EP0582144A1

EP0582144A1 - Laser addressable thermal recording material

Info

Publication number: EP0582144A1
Application number: EP93111757A
Authority: EP
Inventors: Stanley C. C/O Minnesota Mining And Busman; Thomas A. c/o Minnesota Mining and Isberg
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1992-08-03
Filing date: 1993-07-22
Publication date: 1994-02-09
Anticipated expiration: 2013-07-22
Also published as: JPH06194781A; DE69310045T2; EP0582144B1; DE69310045D1

Abstract

A thermal recording material containing a suitable substrate coated with an imaging system, the imaging system containing: (a) a thermally reducible source of silver; (b) a reducing agent for silver ion; (c) a dye which absorbs electromagnetic radiation in the wavelength range of about 500-1100 nm; and (d) a polymeric binder. In a preferred embodiment, the reducing agent comprises a 3-indazoline or a urea compound as a development accelerator. In another preferred embodiment, the electromagnetic radiation absorbing dye is a near-infrared light absorbing dye. In still another preferred embodiment, the electromagnetic radiation absorbing dye is present in the imaging system in a layer adjacent to a layer containing the thermally reducible source of silver and reducing agent for silver ion.

Description

This invention relates to a thermographic material that can be directly imaged using a high power laser diode.
As is widely known in the imaging arts, a thermographic imaging process relies on the use of heat to help produce an image. Typically, a thermally sensitive image forming layer is coated on top of a suitable base or substrate material such as paper, plastics, metals, glass, and the like. The resulting thermographic construction is then heated to an elevated temperature, typically in the range of about 60°-225°C for a period of tens of microseconds, e.g., 20-30 microseconds, resulting in the formation of an image. Many times, the thermographic construction is brought into contact with the thermal head of a thermographic recording apparatus, such as a thermal printer, thermal facsimile, and the like. In such instances, an anti-stick layer is coated on top of the imaging layer to prevent sticking of the thermographic construction to the thermal head of the apparatus utilized.
Thermographic materials whose image-forming layers are based on silver salts of long chain fatty acids, such as silver behenate, are known. At elevated temperatures, silver behenate is reduced by a reducing agent for silver ion such as methyl gallate, hydroquinone, substituted hydroquinones, hindered phenols, catechol, pyrogallol, ascorbic acid, ascorbic acid derivatives, leuco dyes, and the like, whereby an image is formed.
It is also known that other additives can be added to imaging layers of thermographic constructions to enhance their effectiveness. For example, U.S. Pat. No. 2,910,377 discloses that the silver image for such materials can be improved in color and density by the addition of toners to the imaging layer. Toners that give primarily image density enhancement are also referred to as development accelerators.
U.S. Pat. No. 3,080,254 discloses the use of phthalazinone as a toner in heat-sensitive copying paper. U.S. Pat. No. 3,847,612 discloses an improved imaging system containing an imidazole in combination with phthalic acid and the like. Phthalazine in combination with phthalic acid and other organic acids also provide an improvement in image formation. Such disclosed combinations are particularly valuable when relatively weak reducing agents, such as hindered phenols, are used as the developer for silver soaps.
U.S. Pat. No. 4,585,734 discloses the achievement of good toning when a combination of phthalazine and an active hydrogen-containing heterocyclic compound such as phthalimide, naphthalimide, pyrazole, and succinimide are employed in dry silver imaging systems.
High power laser diodes have been used in the past to simultaneously light-expose and thermally-develop photothermographic media that contain near-infrared dyes. In those systems, light is used to generate a latent image in dye-sensitized silver halides while at the same time light-to-heat conversion elements (e.g., near-infrared dyes) convert near-infrared light to heat that thermally develops the silver halide latent image with an organic silver salt and reducing agent. European Pat. Appl. No. 332,455 (published Sept. 13, 1989) and U.S. Pat. No. 5,041,369 disclose splitting a beam of near-infrared light, one portion of which passes through a second harmonic generation device to produce blue light that exposes a silver halide photothermographic medium. The imaged areas are developed by exposure of the imaged areas to the remaining portion of the near-infrared beam.
