JP3827256B2 - Carbon black for compounding functional parts rubber and rubber composition for functional parts containing the same - Google Patents

Description

ｂ． Ｄｓｔと、Ｄｓｔより大きくかつＤｓｔの１／２の頻度を有するＤ^L ₅₀から式（２）で算出されるアグリゲートサイズ分布指数ｓが０．１７以上
【数４】
ｓ＝０．８４９３２×ｌｏｇ（Ｄ^L ₅₀／Ｄｓｔ） （２）
であることを特徴とする機能部品ゴム配合用カーボンブラックに関する。
【００１２】
従来のＳＡＦ級カーボンブラックは粒子径が小さ過ぎてゴムマトリックス中への分散性が低下し、このために本来発揮されるべき補強性能が発現されず、このことがゴム組成物中にカーボンブラック凝集塊の発生をもたらし、その結果として亀裂発生や亀裂成長における性能低下を招来することが機能部品配合用としての利用を妨げたり、回避する結果となっていた。
しかし、本発明の場合には、比表面積が大きく、かつストラクチャーを従来よりも低い範囲に設定し、Ｎ₂ＳＡ／ＩＡの比をある一定値以上にするとともに、アグリゲートの最多頻度値を従来よりも大きい値とし、かつ、その分布幅を大きくするという要件を具備させることにより、ゴムマトリックスへの分散性を向上させ、従来のＳＡＦ級カーボンブラックが有していた耐疲労特性、特に亀裂発生や亀裂成長という欠陥を効果的に抑制し、加えて構造補強材への接着性も改良することができるカーボンブラックとなるのである。
【００１３】
本発明において適用されるカーボンブラックの物理化学特性は、次のようにして測定される。
（１）ＤＢＰ吸油量
ＪＩＳ Ｋ６２２１ ６．１．２項Ａ法に記載の方法で測定され、カーボンブラック１００ｇ当たりに吸収されるジブチルフタレート（ＤＢＰ）のｍｌで表示される。
（２）窒素吸着比表面積（Ｎ₂ＳＡ）
ＡＳＴＭ Ｄ３０３７−８４ Ｂ法に記載の方法で測定され、単位重量当たりの比表面積ｍ²／ｇで表示される。
（３）よう素吸着量
ＪＩＳ Ｋ６２２１ ６．１．１項に記載の方法で測定され、カーボンブラック１ｇ当たりに吸着されるよう素のｍｇで表示される。
（４）遠心沈降分析によるカーボンブラックアグリゲートサイズの分析法
測定機器：
Ｄｉｓｋ Ｃｅｎｔｒｉｆｕｇｅ Ｐｈｏｔｏｓｅｄｉｍｅｎｔｍｅｔｅｒ
〔Ｊｏｙｃｅ Ｌｏｅｂｌ社製、４型機（ＭＡＲＫ IV）〕
測 定 法：
５０Ｖ／Ｖ％メタノール水溶液５０ｍｌを三角フラスコに入れ、０．１ｍｌの界面活性剤のノニオライトＰＮ−１０（共栄社油脂化学工業製）を加える。０．０３〜０．０４重量％のカーボンブラックを加え、超音波処理（４００Ｗ、３８ＫＨｚ、５分）を施して完全に分散させる。蒸留水（スピン液）２０〜３０ｍｌを注加した回転ディスクの回転数を８０００ｒｐｍとし、前記分散液０．０２〜０．０３ｍｌを注加する。
分散液の注加と同時に記録計を作動させ、回転ディスクの外周近傍の一定点を沈降により通過するカーボンブラックのアグリゲートの量を光学的に測定し、その量を時間に対する連続曲線として記録する（図４）。
沈降時間を、下記のストークスの一般式によりストークス相当径に換算し、アグリゲートのストークス相当径とその頻度の対応曲線を得る（図５）。
【数５】

