The present invention relates to the use of oil-soluble copolymers which comprise

The present invention relates to the use of copolymers containing structural units of olefinically unsaturated, hydroxyl-containing compounds and further olefinically unsaturated compounds containing alkyl radicals for improving the lubricity of middle distillates, and to middle distillate fuel oils containing these additives.
Mineral oils and mineral oil distillates which are used as fuel oils generally contain 0.5% by weight or more of sulfur, which causes the formation of sulfur dioxide on combustion. In order to avoid the environmental pollution resulting therefrom, the sulfur content of fuel oils is continually being reduced. The EN 590 standard relating to diesel fuels currently prescribes a maximum sulfur content of 500 ppm in Germany. In Scandinavia, fuel oils containing less than 200 ppm and in exceptional cases containing less than 50 ppm of sulfur are already in use. These fuel oils are generally prepared by hydrorefining the fractions obtained from crude oil by distillation. During the desulfurization, however, other substances which give the fuel oils natural lubricity are also removed. These substances include, inter alia, polyaromatic and polar compounds.
However, it is now been found that the friction- and wear-reducing properties of fuel oils worsen with increasing degree of desulfurization. These properties are frequently so inadequate that signs of corrosion must be expected after only a short time on the materials lubricated by the fuel, for example the distributor injection pumps of diesel engines. The further lowering of the 95% distillation point to below 370xc2x0 C., in some cases to below 350xc2x0 C. or below 330xc2x0 C., which has in the meantime been adopted in Scandinavia intensifies this problem further.
Approaches which claim to be a solution to this problem have therefore been described in the prior art (so-called lubricity additives).
EP-A-0 680 506 discloses esters of carboxylic acids having 2 to 50 carbon atoms as additives for improving the lubricity of low-sulfur middle distillates containing less than 0.5% by weight of S.
DD-126 090 discloses lubricity-improving additives containing copolymers of ethylene and unsaturated carboxylic esters, preferably vinyl acetate, which are added to the fuels in amounts of from 0.01 to 0.5% by weight.
EP-A-0 764 198 discloses additives which improve the lubricity of fuel oils and comprise polar nitrogen compounds based on alkylamines or alkylammonium salts containing alkyl radicals having 8 to 40 carbon atoms.
DE-A-15 94 417 discloses additives for improving the lubricity of oleophilic liquids containing esters of glycols and dicarboxylic acids having at least 11 carbon atoms.
EP-A-0 635 558 discloses diesel oils having sulfur contents of below 0.2% by weight and aromatics contents of below 30% by weight. These diesel oils are mixed with from 100 to 10,000 ppm of C1-C5-alkyl esters of unsaturated straight-chain C12-C22-fatty acids derived from oilseed as additives.
EP-A-0 074 208 discloses middle and heavy distillates which have been mixed with copolymers of ethylene and oxyalkylated acrylates or ethylene and vinyl esters of saturated and unsaturated carboxylic acids as additives.
EP-A-0 856 533 discloses copolymers based on vinyl esters of carboxylic acids, vinylaromatic hydrocarbons, hydroxyl-functional unsaturated monomers and further polymerizable polymers. The polymers have OH numbers of 110-170 mg of KOH/g and have molecular weights of 1500-8000 g/mol. However, the polymers are used, according to the disclosure content of the document, for the production of surface coatings for paints. Use in connection with fuel oils is not disclosed.
U.S. Pat. No. 3,915,668 discloses terpolymers of ethylene, 10-25% by weight of C1-C8-alkylvinyl esters and 10-30% by weight of dialkylvinylcarbinol and their use for improving the cold-flow properties of crude oils and residual oils. The suitability of such terpolymers for improving the lubricity of distillate fuels is not disclosed.
The object of the present invention was to find additives which result in an improvement in lubricity in middle distillates which have been substantially freed from sulfur and aromatic compounds. At the same time, these additives should also have a favorable effect on the cold-flow properties of these middle distillates.
Surprisingly, it is been found that oil-soluble copolymers of ethylenically unsaturated compounds carrying one or more hydroxyl groups and ethylenically unsaturated compounds containing hydrocarbon groups having at least 6 carbon atoms impart the requisite properties to the fuel oils to which they are added as additives.
The invention thus relates to the use of oil-soluble copolymers which comprise
A) from 5 to 80 mol-% of structural units derived from olefinically unsaturated compounds containing at least one free hydroxyl group,
B) from 5 to 95 mol-% of structural units derived from olefinically unsaturated compounds carrying a hydrocarbon radical having at least 6 carbon atoms, and, if desired,
C) from 0 to 40 mol-% of further structural units selected from the group consisting of acrylic acid, acrylates, vinyl esters, vinylethane and alkenes, with the proviso that the structural units mentioned under C) are different from the structural units mentioned under A) and B),
and have a mean molecular weight Mw of from 500 to 100,000 g/mol and an OH number of from 10 to 300 mg of KOH/g, for improving the lubricity and cold flow properties of middle distillates having a sulfur content of less than 0.5% by weight.
The invention furthermore relates to middle distillate fuel oils having a sulfur content of less than 0.5% by weight which contain copolymers of the type defined above.
In a preferred embodiment of the invention, the copolymer has an OH number of from 20 to 250, in particular from 25 to 200, mg of KOH/g. In a further preferred embodiment, the copolymer has a mean molecular weight Mw of from 700 to 10,000 g/mol. In a further preferred embodiment, the proportion of the structural units (A) is from 10 to 70 mol-%, in particular from 15 to 60 mol-%.
The olefinically unsaturated compounds which make up the copolymers (A) are preferably vinyl esters, acrylates, mono- and diesters of ethylenically unsaturated carboxylic acids, methacrylates, alkyl vinyl ethers and/or alkenes carrying hydroxyalkyl, hydroxyalkenyl, hydroxycycloalkyl or hydroxyaryl radicals. These radicals contain at least one hydroxyl group, which can be in any desired position of the radical, but is preferably at the chain end (co-position) or in the para-position in the case of ring systems.
The vinyl esters are preferably those of the formula 1
CH2=CHxe2x80x94OCOR1xe2x80x83xe2x80x83(1)
in which R1 is C1-C30-hydroxyalkyl, preferably C1-C12-hydroxyalkyl, especially C2-C6-hydroxyalkyl, and the corresponding hydroxyoxalkyl radicals. Suitable vinyl esters include 2-hydroxyethyl vinyl ester, xcex1-hydroxypropyl vinyl ester, 3-hydroxypropyl vinyl ester and 4-hydroxybutyl vinyl ester, and diethylene glycol monovinyl ester.
The acrylates are preferably those of the formula 2
CH2=CR2xe2x80x94COOR3xe2x80x83xe2x80x83(2)
in which R2 is hydrogen or methyl, and R3 is C1-C30-hydroxyalkyl, preferably C1-C12-hydroxyalkyl, especially C2-C6-hydroxyalkyl, and the corresponding hydroxyoxalkyl radicals. Suitable acrylates include hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxy-propyl acrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, hydroxyisopropyl acrylate, 4-hydroxybutyl acrylate and glycerol monoacrylate. The corresponding esters of methacrylic acid, and esters of ethylenically unsaturated dicarboxylic acids, such as maleic acid, fumaric acid and itaconic acid, with diols are just as suitable.
The alkyl vinyl ethers are preferably compounds of the formula 3
CH2=CHxe2x80x94OR4xe2x80x83xe2x80x83(3)
in which R4 is C1-C30-hydroxyalkyl, preferably C1-C12-hydroxyalkyl, especially C2-C6-hydroxyalkyl, and the corresponding hydroxyoxalkyl radicals. Suitable alkyl vinyl ethers include 2-hydroxyethylvinylether, hydroxypropyl vinyl ether, hexanediol monovinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether and cyclohexanedimethanol monovinyl ether.
The alkenes are preferably monounsaturated hydroxyhydrocarbons having 3 to 30 carbon atoms, in particular 4 to 16 carbon atoms, especially 5 to 12 carbon atoms. Suitable alkenes include dimethylvinylcarbinol (=2-methyl-3-buten-2-ol), allyloxypropanediol, 2-butene-1,4-diol, 1-buten-3-ol, 3-buten-1-ol, 2-buten-1-ol, 1-penten-3-ol, 1-penten-4-ol, 2-methyl-3-buten-1-ol, 1-hexen-3-ol, 5-hexen-1-ol and 7-octene-1,2-diol.
Preferred comonomers (B) are olefinically unsaturated compounds carrying hydrocarbon radicals having at least 6 carbon atoms (excluding the olefinic group necessary for the polymerization). These hydrocarbon radicals can be linear, branched, cyclic and/or aromatic. Besides hydrocarbon groups, they can also carry secondary amounts of further functional groups containing heteroatoms, such as, for example, nitro, halogen, cyano or amino groups, so long as these do not impair the oil solubility. These are preferably monomers from the following groups:
B1) Vinyl esters of carboxylic acids having at least 7 carbon atoms, such as, for example, vinyl octanoate, vinyl 2-ethylhexanoate, vinyl laurate, vinyl octadecanoate, vinyl neononanoate, vinyl neodecanoate, vinyl neoundecanoate or vinyl neododecanoate.
B2) (Meth)acrylic esters with alcohols having at least 6 carbon atoms, such as, for example, octyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, undecenyl acrylate, dodecyl acrylate, tetradecyl acrylate, hexadecyl acrylate, oleyl acrylate, behenyl acrylate, and the corresponding esters of methacrylic acid, and esters of ethylenically unsaturated dicarboxylic acids, such as maleic acid, fumaric acid or itaconic acid
B3) Alkyl vinyl ethers carrying at least one C6-alkyl radical, such as, for example, octadecyl vinyl ether
B4) Olefins and vinylaromatic compounds having chain lengths of at least 6 carbon atoms, such as, for example, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, technical grade ∀-olefin cuts, such as C20-C24-∀-olefin, C24-C8-∀-olefin, C30+-∀-olefin, styrene, ∀-methylstyrene and p-methoxystyrene.
It is possible to use either individual comonomers B or mixtures of different comonomers of the individual and/or different monomers B1) to B4). Particularly preferred comonomers (B) are the above-mentioned olefinically unsaturated compounds from groups B1) to B4) containing hydrocarbon radicals having at least 8 carbon atoms. Preferably at least 10 mol-%, particularly preferably at least 25 mol-%, especially more than 50 mol-%, of the monomers (B) carry linear hydrocarbon radicals. The proportion of comonomers (B) in the polymers according to the invention is preferably from 30 to 90 mol-%, in particular from 40 to 80 mol-%.
