JP2018096776A - Device and method for visualizing internal structure, current distribution, and resistance distribution of conductive material - Google Patents
Device and method for visualizing internal structure, current distribution, and resistance distribution of conductive materialDownload PDFInfo
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Abstract
Translated fromJapaneseDescription
Translated fromJapanese本発明は、導電性添加物を有する導電材料の試料表面や内部の、物理構造、電流経路、及び／又は、抵抗分布を可視化する装置や方法に関する The present invention relates to an apparatus and method for visualizing a physical structure, a current path, and / or a resistance distribution inside a sample surface or inside of a conductive material having a conductive additive.
炭素原子により構成されるグラファイトシートが円筒状に巻かれたカーボンナノチューブ(ＣＮＴ)や、銀やニッケルなどの金属粒子など、導電性を有する粒子は、導電性樹脂・ゴム、耐熱性樹脂・ゴムなど、樹脂やゴム単一では実現できない機能性材料としての応用が期待されている。 Conductive resin / rubber, heat-resistant resin / rubber, etc. are conductive particles such as carbon nanotubes (CNT) in which graphite sheets composed of carbon atoms are rolled into a cylindrical shape, and metal particles such as silver and nickel. Application as a functional material that cannot be realized with a single resin or rubber is expected.
一方、導電性粒子を含有する樹脂やゴムとは直接の関連は無いが、半導体回路中の不良破断箇所を可視化する手法として、発熱輝点を解析する手法が知られている(特許文献１〜４)。 On the other hand, although there is no direct relationship with the resin or rubber containing conductive particles, as a method for visualizing a defective fracture location in a semiconductor circuit, a method for analyzing a heat generation bright spot is known (
ＣＮＴや導電性金属粒子など、導電性添加物を用いた導電材料は、従来のゴムや樹脂のみを用いた材料には無い、幅広い導電性・耐熱性・耐薬品性、耐候性など様々な有用な機能性を有している。これらの機能性は、導電性粒子同士の接続状態により形成される内部構造により発現している。 Conductive materials using conductive additives such as CNT and conductive metal particles are not useful in conventional materials using only rubber or resin, but have various useful properties such as wide conductivity, heat resistance, chemical resistance, and weather resistance. It has a good functionality. These functionalities are expressed by the internal structure formed by the connection state between the conductive particles.
一方で、これら導電性粒子により形成される内部構造や、電流分布、抵抗分布を比較的簡易に可視化する手法及び装置は知られていない。従来では、電子顕微鏡や光学顕微鏡を用いた表面・断面観察が主になされているが、これら画像観察法だけでは、導電性粒子同士の接続状態が不明の為、導電材料の機能性の向上、製造方法の最適化の為には不十分であるし、また、可視化するには多数に試料を用いた繰り返し試験が必要であるなどの問題点が存在することを本発明者は認識した。 On the other hand, a method and apparatus for visualizing the internal structure formed by these conductive particles, current distribution, and resistance distribution relatively easily are not known. Conventionally, surface / cross-section observation using an electron microscope or an optical microscope has been mainly performed, but only with these image observation methods, the connection state between conductive particles is unknown, so the functionality of the conductive material is improved. The present inventor has recognized that there are problems such as inadequate for optimizing the production method and the necessity of repeated tests using a large number of samples for visualization.
本発明は、上述のような従来技術やそれについて認識された問題点を背景としてなされたものであり、導電性添加物を有する導電材料中の内部構造、電流分布、及び／又は、抵抗分布を比較的簡易に可視化する装置や方法を提供することを課題とする。 The present invention has been made against the background of the above-described prior art and problems recognized therefor, and the internal structure, current distribution, and / or resistance distribution in a conductive material having a conductive additive. It is an object of the present invention to provide an apparatus and method for visualizing relatively easily.