U.S. Pat. No. 4,619,892 discloses a radiation-sensitive element comprising at least three silver halide emulsion layers, two of which are sensitized to infrared radiation by employing infrared sensitizing dyes.
It is well known in the art that the presence of silver halide in photothermographic constructions can lead to high D_min (i.e., background density), both in the visible and ultraviolet (UV) portions of the spectrum. The high D_min is due to the inherent absorption in the near UV by silver halide, particularly silver bromide and silver iodide, and to high haze when silver halide and organic silver salts are present together. High D_min in the UV portion of the spectrum is undesirable for graphic arts scanners and image-setting films and papers since it increases the exposure time required when the photothermographic silver image is in contact with other media such as printing plates, proofing films, and papers. High haze can also lead to image resolution degradation when photothermographic silver halide containing films are contacted to other media. In addition, it is well known that silver halide in photothermographic films can lead to poor light stability of the background areas of the developed image, thereby resulting in fogging.
U.S. Pat. No. 4,904,572 discloses thermographic color recording materials comprising 3,5-dihydroxybenzoic acid, a di- or triarylmethane thiolactone leuco dye, silver behenate, and a binder. Color formation is activated at temperatures of about 100°C. This patent discloses a full-color imaging system using false color, near-infrared laser exposures of individual layers containing yellow, magenta, and cyan dye precursors and three different near-infrared absorbing dyes which cause development of the layer in which they are contained. Additionally, the patent does not disclose the formation of black images. In fact, the silver ions in the silver behenate are not reduced, but simply serve to irreversibly bind the thiobenzoate portion of the dye so that it cannot convert to the leuco form.
Japanese Kokai Application No. 1-274,129 discloses the exposure of compositions containing silver sulfonates having specified infrared (not near-infrared) absorption spectrum characteristics. A carbon dioxide laser tuned to correspond to this infrared absorption wavelength is used to expose and simultaneously thermally develop this film, apparently to give a black image. In this manner, the silver sulfonate acts as its own light-to-heat conversion element. However, that application requires the use of a carbon dioxide laser which is much less desirable for imaging applications than near-infrared laser diodes.
The black silver image that is generated by the heat produced by the light-to-heat converting near-infrared-absorbing dyes becomes its own light-to-heat conversion element since black silver also absorbs in the near-infrared region of the spectrum. Therefore, the developing black silver image becomes its own "catalyst" for production of more black silver in a silver soap system. Consequently, less near-infrared dye is needed and less background stain is left by the dye. One of the dyes used is very neutral colored and is less visible in the final product, giving lower background densities.
In accordance with the present invention, it has now been discovered that a thermographic material containing certain dyes and a reducing agent for silver ion is an effective laser diode addressable imaging system. The present invention provides imageable materials which, when developed, have high image densities for a given development time as opposed to thermographic imaging systems which do not contain the reducing agents and dyes utilized herein.
Thus, the present invention provides a thermal recording material comprising a base or support coated with an imaging system, the imaging system consisting essentially of: (a) a thermally reducible source of silver; (b) reducing agent for silver ion; (c) a dye which absorbs electromagnetic radiation in the wavelength range of about 500-1100 nm; and (d) a polymeric binder. In a preferred embodiment, the reducing agent comprises a 3-indazolinone or a urea compound of the structures disclosed later herein. In another preferred embodiment, the dye employed is a near-infrared absorbing dye. In still another preferred embodiment, the electromagnetic radiation absorbing dye is in a layer adjacent to a layer containing the thermally reducible source of silver and reducing agent for silver ion.
