JPH05127336A - Image forming medium wherein dye diffusion is suppressed - Google Patents

Abstract

PURPOSE: To obtain an image forming medium in which colored material does not diffuse even preserved after image forming. CONSTITUTION: This image forming medium 10 has a color forming layer 16 containing a color forming composition which is suitable for undergoing color change when exposed to active radiation and is dispersed in a first polymer having glass transition temp. of >=50 deg.C and at least one of diffusion reduced layers 14, 18 being in contact with one surface of the color forming layer. The diffusion reduced layer or respective diffusion reduced layer contains(s) a second polymer having glass transition temp. of >=50 deg.C and substantially contain(s) no color forming composition. Since diffusion of the colored material generated during image forming is suppressed after image forming by using the polymer with high glass transition temp. in the color forming layer and by providing the diffusion decreasing layer(s), formed images are stable during preservation.

Description

Detailed Description of the Invention

The present invention relates to an image forming medium having suppressed dye diffusion,
And an imaging method using such an imaging medium.

Subject to a rapid color change (from colorless to colored, from colored to colorless, or from one color to another) when the temperature of the color forming layer rises above the color forming temperature during the color forming time. Imaging media having at least one color-forming layer containing a color-forming composition suitable for The color change in such a medium need not be provided by applying heat directly to the medium; the color-forming composition is a color-forming compound that undergoes a color change when heated above the color-forming temperature, and an actinic radiation. And an absorber capable of absorbing heat and thereby generating heat in the color forming layer. When such a medium is exposed to suitable actinic radiation, this radiation is absorbed by the absorber, thereby heating the color-forming compound and causing the color-forming compound to undergo its color change. Such thermal imaging media have the advantage over conventional silver halide media that they do not require a development step after exposure. Such thermal imaging media also have the advantage that they are inherently insensitive to visible light and therefore can be handled under normal lighting conditions.

For example, US Pat. No. 4,602,263
No. 4,826,976 both describe a thermal imaging system for optical recording, especially for color imaging. These thermal imaging systems rely on irreversible unimolecular splitting of one or more thermolabile carbamate moieties of an organic compound to produce a visually discernible color shift. U.S. Pat. No. 4,72
0,449 describes a similar imaging system.
Therein, the color-developing component is an essentially colorless di- or tri-arylmethane-based imageable compound, which is within its di- or tri-arylmethane structure in the ortho position relative to the meso carbon atom. Possess an aryl group that is substituted by a closed moiety on the meso carbon atom to form a 5- or 6-membered ring. This moiety carries a nitrogen atom that is directly attached to a meso carbon atom, and the nitrogen atom is attached to a group that has a masked acyl substituent that splits when heated to produce an acyl group. Is released to cause intramolecular acylation of the nitrogen atom to form a new group at the ortho position that cannot bond to the meso carbon atom. Thereby, the di- or tri-aryl methane compound becomes colored. Other thermal imaging systems using di- or tri-arylmethane compounds are described in US Pat. Nos. 4,720,450 and 4,960,901, while US Pat. No. 4,745. , 046
In the thermal imaging system described in U.S. Pat. No. 5,096,86, a di- or tri-aryl aryl group substituted in the ortho position by a nucleophilic moiety closed on the meso carbon atom is used as the color-forming co-reactant. A substantially colorless di- or tri-aryl methane compound possessing on a meso carbon atom in the methane structure; said nucleophilic moiety when heated and contacted with the di- or tri-aryl methane compound Two
Electrophilic reagents have been used that undergo molecular nucleophilic substitution reactions to produce colored ring-opened di- or tri-arylmethane compounds. Finally, WO90 / on February 8, 1990
International patent application PCT / published as 00978
In the thermal imaging system described in US89 / 02965, the chromogenic component is a colorless precursor of a preformed image dye, which (a) is cleaved from the precursor when heated. Substituted by at least one thermally removable protecting group and (b) at least one leaving group which irreversibly leaves the precursor when heated. Neither is hydrogen, and the protecting and leaving groups are converted to the colorless precursor until the colorless precursor is converted to an image dye by the application of heat to effect removal of the protecting and leaving groups. Maintain the state of.