本発明者らは、上記課題を達成すべく鋭意研究を重ねた結果、導電材料に電流を印加し、その際に内部の導電性粒子が形成する電流経路からのジュール発熱のみを計測する事で、導電材料の内部構造、電流分布、及び／又は、抵抗分布を可視化出来る事を見出した。すなわち、導電材料へ印加する電流に交流成分を持たせ、同一の周波数成分をもつ参照信号を用いた、ロックイン検出を行う事で、導電材料が持つ強い背景熱を排除し、導電性添加物からの発熱のみを抽出し、導電材料の内部構造、電流分布、及び／又は、抵抗分布を可視化出来る事を見出した。 As a result of intensive research to achieve the above-mentioned problems, the present inventors applied a current to a conductive material and measured only the Joule heat generated from the current path formed by the internal conductive particles at that time. The present inventors have found that the internal structure, current distribution, and / or resistance distribution of a conductive material can be visualized. In other words, by applying an AC component to the current applied to the conductive material and performing lock-in detection using a reference signal having the same frequency component, the strong background heat of the conductive material is eliminated, and the conductive additive It was found that the internal structure, current distribution, and / or resistance distribution of the conductive material can be visualized by extracting only the heat generated from.
本発明はこれらの知見に基づいて完成に至ったものであり、本件によれば以下の発明が提供される。
＜１＞導電性添加物を有する導電材料の内部構造、電流分布、及び／又は、抵抗分布を可視化する装置であって、前記導電材料に交流励起信号を印加する電源と、前記交流励起信号と同一の周波数を有した参照信号とのロックイン発熱画像取得カメラと、前記導電材料を保持する温度可変ホルダーを備えた可視化装置。
＜２＞＜１＞に記載の可視化装置において、さらに、前記導電材料の結露を防止する手段を備える可視化装置。
＜３＞前記導電材料の結露を防止する手段は、乾燥ガス供給装置を含むものである＜１＞又は＜２＞に記載の可視化装置。
＜４＞前記ロックイン発熱画像取得カメラは、前記交流励起信号の１周期内に少なくとも４枚の発熱画像の取得が可能なものである＜１＞〜＜３＞のいずれか１項に記載の可視化装置。
＜５＞前記温度可変ホルダーは、前記導電材料を−５０℃〜１００℃の範囲内の所定の温度に調整可能なものである請求項１〜４のいずれか１項に記載の可視化装置。
＜６＞温度可変ホルダーに保持され導電性添加物を有する導電材料に交流励起信号を印加し、前記導電材料における結露を防止しながら、前記交流励起信号と同一の周波数を有した参照信号とのロックイン発熱画像を取得して前記導電材料の内部構造、電流分布、及び／又は、抵抗分布を可視化する方法。
＜７＞前記導電性添加物を有する導電材料は、１ＧΩ〜１μΩの抵抗値を有するものである＜６＞に記載の方法。
＜８＞前記交流励起信号の１周期内に少なくとも４枚のロックイン発熱画像を取得する＜６＞又は＜７＞に記載の方法。
＜９＞前記導電材料に乾燥ガスを当てる＜６＞〜＜８＞のいずれか１項に記載の方法。
＜１０＞前記導電材料を-５０℃〜１００℃の範囲内の所定の温度に保持してロックイン発熱画像を取得する＜６＞〜＜９＞のいずれか１項に記載の方法。The present invention has been completed based on these findings, and the present invention provides the following invention.
<1> A device for visualizing the internal structure, current distribution, and / or resistance distribution of a conductive material having a conductive additive, the power source for applying an AC excitation signal to the conductive material, and the AC excitation signal A visualization apparatus comprising: a lock-in heat generation image acquisition camera for a reference signal having the same frequency; and a temperature variable holder for holding the conductive material.
<2> The visualization device according to <1>, further comprising means for preventing condensation of the conductive material.
<3> The visualization device according to <1> or <2>, wherein the means for preventing condensation of the conductive material includes a dry gas supply device.
<4> The lock-in heat generation image acquisition camera according to any one of <1> to <3>, wherein at least four heat generation images can be acquired within one cycle of the AC excitation signal. Visualization device.