The term "near-infrared", as used herein, refers to the wavelength region between about 650 nm and 1100 nm, and preferably between about 750-1100 nm.
A further advantage of this invention is that thermographic materials (e.g., films or papers) can be imaged electronically using a simple laser scanner that requires no post-thermal processing step for the media. Laser scanning technology gives higher resolution than a thermal stylus printhead, leading to this media's utility for high resolution applications such as graphic arts and diagnostic imaging. Also, since no mechanical thermal head is required, abrasion of the thermographic media is not a problem.
Other aspects, advantages, and benefits of the present invention are apparent from the detailed disclosure, the examples, and the claims.
In the present invention, the image forming system contains a thermally reducible source of silver. The latter are materials, which in the presence of a reducing agent, undergo reduction at elevated temperatures, e.g., 60°-225°C. Preferably, these materials are silver salts of long chain alkanoic acids (also known as long chain aliphatic carboxylic acids or fatty acids) containing 10 to 30 carbon atoms and more preferably, 10 to 28 carbon atoms. The latter are also known in the art as "silver soaps." Non-limiting examples of silver salts of aliphatic carboxylic acids include silver behenate, silver stearate, silver oleate, silver laurate, silver caproate, silver myristate, silver palmitate, silver maleate, silver fumarate, silver tartarate, silver linoleate, silver butyrate, silver camphorate, and mixtures thereof. Complexes of organic or inorganic silver salts wherein the ligand has a gross stability constant between 4.0-10.0 can also be used. Silver salts of aromatic carboxylic acids and other carboxyl group-containing compounds include silver benzoate, a silver-substituted benzoate such as silver 3,5-dihydroxybenzoate, silver o-methylbenzoate, silver m-methylbenzoate, silver p-methylbenzoate, silver 2,4-dichlorobenzoate, silver acetamidobenzoate, silver p-phenyl benzoate, etc., silver gallate, silver tannate, silver phthalate, silver terephthalate, silver salicylate, silver phenylacetate, silver pyromellitate, silver salts of 3-carboxymethyl-4-methyl-4-thiazoline-2-thiones or the like as described in U.S. Pat. No. 3,785,830; and silver salts of aliphatic carboxylic acids containing a thioether group as disclosed in U.S. Pat. No. 3,330,663. Silver salts of compounds containing mercapto or thione groups and derivatives thereof can also be used. Preferred examples of these compounds include silver 3-mercapto-4-phenyl-1,2,4-triazolate, silver 2-mercaptobenzimidazolate, silver 2-mercapto-5-aminothiadiazolate, silver 2-(S-ethylglycolamido)benzothiazolate; silver salts of thioglycolic acids such as silver salts of S-alkyl thioglycolic acids (wherein the alkyl group has from 12 to 22 carbon atoms); silver salts of dithiocarboxylic acids such as silver dithioacetate, silver thioamidoate, silver 1-methyl-2-phenyl-4-thiopyridine-5-carboxylate, silver triazinethiolate, silver 2-sulfidobenzoxazole; and silver salts as disclosed in U.S. Pat. No. 4,123,274. Furthermore, silver salts of a compound containing an amino group can be used. Preferred examples of these compounds include silver salts of benzotriazoles, such as silver benzotriazolate; silver salts of alkyl-substituted benzotriazoles such as silver methylbenzotriazolate, etc.; silver salts of halogen-substituted benzotriazoles such as silver 5-chlorobenzotriazolate, etc.; silver salts of carboimidobenzotriazoles, etc.; silver salts of 1,2,4-triazoles and 1-H-tetrazoles as described in U.S. Pat. No. 4,220,709; silver salts of imidazoles; and the like. Preferably, the silver source material should constitute from about 5-50 percent by weight of the image forming system and more preferably, from about 10-30 percent by weight.
Any reducing agent for silver ion can be used in the present invention. Such reducing agents are well-known to those skilled in the art. Examples of such reducing agents include, but are not limited to, methyl gallate; hindered phenols; catechol; pyrogallol; hydroquinones; substituted hydroquinones; ascorbic acid; ascorbic acid derivatives; leuco dyes; and the like. Preferably, the reducing agent comprises a 3-indazolinone or urea compound as a development accelerator.
3-indazolinone compounds used in the present invention preferably have the following structure:

