Imaging compositions and methods

Abstract

Imaging compositions and methods of using the compositions are disclosed. The imaging compositions include two discrete components. One component includes opacifying compounds and the second component includes sensitizing dyes. The second component is sensitive to low levels of energy. Application of the low levels of energy induces a color or shade change in the second component. The imaging compositions may be applied to a work piece to mark it such that it may be modified based on the marks.

Description

[0001] This Patent Application is a continuation-in-part of co-pending patent application Ser. No. 10/890,507 filed Jul. 12, 2004, which is a continuation-in-part of co-pending patent applications Ser. Nos. 10/773,989, 10/773,990, and 10/773,991 filed Feb. 6, 2004.

[0002] The present invention is directed to imaging compositions having two separate functional components and methods of using the imaging compositions. More specifically, the present invention is directed to imaging compositions having two separate functional components where one component is opaque and the second component undergoes a color or shade change upon exposure to energy at low powers and methods of using the imaging compositions.

[0003] There are numerous compositions and methods employed in various industries to form images on substrates to mark the substrates. Such industries include the paper industry, packaging industry, paint industry, medical industry, dental industry, electronics industry, textile industry, aeronautical, marine and automotive industries, and the visual arts.

[0004] Imaging or marking also is employed in proofing products, photoresists, soldermasks, printing plates and other photopolymer products. For example, U.S. Pat. No. 5,744,280 discloses photoimageable compositions allegedly capable of forming monochrome and multichrome images, which have contrast image properties. The photoimageable compositions include photooxidants, photosensitizers, photodeactivation compounds and deuterated leuco compounds. The leuco compounds are aminotriarylmethine compounds or related compounds in which the methane (central) carbon atom is deuterated to the extant of at least 60% with deuterium incorporation in place of the corresponding hydrido aminotriaryl-methine. The patent alleges that the deuterated leuco compounds provide for an increased contrast imaging as opposed to corresponding hydrido leuco compounds. Upon exposure of the photoimageable compositions to actinic radiation a phototropic response is elicited.

[0005] Laser imaging has lately been attracting attention as a high-speed and efficient marking method and is already put to practical use in some industries. Many laser imaging techniques involve irradiating only necessary areas of substrates with laser light to denature or remove the irradiated area or irradiating a coated substrate with laser light to remove the irradiated coating layer thereby making a contrast between the irradiated area (imaged area) and the non-irradiated area (background).

[0006] Using a laser to mark an article such as a semiconductor chip is a fast and economical means of marking. There are, however, certain disadvantages associated with state-of-the art laser imaging techniques that burn the surface to achieve a desired mark. For example, a mark burned in a surface by a laser may only be visible at select angles of incidence to a light source. Further, oils or other contaminants deposited on the article surface subsequent to marking may blur or even obscure the laser mark. Additionally, because the laser actually burns the surface of the work piece, for bare die imaging, the associated burning may damage any underlying structures or internal circuitry or by increasing internal die temperature beyond acceptable limits. Moreover, where the manufactured part is not produced of a laser reactive material, a laser reactive coating applied to the surface of a component adds expense and may take hours to cure.

[0007] Alternatively, laser projectors may be used to project images onto surfaces. They are used to assist in the positioning of work pieces on work surfaces. Some systems have been designed to project three-dimensional images onto contoured surfaces rather than flat surfaces. The projected images are used as patterns for manufacturing products and to scan an image of the desired location of a ply on previously placed plies. Examples of such uses are in the manufacturing of leather products, roof trusses, and airplane fuselages. Laser projectors are also used for locating templates or paint masks during the painting of aircraft.

[0008] The use of scanned laser images to provide an indication of where to place or align work piece parts, for drilling holes, for forming an outline for painting a logo or picture, or aligning segments of a marine vessel for gluing requires extreme accuracy in calibrating the position of the laser projector relative to the work surface. Typically six reference points are required for sufficient accuracy to align work piece parts. Reflectors or sensors are positioned in an approximate area where the ply is to be placed. Since the points are at fixed locations relative to the work and the laser, the laser also knows where it is relative to the work. Typically, workers hand mark the place where the laser beam image contacts the work piece with a marker or masking tape to define the laser image. Such methods are tedious, and the workers' hands may block the laser image disrupting the alignment beam to the work piece. Accordingly, misalignment may occur.

[0009] Another problem associated with laser imaging is the potential for opthalmological damage to the workers. Many lasers used in marking may cause retinal damage to workers. Generally, lasers, which generate energy exceeding 5 mW present hazards to workers.

[0010] The inventors of the present invention have addressed the problems associated with laser imaging by formulating compositions which change color or shade by applying energy at powers of 5 mW or less. Applications of such compositions eliminate the problems associated with hand marking the places on a work piece where the laser is directed and at the same time the use of a low power laser eliminates the potential of opthalmological damage to workers.

[0011] In the applications of such compositions a color or shade contrast is desired between the compositions and the work pieces such that the workers may readily distinguish between the work piece and the colored compositions to accurately modify the work piece. The greater the color or shade contrast from the work piece the easier it is for the workers to see the markings and more rapidly and accurately modify the work piece. This is especially important in assembly line operations where speed and accuracy are critical to optimum product output. However, when a work piece is of a similar color or shade as the color or shade of the markings, workers find it difficult to accurately locate the markings on the work piece. Accordingly, speed and accuracy are compromised, and the efficiency of the manufacturing process is hindered.

[0012] The imaging compositions are not always applied to a bare work piece. Often the imaging compositions are applied to work pieces which have been previously treated or coated by various types of chemical compositions. The inventors have discovered that such coatings may cause dye compounds of the imaging compositions to leach out into the coatings and cause undesired chemical reactions which result in the formation of unwanted color changes. Such color changes readily interfere with the desired color or shade contrast between the marks on the imaging compositions and the work pieces and workers are unable to perform their task. For example, airplane bodies are often coated with an epoxy primer material prior to applying paint or any additional coatings to the bodies. When the imaging compositions are applied to such airplane bodies, the dyes in the imaging compositions leach into the epoxy primers and turn the airplane bodies an undesired red.

[0013] Accordingly, there is still a need for improved imaging compositions for marking a work piece.

[0014] Imaging compositions include a first component including one or more opacifying compounds, and a second component including one or more sensitizers. The first component of the imaging compositions inhibits the leaching of compounds from the second component into coatings on work pieces on which the imaging compositions are applied. The first component also provides a color or shade contrast between the second component of the imaging compositions and the work pieces. The second component may be imaged by exposing the compositions to energy levels of 5 mW or less.

[0015] In another aspect the imaging compositions include a first component including one or more opacifying compounds and one or more release agents, and a second component including one or more sensitizers and one or more release agents.

[0016] The imaging compositions also may include one or more film forming polymers, adhesives, plasticizers, flow agents, chain transfer agents, organic acids, accelerators, surfactants, thickeners, monomers, rheology modifiers, release agents, diluents and other optional components to tailor the compositions for a particular imaging method and work piece. The imaging compositions may be applied to a work piece to form an image on the work piece for workers to modify the work piece to make an article.

[0017] In a further aspect methods of imaging include providing a first component of a composition including one or more opacifying compounds; applying the first component of the composition to a work piece; providing a second component of the composition including one or more sensitizers; applying the second component of the composition on the first component; exposing the composition to energy at powers of 5 mW or less to affect a color or shade change in the second component; and executing a task on the work piece as directed by the color or shade change of the second component of the composition to modify the work piece. The energy may be applied selectively to form an imaged pattern on the work piece.

[0018] The image may be used as a mark to drill holes for fasteners, to join parts together, to align segments of parts, and to form an outline for making a logo or picture on articles such as terrestrial vehicles, aeronautical ships, marine vessels, terrestrial structures and textiles. Since the compositions may be promptly applied to the work piece and the image promptly formed by application of energy at intensities of 5 mW or less to create a color or shade contrast, workers no longer need to be adjacent the work piece to mark laser beam images with a hand-held marker or tape in the fabrication of articles. Accordingly, the problems of blocking light caused by the movement of workers hands and the slower and tedious process of applying marks by workers using a hand-held marker or tape is eliminated. Further, the low powers of energy, which are used to cause the color or shade change, eliminate or at least reduce the potential for opthalmological damage to workers.

[0019] The imaging compositions may be applied to the work piece by methods which include, but are not limited to, spray coating, brushing, roller coating, ink jetting, dipping and immersion. Energy sources for applying a sufficient amount of energy to create the color or shade change include laser, infrared and ultraviolet light generating devices and apparatus.

[0020] In one aspect the imaging compositions are peelable from the work piece avoiding the use of undesirable solvents or developers. Such solvents and developers may be carcinogenic and potentially contaminate the environment, thus costly waste treatment is used to reduce environmental pollution. Accordingly, the imaging compositions provide for more efficient manufacturing than many conventional alignment and imaging processes, and also may reduce the amount of waste treatment.