As further comonomers C), up to 40 mol-% of acrylic acid or methacrylic acid, acrylates, such as methyl acrylate, ethyl acrylate or butyl acrylate, and the corresponding methacrylic esters, vinyl esters, such as vinyl acetate, vinyl propionate or vinyl hexanoate, or olefins, such as ethylene, propene, butene, isobutene, pentene, hexene, 4-methylpentene, diisobutylene or norbornene, can be copolymerized if desired. It is likewise possible for nitrogen-containing monomers, such as, for example,
a) aminoalkyl acrylates and methacrylates, such as, for example, aminoethyl acrylate, aminopropyl acrylate, amino-n-butyl acrylate, N-methylaminoethyl acrylate, N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate, N,N-dimethylaminopropyl acrylate or N,N-diethylaminopropyl acrylate, and the corresponding methacrylates,
b) alkylacrylamides and methacrylamides, such as, for example, ethylacrylamide, butylacrylamide, N-octylacrylamide, N-propyl-N-methoxyethylacrylamide, N-acryloylphthalimide, N-acryloylsuccinimide or N-methylolacrylamide, and the corresponding methacrylamides,
c) vinylamides, such as, for example, N-vinyl-N-methylacetamide or N-vinylsuccinimide,
d) aminoalkyl vinyl ethers, such as, for example, aminopropyl vinyl ether, diethylaminoethyl vinyl ether or dimethylaminopropyl vinyl ether,
e) allylamine, N-allyl-N-methylamine, N-allyl-N-ethylamine or diallylamine
f) heterocyclic compounds carrying a vinyl group, such as, for example, N-vinylpyrrolidone, methylvinylimidazole, 2-vinylpyridine, 4-vinylpyridine, 2-methyl-5-vinylpyridine, vinylcarbazole, vinylimidazole, N-vinyl-2-piperidone or N-vinylcaprolactam,
to be copolymerized.
In order to achieve easier handling and better solubility of the additives, preferably up to 20 mol-%, in particular up to 10 mol-%, of the comonomers B) and, if used, C) contain branched alkyl chains. Oligomers and polymers of lower olefins, such as, for example, polypropylene, polybutene and polyisobutylene, are also suitable here, preference being given to oligomers having a high content of terminal double bonds ( greater than 50 mol-%, preferably  greater than 70 mol-%, in particular  greater than 75 mol-%).
The melt viscosities of the copolymers at 140xc2x0 C. are preferably less than 10,000 mPas, in particular from 10 to 2000 mPas, especially from 15 to 1000 mPas. For the purposes of the invention, xe2x80x9coil-solublexe2x80x9d is taken to mean that at least 10% by weight, preferably at least 1% by weight, in particular at least 0.1% by weight, of the additive forms a clear solution in the middle distillates to which the additive is to be added.
The copolymerization of the copolymers is carried out by known batch or continuous polymerization processes (cf. in this respect, for example, Ullmanns Encyclopxc3xa4die der Technischen Chemie [Ullmann""s Encyclopaedia of Industrial Chemistry], 5th Edition, Vol. A21, pages 305 to 413). Suitable polymerizations are in solution, in suspension, in the gas phase, and precipitation and bulk polymerization. Preference is given to bulk and solution polymerization. The reaction of the comonomers is initiated by free radical-forming initiators (free-radical chain initiators). This class of substances includes, for example, oxygen, hydroperoxides, peroxides and azo compounds, such as cumene hydroperoxide, t-butyl hydroperoxide, dilauroyl peroxide, dibenzoylperoxide, bis(2-ethylhexyl) peroxydicarbonate, t-butyl permaleate, t-butylperpivalate, t-butyl perbenzoate, dicumyl peroxide, t-butyl cumyl peroxide, di(t-butyl) peroxide, 2,2xe2x80x2-azobis(2-methylpropionitrile) and 2,2xe2x80x2-azobis-(2-methylbutyronitrile). The initiators are employed individually or as a mixture of two or more substances in amounts of from 0.01 to 20% by weight, preferably from 0.05 to 10% by weight, based on the copolymer mixture.
The polymerization is generally carried out at temperatures of 40-300xc2x0 C., preferably at 80-250xc2x0 C., it being advantageous to work under pressure if monomers and/or solvents having boiling points below the polymerization temperature are used. The polymerization is advantageously carried out with exclusion of air, for example under nitrogen, since oxygen has an adverse effect on the polymerization. When selecting the initiator or initiator system, it is advantageous to ensure that the half-value period of the initiator or initiator system is less than 3 hours at the selected polymerization temperature. It is preferably between 0.5 minute and one hour.
The desired molecular weight of the copolymers is obtained for a given composition of the comonomer mixture by varying the reaction parameters concentration and temperature. In order to produce low-molecular-weight copolymers, it is furthermore possible to add moderators. Suitable molecular weight regulators are, for example, aldehydes, ketones, alcohols and organosulfur compounds, such as mercaptoethanol, mercaptopropanol, mercaptoacetic acid, mercaptopropionic acid, tert-butyl mercaptan, n-butyl mercaptan, n-octyl mercaptan, tert-dodecyl mercaptan and n-dodecyl mercaptan. Depending on the target viscosity, the moderators are used in amounts of up to 20% by weight, preferably from 0.05 to 10% by weight, based on the copolymer mixture.
Suitable apparatuses for the polymerization are, for example, conventional stirred reactors having, for example, anchor, paddle, impeller and multi-stage impulse countercurrent agitators, and for continuous preparation stirred reactor cascades, stirred reactors or static mixers.
Besides solvent-free bulk polymerization, the preferred process for the preparation of the copolymers according to the invention is solution polymerization. It is carried out in the solvents in which the monomer and the copolymers formed are soluble. Suitable solvents here are all those which satisfy this criterion and do not undergo any reactions with the monomers and the copolymers formed. These are, for example, organic, preferably aromatic solvents, such as cumene, toluene, xylene, ethylbenzene or alternatively commercial solvent mixtures, such as (copyright)Solvent Naphtha, (copyright)Shellsol AB or (copyright)Solvesso 150 or 200.
In the preparation, all monomers can be initially introduced and polymerized by addition of a free-radical chain initiator and supply of heat.
However, it is advantageous to initially introduce the solvent and, if desired, a part-amount of the monomers (for example about 5-20%) and to meter the remainder of the monomer mixture in together with the initiator and, if used, co-initiator and regulator.
The concentration of the monomers to be polymerized is from 20 to 95% by weight, preferably from 50 to 90% by weight.
The solid terpolymer can be isolated by precipitation using suitable non-solvents, such as acetone or methanol, or by evaporation of the solvent. However, it is advantageous to select a solvent for the polymerization in which the polymer can be employed directly in accordance with the invention.
Furthermore, the lubricity of oils can be improved in the manner according to the invention by mixing them with copolymers obtained by oxyalkylation of copolymers containing acid groups. Copolymers which are suitable for this purpose are, for example, those of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid or maleic anhydride with the comonomers B and, if used, C. In order to prepare an additive which improves the lubricity of oils, these copolymers containing acid groups are oxyalkylated at the acid groups using C1- to C10-alkylene oxides. Preferred alkylene oxides are ethylene oxide, propylene oxide and butylene oxide. The oxyalkylation can preferably be carried out using from 0.5 to 10 mol. in particular from 1 to 5 mol, especially from 1 to 2 mol, of alkylene oxide per mol of acid groups.
The copolymers according to the invention are added to mineral oils or mineral oil distillates in the form of solutions or dispersions containing from 10 to 90% by weight, preferably 20-80% by weight, of the copolymers. Suitable solvents or dispersion media are aliphatic and/or aromatic hydrocarbons or hydrocarbon mixtures, for example benzine fractions, kerosene, decane, pentadecane, toluene, xylene, ethylbenzene or commercial solvent mixtures, such as solvent naphtha, (copyright)Shellsol AB, (copyright)Solvesso 150, (copyright)Solvesso 200, (copyright)Exxsol, (copyright)ISOPAR and (copyright)Shellsol D grades. Other suitable solvents are oil-soluble esters of native origin, such as, for example, triglycerides of fatty acids and methyl esters of fatty acids, such as methyl esters of rapeseed oil acid and soya oil acid. Mineral oils or mineral oil distillates whose lubricity and/or cold-flow properties have been improved by the copolymers contain from 0.001 to 2, preferably from 0.005 to 0.5% by weight of copolymer, based on the distillate.
The copolymers according to the invention can furthermore be used in the form of mixtures consisting of copolymers of the claimed type, but of different qualitative and/or quantitative composition and/or of different viscosity (measured at 140xc2x0 C.). The mixing ratio (in parts by weight) between the copolymers can be varied over a broad range and can be, for example, from 20:1 to 1:20, preferably from 10:1 to 1:10. In this way, the additives can be matched specifically to individual requirements.
In order to produce additive packages for specific problem solutions, the copolymers according to the invention can also be employed together with one or more oil-soluble co-additives which per se improve the cold-flow properties and/or lubricity of crude oils, lubricating oils or fuel oils. Examples of such co-additives are ethylene copolymers or terpolymers containing vinyl acetate, polar compounds which effect paraffin dispersion (paraffin dispersants), comb polymers, alkylphenol-aldehyde resins and oil-soluble amphiphiles.
Thus, mixtures of the terpolymers with copolymers containing from 10 to 40% by weight of vinyl acetate and from 60 to 90% by weight of ethylene have proven highly successful. In accordance with a further refinement of the invention, the terpolymers prepared in accordance with the invention are employed as a mixture with ethylenevinyl acetate-vinyl neononanoate or ethylene-vinyl acetate-vinyl neodecanoate terpolymers for improving the flow properties of mineral oils or mineral oil distillates. The terpolymers of vinyl neononanoate or vinyl neodecanoate contain, in addition to ethylene, from 10 to 35% by weight of vinyl acetate and from 1 to 25% by weight of the respective neo compounds. Further preferred copolymers contain, in addition to ethylene and from 10 to 35% by weight of vinyl esters, from 0.5 to 20% by weight of an olefin, such as diisobutylene, 4-methylpentene or norbornene. The mixing ratio between the terpolymers prepared in accordance with the invention and the ethylene-vinyl acetate copolymers described above or the terpolymers of ethylene, vinyl acetate and the vinyl esters of neononanoic acid or neodecanoic acid is (in parts by weight) from 20:1 to 1:20, preferably from 10:1 to 1:10.
