【発明の詳細な説明】[Detailed description of the invention]
産業上の利用分野
本発明は各種電子機器のプリント配線板、固定
抵抗器、可変抵抗器等の抵抗素子や電磁波シール
ド板、電波吸収板、静電防止板等に使用する抵抗
用塗料に関するものである。
従来の技術
従来、抵抗用塗料としては導電性粉末としてカ
ーボンブラツク、例えばアセチレンブラツクや黒
鉛粉末をエポキシ樹脂やフエノール樹脂等の合成
樹脂に分散させたものが知られている。又、印刷
適性等の作業性や高負荷条件等の環境安定性を向
上させる目的でSiO2粉末やTiO2粉末等の絶縁性
粉末をカーボンブラツクとともに合成樹脂中に分
散させた抵抗用塗料が知られている。
発明が解決しようとする問題点
前記従来例の場合、高抵抗領域では抵抗組成中
のカーボンブラツクの割合が極めて少ないため、
高湿度雰囲気中で電流を流すと陽極酸化が発生
し、カーボンブラツクが炭酸ガスとして気化する
結果、抵抗値が加速度的に上昇し、無限大（絶縁
物）にまでなる欠点を有していた。更にSiO2粉
末やTiO2粉末等の絶縁性粉末を含有させた抵抗
用塗料においては、例えば可変抵抗器用抵抗素子
等摺動接点として用いる場合、摺動雑音が高くな
る欠点を有していた。又、電流導通パスはカーボ
ンブラツク及びその相互の接触によるものである
ため、カーボンブラツクの割合の少ない高抵抗領
域では湿度や温度の変動時の抵抗値変化が大きい
欠点を有していた。
本発明はこのような問題点を解決するもので、
従来のような陽極酸化による抵抗値上昇がなく、
摺動接点として用いた場合、摺動雑音が低く、し
かも耐湿、耐熱特性が良好な抵抗用塗料を提供す
ることを目的とするものである。
問題点を解決するための手段
この問題点を解決するために本発明は、少なく
とも導電性粉末と合成樹脂よりなる抵抗用塗料に
おいて、前記導電性粉末の一部が二酸化タンダス
テン（WO2）の粉末であり、他の部分がカーボ
ンブラツクであるものである。
作 用
この構成により、高湿度雰囲気中で電流を流し
ても陽極酸化による抵抗値上昇もなく、耐湿、耐
熱特性も良好で、摺動接点として用いた場合、摺
動雑音も低くなる。
実施例
以下、本発明の実施例について、図面に基づい
て説明する。
即ち、本発明は少なくとも導電性粉末と合成樹
脂よりなる抵抗用塗料において、前記導電性粉末
の一部が二酸化タンダステン（WO2）の粉末で
あり、他の部分がカーボンブラツクで構成され、
WO2粉末とカーボンブラツクの重量比率を95：
５〜10：90としたものである。
WO2は従来より公知であるが、WO2粉末単独
でフエノール樹脂等の合成樹脂中に分散せしめて
抵抗用塗料とした場合、第１図に示す如く高湿度
や高温度の雰囲気中では抵抗値の変動が極めて大
きい。WO2粉末とカーボンブラツクとを組み合
わせることによつて、第２図に抵抗用塗料の塗膜
構造を示すように、高湿度や高温度雰囲気中で抵
抗値の変動が極度に少なくなるのは、WO2粉末
１とカーボンブラツク２の構造に原因するものと
推察できる。即ち、WO2粉末１は粒状であるの
に対し、カーボンブラツク２はストラクチヤーと
呼ばれる連鎖状の構造を有している。粒状構造や
連鎖構造単独の導電粉体を使用した場合には粉末
粒子を相互に結着している合成樹脂の吸脱湿や熱
による膨張・収縮のため粉末粒子の相互の接触状
態は雰囲気の状態によつて密になる場合と粗にな
る場合ができる。一方、抵抗値は導電性粉体自体
の抵抗と粉体相互の接触抵抗の総和として表わさ
れるものであるから前記粒状粉末や連鎖状粉末単
独の場合、温湿度雰囲気の変動における抵抗値の
変動が大きくなるものと考えられる。第２図に示
すようにWO2粉末１とカーボンブラツク２を混
合して合成樹脂３中に分散させた場合、雰囲気の
変動による合成樹脂の吸脱湿や熱での膨張・収縮
が発生しても第３図の概念図で示すように導電パ
ス４が得られ易いために抵抗値変化が少ないもの
と推察される。更に、カーボンブラツクもWO2
も良好な導電材料であるため、摺動接点として使
用した場合、摺動雑音のレベルはカーボンブラツ
ク単独の場合に比較しても低くなる。又、高抵抗
領域においても、WO2は温湿度に対して安定な
ことや従来に比較して抵抗皮膜中の合成樹脂比率
を低下させ得るため、吸湿を少なくできることか