[0021] As used throughout this specification, the following abbreviations have the following meaning, unless the context indicates otherwise: .degree. C.=degrees Centigarde; IR=infrared; UV=ultraviolet; gm=gram; mg=milligram; L=liter; mL=milliliter; wt %=weight percent; erg=1 dyne cm=10.sup.-7 joules; J=joule; mJ=millijoule; nm=nanometer=10.sup.-9 meters; cm=centimeters; mm=millimeters; W=watt=1 joule/second; and mW=milliwatt; ns=nanosecond; .mu.sec=microsecond; Hz=hertz; .mu.m=microns; and T.sub.g=glass transition temperature; .DELTA.=delta=mathematical symbol designating a change in a variable.

[0022] The terms "polymer" and "copolymer" are used interchangeably throughout this specification. "Actinic radiation" means radiation from light that produces a chemical change. "Photofugitive response" means that the application of energy causes a colored material to fade or become lighter. "Phototropic response" means that the application of energy causes material to darken. "Changing shade" means that the color fades, or becomes darker. "(Meth)acrylate" includes both methacrylate and acrylate, and "(meth)acrylic acid" includes both methacrylic acid and acrylic acid. "Diluent" means a carrier or vehicle, such as solvents or solid fillers. "Opacity" means the property of being impervious to light rays, i.e. not transparent or translucent. "Opaque" means nontransparent and nontranslucent. "Translucent" means semitransparent. "Transparent" means a passage of rays of the visible spectrum.

[0023] Unless otherwise noted, all percentages are by weight and are based on dry weight or solvent free weight. All numerical ranges are inclusive and combinable in any order, except where it is logical that such numerical ranges are constrained to add up to 100%.

[0024] Imaging compositions include a first component including one or more opacifying compounds, and a second component including one or more sensitizers. The first component of the imaging compositions inhibits leaching of compounds from the second component into coatings on work pieces on which the imaging compositions are applied. The first component also provides a color or shade contrast between the second component of the imaging compositions and the work pieces. Further, including one or more opacifying compounds in the first component, increases the rate of color or shade change of the second component. The second component may be imaged by exposing the compositions to energy levels of 5 mW or less.

[0025] The first component including one or more opacifying compounds is applied to the work piece. The first component is dried then the second component including the one or more sensitizers is applied on the dried first component. The second component is then dried and the imaging composition is then imaged with energy at 5 mW or less. Workers then modify the work piece based on the imaged composition. The composition may be removed from the work piece by any suitable method. Typically, the composition is peeled from the work piece.

[0026] Often a work piece may be sufficiently dark in color or shade such as to reduce the contrast between the imaged second component and the work piece, thus compromising accurate modification of the work piece. Including opacifying compounds in the second component causes a reflection of a portion of the applied energy, thus requiring longer exposure times to affect the color or shade change. By including the opacifying compounds in the first component, faster color and shade changes are achieved in the second component.

[0027] The imaging compositions may be applied to a work piece by any suitable method including, but not limited to, spraying, brushing, roller coating, ink jetting, dipping and immersion. The compositions may be removed from the work piece by any suitable method such as with a developer, stripper or by peeling the unwanted portions from work pieces. Typically, the compositions are peeled by hand or by using a suitable device or apparatus known in the art such as a knife or scrapper. Peelable compositions avoid the use of environmentally hazardous solvents and developers, and reduce the amount of waste.

[0028] Any suitable opacifying compound which provides a desired color or shade contrast between the second component and the work piece may be used. Such compounds are used in the first component in amounts of 1 wt % to 80 wt %, or such as from 5 wt % to 50 wt %, or such as 10 wt % to 20 wt %.

[0029] Opacifying compounds include, but are not limited to, pigments (inorganic and organic), metal salts, silica, silicates and clays. Organic pigments include, but are not limited to, indigo, phthalocyanine, para red and flavanoids such as red, yellow, blue, orange and ivory colors. Inorganic pigments include, but are not limited to, oxides such as titanium dioxide, zirconium oxide, ceric oxide, antimony trioxide, arsenic pentoxide, aluminum oxide, zinc oxide, cobalt oxide, cadmium oxide, chromium oxide, magnesium oxide, iron oxide and lead oxide. Also, mixed phase titanates and mixed phase oxides may be included. Metal salts include, but are not limited to, sulfides, sulfates, carbonates and hydroxides. Typically, the opacifying compounds are inorganic pigments. More typically, the opacifying compounds are inorganic pigments such as titanium dioxide, aluminum oxide, zinc oxide and silicates. Most typically the opacifying compounds are inorganic pigments such as titanium dioxide, aluminum oxide and zinc oxide. The opacifying compounds have an average size of 0.01 .mu.m to 10 .mu.m, or such as from 0.5 .mu.m to 5 .mu.m, or such as from 1 .mu.m to 3 .mu.m.

[0030] In addition to the opacifying agents, the first component may include, but is not limited to, one or more additives such as film forming polymers, diluents, thickeners, rheology modifiers, adhesives, plasticizers, flow agents, organic acids, surfactants and release agents to tailor the first component for compatibility with the second component and the work piece. Typically, such additives are included in the first component as in the second component.

[0031] Film forming polymers are included in the first component to function as binders. Any film forming polymer may be employed in the first component provided the polymers do not cause the opacifying agents to agglomerate or concentrate out of the first component. Suitable film forming polymers for the first component include, but are not limited to, the film forming polymers described below for the second component. The film forming polymers are included in the first component in amounts from 10 wt % to 95 wt %, or such as from 15 wt % to 80 wt %, or such as from 25 wt % to 65 wt % of the first component.

[0032] Optionally, an adhesive may be included in the first component. The adhesive may be a permanent adhesive, a semi-permanent, a repositionable adhesive, a releasable adhesive, or freezer category adhesive. Many such adhesives may be classified as hot-melt, hot-melt pressure sensitive, and pressure sensitive adhesives. Typically, the releasable adhesives are pressure sensitive adhesives. Typically, releasable, pressure sensitive adhesives are used. Such releasable, pressure sensitive adhesives include, but are not limited to, acrylics, polyurethanes, poly-alpha-olefins, silicones, combinations of acrylate pressure sensitive adhesives and thermoplastic elastomer-based pressure sensitive adhesives, and tackified and natural rubbers. Adhesives may be included in the first component in amounts of from 0.5 wt % to 15 wt %, or such as from 5 wt % to 10 wt % of the first component.

[0033] One or more amphoteric surfactants may be included in the first component to act as release agents such that the imaging compositions may be readily peeled from a work piece. Suitable amphoteric surfactants include those described below for the second component of the imaging compositions. The amphoteric surfactants are included in the first component in the same amounts as in the second component.

[0034] One or more diluents may be included in the first component. Such diluents include, but are not limited to, water and organic solvents. Examples of suitable organic solvents are described below for the second component of the imaging compositions.

[0035] Sensitizers employed in the second component are compounds which are activated by energy to change color or shade, or upon activation cause one or more other compounds to change color or shade. The second component includes one or more photosensitizers activated by visible light energy at powers of 5 mW or less. Generally, such sensitizers are included in amounts of from 0.005 wt % to 10 wt %, or such as from 0.05 wt % to 5 wt %, or such as from 0.1 wt % to 1 wt % of the second component.

[0036] Sensitizers, which are activated in the visible range, typically are activated at wavelengths of from above 300 nm to less than 600 nm, or such as from 350 nm to 550 nm, or such as from 400 nm to 535 nm. Such sensitizers include, but are not limited to, xanthene compounds and cyclopentanone based conjugated compounds.

[0037] Suitable xanthene compounds include, but are not limited to, compounds having the general formula: 1

[0038] where X is hydrogen, sodium ion, or potassium ion; Y is hydrogen, sodium ion, potassium ion or --C.sub.2H.sub.5; R.sub.1 is hydrogen, Cl.sup.-, Br.sup.-, or I.sup.-; R.sub.2 is hydrogen, Cl.sup.-, Br.sup.-, or I.sup.-; R.sub.3 is hydrogen, Cl.sup.-, Br.sup.-, I.sup.-, or --NO.sub.2; R.sub.4 is hydrogen, --NO.sub.2, Cl.sup.-, Br.sup.-, or I.sup.-; R.sub.5 is hydrogen, Cl.sup.- or Br.sup.-; R.sub.6 is hydrogen, Cl.sup.-, or Br.sup.-; R.sub.6 is hydrogen, Cl.sup.-, or Br.sup.-; R.sub.7 is hydrogen, Cl.sup.-, or Br.sup.-; and R.sub.8 is hydrogen, Cl.sup.-, or Br.sup.-.