For use as a flow improver and/or lubricity additive, the copolymers according to the invention can furthermore be employed as a mixture with paraffin dispersants. These additives reduce the size of the paraffin crystals and mean that the paraffin particles do not separate out, but instead remain dispersed in colloidal form with significantly reduced sedimentation tendency. Furthermore, they increase the lubricity of the copolymers according to the invention. Paraffin dispersants which have proven successful are oil-soluble polar compounds containing ionic or polar groups, for example amine salts and/or amides obtained by reaction of aliphatic or aromatic amines, preferably long-taking aliphatic amines, with aliphatic or aromatic mono-, di-, tri- or tetracarboxylic acids or anhydrides thereof (cf. U.S. Pat. No 4,211,534). Other paraffin dispersants are copolymers of maleic anhydride and xcex1,xcex2-unsaturated compounds, which can, if desired, be reacted with primary monoalkylamines and/or aliphatic alcohols (cf. EP 0 154 177), the products of the reaction of alkenylspirobislactones with amines (cf. EP 0 413 279 B1) and, in accordance with EP 0 606 055 A2, products of the reaction of terpolymers based on xcex1, xcex2-unsaturated dicarboxylic anhydrides, xcex1,xcex2-unsaturated compounds and polyoxyalkylene ethers of lower unsaturated alcohols. Alkylphenol-aldehyde resins are also suitable as paraffin dispersants.
Thus, the copolymers according to the invention can be employed as a mixture with alkylphenol-formaldehyde resins. In a preferred embodiment of the invention, these alkylphenol-formaldehyde resins are those of the formula 5
which R6 is C4-C50-alkyl or -alkenyl, R7 is ethoxy and/or propoxy, n is a number from 5 to 100, and p is a number from 0 to 50.
Finally, in a further proven variant of the invention, the copolymers according to the invention are used together with comb polymers. These are taken to mean polymers in which hydrocarbon radicals having at least 8, in particular at least 10, carbon atoms are bonded to a polymer backbone. These are preferably homopolymers whose alkyl side chains contain at least 8 and in particular at least 10 carbon atoms. In the case of copolymers, at least 20%, preferably at least 30%, of the monomers have side chains (Comb-like Polymersxe2x80x94Structure and Properties; N. A. Platxc3xa9and V. P. Shibaev, J. Polym. Sci. Macromolecular Revs. 1974, 8, 117 ff). Examples of suitable comb polymers are, for example, fumarate-vinyl acetate copolymers (cf. EP 0 153 176 A1), copolymers of a C6- to C24-xcex1-olefin and an Nxe2x80x94C6- to C22-alkylmaleimide (cf. EP 0 320 766), furthermore esterified olefin-maleic anhydride copolymers, polymers and copolymers of xcex1-olefins, and esterified copolymers of styrene and maleic anhydride.
Comb polymers can be described, for example, by the formula
in which
A is Rxe2x80x2, COORxe2x80x2, OCORxe2x80x2, Rxe2x80x3xe2x80x94COORxe2x80x2 or ORxe2x80x2;
D is H, CH3, A or R;
E is H or A;
G is H, Rxe2x80x3, Rxe2x80x3xe2x80x94COORxe2x80x2, an aryl radical or a heterocyclic radical;
M is H, COORxe2x80x3, OCORxe2x80x3, ORxe2x80x3 or COOH;
N is H, Rxe2x80x3, COORxe2x80x3, OCOR, COOH or an aryl radical;
Rxe2x80x2 is a hydrocarbon chain having 8-150 carbon atoms;
Rxe2x80x3 is a hydrocarbon chain having 1 to 10 carbon atoms;
m is a number between 0.4 and 10; and
n is a number between 0 and 0.6.
The mixing ratio (in parts by weight) between the copolymers prepared in accordance with the invention and paraffin dispersants, resins or comb polymers is in each case from 1:10 to 20:1, preferably from 1:1 to 10:1.
In order to optimize the lubricity, the copolymers according to the invention can be employed as a mixture with further lubricity additives. Lubricity additives which have proven successful are preferably fatty alcohols, fatty acids and dimeric fatty acids, and their esters and partial esters with glycols (in accordance with DE-A-15 94 417), polyols, such as glycerol (in accordance with EP-A-0 680 506 and EP-A-0 739 970) or hydroxylamines (in accordance with EP-A-0 802 961).
The copolymers according to the invention are suitable for improving the lubricating properties and low-temperature properties of animal, vegetable or mineral oils. They are particularly suitable for use in middle distillates. The term xe2x80x9cmiddle distillatesxe2x80x9d denotes, in particular, mineral oils which are obtained by distillation of crude oil and boil in the range from 120 to 450xc2x0 C., for example kerosene, jet fuel, diesel and heating oil. The copolymers according to the invention are preferably used in middle distillates which contain 0.5% by weight or less of sulfur, especially preferably less than 500 ppm sulfur, in particular less than 200 ppm of sulfur, and in specific cases less than 50 ppm of sulfur. These are generally middle distillates which have been subjected to hydrorefining and contain only small proportions of polyaromatic and polar compounds which give them a natural lubricity. The copolymers according to the invention are furthermore used in middle distillates which have a 95% distillation point of below 370xc2x0 C., in particular 350xc2x0 C. and in special cases below 330xc2x0 C. They can also be employed as components in lubricating oils.
The polymers can be used alone or alternatively together with other additives, for example with other pour point depressants or dewaxing auxiliaries, with corrosion inhibitors, antioxidants, sludge inhibitors, dehazers and additives for improving the cloud point.
The effectiveness of the copolymers according to the invention as lubricity additives and cold-flow improvers is explained in greater detail by the examples below.

Use of hydroxyl-containing copolymers for the preparation of fuel oils having improved lubricity


The present disclosure relates to aqueous dispersions of silver (carboxylate-azine toner) particles wherein the azine content of the particles is from about 0.01 to 10% by weight relative to silver carboxylate. The carboxylates are typically silver salts of long chain fatty acids and the azine toners are the compounds that function as development accelerators and toning agents such as phthalazine. These silver (carboxylate-azine) particles can be used to formulate imaging forming compositions that are useful in aqueous thermographic or photothermographic imaging elements.

This invention relates to aqueous dispersions of silver (carboxylate-azine toner) particles. The carboxylates are typically silver salts of long chain fatty acids and the azine toners are the compounds that function as development accelerators and toning agents. These silver (carboxylate-azine) particles are used to formulate imaging forming compositions that are useful in aqueous photothermographic or thermographic imaging elements. In another aspect, the invention relates to a coprecipitation method for producing the particles.
Thermographic and photothermographic materials and imaging elements are well known in the photographic art. These materials are also known as heat developable photographic materials. Thermographic materials can form an image by the imagewise application of heat. Photothermographic materials include a light sensitive material, for example a silver halide. After imagewise exposure photothermographic materials are heated to moderately elevated temperatures to produce a developed image in the absence of separate processing solutions or baths.
An example of a known photothermographic silver halide material comprises (a) a hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer with (b) an organic solvent mixture, (c) a hydrophobic binder and (d) an oxidation-reduction image-forming composition. The oxidation-reduction imaging forming composition typically comprises (i) a silver carboxylate that is usually a silver salt of a long-chain fatty acid, such as silver behenate or silver stearate, in combination with (ii) an organic reducing agent, such as a phenolic reducing agent. It has been desirable to have hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer in such a photothermographic material because of the higher photosensitivity of the silver halide emulsion and the ease of control in preparation of the emulsion based on conventional aqueous silver halide gelatino emulsion technology.
A problem has been encountered in preparing these photothermographic silver halide materials. This problem involves the mixing of a hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer with an oxidation-reduction imaging forming composition. The imaging forming composition contains hydrophobic components including a hydrophobic binder, such as poly(vinyl butyral), and a silver salt of a long-chain fatty acid, such as a silver salt of behenic acid. Typically, when the hydrophilic photosensitive silver halide emulsion is mixed with the hydrophobic imaging forming materials and then coated on a suitable support to produce a photothermographic element, the resulting element produces a less than desired degree of photosensitivity, contrast and maximum density upon exposure and heat processing. This problem has been encountered in photothermographic silver halide materials, as described in, for example, U.S. Pat. No. 3,666,477 of Goffe, issued May 30, 1972. Goffe proposed addition of alkylene oxide polymers and a mercaptotetrazole derivative to the photothermographic material to help provide increased photosensitivity. In addition, a variety of organic solvents have been proposed in order to help prepare a photothermographic silver halide composition containing the described image-forming components. The organic solvents that have been proposed include isopropanol, acetone, toluene, methanol, 2-methoxyethanol, chlorinated solvents, acetone-toluene mixtures and certain non-aqueous polar organic solvents. The described individual solvents, such as isopropanol, have not provided the desired improved properties. There has been a continuing need to provide improved relative speed, contrast and image tone with desired maximum image density.
It is known to provide toners in thermographic and photothermographic compositions to increase chemical reactivity of the development chemistry and to improve the tone of the developed image. The compositions described herein are typically used to produce elements that are useful in x-ray imaging. For diagnostic purposes, doctors prefer neutral images on blue tinted support. The images should have very low minimum density and very high maximum density for optimum diagnostic use. The use of toner compounds can help accomplish these objectives.
A variety of toner compositions are known. For example, in EP 0803764 A1 filed Apr. 16, 1997, there is described a thermographic composition having a succinimide toner incorporated in the composition (See Example 1).
The materials and imaging elements described herein can be used as output media and can be exposed using a laser printer, typically from a digitized x-ray image. Laser printers of interest typically expose the elements to infrared laser radiation, for example in the 800 nm range. Since silver halide is not inherently sensitive to infrared radiation, it must be spectrally sensitized to this wavelength range in order to be effectively exposed.
Recent developments have focused on providing imaging compositions, for example photothermographic compositions, that are aqueous based. Such compositions, compared to organic solvent-based compositions, have numerous coating advantages. For example, expensive organic solvent recovery systems are not necessary in the coating process.
In commonly assigned U.S. Pat. No. 5, 350,669 to Witcomb et al, issued Sep. 27, 1994, there are disclosed compositions comprising silver, carboxylate and azine as the primary non-photosensitive, reducible silver source for a photothermographic element. These compounds contain relatively large amounts of the expensive azine component. The minimum amount of azine disclosed by Witcomb et al is about 14% by weight relative to silver carboxylate. (This assumes the minimum mass associated with the azine structure and a maximum for the carboxylate within the ranges specified.)
We have found that the presence of azine toner compounds significantly impacts the ability to spectrally sensitize a photosensitive silver halide emulsion in an aqueous environment. The inability to maintain sufficient spectral sensitization causes it to be difficult to maintain an adequate maximum density in the processed elements. Succinimide toner does not desensitize infrared sensitized silver halide.
