JP3155381B2 - Thermal image stabilization - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] INDUSTRIAL APPLICABILITY The present invention relates to the stabilization of the thermal image. In particular, the present invention relates to a thermal imaging medium, wherein a color stabilizing additive is used to reduce image fading when projecting an image by passing visible radiation through the image, an image forming method and It relates to an imaged medium. The sensitivity of the thermal imaging media of the present invention is improved by incorporating color stabilizing additives into the media.

[0002] are commonly owned with the prior art application, the international patent application PCT / US92 / 02055 co-pending and Japanese Application No. 112,620 / 92 the temperature of the color-forming layer above a color-forming temperature An image-forming medium is described and claimed that includes a color-forming layer of a thermal color-forming composition adapted to undergo a color change when raised during a color-forming time. The preferred imaging media described in these three applications are substantially as shown in FIG. 1 of the accompanying drawings,
It contains three separate color-forming layers containing yellow, cyan and magenta thermal color-forming compositions; each of these color-forming compositions being capable of producing a predetermined color And an infrared absorbing agent capable of generating heat in the color forming layer by absorbing infrared light. The three color-forming layers use infrared absorbers that absorb at different wavelengths so that each color-forming layer can be imaged independently; for example, the specific examples disclosed in these three applications. The imaging medium uses an infrared absorber having peak absorptions at about 792, 822 and 869 nm.

[0003] Co-pending and commonly owned Japanese Application No. 112,619 / 92 synthesizes bis (heterocyclic) dyes, especially asymmetric dyes in which the two heterocyclic nuclei are different. A specific method is described and claimed. These methods are effective in synthesizing certain infrared dyes used in the imaging media of the present invention shown in FIG. 1 of the accompanying drawings.

[0004] Co-pending and commonly owned International Patent Application No. PCT / US91 / 08695 discloses a croconate (hereinafter referred to as "croconate") used in a thermal imaging medium described with reference to FIG. Certain bis (benzopyrylium) infrared dyes are described and claimed, including croconate dyes.

As already pointed out, when the temperature of the color forming layer is raised above the color forming temperature for the color forming time (from colorless to colored, from colored to colorless, or from one color to another). Image forming media having at least one color forming layer containing a color forming composition adapted to undergo a color change are known. The color change in such media need not be provided by applying heat directly to the media;
The color-forming composition is colored by absorbing actinic radiation (usually infrared rays) with a color-forming compound (also referred to herein as a "leuco dye") that undergoes a color change when heated above the color-forming temperature. An absorbent capable of generating heat may be included in the formation layer. When such a medium is exposed to the appropriate actinic radiation, this radiation is absorbed by the absorber, thereby heating the color-forming compound and causing it to undergo a color change. Many such thermal imaging media are advantageous over conventional silver halide media in that they do not require a post-exposure development step. Such thermal imaging media also have the advantage that they are inherently insensitive to visible light and can be handled under normal lighting conditions.

For example, US Pat. No. 4,602,263
No. 4,826,976 both describe thermal imaging systems for optical recording, in particular for forming color images. These thermal imaging systems rely on the irreversible unimolecular splitting of one or more thermally labile carbamate moieties of an organic compound to produce a visually discernable color shift. U.S. Pat. No. 4,720,4
No. 49 and 4,960,901 describe similar imaging systems wherein the color-developing component is a substantially colorless di- or tri-arylmethane imaging compound, which comprises: Owning an aryl group in the di- or tri-arylmethane structure in which the ortho-position to the meso-carbon atom is replaced by a moiety forming a 5- or 6-membered ring closed on the meso-carbon atom; The moiety possesses a nitrogen atom directly attached to the meso carbon atom, the nitrogen atom being attached to a group having a masked acyl substituent, the masked acyl substituent being heated when heated. Upon splitting, the acyl group is released, causing intramolecular acylation of the nitrogen atom to form a new group at the ortho position that cannot be attached to the meso carbon atom, thereby providing di-
Alternatively, the tri-arylmethane compound becomes colorless. Jee
Alternatively, other thermal imaging systems using tri-arylmethane compounds are disclosed in U.S. Pat. No. 4,720,450.
No. 4,745,075.
No. 46, as a color-forming co-reactant, possesses an aryl group substituted at the ortho position by a nucleophilic moiety closed to a meso carbon atom on the meso carbon atom in the di- or tri-arylmethane structure. Using a substantially colorless di- or tri-arylmethane compound and an electrophile that undergoes a nucleophilic moiety and bimolecular nucleophilic substitution reaction when heated and contacts the di- or tri-arylmethane compound do it,
A thermal imaging system for forming a colored ring-opened di- or triarylmethane compound is described.

The above-mentioned patent describes a preferred form of the image forming medium for forming a multicolor image; in this preferred image forming medium, there are three forms capable of forming yellow, cyan and magenta dyes, respectively. Separate color-forming layers are superimposed one on the other.
Each of the three color forming layers has an infrared absorber associated therewith, which absorbs at different wavelengths, for example, 760, 820 and 880 nm. This medium is imagewise exposed to three lasers having wavelengths of 760, 820 and 880 nm. (In the current technology, about 7
Solid state diode lasers emitting at 60-1000 nm provide maximum output per unit cost. Since most of the color-forming materials described in the above patents do not have a high extinction coefficient in this wavelength range, leuco must be used to ensure efficient absorption of laser radiation and thus efficient heating of the leuco dye. It is necessary to include an infrared absorber together with the dye. ) The resulting imagewise heating of the color forming layer causes the leuco dye to produce a color change in the exposed areas, thereby producing a multicolor image, which does not require development.

[0008] This preferred type of imaging media allows for very high resolution images; for example, this media is suitable for 2K 35 mm slides (ie, slides having 2000 pixels on each line parallel to the long edge of the slide). Can be easily used for making. However, certain dyes, especially those described in the aforementioned U.S. Pat. Nos. 4,720,449 and 4,960,901,
Are prone to fading and / or color shifts when they are projected for extended periods of time using powerful conventional slide projectors, such as xenon projectors. As it is self-evident, fading and color shifting are undesirable,
Accordingly, there is a need for a way to prevent or at least reduce such fading and color shifting.

[0009] The thermal imaging reactions described in the above patents do not result in any amplification as occurs in silver halide based imaging media, so that the media is relatively insensitive; Thermal imaging media requires about 1 J / cm ² of energy input per color-forming layer to achieve the maximum transmission optical density of about 3.0 required for an acceptable slide. Accordingly, it would be advantageous to improve the sensitivity of these thermal imaging media in order to improve the speed of imaging and / or reduce the required power of the energy source used for imaging.

Now, quinone, hydroquinone and specific metal cations are disclosed in US Pat. No. 4,720,44.
9 and 4,960,901 reduce the fading and color shift that occur during the projection of thermal images produced as described in US Pat. No. 4,960,901 and reduce the sensitivity of the thermal imaging media described in these patents. It has been found that it also acts to increase it.

Accordingly, the present invention provides a thermal imaging medium comprising at least one image forming layer, wherein the image forming layer undergoes a color change upon heating above the color forming temperature for a color forming time. A color-forming compound, wherein the color-forming compound has the formula

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And, after its color change, the formula

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The dye compound is formed.

Wherein rings A and B are aromatic nuclei, Z and Z 'may be linked by other than by a meso carbon atom, and the chromophore of the diarylmethane or triarylmethane dye in the dye compound Z and Z 'are such that the dye compound has an absorption in the visible region;
Is a leaving group that is removed upon heating, and the dashed line between the SO ₂ group and ring B indicates that the sulfonamide ring in the color forming compound may be 5- or 6-membered.

In this image forming medium, the image forming layer further comprises
Quinone, hydroquinone, and zinc, nickel, copper (I
I), cobalt (II) or aluminum (III)
And a color stabilizing additive comprising at least one of a cation source.

The term "meso carbon atom" is used herein in its ordinary sense and refers to the carbon atom bonded to groups Z and Z 'in compounds of Formulas I and II.

The term "hydroquinone" is used generically herein to mean any aromatic system in which a single phenyl ring carries two hydroxyl groups para to each other. Thus, the term is used herein to refer to derivatives of hydroquinone itself where the phenyl ring is substituted, for example, 2-phenyl-5-methylhydroquinone, as well as one or more phenyl rings bearing a hydroxyl group. Compounds fused to further aromatic rings, such as naphthohydroquinone,
Also means The term "quinone" is also used in a corresponding manner.