wherein: R is selected from the group consisting of: hydrogen; an alkyl group of 1 to 4 carbon atoms; halogen; -COOH and -R¹COOH wherein R¹ is an alkyl group having from 1 to 4 carbon atoms. Preferably, R is hydrogen or an alkyl group having from 1 to 4 carbon atoms and most preferably, R is hydrogen.
Such 3-indazolinone compounds can be synthesized according to procedures well known to those skilled in the art of synthetic organic chemistry. Alternatively, such materials are commercially available, such as from Aldrich Chemical Company of Milwaukee, Wisconsin; Lancaster Chemical Company of Windham, New Hampshire; and K & K Laboratories of Cleveland, Ohio.
As is well understood in this area, a large degree of substitution is not only tolerated, but is often advisable. Thus, as used herein the phrase "group" is intended to include not only pure hydrocarbon substituents such as methyl, ethyl, and the like, but also such hydrocarbon substituents bearing conventional substituents in the art such as hydroxy, alkoxy, phenyl, halo (F, Cl, Br, I), cyano, nitro, amino, etc.
Urea compounds used in the present invention preferably have the following formula:

wherein: R² and R³ each independently represent hydrogen; a C₁-C₁₀ alkyl or cycloalkyl group; or phenyl; or R² and R³ together form a heterocyclic group containing up to 6 ring atoms. Preferably R² and R³ represent hydrogen; a C₁ to C₅ alkyl or cycloalkyl group; or phenyl; or R² and R³ together form a heterocyclic group containing up to 5 ring atoms.
Such urea compounds can be readily synthesized and are commercially available. Non-limiting examples of such urea compounds include:

Whatever reducing agent is employed in the present invention is preferably used in an amount of about 0.5-10.0 weight percent and more preferably, 1.0-3.0 weight percent; based upon the total weight of the imaging system.
The image forming system of the present invention employs a dye which absorbs electromagnetic radiation having a wavelength in the range of between about 500-1100 nm. Preferably, the dye employed is a near-infrared light absorbing dye which absorbs light in the wavelength range of about 650-1100 nm and more preferably, about 750-1100 nm. The electromagnetic radiation absorbing dye can be employed in the same layer as the thermally reducible source of silver and reducing agent for silver ion or alternatively, the dye can be employed in a layer adjacent to the layer containing the reducible source of silver and the reducing agent for silver ion. Suitable dyes include, but are not limited to, oxonol, squarylium, chalcogenopyrylarylidene, bis(chalcogenopyrylo)polymethine, bis(aminoaryl)polymethine, merocyanine, trinuclear cyanine, indene-bridged polymethine, oxyindolizine, ferrous complex, quinoid, nickel dithiolene complex, and cyanine dyes such as carbocyanine, azacarbocyanine, hemicyanine, styryl, diazacarbocyanine, triazacarbocyanine, diazahemicyanine, polymethinecyanine, azapolymethinecyanine, holopolar, indocyanine, and diazahemicyanine dyes. Since the role of the near-infrared dyes is to convert near-infrared electromagnetic radiation to heat, any near-infrared absorbing dye known in the art may be used. Preferably, the electromagnetic radiation absorbing dyes should be present in an amount of from about 0.1-10.0 weight present and more preferably, in an amount of from about 0.3-6.0 weight present, based upon the total weight of the imaging system employed in the present invention.
The thermographic materials of the present invention are imaged by exposure to near-infrared laser radiation, typically from a near-infrared laser diode. As is well known in the thermal imaging art, near-infrared laser diodes may be advantageously arranged in an array to increase imaging speed. Lasers that can be used to provide near-infrared radiation include substantially any laser capable of generating light in the near-infrared region of the electromagnetic spectrum, including dye lasers; gas lasers such as krypton-ion lasers; solid state diode lasers such as aluminum gallium arsenide diode lasers that emit in the region of 750 to 870 nm; and diode pumped solid state lasers such as Nd:YAG, Nd:YLF, or Nd:Glass.
The imaging elements of the present invention are not light-sensitive in the traditional sense and therefore, do not need to contain photosensitive agents such as silver halides; photoinitiator; or photogenerated bleaching agents. The imaging elements can have less than 1% by weight (substantially no effective amount of) these materials and perform well. They may be totally free of these materials in the imaging element.
The image forming element utilized in the present invention also employs a binder. Any conventional polymeric binder known to those skilled in the art can be utilized. For example, the binder may be selected from any of the well-known natural and synthetic resins such as gelatin, polyvinyl acetals, polyvinyl chloride, cellulose acetate, polyolefins, polyesters, polystyrene, polyacrylonitrile, polycarbonates, and the like. Copolymers and terpolymers are, of course, included in these definitions, examples of which, include, but are not limited to, the polyvinyl aldehydes, such as polyvinyl acetals, polyvinyl butyrals, polyvinyl formals, and vinyl copolymers. Preferably, the binder should be present in the imaging layer in an amount in the range of 15-60 weight percent and more preferably, 25-50 weight percent, based upon the total weight of the imaging system.
The use of conventional toners such as phthalazinone, phthalazine, and phthalimide can also be used in the imaging system, if desired. When utilized, the toner should preferably be present in the imaging system in an amount in the range of 1-6 weight percent and more preferably, 2-5 weight percent, based upon the total weight of the imaging system.
Any suitable base or substrate material known to those skilled in the art can be used in the present invention. Such materials can be opaque, translucent, or transparent. Commonly employed base or substrate materials utilized in the thermographic arts include, but are not limited to, paper; opaque or transparent polyester and polycarbonate films; and specularly light reflective metallic substrates such as silver, gold, and aluminum. As used herein, the phrase "specularly light reflecting metallic substrates" refers to metallic substrates, which when struck with light, reflect the light at a particular angle as opposed to reflecting the light across a range of angles.
Optionally, an anti-stick layer, positioned on top of the imaging system, may be used. Any conventional anti-stick material may be employed in the present invention. Examples of such anti-stick materials, include, but are not limited to waxes, silica particles, styrene-containing elastomeric block copolymers such as styrene-butadiene-styrene, styrene-isoprene-styrene, and blends thereof with such materials as cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate.
Further, an anti-static or anti-stick layer may optionally be applied to the back of the support. Materials for such purpose are well known in the photothermographic imaging art.
The imaging, anti-stick, and anti-static layers employed in the present invention can be applied by any method known to those skilled in the art such as knife coating, roll coating, dip coating, curtain coating, hopper coating, etc.
The following non-limiting examples further illustrate the present invention.

EXAMPLES

Materials used in the following examples were available from standard commercial sources such as Aldrich Chemical Co. (Milwaukee, WI) unless otherwise specified. "Butvar B-76" is a tradename for a polyvinyl butyral resin sold by Monsanto Chemical Co. of St. Louis, MO.
The near-infrared laser diode had a maximum power output of 150 mW. A power supply was used to modulate the power output from the laser diode. A mechanical shutter was used to modulate the exposure time. The laser diode was focused to a spot size ca. 60 microns at the film plane.
Silver behenate homogenate may be prepared as disclosed in U.S. Pat. No. 4,210,717 (column 2, lines 55-57) or U.S. Pat. No. 3,457,075 (column 4, lines 23-45 and column 6, lines 37-44).
The following near-infrared dyes were used in some of the examples which follow:

PC 364 has the structural formula:

(1,5-Bis(p-dimethylaminophenyl)-1,5-bisphenyl-2,4-pentadienolperchlorate(prepared according to the method disclosed in J. Am. Chem. Soc., 1958, 80, 3772.)