[0039] Examples of such xanthene compounds are compounds such as fluorescein and derivatives thereof such as the halogenated xanthenes such as 2',4',5',7'-tetrabromo-3,4,5,6-tetrachlorofluorescein (phloxin B), 2',4',5',7'-tetraiodofluorescein (erythrosin, erythrosin B, or C.I. Acid Red 51), 2',4',5',7'-tetraiodo-3,4,5,6-tetrachlorofluorescein (Rose Bengal), 2',4',5',7',3,4,5,6-octabromofluorescein (octabromofluorescein), 4,5,6,7-tetrabromoerythrosin, 4',5'-dichlorofluorescein, 2',7'-dichlorofluorescein, 4,5,6,7-tetrachlorofluorescein, 2',4',5',7'-tetrachlorofluorescein, dibromofluorescein, Solvent Red 72, diiodofluorescein, eosin B, eosin Y, ethyl eosin, and salts thereof. Typically, the salts are alkali metal salts such as the sodium and potassium salts. Such xanthene compounds typically are used in amounts of from 0.05 wt % to 2 wt %, or such as from 0.25 wt % to 1 wt %, or such as from 0.1 wt % to 0.5 wt % of the composition.

[0040] Examples of suitable cyclopentanone based conjugated compounds are cyclopentanone, 2,5-bis-[4-(diethylamino)phenyl]methylene]-, cyclopentanone, 2,5-bis[(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-9-- yl)methylene]-, and cyclopentanone, 2,5-bis-[4-(diethyl-amino)-2-methylphe- nyl]methylene]-. Such cyclopentanones may be prepared from cyclic ketones and tricyclic aminoaldehydes by methods known in the art.

[0041] Examples of such suitable conjugated cyclopentanones have the following formula: 2

[0042] where p and q independently are 0 or 1, r is 2 or 3; and R.sub.9 is independently hydrogen, linear or branched (C.sub.1-C.sub.10)aliphatic, or linear or branched (C.sub.1-C.sub.10)alkoxy, typically R.sub.9 is independently hydrogen, methyl or methoxy; R.sub.10 is independently hydrogen, linear or branched (C.sub.1-C.sub.10)aliphatic, (C.sub.5-C.sub.7)ring, such as an alicyclic ring, alkaryl, phenyl, linear or branched (C.sub.1-C.sub.10)hydroxyalkyl, linear or branched hydroxy terminated ether, such as --(CH.sub.2).sub.v--O--(CHR.sub.20).sub.w--OH, where v is an integer of from 2 to 4, w is an integer of from 1 to 4, and R.sub.20 is hydrogen or methyl and carbons of each R.sub.10 may be taken together to form a 5 to 7 membered ring with the nitrogen, or a 5 to 7 membered ring with the nitrogen and with another heteroatom chosen from oxygen, sulfur, and a second nitrogen. Such sensitizers may be activated at powers of 5 mW or less.

[0043] Other sensitizers which are activated in the visible light range include, but are not limited to, N-alkylamino aryl ketones such as bis(9-julolidyl ketone), bis-(N-ethyl-1,2,3,4-tetrahydro-6-quinolyl)keton- e and p-methoxyphenyl-(N-ethyl-1,2,3,4-tetrahydro-6-quinolyl)ketone; visible light absorbing dyes prepared by base catalyzed condensation of an aldehyde or dimethinehemicyanine with the corresponding ketone; visible light absorbing squarylium compounds; 1,3-dihydro-1-oxo-2H-indene derivatives; any of the coumarin based dyes which include, but are not limited to, ketocoumarin, and 3,3'-carbonyl bis(7-diethylaminocoumarin), coumarin 6, coumarin 7, coumarin 99, coumarin 314 and dimethoxy coumarin 99; halogenated titanocene compounds such as bis(eta.5-2,4-cyclopentadien- -1-yl)-bis(2,6-difluro-3-(1H-pyrrol-1-yl)-phenyl) titanium; and compounds derived from aryl ketones and p-dialkylaminoarylaldehydes. Methods of making the foregoing sensitizers are known in the art or disclosed in the literature. Also, many are commercially available.

[0044] Optionally, the second component may include one or more photosensitizers that are activated by UV light. Such sensitizers which are activated by UV light are typically activated at wavelengths of from above 10 nm to less than 300 nm, or such as from 50 nm to 250 nm, or such as from 100 nm to 200 nm. Such UV activated sensitizers include, but are not limited to, polymeric sensitizers having a weight average molecular weight of from 10,000 to 300,000 such as polymers of 1-[4-(dimethylamino)phenyl]-1-(4-methoxyphenyl)-methanone, 1-[4-(dimethylamino)phenyl]-1-(4-hydroxyphenyl)-methanone and 1-[4-(dimethylamino)phenyl]-1-[4-(2-hydroxyethoxy)-phenyl]-methanone; free bases of ketone imine dyestuffs; amino derivatives of triarylmethane dyestuffs; amino derivatives of xanthene dyestuffs; amino derivatives of acridine dyestuffs; methine dyestuffs; and polymethine dyestuffs. Methods of preparing such compounds are known in the art. Typically, such UV activated sensitizers are used in amounts of from 0.05 wt % to 1 wt %, or such as from 0.1 wt % to 0.5 wt % of the second component.

[0045] Optionally, the second component may include one or more photosensitizers that are activated by IR light. Such sensitizers which are activated by IR light are typically activated at wavelengths of from greater than 600 nm to less than 1,000 nm, or such as from 700 nm to 900 nm, or such as from 750 nm to 850 nm. Such IR activated sensitizers include, but are not limited to, infrared squarylium dyes, and carbocyanine dyes. Such dyes are known in the art and may be made by methods described in the literature. Typically, such dyes are included in the compositions in amounts of from 0.05 wt % to 3 wt %, or such as from 0.5 wt % to 2 wt %, or such as from 0.1wt % to 1 wt % of the second component.

[0046] Photoreducing agents also may be used in the second component. Compounds which may function as photoreducing agents include, but are not limited to, one or more quinone compounds such as pyrenequinones such as 1,6-pyrenequinone and 1,8-pyrenequinone; 9,10-anthrquinone, 1-chloroanthraquinone, 2-chloro-anthraquinone, 2-methylanthrquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, octamethylanthraquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone, 1,2-benzaanthrquinone, 2,3-benzanthraquinone, 2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone, sodium salt of anthraquinone alpha-sulfonic acid, 3-chloro-2-methylanthraquinone, retenequinone, 7,8,9,10-tetrahydronaphthacenequinone, and 1,2,3,4-tetrahydrobenz(a)anthr- acene-7,12-dione.

[0047] Other compounds which may function as photoreducing agents include, but are not limited to, acyl esters of triethanolamines having a formula:

N(CH.sub.2CH.sub.2OC(O)--R.sub.11).sub.3 (III)

[0048] where R.sub.11 is alkyl of 1 to 4 carbon atoms, and 0 to 99% of a C.sub.1 to C.sub.4 alkyl ester of nitrilotriacetic acid or of 3,3',3"-nitrilotripropionic acid. Examples of such acyl esters of triethanolamine are triethanolamine triacetate and dibenzylethanolamine acetate.

[0049] One or more photoreducing agent may be used in the second component to provide the desired color or shade change. Typically, one or more quinone is used with one or more acyl ester of triethanolamine to provide the desired reducing agent function. Photoreducing agents may be used in the compositions in amounts of from 0.05 wt % to 50 wt %, or such as from 5 wt % to 40 wt %, or such as 20 wt % to 35 wt %.

[0050] Suitable color formers in the second component include, but are not limited to, leuco-type compounds. Such leuco-type compounds include, but are not limited to, aminotriarylmethanes, aminoxanthenes, aminothioxanthenes, amino-9,10-dihydroacridines, aminophenoxazines, aminophenothiazines, aminodihydrophenazines, antinodiphenylmethines, leuco indamines, aminohydrocinnamic acids such as cyanoethanes and leuco methines, hydrazines, leuco indigoid dyes, amino-2,3-dihydroanthraquinone- s, tetrahalo-p,p'-biphenols, 2(p-hydroxyphenyl)-4,5-diphenylimidazoles, and phenethylanilines. Typically, the aminotriarylmethane leuco dyes, such as the o-methyl substituted dyes, are used. The o-methyl substitution is believed to make the structure non-planar and more resistant to oxidation than many other leuco-type dyes. Color formers are included in amounts of from 0.1 wt % to 5 wt %, or such as from 0.25 wt % to 3 wt %, or such as from 0.5 wt % to 2 wt % of the second component.

