クロム皮革に対する直接染料クルクミンSの染着性

摘要

皮革はたんばく質であるコラーゲン線経から成るが，その染色は鞣剤のタンニンやクロムの性質が染着性に影響を与える．クロム革の場合，従来から酸性染料などを用いて表面染色がなされているが，現在では染色堅牢度を考慮し，それに先立ち浸透染色が併用されるため，染色工程を複雑にしている．本報告では，クロム革の染色に直接染料クルクミンSを用い，その染着性について染色皮革のK／S値-λ曲線と顕微鏡写真を元に検討した．その結果，クルクミンSは長分子構造をもつアニオン性の表面型染料であるが，皮革表面に多く含有する金属イオンのクロムと配位結合するため染色初期から中期にかけて見かけ上は酸性染料と同様の挙動が認められ低pHの染浴において高い染着性を示した．同時に，皮革表面でのクロムとの結合が飽和状態以降においても色素構造中のスルホン酸アニオンと皮革コラーゲンのアミノ基カチオンとのイオン結合が長時間で徐々に増加することも明らかになった．クルクミンSの種々染料濃度を用いた実用染色では，染料濃度が高くなるほど赤味が強くなる傾向が認められたが，吸収ピーク波長（420nm）のK／S値にはほとんど差は見られなかった．なお，染色皮革の耐光堅牢度，および洗濯（乾，湿），汗，摩擦堅牢度の測定を行ったところ，アルカリ性の汗，摩擦堅牢度がやや低くなるものの，その他の堅牢度はほとんど4－5の優れた結果を示した．%Leather consists of protein collagen fibres and the dyeing properties of leather are influenced by tanning agents such as tannin and chrome. Surface dyeing of chrome leather has traditionally been performed with acid dyes. Currently, however, penetration dyeing is employed prior to surface dyeing to improve colour fastness, thereby resulting in a complicated process. In this paper, we investigated the dyeability of chrome leather using a direct dye, curcumin S, on the basis of K/S value-λ curve and microscopic photographs of the dyed leathers. Consequently, we have found that curcumin S is an anionic surface-dyeing-type dye with a long molecular structure and that it forms coordinate bonds with chromium metal ions, which are present in large quantities on the leather surface. Therefore, curcumin S behaves like an acid dye during the initial and middle stages of dyeing and therefore exhibits excellent dyeing properties in a dyeing bath with a low pH. In addition, when the bonds of the pigment on the surface and chrome are saturated, ionic bonds between the sulfonic acid anion in the dye structure and the amino cation in leather collagen gradually develop over a long period of time.rnIn the practical dyeing of chrome leather in solutions with various curcumin S. concentrations, the surface colour of dyed chrome leather tends to become more reddish as the dye concentration is increased. However, the K/S value of the absorption peak wavelength (420 nm) changed only slightly. We also measured the colour fastness, of the dyed leather, to light, washing (dry and wet), perspiration and rubbing. The evaluations showed fairly good results, with ratings of 4-5, except in cases of exposure to alkaline sweat or rubbing, where the colour fastness decreased slightly.