IR125 has the structural formula:

(commercially available from Eastman Kodak Co., Rochester, NY).

SQ1 has the structural formula:

(SQ1 was prepared via the following sequence of reactions: 1,2,3,4,4a,9a-hexahydro-4,4,4a,9-tetramethyl-2-oxo-9H-carbazole(Garnick, R.L. et al., J. Org. Chem., 1978, 43, 1226) was allowed to react in refluxing toluene with the ylid of methyltriphenylphosphonium bromide prepared using potassium t-butoxide. The resulting olefin, 1,2,3,4,4a,9a-hexahydro-4,4,4a,9-tetramethyl-2-methylene-9H-carbazole, was purified by distillation. The olefin was oxidized in iodine, sodium iodide and refluxing methanol to yield, after recrystallization, the carbazolium salt 2,4,4,4a,9-pentamethyl-4,4a-dihydro-3H-carbazolium iodide. SQ1 was prepared by condensing two equivalents of the free base form of the carbazolium salt with squaric acid according to the method of Kuramoto (Dyes & Pigments, 1989, 11, 21).

Cyasorb™ 165 dye has the structural formula:

(Cyasorb™ 165 is commercially available from American Cyanamid Corp., Wayne, New Jersey.)

Examples 1-6

The following formulation was used in Examples 1-6:

silver behenate homogenate (10 weight % solids in 80 weight % methyl ethyl ketone and 20 weight % toluene) 82 g

methyl ethyl ketone 100 g

polyvinyl butyral 30 g

The formulations of Examples 1-6 were prepared by mixing 15 g of the above dispersion with additional ingredients as disclosed in Table 1.

Table 1

Ingredient	Ex. 1	Ex. 2	Ex. 3	Ex. 4	Ex. 5	Ex. 6
Methyl gallate	0.3 g	0.3 g	0.3 g	0.3 g	0.3 g	0.3 g
Phthalazinone	0.1 g	0.1 g	0.1 g	0.1 g	0.1 g	0.1 g
3-Indazolinone	0.1g	0.1g	0.1g	0.1g	0.1g	0.1g
IR125*	0.03 g	0.01 g	NA	NA	NA	NA
SQ1*	NA	NA	0.03 g	0.01 g	NA	NA
PC 364*	NA	NA	NA	NA	0.03 g	0.01 g
Methanol	4 ml	4 ml	4 ml	4 ml	4 ml	4 ml
Methyl Ethyl Ketone	1 ml	1 ml	1 ml	1 ml	1 ml	1 ml
"NA" means not added.

* A near-infrared dye.

The dispersions were coated at 0.10 mm wet thickness and dried for 3 minutes at 60° C. A topcoat layer was then applied consisting of 10 g cellulose acetate, 200 g methyl ethyl ketone, and 10 ml of a 1 weight percent hexane diisocyanate solution in methyl ethyl ketone. The topcoat was coated at 0.08 mm wet thickness and dried for 3 minutes at 60°C. Upon exposure (to the laser diode) and development, the results (shown in Table 2) for the materials of Examples 1-6 were obtained.

Table 2

	EXAMPLE
	1	2	3	4	5	6
lowest imaging power (in mw)*	19	42	80	114	19	19
lowest exposure time (in seconds)**	1/250	1/60	1/8	1/15	1/125	1/60

* This is the lowest laser diode power at which a black spot could be observed in the film.
** This is the shortest exposure time that could be used to see a black spot in the film when the laser diode power was set at 80 milliwatts.