The above patent describes a preferred form of imaging medium for producing multicolored images; in this preferred imaging medium, three distinct colors capable of forming yellow, zion and magenta dyes, respectively. The forming layers are superposed. Each of the three color-forming layers is respectively associated with an infrared absorber, which absorbs at different wavelengths, for example 760, 820 and 880 nm. This medium is 760, 820 and 880n
Imagewise exposure to three lasers having a wavelength of m simultaneously. [The current technology is about 760-1000n
A solid-state diode laser emitting at m gives the maximum output per unit cost. Most of the color-forming materials described in the above patents (hereinafter also referred to as "leuco dyes"; with the interpretation that leuco dyes include compounds other than the same) do not have a high extinction coefficient within this wavelength range. Therefore, it is necessary to include an infrared absorber with the leuco dye in order to ensure sufficient absorption of the laser radiation and thus sufficient heating of the leuco dye. The resulting imagewise heating of the imaging layer causes the leuco dye to undergo a color change in the exposed areas, thereby forming a multicolor image which does not require development.

This preferred type of imaging medium is capable of forming very high resolution images; for example, the medium can be readily imaged using a laser which produces a 2000 line 35 mm slide. However,
The quality of the image formed is initially high, but it was often found during storage that the sharpness of the image deteriorates; for example, in the initial image thin lines with sharp and well-defined edges are found. After storing the image at room temperature for weeks or months, it will become wide and show blurred edges. Of course, such blurry images are highly undesirable in high resolution imaging systems.

It has been found that this loss of image sharpness can be reduced or eliminated by controlling the glass transition temperature of the color forming layer and the adjacent layer.

Accordingly, the present invention comprises a thermal color forming composition adapted to undergo a color change when the temperature of the color forming layer rises above the color forming temperature for a color forming time. A color-forming layer, the color-forming composition being at least 50 ° C.
A color-forming layer dispersed in a first polymer having a glass transition temperature of; and a diffusion-reducing layer in contact with one surface of the color-forming layer comprising a second polymer. And a diffusion-reducing layer having a glass transition temperature of at least 50 ° C. and essentially free of a color-forming composition.

The invention also provides an imaging medium of the invention; the color-forming layer is imagewise heated above the color-forming temperature during the color-forming time, whereby a color-forming composition is formed and a heating zone. To produce a colored material in these heated areas and thereby form an image; and for at least about a week the colored material is substantially out of the imaging layer and the diffusion-reducing layer. Without transitioning
Storing; a method of forming and storing an image is provided.

The drawing shows a schematic cross-section of a preferred imaging medium of the present invention.

As mentioned above, the imaging medium of the present invention comprises a color-forming layer containing a color-forming composition dispersed in a first polymer having a glass transition temperature of at least 50 ° C .;
Is in contact with one surface of this color-forming layer and has at least 5
And a diffusion reducing layer having a glass transition temperature of 0 ° C. and essentially free of color forming composition.

As with the image-forming media described in the above-identified US patents, the color-forming composition in the image-forming medium of the present invention desirably undergoes color-forming which undergoes a color change when heated above the color-forming temperature. Comprising a polar compound and an absorber capable of absorbing actinic radiation and thereby generating heat in the color forming layer. This type of imaging medium can be imaged with actinic radiation rather than by direct heating, and high resolution images are more easily achieved using actinic radiation, such as a focused laser.

In some cases it may be desirable to provide two diffusion reducing layers in contact with the face of the color forming layer so that the color forming composition cannot diffuse from the color forming layer in either direction. However, in some cases (eg, when the color-forming layer is in direct contact with the support, and there is no significant transfer of imaging-formed colorant into the support). For this, a single diffusion reduction layer would be satisfactory. However, some high glass transition temperature polymers used in color forming layers do not adhere well to some substrates [eg, poly (methylmethacrylate) does not adhere well to poly (ethylene terephthalate). Do not bond]
Therefore, if a conventional subbing is used to improve the adhesion of the color forming layer to the support, it may occur that the colorant diffuses into the subbing after imaging, resulting in It should be noted that a loss of image sharpness will occur. Where an undercoat is required to improve the adhesion of the color forming layer to the support, it is desirable to provide a diffusion reducing undercoat between the color forming layer and the support. This diffusion-reducing basecoat acts as both a basecoat and a diffusion-reducing layer. An example of such a diffusion-reducing basecoat is shown in the drawings and is described in detail below.

