soapless soap (English spelling) soaplesssoap

Japanese: soapless soap（英語表記）soaplesssoap

For example, sodium higher fatty acids are salts of weak acids and strong bases, so their aqueous solutions are weakly alkaline. Furthermore, in hard water containing inorganic salts such as calcium, magnesium, and barium, they combine with these metal ions to form water-insoluble salts (metal soaps), which do not function as cleaning agents. Therefore, sodium alkylbenzene sulfonate and sodium salts of higher alcohol sulfates have been synthesized as alternatives, and have appeared on the market under the name soapless soap. Currently, various synthetic detergents are manufactured and used, and soap production once reached 380,000 tons in 1959 after World War II, but production has now been halved as it has been replaced by synthetic detergents.

From [Neutral detergent]

…In contrast, alkylbenzene sulfonates and aliphatic sulfates are salts of strong acids and strong bases, so they are neutral in aqueous solution and retain their cleaning power even in hard water. Such detergents are called neutral detergents, or soapless soaps. Synthetic detergents [Uchida Yasuzo]. …

*Some of the terminology that mentions "soapless soap" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…たとえば高級脂肪酸ナトリウムは弱酸･強塩基の塩であるため，その水溶液は弱アルカリ性であり，さらにカルシウム，マグネシウム，バリウムなどの無機塩を含有する硬水中では，これらの金属イオンとで水に不溶性の塩(金属セッケン)をつくり，洗浄剤としての機能を果たさない。そこでこれに代わるものとしてアルキルベンゼンスルホン酸ナトリウム，高級アルコール硫酸エステルナトリウム塩などが合成され，ソープレスソープsoapless soapという名称で市場に登場してきた。現在さまざまな合成洗剤が製造され，利用されており，かつてセッケンは第2次大戦後1959年には38万tの生産量をあげたが，現在では合成洗剤に代替され，生産量は半減している。…