式（３）において、ｄは沈降開始ｔ分後での回転ディスクの光学測定点を通過するカーボンブラックアグリゲートのストークス相当径（ｎｍ）である。
定数Ｋは、測定時のスピン液温度、粘度およびカーボンブラックとの密度差（カーボンブラックの真密度は１．８６ｇ／ｃｍ³とする）、さらに回転ディスクの回転数により決定される。本発明の測定で、スピン液として蒸留水２５ｍｌを用い、測定温度２４℃、ディスク回転数８０００ｒｐｍとし、Ｋ値は２６０．２５を用いた。
【００１４】
Ｄｓｔ測定値の定義…前記の操作により得られたカーボンブラックアグリゲートのストークス相当径の中で、最大吸光度を与えるまでの経過時間Ｔ_Pから算出されるストークス相当径をＤｓｔと称し、そのカーボンブラックアグリゲート径を表わす代表値とする。
【００１５】
また、前記の吸光度曲線において、最大吸光度の１／２に相当する値を与える経過時間Ｔ_L（Ｔ_L＜Ｔ_P）に対するストークス相当径Ｄ^L ₅₀（Ｄｓｔより大きく、かつＤｓｔの１／２の頻度を有するアグリケート径）とすると、アグリケートサイズ分布指数ｓは、
【数６】
ｓ＝０．８４９３２×ｌｏｇ（Ｄ^L ₅₀／Ｄｓｔ） （２）
で定義される。
前述したように、（２）式で定義されるアグリケートサイズ分布指数ｓは、数学的には遠心沈降法で測定したカーボンブラックアグリケートのストークス相当径が対数正規に従うと仮定した場合の分布曲線の標準偏差とほぼ同じ意味合いを持つものであり、この数値が大きいということはアグリケートの分布が広いことを意味している（図５）。図４は、前記遠心沈降法による経過時間と吸光度の測定チャートの１例であり、図５は、図４のチャートの経過時間から算出したアグリゲート値の対数と吸光度の関係を示す図である。図４でのＴ_Sは最大吸光度の１／２に相当する値を与える経過時間（Ｔ_P＜Ｔ_S）であり、図５のＤ^S ₅₀はＤｓｔより小さく、かつＤｓｔの１／２の頻度を有するアグリゲート径である。
【００１６】
【作用】
本発明のカーボンブラックでは、Ｎ₂ＳＡが１３０ｍ²／ｇを越え１６０ｍ²／ｇ以下、ＤＢＰＡが６０〜１００ｍｌ／１００ｇという特性を有することが基本である。
ＤＢＰＡが本発明範囲を越えて低くなるとゴムマトリックスへの分散性が低下し、マトリックス中の未分散カーボン凝集塊が初期亀裂発生の開始点となるとともに、亀裂成長も進行しやすくなるので、下限は６０ｍｌ／１００ｇとする。ＤＢＰＡが高くなるにつれて前述の欠点は望ましい方向となるが、この結果の影響率は徐々に低下し、１００ｍｌ／１００ｇを越えるとこの効果は本発明のカーボンブラックではほとんど飽和状態となり、影響率は極端に低下する。また発熱性の数値（損失正接、ｔａｎδ）は少しずつ大きくなり、１００ｍｌ／１００ｇを越えるとこの傾向は一層強くなって特性は低下する。また、硬さの特性も上がりすぎる傾向にある。
【００１７】
Ｎ₂ＳＡが１３０ｍ²／ｇを越え１６０ｍ²／ｇ以下という範囲は、機械的特性（引張り強さ）と耐疲労特性（亀裂成長性、発熱性）の両特性のバランスを維持するために重要であり、下限の１３０ｍ²／ｇを下回った場合には機械的特性が低下し、１６０ｍ²／ｇを上回った場合は発熱性が低下（６０℃での損失正接の増大）するとともに、カーボンブラックの分散不良の発現による耐疲労特性、特に亀裂成長性が低下する。
【００１８】
Ｎ₂ＳＡ／ＩＡ比の特性は耐疲労特性と接着性に影響を与え、この値が１．１を下回った場合にはこの特性を低下させる。
【００１９】
アグリゲートサイズ分布指数ｓはゴム組成物の耐疲労特性と分散性に影響を与え、０．１７を下回った場合は発熱性〔損失正接（ｔａｎδ）〕の値を大きくし、また分散性の低下をもたらすので０．１７以上とする必要がある。しかしながら、ｓが大きくなりすぎると機械的特性が低下する傾向があるので、０．１７〜０．２３の値を有するカーボンブラックが望ましい。
【００２０】
もう１つのアグリゲート特性であるＤｓｔ／Ｄａの値は機械的特性、耐疲労性、分散性などのバランスを良好に保つ、すなわちこれらの特性の多くは一方が上がると他は低下するという背反関係にあるが、これを解消するために重要な因子であり、この値が１．２５を下回った場合には例えば機械的特性と発熱特性との背反関係を解消することはできなくなる。しかし、Ｄｓｔ／Ｄａの値を大きくしても次第に改善効果が小さくなる傾向があり、また機械的特性が低下する傾向もあるので、１．２５〜２．０、より好ましくは１．３５〜１．９０のカーボンブラツクが望ましい。
【００２１】
【実施例】
以下に実施例を挙げて本発明を説明するが、本発明はこれにより限定されるものではない。
【００２２】
製造例
カーボンブラックの製造
本発明にかかるハード系高ストラクチャーカーボンブラックの製造は、本出願人が出願した特願平３−４５８２４号明細書に記載されたと同様の装置を用いて行った。
【００２３】
図１、図２及び図３に示した製造装置を用い、各部の寸法は次の通りとした。
可燃性流体導入室 ２
内径 ４５０ｍｍφ
長さ ４００ｍｍ
酸素含有ガス導入管 ３
長辺 ４００ｍｍ
短辺 １００ｍｍ
酸素含有ガス導入用円筒 ４
内径 ２５０ｍｍ
長さ ３００ｍｍ
収れん室 ８
上流端内径 ３７０ｍｍ
下流端内径 ８０ｍｍ
長さ １６００ｍｍ
収れん角度 ５．３゜
燃料油導入装置
燃料油導入管７２の内径 ７ｍｍφ
高圧・高湿空気導入管７３の内径 １３ｍｍφ
空気温度 ３００℃
空気圧力 ３ｋｇ／ｃｍ²
低圧・高湿空気導入管７４の内径 ２２ｍｍφ
空気温度 ６０℃
空気圧力 ０．５ｋｇ／ｃｍ²
反応室 １２
内径 １４０ｍｍφ
【００２４】
また、反応継続兼急速冷却室１３内でのａ〜ｈの冷却水噴霧装置は、実用新案登録第１０２８６３号（出願人：旭カーボン株式会社）に開示されているのと同様構造の装置をとりつけた。
【００２５】
原料油及び燃料油としては、表１に示した性状組成を有するものを使用した。
【表１】

【００２６】
本発明カーボンブラックおよび比較カーボンブラックの製造方法
表２〜５に記載のカーボンブラックは、前述のカーボンブラック製造装置において、原料油導入位置、原料油へのアルカリ金属（カリウム）の添加量、導入総空気量、原料油導入量、原料油導入圧および温度、反応停止用冷却水導入位置、燃料導入量などの条件を調整して製造した。
【００２７】
より詳しく説明すると、表面積（Ｎ₂ＳＡ）の調整は原料油導入量と総空気導入量との比率を変化させることにより行うことができ、導入空気量の割合を増加させることにより表面積は増大する。２つの表面積指標の比、Ｎ₂ＳＡ／ＩＡの制御は、カーボンブラック生成反応後の反応停止位置により行うことができ、より上流側（反応停止までの時間が短い）で行うことによりこの値は増大する。アグリゲート径の制御は原料油の導入位置により行うことができ、上流側にすることによりアグリゲート径（Ｄｓｔ）は大きくなる。通常の場合、アグリゲートの代表径（Ｄｓｔ）はストラクチャーの低下とともに低下するが、原料油の噴霧位置を上流側にすることによりこの低下の程度を減少することができる。アグリゲート分布の制御は導入する原料油の噴霧状態と導入燃料量を調節することにより行うことができ、分布を広くする（ｓを大きくする）場合には導入原料油の温度および圧力を低下させ、噴霧状態を悪くすることにより分布を大きくすることができる。さらに、導入燃料量を減少することにより分布を広げることができる。なお、このたびの製造においては導入空気中の二次空気量、空気温度、および原料噴霧ノズルの形状および数は一定とした。
本発明にかかるカーボンブラックおよび比較用カーボンブラックの製造条件を表２〜５に、製造された各カーボンブラックの物理化学特性を表６〜９に示した。
【００２８】
【表２】