As will be appreciated, in multicolor imaging media, one or more color forming layers may be provided with a diffusion reducing layer (s) in accordance with the present invention.

The first polymer used in the imaging medium of this invention is at least 75 ° C, preferably at least 95 ° C.
It has a glass transition temperature of. Preferably, the polymer is an acrylic polymer having a glass transition temperature of about 110 ° C, desirably poly (methylmethacrylate).
The or each diffusion-reducing layer desirably has a glass transition temperature of at least 55 ° C., and preferably consists of an acrylic polymer, with styrene-acrylic polymers being especially preferred. Suitable styrene-acrylic polymers are readily available commercially and good results have been reported in US Pat.
403 Obtained using acrylic latex sold as Joncryl 138 and 538 from Johnson & Sun, Inc. Racine, WI.
However, layers formed solely from these johncryl latices show some tendency to crack during application, and in order to reduce this cracking tendency, a small amount of water-soluble acrylic polymer in the diffusion-reducing layer, For example, B. B. in Akron, Ohio, USA, 44313. F.
The trademark Carboset by Goodrich
set) sold under the name 526 has been found to be desirable. Although the glass transition temperature of the diffusion-reducing layer can be higher than the glass transition temperature of these specialty polymers, difficulties are encountered when making media containing multiple adjacent layers, all with very high glass transition temperatures. In general, very high glass transition temperature materials (Tg> 95 ° C.) for color forming layers, as such media will not be very stable to cracking during storage. , And lower glass transition temperature materials (Tg <
It is convenient to use (75 ° C).

It is ensured that the or each diffusion-reducing layer as well as the color-forming composition diffuses through the diffusion-reducing layer to other layers in the imaging medium which may cause undesired effects. It must have sufficient thickness to make it impossible. However, it is desirable to avoid excessively thick diffusion reducing layers. This is because such thick layers may adversely affect the resolution of the imaging medium. The optimum thickness of the diffusion-reducing layer in a particular imaging medium could be readily determined by experimentation. Generally, it is preferred that the diffusion reducing layer has a thickness of at least 1 μm.

It is known to those skilled in the art that the tendency of dyes to migrate through a polymer decreases as the glass transition temperature of the polymer increases; for example, in dye diffusion thermal transfer imaging It is known that the layer has a low glass transition temperature so that the dye can easily diffuse into it. However, it should be noted that the advantages of the present invention are not achieved by simply incorporating the color forming composition into a layer of polymer having a high glass transition temperature; at least about 50 ° C.
Providing a diffusion reducing layer having a glass transition temperature of
It is essential to substantially reduce or overcome the diffusion problem of the colored material after imaging. The diffusion-reducing layer (s) should also be essentially free (preferably free at all) of the color-forming composition. Because the color-forming composition present in the diffusion-reducing layer (s) tends to migrate laterally during storage after image formation, which is detrimental to the sharpness of the image formed. Because it has an influence.

The color-forming composition used in the imaging media of the present invention may be any of those described in the above patents or various copending applications. Thus, the color forming composition may be:

A. An organic compound capable of undergoing an irreversible unimolecular splitting of at least one thermolabile carbamate moiety when heated, said organic compound initially absorbing radiation in the visible or invisible electromagnetic spectrum, Molecular splitting visually changes the appearance of organic compounds (see US Pat. No. 4,602,263).

B. A substantially colorless di- or tri-arylmethane-based imageable compound having a 5- or 6-membered ring at the position ortho to the meso carbon atom in the di- or tri-arylmethane structure. Bear an aryl group substituted on the meso carbon atom by a ring-closing moiety to form, said moiety having a nitrogen atom directly attached to said meso carbon atom, and said nitrogen atom being a mask A new group that is bonded to a group having an acyl substituent that is released by cleavage when heated causes intramolecular acylation of the nitrogen atom and cannot bond to the meso carbon atom. The di- or tri-aryl methane compound in a colored state (see US Pat. No. 4,720,449).

C. A colored di- or tri-arylmethane based image-forming compound, the di- or tri-
It has an aryl group in the arylmethane structure in which the ortho position with respect to the meso carbon atom is replaced by a thermolabile urea moiety, which undergoes a unimolecular splitting reaction when heated. A new group attached to the meso carbon atom to form a 5- or 6-membered ring is provided at the ortho position, whereby the di- or tri-
The aryl methane compound undergoes ring closure and becomes colorless (see US Pat. No. 4,720,450).

