There are provided a compound represented by general formula (1), a photopolymerization initiator comprising this compound, a photocurable composition having this photopolymerization initiator and a photocurable compound as essential components, and a cured product formed by curing this photocurable composition, wherein in formula (1), R.sup.1 and R.sup.2 each independently represents an alkyl group or the like; R.sup.3 to R.sup.5 each independently represent a hydrogen atom, an alkyl group or the like; X.sup.1 represents a single bond or an alkylene group; and X.sup.2 represents a bonding group represented by general formulas (2) to (4), and wherein n represents an integer of 1 to 6, when n is an integer of 1, Y represents an alkyl group, an aryl group or the like.

The present invention relates to a series of novel multifunctional mono- and bis-acylphosphine oxides, which are useful as photoinitiators, and to photocurable compositions comprising said photoinitiators.

A photoinitiator selected from the group consisting of an acylphosphine oxide, a α-hydroxy-ketone and a α-amino-ketone, characterized in that the photoinitiator includes at least one aliphatic disulfide as functional group.

A radiation curable inkjet ink comprising a polymerizable compound and a photoinitiator, characterized in that the photoinitiator comprises a functional group selected from the group consisting of an aliphatic thio-ether and an aliphatic or a (hetero)aromatic disulfide.

An acyl phosphine oxide initiator wherein the acyl group is selected from the group consisting of a benzoyl group substituted by an urea group or an oxalylamide group; a 2,6-dimethyl benzoyl group substituted in position 3 by an urea group or an oxalylamide group; a 2,6-dimethoxy benzoyl group substituted in position 3 by an urea group or an oxalylamide group; a 2,4,6-dimethyl benzoyl group substituted in position 3 by an urea group or an oxalylamide group; and a 2,4,6-trimethoxybenzoyl group substituted in position 3 by an urea group or an oxalylamide group.

There are provided a compound represented by general formula (1), a photopolymerization initiator comprising this compound, a photocurable composition having this photopolymerization initiator and a photocurable compound as essential components, and a cured product formed by curing this photocurable composition, wherein in formula (1), R.sup.1 and R.sup.2 each independently represents an alkyl group or the like; R.sup.3 to R.sup.5 each independently represent a hydrogen atom, an alkyl group or the like; X.sup.1 represents a single bond or an alkylene group; and X.sup.2 represents a bonding group represented by general formulas (2) to (4), and wherein n represents an integer of 1 to 6, when n is an integer of 1, Y represents an alkyl group, an aryl group or the like.

Certain phosphonate compounds useful as photoinitiators are provided herein.

An inkjet ink composition comprising: one or more UV curable monomers; oligomers having one or more acrylic groups; one or more photoinitiators; one or more surfactants; and paraffin wax.

Thiol modified acylphosphine oxide photoinitiators exhibiting improved smell and extractability are disclosed. Also disclosed is a UV curable inkjet ink containing an acylphosphine oxide photoinitiator and a polymerizable compound, wherein the acylphosphine oxide photoinitiator includes one or more acyl groups substituted by a thiol.

An aqueous curable composition includes a water-soluble photopolymerization initiator having a structure in which one or more carbonyl groups further directly bond to an aromatic ring of an aromatic acyl group that bonds to a phosphorus atom in an acylphosphine oxide structure, water, and a polymerizable compound. A novel water-soluble photopolymerization initiator is a compound represented by formula 1-1 or formula 2-1.

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