<5> The visualization device according to any one of
<6> A reference signal having the same frequency as the AC excitation signal while applying an AC excitation signal to the conductive material held in the temperature variable holder and having a conductive additive, and preventing condensation in the conductive material. A method of acquiring a lock-in heat generation image and visualizing the internal structure, current distribution, and / or resistance distribution of the conductive material.
<7> The method according to <6>, wherein the conductive material having the conductive additive has a resistance value of 1 GΩ to 1 μΩ.
<8> The method according to <6> or <7>, wherein at least four lock-in heat generation images are acquired within one cycle of the AC excitation signal.
<9> The method according to any one of <6> to <8>, wherein a dry gas is applied to the conductive material.
<10> The method according to any one of <6> to <9>, wherein the conductive material is held at a predetermined temperature in a range of −50 ° C. to 100 ° C. to obtain a lock-in heat generation image.
本発明は、次のような態様を含むことができる。
＜１１＞＜１＞〜＜５＞のいずれか１項に記載の可視化装置において、前記温度可変ホルダーを支持し、ｘ、ｙ、ｚ軸の位置制御可能な電動ステージをさらに含む可視化装置。
＜１２＞前記交流励起信号は、矩形波又は正弦波である＜１＞に記載の可視化装置。
＜１３＞前記温度可変ホルダーは、前記導電材料を−５０℃〜１０℃の範囲内の所定の温度に冷却可能なものである＜１＞〜＜４＞のいずれか１項に記載の可視化装置。
＜１４＞前記交流励起信号は、矩形波又は正弦波である＜６＞に記載の方法。
＜１５＞前記導電材料を−５０℃〜１０℃の範囲内の所定の温度に冷却してロックイン発熱画像を取得する＜６＞〜＜１０＞のいずれか１項に記載の方法。The present invention can include the following aspects.
<11> The visualization device according to any one of <1> to <5>, further including an electric stage that supports the temperature variable holder and is capable of position control of x, y, and z axes.
<12> The visualization device according to <1>, wherein the AC excitation signal is a rectangular wave or a sine wave.
<13> The visualization device according to any one of <1> to <4>, wherein the temperature variable holder is capable of cooling the conductive material to a predetermined temperature within a range of −50 ° C. to 10 ° C. .
<14> The method according to <6>, wherein the AC excitation signal is a rectangular wave or a sine wave.
<15> The method according to any one of <6> to <10>, wherein the conductive material is cooled to a predetermined temperature within a range of −50 ° C. to 10 ° C. to acquire a lock-in heat generation image.
本発明によれば、導電材料の内部構造、電流分布、及び／又は、抵抗分布を、比較的簡易に可視化する事が可能となる。 According to the present invention, the internal structure, current distribution, and / or resistance distribution of a conductive material can be visualized relatively easily.
以下、本発明の導電材料の内部構造、電流分布、及び／又は、抵抗分布を可視化する装置や方法について、実施形態と実施例に基づいて詳細に説明する。重複説明は適宜省略する。なお、２つの数値の間に「〜」を記載して数値範囲を表す場合には、この２つの数値も数値範囲に含まれるものとする。 Hereinafter, an apparatus and a method for visualizing the internal structure, current distribution, and / or resistance distribution of the conductive material of the present invention will be described in detail based on embodiments and examples. A duplicate description will be omitted as appropriate. In addition, when “to” is described between two numerical values to represent a numerical range, the two numerical values are also included in the numerical range.