In one aspect of the invention, there is provided an aqueous dispersion of silver-carboxylate particles having incorporated therein an azine toner compound. The azine content of the silver (carboxylate-azine toner) particles is from about 0.01 to 10% by weight relative to silver carboxylate, preferably about 0.05 to 5%. Other species can also be present, for example about 0.01 to 20% by weight relative to the silver carboxylate can be carboxylic acid, preferably 5 to 15% and about 0.01 to 2% by weight relative to the silver carboxylate can be alkali metal carboxylate salt (for example sodium or potassium carboxylate etc.) preferably 0.5 to 1.5%.
As will be seen in the comparative examples below, these silver (carboxylate-azine toner) particles substantially avoid the desensitization of spectrally sensitized silver halide. While not wishing to be bound by any particular theory, we believe that the desensitization by azine toner compounds in prior compositions can be attributed to the desorption of the spectral sensitizing dye from the surface of the silver halide grains. This in turn may be caused by the presence of the xe2x80x9cfreexe2x80x9d azine toner compound. In the present invention, the azine toner is incorporated into the carboxylate particles and is therefore not xe2x80x9cfreexe2x80x9d to desensitize adjacent silver halide grains. These particles provide the desired silver development kinetics, image density and image tone.
As noted, a characteristic of the present invention is that the silver-carboxylate particles have an azine toner compound incorporated into the structure of the particles. Another aspect of the invention is that the azine is present in a small amount. We have found that this small amount provides the desired development acceleration and image toning. Compositions using such small amounts are cheaper and less likely to produce interference with the spectral sensitizer than are compositions using larger amounts of azine toner. Further, high levels of azine, even if complexed with silver carboxylate, results in higher d-min than desired and less than desired raw stock keeping characteristics. Being incorporated into the particle means that the azine toner is not free but rather is part of the particle in the same sense, for example, as would, be a dopant. One of the characteristics of such a particle is that the x-ray diffraction pattern resembles the pattern obtained from the silver-carboxylate. In contrast, if silver carboxylate particles are simply mixed with silver-azine toner particles, a second novel crystallographic phase is observed in the x-ray diffraction pattern of the mixture. These particles will be referred to as xe2x80x9csilver(carboxylate-azine toner) particlesxe2x80x9d.
In preferred embodiments of the invention, the silver (carboxylate-azine toner) particles incorporated into the aqueous composition exhibit nanoparticulate morphology. It is particularly preferred that at least a portion of the non-photosensitive source of reducible silver ions be provided in the form of an aqueous nanoparticulate dispersion of silver (carboxylate-azine toner) particles having the desired content of azine. By nanoparticulate, we mean that the silver (carboxylate-azine toner) particles in such dispersions preferably have a weight average particle size of less than 1000 nm when measured by any useful technique such as sedimentation field flow fractionation, photon correlation spectroscopy, or disk centrifugation. In one particular method of measuring particle size the silver carboxylate and silver (carboxylate-azine toner) particle size and it""s distribution is determined using a Horiba LA-920, Hexe2x80x94Ne, laser particle size analyzer. This analyzer measures the particle size distribution by angular light scattering technique. Obtaining such small silver (carboxylate-azine toner) particles can be achieved using a variety of techniques described in the copending applications identified in the following paragraphs, but generally they are achieved using high speed milling using a device such as those manufactured by Morehouse-Cowles and Hochmeyer. The details for such milling are well known in the art.
In another aspect of the invention, there is provided an aqueous oxidation-reduction imaging forming composition comprising (i) a dispersion silver (carboxylate-azine toner) particles wherein the azine content of the particles is from about 0.01 to 10% by weight relative to silver carboxylate said particles having on the surface of the particles a surface modifier which is a nonionic oligomeric surfactant based on vinyl polymer with an amido function and (ii) an organic reducing agent. This composition can be coated on a support to provide a useful thermographic element.
In another aspect of the invention, there is provided an aqueous photothermographic composition comprising a) an infrared spectrally sensitized photosensitive silver halide emulsion containing a gelatino peptizer and b) an oxidation-reduction imaging forming composition comprising (i) a dispersion of silver (carboxylate-azine) particles wherein the azine content of the particles is from about 0.01 to 10% by weight relative to silver carboxylate said particles having on the surface of the particles a surface modifier which is a nonionic oligomeric surfactant based on a vinyl polymer with an amido function and (ii) an organic reducing agent. The described photothermographic composition can be coated on a support to provide a useful photothermographic element.
This invention solves, or greatly minimizes the prior art desensitization problems referred to above. A process is provided that produces an aqueous silver (carboxylate-azine) particle dispersion. Furthermore, the preferred process of this invention provides aqueous colloidal dispersions containing small particles with narrow particle size distribution. The imaging elements comprising silver (carboxylate-azine) particles exhibit greatly improved photographic properties and superior raw stock keeping characteristics in comparison to the elements formulated by adding xe2x80x9cfreexe2x80x9d azine toner during the preparation of the coating melt. The images produced using photothermographic elements of this invention exhibit low turbidity, high optical density and neutral tone. The potential losses of spectral sensitivity in the extrinsic region of the silver halide photo response e.g. IR, caused by silver halide-sensitizing dyexe2x80x94xe2x80x9cfreexe2x80x9d azine toner interactions, are minimized by the incorporation of the toner in the form of a bound-azine toner compound within the silver (carboxylate-azine) particles. The preferably nanoparticulate, aqueous, silver-carboxylate, silver-azine toner particle dispersions are easy to filter and display excellent shelf life. These dispersions have been successfully incorporated with the other necessary ingredients into an aqueous photothermographic imaging element and successfully exposed and thermally processed using a laser printer and thermal processor.
The particles in such dispersions can be stabilized by having on their surface a surface modifier so the silver salt can more readily be incorporated into aqueous-based photothermographic formulations. Useful surface modifiers include, but are not limited to, nonionic oligomeric surfactants based on vinyl polymers having an amino function, such as polymers prepared from acrylamide, methacrylamide, or derivatives thereof, as described in copending and commonly assigned POLYACRYLAMIDE SURFACE MODIFIERS FOR SILVER CARBOXYLATE NANOPARTICLES, Lelental, Pitt, Dickinson, Wakley and Ghyzel, Published application US 20010031436 A1 Aug. 18, 2001. A particularly useful surface modifier is dodecylthiopolyacrylamide that can be prepared as described in the noted copending application using the teaching provided by Pavia et al., Makromoleculare Chemie, 193(9), 1992, pp. 2505-17.
Other useful surface modifiers are phosphoric acid esters, such as mixtures of mono- and diesters of orthophosphoric acid and hydroxy-terminated, oxyethylated long-chain alcohols or oxyethylated alkyl phenols as described for example in PHOSPHORIC ACID ESTER SURFACE MODIFIERS FOR SILVER CARBOXYLATE NANOPARTICLES, Lelental, Dickinson, Wakley, Orem and Ghyzel, Published application US 20010029001 A1 Aug. 18, 2001. Particularly useful phosphoric acid esters are commercially available from several manufacturers under the trademarks or tradenames EMPHOS(trademark) (Witco Corp.), RHODAFAC (Rhone-Poulenc), T-MULZ(copyright) (Hacros Organics), and TRYFAC (Henkel Corp./Emery Group).
Such dispersions contain smaller particles and narrower particle size distributions than dispersions that lack such surface modifiers. Particularly useful nanoparticulate dispersions are those comprising silver carboxylates such as silver salts of long chain fatty acids having from 8 to 30 carbon atoms, including, but not limited to, silver behenate, silver caprate, silver hydroxystearate, silver myristate, silver palmitate, and mixtures thereof. Silver behenate nanoparticulate dispersions are most preferred. These nanoparticulate dispersions can be used in combination with the conventional silver salts described above, including but not limited to, silver benzotriazole, silver imidazole, and silver benzoate. In another aspect of the invention, there is provided an aqueous oxidation-reduction imaging forming composition comprising (i) a dispersion of silver (carboxylate-azine toner) particles as described having on the surface of the particles a surface modifier which is a nonionic oligomeric surfactant based on vinyl polymer with an amido function and (ii) an organic reducing agent.
In the case of controlled coprecipitation of metal salts or complexes such as water insoluble silver (carboxylate-azine) particles, the surface modifiers offer higher degree of particle size reduction, an improved colloidal stability of the dispersed system, higher chemical reactivity and lower low-shear viscosity. The nanoparticulate silver (carboxylate-azine) particles increase the reactivity of the silver metal-forming oxidation-reduction photothermographic development chemistry and hence, a lower temperature and (or) shorter development time is required to generate final silver image and to maximize image discrimination. Furthermore, the use of nanoparticulate silver(carboxylate-azine toner) particles in the film microstructure provides for a significant reduction of the film turbidity generally attributed to the particle size controlled light scattering improved image density and neutral image tone.
The present invention relates to a dispersion of silver (carboxylate-azine toner) particles. Particularly preferred silver-carboxylates are silver salts of long chain fatty acids such as, for example, silver stearate, silver behenate, silver caprate, silver hydroxystearate, silver myristate and silver palmitate. The preferred azine toner compounds are phthalazine and substituted phthalazine.
X-ray diffraction patterns show the described silver (carboxylate-azine toner) is different from a simple mixture of silver-carboxylate and silver-azine toner. Silver (behenate-phthalazine) has an x-ray diffraction pattern that is very similar to silver-behenate while a mixture of silver-behenate and silver phthalazine exhibits an addition phase.
