Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-08-14
2002-08-13
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S015000, C522S025000, C522S028000, C522S078000, C522S148000, C522S167000, C522S168000, C522S170000, C522S174000, C522S181000, C522S182000, C430S293000, C430S338000, C430S339000, C430S341000, C430S342000, C430S344000
Reexamination Certificate
active
06433035
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to selectively colorable compositions and to a method for forming selectively colored polymeric bodies using such compositions.
Commonly assigned U.S. Pat. No. 5,942,554 discloses a curable composition containing a color precursor and an onium salt which is both cured and colored upon exposure to actinic radiation. Color precursors disclosed as being useful are those which are capable of reacting with acid or whose excited states are capable of donating an election.
Commonly assigned U.S. patent application Ser. No. 09/558,599 filed on Apr. 26, 2000, now U.S. Pat. No. 6,309,797 discloses selectively colorable polymerizable compositions comprising a leucobase color former and a leuconitrile color former. Irradiation of the composition cures and selectively colors the composition. The color at any one location depends on the actinic dose and the interaction of the leucobase and leuconitrile colorformers. In one embodiment, a selectively colorable, polychromic composition is provided wherein low light exposure creates a polymer of one color, intermediate light exposure changes the color of the polymer and a high dosage of light exposure bleaches the color of the polymer.
International Publication Number WO 97/09168 to Zeneca discloses a photocurable, photocolorable composition which is irradiated with a low dose of light to cure and a different dose of light, preferably higher, to cause color formation. Color formation or color change occurs as a result of contact between a colorformer and a photochemically generated developer. The colorformers disclosed as being useful include lactones, fluorans, etc. which are acid sensitive compounds.
A selectively colorable solid object is an object that can be colored at small individual, but specifically defined, sites by irradiating light of a particular wavelength and specific intensity for a specified duration. The light sources capable of producing the selectively colorable solid object include: (a) a laser interfaced with an XY scanner (for polymer films), (b) a laser interfaced with an XYZ scanner (for 3D parts), (c) digital mirror device, (d) UV and Visible lamps with a masking device, etc.
A selectively colorable resin (SCR) system consists of: (a) the matrix (a blend of polymerizable material or a solid polymer), (b) a color former, (c) a color initiator (species that generate other species capable of reacting with color former; may not be needed in some systems); and (d) a chain reaction initiator (radical or cationic or none depending on the system).
The conventional method for forming a colored plastic body is to add a dye or pigment to the liquid prepolymer composition. The composition is then cured with actinic radiation. The latter requires that the absorption spectra of the photoinitiator and the dye/pigment differ. If the dye/pigment absorbs actinic radiation at the same wavelength as the photoinitiator, slower or no cure will be achieved. The color formation method is also not selective. The entire plastic is uniformly colored. Still another problem is that the photopolymerization process requires actinic radiation, but the color forming process requires only that the composition be well mixed. Though one of the processes can be controlled by the intensity/wavelength of the actinic radiation, the other is unaffected by it. Thus there is no selectivity of color formation in the plastic body.
Accordingly, there is a need for selectively colorable polymerizable compositions and for a method of forming selectively colored polymeric bodies using such compositions wherein the colorization process can be controlled as to the location and intensity of the color formed.
SUMMARY OF THE INVENTION
The present invention discloses selectively colorable compositions and a method for forming selectively colored polymeric bodies using such compositions. In accordance with the invention, a selectively colorable polymerizable composition comprising a leucobase color former and an oxidizing agent is irradiated with light of a particular wavelength and specific intensity for a specified duration. Exposure to actinic radiation cures the composition and activates the color former which can be optionally deactivated or bleached by further exposure. The irradiation dosage can be varied to selectively color the polymeric body whereby the resultant color of any particular area depends on the exposure dose received at that location. By varying the dose, a polymeric body can be prepared having distinctly colored elements at specific locations.
It is believed that, upon irradiation of the polymerizable composition of the present invention containing a polymerizable compound, a leucobase color former and an onium salt, two processes occur for color formation and bleaching. One process generates a dye cation via electron transfer process upon exposure of a leucobase dye precursor in the presence of an oxidizing agent and a second process is the bleaching of the dye cation upon further exposure. Accordingly, the composition of the present invention provides a photopolymerizable selectively colorable system. The bleaching process is efficient only when the starting material is an acid non-sensitive leucobase. The initial color is formed by a photooxidation process which involves electron transfer from the leucodye to the oxidizing agent. The bleaching process is not nearly as efficient in the case when the starting material is a dye or an acid-sensitive dye.
Under low dosage, color formation depends primarily on Scheme 1 wherein exposure of a leucobase to light in the presence of a oxidizing agent yields a dye cation. The mechanism is illustrated below for a triarylmethane (TAM) leucobase (TAMH) susceptible to oxidation. Ox represents an oxidizing agent, TAM
+
represents the colored species and hv represents exposure to actinic radiation. It is anticipated that the scheme below will also be valid for diarylmethane (DAM) and other photooxidizable leucodyes which do not form the color with acid on contact.
TAMH+Ox+h&ngr;
TAM
+
(colored) Scheme 1
At higher doses of irradiation, bleaching of TAM
+
occurs (Scheme 2). Therefore, the color of the polymeric body at higher doses disappears and the contrast is produced.
(TAM)
+
+h&ngr;
bleaching products (colorless) Scheme 2
In another embodiment of the present invention, the oxidation process can be inhibited significantly by the introduction of at least one electron-withdrawing group (e.g., halogen, NO
2
, COR, COOR, etc., where R is H, hydrocarbon, etc.) to the TAM-H or DAM-H aromatic structure. In this case, color formation is delayed allowing one to obtain colorless polymer at low doses, colorize the polymer at an intermediate dose and bleach the color by further irradiation.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, a composition which can be selectively colored by exposure to actinic radiation and a method leading to the formation of selectively colored, polymer bodies that can be cured photochemically are provided. The invention is particularly useful for the selective color development and photopolymerization of films using a leucobase color former and an oxidizing agent. The composition of the present invention can be used in a solid or a liquid.
Those skilled in the art will appreciate that the color determinative irradiation step can be conducted before, after or simultaneously with the polymerization or crosslinking step. Furthermore, selective coloration of a polymeric body in accordance with the present invention can be carried out using one exposure or light source to polymerize or crosslink the composition and a second exposure or light source to induce the photochromic response, or using a single light source to polymerize the composition at a first intensity and using the same light source at a plurality of intensities to induce the photochromic response. The latter system has the advantage that it involves the use of only one light source and
Grinevich Oleg V.
Neckers Douglas C.
Berman Susan W.
Spectra Group Limited, Inc.
Thompson Hine LLP
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