【００２９】
【表３】

【００３０】
【表４】

【００３１】
【表５】

【００３２】
【表６】

【数７】

【００３３】
【表７】

【数８】

【００３４】
【表８】

【数９】

【００３５】
【表９】

【数１０】

【００３６】
ゴム配合性能試験
表６〜９に示したカーボンブラックの性能を評価するために、表１０に示した配合比によりゴム組成物を調整し、その特性の試験を行った。その結果を表１１〜１３（カーボンブラック等量配合）に示す。
【表１０】

ＭＢＴＳ：２，２′−ジベンゾチアジルジスルフィド
ＩＰＰＤ：Ｎ−イソプロピル−Ｎ−フェニル−Ｐ−フェニレンジアミン
【００３７】
【表１１】

【００３８】
【表１２】

【００３９】
【表１３】

【００４０】
なお、各配合ゴム組成物のゴム特性の性能評価は、次の試験条件により測定した。
ゴム特性試験条件
▲１▼配合物の加硫条件 ：１４５℃、３０分
▲２▼耐摩耗性試験 ：ランーボン摩耗試験機を用い、スリップ率２５％で摩耗試験を行ない、耐摩耗指数は下式により算出した。
耐摩耗指数＝（Ｓ／Ｔ）×１００
ここでＳ：対照例（Ｒｕｎ．Ｎｏ．１４）配合試験片の摩耗減量
Ｔ：供試試験片における摩耗減量
▲３▼デマッチャ疲れ試験：デマッチャ屈曲試験機を用い、亀裂発生までの屈曲回数および２ｍｍ亀裂を予め入れた試料を１００００回屈曲した時の亀裂成長を測定した。
▲４▼動的粘弾性 ：（株）岩本製作所粘弾性スペクトロメーター
（損失正接） （型式ＶＥＳ−Ｆ−III）を用いて、下記の測定条件で損失正接（ｔａｎδ）を測定し、対照カーボンブラックに対する指数で表示した。
周波数 ：５０Ｈｚ
動的歪み率 ：±１％
測定温度 ：２５℃
初期加重 ：１６０ｇ重
▲５▼接着試験
表面真ちゅうめっきしたスチールコード（１×５×０．２３ｍｍ）を未加硫ゴムに埋設したスチールコード−ゴム複合体を、１５０℃で２０分間加硫した後、ＪＩＳ Ｋ ６３０１ ７のはく離試験に準じて埋設スチールコードとゴム層のはく離試験を行ないスチールコード上に残留した付着ゴムの被覆割合により接着性を評価した。はく離後のスチールコード表面のほとんどがゴム層で被覆されている状態をＡ、所々にスチールコードの表面が見える状態をＢ、スチールコード表面とゴム層の割合がほぼ等しい状態をＣ、スチールコード表面の割合がゴム層よりも多い状態をＤ、ほとんどのスチールコード表面が見える状態をＥとして表示した。
なお、接着試験における引張り速度は２５ｍｍ／分で行なった。
▲６▼分散性
１９６９年９月号のラバーワールド第１６０巻第６号第６３〜７０頁（著者：Ｈ．Ｅ．レイスバックら）に記載の方法に準じて、配合ゴム表面を３２倍に拡大した写真を用い、１０〜１に区分された標準見本のどのランクに該当するかを目視で判定した。なお、中間にあると判定したサンプル、例えば７と８の間の場合には７．５と表示した。
▲７▼その他のゴム特性：ＪＩＳ Ｋ６３００−１９７４およびＫ６３０１−１９７５に記載の方法にしたがって測定した。
【００４１】
【評価】
表６〜９に示した物理化学特性を有する実施例および比較例のカーボンブラックをゴムに配合したゴム組成物の測定結果（表１１〜１３）の結果から、本発明カーボンブラツクの効果を説明する。
Ｒｕｎ Ｎｏ．１〜５のカーボンブラツクは本発明に係るものであり、ＲｕｎＮｏ．６〜１３は本発明の特定要件の１つまたは２つの要件を外れた比較例、Ｒｕｎ Ｎｏ．１４は対照カーボンブラック（商品名 旭＃８０、ＩＳＡＦ級カーボンブラック、旭カーボン株式会社製）である。
Ｒｕｎ Ｎｏ．６はＤＢＰＡが本発明の上限を越えた例であり、Ｒｕｎ Ｎｏ．７は逆に下限を下回った比較例である。Ｒｕｎ Ｎｏ．８はＲｕｎ Ｎｏ．２とほぼ同じ基本特性を有しているが、アグリゲート特性の中のＤｓｔ／Ｄａの値が本発明の範囲を下回り、Ｒｕｎ Ｎｏ．９は表面積範囲の上限を越えた比較例であり、Ｒｕｎ Ｎｏ．１０は逆に表面積範囲の下限を下回った比較例である。Ｒｕｎ Ｎｏ．１１はＲｕｎ Ｎｏ．４とほぼ同じ基本特性であるがアグリゲート分布指数ｓが本発明の範囲を外れたものであり、Ｒｕｎ Ｎｏ．１２はＲｕｎＮｏ．２とほぼ同じ基本特性を有しているが、表面積の比、Ｎ₂ＳＡ／ＩＡの値で本発明範囲を外れた例である。Ｒｕｎ Ｎｏ．１３はＲｕｎ Ｎｏ．５とほぼ同じ基本特性であるが、Ｎ₂ＳＡ／ＩＡ比およびｓの両者の要件で本発明範囲を外れた比較例である。
【００４２】
▲１▼引張り強さについての評価
ＤＢＰＡの値が本発明の範囲の下限を下回ったＲｕｎ Ｎｏ．７においては、引張り強さの特性が大きく低下している。
▲２▼耐摩耗性についての評価
Ｒｕｎ Ｎｏ．７のカーボンブラツクでのランボーン耐摩耗性指数は、他のカーボンブラツクと比較して大きな低下がみられるが、その他のカーボンブラック間では大きな差異は認められない。しかし、表面積が本発明の範囲を外れて大きな数値を有するＲｕｎ Ｎｏ．９のカーボンブラックにおける指数は、その表面積から予想される特性値を大きく下回っている。
▲３▼デマッチャ屈曲試験についての評価
ＤＢＰ吸油量が本発明の範囲を外れて低くなったＲｕｎ Ｎｏ．７では分散性での低下がみられ、これにともなって亀裂発生までの屈曲回数は減少し、また亀裂成長も大きくなっている。この傾向はＮ₂ＳＡ／ＩＡが本発明の範囲を越えて大きなＲｕｎ Ｎｏ．９でも見られる。
また、アグリケートサイズ分布指数が本発明範囲を外れて小さいＲｕｎ Ｎｏ．１１においても分散性の低下と屈曲亀裂特性の低下が認められる。
▲４▼硬さについての評価
硬さは実施例、比較例とも大きな差異は見られないが、ＤＢＰ吸油量が本発明範囲を外れて高くなったＲｕｎ Ｎｏ．６ではこの数値が大きくなり、加工性で問題となる。
▲５▼動的粘弾性についての評価
動的粘弾性（損失正接、ｔａｎδ）の特性でも大きな差異はないが、ＤＢＰ吸油量が本発明範囲を大きい側に外れたＲｕｎ Ｎｏ．６およびＮ₂ＳＡが大きい方向に外れたＲｕｎ Ｎｏ．８、またはアグリゲート分布指数ｓが本発明範囲よりも小さい側のＲｕｎ Ｎｏ．１１およびＲｕｎ Ｎｏ．１３においてはこの値が大きい傾向にあり、これは繰り返し変形が与えられた配合ゴム組成物での蓄熱を招くことを意味し、結果としてゴム組成物を補強する物質（スチール、各種樹脂など）とゴム組成物とのセパレーションを起こす原因となるので好ましくない。
▲６▼接着性についての評価
配合ゴム組成物と補強物質との接着性（本発明では真ちゅうめっきスチールで評価）は、カーボンブラックの表面性状、特にＮ₂ＳＡ／ＩＡの値が本発明範囲である１．１０以上という要件で外れたＲｕｎ Ｎｏ．１２およびＲｕｎ Ｎｏ．１３において性能の低下が認められる。
▲７▼分散性についての評価
分散性は、ＤＢＰ吸油量が本発明範囲を下回ったＲｕｎ Ｎｏ．７、Ｎ₂ＳＡが本発明範囲を上回ったＲｕｎ Ｎｏ．９、アグリゲートサイズ分布指数ｓが本発明を下回ったＲｕｎ Ｎｏ．１１およびＲｕｎ Ｎｏ．１３のカーボンブラック配合物において低下していることが認められる。
【００４３】
【効果】
以上説明したように、本発明カーボンブラックを配合したゴム組成物は、高度の耐摩耗性を有し、かつ耐亀裂発生性、耐亀裂成長性および耐屈曲性において優れた性能を示すとともに、各種ゴム補強材料への接着性にも良好な特性を与えることができるので、特に機能部品用ゴムとして有用である。
【図面の簡単な説明】
【図１】本発明のカーボンブラックの製造に適する一例の装置の縦断正面説明図である。
【図２】図１のＡ−Ａ矢視における断面図である。
【図３】図１の前頭部および燃料導入装置を示す部分拡大図である。
【図４】遠心沈降法による経過時間と吸光度の測定チャートの一例である。
【図５】図４のチャートの経過時間から算出したアグリゲート値の対数と吸光度の関係を示す図である。
【符号の説明】
１ カーボンブラック反応装置
２ 可燃性流体導入室
３ 酸素含有ガス導入管
４ 酸素含有ガス導入用円筒
５ 整流板
７ 燃料油噴霧装置
８ 収れん室
９ バーナータイル
１０ 原料油噴霧装置
１１ 原料油導入室
１２ 反応室
１３ 反応継続兼急冷室
７１ 燃料油噴霧チップ
７２ 燃料油導入管
７３ 酸素含有ガス導入管
７４ 酸素含有ガス導入管
７５ 酸素含有ガスの導管
７６ 酸素含有ガスの導管
ａ 急冷水圧入噴霧装置
ｂ 急冷水圧入噴霧装置
ｃ 急冷水圧入噴霧装置
ｄ 急冷水圧入噴霧装置
ｅ 急冷水圧入噴霧装置
ｆ 急冷水圧入噴霧装置
ｇ 急冷水圧入噴霧装置
ｈ 急冷水圧入噴霧装置
Ａ_P 吸光度ピーク値
Ｔ_P ピーク値までの経過時間
Ｔ_L １／２Ａ_Pの吸光度でＴ_Pよりも小さい経過時間
Ｄｓｔ ストークス式で、Ｔ＝Ｔ_Pのときのアグリゲート径
Ｄ^L ₅₀ ストークス式で、Ｔ＝Ｔ_Lのときのアグリゲート径（１／２Ａ_Pで、Ｄ^L ₅₀＞Ｄｓｔを満たすアグリゲート径）[0001]
[Industrial application fields]
The present invention is mainly used in conveyor belts, high-pressure hoses, rubber rolls, etc., and is a functional component rubber member that is excellent in high wear resistance, crack resistance, and bending resistance and also excellent in adhesion to various materials. The present invention relates to a rubber-reinforcing carbon black and a rubber composition for functional parts containing the same. More specifically, in so-called hard carbon black of SAF class or higher, compared to conventional carbon black having an equivalent specific surface area, the compounded rubber composition has characteristics such as wear resistance, hardness, and crack resistance. The present invention relates to a carbon black for compounding a functional component rubber that can improve adhesion to fabrics, steel cords, and the like while maintaining the same or higher, and a rubber composition for a functional component including the same.
[0002]
[Prior art]
Rubber members used in various industrial rubber products used in conveyor belts, high-pressure hoses, rubber rolls, etc. are required to have excellent crack resistance and fatigue resistance under harsh conditions, and various fibers. In addition, a rubber composition having excellent adhesion to a structural reinforcing material such as a wire is desired.
[0003]
