JPH08290666A - Laser absorbent photo-bleaching composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal imaging medium which can form an image by a laser address. SOLUTION: A laser-induced thermal imaging component contains a thermal imaging medium and a bleachable photo-thermal conversion dye which associates with a reducing agent for dye and has maximum absorption in an area of 600-1,500 nm. The reducing agent bleaches the dye by a laser address of the component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive image forming medium capable of forming an image by laser address.

[0002]

BACKGROUND OF THE INVENTION Many heat-sensitive imaging media that are imageable by laser address include a photothermal converter, which converts a laser beam into heat, which heat is used to induce an imaging process. Infrared emitting lasers such as YAG lasers and laser diodes are most commonly used for reasons of cost, convenience and reliability. Therefore, as disclosed in JP-A-51-88016, the infrared absorbing dyes and pigments are most commonly used as photothermal converters, although addressing at shorter wavelengths in the visible region is also possible. There is.

Of particular interest are laser-addressable heat-sensitive media that form color images. The most well known of these are the various forms of thermal transfer imaging in which a colorant is transferred from a donor to a receiver in response to heat generated by laser irradiation, and dye diffusion transfer (US Pat. No. 5,171,650), mass transfer of dye and pigment layers (disclosed in Japanese Patent No. 63-319192), ablative transfer of dyes and pigments (US Pat. No. A-5,171,650 and International Patent Application No. 90/12342). Other types of laser thermal color imaging media include media based on the formation or destruction of colorant dyes in response to heat (US Pat. No. A-4602263), based on migration of toner particles to a thermal softening layer. Medium (International Patent Application No. 93/04411
No.), various peeling systems in which the adhesion of the colored layer in proportion to the substrate and cover sheet is changed by heat (International Patent Application No. 93
/ 03928, 88/04237, and German Patent No. 4209873).

A common problem with all of these media is the potential for contamination of the final image by the laser absorber. For example, in the case of thermal transfer media, the absorber can be transferred with a colorant. Unless the co-transferred absorber has a complete absorption band in the visible portion of the spectrum, the color of the image will change. Various attempts have been made to identify infrared dyes with minimal visible absorption, but in practice their infrared absorption band almost always has a tail in the visible region, leading to image smearing.

Many methods have been proposed to remove contaminants with the final absorbent. For example British Patent Application No. 940617
No. 5.1 discloses contacting the transferred image of laser thermal transfer imaging with a thermal bleach which is capable of bleaching the absorber. This method complicates the imaging process and cannot bleach certain dyes such as Cyasorb 165 ^™ (American Cyanamid), which is commonly used with YAG lasers. In International Patent Application No. 93/04411 and U.S. Patent No. A-5219703,
Acid generating compounds that bleach infrared absorbing dyes are disclosed. However, additional UV exposure is generally required (optionally in the presence of UV absorbers), further complicating the imaging process.

There is a need for improved methods of bleaching IR absorbing dyes in laser addressed thermal media.

Another problem common to imaging systems using laser irradiation is the inability to control its reaction temperature. The irradiation of the laser excites the photothermal conversion dye, and the outer shell electrons are excited to a higher energy level corresponding to the protons from the laser. Since heat is generated and subsequently this excitation process occurs, it is likely that adjacent molecules will be excited and more heat will be generated. It is desirable to be able to control the generation of this heat during laser addressing.

Photoredox methods involving dyes are known to those skilled in the art. The photoexcited dye accepts electrons from the co-reactant and the dye acts as a photooxidant. Although not found in the literature for laser addressable thermal imaging media, there are numerous examples where this type of method was used. In particular, a number of systems containing cationic dyes associated with organic borate ions (disclosed in U.S. Patent Nos. A-5166041, A-4447521, A-4343891 and J. Chem Soc. Chem Commun 1993 299). ). After transferring an electron to the excited dye, the organic borate ion decomposes into a free radical, which initiates the polymerization reaction (J. Am, Che
m.Soc., 1985, 110, pp. 2326-8), further reacting to form an image (US Pat. Nos. A-4447521 and A-43438).
No. 91)