The present invention also provides a thermal imaging medium having at least one image forming layer containing a color forming compound; imagewise heating the image forming layer above the color forming temperature for a color forming time. And thereby converting at least a portion of the color-forming compound into a dye compound in the heated areas of the image, thereby forming an image. This method is characterized in that the image forming medium is the image forming medium of the present invention.

Finally, the present invention provides an imaged medium having imagewise colored areas and substantially uncolored areas, wherein substantially uncolored areas of the image are above the color forming temperature. A color-forming compound that undergoes a color change when heated during the color-forming time, wherein the color-forming compound is of Formula I above, and the colored region of the image is of Formula I above.
I dye compounds. The imaged medium further comprises colored areas and substantially uncolored areas.
Quinone, hydroquinone, and zinc, nickel, copper (I
I), cobalt (II) or aluminum (III)
And a color stabilizing additive comprising at least one of a cation source.

As mentioned above, the thermal imaging media of this invention form a color-forming compound of formula I (a dye compound of formula II when heated for a color-forming time above the color-forming temperature). ) And color stabilizing additives. If necessary, more than one color stabilizing additive may be used.

[0021] Because hydroquinone appears to be somewhat more efficient than quinone, it is generally preferred to use hydroquinone over quinone in the imaging media and methods of the present invention. Hydroquinone having an electron withdrawing substituent on an aromatic ring carrying two hydroxyl groups is preferred. Because they have been found to be more effective at inhibiting the fading of images produced using the present method; the effectiveness of hydroquinone in inhibiting image fading depends on the substituent (s). 2) has a good correlation with the electron withdrawing ability, but has no correlation with the redox potential of hydroquinone. The or each electron-withdrawing substituent may be, for example, a halogen atom or an alkyl group. Particularly preferred hydroquinones for use in the media and methods of the present invention are chlorohydroquinone, 2,5-dichlorohydroquinone, 2-methyl-5-phenylhydroquinone, phenylhydroquinone and 2,5-di-t-butylhydroquinone. is there.

The imaging layers used in the imaging media of this invention usually contain a polymeric binder and, if the color stabilizing additive is a quinone or hydroquinone, in fact the thermal imaging media Although it is usually not difficult to disperse quinone or hydroquinone in a binder commonly used therein, the quinone or hydroquinone used must, of course, be selected so that it can be dispersed in the required concentration in the polymer binder used. Must. In general, it is recommended to avoid quinones and hydroquinones containing strongly acidic substituents. This is because these acidic substituents may cause the undesired color formation of the color-forming compound during storage at ambient temperature.

In general, zinc is preferred over other metal cations for use in the imaging media and methods of this invention.
When a sensitive color-forming compound is used, zinc typically increases the sensitivity of the medium by at least about 30%. However, as illustrated in Example 2 below, in the absence of zinc, certain relatively insensitive forms that image slowly enough to be impractical for use in commercially available imaging media. The sensitivity of the color-forming compound is increased by several 100% by adding zinc. Suitable zinc salts are readily available and inexpensive. In addition, it appears that zinc is less prone to forming unwanted colored complexes with other components of the imaging medium than other cations.

The metal cation source used in the image forming medium of the present invention can be any metal that can be dispersed in the image forming layer at the required concentration and does not adversely affect any of the components of the image forming layer. It can be a compound. The imaging layer usually contains a polymeric binder, and the polymeric binder generally limits the source of metal cations that can be used. This is because many inorganic metal salts cannot be dispersed at high concentrations in polymeric binders and / or adversely affect such binders. In general, it is recommended to avoid strong acid salts such as salicylates, benzoates, ascorbates and phenolsulphonates of zinc. This is because these acid salts may cause an undesired color change of the color-forming compound during storage at ambient temperature. Zinc chloride and zinc nitrate are also acidic enough to cause undesirable color changes in some leuco dyes and are therefore not recommended for use in the present invention. A preferred metal source is a metal carboxylate;
Zinc acetates and isobutyrates are particularly preferred because of their low cost and low molecular weight. Low molecular weight reduces the amount of salt to be included in the imaging layer to provide a given amount of zinc cation. The use of lower carboxylate salts containing less than about 8 carbon atoms is preferred. This is because higher carboxylate salts are waxy materials and tend not to provide a transparent layer; for example, zinc stearate has been found to be too waxy to provide a clear coating. Nickel, aluminum, copper (II) and cobalt (II) are all conveniently supplied as their acetates.

Another preferred source of zinc and / or nickel in the imaging media of this invention are zinc and nickel rosinates, which are also commercially known as zinc and nickel resinates. . These materials are rosin-based zinc and nickel salts that have good solubility in the polymeric binders typically used in thermal imaging media. Rosin is mainly composed of abietic acid and small amounts of hydrogenated abietic acid and other substances. Examples of rosinates that are commercially available and that are effective in the imaging media of the present invention are described in US Pat.
01 Panama City 98 East Business Highway 1001, Florida Arizona Chemical Company, Inc., registered trademark Zirex, Zinar,
Zitro and Polytac (Polyta)
c) Substance sold under the name 100. Zinc derivatives described in U.S. Pat. No. 5,008,237 can also be used.

The rate of projector fading and / or color shift experienced by the imaged media of the present invention will vary considerably depending on the polymeric binder used in the imaging layer and, therefore, will not be used in the imaging layer. The optimum amount of color stabilizing additive to be performed is best determined experimentally. However, in general, when the color stabilizing additive is quinone or hydroquinone, the quinone or hydroquinone should be provided in at least about 0.25 mole, preferably at least about 0.5 mole per mole of color forming compound. Is preferred, and when the color stabilizing additive is a source of metal cations, the source is at least about 0.1 mole per mole of color forming compound, desirably at least about 0.1 mole.
It is preferable that 25 mol be provided. It should be recognized that increasing the color stabilizing additive / color forming compound ratio does not show any further increase in sensitivity or protection against fading by the projector. However, the exact ratios at which it occurs will vary depending on the particular color stabilizing additives and color-forming compounds used.

The color change which the thermal image forming medium of the present invention undergoes by the color forming compound during image formation may be from colorless to colored, or may be from a certain color to the color of an object. Generally, the color change is preferably from colorless to colored. The term "coloring" as used herein is not limited to colors that can be seen by the human eye;
Although its primary use for the present invention will be found in imaging media intended for the creation of visible images, it is intended for the creation of "images" that can only be read at invisible (eg, infrared) wavelengths. It may be used for forming media.

Preferred color-forming compounds of formula I are those wherein Z and Z 'each contain a benzene ring, wherein Z and Z' are oxygen atoms bonded to two benzene rings ortho to the meso carbon atom. And the ZCZ 'atomic group forms a xanthene nucleus. Particularly preferred compounds of this type are those in which the benzene rings of Z and Z 'carry a substituted amino group para to the meso carbon atom. Also, in the color forming compound of Formula I,
It is also preferred that Ring A comprises a benzene ring bearing a carbamate moiety at the para position relative to the sulfonamide nitrogen atom.

Two particularly preferred color-forming compounds of the formula I are as follows:

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And

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Except for the presence of color stabilizing additives, the various layers of the imaging media of this invention and the techniques used to expose the media are those used in the above-mentioned patents and applications. There can be. Thus, in the practice of the imaging method of the present invention, heat may be applied or induced imagewise in various ways. Preferably, the selective heating is generated within the color-forming layer itself by the conversion of electromagnetic radiation to heat, and preferably the light source is a laser source such as a gas laser or a semiconductor laser diode, preferably an infrared laser. is there. The use of a laser beam is not only well suited for recording in scanning mode, but also allows for recording at high speeds and densities because the use of a highly focused beam allows the radiant energy to be concentrated on a small area. Also, it is a convenient method to record data as a thermal pattern in response to a transmission signal, such as digitized information.

Since most of the color forming compounds used in the image forming medium of the present invention do not strongly absorb in the infrared, the image forming medium in the image forming medium of the present invention is preferably
It contains an absorber capable of absorbing infrared radiation, thereby generating heat in the imaging layer. The heat thus generated is conducted to the color-forming compound to initiate a color-forming reaction and change the absorption characteristics of the color-forming compound from colorless to colored. As is obvious, the infrared absorbing agent (hereinafter referred to as
The "infrared dye") should be in thermal conduction with the color-forming compound, for example, in the same layer as the color-forming compound or in an adjacent layer. While inorganic compounds may be used, the infrared absorber is preferably an organic compound, such as a cyanine, merocyanine, squarylium, thiopyrylium or benzopyrylium dye, preferably it is in the Dmin region or image highlight. It is substantially non-absorbing in the visible region of the electromagnetic spectrum so as not to contribute a substantial amount of color to the region. The light absorbed by each infrared absorber is converted to heat, and the heat initiates a reaction that produces a colored compound in the color-forming layer. Because this type of imaging media is imaged by infrared rather than by direct heating,
High resolution images are more easily achieved.

