Curable white inkjet ink
The present invention pertains to a radiation-curable white inkjet ink and, more particularly, to a radiation-curable inkjet white ink comprising a specified titanium dioxide with at least two dispersants. The first is an acidic polyester dispersant and the second is an acrylic structured copolymer dispersant. Ink sets containing the white inks are also described.
1. A radiation curable ink composition for ink jet recording comprising
a. at least one titanium dioxide white pigment
b. a polymerizable vehicle
c. at least one additional ingredient selected from the group of consisting of a colorant, a photosensitizer, a photosynergist, a photoinitiator and a surfactant,
d. at least one of the titanium dioxide pigments is alumina-treated and stabilized by a mixture of pigment dispersants consisting essentially of
i. at least a first acidic polyester dispersant, and
ii. at least an second acrylic structured copolymer dispersant,
wherein the radiation curable ink composition is substantially free of solvent, and wherein the polymerizible vehicle is a mixture of mono-functional and multi-functional monomers and the mixture of monomers is at least 50 weight % by weight of the total weight of the ink.
2. The radiation curable ink composition of claim 1 ratio of the acidic polyester dispersant and acrylic structured copolymer dispersant dispersants is 1:10 to 10:1 by weight.
3. The radiation curable ink composition of claim 1 where the structured copolymer dispersant is a structured block copolymer dispersant chosen from AB, BAB and ABC block polymers.
4. The radiation curable ink composition of claim 1 where the structured copolymer dispersant is a graft copolymer.
5. The graft copolymer of claim 3 where at least one of the monomers used can contain a UV reactive component.
6. The radiation curable ink composition of claim 1 where the composition has no added conductive agents and has a conductivity of less than 0.075 micro Siemans.
7. An ink set comprising the radiation curable ink composition of claim 1 and plurality of colored, pigmented inks.
8. A method for ink jet printing onto a substrate, comprising the steps of:
(a) providing an ink jet printer that is responsive to digital data signals;
(b) loading the printer with a substrate to be printed;
(c) loading the printer with a radiation curable white inkjet ink set as set forth in claim 7 ; and
(d) printing onto the substrate using said inkjet ink or inkjet ink set, in response to the digital data signals, and forming thereby a printed article.
9. The method of claim 8 , wherein the substrate is selected from the group polycarbonate, polyvinyl chloride board, pressure sensitive adhesive-backed vinyl, polystyrene, foam boards and plywood.
10. The method of claim 8 or claim 9 , further comprising the step of exposing the printed article to radiation suitable for curing the ink printed thereon.
11. The method of claim 10 , wherein the radiation is ultraviolet light.