Other examples of image formation involving photoreduction of dyes include:
It is disclosed in US Pat. No. A-4816379. This patent document discloses a medium containing a photocurable layer containing a UV photoinitiator and a photopolymerizable compound, in which a cationic dye having a specific structure and the dye are reduced to a photoexcited state. It contains a possible mild reducing agent. Imagewise exposure at wavelengths absorbed by the cationic dye causes its photoreduction, generating a polymerization inhibitor, and by substantially uniform UV exposure polymerizes only the previously unexposed areas. Conventional wet development leaves a positive image. Cationic dyes are disclosed to absorb in the visible, and it is not known to have species that absorb IR. The shift in extinction coefficient of the cationic dye (including bleaching) is shown. Preferred reducing agents are salts of N-nitrosocyclohexylhydroxylamine, but other possible include ascorbic acid and thiourea derivatives. There is no disclosure of thermal imaging media.

J. Imaging Sci. & Technol 1993, 37th
Vol. 14, pp. 149-155, discloses photoreductive bleaching of pyrylium dyes with allylthiourea derivatives under UV flood exposure conditions.

European Patent No. A-0515133 and J.Org.Che
m, 1993, 58, 2614-8, discloses photoreduction of neutral xanthene dyes with amines and other electron donors to initiate polymerization and in photosynthetic applications.

Photoexcitation of dihydropyridine derivative Ru (III)
The ability to transfer electrons to the complex was reported by J. Amer. Chem. Soc., 1981,
Vol. 103, pp. 6495-766. The reaction was carried out in solution and was not used for imaging applications.

In a first aspect of the present invention there is provided a laser addressable heat-sensitive medium containing a heat-sensitive imaging system and a heat-sensitive conversion dye associated with a reducing agent, wherein the reducing agent is added during the laser addressing of the medium. Bleach the above dye.

By the term "laser-addressable heat-sensitive medium" is meant an imaging medium in which an image is formed in response to heat, which heat is generated by the absorption of cohesive radiation (emitted by a laser including a laser diode). Represent

To be able to function in this way, the medium must contain a "photothermal converter", ie a substance that absorbs the incident radiation with the associated generation of heat.
When a dye absorbs radiation, some of its molecules are converted to an electronically excited state and photothermal conversion consumes this electronic excitation, primarily as vibrational energy of the surrounding molecules, returning the dye molecule to its ground state. The mechanism of this consumption is not well understood, but the excited state of the dye has a very short lifetime (eg, picosecond order, Schuster JA et al.
m.Chem.Soc., 1990, 112, 6329). Thus, in the absence of a competitive process, dye molecules experience many excitation-deexcitation cycles, even during the shortest laser pulses normally encountered during laser thermal imaging (on the order of nanoseconds). .

Possible competing processes include photoredox processes in which the photoexcited dye molecule donates or accepts electrons from or to the ground state reagent. This initiates further chemical transformation, which undergoes further excitation-deexcitation cycles. Particularly suitable for the present invention is a photoreduction method, in which, when an electron is excited to a higher energy orbit by photoexcitation, a suitable reducing agent donates an electron to fill a hole generated in a lower energy orbit of a dye. It is considered. Cationic dye (has a positive charge associated with the chromogen)
The method is believed to occur most easily in the case of a neutral dye such as xanthene (US Pat. No. A-481637).
No. 9, disclosed in European Patent No. A-0515133),
No thermal imaging media are found in that document. In this patent document, the method provides a convenient and effective bleaching method, without a very great adverse effect on the dye's ability to act as a photothermal converter.

By reducing the photothermal conversion dye and subsequently accepting electrons from the reducing agent, its ability to be excited by laser irradiation is reduced or lost. Therefore, once reduced, the possibility of generating additional heat is reduced.