D. A substantially colorless di-or bearing an aryl group on the meso carbon atom in the di- or tri-aryl methane structure which is substituted in the ortho position by a nucleophilic moiety closed on the meso carbon atom. A ring-opened di- or tri-arylmethane that has undergone a bimolecular nucleophilic substitution reaction between a tri-arylmethane compound and the nucleophilic moiety when contacted with the di- or tri-arylmethane compound by heating. In combination with an electrophile to produce a compound (see US Pat. No. 4,745,046).

E. A compound having the formula:

[Chemical 1]

Where M'is the formula

[Chemical 2]

[Wherein R is alkyl; -SO ₂ R ¹ (wherein R ¹ is alkyl); phenyl; naphthyl; or alkyl, alkoxy, halo, trifluoromethyl, cyano, nitro, carboxy,- CONR ² R
³ (provided that R ² and R ³ are each hydrogen or alkyl), —CO ₂ R ⁴ (provided that R ⁴ is alkyl or phenyl), —COR ⁵ (provided that R ⁵ is amino,
Alkyl or phenyl), —NR ⁶ R ⁷ (provided that R ⁶ and R ⁷ are each hydrogen or alkyl), —SO ₂ NR ⁸ R ⁹ (provided that R ⁸ and R ⁹ are each hydrogen, Phenyl substituted with alkyl or benzyl); Z ′ is of the formula

[Chemical 3]

## STR4 ## wherein R'is halomethyl or alkyl.

X is --N =, --SO _2- , or --CH _2- ; D is taken together with X and M ',
Represents a group of a color-shifted organic dye; q is 0 or 1; and p is an integer of at least 1;
Are removed from the M'on heating and produce a visually discernible change in the spectral absorption properties of the dye (see US Pat. No. 4,826,976).

F. A substantially colorless di- or tri-arylmethane compound having the formula:

[Chemical 4]

In the formula, ring B represents a carbocyclic aryl ring or a heterocyclic aryl ring; C ₁ is the above di- or tri-
Represents a meso carbon atom of an arylmethane compound; X is-
C (= O) -; - SO 2 - or -CH ₂ - represents,
And completing a ring-closing moiety on the meso carbon atom, the moiety including a nitrogen atom directly bonded to the meso carbon atom; Y is -NH-C (= O) -L; In the formula, L is a leaving group which is released by thermal splitting to release -N = C = O and releases -N when the release of mask occurs.
= C = O causes intramolecular acylation of the nitrogen atom to open the nitrogen-containing ring and form a new group at the ortho position of ring B that cannot bond to the meso carbon atom; E is hydrogen, electron donation A group, an electron-withdrawing group, or a group that is either an electron-donating group or an electron-neutral group that undergoes cleavage to release an electron-withdrawing group when heated; s is 0 or 1; and Z and Z 'Represents a moiety for completing the auxochrome system of the diarylmethane or triarylmethane dye when the nitrogen-containing ring is opened, and Z
And Z ′ together represent a bridging moiety to complete the auxochrome system of the bridging triarylmethane dye when the nitrogen-containing ring is opened (US Pat. No. 4,960,901).
No.).

G. A colorless precursor of a preformed image dye, wherein (a) at least one thermally removable protecting group undergoes cleavage from the precursor upon heating and (b) irreversibly from the precursor upon heating Substituted by at least one leaving group to be removed, neither said protecting group nor said leaving group being hydrogen, said protecting group and leaving group being heated to The precursor is maintained in its colorless state until it is converted to an image dye by removal (see International Patent Application PCT / US89 / 02965).

H. A mixed carbonate ester of a quinophthalone dye and a tertiary alcohol having 9 or less carbon atoms.

I. Leuco dyes represented by the formula:

[Chemical 5]

Wherein E represents a thermally removable leaving group; tM represents a thermally transferable acyl group; Q,
Q'and C together represent a dye-forming coupler moiety, C is a coupling carbon of said coupler moiety; and (Y) together with N represents an aromatic amino color developer. One of Q, Q'and (Y) contains an atom selected from the group 5A / 6A groups of the periodic table, and the groups E and tM are heat-applied. Until the leuco dye remains substantially colorless, application of heat causes the group E to leave the leuco dye, and the group tM from the N atom to the group 5A / group. Transfer to a Group 6A atom, which produces a dye represented by the formula:

[Chemical 6]

In the formula, the dotted line indicates that the tM group is bonded to the Group 5A / 6A atom in one of Q, Q'and (Y) (1991). (See US Application No. 696,196, filed May 6, and corresponding applications in other countries).

