative Example 3 was inferior to Example 1 in spite of the large amount of fine carbon fiber added, but was inferior in electromagnetic wave shielding properties. In other words, it can be seen that by controlling the conductivity within the range of the present invention, excellent electromagnetic wave shielding properties can be obtained with a small amount of fine carbon fiber added.
[0142]
Further, in Comparative Example 4, although the electromagnetic wave shielding property was excellent, the ratio ρ of the volume resistivity was ρ. _VS / Ρ _VC However, it is smaller than the range of the present invention (that is, the entanglement of the fine carbon fibers near the surface is not sufficiently reduced), and the moldability and appearance are remarkably inferior.
[0143]
The same applies to Examples 4 to 7 and Comparative Examples 5 to 6 in which carbon fibers are used in combination with fine carbon fibers.
[0144]
In Comparative Examples 7 to 9 in which only carbon fibers were added, the entanglement between the surface and the inner carbon fibers could not be extremely changed, so that the resistance could not be controlled within the range of the present invention, As a result, a molded article having both electromagnetic wave shielding properties and appearance was not obtained. In addition, in Example 7 using the composition using the fine carbon fiber and the flaky graphite in combination, the gloss was low, but the Rz was better than the molded product to which the carbon fiber was added, and the molded product was uniform without unevenness. was gotten.
[0145]
Further, Examples 9 and Comparative Example 12 in which the thermoplastic resin of the component A was changed from polycarbonate resin to polybutylene terephthalate, and Examples 10 and Comparative Example 13 in which the molding method was changed from injection molding to extrusion molding also showed electromagnetic wave shielding properties. There is a clear difference.
[0146]
Also, among the examples, the volume resistivity (ρ) measured through the surface of the molded product _VS ) Is 1 × 10 ⁴ Ω or more 1 × 10 ¹² Those having a resistance of less than Ω have a small contact current and a small charge amount, and also have excellent ESD protection.
[0147]
【The invention's effect】
As described in detail above, according to the present invention, it is an electromagnetic wave shielding component formed of a molded article of the conductive thermoplastic resin composition, and exhibits excellent electromagnetic wave shielding performance with a small amount of added fine carbon fiber, and is excellent. The present invention provides an electromagnetic wave shielding component which maintains a good molded product appearance and fluidity during molding.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a dispersion state of fine carbon fibers on the surface and inside of a molded product.
FIG. 2 is a schematic diagram illustrating a conductive network made of fine carbon fibers.
FIG. 3 (a) is a perspective view of a molded product showing a cutout position of a resistance value measurement sample, and FIG. 3 (b) is a perspective view showing a cutout cut sample.
FIG. 4 (a) shows the volume resistivity (ρ) inside a molded product. _VC FIG. 4B is a cross-sectional view of the fractured sample showing the measurement method of FIG. 4, and FIG. 4B is an equivalent circuit diagram of the resistance value at this time.
FIG. 5 (a) shows a volume resistivity (ρ) measured through the surface of a molded article. _VS FIG. 5B is a cross-sectional view of the fractured sample showing the measurement method of FIG. 5, and FIG. 5B is an equivalent circuit diagram of the resistance value at this time.
FIG. 6 is an explanatory diagram of a method for measuring the degree of bending of fine carbon fibers according to the present invention.
FIG. 7 is a plan view of sheet samples produced in Examples and Comparative Examples.
[Explanation of symbols]
1 Matrix resin
2 Fine carbon fiber
10 Molded products
10A High resistance layer
10B Low resistance layer
20 broken sample
21A, 21B, 22A, 22B electrodes
30 sheet samples

Claims (6)

(A) a thermoplastic resin and (B) a fine carbon fiber having an average fiber diameter of 200 nm or less and a degree of bending of 5 ° or more,
It comprises a molded product obtained by molding a thermoplastic resin composition in which the ratio of (B) the fine carbon fiber to the total of (A) the thermoplastic resin and (B) the fine carbon fiber is 0.05 to 20% by weight. An electromagnetic wave shielding component,
When the volume resistivity (ρ _VC ) inside the molded article is 1 × 10 ³ Ω · cm or less,
The ratio (ρ _VS ) / (ρ _VC ) of the volume resistivity (ρ _VS ) measured through the surface of the molded article to the volume resistivity (ρ _VC ) inside the molded article is 100 or more. An electromagnetic wave shielding part characterized by the above-mentioned. In claim 1, the thermoplastic resin composition comprises conductive fibers having an average fiber diameter of 0.5 to 20 µm based on a total of 100 parts by weight of (A) the thermoplastic resin and (B) the fine carbon fibers. An electromagnetic wave shielding component comprising 30 parts by weight or less. The flaky conductive powder according to claim 1, wherein the thermoplastic resin composition has an average particle diameter of 0.5 to 200 µm with respect to a total of 100 parts by weight of the thermoplastic resin (A) and the fine carbon fiber (B). An electromagnetic wave shielding component comprising 30 parts by weight or less of a filler. The melt viscosity (η ₅₀ ) when the shear rate of the thermoplastic resin composition is 50 (sec ⁻¹ ) and the shear rate is 5000 (sec ⁻¹ ) according to any one of claims 1 to 3. Wherein the ratio (η ₅₀ ) / (η ₅₀₀₀ ) to the melt viscosity (η ₅₀₀₀ ) is 3 or more and 20 or less. The electromagnetic wave according to any one of claims 1 to 4, wherein a volume resistivity (ρ _VS ) measured through a surface of the molded product is 1 × 10 ⁴ Ω or more and less than 1 × 10 ¹² Ω. Shield parts. The electromagnetic wave shielding component according to any one of claims 1 to 5, wherein the component is formed by injection molding.

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