図１は本発明を実施する為の装置構成の一例である。この装置例では、導電材料からの微弱な発熱を検出する、発熱画像取得カメラとしての赤外線カメラ(ＩＲカメラ)、赤外線カメラの最大フレームレート数の１／４以下の周波数の交流励起信号を導電材料に印可可能な電源、導電材料を保持する温度可変ホルダー、ｘ、ｙ、ｚ軸の位置制御可能な電動ステージとその制御コントローラ、冷却時の結露防止手段としての乾燥ガス発生器と乾燥ガス導入ライン(乾燥ガス供給装置)、検出信号の解析及び制御を行うパーソナルコンピューター(制御ＰＣ)を備えている。
温度可変ホルダーは、液体寒剤、ペルチェ素子などの適宜の加熱、冷却手段を備え、導電材料を-５０℃〜１００℃の範囲内の所定の温度に調整可能なものが好ましい。また、温度可変ホルダーは、導電材料のサイズに適した開口部を有するカバーを備えることができる。FIG. 1 shows an example of a device configuration for carrying out the present invention. In this apparatus example, an infrared camera (IR camera) as a heat generation image acquisition camera that detects weak heat generation from a conductive material, and an AC excitation signal having a frequency equal to or less than ¼ of the maximum frame rate number of the infrared camera. Power supply, variable temperature holder for holding conductive material, motorized stage and control controller for x, y, and z axis position, dry gas generator and dry gas introduction line as means for preventing condensation during cooling (Dry gas supply device) and a personal computer (control PC) for analyzing and controlling the detection signal.
The temperature variable holder is preferably provided with appropriate heating and cooling means such as a liquid cryogen and a Peltier element, and the conductive material can be adjusted to a predetermined temperature within a range of −50 ° C. to 100 ° C. In addition, the temperature variable holder can include a cover having an opening suitable for the size of the conductive material.
図２は、典型的な導電材料の例である、１ｗｔ％のカーボンナノチューブ(以下、ＣＮＴと称する)とポリカーボネイト(以下、ＰＣと称する)からなる導電材料について、従来手法による光学写真(図２(ａ))と赤外線画像を示したものである(図２(ｂ))。どちらの波長域における表面観察においても、平坦清浄な表面が観察され、導電材料の内部構造を可視化、計測する事は出来ない。 FIG. 2 shows an example of a typical conductive material, an optical photograph (FIG. 2 (FIG. 2)) of a conductive material composed of 1 wt% carbon nanotubes (hereinafter referred to as CNT) and polycarbonate (hereinafter referred to as PC). a)) and an infrared image are shown (FIG. 2B). In the surface observation in either wavelength range, a flat and clean surface is observed, and the internal structure of the conductive material cannot be visualized and measured.
図３に、ある周波数をもったパルス状の励起信号を印加した際の、導電材料の模式的な発熱強度変化を示す。導電材料へ印加した交流励起信号により、局所的な抵抗分布に比例した電界勾配が発生し、その局所電界勾配と電流値の積として、印加周波数と同一の周波数を有するジュール発熱が発生する。そのジュール発熱の拡散により導電材料温度が上昇し、全体の発熱量に占める、励起周波数成分を持たない背景熱成分が徐々に増加する。これにより、ロックイン処理を行わない場合、導電材料中の導電性添加物であるＣＮＴと、絶縁体であるＰＣの識別は、導電材料全体の温度上昇に伴う発熱により困難となる。
これに対し、後述の実施例のようにロックイン処理を行った場合には、背景熱成分を排除でき、内部構造や電流分布、抵抗分布の可視化が可能となる。さらに、冷却等の温度調節により導電材料の温度を低下すると、導電材料の交流励起以外の成分の発熱寄与が低減し、ロックイン検出による交流励起成分が増加して検出感度を最大化することもできる。FIG. 3 shows a schematic change in heat generation intensity of the conductive material when a pulsed excitation signal having a certain frequency is applied. The AC excitation signal applied to the conductive material generates an electric field gradient proportional to the local resistance distribution, and Joule heat generation having the same frequency as the applied frequency is generated as the product of the local electric field gradient and the current value. The conductive material temperature rises due to the diffusion of the Joule heat generation, and the background heat component having no excitation frequency component occupying the total heat generation amount gradually increases. Thus, when the lock-in process is not performed, it is difficult to distinguish between the CNT that is the conductive additive in the conductive material and the PC that is the insulator due to heat generation due to the temperature rise of the entire conductive material.