Example 7

The same formulation was used as in Examples 1-6 except that 3,3'-diethylthiatricarbocyanine iodide (formula shown below) was used as the near-infrared dye. An amount of 0.03 g dye gave the following data:

lowest image power (in milliwatts) 42

lowest exposure time (in seconds) .017

3,3'-diethylthiacarbocyanine iodide (available from Eastman Kodak Company of Rochester, NY)

Example 8

The same formulation was used as in Example 7 except that 0.01 g of 3,3'-diethylthiatricarbocyanine iodide was used as the near-infrared sensitizing dye. The following data were obtained:

lowest imaging power (in milliwatts) 80

lowest exposure time (in seconds) 0.067 sec

Example 9

This example demonstrates the utility of various urea compounds as reducing agents (in particular, development accelerators) for thermographic imaging constructions.

Silver behenate full soap (160 g) was mixed with 20 g of Butvar™ B-76. Five samples (A-E) were prepared by adding the following ingredients to 15 g of the above dispersion:

	A	B	C	D	E
methyl gallate	0.6 g	0.6 g	0.6 g	0.6 g	0.6 g
L-ascorbic acid palmitate	0.05 g	0.05 g	0.05 g	0.05 g	0.05 g
succinimide	0.2 g	0.2 g	0.2 g	0.2 g	0.2 g
tetrachlorophthalic anhydride	0.05 g	0.05 g	0.05 g	0.05 g	0.05 g
IR125 (infrared dye)	0.03 g	0.03 g	0.03 g	0.03 g	0.03 g
2-imidazolidone		0.1 g			0.2 g
N,N'-dimethylurea			0.1 g
Carbanilide				0.1 g
methanol	4 ml	4 ml	4 ml	4 ml	4 ml
methyl ethyl ketone	1 ml	1 ml	1 ml	1 ml	1 ml

The above dispersions were coated at 4 mils wet thickness and then air dried. A topcoat consisting of 5 g Kraton™ D1101 styrene-butadiene-styrene block copolymer (available from Shell Chemical Co.), 15 g Styron™ 685D polystyrene resin (available from Dow Chemical Co.), and 250 g methyl ethyl ketone was coated over the first coating at 2 mils wet thickness and then air dried.
A laser beam produced by a laser diode (Spectra-Diode Labs, 2370-H1) emitting at 810 nm was focused to a 160 µm x 45 µm spot (full width at 1/e² value) on an image plane. The power on the image plane was aperture-limited to 600 mW. The beam was scanned across the media at 15 cm/sec. The following laser exposure results were obtained for the samples described above:

A B C D E

D_max 1.95 1.98 2.32 2.33 3.44

D_min 0.22 0.23 0.20 0.17 0.20

Haze was measured on a Hunter hazemeter (available from Hunter Associates laboratory, Inc.; Reston, Virginia) and gave the following results:

A B C D E

% Haze 20% 15% 14.7% 15% 8%

Example 10

This example discloses a thermographic imaging formulation using pyrogallol. Silver behenate full soap (160 g, 10 weight % in methyl ethyl ketone) was mixed with 20 g of Butvar™ B-76. To 20 g of this dispersion, the following were added: 0.6 g of methyl gallate; 0.2 g of pyrogallol; 0.2 g of phthalazinone; 0.1 g of succinimide; and 0.1 g of 2-imidazolidone.
The above dispersion was coated at 4 mils wet thickness and was dried for 3 minutes at 140° F. A second coating was applied as an infrared energy absorbing layer. This was composed of 1.0 g CA 398-6 cellulose acetate (Eastman Chemicals), 20.0 g methyl ethyl ketone, and 0.03 g IR 125 infrared dye. This was coated at 2 mils wet thickness and was dried for 3 min at 60°C.
A black image with a D_max of 3.73 and a D_min of 0.09 was achieved using the same laser exposure conditions as described in Example 9.