Carbon black is widely used as a rubber reinforcing agent because it has a reinforcing property that improves mechanical properties and the like with respect to rubber, but the characteristics of carbon black have a great influence on the required performance of compounded rubber compositions. There are grades with various characteristics to be a major factor to be given, and varieties suitable for use are used as appropriate.
[0004]
For example, carbon black having a relatively large particle size and a small structure is considered to be effective for rubber members that require low heat generation properties such as vibration-proof rubber. Further, in order to improve the fatigue fracture resistance in the rubber composition used for the skeleton member, it is recommended that a large amount of carbon black (N326, etc.) having a small particle size and a low structure be blended.
[0005]
As an example, in Japanese Patent Application Laid-Open No. 62-57438 (Applicant: Bridgestone Corporation) relating to hard carbon black, arithmetic average diameter (Dn) by electron microscope: 22 mμ ≦ Dn ≦ 38 mμ, aggregate diameter (Dst): 60 mμ ≦ Dst ≦ 130 mμ, standard deviation S (mμ) of arithmetic average particle size distribution: [S] ≦ 0.333 × [D _A ] +0.0800, half width of aggregate distribution ΔD ₅₀ (mμ): [ΔD ₅₀ ] ≦ 0.333 × [Dst] +45.0, aggregate strength: ΔDBP = DBP-24M4DBP (ml / 100 g) ≦ 10 ml / 100 g, N ₂ SA (m ² / g) / IA (m ² / g) ≧ A rubber composition in which 20 to 100 parts by weight of carbon black having colloidal characteristics of 1.08 is blended with a rubber component is suitable for rubber members that require fatigue resistance and heat generation resistance. It is described as providing an object.
[0006]
The grade of carbon black described in the present invention is presumed to belong to the HAF to ISAF class from the range of the arithmetic mean diameter, and if it has a higher grade than that, that is, the arithmetic mean particle diameter becomes smaller than 22 mμ, it is fatigue resistant. Although the fracture performance is improved, it is stated that the exothermic property of the compounded rubber increases and the heat generation durability is lowered.
[0007]
[Problems to be solved by the invention]
However, in recent years, it has been desired to develop a rubber composition having a higher degree of durability. In particular, when a large load is applied to the compounded rubber composition, cracking from the end of the rubber member, and this crack Highly reinforcing performance that effectively suppresses crack growth caused by further progress and provides a rubber composition with excellent adhesion to various reinforcing materials such as fibers and wires present in the rubber composition. The carbon black possessed was eagerly desired.
[0008]
The present invention provides a carbon black having colloidal characteristics suitable for providing a rubber composition that satisfies the above-mentioned requirements, that is, a carbon black for compounding a functional component rubber having an arithmetic average diameter smaller than that of the conventional carbon black. The rubber composition for functional parts which mix | blended this is provided.
[0009]
[Means for Solving the Problems]
It is a well-known fact that the structure represented by the specific surface area and DBP oil absorption of carbon black is two major characteristics of carbon black and has a great influence on the wear resistance of the compounded rubber composition. Various rubber compositions for industrial rubber products used in conveyor belts, high pressure hoses, rubber rolls, etc. have a higher nitrogen resistance specific surface area of about 70 m ² / g or higher in order to obtain the required fatigue resistance. When wearability is required, so-called hard carbon black higher than this is used, while the structure has a DBP oil absorption of approximately 105 to 135 ml / 100 g.
[0010]
However, the present inventors have conducted extensive research on SAF grade carbon black having a larger surface area (smaller particle size) than those used for hard systems, particularly those used for conventional industrial rubber products. The structure characteristics evaluated by the amount are set to the lower side of 60 to 100 ml / 100 g, and the ratio between the nitrogen adsorption specific surface area (N ₂ SA) and the iodine adsorption amount (IA) (N ₂ SA / When IA) is set to a certain value or more, the most frequent value of the aggregate is increased to a specific range, and the aggregate distribution is specified to be larger than the conventional range, it greatly exceeds the expected level. Thus, the present invention has been completed by finding out that the heat generation durability is improved and there is an improvement effect on the adhesion to the structural reinforcing material.
[0011]
That is, the present invention has a basic characteristic that the nitrogen adsorption specific surface area (N ₂ SA) exceeds 130 m ² / g and is 160 m ² / g or less, and the dibutyl phthalate (DBP) oil absorption (DBPA) is 60 to 100 ml / 100 g. 1) The ratio of N ₂ SA to iodine adsorption (IA) (N ₂ SA / IA) is 1.10 or more 2) The aggregate characteristics by centrifugal sedimentation analysis are as follows:
a. The ratio Dst / Da between the most frequent value (Dst) of the aggregate and the calculated aggregate diameter (Da) calculated by the equation (1) is 1.25 or more.