Among these color-forming compounds, the coloring substances produced from those leuco dyes described in the above-mentioned international application PCT / US89 / 02965 have a particular tendency to migrate in the image-forming medium after image formation, and therefore, The present invention has been found to be particularly effective with these imaging dyes. Of this class of imaging dyes, one particularly preferred leuco dye is that having the formula:

[Chemical 7]

(Hereinafter referred to as "leuco dye A").

As mentioned above, each of the above patents describes a multicolor imaging medium having two or more (usually three) different color forming layers that produce different colors. In the preferred form of such imaging media, the color forming layers are separated by a solvent resistant interlayer. Accordingly, a preferred embodiment of the imaging medium of the present invention comprises a support; a first color forming layer located on the support; a diffusion reducing layer located on the first color forming layer; a second diffusion reducing layer. A second color forming layer located at, the second color forming layer being adapted to undergo a color change when the temperature of the color forming layer rises above the second color forming temperature for a second color forming time. A two-color-forming composition, wherein the color change experienced by the second color-forming layer is different from the color change experienced by the other color-forming layer; and between the diffusion-reducing layer and the second color-forming layer An intermediate layer having a glass transition temperature of less than 50 ° C .;

Other than the high glass transition temperature color forming layer and the diffusion reducing layer, the other layers of the imaging medium of this invention and the techniques used to make and expose the medium are described in the above-referenced US Pat. No. 4,602. , 263, 4,720,4
No. 49, No. 4,720,450, No. 4,745,04
6, No. 4,826,976, and No. 4,960,
No. 901 can be used. Thus, heat may be imagewise applied or induced in a variety of ways to practice the imaging methods of this invention. Preferably, the selective heating is produced in the color forming layer itself by converting electromagnetic radiation into heat, and preferably the light source is a laser beam source such as a gas laser or a semiconductor laser diode. Not only is the use of lasers well suited for scanning mode recording, but by utilizing a highly concentrated beam, the radiant energy can be concentrated into a small area to enable recording at high speed and high resolution. .. It is also a convenient way to record data as a thermal pattern in response to a transmitted signal such as digitized information, and by using multiple laser sources emitting at different wavelengths a multicolor image can be obtained. It is a convenient way to form.

Most of the preferred leuco dyes mentioned above do not absorb strongly in the infrared. At the present time, the imaging method is preferably carried out using an infrared laser, so in a preferred embodiment the heat-sensitive element contains an infrared absorbing material for converting infrared radiation into heat. The heat is transferred to the leuco dye, initiating the color-forming reaction, and changing the absorption properties of the leuco dye from colorless to colored. Obviously, the infrared absorber should be in heat transfer relationship with the leuco dye, for example in the same layer as the leuco dye or in an adjacent layer. Although inorganic compounds may be used, the infrared absorbers are preferably organic compounds, such as cyanine, merocyanine, squarylium, thiopyrylium, or benzopyrylium dyes, and also preferably in substantial amounts. It is substantially non-absorptive in the visible electromagnetic spectrum so that the color does not contribute to the Dmin portion or the highlight portion of the image. The light absorbed by each infrared absorber is converted to heat, and the heat initiates a reaction that produces a colored material in the color forming layer.

In forming such a multicolor image, the infrared absorber is preferably separated from the others by the use of infrared radiation of a specific wavelength which each color-forming layer selectively absorbs by the respective infrared absorber. Selected to absorb radiation of 700 nm or more different predetermined wavelengths that are sufficiently separated to be independently exposed. As illustrated, the color-forming layers containing yellow, magenta and cyan leuco dyes were combined therewith to give 7
It may have an infrared absorber that absorbs radiation at 60 nm, 820 nm and 880 nm and emits at its respective wavelength so that the laser source, eg the three color forming layers, can be exposed independently of each other. It may be addressed by an infrared laser diode. Each layer may be exposed in a separate scan, but it is usually preferred to expose all color forming layers simultaneously in a single scan using multiple laser sources of the appropriate wavelengths. As an alternative to using superposed imaging layers, the leuco dye and infrared absorber combined therewith may be arranged as rows of parallel dots or stripes in a single recording layer.