The term "bleaching" in the present invention refers to the effective reduction of the absorption band resulting in visible coloration by the photoheat exchange dye. Bleaching is achieved by the destruction of the absorption bands mentioned above or by shifting them to wavelengths which do not cause visible coloring. It is believed that the photoreduction mechanism described above acts like the preferred embodiments described herein, but the invention is not limited to this particular bleaching mechanism. Other mechanisms containing reducing agents are also feasible, eg pure thermal mechanisms, or mechanisms containing both thermal and photostimulants.

Dyes suitable for use in the present invention include cationic dyes such as polymethine dyes, pyrylium dyes, cyanine dyes, diamine dicationic dyes, phenazinium dyes, phenoxazinium dyes, phenothiazinium dyes, acridinium dyes, and medium dyes. Volatile dyes, such as the xanthene dyes and the squarylium dyes disclosed in EP-A-0515133. Preferred dyes have absorption maxima that match the output of the most commonly used laser sources for thermal imaging, such as laser diodes and YAG lasers. Absorption in the 600-1500 nm region is preferred, and absorption in the 700-1200 nm region is most preferred.

A preferred class of cationic dyes for use in the present invention include tetraarylpolymethine (TAPM) dyes. These absorb in the region of 700 to 900 nm, which makes them suitable for diode laser addressing, and laser addressing in the patent literature, for example Japanese Patent Nos. 63-319191, 63-319192 and U.S. Pat.A-4950639. There are various references to its use as an absorber in thermal transfer media. When these dyes are transferred with a colorant, TAPM dyes generally have an absorption peak with a tail in the red region of the spectrum, thus providing a blue tint to the transferred image. Applicant's co-pending British Patent Application No. 9406175.1 discloses thermal bleaching of TAPM dyes in thermal transfer media by providing a thermal bleach to the receiving layer. As described in the present invention, TA
It was revealed that the PM dye can be bleached clearly by the photoreduction method.

The general formula for TAPM dyes is described in US Pat.
No. 5,135,842. Preferred examples are of general formula I:

[Chemical 6] (Wherein, Ar ¹ to Ar ⁴ independently represent an aryl group, Ar ¹
At least two of ~ Ar ⁴ have a tertiary amino group at the 4-position and X is an anion).

Examples of tertiary amino groups include dialkylamino groups, diarylamino groups, and cyclic substituents such as pyrrolidino, morpholino, piperidino. The tertiary amino group may be part of a fused ring system, eg Ar ^1-
One or more of Ar ⁴ may represent a julolidine group.

Preferably, the anion X is a strong acid (eg
HX is derived from pKa3 or less, preferably 1 or less). Suitable X includes ClO ₄ , BF ₄ , CF ₃ SO ₃ , P
It includes F ₆ , AsF ₆ , and SbF ₆ .

Preferred dyes of formula I have Ar ¹ = Ar ³ = 4-dimethylaminophenyl, and Ar ² = Ar ⁴ = phenyl and X = CF ₃ SO ₃ .

Another preferred class of cationic dyes are amine cation radical dyes, eg International Patent Application No. 90
/ 12342 and Japanese Patent No. 51-88016 are also known as immonium dyes. These include diamine dicationic dyes exemplified by the commercially available Cyasorb IR165 (American Cyanamid), which have the general formula II:

[Chemical 7] (Wherein Ar ^{1 to} Ar ⁴ and X are defined as above). These dyes have relatively long wavelengths (about 10
Peak absorption at 50 nm, suitable for YAG laser address), but its absorption band is broad and has a tail in the red region. Applicant's co-pending UK patent application No. 94
No. 06175.1 discloses that it is possible to partially bleach a diamine dicationic dye by a thermal process,
It has been found that total bleaching can be achieved by a photoreduction process.