b. The aggregate size distribution index s calculated by the formula (2) from Dst and D ^L ₅₀ having a frequency larger than Dst and ½ of Dst is 0.17 or more.
s = 0.84932 × log (D ^L ₅₀ / Dst) (2)
It is related with carbon black for functional component rubber compounding characterized by being.
[0012]
Conventional SAF grade carbon black has a particle size that is too small to reduce its dispersibility in the rubber matrix, and therefore, the reinforcing performance that should be exhibited originally is not expressed. This is because the carbon black agglomerates in the rubber composition. The generation of lumps and, as a result, the deterioration of performance in the generation of cracks and crack growth has resulted in hindering or avoiding use as a functional component formulation.
However, in the case of the present invention, the specific surface area is large and the structure is set to a range lower than the conventional one, the N ₂ SA / IA ratio is set to a certain value or more, and the most frequent value of the aggregate is set to the conventional value. By increasing the distribution range and increasing the distribution width, the dispersibility in the rubber matrix is improved, and the fatigue resistance characteristics of conventional SAF grade carbon black, especially cracks, are generated. And carbon black that can effectively suppress defects such as crack growth and improve adhesion to structural reinforcement.
[0013]
The physicochemical properties of the carbon black applied in the present invention are measured as follows.
(1) DBP oil absorption amount Measured by the method described in JIS K6221 Section 6.1.2, Method A, and expressed in ml of dibutyl phthalate (DBP) absorbed per 100 g of carbon black.
(2) Nitrogen adsorption specific surface area (N ₂ SA)
It is measured by the method described in ASTM D3037-84 B method, and is expressed as a specific surface area m ² / g per unit weight.
(3) Iodine adsorption amount Measured by the method described in Section 6.1.1 of JIS K6221, and expressed in mg of iodine adsorbed per 1 g of carbon black.
(4) Analytical measuring instrument for carbon black aggregate size by centrifugal sedimentation analysis:
Disk Centrifugal Photodimension meter
[Joyce Loebl 4 type machine (MARK IV)]
Measurement method:
50 ml of 50 V / V% methanol aqueous solution is put into an Erlenmeyer flask, and 0.1 ml of surfactant Noniolite PN-10 (manufactured by Kyoeisha Yushi Chemical Co., Ltd.) is added. Add 0.03-0.04 wt% carbon black and apply sonication (400 W, 38 KHz, 5 minutes) to completely disperse. The number of revolutions of the rotating disk into which 20 to 30 ml of distilled water (spin solution) is poured is 8000 rpm, and 0.02 to 0.03 ml of the dispersion is poured.
Simultaneously with the addition of the dispersion, the recorder is operated to optically measure the amount of carbon black aggregate passing through a fixed point near the outer periphery of the rotating disk by sedimentation and recording that amount as a continuous curve with respect to time. (FIG. 4).
The settling time is converted into the Stokes equivalent diameter by the following Stokes general formula to obtain a corresponding curve of the Stokes equivalent diameter of the aggregate and its frequency (FIG. 5).
[Equation 5]