[0051] Oxidizing agents also may be included in the second component to influence the color or shade change. Typically such oxidizing agents are used in combination with one or more color formers. Compounds, which may function as oxidizing agents include, but are not limited to, hexaarylbiimidazole compounds such as 2,4,5,2',4',5'-hexaphenylbiimidazol- e, 2,2',5-tris(2-chlorophenyl)-4-(3,4-dimethoxyphenyl)-4,5-diphenylbiimida- zole (and isomers), 2,2'-bis(2-ethoxyphenyl)-4,4',5,5',-tetraphenyl-1,1'-b- i-1H-mimidazole, and 2,2'-di-1-naphthalenyl-4,4',5,5'-tetraphenyl-1'-bi-1H- -imidazole. Other suitable compounds include, but are not limited to, halogenated compounds with a bond dissociation energy to produce a first halogen as a free radical of not less than 40 kilocalories per mole, and having not more than one hydrogen attached thereto; a sulfonyl halide having a formula: R'--SO.sub.2--X' where R' is an alkyl, alkenyl, cycloalkyl, aryl, alkaryl, or aralkyl and X' is chlorine or bromine; a sulfenyl halide of the formula: R"--S--X" where R" and X" have the same meaning as R' and X' above; tetraaryl hydrazines, benzothiazolyl disulfides, polymetharylaldehydes, alkylidene 2,5-cyclohexadien-1-ones, azobenzyls, nitrosos, alkyl (T1), peroxides, and haloamines. Typical examples of suitable halogenated sulfones include tribromomethyl aryl sulfones such as tribromomethylphenyl sulfone, tribromomethyl p-tolyl sulfone, tribromomethyl 4-chlorophenyl sulfone, tribromomethyl 4-bromophenyl sulfone, and tribromomethyl phenyl sulfone. Such compounds are included in the second component in amounts of from 0.25 wt % to 10 wt %, or such as from 0.5 wt % to 5 wt %, or such as from 1 wt % to 3 wt %. Methods are known in the art for preparing the compounds and many are commercially available.

[0052] Film forming polymers may be included in the second component to function as binders. Any film forming binder may be employed provided that the film forming polymers do not adversely interfere with the desired color or shade change, and have a T.sub.g of from -60.degree. C. to greater than 80.degree. C. or such as from -60.degree. C. to 80.degree. C., or such as from greater than -60.degree. C. to greater than 40.degree. C., or such as from 0.degree. C. to 35.degree. C. The film forming polymers are included in amounts of from 10 wt % to 90 wt %, or such as from 15 wt % to 70 wt %, or such as from 25 wt % to 60 wt %. Typically, the film forming polymers are derived from a mixture of acid functional monomers and non-acid functional monomers. Suitable acid functional monomers include, but are not limited to, (meth)acrylic acid, maleic acid, fumaric acid, citraconic acid, 2-acrylamido-2-methylpropanes- ulfonic acid, 2-hydroxyethyl acrylol phosphate, 2-hydroxypropyl acrylol phosphate, and 2-hydroxy-alpha-acrylol phosphate.

[0053] Suitable non-acid functional monomers include, but are not limited to, esters of (meth)acrylic acid such as methyl acrylate, 2-ethyl hexyl acrylate, n-butyl acrylate, n-hexyl acrylate, methyl methacrylate, hydroxyl ethyl acrylate, butyl methacrylate, octyl acrylate, 2-ethoxy ethyl methacrylate, t-butyl acrylate, 1,5-pentanediol diacrylate, N,N-diethylaminoethyl acrylate, ethylene glycol diacrylate, 1,3-propanediol diacrylate, decamethylene glycol diacrylate, decamethylene glycol dimethacrylate, 1,4-cyclohexanediol diacrylate, 2,2-dimethyylol propane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, glycerol triacrylate, 2,2-di(p-hydroxyphenyl)-propane dimethacrylate, triethylene glycol diacrylate, polyoxyethyl-2,2-di(p-hydr- oxyphenyl)-propane dimethacrylate, triethylene glycol dimethacrylate, polyoxypropyltrimethylol propane triacrylate, ethylene glycol dimethacrylate, butylenes glycol dimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate, pentaerythritol trimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate, pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate, 1,5-pentanediol dimethacrylate; styrene and substituted styrene such as 2-methyl styrene and vinyl toluene and vinyl esters such as vinyl acrylate and vinyl methacrylate.

[0054] When the film forming polymer has a T.sub.g of -60.degree. C. to 0.degree. C., the film forming polymers typically have from 0.1 wt % to 6 wt % of the total weight of the polymer at least one carboxy functional monomer, or such as from 0.5 wt % to 6 wt %, or such as from 1 wt % to 5 wt % of at least one carboxy functional monomer. When the film forming polymer has a T.sub.g of greater than 0.degree. C. to greater than 80.degree. C., and one or more bases are included in the composition to maintain a pH range of 3 to 11 or such as from 8 to 11, the polymer may optionally include, as polymerized units, carboxy functional monomers in amounts of from 0.1 wt % to 6 wt %, based on the total weight of the dry film forming polymer, or such as from 0.5 wt % to 6 wt %, or such as from 0.1 wt % to 5 wt % of the total weight of the dry film forming polymer.

[0055] Other suitable polymers include, but are not limited to, nonionic polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, hydroxyl-ethylcellulose, and hydroxyethylpropyl methylcellulose. Also polymers such as polyvinyl acetate may be used.

[0056] Amphoteric surfactants may be included in the second component to function as release agents such that the compositions may be peeled from a work piece. Such surfactants also stabilize particles of the polymers during and after aqueous emulsion polymerization, or other dispersion polymerizations. Suitable amphoteric surfactants are those which have weakly acidic functionalities such as carboxy functionalities, and have isoelectric points of from pH 3 to pH 8. Such amphoteric surfactants may be included in the second component in amounts of from 0.1 wt % to 6 wt %, or such as from 0.25 wt % to 5 wt %, or such as from 0.5 wt % to 4 wt % of the film forming binder polymer. Such amphoteric surfactants include, but are not limited to, amino carboxylic acids, amphoteric imidazoline derivatives, betaine, fluorocarbon and siloxane versions thereof, macromolecular amphoteric surfactants and mixtures thereof.

[0057] Any of the aminocarboxylic acids may have carboxy moieties present in either protonated form or in carboxylate form. Where more than one carboxy group is present on a molecule, those carboxy groups may all be in protonated form, in carboxylate form, or they may be present as some mixture of protonated and carboxylate forms. Furthermore, the ratio of protonated to unprotonated carboxy moieties may vary from one molecule to another, otherwise identical, molecule in a given system. Cations present as counter ions for the carboxylate moieties include cations of lithium, sodium, potassium, amines (i.e., ammonium cations derived from protonation or other quaternary substitution of amines), zinc, zirconium, calcium, magnesium, and aluminum. Any of the aminocarboxylic acids may have amino moieties present in either protonated (ammonium) or free amine form (i.e., as deprotonated primary, secondary, or tertiary amine). Where more than one amino group is present on a molecule, those amino groups may all be in protonated form, in free amine form, or they may be present as some mixture of protonated and free amine forms. Again, the ratio of protonated to unprotonated amine moieties may vary from one molecule to another, otherwise identical, molecule in a given system. Anions present as counter ions for the ammonium moieties include chloride, bromide, sulfate, carbonate, hydroxide, formate, acetate, propionate and other carboxylate anions.

[0058] Suitable aminocarboxylic acids include, but are not limited to: .alpha.-aminocarboxylic acids having the general formula R.sub.12--NH--CH.sub.2COOH, where R.sub.12.dbd.C.sub.4-C.sub.20 linear or branched, alkyl, alkenyl, or fluoro or silicone functional hydrophobe group; and .beta.-aminocarboxylic acids having the general structures: R.sub.12--NH--CH.sub.2CH.sub.2COOH and R.sub.12N(CH.sub.2CH.sub.2COOH).su- b.2, where R.sub.12.dbd.C.sub.4-C.sub.20 linear or branched, alkyl, alkenyl, or fluoro or silicone functional hydrophobe group, .beta.-aminocarboxylic acids are available from Henkel Corporation, King of Prussia, Pa., under the name DERIPHAT.TM.. Unless otherwise stated, the DERIPHAT.TM. ampholytes have the general formula R.sub.13--NHCH.sub.2CH.sub.2COOH, where R.sub.13=residue of coconut fatty acids, residue of tallow fatty acids, lauric acid, myristic acid, oleic acid, palmitic acid, stearic acid, linoleic acid, other C.sub.4-C.sub.20 linear or branched, alkyl, alkenyl, and mixtures thereof DERIPHAT.TM. ampholytes useful in the present invention include: sodium-N-coco-.beta.-aminopropionate (DERIPHAT.TM. 151, flake 97% active); N-coco-.beta.-aminopropionic acid (DERPHAT.TM. 151C, 42% solution in water); N-lauryl/myristyl-.beta.-aminopropionic acid (DERIPHAT.TM. 17.degree. C., 50% in water); disodium-N-tallow-.beta.-imin- odipropionate, R.sub.14N(CH.sub.2CH.sub.2COONa).sub.2, (DERIPHAT.TM. 154, flake 97% active); disodium-N-lauryl-.beta.-iminodipropionate (DERIPHAT.TM. 160, flake 97% active); and partial sodium salt of N-lauryl-.beta.-iminodipropionic acid, R.sub.14N(CH.sub.2CH.sub.2COOH)(CH- .sub.2CH.sub.2COONa), (DERIPHAT.TM. 16.degree. C., 30% in water). Useful polyaminocarboxylic acids include R.sub.14C(.dbd.O)NHC.sub.2H.sub.4(NHC.s- ub.2H.sub.4).sub.yNHCH.sub.2COOH and R.sub.14-substituted ethylenediaminetetraacetic acid (EDTA), where R.sub.14.dbd.C.sub.4-C.sub.- 20 linear or branched, alkyl or alkenyl, and y=0-3.