The use of nonsilver (carboxylate-azine toner) toners/development accelerators or derivatives thereof which improve the image density and tone, is highly desirable, to the element. Toners may be present in amounts of from 0.01 to 20 percent by weight of the emulsion layer, preferably from 0.1 to 10 percent by weight. In addition to the toner that is present in the silver (carboxylate-azine toner) particles, additional toner may be present. These other toners can be present to provide enhanced chemical reactivity and to adjust tone as desired. For sensitized materials, toners should be chosen that do not desensitize the spectrally sensitized silver halide. Toners are well known materials in the photothermographic art as shown in U.S. Pat. Nos. 3,080,254; 3,847,612 and 4,123,282. Examples of useful toners include phthalimide and N-hydroxyphthalimide; cyclic imides such as succinimide, pyrazoline-5-ones, and a quinazolinone, 1-phenylurazole, 3-phenyl-2-pyrazoline-5-one, quinazoline and 2,4-thiazo lidinedione; naphthalimides such as N-hydroxy-1,8-naphthalimide; cobalt complexes such as cobaltic hexaminetrifluoroacetate; mercaptans as illustrated by 3-mercapto-1,2,4-triazole, 2,4-dimercaptopyrimidine, 3-mercapto-4,5-diphenyl-1,2,4-triazole and 2,5-dimercapto-1,3,4-thiadiazole; N-(aminomethyl)aryldicarboximides, e.g. (N,N-dimethylaminomethyl)phthalimide, and N-(dimethylaminomethyl)naphthalene-2,3-dicarboximide, and a combination of blocked pyrazoles, isothiuronium derivatives and certain photobleach agents, e.g., a combination of N,Nxe2x80x2-hexamethylene-bis(1-carbamoyl-3,5-dimethylpyrazole), 1,8-(3,6-diazaoctane)bis(isothiuronium)trifluoroacetate and 2-(tribromomethylsulfonyl benzothiazole); and merocyanine dyes such as 3-ethyl-5-[(3-ethyl-2-benzothiazolinylidene)-1-methylethylidene]-2-thio-2,4-oazolidinedione; phthalazinone, phthalazinone derivatives or metal salts or these derivatives such as 4-(1-naphthyl)phthalazinone, 6-chlorophthalazinone, 5,7-dimethoxyphthalazinone, and 2,3-dihydro-1,4-phthalazinedione; a combination of phthalazine plus one or more phthalic acid derivatives, e.g., phthalic acid, 4-methylphthalic acid, 4-nitrophthalic acid, and tetrachlorophthalic arthydride; quinazolinediones, benzoxazine or naphthoxazine derivatives; rhodium complexes e.g., ammonium peroxydisulfate and hydrogen peroxide; benzoxazine-2,4-diones such as 1,3-benzoxazine-2,4-dione, 8-methyl-1,3-benzoxazine-2,4-dione, and 6-nitro-1,3-benzoxazine-2,4-dione; pyrimidines and asymtriazines, e.g., 2,4-dihydroxypyrimidine, 2-hydroxy-4-aminopyrimidine, and azauracil, and tetrazapentalene derivatives, e.g., 3,6-dimercapto-1,4-diphenyl-1H,4H-2,3a,5,6a-tetrazapentalene, and 1,4-di(o-chlorophenyl)-3,6-dimercapto-1H,4H-2,3a,5,6a-tetrazapentalene.
The azine in the silver (carboxylate-azine) particles of the invention is from the class of organic compounds known as azines having the general structure R1R2Cxe2x95x90Nxe2x80x94Nxe2x95x90CR3R4. The azine structure preferably completes a six membered ring to form pyridazine or two six membered fused rings to form phthalazine and cinnoline. The rings can be substituted with for example, alkyl, substituted alkyl, hydroxy, alkoxy, and carboxy and carboxy-ester groups. Suitable azine compounds are: phthalazine, pyridazine, cinnoline, benzo(c) cinnoline, Examples of preferred substituted diazine compounds are: 1(2H)-phthalazinone, substituted 1(2H)-phthalazinones, 2,3-dihydro-1,4-phthalazinedione, substituted 2,3-dihydro-1,4-phthalazinediones and the like. In a particularly preferred embodiment the azine compound is phthalazine or a substituted phthalazine.
Other compounds can also be incorporated in silver-carboxylate particles. Silver-thiolates incorporated into the particles reduce the photographic fog associated with the compositions. The incorporation of silver thiolates is not our invention but is the invention of our coworkers, Ghyzel, Lelental, Dickinson, Pitt and Wear and is the subject of copending, commonly assigned U.S. Ser. No. 10/200,417 filed on the same date as this application. The preferred thiols are linear alkyl thiolates having alkyl chains of 2 to 24 carbons with the most preferred thiolates have alkyl chains of 6 to 18 carbons. Examples include but are not limited to silver 1-hexanethiolate, silver 1-dodecanethiolate, and silver 1-octadecanethiolate. The preferred level of silver-thiolate is from 0.1 to 1.2% by weight based on the weight of the silver-carboxylate. The thiols can be incorporated along with carboxylate and azine toner to produce a silver(carboxylate-azine toner-thiol) particle. Alternatively, particles of silver(carboxylate-thiol) can be prepared and used in combination with silver(carboxylate-azine toner) particles.
A number of surface modifiers can be used to facilitate the formation of nanoparticulate silver (carboxylate-azine) particles. Particular examples are disclosed in the following copending, commonly assigned applications: POLYACRYLAMIDE SURFACE MODIFIERS FOR SILVER CARBOXYLATE NANOPARTICLES, Lelental, Pitt, Dickinson, Wakley and Ghyzel, cited above; and PHOSPHORIC ACID ESTER SURFACE MODIFIERS FOR SILVER CARBOXYLATE NANOPARTICLES, Lelental, Dickinson, Wakley, Orem and Ghyzelalso cited above.
The preferred surface modifiers are polyacrylamide modifiers that are broadly defined by either of the following formulas:
The number of hydrophobic groups (R or R1 and R2) depends on the linking group L. The hydrophobic group or groups comprise a saturated or unsaturated alkyl, aryl-alkyl or alkyl-aryl group where the alkyl parts can be straight or branched. Typically the groups R or R1 and R2 comprise 8-21 carbon atoms. The linking group L is linked to the hydrophobic groups by a simple chemical link and to the oligomeric part T by a thio link (xe2x80x94Sxe2x80x94).
Typical linking groups for materials with one hydrophobic group are illustrated as follows:
Typical linking groups for materials with two hydrophobic groups are illustrated as follows:
The oligomeric group T is based on the oligomerisation of vinyl monomers with an amido function, the vinyl part providing the route to oligomerisation and the amido part providing a nonionic polar group to constitute the hydrophilic functional group (after oligomerisation). The oligomeric group T can be made up from a single monomer source or a mixture of monomers provided the resulting oligomeric chain is sufficiently hydrophilic to render the resulting surface active material soluble or dispersible in water. Typical monomers used to create the oligomeric chain T are based on acrylamide, methacrylamide, derivatives of acrylamide, derivatives of methacrylamide and 2-vinylpyrollidone, though the latter is less favored due to adverse photographic effects sometimes found with polyvinyl pyrrolidone (PVP).
These monomers can be represented by two general formulas:
X is typically H or CH3, which leads to an acrylamide or methacrylamide based monomer respectively.
Y and Zxe2x80x2 are typically H, CH3, C2H5, C(CH2OH)3 where X and Y can be different or the same.
The described oligomeric surfactant based on vinyl polymer with an amido function can be made by methods that are known in the art or are simple modifications of known methods. An illustrative preparation is provided below.
In another aspect, the present invention provides a process for making aqueous silver (carboxylate-azine) particle dispersions.
Nanoparticulate silver (carboxylate-azine toner) particle dispersions can be prepared by a precipitation process commonly used for the precipitation of photographic silver halide emulsions. Into a conventional reaction vessel for silver precipitation equipped efficient stirring mechanism is introduced a surface modifier. Typically the surface modifier initially introduced into the reaction vessel is at least about 5 percent, preferably 10 to 30 percent, by weight based on total weight of the surface modifier present in the nanoparticulate-silver (carboxylate-toner) dispersion the conclusion of grain precipitation. Since surface modifier can be removed from the reaction vessel by ultrafiltration during silver (carboxylate-azine) particle dispersion precipitation, as taught by Mignot U.S. Pat. No. 4,334,012, it is appreciated that the volume of surface modifier initially present in the reaction vessel can equal or even exceed the volume of the silver-carboxylate, silver-azine toner particles present in the reaction vessel at the conclusion of grain precipitation. The surface modifier initially introduced into the reaction vessel is preferably aqueous solution or an aqueous dispersion of surface modifier, optionally containing other ingredients, such as one or more antifoggant and/or various dopants, more specifically described below. Where a surface modifier is initially present, it is preferably employed in a concentration of at least 5 percent, most preferably at least 10 percent, of the total surface modifier present at the completion of silver (carboxylate-azine) particle dispersion precipitation. Additional surface modifier can be added to the reaction vessel with the water-soluble silver salts and can also be introduced through a separate jet.
During precipitation silver carboxylate salts and azine toner compound(s) are added to the reaction vessel by techniques well known in the precipitation of photographic silver halide grains. The carboxylate salts are typically introduced as aqueous salt solutions, such as aqueous solutions of one or more soluble ammonium, alkali metal (e.g., sodium or potassium), or alkaline earth metal (e.g., magnesium or calcium) carboxylate salts. The water-soluble or water dispersible toner compound(s) and the silver salt are at least initially introduced into the reaction vessel separately from the carboxylate salt.
With the introduction of silver salt into the reaction vessel the nucleation stage of silver (carboxylate-azine) grain(s) formation is initiated. A population of grain nuclei is formed which is capable of serving as precipitation sites for silver (carboxylate-azine) particles or grains as the introduction of silver and (or) carboxylic acid salts and (or) azine toner compound(s) continues. The precipitation of silver (carboxylate-azine) particles onto existing grain nuclei constitutes the growth stage of nanoparticulate grain formation.
The silver, azine toner compound(s) and carboxylic salt or carboxylic acid grains are preferably very fine e.g., less than 1.0 micron in mean diameter. The concentrations and rates of silver, toner compound(s) and carboxylic acid salt introductions can take any convenient conventional form. The silver, azine toner compound(s) and carboxylic acid salts are preferably introduced in concentrations of from 0.1 to 5 moles per liter, although broader conventional concentration ranges, such as from 0.01 mole per liter to saturation, for example, are contemplated. Specifically preferred coprecipitation techniques are those which achieve shortened precipitation times by increasing the rate of silver, toner compound(s) and carboxylic acid salt introduction during the run. The rate of silver, toner compound(s) and or carboxylic acid salt introduction can be increased either by increasing the rate at which the silver and or carboxylic acid salts are introduced or by increasing the concentrations of the silver, toner compound(s) and carboxylic acid salts within the solution.
The individual silver and (or) toner compound(s) carboxylic acid salts can be added to the reaction vessel through surface or subsurface delivery tubes by gravity feed or by delivery apparatus for maintaining control of the rate of delivery and the pH, and/or pAg of the reaction vessel contents, as illustrated by Culhane et al. U.S. Pat. No. 3,821,002, Oliver U.S. Pat. No. 3,031,304 and Claes et al., Photographische Korrespondenz, Band 102, Nov. 10, 1967, p. 162. In order to obtain rapid distribution of the reactants within the reaction vessel, specially constructed mixing devices can be employed, as illustrated by Audran U.S. Pat. No. 2,996,287, McCrossen et al. U.S. Pat. No. 3,342,605, Frame et al. U.S. Pat. No. 3,415,650, Porter et al. U.S. Pat. No. 3,785,777, Finnicum et al. U.S. Pat. No. 4,147,551, Verhille et al. U.S. Pat. No. 4,171,224, Calamur U.K. Patent Application No. 2,022,431 A, Saito et al. German OLS Nos. 2,555,364 and 2,556,885, and Research Disclosure, Volume 166, February 1978, Item 16662.
