There is provided a radiation curable ink composition for ink jet, which contains a polymerizable compound, a polymerization initiator, and a thioxanthone sensitizing agent having a molecular weight of 300 or more, in which the polymerizable compound includes a monofunctional polymerizable compound and a difunctional polymerizable compound, the polymerization initiator includes phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, the monofunctional polymerizable compound includes a hydroxyl group-containing monofunctional polymerizable compound, and a content of the difunctional polymerizable compound is 30% by mass or more with respect to a total amount of the ink composition.

There is provided a radiation curable ink composition for ink jet, which contains a polymerizable compound, a polymerization initiator, and a thioxanthone sensitizing agent having a molecular weight of 300 or more, in which the polymerizable compound includes a monofunctional polymerizable compound and a difunctional polymerizable compound, the polymerization initiator includes phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, the monofunctional polymerizable compound includes a hydroxyl group-containing monofunctional polymerizable compound, and a content of the difunctional polymerizable compound is 30% by mass or more with respect to a total amount of the ink composition.

Glycerin and sodium polyacrylate may be mixed at a first mixing speed for a first mixing time. Free water and a fibrillated cellulose mixture may be added to second mixer and mixed at a second mixing time speed for a second mixing time. The glycerin and the sodium polyacrylate may be mixed with the free water and fibrillated cellulose mixture at a third mixing speed for a third mixing time. One or more of sodium citrate, sodium bicarbonate, and sodium benzoate may be added and mixed at a fourth mixing speed for a fourth mixing time. Sodium carbonate may be added and mixed at a fifth mixing speed for a fifth mixing time. A surfactant mixture and optionally fragrances may be added and mixed at a sixth mixing speed for a sixth mixing time to form a final mixture, which may be transferred to molds, dehydrated, and removed.

Glycerin and sodium polyacrylate may be mixed at a first mixing speed for a first mixing time. Free water and a fibrillated cellulose mixture may be added to second mixer and mixed at a second mixing time speed for a second mixing time. The glycerin and the sodium polyacrylate may be mixed with the free water and fibrillated cellulose mixture at a third mixing speed for a third mixing time. One or more of sodium citrate, sodium bicarbonate, and sodium benzoate may be added and mixed at a fourth mixing speed for a fourth mixing time. Sodium carbonate may be added and mixed at a fifth mixing speed for a fifth mixing time. A surfactant mixture and optionally fragrances may be added and mixed at a sixth mixing speed for a sixth mixing time to form a final mixture, which may be transferred to molds, dehydrated, and removed.