[0059] Amphoteric imidazoline derivatives useful include those derived from variously substituted 2-alkyl-2-imidazolines and 2-alkenyl-2-imidazolines which have nitrogen atoms at the 1 and 3 positions of the five-membered ring and a double bond in the 2,3 position. The alkyl or alkenyl group may be a C.sub.4-C.sub.20 linear or branched chain. The amphoteric imidazoline derivatives are produced via reactions in which the imidazoline ring opens hydrolytically under conditions allowing further reaction with such alkylating agents as sodium chloroacetate, methyl (meth)acrylate, ethyl (meth)acrylate, and (meth)acrylic acid. Useful amphoteric surfactants derived from the reaction of 1-(2-hydroxyethyl)-2-(R.sub.1)-2-imidazolines with acrylic acid or acrylic acid esters, where R.sub.15=residue of coconut fatty acids, are:

[0060] cocoamphopropionate, R.sub.15--(.dbd.O)NHCH.sub.2CH.sub.2N(CH.sub.2- CH.sub.2OH)(CH.sub.2CH.sub.2COONa);

[0061] cocoamphocarboxypropionic acid,

R.sub.15--C(.dbd.O)NHCH.sub.2CH.sub.2N(CH.sub.2CH.sub.2COOH)(CH.sub.2CH.su- b.2CH.sub.2CH.sub.2COOH);

[0062] cocoamphocarboxypropionate,

R.sub.15--C(.dbd.O)NHCH.sub.2CH.sub.2N(CH.sub.2CH.sub.2COONa)(CH.sub.2CH.s- ub.2CH.sub.2CH.sub.2COONa);

[0063] cocoamphoglycinate, R.sub.15--(.dbd.O)NHCH.sub.2CH.sub.2N(CH2CH.sub- .2OH)(CH.sub.2COONa); and

[0064] cocoamphocarboxyglycinate,

[R.sub.5--C(.dbd.O)NHCH.sub.2CH.sub.2N.sup.+(CH.sub.2CH.sub.2OH)(CH.sub.2C- OONa).sub.2OH.sup.-.

[0065] Surface-active inner salts containing at least one quaternary ammonium cation and at least one carboxy anion are called betaines. The nomenclature for betaines derives from the single compound (trimethylammonio)acetate which is called betaine and exists as an inner salt. Betaines useful as amphoteric surfactants in the claimed invention include compounds of the general formulae: R.sub.16N.sup.+(CH.sub.3).sub.- 2CH.sub.2COO.sup.-; R.sub.16CONHCH.sub.2CH.sub.2CH.sub.2N.sup.+(CH.sub.3).- sub.2COO.sup.-; and R.sub.16--O--CH.sub.2--N.sup.+(CH.sub.3).sub.2CH.sub.2- COO.sup.-, where R.sub.16.dbd.C.sub.4-C.sub.20 linear or branched, alkyl, alkenyl, or fluoro or silicone functional hydrophobe group. Specific examples of betaines include N-dodecyl-N,N-dimethylglycine and cocamidopropyl betaine and (MONATERIC.TM. CAB available from Mona Industries).

[0066] Typically, when fluorocarbon substituents are attached to amphoteric surfactants, those substituents are perfluoroalky groups, branched or unbranched, having 6 to 18 carbon atoms. However, these substituents may instead be partially fluorinated. They may also bear aryl functionality. Examples of fluorocarbon amphoteric surfactants include fluorinated alkyl FLUORAD.TM. FC100 and fluorinated alkyl ZONYL.TM. FSK, produced by 3M and Dupont, respectively.

[0067] Typical siloxane functional amphoteric surfactants have, for example, the structures: 3

[0068] wherein R.sub.17 represents an amphoteric moiety and m+n=3 to 50. An example is the polyalkyl betaine polysiloxane copolymer ABIL.TM. B9950 available from Goldschmidt Chemical Corporation.

[0069] Macromolecular amphoteric surfactants useful in the claimed invention include: proteins, protein hydrolysates, derivatives of protein hydrolysates, starch derivatives, and synthetic amphoteric oligomers and polymers. Of particular utility are those macromolecular ampholytes bearing carboxy functionality.

[0070] Typically the imaging compositions are within a pH range of from 3 to 11 or such as from 4 to 7. Optionally, a base may be employed to maintain the desired pH. To assist in maintaining the second component within a desired pH range, any suitable base may be used. Examples of such bases include calcium carbonate, zinc oxide, magnesium oxide, calcium hydroxide or mixtures thereof. Bases are present in the imaging compositions in amounts of greater than 0.2 moles/100 gm of polymer to 2 moles/100 gm of polymer, or such as from 0.3 moles/100 gm of polymer to 1.75 moles/100 gm of polymer, or such as from 0.4 moles/100 gm of polymer to 1.5 moles/100 gm of polymer.

[0071] Optionally, polyvalent metal cations may be included to form an ionic bond with a carboxylic acid group on one or more of the monomers which compose the polymers. Any suitable polyvalent cation may be used which forms an ionic bond with the carboxylic acid groups to achieve cross-linking. Such cations include, but are not limited to, Mg.sup.2+, Sr.sup.2+, Ba.sup.2+, Ca.sup.2+, Zn.sup.2+, Al.sup.3+, Zr.sup.4+ or mixtures thereof. Such polyvalent cations are included in the imaging compositions in amounts of 0.001 to 0.1 moles/100 gm of dry polymer, or such as from 0.01 to 0.08 moles/100 gm of dry polymer, or such as from 0.02 to 0.05 moles/100 gm of dry polymer.

[0072] When one or more bases containing polyvalent cations are included in combination with another source of polyvalent cations, the sum of the amounts of base and polyvalent metal cation is greater than 0.2 to 2 moles/100 gm of polymer, or such as from 0.3 to 1.75 moles/100 gm of polymer, or such as from 0.4 to 1.5 moles/100 gm of polymer.

[0073] Optionally, antioxidants may be included in the second component to stabilize the color or shade change to ambient radiation. The antioxidants are believed to arrest the oxidation of color formers when the compositions are exposed to ambient radiation. Arresting the oxidation of the color formers inhibits further color or shade change from ambient radiation. Accordingly, a color or shade contrast between the portions of the composition marked by exposure to low intensity energy, such as by a laser, and the portions not exposed to the low intensity energy, but only to ambient radiation, are maintained or stabilized. Any suitable antioxidant which arrests the oxidation of color formers may be used. Examples of such antioxidants are hindered phenols and hindered amines.

[0074] Hindered phenols include one or two sterically bulky groups bonded to the carbon atom or atoms contiguous to the hydroxyl group-bonded carbon atom to sterically hinder the hydroxyl group. Examples of such hindered phenols are 2,6-di-tert-butyl-4-methylphenol, 2,2'-methylene-bis(4-methyl-6-tertbutylphenol), 2,6-methylene-bis(2-hydro- xy-3-tert-butyl-5-methyl-phenyl)4-methylphenol, 2,2'-methylene-bis(4-ethyl- -6-tert-butylphenol), 2,6-bis(2'-hydroxy-3'-tert-butyl-5'-methylbenzyl)4-m- ethyl-phenol, 2,4,4-trimethylphenyl-bis(2-hydroxy-3,5-dimethylphenyl)metha- ne, 2,2'-methylene-bis[4-methyl-6-(1-methylcyclohexyl)]phenol, 2,5-di-tert-butyl-4-methoxyphenol, 4,4'-butylidenebis(6-tert-butyl-3-meth- yl-phenol), and 1,1,3-tris(2-methyl-4-hydroxy-5-tertbutyl-phenyl)butane.

[0075] Hindered amines include one or two sterically bulky groups bonded to the carbon atom or atoms adjacent to a nitrogen atom to sterically hinder the nitrogen. The nitrogen itself may have bulky groups bonded to it. Examples of suitable hindered amines include 2,2,6,6-tetraalkylpiperi- dine compounds including N-substituted 2,2,6,6-tetraalkylpiperidine compounds. Such compounds contain a group having a formula: 4

[0076] where R.sub.18 hydrogen, (C.sub.1-C.sub.18)alkyl, (C.sub.1-C.sub.6)hydroxyalkyl, cyanomethyl, (C.sub.3-C.sub.8)alkenyl, (C.sub.3-C.sub.8)alkynyl, (C.sub.7-C.sub.12)aralkyl which may be unsubstituted or substituted in the alky moiety by hydroxyl, (C.sub.1-C.sub.8)alkanoyl or (C.sub.3-C.sub.5)alkenoyl; and R.sub.19 is hydrogen or methyl.