The reducing agent used in the present invention may be any compound or group capable of interacting with the photothermal conversion dye and bleaching it under the photoexcitation and elevated temperature conditions associated with the laser address of the thermal imaging medium. Do not react with ground-state dyes under normal storage conditions. Preferably,
The reducing agent acts as a photoreducing agent for the dye, ie it transfers electrons only to the photoexcited form of the dye and stabilizes the composition without photoexcitation. However,
Compositions capable of reacting with the dye in the ground state may be used if the reaction rate is very slow at normal storage temperatures. The choice of reducing agent may depend on the choice of laser absorbing dye. Candidate combinations of dyes and reducing agents may be screened for compatibility by a coating mixture of dyes and reducing agents on transparent substrates, optionally in mutually compatible binders, after which (a ) Monitor the effect of dye storage on the absorption spectrum, and (b) storage of the film for several days in the dark at moderately elevated temperature and (b) irradiation of the film at the absorption maximum of the dye by a laser source. For the preferred combinations, condition (a) should have a minimal effect and condition (b) should bleach the dye.

The reducing agents suitable for the present invention are generally good electron donors, ie have a low oxidation potential (Eox), usually 1.0 V or less, preferably 0.40 V or more. They may be neutral molecules or anionic groups. Examples of anionic groups include salts of N-nitrosocyclohexylhydroxylamine, N-phenylglycine salts and formula III disclosed in US Pat. No. 4,816,379.

Embedded image (In the formula, R ^{1 to} R ⁴ independently represent an alkyl, aryl, alkaryl, aralkyl, alkenyl, alkynyl, silyl, alicyclic or saturated or unsaturated heterocyclic group, and at least one R ¹ to R ⁴ Where R ⁴ is an alkyl group having up to 8 carbon atoms, including substituted derivatives of these groups).

US Pat. No. A-5166041 discloses photobleaching of various IR absorbing cationic dyes with such chemical species, but does not disclose laser addressed thermal imaging. . Similarly, photobleaching of visible absorbing cyanine dyes with alkyl borate ions is disclosed in US Pat. Nos. A-4,447,521 and A-4,343,891.
An anion reducing agent may be added to the cationic dye as a counter ion.

Neutral reducing agents suitable for the present invention generally (although not necessarily) have one or more labile hydrogen atoms or acyl groups which are transferred to the dye and then to the electron and thus its Performs irreversible bleaching of the dye. Examples of neutral reducing agents include thiourea derivatives, ascorbic acid, benzhydrols, phenols, amines and leuco dyes (including their acylated derivatives) disclosed in US Pat. No. A-4816379. . The photooxidation product of the reducing agent must not itself be visible colored. Surprisingly,
It has been found that, in certain cases, leuco dyes can be used as reducing agents without undesired coloring.

A preferred class of reducing agents has the general formula IV:

[Chemical 9] Where R ⁵ and R ⁶ are independently selected from H, alkyl, aryl, alicyclic or heterocyclic; each R ⁷ and R ⁸ is independently alkyl, aryl, alicyclic and heterocyclic. Selected from cyclic, Z represents a 1,4-dihydropyridine derivative having a core of covalent bond or oxygen atom).

The term "alkyl" refers to an alkyl group having a lower alkyl meaning no more than 20 carbon atoms, preferably no more than 10 and most preferably no more than 5.

The term "aryl" represents an alkyl group having up to 14 carbon atoms, preferably up to 10 carbon atoms and most preferably up to 6 carbon atoms.

The term "cycloaliphatic" refers to a non-aromatic ring or fused ring system having up to 14 carbon atoms, preferably up to 10 carbon atoms and most preferably up to 6 carbon atoms.

By the term "heterocyclic", 14 or less, preferably 10 or less, most preferably 6 or less C, N, O
And an aromatic or non-aromatic ring or fused ring system having atoms selected from S. As is known in the art, not only is a high degree of substitution tolerated, but a high degree of substitution is often desirable. For simplification of the discussion, "nuclear",
The terms "group" and "moiety" are used to distinguish between a chemical species that can be substituted or that can be substituted and a chemical species that is not substituted or can be so substituted. For example, the term "alkyl group" includes pure hydrocarbon alkyl chains such as methyl, ethyl, octyl, cyclohexyl, isooctyl, t-butyl, etc., as well as conventional substituents known to those skilled in the art, such as Also included are alkyl chains having hydroxyl, alkoxy, phenyl, halogen (F, Cl, Br and I), cyano, nitro, amino and the like. The word "nucleus" is also considered to be permutable. By contrast, "alkyl moieties" are limited to those containing only pure hydrocarbon alkyl chains such as methyl, ethyl, octyl, cyclohexyl, isooctyl, t-butyl and the like.