On the other hand, when the lock-in process is performed as in the embodiments described later, the background heat component can be eliminated, and the internal structure, current distribution, and resistance distribution can be visualized. Furthermore, if the temperature of the conductive material is decreased by adjusting the temperature such as cooling, the heat generation contribution of components other than the AC excitation of the conductive material is reduced, and the AC excitation component due to lock-in detection increases to maximize the detection sensitivity. it can.
本発明で用いる試料の導電材料は、ＣＮＴが添加されたＰＣに限定されず、導電性添加物を有する導電材料であればどのようなものでもよい。
導電性添加物としては、限定するものではないが、ＣＮＴ、炭素繊維等の炭素材料、銅、アルミニウム、ニッケル、銀、金、それらの合金等の金属材料などが挙げられる。導電性添加物の形状は、限定されないが、粒子状乃至繊維状のものが挙げられる。導電性添加物の大きさは、限定されないが、通常、ＳＥＭ等の顕微鏡観察による平均粒径〔＝(長径＋短径)／２〕が５ｎｍ〜２ｍｍ(好ましくは１０ｎｍ〜５００μｍ)のものが挙げられ、繊維状のものについては、長さが５０ｎｍ〜５ｍｍ(好ましくは１００ｎｍ〜１０００μｍ)のものが挙げられる。
導電材料のマトリックスの材料としては、絶縁性(１０6Ωｍ以上)のものや半導体性(１０-4〜１０6Ωｍ)のものが挙げられる。具体的には、ＰＣのほか、エポキシ樹脂、ポリエステル、塩化ビニル樹脂、ウレタン樹脂などの各種樹脂、フッ素ゴム、シリコーンゴムなどの各種ゴム、アルミナ、ジルコニアなどの各種セラミックス、各種ガラスなどが挙げられる。The conductive material of the sample used in the present invention is not limited to PC to which CNT is added, and any conductive material having a conductive additive may be used.
Examples of the conductive additive include, but are not limited to, carbon materials such as CNT and carbon fiber, and metal materials such as copper, aluminum, nickel, silver, gold, and alloys thereof. The shape of the conductive additive is not limited, and examples thereof include particles and fibers. The size of the conductive additive is not limited, but usually the one having an average particle diameter [= (major axis + minor axis) / 2] of 5 nm to 2 mm (preferably 10 nm to 500 μm) as observed by a microscope such as SEM. Examples of the fibrous material include those having a length of 50 nm to 5 mm (preferably 100 nm to 1000 μm).
Examples of the matrix material of the conductive material include insulating (106 Ωm or more) and semiconducting (10−4 to 106 Ωm). Specifically, in addition to PC, various resins such as epoxy resin, polyester, vinyl chloride resin and urethane resin, various rubbers such as fluorine rubber and silicone rubber, various ceramics such as alumina and zirconia, various glasses and the like can be mentioned.
以下、実施例により本発明を更に詳細に説明する。本発明の内容はこの実施例に限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples. The content of the present invention is not limited to this embodiment.
［実施例１］
図２で示したＣＮＴとＰＣの複合材料(導電材料)の試料へ２５Ｈｚのパルス状の電圧３０Ｖを印加した際の発熱赤外線画像(図４(ａ))に対して、ロックイン処理を行った後の発熱強度像(以下、強度像と称することがある)と発熱位相像(以下、位相像と称することがある)を図４に示している。強度像(図４(ｂ))には、左右の電極部での強い発熱構造以外に、中央試料部においてもＰＣ内部のＣＮＴ分布やＣＮＴ同士の接合状態に起因する、発熱強弱パターンが得られている。位相像(図４(ｃ))は、励起信号に対する発熱タイミングを画像化したものである。強度が弱く位相が遅い高抵抗領域の周囲に、強度が強く位相が早い抵抗領域が形成されている事から、本計測によりＣＮＴ／ＰＣ複合材料内のＣＮＴが形成する、内部構造、電流分布及び抵抗分布が可視化されている。[Example 1]
A lock-in process was performed on a heat-generated infrared image (FIG. 4A) when a pulsed voltage 30V of 25 Hz was applied to the sample of the composite material (conductive material) of CNT and PC shown in FIG. FIG. 4 shows a later exothermic intensity image (hereinafter sometimes referred to as an intensity image) and an exothermic phase image (hereinafter sometimes referred to as a phase image). In the intensity image (FIG. 4 (b)), in addition to the strong heat generation structure at the left and right electrode parts, the heat generation intensity pattern resulting from the CNT distribution inside the PC and the bonding state between the CNTs is also obtained in the central sample part. ing. The phase image (FIG. 4C) is an image of the heat generation timing for the excitation signal. Since a resistance region having a strong intensity and a fast phase is formed around a high resistance region having a weak strength and a slow phase, the internal structure, current distribution, and CNT in the CNT / PC composite material are formed by this measurement. The resistance distribution is visualized.