A particularly preferred form of the image-forming medium of the present invention has at least two image-forming layers, wherein at least two of the image-forming layers are color-formed arranged to produce dye compounds having different colors. And an absorbent that absorbs at different wavelengths. The infrared absorbers are desirably well separated so that each color-forming layer is selectively and independently exposed at a particular wavelength that is selectively absorbed by each infrared absorber by using infrared light. It is selected to absorb radiation at a predetermined wavelength of 700 nm or more. By way of example, three color-forming layers containing yellow, magenta and cyan color-forming compounds can have an infrared absorber associated with them, absorbing radiation at 792 nm, 848 nm and 926 nm, respectively, and The three color-forming layers can be addressed by a laser source which generates a laser beam of each of these wavelengths, such as an infrared laser diode, so that they can be exposed independently of one another. Although each layer may be exposed in a separate scan, it is usually preferred to expose all color forming layers in a single scan using multiple laser sources of the appropriate wavelength. Instead of using superimposed imaging layers, the color-forming compounds and their associated infrared absorbers may be arranged in rows of parallel dots or stripes in a single recording layer. In such multicolor imaging media, the color-forming compound may consist of subtractive primary colors, yellow, magenta and cyan, or other color combinations, which combinations may additionally include black. . Leuco dyes are generally selected to provide subtractive colors, cyan, magenta and yellow, as commonly used in photographic methods to provide fully natural colors. This type of full color imaging medium having three imaging layers will be described later with reference to FIG. 1 of the accompanying drawings.

Although imagewise heating is induced by converting light to heat, the imaging medium may be heated before or during exposure. This may be achieved using a heated platen or heated drum, or by using an additional laser source or other suitable means for heating the medium while the medium is being exposed.

The image forming medium of the present invention can be manufactured in a manner similar to the image forming medium described in the above-mentioned patents and applications. Typically, the color-forming compound and other components of the image-forming layer (eg, a polymeric binder and an infrared absorber) are dispersed in a suitable solvent, and the resulting liquid dispersion is processed using conventional coating equipment. The coating is used on a support, generally on a polymeric film, and the resulting liquid film is dried to yield an imaging layer. The layers may be applied as a dispersion or emulsion instead of a solution application. The coating composition may also contain dispersants, plasticizers, defoamers, hindered amine light stabilizers and coating aids. When forming the imaging layer (s) and intermediate or other layers, the temperature should be kept below the level at which the color forming reaction occurs rapidly so that the color forming compound does not prematurely color.

According to the present invention, for incorporation of color stabilizing additives into the image forming layer, the additives are simply dispersed in the liquid dispersion together with the other components of the image forming layer. Thus, the present invention does not require significant changes to the apparatus or method used to manufacture the thermal imaging media.

Apart from the presence of color stabilizing additives, the imaging media of the present invention may contain additional layers and components as described in the above patents and applications. Thus, as noted above, the imaging medium typically includes a support to which the imaging layer (s) is deposited. The support should be thick enough to allow easy handling of the imaging medium and can be any material that substantially maintains its dimensional stability during imaging. Desirably, the support has at least about 50
It has a thickness of μm. The support must be sufficiently transparent so as not to unduly increase the Dmin of the final image. If it is desired to image through the support, the support must be transparent enough to not interfere with the imaging process, and preferably is not birefringent. Because the medium is imaged through the support, the birefringent support makes it difficult to image the laser (or other radiation source) to the proper level in the imaging medium. It will be. Suitable supports include polyethylene, polypropylene, polycarbonate, cellulose acetate, and polystyrene.
A preferred material for the support is a polyester, preferably poly (ethylene terephthalate).

Examples of binders which may be used are poly (vinyl alcohol), poly (vinyl pyrrolidone), methyl cellulose, cellulose acetate butyrate, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, poly (methyl methacrylate) , A copolymer of methyl acrylate and ethyl acrylate, poly (vinyl acetate),
Includes poly (vinyl butyral), polyurethane, polycarbonate and poly (vinyl chloride). It will be appreciated that the binder selected should not adversely affect the leuco dye incorporated therein and may be selected to have a beneficial effect. Also, the binder should be substantially thermostable at the temperatures encountered during imaging and should be transparent so as not to interfere with the viewing of the color image. If electromagnetic radiation is used to induce imagewise heating, then the binder should also transmit light intended to initiate imaging.

As described in more detail in Japanese Patent Application No. 112,620 / 92, in some imaging media of the type described in the above patents, the coloration produced during Although one or more of the materials tend to diffuse from their color forming layers, such undesired diffusion of the colored material is at least about 50 ° C, preferably at least about 75 ° C, and most preferably at least about 95 ° C Can be alleviated or eliminated by dispersing the leuco dye in a first polymer having a glass transition temperature of 0.degree. Consisting of a second polymer having a glass transition temperature of 0.degree. C. and containing essentially no color-forming composition. Desirably, the diffusion mitigation layer has a thickness of at least about 1 μm. The first polymer is desirably an acrylic polymer, preferably poly (methyl methacrylate).

The above international application PCT / US92 / 0205
As discussed in No. 5, certain color-forming compounds have a tendency to generate bubbles during imaging. Thus, the image forming medium of the present invention advantageously has the image forming layer undergoing its color change in the heated area when the temperature of the image forming layer is raised imagewise above the color forming temperature during the color forming time. To maintain essentially bubble-free, it includes a bubble suppression layer superimposed on the imaging layer and having a thickness of at least about 10 μm.

Other layers which may be included in the image forming medium of the present invention include, for example, a subbing layer for improving adhesion to a support, and an intermediate layer for insulating the image forming layers from each other. , An ultraviolet blocking layer having an ultraviolet absorber, or other auxiliary layers. To provide good protection from ultraviolet light, an ultraviolet blocking layer is desirably provided on both sides of the imaging layer (s), one ultraviolet blocking layer comprising a polymer film containing an ultraviolet absorber on a support. And such sorbent-containing films are commercially available.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to FIG. 1 of the accompanying drawings. FIG. 1 is a schematic sectional view of the image forming medium of the present invention. The thickness of each layer shown in the drawings is not to be measured.

The imaging medium shown in FIG. 1 (designated generically at 10) is intended for use in making transparencies and is 4 mil (101 μm) incorporating an ultraviolet absorber. ) Poly (ethylene terephthalate) (P
ET). Suitable PET films are, for example, P4C from DuPont Nemours, Inc., Wilmington, Del., USA.
It is readily commercially available as a 1A film.

The imaging medium 10 further comprises a water-dispersible styrene acrylic polymer (Joncryl 538 sold by SC Johnson & Sun Company, Racine, Wisconsin, USA 53403) and a water-soluble acrylic polymer. 10: 1 (Carboset 526 sold by BF Goodrich, Akron, Ohio, USA 44313).
(Weight / Weight) Includes a diffusion-reducing underlayer 14 of about 1 μm formed from the mixture. The presence of this small amount of water-soluble acrylic polymer reduces the tendency of layer 14 to crack during the coating process. The diffusion-reducing undercoat layer 14 has a glass transition temperature of about 55 ° C. and performs the function of a normal undercoat layer.
That is, the support 1 of the image forming layer 16 (to be described in detail later)
2 to increase adhesion. The subbing layer 14 also serves to reduce or eliminate the migration of the dye compound from the image forming layer 16 after image formation; when a subbing layer 14 is used instead of the diffusion reducing sublayer 14, Layer 1 after image formation
Diffusion of the dye compound from 6 into the subbing layer will cause a loss of image sharpness. The undercoat layer 14 is coated on the support 12 from an aqueous medium containing a water-dispersible polymer and a water-soluble polymer.

The yellow image forming layer 16 is an undercoat layer 1 for reducing diffusion.
4 is in contact. This imaging layer 16 is about 5 μm thick and has about 47.5 parts by weight of the formula

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A leuco dye of the formula wherein R 'is a tert-butyl group (compounds where R' is an isobutyl or benzyl group may be used instead)
And 1.6 parts by weight formula

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Infrared dyes (prepared as described in co-pending, commonly owned International Application No. PCT / US91 / 08695; essentially, this dye comprises 2 moles of 2- ( 1,1-dimethylethyl) -5,7-dimethoxy-4-methylbenzopyrylium salt with a croconate salt) and 3.3 parts by weight of a hindered amine stabilizer (HALS-63, USA 0
(Available from Fairmont Chemical Company, 117, Blanchard Street, Newark, NJ 7105N) and 47.5 parts by weight of a poly (methyl methacrylate) binder (Elvacite 2).
021, sold by DuPont Nemours, Inc. of Wilmington, Del., USA. (This material is said to be a methyl methacrylate / ethyl acrylate copolymer by its manufacturer, but its glass transition temperature is poly (methyl methacrylate). ), Which has a glass transition temperature of about 110 ° C.). The image forming layer 16 is applied by applying from a mixture of heptane and methyl ethyl ketone.

