FIELD OF THE INVENTION

The present invention is directed to actinic radiation curable compositions which undergo free radical polymerizations upon exposure to actinic radiation, such as the emission of a UV light source. The compositions include semiconductor metal oxide materials that initiate curing and improve the color of the compositions. The semiconductor metal oxide materials may provide a replacement for all or part of the photoinitiator materials that may be present in actinic radiation curable compositions.

BACKGROUND

Actinic radiation curable compositions, such as inks, primers, coatings and adhesives, are commonly employed in printing operations such as flexo, gravure, digital, among others. Such compositions include polymerizable materials, such as ethylenically unsaturated monomers and oligomers, photoinitiators, colorants, inhibitors, waxes, etc. The compositions undergo curing when exposed to actinic radiation. The curing involves a free radical polymerization of the ethylenically unsaturated monomers and oligomers present in the compositions. The photoinitiators start a polymerization reaction when the composition is exposed to a reaction-starting dose of actinic radiation. The actinic radiation is emitted by an actinic light source, such as for example UV-light, which can be provided by a high- or medium-voltage mercury bulbs, a xenon bulb, a carbon arc lamp, a metal halide bulb, a LED light source (i.e., UV-LED lamp) and/or visible light, such as sunlight. Electron beam radiation may also be used to initiate curing of such compositions, in which case the compositions do not have to include photoinitiators.

One of the problems that arise from the inclusion of photoinitiators in actinic radiation curable compositions is that after printing the compositions onto substrates such as food packaging and then curing same, photoinitiator residues may migrate out of the compositions over time. Migratable residues may contaminate the goods packaged within the printed packaging, which is particularly problematic if the goods are foods, medicines, and the like. Further, migratable components may contaminate the environment outside of the packaging. Many photoinitiators are classified as toxic materials, and thus they cannot be included in compositions printed on items that come in direct contact with food.

While high energy electron beam (E-beam or EB) curing may not require the presence of a photoinitiator, this curing method may not provide full and complete curing of ethylenically unsaturated monomers and oligomers. Thus, E-beam curing does not solve the problem of migratables.

It would be advantageous and beneficial to provide actinic radiation curable compositions that are more eco-friendly, renewable, and environmentally sustainable.

References that may be of interest include:

U.S. Pat. Nos. 3,083,113, 4,959,297, 5,212,212, 6,267,949, 8,512,467 and 8,623,220; U.S. Patent Appl. Publ. Nos. 2005/0153068, 2007/0259986, 2008/0306201, 2010/0074837, 2012/0177928, 2014/0183141 and 2017/0216821; WO 2011/116972 and EP 2 368 919 A1;

The following non-patent literature documents:Azan V, Lecamp L, Lebaudy P, Bunel C.,Simulation of the Photopolymerization Gradient Inside a Pigmented Coating—Influence of TiO2Concentration on the Gradient; Prog Org Coat 2007:58(1):70-75;Danu S, Darsono, Marsongko,UV-Curing of Titanium Dioxide Pigmented Epoxy Acrylate Coating on Ceramic Tiles; Journal of the Ceramic Society of Japan 2008:116(1356):896-903;J. A. Burunkova, I. Yu. Denisyuk, and S. A. Semina,Self-Organization of ZnO Nanoparticles on UV-Curable Acrylate Nanocomposites; Journal of Nanotechnology, vol. 2011, Article ID 951036, 6 pages, 2011. doi:10.1155/2011/951036;Nakayama, N. & Hayashi, T.,Preparation and Characterization of TiO—ZrO2and Thiol-Acrylate Resin Nanocomposites with High Refractive Index via UV-Induced Crosslinking Polymerization; Compos. Part A 38, 1996-2004 (2007);Trouillas, P, et al., (2016),Stabilizing and Modulating Color by Copigmentation: Insights from Theory and Experiment; Chem. Rev., 11; 116(9):4937-82.

SUMMARY OF THE INVENTION

Described herein are actinic radiation curable compositions, such as inks and coatings that are curable by exposure to actinic radiation. The compositions comprise a polymerizable component selected from an ethylenically unsaturated monomer, an ethylenically unsaturated prepolymer, and combinations thereof; and

a semiconductor metal oxide material, optionally present as a composite comprising the semiconductor metal oxide material and another composite forming material.

In one aspect, wherein the semiconductor metal oxide is as defined in formula (I):
MxOyHz(I)wherein M is a metal selected from Ti, Zn, Mg, Ce, Bi, and Fe;O is oxygen;H is a halogen;x is an integer of 1 to 3;y is an integer of 1 to 3; andz is an integer of 0 to 3.

Combinations of metal oxides as defined in formula (I) may be used.

In one aspect, the semiconductor metal oxide material is present as a composite of the semiconductor metal oxide material and another composite forming material selected from pigments, clays, humic acid, humic acid polymers, and photoactive substances that are capable of responding to light or electromagnetic radiation, such as optical brighteners and photoinitiators.

In one aspect, the semiconductor metal oxide semiconductor metal oxide material is present as a composite of the semiconductor metal oxide material and a pigment selected from carbon black, halloysite clays, aluminosilicate clays, magenta pigments such as lithol rubine pigments, and combinations thereof.

In one aspect, the semiconductor metal oxide material is present as a composite of the semiconductor metal oxide material and another composite forming material selected from carbon black, aluminosilicate clays and combinations thereof.