In Equation (3), d is the Stokes equivalent diameter (nm) of the carbon black aggregate passing through the optical measurement point of the rotating disk t minutes after the start of sedimentation.
The constant K is determined by the spin liquid temperature at the time of measurement, the viscosity, the density difference from the carbon black (the true density of the carbon black is 1.86 g / cm ³ ), and the rotational speed of the rotating disk. In the measurement of the present invention, 25 ml of distilled water was used as the spin liquid, the measurement temperature was 24 ° C., the disk rotation speed was 8000 rpm, and the K value was 260.25.
[0014]
Dst defined measurements ... in the Stokes equivalent diameter of the obtained carbon black aggregate by the above operation, called Dst the Stokes equivalent diameter calculated from the elapsed time T _P until giving the maximum absorbance, the carbon black This is a representative value that represents the aggregate diameter.
[0015]
In the absorbance curve, the Stokes equivalent diameter D ^L ₅₀ (greater than Dst and 1/2 of Dst with respect to the elapsed time T _L (T _L <T _P ) giving a value corresponding to 1/2 of the maximum absorbance. (Aggregate diameter with frequency)), the aggregate size distribution index s is
[Formula 6]
s = 0.84932 × log (D ^L ₅₀ / Dst) (2)
Defined by
As described above, the aggregate size distribution index s defined by the equation (2) is a distribution curve when it is assumed that the Stokes equivalent diameter of the carbon black aggregate measured mathematically by centrifugal sedimentation follows a logarithmic normal. It has almost the same meaning as the standard deviation, and a large value means that the distribution of the aggregate is wide (FIG. 5). FIG. 4 is an example of an elapsed time and absorbance measurement chart by the centrifugal sedimentation method, and FIG. 5 is a diagram showing the relationship between the logarithm of the aggregate value calculated from the elapsed time in the chart of FIG. 4 and the absorbance. . T _{S in} FIG. 4 is an elapsed time (T _P <T _S ) giving a value corresponding to 1/2 of the maximum absorbance, D ^S _{50 in} FIG. 5 is smaller than Dst, and has a frequency of 1/2 of Dst. Is an aggregate diameter.
[0016]
[Action]
The carbon black of the present invention, N ₂ SA is 130m ² / g to over 160 m ² / g or less, DBPA that has the property that 60~100ml / 100g is fundamental.
When DBPA is lower than the range of the present invention, the dispersibility in the rubber matrix is lowered, and the undispersed carbon aggregates in the matrix become the starting point of initial crack generation, and crack growth also easily proceeds. 60 ml / 100 g. The above-mentioned drawbacks become desirable as DBPA becomes higher, but the influence rate of this result gradually decreases, and when it exceeds 100 ml / 100 g, this effect becomes almost saturated in the carbon black of the present invention, and the influence rate is extremely high. To drop. Further, the exothermic numerical value (loss tangent, tan δ) gradually increases, and when it exceeds 100 ml / 100 g, this tendency becomes stronger and the characteristics deteriorate. Also, the hardness characteristics tend to be too high.
[0017]
N ₂ SA is 130m ² / g and beyond range of 160 m ² / g or less, important to maintain a balance of both characteristics of fatigue resistance and mechanical properties (tensile strength) (crack growth resistance, exothermic) , and the conjunction when below 130m ² / g lower limit decreases mechanical properties, if exceeded 160 m ² / g is exothermic to (increase of the loss tangent at 60 ° C.) reduction, carbon black The fatigue resistance, particularly crack growth, is reduced due to the occurrence of poor dispersion.
[0018]
The N ₂ SA / IA ratio characteristic affects the fatigue resistance and adhesion, and if this value falls below 1.1, this characteristic is degraded.
[0019]
The aggregate size distribution index s affects the fatigue resistance and dispersibility of the rubber composition. When the aggregate size distribution index s is less than 0.17, the exothermic property (loss tangent (tan δ)) is increased and the dispersibility is lowered. Therefore, it should be 0.17 or more. However, if s becomes too large, the mechanical properties tend to deteriorate, so carbon black having a value of 0.17 to 0.23 is desirable.
[0020]
The value of Dst / Da, which is another aggregate characteristic, keeps a good balance of mechanical characteristics, fatigue resistance, dispersibility, etc., that is, many of these characteristics decrease when the other increases. However, this is an important factor for solving this problem. When this value is less than 1.25, for example, the contradiction between mechanical characteristics and heat generation characteristics cannot be resolved. However, even if the value of Dst / Da is increased, the improvement effect tends to decrease gradually, and the mechanical characteristics also tend to decrease, so 1.25 to 2.0, more preferably 1.35 to 1. .90 carbon black is preferred.
[0021]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
[0022]
Production Example Production of Carbon Black Production of a hard high structure carbon black according to the present invention was carried out using the same apparatus as described in Japanese Patent Application No. 3-45824 filed by the present applicant.
[0023]
The manufacturing apparatus shown in FIGS. 1, 2 and 3 was used, and the dimensions of each part were as follows.
Flammable fluid introduction chamber 2
Inner diameter 450mmφ
Length 400mm
Oxygen-containing gas introduction pipe 3
400mm long side
Short side 100mm
Cylinder for introducing oxygen-containing gas 4
250mm inside diameter
Length 300mm
Convergence room 8
Upstream inner diameter 370mm
Downstream end inner diameter 80mm
Length 1600mm
Convergence angle 5.3 ° Fuel oil introduction device Fuel oil introduction pipe 72 inner diameter 7mmφ
Inner diameter of high-pressure, high-humidity air introduction pipe 73 13mmφ
Air temperature 300 ℃
Air pressure 3kg / cm ²
Inner diameter of low-pressure, high-humidity air introduction pipe 74 22mmφ
Air temperature 60 ℃
Air pressure 0.5kg / cm ²
Reaction chamber 12
140mm inside diameter
[0024]
Further, the cooling water spraying devices a to h in the reaction continuation / rapid cooling chamber 13 have the same structure as that disclosed in Utility Model Registration No. 102863 (Applicant: Asahi Carbon Co., Ltd.). It was.
[0025]
As the raw material oil and fuel oil, those having the property composition shown in Table 1 were used.
[Table 1]