It is clear that the compounds of formula IV bleach cationic dyes (especially the compounds of formulas I and II) rapidly and fully when the latter are photoexcited, but in the dark, at room temperature, to dyes. On the other hand, it is stable. Furthermore, they are stable compounds that are easily synthesized, do not give rise to colored degradation products and are suitable for use in media forming colored images.

Accordingly, in yet another aspect of the present invention, there is provided a method of bleaching a cationic dye by exposing it to an electronically excited state in the presence of a compound having a nucleus of the general formula IV. To do.

In formula IV, R ⁵ is H or phenyl (optionally substituted), R ⁶ is preferably phenyl (optionally substituted) and R ⁷ is preferably lower alkyl (especially substituted). , Methyl), and R ⁸ is preferably lower alkyl (eg, ethyl).

The compound of formula IV is prepared according to the known Hantsc
Co-condensation of aldehydes, amines and 2 equivalents of beta-ketoesters in the application of h) pyridine synthesis:

[Chemical 10] May be synthesized by The combination of the compound of formula IV or other reducing agent is usually coated in the same layer or layers as the dye, but if no reactive association of the dye and reducing agent during light irradiation is possible, an additional or Alternatively it may be present in one or more separating layers. The absorption of the laser pulse causes a very fast rise in temperature and pressure, which mixes and interacts with the components of two or more adjacent layers.

Preferably at least 1 mole of reducing agent is
It is present per mole of dye, but more preferably in excess, eg 5 to 50 times. In the case of compounds of formula IV, metal salt stabilizers, for example magnesium salts, may be introduced, which obviously improve the thermal stability of the system without adversely affecting the photoactivity. An addition amount of about 10 mol% based on the compound of formula IV is effective.

The laser-addressable thermal imaging medium may contain any imaging medium that uses photothermal conversion to form an image, but in the present invention it is particularly dependent on the presence of unbleached photothermal conversion dyes. The use of media to form the resulting color image was found. Such media may take various forms, such as colorant transfer systems, release systems, phototackifier systems and systems based on unimolecular thermal fragmentation of certain compounds.

Preferred laser-addressable thermal imaging media include various types of laser thermal transfer media.
In these systems, a donor sheet containing a layer of colorant and a suitable absorber is placed in contact with an assembly exposed to a pattern of radiation from a receiver and scanning laser source. The radiation is absorbed by the absorber and rapidly generates heat in the exposed areas of the donor, which in turn transfers the colorant to the receiver. Multicolor images may be assembled on conventional receivers by repeating the process with one or more differently colored donors. The system is particularly well suited to the color proofing industry where color separation information is routinely generated and stored electronically, and the ability to convert such data to hard copy by the digital address of a "dry" medium is particularly useful. is there.

The generated heat causes colorant transfer by various mechanisms. For example, rapid pressure build-up as a result of the decomposition of binders or other components into a gaseous product, U.S. Patent No.A-5171650 and International Patent Application No. 9
As disclosed in 0/12342, it provides the physical driving force (“ablation”) of the colorant material to the receiver. Further, the colorant and associated binder agent may be transferred in the melt (melt-stick transfer), as disclosed in JP 63-319191. Both of these mechanisms result in mass transfer, ie essentially 0 or 100% transfer of colorant, depending on whether the applied energy exceeds certain limits. A slightly different mechanism is diffusion or sublimation transfer whereby the colorant diffuses (or sublimates) to the receiver without transfer with the binder. This is the case, for example, in US Pat.
No. 26760, the amount of transferred colorant varies continuously with input energy.

