Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfur containing
Reexamination Certificate
1999-04-16
2001-09-25
Seidleck, James J. (Department: 1711)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfur containing
C568S018000, C568S037000, C568S038000, C568S042000, C568S075000, C568S077000, C522S036000, C522S054000, C522S055000, C522S049000
Reexamination Certificate
active
06294698
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel photoinitiators and methods for generating a reactive species using the photoinitiators. The present invention, further relates to methods of polymerizing or photocuring polymerizable unsaturated material using the above-mentioned photoinitiators.
BACKGROUND OF THE INVENTION
Polymers have served essential needs in society. For many years, these needs were filled by natural polymers. More recently, synthetic polymers have played an increasingly greater role, particularly since the beginning of the 20th century. Especially useful polymers are those prepared by an addition polymerization mechanism, i.e., free radical chain polymerization of unsaturated monomers, and include, by way of example only, coatings and adhesives. In fact, the majority of commercially significant processes is based on free-radical chemistry. That is, chain polymerization is initiated by a reactive species which often is a free radical. The source of the free radicals is termed an initiator or photoinitiator.
Improvements in free radical chain polymerization have focused both on the polymer being produced and the photoinitiator. Whether a particular unsaturated monomer can be converted to a polymer requires structural, thermodynamic, and kinetic feasibility. Even when all three exist, kinetic feasibility is achieved in many cases only with a specific type of photoinitiator. Moreover, the photoinitiator can have a significant effect on reaction rate which, in turn, may determine the commercial success or failure of a particular polymerization process or product.
A free radical-generating photoinitiator may generate free radicals in several different ways. For example, the thermal, homolytic dissociation of an initiator typically directly yields two free radicals per initiator molecule. A photoinitiator, i.e., an initiator which absorbs light energy, may produce free radicals by either of two pathways:
(1) the photoinitiator undergoes excitation by energy absorption with subsequent decomposition into one or more radicals; or
(2) the photoinitiator undergoes excitation and the excited species interacts with a second compound (by either energy transfer or a redox reaction) to form free radicals from the latter and/or former compound(s).
While any free radical chain polymerization process should avoid the presence of species which may prematurely terminate the polymerization reaction, prior photoinitiators present special problems. For example, absorption of the light by the reaction medium may limit the amount of energy available for absorption by the photoinitiator. Also, the often competitive and complex kinetics involved may have an adverse effect on the reaction rate. Moreover, commercially available radiation sources, such as medium and high pressure mercury and xenon lamps, emit over a wide wavelength range, thus producing individual emission bands of relatively low intensity. Most photoinitiators only absorb over a small portion of the emission spectra and, as a consequence, most of the lamps' radiation remains unused. In addition, most known photoinitiators have only moderate “quantum yields” (generally less than 0.4) at these wavelengths, indicating that the conversion of light radiation to radical formation can be more efficient.
Thus, there are continuing opportunities for improvements in free radical polymerization photoinitiators. Moreover, there is a need in the art for new, energy-efficient photoinitiators for use in a variety of polymerization and photocuring processes.
SUMMARY OF THE INVENTION
The present invention addresses some of the difficulties and problems discussed above by the discovery of energy-efficient photoinitiators having the following general formula:
wherein x is an integer from 1 to 4, and R
1
and R
2
each independently represent H—;
(R)
2
N— where R is an alkyl group having from one to six carbon atoms; a chalcone; HSO
3
—; and NaSO
3
—. In a further embodiment, the present invention is directed to photoinitiators having the following formula:
wherein x is an integer from 1 to 4.
The present invention is directed to the above-described photoinitiators, compositions containing the same, and methods for generating a reactive species which includes providing one or more of the photoinitiators and irradiating the one or more photoinitiators. One of the main advantages of the photoinitiators of the present invention is that they efficiently generate one or more reactive species under extremely low energy lamps, such as excimer lamps, as compared to prior art photoinitiators.
The present invention is further directed to methods of using the above-described photoinitiators to polymerize and/or photocure a polymerizable material. The photoinitiators of the present invention result in rapid curing times in comparison to the curing times of prior art photoinitiators, even with relatively low output lamps. The present invention includes a method of polymerizing an unsaturated monomer by exposing the unsaturated monomer to radiation in the presence of the efficacious wavelength specific photoinitiator composition described above. When an unsaturated oligomer/monomer mixture is employed in place of the unsaturated monomer, curing is accomplished.
The present invention further includes a film and a method for producing a film, by drawing an admixture of unsaturated polymerizable material and one or more photoinitiators of the present invention, into a film and irradiating the film with an amount of radiation sufficient to polymerize the composition. The admixture may be drawn into a film on a nonwoven web or on a fiber, thereby providing a polymer-coated nonwoven web or fiber, and a method for producing the same.
The present invention is also directed to an adhesive composition comprising an unsaturated polymerizable material admixed with one or more photoinitiators of the present invention. Similarly, the present invention includes a laminated structure comprising at least two layers bonded together with the above-described adhesive composition, in which at least one layer is a nonwoven web or film. Accordingly, the present invention provides a method of laminating a structure wherein a structure having at least two layers with the above-described adhesive composition between the layers is irradiated to polymerize the adhesive composition.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to energy-efficient reactive photoinitiators and methods for utilizing the same. More particularly, the present invention is directed to new photoinitiators having the following general formula:
wherein x is an integer from 1 to 4, and R
1
and R
2
each independently represent H—;
(R)
2
N— where R is an alkyl group having from one to six carbon atoms; a chalcone; HSO
3
—; and NaSO
3
—. In a further embodiment of the present invention, the photoinitiator comprises bis-phthaloylglycine sulfide compounds having the following formula:
wherein x is an integer from 1 to 4.
The present invention also includes a method of polymerizing an unsaturated polymerizable material by exposing the unsaturated material to radiation in the presence of one or more of the photoinitiators described above. Further, the present invention is directed to a film and a method for producing a film, by drawing an admixture of unsaturated polymerizable material and one or more of the photoinitiators described above, into a film and irradiating the film with an amount of radiation sufficient to polymerize the admixture.
The present invention is further directed to an adhesive composition comprising an unsaturated polymerizable material admixed and one or more photoinitiators of the present invention. Similarly, the present invention includes a laminated structure comprising at least two layers bonded together with the above-described adhesive composition
MacDonald J. Gavin
Nohr Ronald S.
Jones & Askew LLP
Kimberly--Clark Worldwide, Inc.
McClendon Sanza L.
Seidleck James J.
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