[0026]
Production method of carbon black of the present invention and comparative carbon black The carbon blacks listed in Tables 2 to 5 are the same as the carbon black production apparatus described above, the feed oil introduction position, the amount of alkali metal (potassium) added to the feed oil, Manufactured by adjusting conditions such as the amount of air, the amount of feedstock introduced, the feedstock feed pressure and temperature, the cooling water introduction position for stopping the reaction, and the amount of fuel introduced.
[0027]
More specifically, the adjustment of the surface area (N ₂ SA) can be performed by changing the ratio of the feedstock introduction amount and the total air introduction amount, and the surface area increases by increasing the ratio of the introduction air amount. . The ratio of the two surface area indices, N ₂ SA / IA, can be controlled by the reaction stop position after the carbon black production reaction, and this value can be obtained by performing further upstream (the time until the reaction stop is short). Increase. The aggregate diameter can be controlled by the position where the raw material oil is introduced, and the aggregate diameter (Dst) is increased by setting the upstream side. In a normal case, the representative diameter (Dst) of the aggregate decreases as the structure decreases. However, the degree of the decrease can be reduced by setting the spray position of the raw material oil upstream. The aggregate distribution can be controlled by adjusting the spray state of the feedstock to be introduced and the amount of fuel to be introduced. When the distribution is widened (s is increased), the temperature and pressure of the feedstock feedstock are reduced. The distribution can be increased by making the spray state worse. Furthermore, the distribution can be broadened by reducing the amount of fuel introduced. In this production, the amount of secondary air in the introduced air, the air temperature, and the shape and number of raw material spray nozzles were constant.
The production conditions of the carbon black according to the present invention and the comparative carbon black are shown in Tables 2 to 5, and the physicochemical characteristics of each produced carbon black are shown in Tables 6 to 9.
[0028]
[Table 2]

[0029]
[Table 3]

[0030]
[Table 4]

[0031]
[Table 5]

[0032]
[Table 6]

[Expression 7]

[0033]
[Table 7]

[Equation 8]

[0034]
[Table 8]

[Equation 9]

[0035]
[Table 9]

[Expression 10]

[0036]
Rubber compounding performance test In order to evaluate the performance of the carbon black shown in Tables 6 to 9, the rubber composition was adjusted according to the compounding ratio shown in Table 10, and the characteristics were tested. The results are shown in Tables 11 to 13 (equal carbon black content).
[Table 10]

MBTS: 2,2′-dibenzothiazyl disulfide IPPD: N-isopropyl-N-phenyl-P-phenylenediamine
[Table 11]

[0038]
[Table 12]

[0039]
[Table 13]