Overlying the yellow image forming layer 16 is a diffusion reducing layer 18, which, like the first diffusion reducing layer 14, allows the dye compound to be removed from the yellow image forming layer 16 during storage after imaging. Acts to prevent movement. Diffusion abatement layer 18 is about 2 μm thick and is comprised of a water dispersible styrene acrylic polymer (John Krill 138 sold by SC Johnson & Sun Company, Racine, Wisconsin, USA), an aqueous dispersion. Applied from an object. This layer has a glass transition temperature of about 60 ° C.

The next layer of the image forming medium 10 is about 4.6 μm
A solvent-resistant intermediate layer 20 comprising a major amount of partially crosslinked polyurethane (Wilmington, Mass., USA).
Neoles sold by CI Resin US
Rez) XR-9637) and a small amount of poly (vinyl alcohol) (Airvol 540, US 181)
95 Air Products & Services, Allentown, PA
Chemicals). This solvent resistant intermediate layer 20 is applied from an aqueous dispersion. Middle layer 2
0 not only helps to insulate the image forming layers 14 and 22 (described below) from each other during image formation, but also the yellow image forming layer 16 when the magenta image forming layer 22 is applied.
And, the destruction and / or damage of the diffusion reducing layer 18 is prevented. Yellow image forming layer 16 and main center image forming layer 2
2 is applied from an organic solvent, the organic solvent used to apply layer 22 will be the same if no solvent resistant intermediate layer is provided on layer 16 prior to applying layer 22. It will destroy, damage, or extract the leuco dye or infrared absorber therefrom. The application of the solvent resistant intermediate layer 20 that is not dissolved or swelled by the organic solvent used to apply the layer 22 serves to prevent the layer 16 from being broken or damaged when the layer 22 is applied.
In addition, the solvent resistant interlayer 20 prevents the magenta leuco dye, infrared absorber and hindered amine light stabilizer from penetrating from the layer 22 into the diffusion reducing layer 18 and the yellow image forming layer 16 when coating the layer 22. Acts to prevent.

On the solvent-resistant intermediate layer 20, a magenta image forming layer 22 is overlaid. This layer is about 3 μm thick and about 47.25 parts by weight of a leuco dye of the above formula III (the leuco dye is a US-A-4,720,4
49 and 4,960,901) and about 5.02 parts by weight of chlorohydroquinone (hence about 1: 0.75 of the leuco dye: chlorohydroquinone). Giving a molar ratio; alternatively, about 3.4 parts by weight of zinc acetate may be used, thereby giving a molar ratio of leuco dye: zinc cation of about 1: 0.4); 62 parts by weight formula

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An infrared dye of the formula:

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(Wherein R is a halogen atom or an alkyl group) is reacted with diethylamine to introduce a —NEt ₂ group on the squarylium ring, and then the product is converted to a 4-methylbenzopyrylium salt And 3.6 parts by weight of a hindered amine stabilizer (HALS-63), 0.27 parts by weight of a wetting agent,
47.25 parts by weight of a polyurethane binder (Estane 5715, supplied by BF Goodrich, Akron, Ohio, USA). The image forming layer 22 is applied by applying from a chlorohexanone / methyl ethyl ketone mixture.

(The infrared dye of the above formula IR2 is alternatively
formula

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(Used in the formation of its tetrafluoroborate salt) (this infrared dye is prepared by a method analogous to that used to prepare the infrared dye of formula IR2 above) by the corresponding selenopyrylium An amino group is introduced using a squaric acid derivative and ammonia, followed by
May be prepared by condensing the product with a selenopyrylium salt; to prepare a selenopyrylium squaric acid derivative, replace the benzopyrylium salt IV with the corresponding selenopyrylium salt) It may be replaced.

On the image forming layer 22, a second solvent-resistant intermediate layer 24 is applied. It is formed from the same material as the solvent resistant intermediate layer 20 and is applied in the same manner.

On top of the second solvent-resistant intermediate layer 24 is overlaid a cyan imaging layer 26, which is about 3 μm thick, and about 49.5 parts by weight of the leuco dye of formula IV above ( This leuco dye is described in US-A-4,720,
449 and 4,960,901) and about 5.86 g of chlorohydroquinone (hence a molar ratio of leuco dye: chlorohydroquinone of about 1: 0.75). Alternatively, about 3.97 g of zinc acetate may be used, thereby giving a molar ratio of leuco dye: zinc cation of about 1: 0.4) and 1.62 parts by weight formula

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Infrared dyes, which are preferably prepared by the method described in co-pending, commonly owned Japanese Application No. 112,619 / 92; The diester, diacid chloride or monoester monoacid chloride of the acid is reacted with 2- (1,1-dimethylethyl) 7-diethylamino-4-methylbenzopyrylium salt and hydrolyzed to benzopyrylium A methylidene compound is formed, which is then converted to a 7-alkoxy-2- (1,1-dimethylethyl)-
Reacting with a 4-methylbenzopyrylium salt to produce the final infrared dye], 0.2 parts of a wetting agent,
9.5 parts by weight of polyurethane binder (Estan 57
15). The image forming layer 26 is applied by applying from methyl ethyl ketone.

(The infrared dye of the above formula IR4 is alternatively
formula

Embedded image

The intermediate of formula V is reacted with ammonia to introduce an amino group on the squarylium ring by a method similar to that used to prepare the infrared dye of formula IR2 above. And the product is
Prepared by reacting with a methylbenzopyrylium salt to form an aminosquarylium dye, and finally reacting the aminosquarylium dye with pivaloyl chloride to produce the final pivaloylamino group on the squarylium ring. May be replaced by

As pointed out above, the layers 14 to 26 of the image forming medium 10 are manufactured by coating on the transparent support 12. However, the remaining layers of the imaging medium 10, namely, the transparent bubble suppression layer 32, the UV filter layer 30, and the adhesive layer 28, are not applied over the layer 26, but are created as separate units, and Laminated to the remaining layers of the media.

The transparent bubble suppression layer 32 is 1.75 mil (4
4 μm) PET film, the preferred film being sold as ICI 505 film by ICI Americas, Inc. of Wilmington, Del. The bubble suppression layer 32 prevents the formation of bubbles in the image forming layers 16, 22, and 26 of the image forming medium 10 during image formation.

The ultraviolet filter layer 30 comprises the image forming layer 16,
It serves to protect 22 and 26 from the effects of ambient ultraviolet radiation. Leuco dyes have been found to be susceptible to color changes when exposed to ultraviolet light during storage before or after imaging; such color changes may increase the Dmin of the image and disturb the color of the image. Obviously undesirable. The UV filter layer 30 is about 5 μm thick and about 83% by weight poly (methyl methacrylate) (Elvacite 2043, sold by DuPont Nmour, Inc. of Wilmington, Mass., USA).
And a 16.6% by weight ultraviolet filter [Tinuvin (T
Inuvin) 328, sold by Ciba-Geigy Inc. of Alsdale, NY, USA].
Consists of 4% by weight of wetting agent. The UV filter layer 30 is formed by applying a solution in methyl ethyl ketone onto the bubble suppression layer 32.

The adhesive layer is about 2 μm thick and is composed of a water-dispersible styrene acrylic polymer (John Krill 138, sold by SC Jon Krill & Sun Company, Racine, Wisconsin, 53403, USA). Then, the aqueous dispersion is applied onto the ultraviolet filter layer 30.

After coating layers 30 and 28 on bubble suppression layer 32, the entire structure containing these three layers is subjected to heat (approximately 225 ° F., 107 ° C.) and pressure to form layer 12
To form a complete imaging media 10.

If desired, bubble suppression layer 32 may be formed by coating, rather than by laminating a pre-formed film on layers 12-26. If the bubble suppression layer 32 is to be formed by application, it is convenient to incorporate the UV absorber into the bubble suppression layer, thereby avoiding the need for a separate UV absorber layer. Thus, in this case, layer 28 is applied over layer 26 using the solvent described above, and then a bubble suppression layer 32 containing an ultraviolet absorber is applied over layer 28 from an aqueous medium. Is also good.