Any donor component structure known in the laser thermal transfer imaging art may be used in the present invention. Therefore, the donor may be used for sublimation transfer, ablation transfer, or melt stick transfer. Usually, the donor component includes a substrate (for example, a polyester sheet), a colorant layer,
Dyes (preferably cations) as photothermal converters
Layer and reducing agent layer. The dye and reducing agent may be in the same layer as the colorant, in one or more separate layers, or both. Other layers may be present, such as the dynamic release layer disclosed in US Pat. No. A-5171650. Moreover, the donor may be self-supporting as disclosed in EP-A-0491564. Binder-free colorant layers are possible, as disclosed in International Patent Application PCT / GB92 / 01489, although the colorants are generally dyes or dyes of the desired color dissolved or dispersed in one or more binders. Contains a pigment.
Preferably, the colorant includes an International Prepress Proofing Association known as the SWOP color standard.
It contains dyes or pigments that reproduce the colors shown by the standard printing ink standards provided by the Association).

Particularly preferred donor components are of the type disclosed in British patent application No. 9225724 in which the colorant layer contains a fluorocarbon compound in addition to the pigment and binder. The acceptor components used in the present invention are entirely conventional. Thus, they usually include substrates, such as paper or plastic sheets with one or more resin coatings. The choice of resin for the receiver layer (eg, with respect to Tg, softening point, etc.) depends on the type of transfer involved (ablation, melt stick or sublimation), but for the preferred donor component use, the bat bar Butvar ^™ B76 polyvinyl butyral (from Monsanto), polyvinyl resins, and similar thermoplastic materials are suitable.

The method of image transfer of colorant from the donor to the receiver is quite conventional. The two components are assembled in face-to-face intimate contact, for example under vacuum, or additionally by means of a cylinder lens arrangement as disclosed in British patent application No. 9220271 and scanned by a suitable laser.
The assembly may be imaged by any commonly used laser, depending on the absorber used,
Addressing with near infrared and infrared emitting lasers such as diode lasers and YAG lasers is preferred.
Best results are obtained with relatively high intensity laser irradiation, eg at least 10 ²³ protons / cm ² / sec. For a laser diode emitting at 830 nm, this roughly corresponds to a power of 0.1 W concentrated in a 20 micron spot with a dwell time of about 1 microsecond. For YAG laser exposure at 1064 nm, the flux is at least 3 × 10 ²⁴ protons / c
m ² / sec is preferred and corresponds approximately to an output of 2 W concentrated in a 20 micron spot with a residence time of approximately 1 microsecond.

Any known scanning device may be used, such as a flat-bed scanner, an external drum scanner or an internal drum scanner, and the assembly to be imaged is placed on the drum or bed (eg vacuumed). Held by the laser beam at a spot on the IR absorbing layer of the donor (for example, about 10-2).
5, preferably about 20 microns diameter). The spot is scanned over the entire area to be imaged while adjusting the laser power according to electronically stored image information. Two or more lasers may be simultaneously scanned in different areas of the donor-acceptor assembly, and if desired,
The outputs of two or more lasers may be combined into a single spot of higher intensity. Laser addressing is usually performed from the donor side, but may be performed from the receptor side when the receptor is permeable to laser light. Peeling off the donor and receiver reveals a monochrome image on the receiver. The process is repeated one or more times with different color donor sheets to form a multicolor image on a conventional receiver. Due to the interaction of the photothermal conversion dye and the reducing agent during the laser address, the final image can be released from contamination by the photothermal converter. In some cases, the receiver onto which the colorant image is first transferred is not the last visible substrate of the image. For example, US Pat. No. A-5126760 discloses thermal transfer of an image from a first receiver to a second receiver for viewing.