In forming the silver (carboxylate-azine) particle dispersions a surface modifier is initially contained in the reaction vessel. In a preferred form the surface modifier is comprised of an aqueous solution. Surface modifier concentrations of from 0.1 to about 30 percent by weight, based on the total weight of dispersion components in the reaction vessel, can be employed. It is common practice to maintain the concentration of the surface modifier in the reaction vessel in the range of below about 15 percent, based on the total weight, prior to and during silver carboxylate-silver toner compound combination formation. It is contemplated that the silver (carboxylate-azine) particle dispersion as initially formed will contain from about 1 to 150 grams of surface modifier per mole of silver carboxylate preferably about 25 to 75 grams of surface modifier per mole of silver. Additional surface modifier can be added later to bring the concentration up to as high as 200 grams per mole of silver.
Vehicles (which include both binders and peptizers) can be employed. Preferred peptizers are hydrophilic colloids, which can be employed alone or in combination with hydrophobic materials. Suitable hydrophilic materials include substances such as proteins, protein derivatives, cellulose derivatives e.g., cellulose esters, gelatin e.g., alkali-treated gelatin (cattle bone or hide gelatin) or acid-treated gelatin (pigskin gelatin), gelatin derivatives e.g., acetylated gelatin, phthalated gelatin and the like, polysaccharides such as dextran, gum arabic, zein, casein, pectin, collagen derivatives, agaragar, arrowroot, albumin and the like as described in Yutzy et al. U.S. Pat. Nos. 2,614,928 and ""929, Lowe et al., U.S. Pat. Nos. 2,691,582, 2,614,930, ""931, 2,327,808 and 2,448,534, Gates et al. U.S. Pat. Nos. 2,787,545 and 2,956,880, Himmelmann et al. U.S. Pat. No. 3,061,436, Farrell et al. U.S. Pat. No. 2,816,027, Ryan U.S. Pat. Nos. 3,132,945, 3,138,461 and 3,186,846, Dersch et al. U.K. Pat. No. 1,167,159 and U.S. Pat. Nos. 2,960,405 and 3,436,220, Geary U.S. Pat. No. 3,486,896, Gazzard U.K. Pat. No. 793,549, Gates et al. U.S. Pat. Nos. 2,992,213, 3,157,506, 3,184,312 and 3,539,353, Miller et al. U.S. Pat. No. 3,227,571, Boyer et al. U.S. Pat. No. 3,532,502, Malan U.S. Pat. No. 3,551,151, Lohmer et al. U.S. Pat. No. 4,018,609, Luciani et al. U.K. Pat. No. 1,186,790, Hori et al. U.K. Pat. No. 1,489,080 and Belgian Pat. No. 856,631, U.K. Pat. No. 1,490,644, U.K. Pat. No. 1,483,551, Arase et al. U.K. Pat. No. 1,459,906, Salo U.S. Pat. Nos. 2,110,491 and 2,311,086, Fallesen U.S. Pat. No. 2,343,650, Yutzy U.S. Pat. No. 2,322,085, Lowe U.S. Pat. No. 2,563,791, Talbot et al. U.S. Pat. No. 2,725,293, Hilborn U.S. Pat. No. 2,748,022, DePauw et al. U.S. Pat. No 2,956,883, Ritchie U.K. Pat. No. 2,095, DeStubner U.S. Pat. No. 1,752,069, Sheppard et al. U.S. Pat. No. 2,127,573, Lierg U.S. Pat. No. 2,256,720, Gaspar U.S. Pat. No. 2,361,936, Farmer U.K. Pat. No. 15,727, Stevens U.K. Pat. No. 1,062,116 and Yamamoto et al. U.S. Pat. No. 3,923,517.
Photosensitive silver halide grains made using water dispersible cationic starch to control fog can also be used. The use of cationic starch in photothermographic elements is not our invention but is the invention of our coworkers, Maskasky, Dickinson and Lelental and is described in copending, commonly assigned U.S. Ser. No. 09/703,050 filed Oct. 31, 2000.
Other materials commonly employed in combination with hydrophilic colloid peptizers as vehicles (including vehicle extendersxe2x80x94e.g., materials in the form of lattices) include synthetic polymeric peptizers, carriers and/or binders such as poly(vinyl lactams), acrylamide polymers, polyvinyl alcohol and its derivatives, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridine, acrylic acid polymers, maleic anhydride copolymers, polyalkylene oxides, methacrylamide copolymers, polyvinyl oxazolidinones, maleic acid copolymers, vinylamine copolymers, methacrylic acid copolymers, acryloyloxyalkylsulfonic acid copolymers, sulfoalkylacrylamide copolymers, polyalkyleneimine copolymers, polyamines, N,N-dialkylaminoalkyl acrylates, vinyl imidazole copolymers, vinyl sulfide copolymers, halogenated styrene polymers, amineacrylarnide polymers, polypeptides and the like as described in Hollister et al. U.S. Pat. Nos. 3,679,425, 3,706,564 and 3,813,251, Lowe U.S. Pat. Nos. 2,253,078, 2,276,322, ""323, 2,281,703, 2,311,058 and 2,414,207, Lowe et al. U.S. Pat. Nos. 2,484,456, 2,541,474 and 2,632,704, Perry et al. U.S. Pat. No. 3,425,836, Smith et al. U.S. Pat. Nos. 3,415,653 and 3,615,624, Smith U.S. Pat. No. 3,488,708, Whiteley et al. U.S. Pat. Nos. 3,392,025 and 3,511,818, Fitzgerald U.S. Pat. Nos. 3,681,079, 3,721,565, 3,852,073, 3,861,918 and 3,925,083, Fitzgerald et al. U.S. Pat. No. 3,879,205, Nottorf U.S. Pat. No. 3,142,568, Houck et al. U.S. Pat. Nos. 3,062,674 and 3,220,844, Dann et al. U.S. Pat. No. 2,882,161, Schupp U.S. Pat. No. 2,579,016, Weaver U.S. Pat. No. 2,829,053, Alles et al. U.S. Pat. No. 2,698,240, Priest et al. U.S. Pat. No. 3,003,879, Merrill et al. U.S. Pat. No. 3,419,397, Stonham U.S. Pat. No. 3,284,207, Lohmer et al. U.S. Pat. No. 3,167,430, Williams U.S. Pat. Nos. 2,957,767, Dawson et al. U.S. Pat. No. 2,893,867, Smith et al. U.S. Pat. Nos. 2,860,986 and 2,904,539, Ponticello et al. U.S. Pat. Nos. 3,929,482 and 3,860,428, Ponticello U.S. Pat. No. 3,939,130, Dykstra U.S. Pat. No. 3,411,911 and Dykstra et al. Canadian Pat. No. 774,054, Reamn et al. U.S. Pat. No. 3,287,289, Smith U.K. Pat. No. 1,466,600, Stevens U.K. Pat. No. 1,062,116, Fordyce U.S. Pat. No. 2,211,323, Martinez U.S. Pat. No. 2,284,877, Watkins U.S. Pat. No. 2,420,455, Jones U.S. Pat. No. 2,533,166, Bolton U.S. Pat. No. 2,495,918, Graves U.S. Pat. No. 2,289,775, Yackel U.S. Pat. No. 2,565,418, Unruh et al. U.S. Pat. Nos. 2,865,893 and 2,875,059, Rees et al. U.S. Pat. No. 3,536,491, Broadhead et al. U.K. Pat. No. 1,348,815, Taylor et al. U.S. Pat. No. 3,479,186, Merrill et al. U.S. Pat. No. 3,520,857, Bacon et al. U.S. Pat. No. 3,690,888, Bowman U.S. Pat. No. 3,748,143, Dickinson et al. U.K. Pat. Nos. 808,227 and ""228, Wood U.K. Pat. No. 822,192 and Iguchi et al. U.K. Pat. No. 1,398,055. These additional materials need not be present in the reaction vessel during nanoparticulate silver (carboxylate-azine) dispersion precipitation, but rather are conventionally added to the dispersion prior to coating. The vehicle materials, including particularly the hydrophilic colloids, as well as the hydrophobic materials useful in combination therewith can be employed not only in the emulsion layers of the photographic elements of this invention, but also in other layers, such as overcoat layers, interlayers and layers positioned beneath the emulsion layers. The silver (carboxylate-azine) particle dispersions are preferably free of soluble salts. The soluble salts can be removed by decantation, filtration, and/or chill setting and leaching, as illustrated by Craft U.S. Pat. No. 2,316,845 and McFall et al U.S. Pat. No. 3,396,027; by coagulation washing, as illustrated by Hewitson et al. U.S. Pat. No. 2,618,556, Yutzy et al. U.S. Pat. No. 2,614,928, Yackel U.S. Pat. No. 2,565,418, Hart et al. U.S. Pat. No. 3,241,969, Waller et al. U.S. Pat. No. 2,489,341, Klinger U.K. Pat. No. 1,305,409 and Dersch et al. U.K. Pat. No. 1,167,159; by centrifugation and decantation of a coagulated dispersion as illustrated by Murray U.S. Pat. No. 2,463,794, Ujihara et al. U.S. Pat. No. 3,707,378, Audran U.S. Pat. No. 2,996,287 and Timson U.S. Pat. No. 3,498,454; by employing hydrocyclones alone or in combination with centrifuges, as illustrated by U.K. Pat. No. 1,336,692, Claes U.K. Pat. No. 1,356,573 and Ushomirskii et al. Soviet Chemical Industry, Vol. 6, No. 3, 1974, pp.181-185; by diafiltration with a semipermeable membrane, as illustrated by Research Disclosure, Vol. 102, October 1972, Item 10208, Hagemaier et al. Research Disclosure, Vol. 131, March 1975, Item 13122, Bonnet Research Disclosure, Vol. 135, July 1975, Item 13577, Berg et al. German OLS No. 2,436,461, Bolton U.S. Pat. No. 2,495,918, and Mignot U.S. Pat. No. 4,334,012, cited above, or by employing an ion exchange resin, as illustrated by Maley U.S. Pat. No. 3,782,953 and Noble U.S. Pat. No. 2,827,428.