In one aspect, the polymerizable component comprises an ethylenically unsaturated material selected from one or more of an ethylenically unsaturated monomer and an ethylenically unsaturated prepolymer.

In one aspect, the ethylenically unsaturated prepolymer of the polymerizable component is selected from epoxyacrylates, acrylated oils, urethane acrylates, polyester acrylates, polyether acrylates, vinyl/acrylic oligomers, polyene/thiol systems, and combinations thereof.

In one aspect, the actinic radiation curable compositions further comprise one or more photoinitiators.

In one aspect, the actinic radiation curable compositions include photoinitiators in lesser amounts than the amounts that are included in actinic radiation curable compositions that do not include the semiconductor metal oxide materials described herein.

In one aspect, the actinic radiation curable compositions exhibit improved color when compared to actinic radiation curable compositions that do not include the semiconductor metal oxide materials described herein.

In one aspect, actinic radiation curable compositions are curable by exposure to sources of actinic radiation, such as, for example, visible light, such as sunlight, and UV-light. The UV-light for curing may be provided by one or more of a high-voltage mercury bulb, a medium-voltage mercury bulb, a xenon bulb, a carbon arc lamp, a metal halide bulb, and a UV-LED light source.

In one aspect, the actinic radiation curable compositions are inks and coatings suitable for application by process such as, for example, lithographic, flexographic, gravure, screen, spray, rod, spray, curtain coater and digital.

As used in the present application the “semiconductor metal oxide” is a material that, in the presence of a polymerizable, ethylenically unsaturated component and when exposed to a reaction-starting dose of actinic radiation, creates a free radical polymerization reaction pathway in the polymerizable, ethylenically unsaturated component, the creation of the pathway being solely attributable to the metal oxide, and without loss of the semiconductor metal oxide during the photopolymerization process. The activity is catalytic in that the metal oxide composite is not consumed and does not undergo an irreversible chemical change and is available to assist with additional radical reactions.

The initiation of a free radical polymerization reaction in the polymerizable, ethylenically unsaturated component by the semiconductor metal oxide and which is solely attributable thereto can be demonstrated by a Differential Scanning calorimetry (DSC) plot of heat flow vs. time generated for a reaction system that has been exposed to a reaction-starting dose of actinic radiation, wherein the reaction system includes an ethylenically unsaturated material and a semiconductor metal oxide material and whereby the system is free of photoinitiators (i.e., not including photoinitiators), wherein the DSC plot shows the generation of heat (i.e., heat flow) indicative of a free radical polymerization reaction that is or has taken place in the system.

Photo DSCs are acquired using a TA DSC Q2000 w/TA PCA (Photocalorimeter Accessory) Accessory w/012-64000 Hg Lamp. The pans used are T Zero Aluminum pans with one bare pan as the reference pan and a sample pan that contains between 10-15 mg of either the non-photoreactive or photoreactive system. The sample and reference pans are irradiated with light for 0.5 seconds to 2 seconds with the remainder of a 60 second interval being well time over the course of 10 total irradiation cycles. The lamp intensity may be set for 1% to 5% (2.0 W to 10 W) and at a temperature of 25° C. (isothermal). The PCA Accessory contains a 200 W Hg High Vapor Pressure Lamp with a spectral output of 320 to 500 nm. To evaluate the photoactivity of a BGA, the enthalpy (J/g) of the system per cycle compared to a baseline monomer system was considered. In this case, monomers serve as the baseline and monomer blended with BGA as the photoreactive system.

An Example of a DSC plot is provided herewith as the FIGURE and demonstrates enhanced curing activity for a composite of a semiconductor TiO2metal oxide and carbon black (BGA1) in 1,6-hexanediol diacrylate without a photoinitiator being present. The activity is catalytic in that the metal oxide composite is not consumed and does not undergo an irreversible chemical change and is available to assist with additional radical reactions.

The above definition does not exclude the inventive actinic radiation curable compositions described herein that include semiconductor metal oxide materials and one or more photoinitiators. In such compositions, the photoinitiators initiate curing upon actinic radiation exposure.

It has been found that actinic radiation curable compositions, optionally including photoinitiators, and semiconductor metal oxides undergo a more complete and thorough cure than compositions that contain only photoinitiators. Also, compositions including photoinitiators and semiconductor metal oxides exhibit improved color properties after curing. Such properties include improved color appearance, density, and gloss, which improvements are measurable. The cure and color improvements are demonstrated in the examples that follow.

As best understood, and not wishing to be bound by any theory, reaction pathway creation as mentioned in the above definition is not the initiation of a free radical polymerization in the manner that organic photoinitiators initiate free radical photopolymerization.

It should further be understood that the actinic radiation curable composition described herein can be cured by energy from an electron beam apparatus (E-beam). In such instances, photoinitiator components may not be present in the compositions. As shown in the examples that follow, inks and coatings that include the semiconductor metal oxides exhibit improved curing when they include the semiconductor metal oxides.

The described actinic radiation curable inks and coating compositions are more environmentally friendly than compositions that rely solely on photoinitiator to initiate curing. The semiconductor metal oxide materials contained in the inks and coating compositions operate according to green-technology principles (e.g., photocatalysis and radiation enhancement). The semiconductor metal oxide materials (considered to be metal oxide semiconductor materials) are renewable and sustainable. By including the semiconductor metal oxide materials (and composites thereof) in the actinic radiation curable compositions, the amounts and concentrations of traditional photoinitiators can be reduced.

