Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/30—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using chemical colour formers

Definitions

• This invention relates to thermally imageable compositions and to stabilizers for these compositions.
• the leuco dyes may initially be relatively colorless, but can return to a colored form when oxidized, e.g., by air under acidic conditions or any other suitable oxidizing agent.
• leuco dyes used in color image forming systems include triarylmethanes, xanthenes, styryl dyes, and azine dyes, such as, for example, phenoxazines, phenothiazines, and phenazines.
• thermally sensitive materials of the type wherein at least one leuco dye is in reactive proximity with an inorganic nitrate salt, whereby imagewise application of heat causes said nitrate salt to oxidize said leuco dye to produce a change in color a problem may arise from premature spotting or backgrounding of the thermally sensitive material during the drying step of the manufacturing process.
• the term "spotting” means oxidation of the leuco dye to a colored dye form in random irregular spots;
• backgrounding means oxidation of the leuco dye to a colored dye form in uniform fashion, resulting in an evenly colored background. Either spotting or backgrounding can destroy the usefulness of a transparency film bearing a thermally imageable composition.
• One method for preventing spotting involves drying of the imageable coating at low temperatures. This method, however, requires long drying times, slow coating speeds, ana nigh costs, and in most cases, does not offer a practical solution to the problem.
• thermally imageable transparency films based upon combinations of leuco dyes ano nitrate salts it is essential that the thermally imageable compositions show considerable stability to the thermal effects of the manufacturing process in order to have a useful shelf life.
• This invention involves the prevention of spotting and backgrounding of transparency films bearing thermally imageable compositions that contain combinations of leuco dyes and nitrate salts. Spotting and backgrounding which often occur during the drying step of the manufacturing process can be prevented by the addition of one or more Bronsted-Lowry bases, i.e. proton acceptors, which have conjugate acids with pKa values of zero or higher. These bases have conjugate acids with Ka values equal to or less than one.
• Bronsted-Lowry bases i.e. proton acceptors
• Effective additives include amines; amine oxides; amides; ureas; salts of phosphinic, phosphonic, and phosphoric acids; phosphines; salts of carboxylic acids; oxygen acids, e.g., alcohols and phenols; thioacids, e.g. mercaptans and thiophenols; salts or complexes of carbon acids; and inorganic bases.
• Addition of one or more of those bases which have conjugate acids with pKa values of zero or above results in decreases or elimination of spotting, thus allowing an increase in the drying temperature during the drying step of the manufacturing process, further resulting in faster drying, higher coating rates, decreased moisture sensitivity, and lower manufacturing costs,
• Reduction and elimination of defects in the coated film resulting from premature dye color formation can also be brought about by adding the anti-spotting compounds of the present invention to the imaging compositions.
• compositions which are imageable by thermal energy, e.g. infrared radiation, and coated substrates prepared therefrom, which compositions comprise (1) at least one leuco dye, (2) at least one inorganic nitrate salt, (3) a polymeric binder, (4) an optional acid, and (5) at least one antispotting compound selected from the group consisting of
• R l , R 2 , and R 3 can be the same or different and represent a member of the group selected from substituted or unsubstituted alkyl groups having 1 to 20 carbon atoms, substituted or unsubstituted alkenyl groups having from 1 to 16 carbon atoms, substituted or unsubstituted aryl groups having up to 3 fused rings.
• the tertiary amine can have the following structure: wherein R 1 is as defined above and represents, for example, where 1 is an integer from 0 to 6, inclusive, m is an integer from 0 to 6, inclusive, and n is an integer from 0 to 6, inclusive; where 1 and m are as defined above and n' is 0 or 4; where 1 and m are as defined above, and n" is an integer from 0 to 4, inclusive; where 1' is 0 or 4, m and n" are as defined above.
• the tertiary amine can also have the following structure: wherein R l is as defined above, and R 4 represents CR 5 R 6 where R 5 and R 6 represents a member of the class from which R 1 , R 2 , and R 3 are selected, with the proviso that R 5 and R 6 need not be the same as R l , R 2, or R 3.
• the tertiary amine can further have the following structure: wherein represents, for example, where x is 0, 1, or 2, y is an integer from 0 to 8, inclusive, and z is 0, 1, or 2, and R 7 represents a member of the class from which R 1 , R 2 , and R 3 are selected, with the proviso that R 7 need not be the same as R l, R 2, R 3; wherein R l and R 2 are as defined above. wherein R 1 and R 2 are as defined above. wherein R 1 is as defined above. wherein R 1 and R 2 are as defined above. wherein R 1 , R 2 , and R 3 are as defined above. wherein R 1 , R 2 and R 3 are as defined above.
