Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2002-01-18
2003-12-09
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S325000, C428S323000, C428S331000, C428S332000, C428S333000, C428S334000, C428S336000, C428S402000, C428S404000, C428S407000, C428S426000, C428S413000
Reexamination Certificate
active
06660374
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to radiation-curable compositions and articles comprising at least one solid, non-crystalline, radiation-transmissible material dispersed in at least one cationic-curable or free-radical curable composition.
BACKGROUND OF THE INVENTION
Radiation-curable coatings, inks, adhesives, and sealants are well known. These compositions may be cured with electron beam radiation, ultraviolet (“UV”) light, visible light, gamma rays, and the like. The compositions are based on technology that invokes cure through a free-radical cure mechanism and usually involves acrylates (
Free Radical Radiation Curing,
Federation Series on Coatings Technology, 29 pp, Federation of Societies for Coatings Technology, 1997), or through a cationic cure mechanism and usually involves cycloaliphatic epoxides (
Cationic Radiation Curing
, Federation Series on Coatings Technology, 27 pp, Federation of Societies for Coatings Technology, 1991). An overview of both technologies can be found in J. Coatings Technology, “A Radiation-Cure Primer,” Vol. 69, No. 866, p. 29, 1997. Such radiation-curable coatings are considered to be ecologically friendly, since they are usually substantially volatile-organic-solvent free. Furthermore, such radiation-curable coatings are typically low-energy requiring systems, since essentially 100% of the uncured system is transformed into the final coating in a very short time under a radiation source that is usually ultraviolet and visible light, an electron beam, a carbon arc, or the like. The exact nature or wavelength of the radiation energy used is dependent on the photolysis characteristics of the particular photoinitiator or photoinitiators involved.
Electron beam curing is used for compositions based on acrylates and methacrylates and that require free radicals to initiate the curing process, but electron beam curing can be used for cationic systems. Because of high equipment costs associated with electron beam systems, they are usually used for curing clear or pigmented coating formulations on large quantities of coated articles and at high cure speeds. However, recently smaller electron beams units that can be used in conjunction with conveyer belts have been introduced commercially for small-scale production processes. The high energy electrons produced by an electron beam pass easily through solid objects such as pigment particles, and the electrons' contact with certain molecules, such as those containing ethylenic unsaturation, can cause free radical formation and cure without the use of an added photoinitiator.
Photocure technology requires the addition of a compound known as a photoinitiator to the formulation. The photoinitiator photolyzes, i.e., breaks down or degrades in the presence of radiation of the proper wavelength (which can vary from the ultraviolet range through the visible range according to the photoinitiator selected) to form an active species that will initiate polymerization either directly or indirectly. While such technology is readily applicable to clear, thin compositions, there is a need for improved photocuring technology that will allow easy cure of opaque and/or colored compositions as well as clear, thick compositions at reasonable production rates. Such an improvement also should benefit both industry and the environment by eliminating the use of organic solvents and decreasing the amount of energy required for production while increasing productivity.
U.S. Pat. No. 5,453,451 relates to a substantially solvent free, liquid, sprayable coating composition including one or more acrylates and one or more photoinitiators that polymerize the composition when exposed to ultraviolet light. U.S. Pat. No. 4,721,734 relates to photoinitiator products and technology for photochemically-initiated polymerization reactions.
U.S. Pat. No. 4,425,287 relates to a process for the production of moldings from unsaturated polyester resins. A pulverulent filler is employed that transmits ultraviolet light so that curing is complete even in the deeper lying layers. Examples given of suitable fillers are aluminum oxide hydrate, glass powder, quartz powder, quartz sand, glass beads, barium sulfate, talc, and finely disperse silica. However, aluminum oxide trihydrate is crystalline, highly absorbent to components of reaction mixtures in which it is used, and has been found to produce unsatisfactory cures in the compositions of the present invention. Furthermore, glass in general is opaque to ultraviolet light. See Handbook of Chemistry and Physics, 76
th
edition, 1995-1996, p. 10-305. The Handbook also notes that quartz is very transparent to both ultraviolet light and the visible spectrum. However, not all quartzes are in fact transparent to said spectrum. Furthermore, quartz is typically crystalline, which makes it not economically feasible in most applications and presents health hazards. Furthermore, quartz sand contains impurities that interfere with transmission of radiation wavelengths employed in the present invention. Barium sulfate is unsatisfactory in the compositions of the present invention because it is crystalline and has a high specific gravity (about 4.50) that renders it poorly mixable with the compositions of the present invention. Talc is unsatisfactory because it is crystalline and also tends to absorb components of reaction mixtures in which it is used. The term “finely disperse silica” does not indicate whether it is crystalline or non-crystalline, and also does not indicate its purity, transparency/opacity, index of refraction, or absorbency. Crystalline silica presents the same health hazards as crystalline quartz.
An overview of powder coating technology can be found in the December 1997 issue of
Modern Paints and Coatings,
pp. 72-78. The technology of powder coating also has been described in
Powder Coatings, Federation Series on Coatings Technology,
35 pp., Federation of Societies for Coatings Technology, 1991.
Although many types of radiation-curable coating and ink compositions and substrates exist, most of them are clear coatings that are rapid curing, cost effective, and environmentally friendly. However, there still are problems in curing opaque and/or colored systems using photocure technology due to the difficulty in making ultraviolet and/or visible light penetrate through pigments, fillers, and similar opaque and/or colored materials, or through thick masses or films of clear compositions. It is especially difficult to achieve such penetration in economically feasible time periods of about a fraction of a second to about a few seconds. This is particularly true for 3-dimensional articles and for thick films greater than about 0.5 mil to about 3 or more mils in thickness.
There is a need for materials that, when combined with opaque and/or colored photocurable reactants, will produce compositions that can be readily cured thoroughly (i.e., deeply and uniformly) with ultraviolet and visible light. There is also a need for materials that, when combined with clear photocurable reactants, will produce compositions that can be readily cured thoroughly (i.e., deeply and uniformly) as thick films or masses. This invention provides such novel compositions.
SUMMARY OF THE INVENTION
A radiation-curable composition in a liquid or solid form comprises at least one solid, non-crystalline, radiation-transmissible material, dispersed in at least one cationic-curable or free-radical curable composition or mixture thereof. The term “transmissible” means substantially transparent to radiation as defined more fully below. The solid, non-crystalline, radiation-transmissible materials comprise certain glasses, quartzes, and other inorganic or organic solids that will not interfere with the radiation-induced polymerization by dissolution, swelling, or other mechanism, and that transmit at least about 40% of radiation having a wavelength from about 180 to about 600 nanometers.
The cationic-curable compositions comprise at least one cycloaliphatic epoxide, at least one cation-generating photoinitiator,
Koleske Joseph V.
Smetana David A.
McClendon Sanza L.
Renner , Otto, Boisselle & Sklar, LLP
Seidleck James J.
Suncolor Corporation
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