In one aspect, there is provided an aqueous oxidation-reduction imaging forming composition comprising (i) a dispersion of silver-carboxylate and silver (carboxylate-azine) particles wherein the azine content of the particles is from about 0.01 to 10% by weight relative to silver carboxylate said particles having on the surface of the particles a surface modifier which is a nonionic oligomeric surfactant based on vinyl polymer with an amido function and (ii) an organic reducing agent. Such a composition is useful, for example, in a thermographic element. An image can be formed in such an element by imagewise heating. Imagewise heating can be accomplished using an array of heating elements as the element is passed through a machine similar to a facsimile machine.
In another aspect, the compositions of the invention can be used in photothermographic elements wherein a photosensitive silver halide is present. Exposure of the silver halide produces a latent image that is then developed by a composition of the invention including silver (carboxylate-azine) particles. An aqueous photothermographic composition according to the invention can be prepared by very thoroughly mixing (I) a hydrophilic photosensitive silver halide emulsion with (II) (a) a hydrophilic binder and (b) an oxidation-reduction image-forming composition comprising (i) an aqueous dispersion of silver-carboxylate and silver (carboxylate-azine toner) particles wherein the azine content of the particles is from about 0.01 to 10% by weight relative to silver carboxylate with (ii) an organic reducing agent in water. A photothermographic can be prepared by coating the resulting photothermographic composition on a suitable support.
The aqueous photothermographic materials can comprise a photosensitive silver halide. The photosensitive silver halide is in the form of a hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer. The photosensitive silver halide is especially useful due to its high degree of photosensitivity compared to other photosensitive components.
Spectral sensitization is the addition of compounds to silver halide grains which absorb radiation at wavelengths other than those to which silver halide is naturally sensitive (i.e., only within the UV to blue) or which absorb radiation more efficiently than silver halide (even within those natural regions of spectral sensitivity). It is generally recognized that spectral sensitizers extend the responses of photosensitive silver halide to longer wavelengths and can accomplish spectral sensitization the UV, visible or infrared regions of the electromagnetic spectrum. These compounds, after absorption of the radiation, transfer energy to the silver halide grains to cause the necessary local photoinduced reduction of silver salt to silver metal. The compounds are usually dyes, and the best method of spectrally sensitizing silver halide grains causes or allows the dyes to align themselves on the surface of the silver halide grain, particularly in a stacked, almost crystalline pattern on the surface of the individual grains.
Many cyanine and related dyes are well known for their ability to impart spectral sensitivity to a gelatino silver halide element. The wavelength of peak sensitivity is a function of the dye""s wavelength of peak light absorbance. While many such dyes provide some spectral sensitization in photothermographic formulations, the dye sensitization is often very inefficient and it is not possible to translate the performance of a dye in gelatino silver halide elements to photothermographic elements. The emulsion making procedures and chemical environment of photothermographic elements are very harsh compared to those of gelatino silver halide elements. The presence of large surface areas of fatty acids and fatty acid salts as well as other components of photothermographic formulations restricts the surface deposition of sensitizing dyes onto silver halide surfaces and may remove sensitizing dye from the surface of the silver halide grains. The large variations in pressure, temperature, pH and solvency encountered in the preparation of photothermographic formulation aggravate the problem. Thus sensitizing dyes that perform well in gelatino silver halide elements are often inefficient in photo-thermographic formulations. In general, it has been found that merocyanine dyes are superior to cyanine dyes in photothermographic formulations as disclosed, for example, in British Patent No 1,325,312 and U.S. Pat. No. 3,719,495. Recently, certain cyanine dyes have been disclosed as spectral sensitizers for use in photothermographic elements. For example, U.S. Pat. Nos. 5,441,866 and 5,541,054 describe photothermographic elements spectrally sensitized with benzothiazole heptamethine dyes substituted with various groups, including alkoxy and thioalkyl. Although spectral sensitizing dyes for photothermographic elements are now known which absorb through-out the visible and near-infrared regions (i.e., 400-850 nm) photothermographic emulsions which provide higher photographic speeds and which have improved shelf-life stability, sensitivity, contrast and low Dmin are still needed for photothermography. U.S. Pat. No. 4,207,108 (Hiller) describes improved speed in photothermographic materials by addition of a photographic speed increasing concentration of a certain non-dye, thione speed increasing addendum (including compounds with cyclic thiocarbonyl [ greater than COS] groups within the cyclic structure). No decomposition of the cyclic thione compounds is reported. U.S. Pat. No. 5,541,055 (Ooi et al.) describes photothermographic elements that comprise both a cyanine dye and a colorless cyclic carbonyl compound. Rhodanine, hydantoin, barbituric acid, or derivatives thereof (all shown to be monocyclic in columns 4-6) are particularly preferred as the colorless cyclic carbonyl compound. The recent commercial availability of relatively high powered semiconductor light sources, and particularly laser diodes which emit in the red and near-infrared region of the electromagnetic spectrum, as sources for out-put of electronically stored image data onto photosensitive film or paper is becoming increasingly wide spread. This has led to a need for high quality imaging articles, which are sensitive at these wavelengths, and has created a need for more highly sensitive photothermographic elements to match such exposure sources both in wavelength and intensity.
To get the speed of the photothermographic elements up to maximum levels and further enhance sensitivity, it is often desirable to use supersensitizers. Any supersensitizer can be used which increases the sensitivity. For example, preferred infrared supersensitizers are described in U.S. patent application Ser. No. 08/091,000 (filed Jul. 13, 1993) and include heteroaromatic mercapto compounds or heteroaromatic disulfide compounds of the formulae: Arxe2x80x94Sxe2x80x94M and Arxe2x80x94Sxe2x80x94Sxe2x80x94Ar,
wherein M represents a hydrogen atom or an alkali metal atom. In the above noted supersensitizers, Ar represents a heteroaromatic ring or fused heteroaromatic ring containing one or more of nitrogen, sulfur, oxygen, selenium or tellurium atoms. Preferably, the heteroaromatic ring comprises benzimidazole, naphthimidazole, benzothiazole, naphthothiazole, benzoxazole, naphthoxazole, benzoselenazole, benzotellurazole, imidazole, oxazole, pyrazole, triazole, thiazole, thiadiazole, tetrazole, triazine, pyrimidine, pyridazine, pyrazine, pyridine, purine, quinoline or quinazolinone. However, other heteroaromatic rings are envisioned under the breadth of this invention. The heteroaromatic ring may also carry substituents with examples of preferred substituents being selected from the group consisting of halogen (e.g., Br and Cl), hydroxy, amino, carboxy, alkyl (e.g., of 1 or more carbon atoms, preferably 1 to 4 carbon atoms) and alkoxy (e.g., of 1 or more carbon atoms, preferably of 1 to 4 carbon atoms. Most preferred supersensitizers are 2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole (MMBI), 2-mercaptobenzothiazole, and 2-mercaptobenzoxazole (MBO). The supersensitizers are used in general amount of at least 0.001 moles of sensitizer per mole of silver in the emulsion layer. Usually the range is between 0.001 and 1.0 moles of the compound per mole of silver and preferably between 0.01 and 0.3 moles of compound per mole of silver.
A typical concentration of hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer and the imaging forming composition according to the invention is within the range of about 0.02 to about 1.0 mole of photosensitive silver halide per mole of the described silver (carboxylate-azine) particles in the photothermographic material. Other photosensitive materials can be useful in combination with the described photosensitive silver halide if desired. Preferred photosensitive silver halides are silver chloride, silver bromoiodide, silver bromide, silver chlorobromoiodide or mixtures thereof. For purposes of the invention, silver iodide is also considered to be a photosensitive silver halide. A range of grain size and grain morphology of photosensitive silver halide from very coarse grain to very fine grain and from 3D to tabular silver halide is useful. Tabular grain photosensitive silver halide is useful, as described in, for example, U.S. Pat. No. 4,435,499. Very fine grain silver halide is typically preferred.
The hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer can be prepared by any of the procedures known in the photographic art which involve the preparation of photographic silver halide gelatino emulsion. Useful procedures and forms of photosensitive silver halide gelatino emulsions for purposes of the invention are described in, for example, the Product Licensing Index, Volume 92, December 1971, Publication 9232 on page 107, published by Industrial Opportunities Limited, Homewell, Havant Hampshire, P091 EF, UK. The photographic silver halide, as described, can be washed or unwashed, can be chemically sensitized using chemical sensitization procedures. Materials known in the photographic art can be protected against the production of fog and stabilized against loss of sensitivity during keeping as described in the mentioned Product Licensing Index publication.
A hydrophilic photosensitive silver halide emulsion containing a gelatino peptizer that contains a low concentration of gelatin is often very useful. The concentration of gelatin that is very useful is typically within the range of about 9 to about 40 grams per mole of silver.(The term xe2x80x9chydrophilicxe2x80x9d is intended herein to mean that the photosensitive silver halide emulsion containing a gelatino peptizer is compatible with an aqueous solvent.)
The gelatino peptizer that is useful with the photosensitive silver halide emulsion can comprise a variety of gelatino peptizers known in the photographic art. The gelatino peptizer can be, for example, phthalated gelatin or non-phthalated gelatin. Other gelatino peptizers that are useful include acid or base hydrolyzed gelatins. A non-phthalated gelatin peptizer is especially useful with the described photosensitive silver halide emulsion.
The photosensitive silver halide emulsion can contain a range of concentration of the gelatino peptizer. Typically, the concentration of the gelatino peptizer is within the range of about 5 grams to about 60 grams of gelatino peptizer, such as gelatin, per mole of silver in the silver halide emulsion. This is described herein as a low-gel silver halide emulsion. An especially useful concentration of gelatino peptizer is within the range of about 10 to about 25 grams of gelatino peptizer per mole of silver in the silver halide emulsion. The optimum concentration of the gelatino peptizer will depend upon such factors as the particular photosensitive silver halide, the desired image, the particular components of the photothermographic composition, coating conditions and the like.
The temperature of the reaction vessel within which the silver halide emulsion is prepared is typically maintained within a temperature range of about 35xc2x0 C. to about 75xc2x0 C. during the composition preparation. The temperature range and duration of the preparation can be altered to produce the desired emulsion grain size and desired composition properties. The silver halide emulsion can be prepared by means of emulsion preparation techniques and apparatus known in the photographic art.
A variety of hydrophilic binders are useful in the described photothermographic materials. The binders that are useful include various colloids alone or in combination as vehicles and/or binding agents. The hydrophilic binders which are suitable include transparent or translucent materials and include both naturally occurring substances, such as proteins, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides, such as dextrin, gum arabic and the like: and synthetic polymeric substances such as water-soluble polyvinyl compounds like polyvinyl alcohol, poly (vinyl pyrrolidone), acrylamide polymers and the like. Other synthetic polymeric compounds, which can be employed, include dispersed vinyl compounds such as latex form and particularly those that increase dimensional stability of photographic materials. A range of concentration of hydrophilic binder can be useful in the photothermographic silver halide materials according to the invention. Typically, the concentration of hydrophilic binder in a photothermographic silver halide composition according to the invention is within the range of about 0.5 to about 10 g/m2. An optimum concentration of the described binder can vary depending upon such factors as the particular binder, other components of the photothermographic material, coating conditions, desired image, processing temperature and conditions and the like.