• R 1 , R 2 , and R 3 are as defined above, and R 8 represents a member of the class from which R 1 , R 2 , and R 3 are selected, with the proviso that R 8 need not be the same as R 1 , R 2 , or R 3 .
• R 1 is as defined above, and A+ represents a metallic cation, e.g. Li + , Na + , K + , Mg +2 , Ca +2 , Mn +2 , Fe +3 , Ni +2 , Cu +2 , Zn +2 .. wherein R 1 and A+ are as defined above. wherein R 1 and A+ are as defined above.
• R 9 , R 10 , and R 11 can be the same or different and represent a member of the group selected from H, -NO 2 , -CN, -COR 12 , -COOR 12 , and -SO 2 R 12 where R 12 is selected from the group consisting of phenyl group, naphthyl group, alkyl group having 1 to 4 carbon atoms, and A+ is as defined above.
• the salts or complexes of carbon acids can also include the following structures wherein R 9 and A+ are as defined above and represent, for example, wherein a is 2, 3, or 4; where b is 0 or 4.
• the salts or complexes of carbon acids can further include the following structure wherein A+ is as defined above, and R 1 3 represents the phenyl or naphthyl group. wherein R 1 , R 2 , and A + are as defined above. wherein R l , R 2 , and A+ are as defined above. wherein R 1 , R 2 , and A+ are as defined above. wherein R 1 , R 2 , and R 3 are as defined above. wherein A+ is as defined above, and Y - represents a member of the group selected from - OH , S , HS , C03 , HC 0 3.
• R l , R 2 , or R 3 is a substituted alkyl or aryl group
• substituents can be any which do not deleteriously affect the function of the thermographic system.
• Suitable substituents include halo groups, e.g. chloro, bromo, iodo, fluoro; hydroxyl group; cyano group; nitro group; alkoxy group having, for example, 1 to 20 carbon atoms; alkyl carbonyl group having, for example, 1 to 20 carbon atoms; alkylsulfonyl group, having, for example, 1 to 20 carbon atoms.
• R 1 , R 2 , or R 3 is a substituted aryl group
• the substituent can be alkylthio, having, for example, from 1 to 20 carbon atoms.
• R 1 , R 2 , R 3 can be mono-, di-, tri-, or tetra- substituted.
• Dye classes which can be stabilized by the bases include styryl, phenoxazine, phenothiazine, and phenazine.
• styryl dyes are (a) 2,3-dihydro-1,3,3-trimethyl-2-[2-(2,4,6-trimethoxyphenyl)ethenyl]-1H-Indole; (b) 2-bromo-4-[2-(5-chloro-2,3-dihydro-1,3,3-trimethyl-lH-indol-2-yl)ethenyl]-N,N-dimethylbenzenamine; (c) 2,3-dihydro-1,3,3-trimethyl-2-[2-(4-dimethylamino)-phenyl-ethenyl]-lH-Indole; (d) 2,3-dihydro-1,3,3-trimethyl-2-[2-(4-N-morpholino-)phenyl-ethenyl]
• phenoxazine and phenothiazine dyes are: (f) 3,7-bis-(N,N-diethylamino)-10-benzoyl-phenoxazine and (g) 3,7-bis-(N,N-dimethylamino)-10-benzoyl-phenothiazine, respectively.
• phenazine dyes are; (h) 5,10-di- hydro-5-phenyl-10-benzoyl-3,7-bis-(N,N-diethylamino)phenazine and (i) 5,10-dihydro-5-ethyl-10-benzoyl-3,7-bis-(N,N-dimethylamino)phenazine.
• Nitrate salts suitable for this invention are themselves well known. They may be supplied as various chemical compounds, but are desirably provided as a metal salt, and most preferably provided as a hydrated metal salt. Most means of supplying the nitrate salt into the imaging composition are satisfactory. For example, organic salts, metal salts, acid salts, mixtures of acids and salts, and other means of supplying the ion are useful. Nitrates of zinc, cadmium, potassium, calcium, zirconyl (zr0 2 ), nickel, aluminum, chromium, iron, copper, tin, magnesium, lead, and cobalt, ammonium nitrate, and cerous ammonium nitrate can be used.