Another type of laser addressable thermal imaging medium suitable for use in the present invention is the use of migration imaging disclosed in International Patent Application No. 93/04411. Specifically, this involves vapor deposition of the marking particles as a substantially continuous layer on the thermoplastic imaging element and creating an attractive force between the two (eg, by electrostatic charge). If the particles, the thermoplastic imaging component, or both, contain an IR absorbing dye, and the assembly is imagewise exposed by a laser, softening of the thermoplastic component occurs, migrating the marking particles under attractive force. And then fixed by subsequent cooling.
The particles are removed from the non-image areas by wiping or other suitable means. Introducing an acid generating compound, such as an iodonium salt, into the particles, the thermoplastic component or both,
IR, either during laser addressing or (more effectively) by uniform UV exposure as an additional step
Bleach the dye. This type of medium may be used in the present invention by using a dye in the marking particles as a laser absorber together with the reducing agent present in the particles and / or the thermoplastic component. Effective bleaching of laser absorbers is possible without the need for further UV exposure. Other types of laser thermal color imaging media within the scope of this invention include media based on the formation or destruction of colorable dyes in response to heat (US Pat. No. 4,602,263), and substrates and covers. Various peeling systems in which the adhesion of the colored layer in proportion to the sheet changes due to heat (International Patent Application Nos. 93/03928, 88
/ 04237, German Patent No. 4209873).

[0048]

The invention is explained in more detail below by the description of only the following examples.

The following materials are used in the examples.

[Chemical 11]

[Chemical 12]

[Chemical 13]

Embedded image Battoba (Butvar ^TM) B-76- polyvinyl butyral (Monsanto (Monsanto)) VAGH and VYNS- Union Carbide (Union Carbide) company from a commercial vinyl copolymer resin MEK- methyl ethyl ketone (2-butanone) FC-N-methyl perfluorooctane Sulfonamide

Example 1 This example illustrates the photoreducible bleaching of Dye 1 and Dye 2 with Donor 1 (a) and Donor 2.

The following formulations were coated on a 100 micron unprimed polyester substrate to a wet thickness of 12 microns and air dried to give components 1-4.

[Table 1]

Components 1 and 2 were light blue / pink in appearance, and components 3 and 4 were light gray.
A 5 cm x 5 cm sample was loaded into a drum scanner and exposed with a 20 micron laser spot scanned at various speeds. The light source was either a laser diode delivering 115 mW at 830 nm at the image plane (components 1 and 2) or a YAG laser delivering 2 W at 1068 nm (components 3 and 4). The results are shown in the table below, where OD stands for optical density. Component 1 Component 2 OD (830nm) (initial) 1.9 1.3 OD (after scanning at 600 cm / sec) 1.7 1.2 OD (after scanning at 400 cm / sec) 1.5 0.6 OD (after scanning at 200 cm / sec) 0.7 0.3 component 3 components 4 (c) OD (1100 nm) (initial) 1.3 1.3 OD (after scanning at 6400 cm / sec) 0.9 1.3 OD (after scanning at 3200 cm / sec) 0.6 1.1

Component 4 (control lacking donor compound) showed slight bleaching, while components 1 to 3 were colorless tracks in the exposed areas with a bleaching degree related to scan speed ( track) was formed.

Donor 2 may be represented as an aroyl protected leuco acid and no coloration due to its corresponding dye will occur.

Although the formulation containing Donor 1 (e) had a shorter shelf life compared to the other formulations, donor 1 (b) -1 (e) was replaced with Donor 1 (a) to image Component 1. Repeat the formation,
Similar results were obtained.

Example 2 This example illustrates the photoreducible bleaching of Dye 3 and Dye 4 with Donor 3, which may be represented as an acyl protected leuco acid. Ingredients 5 and 6 were prepared in the same manner as ingredients 1-4 by the following formulation.

Laser diode irradiation at a scan rate of 200 cm / sec (as described in Example 1) produced the following optical density changes. OD change (670nm) OD change (IR band) Component 5 <0.1 -1.2 Component 6 <0.1 -0.8

Thus, effective bleaching of IR dyes without significant dye concentration due to the phenoxazine dye corresponding to Donor 3 was observed.

Example 3 This example illustrates the thermal transfer medium of the present invention. Mill base by dispersing magenta pigment chips in 32g MEK using a McCrone Micronising Mill
(mill base) was prepared. The pigment chips were prepared by standard methods and contained a blue tint of magenta pigment and VAGH binder in a weight ratio of 3: 2.

The following formulations were prepared and coated as described in Example 1 to give components 7-10.