If desired, a portion of the photographic silver halide in the photothermographic composition according to the invention can be prepared in situ in the photothermographic material. The photothermographic composition, for example, can contain a portion of the photographic silver halide that is prepared in or on one or more of the other components of the described photothermographic material rather than prepared separate from the described components and then admixed with them. Such a method of preparing silver halide in situ is described in, for example, U.S. Pat. No. 3,457,075 of Morgan et al., issued Jul. 22, 1969.
The described photothermographic composition comprises an oxidation-reduction image-forming combination containing silver (carboxylate-azine) particles, with a suitable reducing agent. The oxidation-reduction reaction resulting from this combination upon heating is believed to be catalyzed by the latent image silver from the photosensitive silver halide produced upon imagewise exposure of the photothermographic material followed by overall heating of the photothermographic material. The exact mechanism of image formation is not fully understood.
A variety of organic reducing agents are useful in the described photothermographic silver halide materials. These are typically silver halide developing agents that produce the desired oxidation-reduction image-forming reaction upon exposure and heating of the described photothermographic silver halide material. Examples of useful reducing agents include: polyhydroxybenzenes, such as hydroquinone and alkyl substituted hydroquinones; catechols and pyrogallol; phenylenediamine developing agents; aminophenol developing agents; ascorbic acid developing agents, such as ascorbic acid and ascorbic acid ketals and other ascorbic acid derivatives; hydroxylamine developing agents; 3-pyrazolidone developing agents such as 1-phenyl-3-pyrazolidone and 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone; hydroxytetronic acid and hydroxytetronamide developing agents; reductone developing agents; bis-naphthol reducing agents; sulfonamidophenol reducing agents: hindered phenol reducing agents and the like. Combinations of organic reducing agents can be useful in the described photothermographic silver halide materials. Sulfonamidophenol developing agents, such as described in Belgian Pat. No. 802,519 issued Jan. 18, 1974 can be especially useful in the photothermographic silver halide composition.
A range of concentration of the organic reducing agent can be useful in the described photothermographic silver halide materials. The concentration of organic reducing agent is typically within the range of about 0.5 g/m2 to about 5g/m2, such as within the range of about 1.0 to about 3.0 g/m2. The optimum concentration of organic reducing agent will depend upon such factors as the particular carboxylate, e.g. long-chain fatty acid, the desired image, processing conditions, the particular solvent mixture, coating conditions and the like.
The order of addition of the described components for preparing the photothermographic composition before coating the composition onto a suitable support is important to obtain optimum photographic speed, contrast and maximum density.
Various mixing devices are useful for preparing the described compositions. However, the mixing device should be one that provides very thorough mixing. Mixing devices that are useful are commercially available colloid mill mixers and dispersator mixers known in the photographic art.
Photothermographic materials according to the invention can contain other addenda that are useful in imaging. Suitable addenda in the described photothermographic materials include development modifiers that function as speed-increasing compounds, hardeners, antistatic layers, plasticizers and lubricants, coating aids, brighteners, spectral sensitizing dyes, antifogants, charge control agents, absorbing and filter dyes, matting agents and the like.
The specific addenda depend on the exact nature of the imaging element. The present invention is useful for forming laser output media useful for reproducing x-ray images; it is useful for forming microfilm elements and it is useful to form graphic arts elements. Each of these applications has well known features requiring specialized addenda known in the respective arts for these elements.
As noted, the present invention provides silver (carboxylate-azine) particles. An important advantage of these compositions is that they can be coated from an aqueous environment. Several current elements of this type are currently coated from organic solvents. The described materials can be used to convert these products into aqueous coated products, particularly where the particles are nanoparticulate. In this process, some of the components that are typically found in these elements might not be as soluble in water as desired. These components also can be made into nanoparticulate dispersions using the same or compatible surface modifiers as are described.
It is useful in certain cases to include a stabilizer in the described photothermographic material. This can help in stabilization of a developed image. Combinations of stabilizers can be useful if desired. Typical stabilizers or stabilizer precursors include certain halogen compounds, such as tetrabromobutane and 2-(tribromomethyl)sulfonyl, benzothiazole, which provide improved postprocessing stability and azothioethers and blocked azoline thione stabilizer precursors.
A photothermographic element according to the invention can have a transparent protective layer comprising a film forming binder, preferable a hydrophilic film forming binder. Such binders include, for example, crosslinked polyvinyl alcohol, gelatin, poly (silicic acid), and the like. Particularly preferred are binders comprising poly (silicic acid) alone or in combination with a water-soluble hydroxyl-containing monomer or polymer as described in the U.S. Pat. No. 4,828,971.
The term xe2x80x9cprotective layerxe2x80x9d is used to mean a transparent, image insensitive layer that can be an overcoat layer, that is a layer that overlies the image sensitive layer(s). The protective layer can also be a backing layer, that is, a layer that is on the opposite side of the support from the image sensitive layer(s). The imaging element can contain an adhesive interlayer or adhesion promoting interlayer between the protective layer and the underlying layer(s). The protective layer is not necessarily the outermost layer of the imaging element.
The protective layer can contain an electrically conductive layer having a surface resistivity of less than 5xc3x971011 ohms/square. Such electrically conductive overcoat layers are described, for example, in U.S. Pat. No. 5,547,821.
A photothermographic imaging element can include at least one transparent protective layer containing matte particles. Either organic or inorganic matte particles can be used. Examples of organic matte particles are beads of polymers such as polymeric esters of acrylic and methacrylic acid, e.g., poly (methylmethacrylate), styrene polymers and copolymers, and the like. Examples of inorganic matte particles are glass, silicon dioxide, titanium dioxide, magnesium oxide, aluminum oxide, barium sulfate, calcium carbonate, and the like. Matte particles and the way they are used are further described in U.S. Pat. Nos. 3,411,907, 3,754,924, 4,855,219, 5,279,934, 5,288,598, 5,378,577, 5,563,226 and 5,750,328.
A wide variety of materials can be used to prepare the protective backing layer that is compatible with the requirements of photothermographic elements. The protective layer should be transparent and should not adversely affect sensitometric characteristics of the photothermographic element such as minimum density, maximum density and photographic speed. Useful protective layers include those comprised of poly (silicic acid) and a water-soluble hydroxyl containing monomer or polymer that is compatible with poly (silicic acid) as described in U.S. Pat. Nos. 4,741,992 and 4,828,971, the entire disclosures of which are incorporated herein by reference. A combination of poly (silicic acid) and poly (vinyl alcohol) is particularly useful. Other useful protective layers include those formed from polymethylmethacrylate, acrylamide polymers, cellulose acetate, crosslinked polyvinyl alcohol, terpolymers of acrylonitrile, vinylidene chloride, and 2-(methacryloyloxy)ethyl-trimethylammonium methosulfate, crosslinked gelatin, polyesters and polyurethanes.
Particularly preferred protective layers are described in above-mentioned U.S. Pat. Nos. 5,310,640 and 5,547,821.
The photothermographic elements can comprise a variety of supports that can tolerate the processing temperatures useful in developing an image. Typical supports include cellulose ester, poly(vinyl acetal), poly(ethylene terephthalate), polycarbonate and polyester film supports. Related film and resinous support materials, as well as paper, glass, metal and the like supports that can withstand the described processing temperatures are also useful. Typically a flexible support is most useful.
Coating procedures known in the photographic art can coat the photothermographic compositions on a suitable support. Useful methods including dip coating, air-knife coating, bead coating using hoppers, curtains coating or extrusion coating using hoppers. If desired, two or more layers can be coated simultaneously.
The described silver halide and oxidation-reduction image-forming combination can be in any suitable location in the photothermographic element which produces the desired image. In some cases it can be desirable to include certain percentages of the described reducing agent, the silver salt oxidizing agent and/or other addenda in a protective layer or overcoat layer over the layer containing the other components of the element as described. The components, however, must be in a location that enables their desired interaction upon processing.
It is necessary that the photosensitive silver halide, as described and other components of the imaging combination are xe2x80x9cin reactive associationxe2x80x9d with each other in order to produce the desired image. The term xe2x80x9cin reactive association,xe2x80x9d as employed herein, is intended to mean that the photosensitive silver halide and the image-forming combination are in a location with respect to each other, which enables the desired processing and produces a useful image.
A useful embodiment of the invention is a photothermographic silver halide composition capable of being coated on a support. The composition comprises (a) an aqueous photosensitive silver halide emulsion containing a gelatin peptizer with (b) a hydrophilic polymeric binder consisting essentially of a gelatin and (c) an oxidation-reduction image-forming combination comprising (i) a silver carboxylate and the described silver (carboxylate-azine toner) particles and a surface modifier as described (ii) an organic reducing agent consisting essentially of a hindered phenol. This composition can be coated on a suitable support to produce a photothermographic element. Another embodiment is a method of preparing a photothermographic element comprising coating the resulting composition onto a suitable support to produce a photothermographic element as desired.
Elements can be imaged using a variety of methods. The elements can be imaged using any suitable source of infrared radiation to which the photothermographic material is sensitive. Typically, a photothermographic material is exposed imagewise with an infrared light source, such as a laser or a light emitting diode (LED) to produce a developable latent image.
A visible image can be developed in the photothermographic material within a short time, such as within several seconds, merely by heating the photothermographic material to moderately elevated temperatures. For example, the exposed photothermographic material can be heated to a temperature within the range of about 100xc2x0 C. to about 200xc2x0 C., such as a temperature within the range of about 110xc2x0 C. to about 140xc2x0 C. Heating is carried out until a desired image is developed, typically within about 2 to about 60 seconds, such as 8 to 30 seconds. Selection of an optimum processing time and temperature will depend upon such factors as the desired image, particular components of the photothermographic element, the particular latent image and the like.
The necessary heating of the described photothermographic material to develop the desired image can be accomplished in a variety of ways. Heating can be accomplished using a simple hot plate, iron, roller, infrared heater, hot air or the like.
Processing is typically carried out under ambient conditions of pressure and humidity. Pressures and humidity outside normal atmospheric conditions can be useful if desired; however, normal atmospheric conditions are preferred.

Silver-(carboxylate-azine toner) particles for photothemographic and thermographic imaging