[0077] The antioxidants may be micro-encapsulated in any suitable microcapsule formulation and by any suitable micro-encapsulating method. The microcapsule prevents mutual contact of the antioxidant contained in the microcapsule with the other materials outside of the microcapsule by the isolating action of the microcapsule wall at room and storage temperatures. The microcapsules have increased permeability of their contents upon application of sufficient heat or pressure. Permeation may be controlled by selecting suitable microcapsule wall materials and microcapsule core materials. Examples of suitable wall materials include polyurethanes, polyureas, polyamides, polyesters, polycarbonates and combinations thereof. Typically, polyurethanes and polyureas are used to make the microcapsule wall.

[0078] The microcapsules may be formed by emulsifying the core material containing the antioxidant and subsequently forming a wall around drops of the emulsified core material. In preparation of the microcapsule, a reactant which forms the wall is added to the inside or outside of the drops. Specific procedures for forming microcapsules are described, for example, in U.S. Pat. No. 3,726,804, U.S. Pat. No. 3,796,696, U.S. Pat. No. 4,962,009, and U.S. Pat. No. 5,244,769.

[0079] Solvents suitable for forming the emulsion with the antioxidant include, but are not limited to, organic compounds such as phosphoric acid esters, phthalic acid esters, (meth)acrylic acid esters, other carboxylic acid esters, fatty acid amides, alkylated biphenyls, alkylated terphenyls, alkylated naphthalenes, diarylethanes, chlorinated paraffins, and mixtures thereof.

[0080] Auxiliary solvents may be added to the above-described organic solvents. Such solvents include, but are not limited to, ethyl acetate, isopropyl acetate, butyl acetate, methylene chloride, cyclohexanone, and mixtures thereof.

[0081] Protective colloids or surface active agents may be added to the aqueous phase for stabilizing the emulsified drops. Water-soluble polymers may be used as the protective colloids. An example of a suitable water-soluble polymer is carboxyl-modified polyvinyl alcohol.

[0082] The size of the microcapsules may vary in size. Typically, the microcapsules have an average diameter of 0.5 .mu.m to 15 .mu.m, or such as from 0.75 .mu.m to 10 .mu.m, or such as from 1 .mu.m to 5 .mu.m.

[0083] Optionally, one or more chain transfer agents may be used in the second component. Such chain transfer agents function as accelerators. Chain transfer agents or accelerators increase the rate at which the color or shade change occurs after exposure of energy. Any compound which accelerates the rate of color or shade change may be used. Accelerators may be included in the second component in amounts of from 0.01 wt % to 25 wt %, or such as from 0.5 wt % to 10 wt %. Suitable accelerators include, but are not limited to, onium salts, and amines.

[0084] Suitable onium salts include, but are not limited to, onium salts in which the onium cation is iodonium or sulfonium such as onium salts of arylsulfonyloxybenzenesulfonate anions, phosphonium, oxysulfoxonium, oxysulfonium, sulfoxonium, ammonium, diazonium, selononium, arsonium, and N-substituted N-heterocyclic onium in which N is substituted with a substituted or unsubstituted saturated or unsaturated alkyl or aryl group.

[0085] The anion of the onium salts may be, for example, chloride, or a non-nucleophilic anion such as tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, triflate, tetrakis-(pentafluorophosphate) borate, pentafluoroethyl sulfonate, p-methyl-benzyl sulfonate, ethylsulfonate, trifluoromethyl acetate and pentafluoroethyl acetate.

[0086] Examples of typical onium salts are diphenyl iodonium chloride, diphenyliodonium hexafluorophosphate, diphenyl iodonium hexafluoroantimonate, 4,4'-dicumyliodonium chloride, dicumyliodonium hexafluorophosphate, N-methoxy-a-picolinium-p-toluene sulfonate, 4-methoxybenzene-diazonium tetrafluoroborate, 4,4'-bis-dodecylphenyliodon- ium-hexafluoro phosphate, 2-cyanoethyl-triphenylphosphonium chloride, bis-[4-diphenylsulfonionphenyl]sulfide-bis-hexafluoro phosphate, bis-4-dodecylphenyliodonium hexafluoroantimonate and triphenylsulfonium hexafluoroantimonate.

[0087] Suitable amines include, but are not limited to primary, secondary and tertiary amines such as methylamine, diethylamine, triethylamine, heterocyclic amines such as pyridine and piperidine, aromatic amines such as aniline and n-phenyl glycine, quaternary ammonium halides such as tetraethylammonium fluoride, and quaternary ammonium hydroxides such as tetraethylammonium hydroxide. The triethanolamines of formula III also have accelerator activity.

[0088] Plasticizers also may be included in the second component. Any suitable plasticizer may be employed. Plasticizers may be included in amounts of from 0.5 wt % to 15 wt %, or such as from 1 wt % to 10 wt % of the second component. Suitable plasticizers include, but are not limited to, phthalate esters such as dibutylphthalate, diheptylphthalate, dioctylphthalate and diallylphthalate, glycols such as polyethylene glycol and polypropylene glycol, glycol esters such as triethylene glycol diacetate, tetraethylene glycol diacetate, and dipropylene glycol dibenzoate, phosphate esters such as tricresylphosphate, triphenylphosphate, amides such as p-toluenesulfoneamide, benzenesulfoneamide, N-n-butylacetoneamide, aliphatic dibasic acid esters such as diisobutyl-adipate, dioctyladipate, dimethylsebacate, dioctylazelate, dibutylmalate, triethylcitrate, tri-n-butylacetylcitrate, butyl-laurate, dioctyl-4,5-diepoxycyclohexane-1,2-dicarboxylate, and glycerine triacetylesters.

[0089] One or more flow agents also may be included in the second component. Flow agents may be included in amounts of from 0.05 wt % to 5 wt % or such as from 0.1 wt % to 2 wt % of the second component. Suitable flow agents include, but are not limited to, copolymers of alkylacrylates. An example of such alkylacrylates is a copolymer of ethyl acrylate and 2-ethylhexyl acrylate.

[0090] Optionally, one or more organic acids may be employed in the second component. Organic acids may be used in amounts of from 0.01 wt % to 5 wt %, or such as from 0.5 wt % to 2 wt %. Suitable organic acids include, but are not limited to, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, phenylacetic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, adipic acid, 2-ethylhexanoic acid, isobutyric acid, 2-methylbutyric acid, 2-propylheptanoic acid, 2-phenylpropionic acid, 2-(p-isobutylphenyl)propionic acid, and 2-(6-methoxy-2-naphthyl)propionic acid.

[0091] Optionally, one or more non-ionic and ionic surfactants may be used. Surfactants may be included in the compositions in amounts of from 0.5 wt % to 10 wt %, or such as from 1 wt % to 5 wt % of the component. Suitable non-ionic surfactants include, but are not limited to, polyethylene oxide ethers, derivatives of polyethylene oxides, aromatic ethoxylates, acetylenic ethylene oxides and block copolymers of ethylene oxide and propylene oxide. Suitable ionic surfactants include, but are not limited to, alkali metal, alkaline earth metal, ammonium, and alkanol ammonium salts of alkyl sulfates, alkyl ethoxy sulfates, and alkyl benzene sulfonates.

[0092] Thickeners may be included in conventional amounts. Any suitable thickener may be incorporated in the components. Typically, thickeners range from 0.05 wt % to 10 wt %, or such as from 1 wt % to 5 wt %. Suitable thickeners include, but are not limited to, low molecular weight polyurethanes such as having at least three hydrophobic groups interconnected by hydrophilic polyether groups. The molecular weight of such thickeners ranges from 10,000 to 200,000. Other suitable thickeners include hydrophobically modified alkali soluble emulsions, hydrophobically modified hydroxyethyl cellulose and hydrophobically modified polyacrylamides.

[0093] Rheology modifiers may be included in the components in conventional amounts. Typically rheology modifiers are used in amounts of from 0.5 wt % to 20 wt %, or such as from 5 wt % to 15 wt %. Rheology modifiers include, but are not limited to, vinyl aromatic polymers and acrylic polymers.

[0094] Diluents may be included to provide a vehicle or carrier for the components. Diluents are added as needed. Solid diluents or fillers are typically added in amounts to bring the dry weight of the components to 100 wt %. Solid diluents include, but are not limited to, celluloses. Liquid diluents or solvents are employed to make solutions, suspensions, dispersions or emulsions of the components. The solvents may be aqueous or organic, or mixtures thereof. Organic solvents include, but are not limited to, alcohols such as methyl, ethyl and isopropyl alcohol, diisopropyl ether, diethylene glycol dimethyl ether, 1,4-dioxane, terahydrofuran or 1,2-dimethoxy propane, and ester such as butyrolactone, ethylene glycol carbonate and propylene glycol carbonate, an ether ester such as methoxyethyl acetate, ethoxyethyl acetate, 1-methoxypropyl-2-acetate, 2-methoxypropyl-1-acetate, 1-ethoxypropyl-2-acetate and 2-ethoxypropyl-1-acetate, ketones such as acetone and methylethyl ketone, nitriles such as acetonitrile, propionitrile and methoxypropionitrile, sulfones such as sulfolan, dimethylsulfone and diethylsulfone, and phosphoric acid esters such as trimethyl phosphate and triethyl phosphate. Solvents also include coalescing solvents such as ethers. Examples of such ethers include ethylene glycol phenyl ether and tripropylene glycol n-butyl ether.