ら陽極酸化も実質的に防止できる。又、本発明に
よる抵抗用塗料は塗料中の導電性粉末量が従来の
カーボン単独の場合に比較して多くできるため、
適度なチクソトロピツクな性質を有しており、ス
クリーン印刷等の作業性も良いものである。
次に具体実施例について説明する。
具体実施例 １
平均粒径0.2μｍのWO2粉末255ｇ、アセチレン
ブラツク40ｇ、人造黒鉛５ｇを秤量混合してエポ
キシ樹脂（油化シエル、品名：エピコート815）
200ｇ中に三本ロールで分散させた。次にイミダ
ゾール系硬化剤20ｇを加え、エチルカルビトール
アセテートを添加して塗料粘度100ポイズに調整
し、抵抗用塗料を得た。
比較例
アセチレンブラツク60ｇ、人造黒鉛７ｇをエポ
キシ樹脂（油化シエル、品名：エピコート815）
200ｇ中に分散させ、イミダゾール系硬化剤20ｇ
を加え、エチルカルビトールアセテートを添加し
て塗料粘度100ポイズに調整し、抵抗用塗料を得
た。
比較試験例
前記具体実施例１及び比較例の抵抗用塗料を
夫々フエノール積層板にスクリーン印刷法にてパ
ターン印刷し、160℃30分間でエポキシ樹脂を硬
化させた。前記具体実施例１及び比較例による
夫々の抵抗素子について下記の比較試験を行なつ
た。試験１；70℃の恒温槽に放置し1000時間後迄
の抵抗値変化率を測定、試験２；60℃90〜95％相
対湿度槽に放置し1000時間後迄の抵抗値変化率を
測定、試験３；60℃90〜95％相対湿度槽中で抵抗
素子の両端に直流電圧24Vを印加し、1000時間後
迄の抵抗値変化率を測定、試験４；抵抗塗膜上を
銀メツキベリリウム銅の金属刷子を加圧20ｇ、15
mm／秒の速度で摺動させたときの摺動雑音を測定
（抵抗素子両端に直流電圧24V印加）。これら試験
１〜３の結果を第４図ａ〜ｃに夫々示す。尚第４
図ａ〜ｃにおいてＡは具体実施例１の抵抗変化特
性、Ｂは比較例の抵抗変化特性である。又、試験
４の結果を次表に示す。
INDUSTRIAL APPLICATION FIELD The present invention relates to a resistive paint used for printed wiring boards of various electronic devices, resistive elements such as fixed resistors and variable resistors, electromagnetic wave shielding plates, radio wave absorbing plates, antistatic plates, etc. be. BACKGROUND TECHNOLOGY Conventionally, as a resistive paint, one in which conductive powder such as carbon black, such as acetylene black or graphite powder is dispersed in a synthetic resin such as an epoxy resin or a phenolic resin, is known. In addition, resistance paints in which insulating powders such as SiO 2 powder and TiO 2 powder are dispersed together with carbon black in synthetic resin are known for the purpose of improving workability such as printability and environmental stability under high load conditions. It is being Problems to be Solved by the Invention In the case of the conventional example, the proportion of carbon black in the resistance composition is extremely small in the high resistance region.