If imagewise heating is induced by conversion of light to heat as in the above embodiment, the imaging medium may be heated before or during exposure. This may be accomplished by using a heating platen or drum, or by using an additional laser source or other suitable means to heat the medium while it is being exposed.

In addition to the color-forming layer and the diffusion-reducing layer, the imaging medium of the present invention provides additional layers, for example a subbing layer for improving adhesion to the support, to insulate the color-forming layer from each other. The intermediate layer, the abrasion-resistant top layer, the ultraviolet light-shielding layer containing an ultraviolet absorber, or other auxiliary layer may be included. To give good protection against UV rays,
An ultraviolet light-shielding layer, preferably a color-forming layer (s)
Conveniently one of the UV light-blocking layers is prepared by using a polymer film containing an UV absorber as a support, and such absorber-containing films are commercially available. The leuco dye is selected to give the desired color or combination of colors, and for multicolor images, the selected compound is a subtractive primary color, yellow,
It may consist of magenta and cyan, or it may consist of other color combinations which additionally include black. In general, leuco dyes are selected to give subtractive colors, cyan, magenta and yellow, as is customary in photographic processes to provide fully natural colors.

The support used may be transparent or opaque and may be any material which substantially retains its dimensional stability during imaging. Suitable supports include paper, resins or pigments such as calcium carbonate or calcined clay coated paper, synthetic paper or plastic films such as polyethylene, polypropylene, polycarbonate, cellulose acetate, poly (ethylene terephthalate) and polystyrene. If it is necessary to image through the support, the support must, of course, be sufficiently transparent so as not to interfere with the imaging process, and in this case the support is substantially non-birefringent. Is also desirable.

Usually, the or each color forming layer contains a binder and the leuco dye, infrared absorber and binder are combined in a common solvent and the layer of this coating composition is applied to a support. Manufactured by applying to, and then drying. The layers may be applied as a dispersion or emulsion rather than solvent coated. The coatable composition may further contain dispersants, plasticizers, defoamers, hindered amine light stabilizers and coating aids. During the formation of the color-forming layer (s) and the interlayer or other layers, the temperature is maintained below the level at which the color-forming reaction is rapidly triggered so that the leuco dye does not prematurely color or bleach. Should be.

Examples of binders which may be used are poly (vinyl alcohol), poly (vinyl pyrrolidone), methyl cellulose, cellulose acetate butyrate, styrene-acrylonitrile copolymers, styrene-butadiene copolymers, poly (methyl methacrylate). ), Copolymers of methyl and ethyl acrylate, poly (vinyl acetate), poly (vinyl butyral), polyurethanes, polycarbonates, 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 beneficial effects. Also, the binder should be substantially heat stable at the temperatures encountered during imaging and should be transparent so as not to interfere with the viewing of the color image. When electromagnetic radiation is used to induce imagewise heating, the binder should also be transparent to the light intended to initiate image formation.

Preferred embodiments of the invention are described below,
It is merely exemplary and will be described with reference to the drawings, which are schematic cross-sectional views of the imaging media of the present invention. The thickness of each layer shown in the drawings is not the correct size.

The imaging medium shown in the drawings (generally designated 10) is for use in making transparency and is 4 mil (101 μm) incorporating an ultraviolet absorber.
m) It comprises a substantially transparent support 12 made of a poly (ethylene terephthalate) (PET) film. A suitable PET film is, for example, P4C1A from DuPont Donumur, Wilmington, Delaware, USA.
As, it is easily available commercially.