The medium 10 has about 792, 848 and 926
The image is formed by exposure to beams from three infrared lasers having a wavelength of nm. The 926 nm beam causes the yellow image forming layer 16 to form an image,
The beam images the magenta imaging layer 22 and the 792 nm beam images the cyan imaging layer 26. Thus, a multicolor image is formed on the image forming medium 10, and the multicolor image requires no further development steps. Further, the media 10 may be handled under normal room lighting prior to exposure, and the imaging equipment need not be shielded.

The following examples are merely illustrative, in increasing the sensitivity of the image forming media of the present invention, and in reducing the fading of images made from the media by a projector.
It is provided to show the effect of color stabilizing additives.
The infrared dyes used in combination with the leuco dyes of these examples, unlike those used in the preferred imaging media previously described with reference to FIG. 1, are as follows: with the magenta leuco dye Infrared dye used :

Embedded image

(See US Pat. No. 4,508,811); and infrared dyes for use with cyan leuco dyes :

Embedded image

(This is described in co-pending application Ser.
67,959).

Example 1 This example demonstrates the effect of chlorohydroquinone in increasing the sensitivity of an imaging medium containing a cyan leuco dye of Formula IV above and in reducing projector fading of images made from the imaging medium. Illustrate.

Part A: Sensitivity Experiment The following experiment used a simplified monochromatic model of the image forming medium previously described with reference to FIG. This simplified model includes a support 12 incorporating an ultraviolet absorber, a cyan image layer 26 (as described below, instead of estane 5715 in which various amounts of chlorohydroquinone were used in the imaging media shown in FIG. 1). With the above-mentioned Elvacite 2021 poly (methyl methacrylate) and with an infrared absorber which is an infrared absorber of the above formula VII), an adhesive layer 28 and a bubble suppression layer 32 (same as the support 12). (Formed from a polymeric binder and thus incorporates an ultraviolet absorber).

Three image forming media were manufactured. One is the control, where the imaging medium does not contain chlorohydroquinone. The other two have a leuco dye: chlorohydroquinone molar ratio of 1: 0.5 and 1: 1 (hereinafter "CH / LC = 0.5" and "CHQ / LC = 1, respectively"). ). All three media were then imaged with a 792 nm laser at various writing speeds, at which speed the imaged spot from the laser moved across the media. The image was imaged in a separate area of the media to produce an image having regions of various red optical densities, the red optical density of each region of the resulting image being X with appropriate filters.
-Measured using a Rite 310 photographic densitometer (supplied by X-Light Company, Grandville, MI). The results are shown in Table 1 and are plotted in FIG. 2 of the accompanying drawings, in which the achieved red optical density is plotted against writing speed.

Part B: Photobleaching Experiment with Projector The image formed in Part A above was converted to a Kodak Ektagraphic model AF-2 slide projector (Sylvania tungsten-halogen E).
(Equipped with a LH300W 120V bulb) for 10 minutes and the red optical density of various areas of the image after exposure by the projector was measured in the same way as before. The results are shown in Table 1 and are plotted in FIG. 3 of the accompanying drawings, where the percent change in red optical density of the image is plotted against the initial red optical density. This% change in optical density is calculated as follows:

## EQU1 ##% change in OD (optical density) = 100 (Da-D)
b) / Db

Where Da is the optical density after projector exposure and Db is the optical density before projector exposure. As will be appreciated, a negative% change in optical density indicates image fade.

[Table 1]

From Table 1 and FIG. 2, it can be seen that the hydroquinone-containing media both produce higher optical densities at a given writing speed than those obtained with the control media without hydroquinone. A medium with a leuco dye: hydroquinone ratio of 1: 1.0 usually gives a lower optical density at a given writing speed than a medium with a leuco dye: hydroquinone ratio of 1: 0.5. Thus, the addition of hydroquinone to the cyan imaging layer makes the media more photosensitive.

The quantification of the increase in sensitivity caused by a given hydroquinone or quinone additive is only noticeable in FIG. 2 but more readily recognized in the other experiments described below (see, for example, FIG. 9) as "burnout ( burn-o
ut) "phenomena. Although this "burr-out" phenomenon is not described in the above patent, thermal imaging media having a color-forming layer as used in the present invention can be used with progressively higher exposure doses (i.e., unit area of the media). When the image is formed with an energy input that gradually increases, the optical density of the image increases steadily with the exposure until it reaches the maximum optical density. It is known that very severely exposed media samples have optical densities significantly lower than the maximum achievable by the media, as the density decreases with exposure. "Burnout"
Is referred to as a decrease in optical density due to this increased exposure. In experiments where the result of varying the writing speed using a laser of constant energy output is shown in FIG. 2, the burnout is a positive slope of the optical density vs. writing speed curve at low writing speeds. Appear as. This is because the exposure amount is inversely proportional to the writing speed.

As expected, the experiments described herein show that media sensitized with hydroquinone or quinone in accordance with the present invention burn out at lower exposures (and thus at higher writing speeds) than similar unsensitized media. Start showing. Thus, at low writing speeds, the sensitized media produces a lower optical density than the corresponding non-sensitized media. This is because at the lower writing speeds, sensitized media already suffer severe burnout, while non-sensitized media do not begin to undergo burnout. Thus, the sensitivity of each medium can be properly compared only at the exposure and writing speed where none of the compared media undergoes burnout; in other words, when comparing sensitivities, the comparison is optical. All the relationship curves of the density / write speed curve must be performed in a region having a significantly negative slope. The sensitivity increase% quoted below is the formula

## EQU2 ## [Average of (optical density of sensitized medium / optical density of non-sensitized medium) -1] × 100%

The appropriate range of writing speeds is shown in parentheses after the%.

Using this equation, CHQ / LC = 0.5
Medium has an increase in sensitivity of 42% (writing speed of 0.26-0.
51m / s), and the medium with CHQ / LC = 1.0 has an increase in sensitivity of 34% (writing speed of 0.26 to 0.51).
m / s).

Also, from Table 1 and FIG. 3, it can be seen that the hydroquinone-containing media both have substantially eliminated the fading experienced in the control media after 10 minutes exposure by the projector.

Example 2 This example demonstrates the use of 2-methyl-5-phenylhydroquinone in increasing the sensitivity of media containing cyan leuco dyes of formula IV above and in reducing projector fading of images formed from the media. ("MPHQ").

Example 1 was repeated except that the chlorohydroquinone used in Example 1 was replaced with an equimolar amount of 2-methyl-5-phenylhydroquinone. These media were imaged and exposed with a projector as in Example 1. The results are shown in Table 2; the results of the imaging experiments are plotted in FIG. 4 and the results of the projector experiments are plotted in FIG.

[Table 2]

From Table 2 and FIG. 4, it can be seen that the hydroquinone-containing media both produced some increase in optical density at low writing speeds, but the improvement was less than for the chlorohydroquinone-containing media in Example 1 above. The medium having a leuco dye: hydroquinone ratio of 1: 0.5 has an average sensitivity increase of about 12% (writing speed of 0.26 to
0.51 m / s), but the media with a leuco dye: hydroquinone ratio of 1: 1.0 showed a smaller increase in sensitivity.

It can also be seen from Table 2 and FIG. 5 that the hydroquinone containing media both had substantially reduced fading experienced in the control media after 10 minutes exposure by the projector, and the leuco dye: hydroquinone Is 1: 0.
In the case of the medium of No. 5, it can be seen that the medium was substantially eliminated.

Example 3 This example demonstrates the effect of varying the amount of 2-methyl-5-phenylhydroquinone in reducing projector fading of an image formed from an imaging medium containing a cyan leuco dye of Formula IV above. Illustrate.

Example 2 was repeated. However, the medium used was a control medium without hydroquinone, and the image forming layer was MP
HQ was prepared using a leuco dye: MPHQ molar ratio of 1: 0.14,
1: 0.28, 1: 0.37, and 1: 0.49,
It was the medium that contained it. Write speeds of these media are 0.18 m / s, 0.22 m / s, 0.26 m
/ S, 0.32 m / s, 0.42 m / s and 0.51
Imaged at m / s and exposed on the projector in the same manner as in Examples 1 and 2. The results are shown in Table 3,
And it is plotted in FIG.

[Table 3]

From Table 3 and FIG. 6, all of the MPHQ containing media showed lower fading than the control media, with LC: MPH
It can be seen that the medium with Q = 1: 0.49 showed the lowest average fading.