［比較例１］
実施例１と同一の試料に、周波数変化の無い直流電圧３０Ｖを印加した際の赤外線画像を図５に示す。ロックイン未処理の場合、印加電圧電流由来のＣＮＴ経路からの発熱以外に、試料全体へ拡散した発熱成分が足し合わされて観測されるため、微細な導電性構造由来の発熱パターンは消失し、導電材料中の内部構造を可視化する事は困難である。[Comparative Example 1]
FIG. 5 shows an infrared image when a DC voltage of 30 V having no frequency change is applied to the same sample as in Example 1. In the case of non-lock-in treatment, in addition to the heat generation from the CNT path derived from the applied voltage current, the heat generation component diffused throughout the sample is added and observed, so the heat generation pattern derived from the fine conductive structure disappears and becomes conductive. It is difficult to visualize the internal structure in the material.
［実施例２］
ＣＮＴとフッ素ゴム(以下、ＦＫＭと称する)の導電材料において、ＣＮＴ濃度を変化させたそれぞれの試料における、ロックイン処理後の発熱強度像を図６に示す。それぞれの試料におけるＣＮＴ濃度は、(ａ)０.２５ｗｔ％、(ｂ)０.５ｗｔ％、(ｃ)１.０ｗｔ％、(ｄ)５.０ｗｔ％である。これら強度像における発熱強度は、強度が強い部分を白色、弱い部分を黒色で表記している。低ＣＮＴ濃度試料(０.２５ｗｔ％、０.５ｗｔ％)では、複合材料内の不均一なＣＮＴ分布を反映した不均一な発熱構造が見られるが、徐々にＣＮＴ濃度を増加させていくことで、ＣＮＴ分布が均一となり、発熱分布も面内一様な均一な発熱分布へと変化していくことが分かった。[Example 2]
FIG. 6 shows a heat intensity image after lock-in processing in each sample in which the CNT concentration is changed in the conductive material of CNT and fluororubber (hereinafter referred to as FKM). The CNT concentration in each sample is (a) 0.25 wt%, (b) 0.5 wt%, (c) 1.0 wt%, and (d) 5.0 wt%. The intensity of heat generation in these intensity images is indicated by white for a strong part and black for a weak part. Low CNT concentration samples (0.25 wt%, 0.5 wt%) show a non-uniform heat generation structure reflecting non-uniform CNT distribution in the composite material. By gradually increasing the CNT concentration, It was found that the CNT distribution became uniform and the heat generation distribution changed to a uniform heat generation distribution in the plane.