[0040]
The performance evaluation of the rubber properties of each compounded rubber composition was measured under the following test conditions.
Rubber characteristic test conditions (1) Vulcanization condition of the compound: 145 ° C, 30 minutes (2) Abrasion resistance test: A wear test was performed at 25% slip rate using a Lambon abrasion tester. Calculated by
Wear resistance index = (S / T) x 100
Here, S: wear loss of the control sample (Run No. 14) compounded test piece T: wear loss of the test specimen (3) Dematcher fatigue test: using a dematcher bending tester, the number of flexing until crack initiation and 2 mm Crack growth was measured when a sample with a crack in advance was bent 10,000 times.
(4) Dynamic viscoelasticity: The loss tangent (tan δ) was measured under the following measurement conditions using a viscoelastic spectrometer (loss tangent) (Model VES-F-III), Iwamoto Seisakusho Co., Ltd., control carbon black It was expressed as an index against.
Frequency: 50Hz
Dynamic strain rate: ± 1%
Measurement temperature: 25 ° C
Initial load: 160 g weight (5) Adhesion test After vulcanizing a steel cord-rubber composite with a steel cord (1 × 5 × 0.23 mm) plated with brass on an unvulcanized rubber at 150 ° C. for 20 minutes In accordance with the peel test of JIS K 6301 7, the peel test of the embedded steel cord and the rubber layer was conducted, and the adhesion was evaluated by the coating ratio of the adhered rubber remaining on the steel cord. A is the state where most of the peeled steel cord surface is covered with the rubber layer, B is the state where the surface of the steel cord is visible in some places, C is the state where the ratio of the steel cord surface and the rubber layer is approximately equal, and the steel cord surface Is indicated as D, and the state where most steel cord surfaces are visible is indicated as E.
The tensile rate in the adhesion test was 25 mm / min.
(6) Dispersibility In accordance with the method described in the September 1969 issue of Rubber World Vol. 160, No. 6, pp. 63-70 (author: HE Wraithback et al.), The surface of the compounded rubber was increased by 32 times. Using the enlarged photograph, it was visually determined which rank of the standard sample divided into 10 to 1 corresponds. In the case of a sample determined to be in the middle, for example, between 7 and 8, 7.5 is displayed.
(7) Other rubber properties: Measured according to the methods described in JIS K6300-1974 and K6301-1975.
[0041]
[Evaluation]
The effects of the carbon black of the present invention will be described from the results of measurement results (Tables 11 to 13) of rubber compositions obtained by blending the carbon blacks of Examples and Comparative Examples having the physicochemical characteristics shown in Tables 6 to 9 with rubber. .
Run No. The carbon blacks of 1 to 5 are according to the present invention, and run no. Nos. 6 to 13 are comparative examples, Run No. 1 that deviate from one or two of the specific requirements of the present invention. 14 is a control carbon black (trade name Asahi # 80, ISAF grade carbon black, manufactured by Asahi Carbon Co., Ltd.).
Run No. 6 is an example in which DBPA exceeded the upper limit of the present invention. On the other hand, 7 is a comparative example that is below the lower limit. Run No. 8 is Run No. Although the basic characteristics are almost the same as those of No. 2, the Dst / Da value in the aggregate characteristics falls below the range of the present invention. No. 9 is a comparative example exceeding the upper limit of the surface area range. On the contrary, 10 is a comparative example that is below the lower limit of the surface area range. Run No. 11 is Run No. Although the basic characteristics are almost the same as those of No. 4, the aggregate distribution index s is outside the scope of the present invention. 12 is RunNo. Although it has almost the same basic characteristics as No. ₂ , it is an example outside the scope of the present invention in terms of the surface area ratio, N ₂ SA / IA. Run No. 13 is Run No. 5 is a comparative example which is almost the same basic characteristic as 5, but is out of the scope of the present invention due to the requirements of both N ₂ SA / IA ratio and s.
[0042]
{Circle around (1)} Evaluation for Tensile Strength Run No. with a DBPA value lower than the lower limit of the range of the present invention. In No. 7, the tensile strength characteristics are greatly reduced.
(2) Evaluation of wear resistance Run No. Although the Lambourn abrasion resistance index of carbon black No. 7 is greatly reduced as compared with other carbon blacks, no significant difference is observed among other carbon blacks. However, Run No. having a large surface area outside the scope of the present invention. The index of 9 in carbon black is well below the characteristic value expected from its surface area.
{Circle around (3)} Evaluation for Dematcher Bending Test Run No. 2 in which the DBP oil absorption decreased outside the scope of the present invention. In No. 7, a decrease in dispersibility was observed, and accordingly, the number of flexures until the occurrence of cracks decreased, and crack growth also increased. This trend indicates that N ₂ SA / IA exceeds the scope of the present invention and has a large Run No. 9 is also seen.
In addition, the Run No. with a small aggregate size distribution index outside the scope of the present invention. 11 also shows a decrease in dispersibility and a decrease in flex cracking properties.
(4) Hardness Evaluation Although no significant difference was found in the hardness of the examples and comparative examples, the run No. in which the DBP oil absorption increased outside the scope of the present invention was high. In 6, the numerical value becomes large, which causes a problem in workability.
(5) Evaluation of dynamic viscoelasticity Although there is no significant difference in the characteristics of dynamic viscoelasticity (loss tangent, tan δ), run no. 6 and N ₂ SA deviated in the large direction. 8 or Run No. on the side where the aggregate distribution index s is smaller than the range of the present invention. 11 and Run No. 13, this value tends to be large, which means that heat is stored in the compounded rubber composition subjected to repeated deformation, and as a result, a substance (steel, various resins, etc.) that reinforces the rubber composition and This is not preferable because it causes separation from the rubber composition.
(6) Evaluation of adhesion The adhesion between the compounded rubber composition and the reinforcing material (evaluated by brass plating steel in the present invention) is the surface property of carbon black, especially the value of N ₂ SA / IA within the scope of the present invention. Run No. with a requirement of 1.10. 12 and Run No. In FIG. 13, a decrease in performance is observed.
(7) Evaluation of dispersibility The dispersibility was measured according to Run No. whose DBP oil absorption was below the range of the present invention. 7, Run No. N ₂ SA exceeded the scope of the present invention. 9, the aggregate size distribution index s was less than that of the present invention. 11 and Run No. It is observed that there is a reduction in 13 carbon black formulations.
[0043]
【effect】
As described above, the rubber composition containing the carbon black of the present invention has a high degree of wear resistance, and exhibits excellent performance in crack resistance, crack growth resistance and bending resistance, Since the adhesive property to the rubber reinforcing material can be given good characteristics, it is particularly useful as a rubber for functional parts.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional front view of an example of an apparatus suitable for producing carbon black of the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is a partially enlarged view showing the frontal head and the fuel introduction device of FIG. 1;
FIG. 4 is an example of a measurement chart of elapsed time and absorbance by a centrifugal sedimentation method.
FIG. 5 is a diagram showing the relationship between the logarithm of the aggregate value calculated from the elapsed time in the chart of FIG. 4 and the absorbance.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Carbon black reactor 2 Flammable fluid introduction chamber 3 Oxygen-containing gas introduction pipe 4 Oxygen-containing gas introduction cylinder 5 Rectifier plate 7 Fuel oil spraying device 8 Converging chamber 9 Burner tile 10 Raw material oil spraying device 11 Raw material oil introduction chamber 12 Reaction Chamber 13 Reaction continuation and quenching chamber 71 Fuel oil spray tip 72 Fuel oil introduction tube 73 Oxygen-containing gas introduction tube 74 Oxygen-containing gas introduction tube 75 Oxygen-containing gas conduit 76 Oxygen-containing gas conduit a Quenched water injection spray device b Quenched water Press-in spraying device c Quenched water press-in spraying device d Quenched water press-in spraying device e Quenched water press-in spraying device f Quenched water press-in spraying device g Quenched water press-in spraying device h Quenched water press-in spraying device A _P Absorption peak value T _P Up to peak value elapsed small elapsed time Dst Stokes equation than T _P in absorbance time T _L 1 / 2A _P, an aggregate size D ^L ₅₀ Stokes equation when the T = T _P, = Aggregate diameter when the T _L (in 1 / 2A _P, aggregate diameter satisfying D ^L _50> Dst)

Claims (3)

In the hard carbon black having basic characteristics such that the nitrogen adsorption specific surface area (N ₂ SA) exceeds 130 m ² / g and is 160 m ² / g or less, and the dibutyl phthalate (DBP) oil absorption (DBPA) is 60 to 100 ml / 100 g.
1) The ratio of N ₂ SA to iodine adsorption (IA) (N ₂ SA / IA) is 1.10 or more 2) The aggregate characteristics by centrifugal sedimentation analysis are
a. The ratio Dst / Da between the most frequent value (Dst) of the aggregate and the calculated aggregate diameter (Da) calculated by the equation (1) is 1.25 or more.

b. The aggregate size distribution index s calculated by the expression (2) from Dst and D ^L ₅₀ having a frequency larger than Dst and ½ of Dst is 0.17 or more.
s = 0.84932 × log (D ^L ₅₀ / Dst) (2)
Carbon black for compounding rubber with functional parts. The carbon black for blending functional parts rubber according to claim 1, wherein DBPA is more than 70 ml / 100 g and less than 90 ml / 100 g, and Dst / Da is 1.35 to 1.90. A rubber composition for functional parts, comprising 10 to 150 parts by weight of carbon black for blending functional parts according to claim 1 or 2 with respect to 100 parts by weight of a rubber component comprising natural rubber and / or synthetic rubber.

Images