From the viewpoint of simple and inexpensive image production, inkjet recording has been used in a variety of printing fields such as coating materials for plastics, paper, woodwork, inorganic and materials, adhesives, printing inks, printed circuit boards, and electrical insulation. As the inkjet recording method, there is an UV-curable inkjet method wherein droplets of UV-curable ink are landed on a recording medium and then cured by irradiation with ultraviolet rays to form an image. Recently, the UV-curable inkjet method has been attracting attention for its capability of forming images having high rubfastness and adhesiveness even on recording media which lack ink absorbing properties.
However, the image forming methods using the UV-curable inkjet systems have the drawback of poor image quality due to failure to prevent combining of neighboring dots during high-speed recording such as single pass recoding using a line recording head or high speed serial recording. Moreover, in the case of color image recording, color blending occurs and thus image quality decreases. Furthermore, since the light amount of UV irradiation is small during high-speed printing, the curability or adhesiveness of ink droplets may not be sufficient and thus there is a problem in image fastness such as surface tackiness or reduced rubfastness.
As a technique of preventing “combining of neighboring dots” during inkjet recording regardless of the kind of recording medium, it is known to use an UV-curable ink containing a gelling agent (see PTL 1 and PTL 2).
For example, PTL 1 discloses a radiation-curable hot-melt inkjet ink containing a curable monomer and a gelling agent. PTL 2 discloses a phase change ink containing a white pigment, a curable monomer, a gelling agent, and a photopolymerization initiator, wherein a radical polymerizable compound is disclosed as the curable monomer.
As a technique of preventing reduction in “image fastness” during high-speed printing, it is known to use an UV-curable ink containing a radical polymerizable compound having a hydroxyl group (see PTL 3 and PTL 4).
For example, PTL 3 discloses an active energy ray-curable ink for inkjet, which contains 2-hydroxy-3-phenoxypropyl acrylate having a hydroxyl group. PTL 4 discloses a technique of applying a radical polymerizable compound having a hydroxyl group as an undercoating liquid in advance.