Example 4 This example illustrates the use of 2,5-di-t-butylhydroquinone ("DtBHQ") in reducing projector fading of images formed from imaging media containing a cyan leuco dye of formula IV above. ) Illustrates the effect of varying the amount of).

Example 3 was repeated. However, the medium used was a control medium without hydroquinone and the image forming layer was D
The tBHQ was converted to a leuco dye: DtBHQ molar ratio of 1: 0.
24, 1: 0.48, 1: 0.71, and 1: 0.8
In No. 4, the medium was contained. These media were written at a writing speed of 0.18 m / s, 0.22 m / s,
Imaged at 0.26 m / s, 0.32 m / s, 0.42 m / s and 0.51 m / s and exposed on the projector in the same manner as in Examples 1-3. The results are shown in Table 4 and are plotted in FIG.

[Table 4]

From Table 4 and FIG. 7, all of the DtBHQ containing media show lower fading than the control media, with LC: Dt
It can be seen that the medium with BHQ = 1: 0.84 showed the lowest average fading. However, by comparing Table 4 with Table 3 and comparing FIG. 7 with FIG. 6, DtB
HQ is an M in reducing the fading of the leuco cyan dye.
It turns out to be less efficient than PHQ; DtBHQ / L
The medium with C = 0.84 showed almost the same fading as the medium with MPHQ / LC = 0.49.

EXAMPLE 5 This example demonstrates the effect of 2,5-di-t-butylhydroquinone on reducing projector fading of images formed from magenta leuco dye containing imaging media of Formula III above. Illustrate.

Instead of the cyan image forming layer, the magenta image forming layer similar to the magenta image forming layer 22 described above with reference to FIG. 1 but containing the infrared dye of the above formula VI is replaced. Example 4 was repeated except that: Only two media were used, a control media without hydroquinone and a media where the imaging layer contained DtBHQ in a leuco dye; DtBHQ molar ratio of 1: 0.76. These media were written at a writing speed of 0.18 m / s, 0.22 m / s, 0.26 m / s,
Imaged at 0.32 m / s, 0.42 m / s, 0.51 m / s and 0.63 m / s and exposed on a projector in the same manner as Examples 1-4 but for 20 minutes. The results are shown in Table 5 and are plotted in FIG. 8; for obvious reasons, green optical density was measured for magenta dye images instead of red optical density.

[Table 5]

From Table 5 and FIG. 8, it can be seen that the addition of DtBHQ to the magenta image forming layer greatly reduced the fading of the image formed from the image forming layer by the projector.

[0094]

[0095]

[0096]

[0097]

Example 7 This example demonstrates the use of 2-phenyl-5-t in increasing the sensitivity of imaging media containing cyan leuco dyes of Formula IV above and reducing projector fading of images formed from those media. -Butylhydroquinone ("PtBH
Q "), phenylhydroquinone (" PHQ "), and 2,5-dichlorohydroquinone (" DC1HQ ").

Example 1 was repeated. However, the medium used was a control medium and the cyan image forming layer was PtBH.
There were three media containing Q, PHQ and DC1HQ, respectively, at a leuco dye: hydroquinone molar ratio of 1: 0.5. These media were imaged in the same manner as in Example 1 and exposed with a projector. The results are shown in Table 7, the results of the image forming experiments are plotted in FIG. 9, and the results of the experiments with the projector are plotted in FIG.

[Table 7]

From Table 7 and FIG. 9, it can be seen that all three hydroquinone-containing media produce a significant improvement in sensitivity, and in particular, that the burnout phenomenon described above, which causes these media to display at low writing speeds. When it is acceptable, it turns out to be so. FIG. 9 shows that the effectiveness as a sensitizer is in the following order:

(Equation 3)

Further, from Table 7 and FIG. 10, it can be seen that in all three of these hydroquinone-containing media, the fading experienced in the control media after 10 minutes exposure by the projector was significantly reduced. I understand.

Example 8 This example illustrates the use of 2-methyl-5-phenylhydroquinone ("MPHQ") in reducing projector fading of an image formed from an imaging medium containing a cyanocyanic leuco dye of formula IV above. Phenylhydroquinone ("PH
Q "), 2-phenyl-5-t-butylhydroquinone (" PtBHQ "), 2,5-di-t-butylhydroquinone (" DtBHQ ") and 2,5-dichlorohydroquinone (" DC1HQ "). Illustrate.

Example 1 was repeated. However, the media used were a control medium without hydroquinone and a cyan image forming layer having MPHQ, PHQ, PtBHQ, DtBH
Vehicles containing Q and DC1HQ, each in a leuco dye: hydroquinone molar ratio of 1: 0.25. Writing speed of 0.18m /
s, 0.22 m / s, 0.26 m / s, 0.32 m /
s, 0.42 m / s and 0.51 m / s and were exposed on the projector in the same manner as in Examples 1-3. The results are shown in Table 8 and are plotted in FIGS. 11 and 12 (control results are shown in both figures for ease of comparison).

[Table 8]

From Table 8 and FIGS. 11 and 12, all the hydroquinone-containing media showed significantly lower fading than the control media, and the MPHQ, PHQ and DC1HQ-containing media showed a significant reduction in fading. Based on these results, the order of effectiveness of hydroquinone in preventing fading is as follows:

(Equation 4)

Example 9 This example demonstrates that the addition of hydroquinone to an imaging medium according to the present invention does not result in an unacceptable increase in the minimum optical density of the medium.

It is known that hydroquinone, when used in various types of imaging media, sometimes causes contamination problems because the air oxidation of hydroquinone results in the formation of a yellowish substance. To determine if such a contamination problem is significant in the imaging media of the present invention, 25 μl of a 2 × 10 ⁻⁵ M solution of various hydroquinones (0.5 nmol) is deposited on a silica gel plate and processed. Three separate samples of the plate were taken for 18.5 hours at room temperature in the dark, at room temperature under strong fluorescent lighting (510 ft candle, about 10 times normal room lighting intensity), and in a 70 ° C oven. In each case. The red, green and blue optical densities of each sample on the silica gel plate were read on a white target using an X-Light 310 photographic densitometer. The result is FIG. 13 of the accompanying drawings.
(A to C).

From these figures it can be seen that the main effect of the addition of hydroquinone is an increase in the blue optical density of the medium, especially when the samples are stored under strong light or at elevated temperatures. Based on these results, PtBH
Q or DtBHQ is preferred because there is no contamination.

It should be noted that the conditions used in these experiments are such that the hydroquinone is intentionally contaminated by placing hydroquinone on a material having a large surface area that is freely exposed to atmospheric oxygen. . FIG. 1 shows a hydroquinone-containing layer sandwiched between two plastic films.
The increase in minimum optical density resulting from the use of hydroquinone in a thermal imaging medium as previously described with reference to is probably much smaller than that obtained by these experiments.

Example 10 This example illustrates the use of quinone in the present invention.

The medium used in these experiments was the same as in Example 1 above.
Is substantially the same as that used in the above. Infrared dye (VI
I-0.36 g, 1% (w / v) solution in 2-butanone), cyan leuco dye (IV-0.22 g), and 15% of poly (methyl methacrylate) in acetone
1.46 g of the (w / v) solution were combined to produce a clear solution, which was divided into four equal portions of about 500 μl each. One of these moieties was used as a control; the other three moieties each contained 3 mg of 2-methyl-5-phenylhydroquinone (MPHQ), 2,6-dichloro-1,4-benzoquinone (DCBQ) and 9,10-anthraquinone (AQ) was added. Each portion was then coated on a 4 mil poly (ethylene terephthalate) base using a coating rod, the coating was dried overnight, and overcoated at about 220 ° F (104 ° C). The cover sheet was laminated. Writing speed of 0.2
2 m / s, 0.25 m / s, 0.32 m / s and 0.1 m / s.
An image was formed at 42 m / s and projected for 10 minutes in the same manner as in Example 1, and the red optical density was measured before and after projection. The results are shown in Table 9. FIG. 15 shows a change in the red optical density with the writing speed, and FIG. 16 shows a change in the optical density with the initial red optical density.

After the image formation, the red and visible optical densities of the non-image areas of the four films were measured. The films were stored in an oven at 70 ° C. and their concentrations were measured after 17, 41 and 65 hours of storage. FIG. 14 (A-B) shows the variation of red and visible optical density with storage time, respectively.

[Table 9]

From FIG. 14 (A and B), MPHQ and D
While CBQ has only a small effect on the red and visible optical densities of the film and does not significantly affect its optical density when stored at high temperatures, AQ does
It can be seen that the optical density is significantly increased even during storage at high temperature.