図６で示した４種の試料の発熱強度分布をプロットしたものを図７(ａ)に示した。導電材料内で不均一なＣＮＴネットワーク構造を有する試料では、局所的に不均一な電流経路が形成され、局所的な高抵抗箇所が存在し、その場所への電界集中により、局所的に強い発熱が観測される。この局所発熱と高抵抗領域の発熱強度の弱い領域の寄与により、導電材料が不均一であればあるほど、発熱強度分布での非対称さが増加する事が分かった。図７(ｂ)には横軸に試料の抵抗率を、縦軸に発熱強度分布の標準偏差をプロットしたものを示す。前述のように、試料のＣＮＴ濃度が高まり、ＣＮＴの空間分布と発熱構造が均一になるにつれて、発熱分布の標準偏差は一様に減少し、それと共に試料の抵抗率も低減する事が明らかに示されている。これにより、発熱分布構造の強度分布形状を解析する事で、導電材料内の内部構造の均一さを定量的に評価できる事が分かった。 A plot of the heat intensity distribution of the four types of samples shown in FIG. 6 is shown in FIG. In a sample having a non-uniform CNT network structure in a conductive material, a locally non-uniform current path is formed, a local high-resistance point exists, and a strong heat is generated locally due to electric field concentration at that point. Is observed. It was found that due to the contribution of the local heat generation and the low resistance region of the high resistance region, the non-uniform conductive material increases the asymmetry in the heat generation intensity distribution. FIG. 7B shows a plot of the resistivity of the sample on the horizontal axis and the standard deviation of the heat generation intensity distribution on the vertical axis. As mentioned above, as the CNT concentration in the sample increases and the spatial distribution and heat generation structure of the CNT become uniform, the standard deviation of the heat generation distribution decreases uniformly, and the resistivity of the sample also decreases with it. It is shown. Thus, it was found that the uniformity of the internal structure in the conductive material can be quantitatively evaluated by analyzing the intensity distribution shape of the heat generation distribution structure.
［実施例３］
導電材料の内部構造を可視化する際には、低抵抗領域・高抵抗領域・絶縁領域が混在する発熱パターンを、いかに高感度に区別して計測できるかが内部構造評価の分解能に大きく影響する。同一の試料を、−２０℃から７０℃まで変化させていった際の計測結果を図８に示した。試料が結露しないよう試料室雰囲気を乾燥空気(もしくは窒素ガス、ヘリウムガス等のガス)により制御してロックイン発熱強度画像を得た。試料温度の低下に伴い、試料全体の交流励起以外の成分の発熱の寄与が低減し、ロックイン検出による交流励起成分が増加する事で、試料中の電流経路可視化の際の分解能が向上する事が示されている。これは、試料全体の発熱強度が大きく、導電性内部構造からの発熱寄与が小さい、導電材料に特徴的な結果であり、本装置の検出感度を最大化させるための手法の根拠となる結果を得た。[Example 3]
When visualizing the internal structure of a conductive material, the resolution of internal structure evaluation greatly affects how sensitively the heat generation pattern in which a low resistance region, a high resistance region, and an insulating region coexist can be measured. FIG. 8 shows the measurement results when the same sample was changed from −20 ° C. to 70 ° C. A lock-in heat intensity image was obtained by controlling the atmosphere in the sample chamber with dry air (or a gas such as nitrogen gas or helium gas) so that the sample did not condense. As the sample temperature decreases, the contribution of heat generation of components other than AC excitation of the entire sample decreases, and the AC excitation component due to lock-in detection increases, improving the resolution when visualizing the current path in the sample. It is shown. This is a characteristic result of conductive materials, where the heat generation intensity of the entire sample is large and the contribution of heat generation from the conductive internal structure is small, and the results that serve as the basis for the method for maximizing the detection sensitivity of this device. Obtained.