[Table 2]

The resulting coated sample was assembled in contact with a VYNS coated paper receiver, vacuum held and loaded onto an external drum scanner, then scanned at 100 or 200 cm / sec with a laser diode (830 nm, 110 mW, 20 nm). Micron spots) were used for addressing. The receiver sheet exhibited lines of magenta pigment that were contaminated to varying degrees with Dye 1 or Dye 2 after peeling from the donor. The degree of pollution is 83
It was evaluated by measuring the reflection density of the transfer track at 0 nm or 1050 nm.

The components of the present invention showed much reduced staining with the IR dyes, resulting in purer magenta images.

Claims (12)

[Claims] 1. A laser-addressable thermal imaging component containing a bleachable photothermal conversion dye, which is associated with a thermal imaging medium and a reducing agent for a dye and has an absorption maximum in the region of 600 to 1500 nm, A laser-addressable thermosensitive image-forming component in which a reducing agent bleaches the dye by laser-addressing the component. 2. A thermal imaging element according to claim 1 wherein said dye has an absorption maximum in the 700 to 1200 nm region. 3. The dye is a polymethine dye, a pyrilian dye, a diamine dicationic dye, a phenazinium dye,
The thermal imaging element of claim 1 selected from phenoxazinium dyes and acridinium dyes. 4. The dye has the formula I: (Wherein, Ar ¹ to Ar ⁴ independently represent an aryl group, Ar ^1
4. A thermal imaging element according to claim 3 wherein at least two of ~ Ar4 have a tertiary amino group in the 4-position and X is an anion. 5. The dye has the formula: (Wherein, Ar ¹ to Ar ⁴ independently represent an aryl group, Ar ^1
4. A thermal imaging element according to claim 3 wherein at least two of Ar to Ar4 are diamine dicationic dyes having a tertiary amino group at the 4-position and X is an anion. 6. X is ClO ₄ , BF ₄ , CF ₃ , SO ₃ , P
Thermal imaging component according to any one of F _6, AsF _6, 1 On One aspect of the SbF ₆ 4 or claim 5. 7. The method according to claim 4, wherein the tertiary amino group is selected from a dialkylamino group, a diarylamino group, or a cyclic substituent selected from pyrrolidino, morpholino, piperidino or a part of a condensed ring system. The heat-sensitive image-forming component according to any one of 6 above. 8. The reducing agent has the formula IV: Where R ⁵ and R ⁶ are independently selected from H, alkyl, aryl, alicyclic or heterocyclic; each R ⁷ and R ⁸ is independently alkyl, aryl, alicyclic and heterocyclic. 1-dihydropyridine having a nucleus selected from the group consisting of a cyclic group and Z representing a covalent bond or an oxygen atom.
The thermal imaging element described. 9. The method according to claim 1, wherein the reducing agent contains an anionic group.
8. The heat-sensitive image-forming component according to any of 8. 10. The anionic group is a salt of N-nitrosocyclohexylhydroxylamine, N-phenylglycine and a compound of formula III (In the formula, R ^{1 to} R ⁴ independently represent an alkyl, aryl, alkaryl, aralkyl, alkenyl, alkynyl, silyl, alicyclic or saturated or unsaturated heterocyclic group, and at least one R ¹ to R ⁴ thermal imaging component of R ⁴ may be an alkyl group to claim 9, wherein the selected organic borate salt containing an anion containing) substituted derivatives of these groups having up to 8 carbon atoms. 11. The thermal image-forming component according to claim 1, wherein the component is a colorant transfer system, a release system, a phototackifier system, or a monomolecular thermal fragmentation system. 12. General formula IV: Where R ⁵ and R ⁶ are independently selected from H, alkyl, aryl, alicyclic or heterocyclic; each R ⁷ and R ⁸ is independently alkyl, aryl, alicyclic and heterocyclic. A method for bleaching a cationic dye, which comprises the step of irradiating the dye to an electronically excited state in the presence of 1,4-dihydropyridine having a nucleus selected from a cyclic group and Z represents a covalent bond or an oxygen atom.