Example 11

This example describes a thermographic imaging formulation using L-ascorbic acid palmitate: 160 g of silver behenate full soap (10% in methyl ethyl ketone) was mixed with 20 g of Butvar™ B-76. To 20 g of this dispersion were added: 0.6 g of methyl gallate; 0.2 of L-ascorbic acid palmitate; 0.1 g of succinimide; and 0.1 g of 2-imidazolidone. The dispersion was coated at 4 mils wet thickness and dried for 3 minutes at 60°C. A topcoat consisting of 1.0 g CA 398-6 cellulose acetate, 210 g methyl ethyl ketone, and 0.03 g of IR 125 infrared dye was coated at 2 mils wet thickness and was dried for 3 min at 60°C.
A D_max of 2.73 and a D_min of 0.10 were obtained using the same laser exposure conditions described in Example 9.

Example 12

This example describes the use of Cyasorb™ 165 as an infrared dye in the following thermographic imaging composition:
Silver behenate full soap (160 g, 10 weight % in methyl ethyl ketone) was mixed with 20 g of Butvar™ B-76. To 15 g of this dispersion were added 0.6 g of methyl gallate, 0.2 g of pyrogallol, 0.2 g of phthalazinone, 0.2 of succinimide, and 0.1 of 2-imdazolidone, all dissolved in 4 ml of methanol and 1 ml of methyl ethyl ketone. This dispersion was coated at 4 mils wet thickness and dried for 3 min at 50°C. A topcoat consisting of 1.0 g CA 398-6 cellulose acetate, 20 g methyl ethyl ketone, and 0.03 g of Cyasorb™ 165 infrared dye was coated at 2 mils wet thickness and dried 5 min at 50°C.
Black images of D_max of 2.98 and D_min of 0.10 were obtained upon exposure with a 30W, 100pps Q-switched Nd:YAG laser that was focused to a 120 µm spot.
Reasonable variations and modifications are possible from the foregoing disclosure without departing from either the spirit or scope of the present invention as defined by the claims.

Claims

A thermal recording material comprising a substrate coated with an imaging system, said imaging system consisting essentially of: (a) a thermally reducible source of silver; (b) a polymeric binder; (c) a dye which absorbs electromagnetic radiation in the wavelength range of about 500-1100 nm; and (d) a reducing agent for silver ion.
The thermal recording material of Claim 1 where said thermally reducible source of silver is a silver salt of a carboxylic acid containing 10-30 carbon atoms.
The thermal recording material of Claim 2 where said silver salt is silver behenate.
The thermal recording material of Claim 1 wherein said thermally reducible source of silver is present in said imaging system in an amount in the range of 5-50 weight percent, based upon the total weight of said imaging system.
The thermal recording material of Claim 1 wherein said reducing agent for silver ion comprises at least one development accelerator selected from the group consisting of:
(i) a 3-indazolinone compound of the formula:
wherein: R is selected from the group consisting of hydrogen; an alkyl group of 1 to 4 carbon atoms; halogen; -COOH; and R¹COOH wherein R¹ is an alkyl group of 1 to 4 carbon atoms; and

(ii) a urea compound of the formula:
wherein: R² and R³ each independently represent hydrogen; a C₁ to C₁₀ alkyl or cycloalkyl group; or phenyl; or R² and R³ together form a heterocyclic group containing up to 6 ring atoms.
The thermal recording material of Claim 5 wherein R represents hydrogen; R² and R³ each independently represent a C₁ to C₅ alkyl or cycloalkyl group; or phenyl; or R² and R³ together form a heterocyclic group containing up to 5 ring atoms.
The thermal recording material of Claim 1 wherein said dye is a near-infrared dye which absorbs light having a wavelength in the range of from about 650-1100nm.
The thermal recording material of Claim 7 wherein said near infrared dye absorbs light having a wavelength in the range of from about 750-1100 nm.
The thermal recording material of Claim 1 wherein said electromagnetic radiation absorbing dye is selected from the group consisting of:
The thermal recording material of Claim 1 wherein said electromagnetic radiation absorbing dye is present in said imaging system in a layer adjacent to a layer containing said thermally reducible source of silver and said reducing agent for silver ion.