• the nitrate salt component of the present invention must be present in a form within the imaging composition so that oxidant (i.e., decomposition products of the nitrate) will be provided within the composition when it is heated to a temperature no greater than 200°F (93°C) for 60 seconds and preferably no greater than 160°F (71°C) for 60 or most preferably 30 seconds.
• the salt must be chosen so that the cation thereof is non-reactive with the leuco dye.
• non-reactive salts are defined as those salts the cations of which do not spontaneously oxidize the dyes that they are associated with at room temperature.
• Preferred salts are the hydrated metal salts such . as nickel nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, ferric nitrate nonahydrate, cupric nitrate trihydrate, zinc nitrate hexahydrate, cadmium nitrate tetrahydrate, bismuth nitrate pentahydrate, thorium nitrate tetrahydrate, cobalt nitrate hexahydrate, gadolinium or lanthanum nitrate nonahydrate, and mixtures of these hydrated nitrates.
• Nonhydrated or organic nitrates may be admixed therewith.
• nitrate ion per mole of dye It is preferred to have at least 0.10 mole of nitrate ion per mole of dye. It is more preferred to have at least 0.30 or 0.50 mole of nitrate ion per mole of dye.
• the bases described in this invention can be used at as low a concentration as 0.05 equivalent of base per equivalent of nitrate ion, or as high as 1.0 equivalent of base per equivalent of nitrate ion.
• the preferred range is from about 0.3 to about 0.6 equivalent of base per equivalent of nitrate ion.
• the thormally stimulated oxidation of the leuco dye by the nitrate salt can be facilitated by the presence of an acid.
• the acids optionally useful in the thermographic system of this invention are acids as generally known to the skilled chemist.
• Organic acids, preferably those having carboxylic groups, such as phthalic acid, are preferred, but inorganic acids can also be used.
• the acid can be present in a ratio of from 0 to 10 times the amount of the nitrate ion.
• the binder be selected from polymeric materials.
• Such resins as polyvinyl acetals, e.g., polyvinyl butyral, polyVinyl resins: polyvinylpyrrolidone, polyesters, polycarbonates, polyamides, polyacrylates, cellulose esters, copolymers and blends of these classes of resins, can be used. Saran, a vinyl chloride-vinylidene chloride copolymer, is particularly preferred. Natural polymeric materials such as gelatin and gum arabic can also be used.
• the leuco dye should be present at a concentration of at least 0.3% by weight, based on the weight of the binder, preferably at a concentration of at least 1% by weight, based on the weight of the binder, and most preferably at a concentration of from 2 to 10% or more by weight, based on the weight of the binder.
• a formulation which can be applied by conventional coating techniques can be produced by dissolving the leuco dye, the metal nitrate, and the polymeric binder, together with an organic acid, and, optionally, a conventional stabilizing compound, e.g. catechol, phenidone, along with the base whose conjugate acid has the required pKa in an inert organic solvent, such as, for example, acetone, methyl ethyl ketone, or tetrahydrofuran.
• a conventional stabilizing compound e.g. catechol, phenidone
• the formulation can be coated onto a support by methods well known in the art, such as, for example, wire-wound rod, knife, or extrusion coating.
• Typical wet thickness of the layer can range from about 10 to about 100 micrometers ( m), and the layer can be dried in forced air at temperatures ranging from 20°C to 50°C. It is preferred that the coating thickness be selected to provide maximum image densities greater than 0.2, and more preferably in the range of 0.5 to 1.5, as measured on a MacBeth Color Densitometer Model TD 504 using the color filter complementary to the dye color.
• the support material can be selected from a wide range of materials, including paper, glass, polymeric film, and the like, depending upon the particular imaging requirement.
• Preferred materials include polymers having good heat stability, such as polyesters.
• a particularly preferred polyester is polyethylene terephthalate.
• the additive is less effective as an antispotting agent.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Heat Sensitive Colour Forming Recording (AREA)

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• 1985
  • 1985-03-07 CA CA000475897A patent/CA1236299A/en not_active Expired
  • 1985-03-13 AU AU39800/85A patent/AU580034B2/en not_active Ceased
  • 1985-04-12 EP EP85302573A patent/EP0159874B1/de not_active Expired - Lifetime
  • 1985-04-12 DE DE8585302573T patent/DE3583524D1/de not_active Expired - Fee Related
  • 1985-04-12 BR BR8501734A patent/BR8501734A/pt not_active IP Right Cessation
  • 1985-04-15 JP JP60080044A patent/JPH0671823B2/ja not_active Expired - Lifetime

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