When a current is passed in a high humidity atmosphere, anodic oxidation occurs, and the carbon black vaporizes as carbon dioxide gas, which causes the resistance value to increase at an accelerated rate, reaching infinity (an insulating material). Furthermore, resistance coatings containing insulating powder such as SiO 2 powder or TiO 2 powder have the disadvantage of high sliding noise when used as a sliding contact, such as a resistance element for a variable resistor. Furthermore, since the current conduction path is due to carbon blacks and their mutual contact, there is a drawback that in a high resistance region where the proportion of carbon blacks is small, the resistance value changes greatly when humidity or temperature changes. The present invention solves these problems,
There is no increase in resistance due to anodization as in conventional methods,
The object of the present invention is to provide a resistance coating material that has low sliding noise and good moisture resistance and heat resistance properties when used as a sliding contact. Means for Solving the Problems In order to solve this problem, the present invention provides a resistance paint made of at least conductive powder and a synthetic resin, in which part of the conductive powder is tundastene dioxide (WO 2 ) powder. The other parts are carbon black. Function: With this configuration, there is no increase in resistance due to anodic oxidation even when current is passed in a high humidity atmosphere, the moisture resistance and heat resistance properties are good, and when used as a sliding contact, the sliding noise is low. Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings. That is, the present invention provides a resistive paint made of at least conductive powder and synthetic resin, in which a part of the conductive powder is tundastene dioxide (WO 2 ) powder, and the other part is composed of carbon black.
The weight ratio of WO 2 powder and carbon black is 95:
The time was 5:90 to 10:90. WO 2 has been known for a long time, but when WO 2 powder alone is dispersed in a synthetic resin such as phenol resin to make a resistance paint, the resistance value decreases in an atmosphere of high humidity and temperature, as shown in Figure 1. fluctuations are extremely large. By combining WO 2 powder and carbon black, as shown in Figure 2, which shows the coating film structure of the resistance paint, the fluctuation of the resistance value is extremely reduced in a high humidity and high temperature atmosphere. It can be inferred that this is caused by the structure of WO 2 powder 1 and carbon black 2. That is, while the WO 2 powder 1 is granular, the carbon black 2 has a chain-like structure called a structure. When a conductive powder with a granular or chain structure is used, the state of contact between the powder particles may be affected by the atmosphere due to moisture absorption and desorption of the synthetic resin that binds the powder particles together, as well as expansion and contraction due to heat. Depending on the condition, it can be dense or coarse. On the other hand, the resistance value is expressed as the sum of the resistance of the conductive powder itself and the contact resistance between the powders, so in the case of the granular powder or chain powder alone, the resistance value changes due to changes in temperature and humidity atmosphere. It is thought that it will become larger. As shown in Figure 2, when WO 2 powder 1 and carbon black 2 are mixed and dispersed in synthetic resin 3, the synthetic resin absorbs and desorbs moisture due to changes in the atmosphere and expands and contracts due to heat. As shown in the conceptual diagram of FIG. 3, it is presumed that the change in resistance value is small because the conductive path 4 is easily obtained. Furthermore, carbon black is also WO 2
Since carbon black is also a good conductive material, when used as a sliding contact, the level of sliding noise is lower than when using carbon black alone. Furthermore, even in the high resistance range, WO 2 is stable with respect to temperature and humidity, and can lower the synthetic resin ratio in the resistance film compared to conventional ones, so it can reduce moisture absorption and virtually prevent anodic oxidation. can. In addition, since the resistance paint according to the present invention can have a larger amount of conductive powder in the paint than when using conventional carbon alone,
It has moderate thixotropic properties and is easy to work with, such as screen printing. Next, specific examples will be described. Specific Example 1 255 g of WO 2 powder with an average particle size of 0.2 μm, 40 g of acetylene black, and 5 g of artificial graphite were weighed and mixed to make an epoxy resin (Yuka Ciel, product name: Epicote 815).
