Deodorization of N-Vinyl Monomers

Various N-vinyl monomers such as N-vinyl-2-pyrrolidone (NVP) have an unpleasant odor. The unpleasant odor of NVP has been a particular problem since its introduction as a monomer into the radiation cure coatings (RC) market. In such coating techniques the monomer must be spread over a relatively large area, and the unpleasant odor associated with NVP cannot be contained.

This invention provides deodorized compositions comprising at least one odoriferous N-vinyl monomer and a sufficient deodorizing amount of an alkali metal bisulfite (especially NaHSO.sub.3).

The invention further provides a method for deodorizing an odoriferous N-vinyl monomer comprising incorporating into the monomer a sufficient deodorizing amount of an alkali metal bisulfite (especially NaHSO.sub.3).

Particular odoriferous N-vinyl monomers include N-vinyl caprolactam, N-vinyl carbazole and, especially, N-vinyl-2-pyrrolidone. When N-vinyl-2-pyrrolidone is deodorized in accordance with the present invention, preferred deodorizing amounts of NaHSO.sub.3 are from about 0.05% to about 2% by weight, especially from about 1% by weight to about 2% by weight, based upon the weight of N-vinyl pyrrolidone, particularly depending upon the manner in which the sodium bisulfite is incorporated into the N-vinyl pyrrolidone and the desired degree of deodorization.

Preferably, the NaHSO.sub.3 is incorporated into the odoriferous N-vinyl monomer by admixture and heating for a sufficient time and temperature to accomplish the desired degree of deodorization. Preferably, the NaHSO.sub.3 is substantially dissolved in the deodorized composition.

The alkali metal bisulfite may be mixed with an N-vinyl monomer, per se, or with a composition comprising an N-vinyl monomer and other ingredients. For example, NaHSO.sub.3 may be incorporated into a radiation curable coating composition comprising about 10-15% by weight of N-vinyl-2-pyrrolidone and the remainder being essentially a pigment such as TiO.sub.2 and copolymerizable monomer such as one or more acrylic monomers.

Four samples of commercially available NVP monomer (V-Pyrol, a tradename of GAF, radiation cure grade) were prepared in the lab to evaluate odor reduction by addition of sodium bisulfite. The lab preparations contained 2% NaHSO.sub.3, 1% NaHSO.sub.3, 0.2% NaHSO.sub.3 and 0.05% NaHSO.sub.3 by weight. Approximately 100 g of NVP were weighed into suitable containers (120 g brown glass bottles) and the NaHSO.sub.3 added. The samples were then placed into a hot water (about 60.degree. C.) bath and stirred closed for about four hours. The heat was turned off and the samples were allowed to cool to room temperature while stirring.

The four samples of NVP/NaHSO.sub.3 were rated for odor when they had reached room temperature, versus a control (0.0% NaHSO.sub.3). The 2% and 1% NaHSO.sub.3 samples were rated as having essentially no odor, and the 0.2% and 0.05% were rated as "improved" but still detectable odor. The samples were then aged over the weekend (about 60 hours) and rerated for odor versus the control. At this time, all detectable unpleasant odor had disappeared from the NVP samples containing the NaHSO.sub.3. These samples were subsequently aged about 20 days at room temperature with no side effect (gels, etc.) and the unpleasant odor was not detectable.

A sample of a coating composition was also prepared to contain 0.1% by weight NaHSO.sub.3 (1.0% of the NVP). The sample was prepared in a similar fashion to that set forth in Example 1, e.g., about four hours of heat and stir at 60.degree. C., followed by cooling to room temperature. The strong, unpleasant odor associated with the NVP was no longer detectable in the cooled sample. Curing of the sample was then induced by an electon beam. Cure rate, completeness of cure and the physical properties of the cured coating, including E-beam cure response were not altered.

The present invention may comprise, consist essentially of or consist of the elements or method steps recited herein.