1. Field of the Invention
The present invention relates to a novel curable resin, and more particularly to a novel curable resin which cures upon irradiation of activation energy rays such as ultraviolet rays, electron beams or the like and exhibits a high curing rate and a good adhesion property when used as a binder for printing inks or coating materials.
2. Description of Prior Art
Radiation-curable resins, which cure upon irradiation of activation energy such as ultraviolet rays and electron beams, have been given attention because of their advantageous features such as high curing rate, lower energy requirement, low environmental pollution, and therefore extensive investigations have been made on development of their applications in various fields such as printing inks, coating materials, adhesives and the like.
The curable resins are used usually as a blend with a radical polymerizable monomer such as trimethylolpropane triacrylate and optionally a radical polymerization initiator, a pigment and the like, if desired.
Among the components of the printing ink, coating material or the like, radiation-curable resins are particularly important because they give controlling influences on various properties of the resulting composition such as curing rate, viscosity, and film performance.
While multi-functional oligomers such as epoxy acrylates, urethane acrylates, alkyds or polyester acrylates are used as a radiation-curable resin, no radiation-curable resin has been known yet that is satisfactory for all of curing rate, film performance and adhesion property. For example, epoxy acrylates and urethane acrylates have high viscosities for their molecular weights and vary greatly in their viscosity. When they are used in printing inks, pigments disperse therein poorly. Because epoxy acrylates contain hydroxyl groups as well in the resin in the same number as the acryloyl groups, the resins are highly hydrophilic and thus they have a low emulsification suitability when used in, for example, printing inks. On the other hand, polyester acrylates have low curing rates and are susceptible to oxygen in the air. Conventional films obtained by photo-setting shrink to a greater extent during the setting and are disadvantageous in that their adhesion is poor when bonded on metals and plastics such as polyolefin films, although they have no problem when printed on paper.
Japanese Patent Publication Laid-Open No. 124133/1974 discloses resins obtained by esterifying DCPD/allyl alcohol copolymers with acrylic acid or methacrylic acid. This type of resin has a good adhesion property but has a poor curability, and often causes misting when used in printing inks. While improvement of characteristics of resins and increase of productivity have recently been strongly desired, it appears that the conventional multi-functional oligomer-type resins are difficult to meet such requirements. Therefore, it has been strenuously demanded to develop a novel radiation-curable resin which can form films having a high curing rate and a high performance and can be produced at a high productivity.