Also, from FIGS. 15 and 16, MPHQ,
DCBQ and AQ both increase the sensitivity of the media, AQ increases the sensitivity most, and MPHQ
It can be seen that DCBQ and DCBQ greatly reduce projector fading, while AQ does not provide such protection against projector fading.

Example 11 This example demonstrates the use of zinc, aluminum and nickel cations in increasing the sensitivity of imaging media containing cyan leuco dyes of Formula IV above and in reducing projector fading of images formed from the media. Illustrate the effect of

Part A: Sensitivity Experiment The medium used in this experiment is the same as in Example 1 above, and the leuco dye: polymer weight ratio is 0.
5: 1. Four imaging media were produced. One of them is the control, in which the cyan forming layer does not contain metal cations. The second medium has a color-forming layer containing zinc acetate and a leuco dye: zinc molar ratio of 1: 0.36, and the third medium has a color-forming layer containing aluminum acetate and a leuco dye: aluminum mole. The fourth medium contains a ratio of 1: 0.23, and the fourth medium has a color-forming layer containing nickel acetate in a leuco dye: nickel molar ratio of 1: 0.32. Images were formed on these four media in the same manner as in Example 1, and their optical densities were recorded. The results are shown in Table 10 and are plotted in FIG. 17 of the accompanying drawings.

Part B: Fading Experiment Using Projector The image formed in Part A was converted to a Kodak Ectagraphic Model AF-2 slide projector (Sylvania tungsten-halogen ELH300W120V).
(Equipped with a bulb) for 10 minutes and the red optical density of the various areas of the image after exposure by the projector was measured in the same way as before. The results are shown in Table 10 and are plotted in FIG. 18 of the accompanying drawings, where the percent change in optical density of the image is plotted against the initial red optical density.

[Table 10]

From Table 10 and FIG. 17, it can be seen that the metal-containing medium produces a higher optical density at a particular writing speed than that produced by the no-metal control medium; in fact, Zn / LC = 0. 36 media increase sensitivity 2
4% (write speed 0.16-0.32 m / s), the medium with Al / LC = 0.23 shows a 98% increase in sensitivity (write speed 0.16-0.32 m / s), and Ni The medium with /LC=0.32 showed an increase in sensitivity of 13% (writing speed 0.16 to 0.32 m / s). Therefore,
The addition of these metals to the cyan imaging layer made the media more photosensitive.

Also, from Table 10 and FIG. 18, it can be seen that the addition of metal substantially reduced the fading experienced in the control medium after 10 minutes exposure by the projector.

Example 12 This example demonstrates the effect of zinc isobutyrate in increasing the sensitivity of imaging media containing cyan leuco dyes of Formula IV above and in reducing projector fading of images formed from the media. Illustrate.

Part A: Sensitivity Experiment The medium used in this experiment is the same as in Example 1 above. Four imaging media were produced. One is the control, where the cyan forming layer does not contain zinc. The other three media have the color-forming layer containing zinc isobutyrate in a leuco dye: zinc molar ratio of 1: 0.2, 1: 0.04 and 1: 0.8. Images were formed on these four media in the same manner as in Example 1, and their optical densities were recorded. However, a 785 nm laser was used for image formation. The results are shown in Table 11 and are plotted in FIG. 19 of the accompanying drawings.

Part B: Fading Experiment Using Projector The image formed in Part A was converted to a Kodak Ectagraphic Model AF-2 slide projector (Sylvania tungsten-halogen ELH300W120V).
(Equipped with a bulb) for 10 minutes and the red optical density of the various areas of the image after exposure by the projector was measured in the same way as before. The results are shown in Table 11 and are plotted in FIG. 20 of the accompanying drawings, where the percent change in optical density of the image is plotted against the initial red optical density.

[Table 11]

From Table 11 and FIG. 19, it can be seen that at a given writing speed, the zinc-containing medium produces a higher optical density than that produced by the control medium; in fact, Zn / LC = 0.2 The medium shows an increase in sensitivity of 21% (writing speed 0.22 to 0.42 m / s), and Zn / L
The medium with C = 0.4 has an increase in sensitivity of 23% (writing speed of 0.
22-0.42 m / s) and Zn / LC =
0.8 medium increases sensitivity 49% (write speed 0.22
０．４0.42 m / s). Thus, the addition of zinc to the cyan imaging layer made the media more photosensitive.

Also, from Table 11 and Figure 20, it can be seen that the addition of zinc substantially reduced the fading experienced in the control medium after 10 minutes exposure by the projector; however, the leuco dye: zinc molar ratio It can be seen that zinc at 1: 0.8 is less effective at preventing fading than at a molar ratio of 1: 0.4.

Example 13 This example illustrates the effect of copper (II) and cobalt (II) cations in reducing projector fading of images formed from imaging media containing a cyan leuco dye of Formula IV above. I do.

The medium used in this experiment was the same as in Example 1 above.
And the same. Three imaging media were produced. One of them is a control, in which the cyan forming layer does not contain metal cations. The other two media have copper (II) acetate and cobalt (II) acetate color forming layers, respectively.
In a leuco dye: metal molar ratio of 1: 0.2. Images were formed on these three media in the same manner as in Example 1, and their optical densities were recorded. However, a 785 nm laser was used for image formation. These images were converted to Kodak Ectagraphic Model AF-2 slides.
Projector (Sylvania tungsten-halogen ELH3
(Equipped with a 00W 120V bulb) for 10 minutes and after exposure by the projector the red optical density of the various areas of the image was measured in the same way as before. The results are shown in Table 12 and are plotted in FIG. 21 of the accompanying drawings, where the percent change in optical density of the image is plotted against the initial red optical density.

[Table 12]

From Table 8 and FIG. 13, it can be seen that the addition of copper (II) or cobalt (II) substantially reduced the fading experienced in the control medium after 10 minutes exposure by the projector.

Example 14 This example demonstrates the effect of zinc rosinate on increasing the sensitivity of imaging media containing cyan leuco dyes of Formula IV above and in reducing projector fading of images formed from the media. Illustrate.

Part A: Sensitivity experiment The medium used in this experiment is the same as in Example 1 above. Five imaging media were produced. One is the control, where the cyan forming layer does not contain zinc. The other four media have a color-forming layer of one of zinc rosinate Zirex, Zinal, Zitro and Polytac 100 (Zirex, Zinal, Zitro and Polytac 10).
0 are registered trademarks) in a molar ratio of leuco dye: zinc of 1: 0.2. Images were formed on these four media in the same manner as in Example 1, and their optical densities were recorded. However, a 784 nm laser was used for image formation. The results are shown in Table 13 and are plotted in FIG. 22 of the accompanying drawings.

Part B: Fading Experiment Using Projector The image formed in Part A was converted to a Kodak Ectagraphic Model AF-2 slide projector (Sylvania tungsten-halogen ELH300W120V).
(Equipped with a bulb) for 10 minutes and the red optical density of the various areas of the image after exposure by the projector was measured in the same way as before. The results are shown in Table 13 and are plotted in FIG. 23 of the accompanying drawings, where the percent change in optical density of the image is plotted against the initial red optical density.

[Table 13]

From Table 11 and FIG. 19, it can be seen that the medium containing zinc rosinate produces a higher optical density at a given writing speed than that produced by the control medium; in fact, Gilex / LC = A medium with 0.2 shows a 190% increase in sensitivity, a medium with Zinal / LC = 0.2 shows a 106% increase in sensitivity, a medium with Zitro / LC = 0.2 shows a 117% increase in sensitivity, and Polytac 100
The medium with /LC=0.2 shows a 188% increase in sensitivity, all of which were calculated over the entire range of writing speeds of 0.18 to 0.42 m / s. Thus, the addition of zinc rosinate to the cyan imaging layer made the media more photosensitive.

Also, from Table 13 and FIG. 23, it can be seen that the addition of zinc rosinate substantially reduced the fading experienced in the control medium after 10 minutes exposure by the projector.

As described above, the addition of the color stabilizing additive to the image forming layer of the thermal image forming medium according to the present invention is effective in increasing the sensitivity of the image forming medium and by using a projector for the image formed from the medium. It is understood that it is effective in reducing fading.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a preferred image forming medium of the present invention.

FIG. 2 shows the effect of chlorohydroquinone on increasing the sensitivity of a thermal imaging medium containing a cyan-forming compound as described in Example 1.

FIG. 3 shows the effect of chlorohydroquinone in preventing fading of an image formed from a cyan-forming compound as described in Example 1.