温度を−２０℃から７０℃まで変化させた際の、発熱強度分布を図９に示した。交流励起した際の発熱画像をロックイン処理すると、定常的な母材の蓄熱成分などは除外されるが、検出カメラには到達しているため、この様な定常熱成分が増加する事で、ロックイン発熱画像の検出感度が低下する。一方で、この様な強い背景熱成分を温度制御により除外する事が出来れば、交流励起成分による発熱がカメラ感度に占める割合が向上する為、導電材料を計測する際に分解能の向上が期待される。実際の発熱強度分布においても、測定時の導電材料温度を低減させることで発熱強度画像の輝度分布が高強度側へシフトし、この結果として発熱画像の分解能が向上していたという結果を得た。 FIG. 9 shows the heat generation intensity distribution when the temperature is changed from −20 ° C. to 70 ° C. When lock-in processing is performed on the exothermic image when AC excitation is performed, the steady heat storage component of the base material is excluded, but since it has reached the detection camera, such a steady heat component increases, The detection sensitivity of the lock-in heat generation image decreases. On the other hand, if such a strong background heat component can be excluded by temperature control, the ratio of heat generated by the AC excitation component to the camera sensitivity will increase, so an improvement in resolution is expected when measuring conductive materials. The In the actual heat generation intensity distribution, the brightness distribution of the heat generation intensity image shifted to the high intensity side by reducing the conductive material temperature at the time of measurement, and as a result, the resolution of the heat generation image was improved. .
［実施例４］
これまで計測してきたロックイン発熱画像のパターンが、実際の導電材料の内部構造を反映したものである事を確認するために、引っ張り試験による破断特性と発熱強度分布の比較例を図１０に示した。引っ張り試験の試験片の光学顕微鏡像を図１０(ａ)に示した、引っ張り試験の際に押え治具の根元に応力集中が起こらないよう、ダンベル型に加工した試験片を用いた。(ｂ)に引っ張り試験前の発熱強度分布の断面例、(ｃ)に赤外線画像、(ｄ)に試験片全体の発熱強度画像を示した。図(ｂ)及び(ｄ)から、導電材料の試料中には(ｄ)中矢印で示したような高抵抗箇所が存在し、物理的に弱い構造である事が推測される。この試験片を、実際に４０％の歪みで引っ張った際の、(ｅ)赤外線画像、及び(ｆ)発熱強度画像を示した。試験片全体が大きく延伸されているが、赤外線画像からは大きな変化は観測されない。一方で、発熱強度画像は試験前に高抵抗であった箇所がより強調されている事が示されている。実際に破断が発生した際の歪み５０％時の赤外線画像を(ｇ)に示した。この画像中矢印で示された破断箇所は、引っ張り試験前に発熱強度画像で高抵抗箇所である事が示唆された箇所であり、これにより本発明の実施例によるロックイン発熱画像が、導電材料の内部構造を、正確に計測可能であることが示された。[Example 4]
In order to confirm that the pattern of the lock-in heat generation image that has been measured so far reflects the internal structure of the actual conductive material, FIG. 10 shows a comparative example of the rupture characteristics and heat generation intensity distribution by the tensile test. It was. An optical microscope image of the test piece of the tensile test is shown in FIG. 10A. A test piece processed into a dumbbell shape was used so that stress concentration did not occur at the base of the holding jig during the tensile test. (b) shows a cross-sectional example of the heat generation intensity distribution before the tensile test, (c) shows an infrared image, and (d) shows a heat generation intensity image of the entire test piece. From FIGS. (B) and (d), it can be inferred that the conductive material sample has a high resistance portion as indicated by an arrow in (d), and is a physically weak structure. When this test piece was actually pulled at a strain of 40%, (e) an infrared image and (f) an exothermic intensity image were shown. Although the entire specimen is stretched greatly, no significant change is observed from the infrared image. On the other hand, the exothermic intensity image shows that the portion having high resistance before the test is more emphasized. An infrared image at a strain of 50% when the fracture actually occurred is shown in (g). In this image, the fractured part indicated by the arrow is a part suggested to be a high-resistance part in the heat generation intensity image before the tensile test, whereby the lock-in heat generation image according to the embodiment of the present invention is a conductive material. It was shown that the internal structure of can be measured accurately.
本発明によれば、導電材料の内部構造や電流分布、抵抗分布を比較的簡易に可視化する事が可能となるので、機能性を有する導電材料開発の特性向上や最適化を図る際に効果的に利用することができる。 According to the present invention, the internal structure, current distribution, and resistance distribution of a conductive material can be visualized relatively easily, which is effective in improving the characteristics and optimizing the development of functional conductive materials. Can be used.
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