[0095] Additional optional additives which may be included in the components include, but are not limited to, defoaming agents, coalescing monomers, preservatives and mold inhibitors. They are included in conventional amounts.

[0096] The first and second components of the imaging compositions may be prepared by any suitable method. One method is to solubilize or disperse the water-insoluble imaging compounds and other water-insoluble compounds in a coalescing solvent. Any solvent which disperses or solubilizes the water-insoluble imaging compounds may be used. Such coalescing solvents include, but are not limited to, ester alcohols and glycol ethers. The solution or dispersion is then emulsified with an aqueous base portion containing polymer binders and other water-soluble compounds. Conventional emulsification methods may be used to prepare oil in water emulsions.

[0097] The components of the imaging compositions may be in the form of a concentrate. In such concentrates, the solids content may range from 80 wt % to 98 wt %, or such as from 85 wt % to 95 wt %. Concentrates may be diluted with water, one or more organic solvents, or a mixture of water and one or more organic solvents. Concentrates may be diluted such that the solids content ranges from 5 wt % to less than 80 wt %, or such as from 10 wt % to 70 wt %, or such as from 20 wt % to 60 wt %.

[0098] The imaging compositions may be applied to a work piece by any suitable method. Such methods include, but are not limited to, spray coating, brushing, roller coating, ink jetting, dipping and immersion.

[0099] Upon application of a sufficient amount of energy to the imaging compositions, a photofugitive or a phototropic response occurs. The amount of energy may be from 0.2 mJ/cm.sup.2 and greater, or such as from 0.2 mJ/cm.sup.2 to 100 mJ/cm.sup.2, or such as from 2 mJ/cm.sup.2 to 40 mJ/cm.sup.2, or such as from 5 mJ/cm.sup.2 to 30 mJ/cm.sup.2.

[0100] The second component of the imaging compositions undergoes color or shade changes with the application of intensities of 5 mW of energy or less (i.e., greater than 0 mW), or such as from less than 5 mW to 0.01 mW, or such as from 4 mW to 0.05 mW, or such as from 3 mW to 0.1 mW, or such as from 2 mW to 0.25 mW or such as from 1 mW to 0.5 mW. Typically, such intensities are generated with light sources in the visible range. Other photosensitizers and energy sensitive compounds, which may be included in the second component of the imaging compositions, may elicit a color or shade change upon exposure to energy from light outside the visible range. Such photosensitizers and energy sensitive compounds are included to provide a more pronounced color or shade contrast with that of the response caused by the application of 5 mW or less. Typically photosensitizers and energy sensitive compounds, which form the color or shade contrast with photosensitizers activated by energy at intensities of 5 mW or less, elicit a phototropic response.

[0101] While not being bound by theory, one or more color or shade changing mechanisms are believed involved to provide a color or shade change after energy is applied. For example, when a photofugitive response is induced, the one or more sensitizers release a free radical to activate the one or more photoreducing agents to reduce the one or more sensitizers to affect the color or shade change in the composition. When a phototropic response is induced, for example, free radicals from one or more sensitizers induce a redox reaction between one or more leuco-type compounds and one or more oxidizing agents to affect the color or shade change. Some formulations have combinations of photofugitive and phototropic responses. For example, exposing a composition to artificial energy, i.e., laser light, generates a free radical from one or more sensitizers which then activates one or more photoreducing agents to reduce the sensitizer to cause a photofugitive response, and then exposing the same composition to ambient light to cause one or more oxidizing agents to oxidize one or more leuco-type compounds.

[0102] Any suitable energy source may be used to induce the photofugitive or phototropic response. Examples of suitable energy sources include, but are not limited to, lasers, including lasers generated from hand held lasers and 3-D imaging systems, and flash lamps. Operating wavelengths of lasers may range from IR through UV. An example of a suitable laser is a neodymium (Nd) doped YAG laser operating at frequencies of 473 nm and 532 nm.

[0103] The imaging compositions provide a rapid and efficient means of changing the color or shade of a work piece or of placing an image on a work piece. After the imaging composition is applied to a work piece, a sufficient amount of energy is applied to the imaging composition to change its color or shade. The energy may be applied selectively to the imaging compositions. Generally, the color or shade change is stable. The term "stable" means that the color or shade change lasts at least 10 seconds, or such as from 20 minutes to 2 days, or such as from 30 minutes to 8 hours. Certain formulations which are sensitive to light at 473 nm are stable indefinitely under controlled conditions where blue light is filtered.

[0104] The image may be used as a mark or indicator to drill holes for fasteners to join parts together, cutting portions of the work piece and masking such as in the assembly of terrestrial vehicles such as automobiles, trucks, terrestrial and amphibious military vehicles, aeronautical ships such as airplanes and interplanetary vessels, marine vessels such as ships and boats, and terrestrial structures such as houses, buildings in general and furniture; and to form an outline for making a logo or picture on parts of terrestrial vehicles, aeronautical ships, marine vessels, terrestrial structures, and textiles. Since the compositions may be promptly applied to a work piece and the image promptly formed by application of energy to create color or shade contrast, workers no longer need to work adjacent the work piece to mark laser beam images with hand-held ink markers or tape in the fabrication of articles. Accordingly, the problems of blocking laser beams caused by workers using the hand-held markers and tape are eliminated.

[0105] Further, the reduction of human error increases the accuracy of marking. This is important when the marks are used to direct the alignment of parts where accuracy in fabrication is critical to the reliable and safe operation of the machine.

EXAMPLE 1

Imaging Composition

[0106] A primer or first component of the imaging composition has a formula as disclosed in Table 1 below.

1 TABLE 1 Compounds Percent Weight Film forming acrylic polymer binder 80 Zinc oxide 10 Cocoamphopropionate 5 Ethylene glycol phenyl ether 1 Water 4

[0107] The acrylic polymer is a latex polymer which may be prepared by known methods in the art, or may be obtained commercially from Rohm and Haas Company of Philidelphia, Pa. under the tradename RHOPLEX.TM. E-1801. The liquid compounds are blended together at room temperature to form an emulsion. The zinc oxide particles with an average size of 1 .mu.m are then blended with the emulsion at room temperature to form a suspension. The suspension has a white appearance due to the zinc oxide pigment.

[0108] The second component or photosensitive component has a formula as disclosed in Table 2 below. The compounds are combined at room temperature under red light.

2 TABLE 2 Compounds Weight Percent Copolymer of styrene and acrylic acid 25 Calcium carbonate 20 Cyclopentanone-2,5-bis[[4- 0.5 (diethylamino)phenyl]methylene]- Leuco Crystal Violet 1 o-chloro-hexaarylbiimidazole 6.5 1,2-naphoquinone 0.5 Triethanolamine triacetate 1.5 Polyalkyl betaine polysiloxane copolymer 2 Ester alcohol 8 Water 35

[0109] Copolymers of styrene and acrylic acid are known and methods for preparing them may be found in the literature. They also are commercially available from Rohm and Haas Company under the tradename RHOPLEX.TM. P-376. The copolymer is mixed in water with the polyalkyl betaine polysiloxane copolymer to form an aqueous suspension. Calcium carbonate is added to the suspension to maintain a pH of 8 to 11.

[0110] The imaging compounds: leuco crystal violet, o-chloro-hexaarylbiimidazole, 1,2-naphthaquinone, triethanolamine triacetate and cyclopentanone-2,5-bis[[4-(diethylamino)phenyl]methylene]-- are mixed together in the ester alcohol to form an organic solution. A commercially available ester alcohol is TEXANOL.TM., which is available from Eastman Chemical Co., Kingsport, Tenn. The aqueous suspension is emulsified with the organic solution using a conventional emulsifier to form an oil in water emulsion.

[0111] The primer is spray coated on a surface of an aluminum airplane body which is coated with an epoxy primer designated as BR127 manufactured and sold by American Cyanamide Corporation. The epoxy primer gives the aluminum surface a dark green appearance. The primer described in Table 1 provides a white contrast with the dark green aluminum surface.

[0112] The second component or photosensitive component is spray coated on the first component. The second component is amber in appearance. The workers selectively form a pattern of cross-marks on the imaging composition with a 532 nm green light laser at 5 mW to designate where holes are to be drilled for fasteners. The points on the photosensitive layer exposed to the laser turn from amber to a clear appearance revealing the white primer underlayer. The white of the cross-marks provides a clear contrast with the amber and dark green backgrounds such that workers may clearly determine where they are to drill the holes. After the holes are drilled the imaging composition is hand peeled from the aluminum surface and discarded. No developers or strippers are used to remove the imaging composition.