Imaging medium 10 further comprises a water-dispersible styrene-acrylic polymer (John Krill 538, US 534).
03 WI, sold by Johnson & Sun, Inc. Racine, USA and water-soluble acrylic polymer (Carboset 52).
6, 44313, Akron, Ohio, USA B. F. 10: 1 (weight / sold by Goodrich)
(By weight) may include a diffusion-reducing basecoat 14 formed from the mixture of about 1 μm thickness. As I explained earlier,
The presence of a small amount of water-soluble acrylic polymer prevents the formation of layer 1 during the coating process.
The cracking tendency of No. 4 is reduced. Diffusion reducing undercoat 14
Has a glass transition temperature of about 55 ° C. and also serves the function of a normal basecoat, ie increases the adhesion of the color-forming layer 16 (described in more detail below) to the support 12. .. The basecoat 14 also serves to reduce or eliminate migration of colored material from the color forming layer 16 after imaging;
As previously mentioned, when a conventional basecoat is used in place of the diffusion-reducing basecoat 14, the coloring material diffuses from layer 16 into the basecoat after imaging, causing a loss of image sharpness. The undercoat 14 is applied onto the support 12 from an aqueous medium containing a water-dispersible polymer and a water-soluble polymer.

The yellow-forming layer 16 is in contact with the diffusion-reducing basecoat 14. The color forming layer 16 is about 5 μm thick and contains about 47.5 parts by weight of the leuco dye A.
1.6 parts by weight formula

[Chemical 8]

Infrared absorbers of US Pat. No. 4,50
2,6-bis (1,1-dimethylethyl) -as described in co-pending application No. (Attorney Docket C-7660) by a method similar to that described in No. 8,811. 4-methylselenopyrylium salt] and 3.3 parts by weight of hindered amine stabilizer (HALS-63, USA 07).
105 sold by Fairmont Chemical Company, Inc. 117, Blanchard Road, Newark, NJ, and 47.5 parts by weight of poly (methylmethacrylate) binder [Elvacite].
2021, sold by DuPont Donumur, Wilmington, Del., USA; this material is described by the manufacturer as a methyl methacrylate / ethyl acrylate copolymer, but whose glass transition temperature is poly (methyl methacrylate). Close to that). This binder has a glass transition temperature of about 110 ° C. Color forming layer 16 is applied by coating from a mixture of heptane and methyl ethyl ketone.

Disposed on the yellow-forming layer 16 is a diffusion-reducing layer 18, which, like the first diffusion-reducing layer 14,
It serves to prevent migration of colored material from the yellow forming layer 16 during storage after image formation. The diffusion-reducing layer 18 is about 2 μm thick and is composed of a water-dispersible styrene-acrylic polymer (John Krill 138, sold by Johnson & Sun, Inc. Racine, 53403, USA) and coated from an aqueous dispersion. To be done. This layer is about 6
It has a glass transition temperature of 0 ° C.

The next layer of imaging medium 10 is a solvent resistant intermediate layer 20 of about 4.6 .mu.m, which is based on a partially cross-linked polyurethane [NeoRez XR-96.
37, polyurethane sold by ICI Resins US, Wilmington, Mass., USA, and a small amount of poly (vinyl alcohol) [Airvol (Airvo
l) 540, sold by Ae Products & Chemicals, Inc., Allentown, PA 18195]. The solvent resistant intermediate layer 20 is applied from an aqueous dispersion. The intermediate layer 20 is the color forming layer 14 during image formation.
And 22 (discussed below) not only help to insulate each other from each other, but also prevent destruction and / or damage to the yellow forming layer 16 and the diffusion reducing layer 18 during application of the magenta forming layer 22. To do. Both the yellow-forming layer 16 and the magenta-color forming layer 22 are applied from an organic solution, so if no solvent-resistant intermediate layer is provided on the layer 16 before the layer 22 is applied, the The organic solvent used to apply 22 will destroy or damage layer 16 or extract the leuco dye or infrared absorber from layer 16. Providing a solvent resistant intermediate layer 20 that is not dissolved or swollen by the organic solvent used to apply layer 22 prevents layer 16 from being destroyed or damaged during application of layer 22. In addition, the solvent resistant intermediate layer 20 also serves to prevent the magenta leuco dye from depositing from the layer 22 into the diffusion reducing layer 18 and the yellow forming layer 16 during application of the layer 22.

A magenta color forming layer 22 is disposed on the solvent resistant intermediate layer 20. Layer 22 is about 3 μm thick and has about 47.25 parts by weight of formula.

[Chemical 9]

The leuco dye (hereinafter referred to as "leuco dye B"); this leuco dye is described in the above-mentioned US Pat.
449 and 4,960,901) and 1.62 parts by weight of the formula.