FIG. 4 shows the increase in sensitivity of a thermal imaging medium containing a cyan-forming compound as described in Example 2.
The effect of -methyl-5-phenylhydroquinone is shown.

FIG. 5 shows the effect of 2-methyl-5-phenylhydroquinone in preventing fading of an image formed from a cyan-forming compound as described in Example 2.

FIG. 6 shows the effect of varying concentrations of 2-methyl-5-phenylhydroquinone on preventing fading of images formed from cyan-forming compounds as described in Example 3.

FIG. 7 describes a method for preventing 2,5-color fading of an image formed from a cyan-forming compound as described in Example 4.
9 shows the effect of various concentrations of di-t-butylhydroquinone.

FIG. 8 shows a method for preventing fading of an image formed from a magenta color-forming compound, as described in Example 5.
The effect of -di-t-butylhydroquinone is shown.

FIG. 9 shows the increase in sensitivity of a thermal imaging medium containing a cyan color forming compound as described in Example 7.
The effect of 2-phenyl-5-t-butylhydroquinone, phenylhydroquinone and 2,5-dichlorohydroquinone is shown.

FIG. 10 shows 2- in preventing fading of an image formed from a cyan-forming compound as described in Example 7.
The effects of phenyl-5-t-butylhydroquinone, phenylhydroquinone and 2,5-dichlorohydroquinone are shown.

FIG. 11 shows a method for preventing fading of an image formed from a cyan-forming compound, as described in Example 8.
The effect of methyl-5-phenylhydroquinone, phenylhydroquinone and 2-phenyl-5-t-butylhydroquinone is shown.

FIG. 12 shows a method for preventing fading of an image formed from a cyan-forming compound as described in Example 8.
5 shows the effects of 5-di-t-butylhydroquinone and 2,5-dichlorohydroquinone.

FIGS. 15 (A-C) show the effect on the red, green and blue minimum optical densities of the media caused by the addition of various hydroquinones as described in Example 9.

FIG. 16 (A-B) shows 2-methyl-5-phenylhydroquinone, 2, as described in Example 10.
6-dichloro-1,4-benzoquinone and 9,10-
4 illustrates the effect on red and visible minimum optical density of the thermal imaging media of the present invention caused by the addition of anthraquinone.

FIG. 15: 2-Methyl-5-phenylhydroquinone, 2,6- in increasing sensitivity of a thermal imaging medium containing a cyan-forming compound as described in Example 10.
9 shows the effects of dichloro-1,4-benzoquinone and 9,10-anthraquinone.

FIG. 16 illustrates the protection of an image formed from a cyan-forming compound from fading as described in Example 10.
9 shows the effects of -methyl-5-phenylhydroquinone, 2,6-dichloro-1,4-benzoquinone and 9,10-anthraquinone.

FIG. 17 shows the effect of zinc, nickel and aluminum cations on increasing the sensitivity of a thermal imaging medium containing a cyan-forming compound, as described in Example 11.

FIG. 18 illustrates the effect of zinc, nickel and aluminum cations in protecting the image formed from a cyan-forming compound from fading, as described in Example 11.

FIG. 19 shows the effect of varying the amount of zinc cation on increasing the sensitivity of a thermal imaging medium containing a cyan-forming compound as described in Example 12.

FIG. 20 illustrates the effect of varying the amount of zinc cation in protecting the image formed from a cyan-forming compound from fading, as described in Example 12.

FIG. 21 shows the effect of copper (II) and cobalt (II) cations in protecting images formed from cyan-forming compounds from fading, as described in Example 13.

FIG. 22 shows the effect of various zinc rosinates on increasing the sensitivity of a thermal imaging medium containing a cyan-forming compound as described in Example 14.

FIG. 23 shows the effect of various zinc rosinates on protecting the image formed from a cyan-forming compound from fading, as described in Example 14.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thermal image forming medium 32 Thick transparent and bubble suppression layer 30 UV filter layer 28 Adhesive layer 26 Cyan-color forming layer 24 Solvent-resistant intermediate layer 22 Magenta-color forming layer 20 Solvent-resistant intermediate layer 18 Diffusion reducing layer 16 Yellow Forming layer 14 Diffusion reducing layer 12 Transparent support

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Stephen R. Sofen Avanahashi Road, Lexington, Mass., USA 3 (72) Inventor Mike A. Young 22 Farm Hill Road, Natick, MA, USA (72) William C. Inventor. Schwarzell Montclair Circle 2, Billerica, Mass., USA (72) Robert P. Inventor. Short Edmund Road, Arlington, Mass., USA 10 (72) Inventor Larry Sea. Takiff 14 Trowbridge Street, Arlington, Mass., USA 58) Field surveyed (Int.Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (8)

(57) [Claims] 1. A thermal imaging medium comprising at least one image-forming layer, said image-forming layer comprising a color-forming compound which undergoes a color change when heated above a color-forming temperature for a color-forming time. And the color-forming compound has the formula: And, after its color change, the formula Wherein rings A and B are aromatic nuclei, Z and Z ′ may be linked without via a meso carbon atom, and the diarylmethane or triarylmethane in the dye compound Auxiliary chromophore of the dye represents a portion sufficient to complete the chromophore system, Z and Z 'are such that the dye compound has an absorption in the visible range, and L is the elimination property removed upon heating. The dashed line between the SO ₂ group and ring B indicates that the sulfonamide ring in the color forming compound may be 5- or 6-membered, and the image forming layer further comprises chlorohydroquinone, , 5-dichloro-hydroquinone, 2-methyl-5-phenyl-hydroquinone, phenyl hydroquinone, 2, 5-di -t- butyl hydroquinone, 2-phenyl -5-t-butyl hydroperoxide
Quinone, 2,6-dichloro-1,4-benzoquinone and
Or a hydroquinone or quinone selected from 9,10-anthraquinones and a source of zinc, nickel, copper (II), cobalt (II) or aluminum (III) cations or more. The thermal image forming medium according to claim 1, further comprising an additive. 2. The image forming medium according to claim 1, wherein the color stabilizing additive comprises a zinc cation source. 3. In a color-forming compound and a dye compound, Z and Z 'each contain a benzene ring, and Z and Z' are oxygens bonded to two benzene rings at an ortho position to a meso carbon atom. Linked via an atom to form ZC-
3. The image forming medium according to claim 1, wherein the Z 'atomic group forms a xanthene nucleus. 4. An absorber capable of generating heat in the image forming layer by absorbing infrared rays to promote a color change of the color-forming compound. Item image forming medium. 5. The method of claim 1, wherein the at least two image-forming layers include a color-forming compound arranged to form a dye compound having a different color, and wherein the different wavelengths are different. 5. The composition according to claim 4, comprising at least two absorbents for absorbing the lipase.
Image forming medium. 6. A method of providing a thermal image forming medium having at least one image forming layer containing a color forming compound, wherein the image forming layer is imagewise heated to a color forming temperature or higher for a color forming time. An image forming method comprising the step of converting at least a part of the color-forming compound into a dye compound in a heated region of the image, thereby forming an image, and wherein the thermal image forming medium is used. The method according to claim 1, wherein the image forming medium is an image forming medium. 7. The image formed is projected by passing visible radiation through the image, and the color stabilizing additive present in the image forming medium reduces fading of the image during projection. the method of. 8. An imaged medium having imagewise colored areas and substantially uncolored areas, wherein substantially uncolored areas of the image are above a color forming temperature during a color forming time. It contains a color-forming compound that undergoes a color change upon heating, the color-forming compound having the formula: And the image-colored area above has the formula: Wherein rings A and B are aromatic nuclei, and Z and Z ′ may be linked without a meso carbon atom to support a diarylmethane or triarylmethane dye. Chromophore represents a portion sufficient to complete a chromophore system, Z and Z 'are such that the dye compound has absorption in the visible region, L is a leaving group that is removed upon heating, The dashed line between the SO ₂ group and ring B indicates that the sulfonamide ring in the color-forming compound may be 5- or 6-membered, wherein the colored and substantially uncolored regions are further chloro. hydroquinone, 2,5-dichloro-hydroquinone, 2-methyl-5-phenyl-hydroquinone, phenyl hydroquinone, 2, 5-di -t- butyl hydroquinone, 2-phenylcarbamoyl
Ru-5-t-butylhydroquinone, 2,6-dichloro-
A hydroquinone or quinone selected from 1,4-benzoquinone and 9,10-anthraquinone , and zinc;
The image forming process comprising a color stabilizing additive comprising one or more of a source of nickel, copper (II), cobalt (II) or aluminum (III) cations. Medium.