[0113] There is no indication that any of the dyes such as the leuco crystal violet or the cyclopentanone sensitizer dye leach out of the second component and into the epoxy primer. The red color characteristic of such leaching is not observed. Additionally, the inclusion of the zinc oxide pigment in the first component is expected to increase the photospeed of the color change by a .DELTA.=+0.5 to +1 as measured by a reflection densitometer.

EXAMPLE 2

Imaging Composition

[0114] A primer or first component of an imaging composition is composed of the compounds disclosed in Table 3 below.

3 TABLE 3 Compounds Weight Percent Vinyl acetate/acrylic copolymer emulsion 75 2-alkyl-2-imidazoline 4 Titanium dioxide 10 Ethylene glycol phenyl ether 1 Water 10

[0115] The vinyl acetate/acrylic copolymer is known in the art and methods of preparing it are well known. Such copolymers are commercially available from Rohm and Haas Company under the tradename ROVACE.TM. 661. The imidazoline is mixed with the ethylene glycol to form a uniform suspension and then added to the copolymer emulsion and mixed. This mixture is then mixed with water to form a suspension. The tintanium dioxide pigment with an average particle size of 0.51 .mu.m is mixed with the suspension to form a dispersion. The dispersion has a white appearance.

[0116] The following photosensitive component is prepared at room temperature under red light.

4TABLE 4 Component Weight Percent Vinyl acetate/acrylic copolymer emulsion 75 2-alkyl-2-imidazoline 2 Vinyl aromatic polymer 4 Leuco Crystal Violet 1 Tribromo methyl phenyl sulfone 5 2',4',5',7'-tetraiodo-3,4,5,6-tetrachlorofluorescein 1 disodium salt 2,2'-methylene-bis(4-methyl-6-tertbutylphenol) 1 Ethylene glycol phenyl ether 1 Water 10

[0117] The copolymer, vinyl aromatic polymer, and the 2-alky-2-imidazoline are mixed in water to form an aqueous emulsion.

[0118] The imaging components: leuco crystal violet, tribromo methyl phenyl sulfone, 2',4',5',7'-tetraiodo-3,4,5,6-tetrachlorofluorescein disodium salt, and micro-encapsulated 2,2'-methylene-bis(4-methyl-6-tertb- utylphenol) are solubilized in ethylene glycol phenyl ether to form an organic solution. The aqueous emulsion and the organic solution are mixed to form an oil in water emulsion imaging composition.

[0119] The first component of the imaging composition is roller coated on a surface of an aluminum airplane fuselage and dried. The fuselage is coated with BR127 epoxy primer which gives the aluminum surface a dark green color. The first component is white and provides a color contrast with the aluminum surface.

[0120] The second component of the imaging composition is spray coated on the first component. The second component is translucent and the white first component is visible under the photosensitive second component. The second component is then dried.

[0121] Workers selectively image an outline of a company logo on the second component of the imaging composition using a 3D, 532 nm Nd:YAG laser at 5 mW. The outline on the second component turns purple and the white background from the first component provides a sharp contrast between the purple outline and the dark green aluminum surface such that workers can readily distinguish the purple outline.

[0122] The imaging composition is scored along the purple outline and the portion within the outline is peeled from the fuselage and discarded leaving an exposed aluminum surface. The exposed aluminum is then painted to form the logo on the fuselage. The remainder of the imaging composition is then peeled from the fuselage and discarded. No developer or organic solvents are used to remove the imaging composition from the fuselage.

[0123] There is no indication of leaching of the dyes from the second component into the epoxy primer. No red color characteristic of such leaching is observed. Additionally, the inclusion of the pigment in the first component is expected to increase the photospeed of the color change by a .DELTA.=+0.5 to +1, as measured by a conventional reflection densitometer.

EXAMPLE 3

Comparative

[0124] The following composition is prepared at room temperature in an area having ambient light filtered of green light.

5 TABLE 5 Component Weight Percent Copolymer of styrene and acrylic acid 70 Sodium-N-coco-.beta.-aminopropionate 4 Aluminum oxide 10 Aminotriarylmethane dye 2 Tripropylene glycol n-butyl ether 2 Tribromo methyl sulfone 0.5 n-Phenyl glycine 0.5 Eosin B 1 Water 10

[0125] The sodium-N-coco-.beta.-aminopropionate is mixed with the styrene and acrylic copolymer to form a suspension. The dye, eosin B, n-phenyl glycine and sulfone are mixed together with tripropylene glycol n-butyl ether to form a second suspension. The two suspensions are mixed and then water is added to the mixture to form an oil in water emulsion. The mixing process is done at room temperature.

[0126] The aluminum oxide pigment with an average particle size of 0.5 .mu.m is added to the oil in water emulsion and mixed to form a dispersion. The mixing is done at room temperature.

[0127] The photosensitive dispersion is then spray coated on an aluminum plate 5 meters.times.5 meters. The aluminum plate is coated with a conventional epoxy primer used in priming aluminum airplane fuselages prior to painting. After application of the photosensitive dispersion to the primed aluminum plate, the interface between the aluminum plate and the photosensitive dispersion begins to turn a red color. The red color expands across the aluminum and also into the imaging composition. This undesired color change compromises the color or shade contrast between the portions of the imaging composition exposed to laser light and the aluminum plate. Accordingly, workers find it difficult to locate the marks formed on the imaging composition indicating the marks for modification of the aluminum plate. The red color is believed to be caused by the sensitizer dye eosin B leaching into the epoxy primer on the aluminum plate.

[0128] A primer having a formulation disclosed in the table below is prepared.

6 TABLE 6 Compound Percent Weight Copolymer of styrene and acrylic acid 80 Sodium-N-coco-.beta.-aminopropionate 2 Tripropylene glycol n-butyl ether 3 Aluminum oxide 10 Water 5

[0129] The primer is prepared by mixing the copolymer, sodium-N-coco-.beta.-aminopropionate and tripropylene glycol n-butyl ether to form a suspension. Aluminum oxide is added to the suspension followed by mixing in a conventional sonic mixer with water added during the process. The mixing is done at room temperature.

[0130] A photosensitive component is prepared as described in Table 5 above, except that the aluminum oxide pigment is excluded in the formulation. Water is added to the component to make up the weight difference and bring the component to 100 wt %.

[0131] The primer described in Table 6 is roller coated on a 5 meters.times.5 meters aluminum plate which is coated with an epoxy primer used in priming aluminum airplane fuselages prior to applying paint. The primer is dried and presents a white contrast with the dark green of the primer coated aluminum plate.

[0132] The photosensitive component is spray coated over the primer of Table 6 to form an imaging composition on the aluminum plate. The photosensitive component is dried over the primer or first component. The photosensitive component is translucent and the white underlying primer is visible creating a color contrast between the imaging composition and the dark green aluminum plate. No red color is observed forming on the aluminum or in the imaging composition. Accordingly, the eosin B sensitizer dye is not believed to be leaching from the photosensitive component.

[0133] A 532 nm laser at 5 mW is used to selectively affect a color change in the imaging composition with cross-marks. The color of the cross-marks is purple and presents a clear, visible contrast with the white background of the unexposed portions of the imaging composition and the dark green aluminum plate. Accordingly, workers can readily modify the aluminum plate based on the purple cross-marks.

[0134] In addition to preventing the sensitizer dye from leaching into the epoxy primer on the aluminum plate, and presenting improved color contrast over the photosensitive component, the imaging composition is expected to have an increased photospeed by a .DELTA.=+0.5 to +1, as measured by a reflection densitometer.

Claims

What is claimed is:

1. An imaging composition comprising a first component comprising one or more opacifying compounds, and a second component comprising one or more sensitizers.

2. The imaging composition of claim 1, wherein the one or more opacifying compounds are chosen from pigments, metal salts, silica, silicates and clays.

3. The imaging composition of claim 1, wherein the one or more sensitizers are chosen from xanthene compounds and cyclopentanone based conjugated compounds.

4. The imaging composition of claim 1, wherein the first component further comprises one or more adhesives.

5. The imaging composition of claim 1, wherein the second component further comprises one or more color formers.

6. The imaging composition of claim 1, wherein the second component further comprises one or more micro-encapsulated antioxidants.

7. An imaging composition comprising a first component comprising one or more opacifying compounds and one or more release agents, and a second component comprising one or more sensitizers and one or more release agents.

8. A method comprising: a) providing a first component of an imaging composition, the first component comprises one or more opacifying compounds; b) applying the first component of the imaging composition to a work piece; c) providing a second component of the imaging composition, the second component comprises one or more sensitizers; d) applying the second component of the imaging composition on the first component; e) applying energy to the imaging composition at powers of 5 mW or less to affect a color or shade change in the second component of the imaging composition; and f) executing a task on the work piece as directed by the color or shade change of the second component of the imaging composition to modify the work piece.

9. The method of claim 8, further comprising the step of removing the imaging composition from the work piece by peeling the imaging composition from the workpiece.

10. The method of claim 8, wherein the work piece is chosen from a terrestrial vehicle, an aeronautical ship, a marine vessel, a terrestrial structure, and a textile.