It was dispersed in 200g using three rolls. Next, 20 g of an imidazole curing agent was added, and ethyl carbitol acetate was added to adjust the viscosity of the paint to 100 poise to obtain a resistance paint. Comparative example: 60 g of acetylene black and 7 g of artificial graphite were mixed with epoxy resin (Yuka Ciel, product name: Epicote 815)
Disperse in 200g and add 20g of imidazole curing agent.
and ethyl carbitol acetate was added to adjust the paint viscosity to 100 poise to obtain a resistance paint. Comparative Test Example The resistance paints of Example 1 and Comparative Example were each pattern-printed on a phenol laminate by screen printing, and the epoxy resin was cured at 160°C for 30 minutes. The following comparative tests were conducted on each of the resistance elements according to the specific example 1 and comparative example. Test 1: Leave it in a constant temperature bath at 70℃ and measure the rate of change in resistance value after 1000 hours. Test 2: Leave it in a bath with 90-95% relative humidity at 60℃ and measure the rate of change in resistance value after 1000 hours. Test 3: Apply a DC voltage of 24 V to both ends of the resistance element in a 60°C 90-95% relative humidity chamber, and measure the rate of change in resistance value after 1000 hours. Test 4: Silver-metsuki beryllium copper on the resistive coating. Pressure 20g of metal brush, 15
Measure the sliding noise when sliding at a speed of mm/sec (DC voltage 24V applied across the resistance element). The results of these tests 1 to 3 are shown in FIGS. 4a to 4c, respectively. Furthermore, the fourth
In Figures a to c, A is the resistance change characteristic of the first specific example, and B is the resistance change characteristic of the comparative example. Additionally, the results of Test 4 are shown in the following table.
【表】
具体実施例 ２
具体実施例１と同一の各材料を使用し、カーボ
ンブラツクとWO2粉末の比率を変化させたとき
の抵抗用塗料について比較試験例と同様の方法で
1000時間後の耐湿及び耐熱抵抗変化率を調べた。
その結果を第１図に示す。
発明の効果
以上のように本発明によれば、高湿度雰囲気中
で電流を流しても陽極酸化による抵抗値上昇がな
く、耐湿、耐熱特性も良好で、摺動接点として用
いた場合摺動雑音も低く、且つカーボンブラツク
単独の場合に比較して導電性粉末量を多くできる
ため、スクリーン印刷等の際に塗料特性として要
求される適度なチクソトロピツクな性質を有して
いるため作業性も良いものである。又、使用する
各材料については何れも安価であることから、産
業上極めて有用なものである。[Table] Specific Example 2 Using the same materials as in Specific Example 1, resistance paints were tested in the same manner as in the comparative test example, with the ratio of carbon black and WO 2 powder changed.
The humidity resistance and heat resistance change rate after 1000 hours were investigated.
The results are shown in FIG. Effects of the Invention As described above, according to the present invention, there is no increase in resistance due to anodic oxidation even when current is passed in a high humidity atmosphere, the moisture resistance and heat resistance are good, and there is no sliding noise when used as a sliding contact. It also has low conductive powder and allows for a larger amount of conductive powder compared to carbon black alone, so it has the appropriate thixotropic properties required as paint properties for screen printing, etc., and has good workability. It is. In addition, since the materials used are all inexpensive, they are extremely useful industrially.
【図面の簡単な説明】[Brief explanation of drawings]
図面は本発明の実施例を示すもので、第１図は
カーボンブラツクとWO2粉末との比率と抵抗変
化特性との関係を示すグラフ、第２図は本発明に
よる抵抗用塗料の塗膜構造図、第３図は塗膜中の
導電パスの概念図、第４図ａ〜ｃは本発明及び比
較例による比較試験例を示すグラフである。
１……WO2粉末、２……カーボンブラツク、
３……合成樹脂、４……導電パス。
The drawings show examples of the present invention. Figure 1 is a graph showing the relationship between the ratio of carbon black and WO 2 powder and resistance change characteristics, and Figure 2 is a graph showing the coating film structure of the resistance paint according to the present invention. 3 are conceptual diagrams of conductive paths in a coating film, and FIGS. 4 a to 4 c are graphs showing comparative test examples according to the present invention and a comparative example. 1...WO 2 powder, 2...Carbon black,
3...Synthetic resin, 4...Conductive path.