[Chemical 10]

Infrared absorbers of the above-mentioned US Pat.
No. 8,811), 3.6 parts by weight of hindered amine stabilizer (HALS-63), 0.27 parts by weight of wetting agent, and 47.25 parts by weight of polyurethane binder [Estane 5715, 44313, Akron, Ohio, USA B. F. Supplied by Goodrich Inc.]. Color forming layer 22 is applied by coating from a cyclohexanone / methyl ethyl ketone mixture.

On the color forming layer 22, the solvent resistant intermediate layer 2 is provided.
A second solvent resistant intermediate layer 24 is applied which is made of the same material as 0 and is applied in the same manner.

A cyan color forming layer 26 is disposed on the second solvent resistant intermediate layer 24. Layer 26 is about 3 μm thick and has a formula of about 49.5 parts by weight.

[Chemical 11]

The leuco dye (hereinafter referred to as "leuco dye C"); this leuco dye is described in the above-mentioned US Pat. No. 4,720,
449 and 4,960,901) and 0.7 parts by weight of the formula.

[Chemical 12]

Infrared absorber [This is the above-mentioned copending application No. (Reference No. C-766 by the agent]
0)], and
It consists of 0.2 parts of wetting agent and 49.5 parts by weight of polyurethane binder (Estan 5715). Color forming layer 26 is applied by coating from methyl ethyl ketone.

As described above, the layers 14 to
26 is 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 ultraviolet filter layer 30 and the adhesive layer 28, are not applied on top of the layer 26,
It is manufactured as a separate unit and then laminated to the rest of the media.

The transparent bubble suppression layer 32 has a thickness of 1.75 mils (4
4 μm) PET film, the preferred film being sold as ICI 505 film by ICI Americas, Inc. of Wilmington, Del. US Application No. 07 / dated May 6, 1991
695, 641 (reference number C-768 by agent)
Co-pending International Application PCT / claiming priority from 1)
As described in detail in US92 /, the bubble suppression layer 32 prevents the formation of bubbles in the imaging medium 10 during imaging, thus the color in the imaged medium is not affected by bubble formation. Help ensure that.

The ultraviolet filter layer 30 is the color forming layers 16 and 2.
It serves to protect 2 and 26 from the effects of ambient UV radiation. Leuco dyes have been found to be susceptible to color changes when exposed to UV light during storage before or after image formation; such color changes increase the Dmin of the image and distort the color of the image. Obviously not desired. The UV filter layer 30 is about 5 μm thick and contains about 83% by weight of poly (methyl methacrylate) (ervasite 20).
43, sold by DuPont Donmour, Wilmington, Mass., USA), 16.6
Wt% UV filter [Tinuvin]
328, sold by Ciba-Geigy, Inc., Alsdale, NY, USA) and 0.4% by weight of wetting agent. The UV filter layer 30 is made by applying a solution in methyl ethyl ketone onto the bubble suppression layer 32.

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

After layers 30 and 28 have been applied over bubble suppression layer 32, the entire structure containing these three layers is heated (about 225 ° F., 107 ° C.) and under pressure to layers 12-. It is laminated to the structure containing 26 to form the complete imaging medium 10.

If desired, bubble suppression layer 32 may be formed by coating rather than by laminating a prefabricated film onto layers 12-26. When the bubble suppression layer 32 is to be formed by coating,
It is convenient to incorporate the UV absorber into the bubble suppression layer, thereby avoiding the need for a separate UV absorber layer. Therefore, in this case, the above solvent is used to form the layer 2
6 may be coated with layer 28, and then a bubble suppressor layer 32 containing an ultraviolet absorber may be coated over layer 28 from an aqueous medium.

The imaging medium 10 may be provided such that an additional layer, such as an abrasion resistant layer, overlies the bubble suppression layer 32.

Medium 10 has approximately 792, 822 and 869
Imaged by simultaneous exposure to beams from three infrared lasers having a wavelength of nm. The 869 nm beam is imaged on the yellow forming layer 16, the 822 nm beam is imaged on the magenta forming layer 22, and 792
The nm beam is imaged on the cyan forming layer 26. Therefore, a multicolor image is formed on the imaging medium 10, and the multicolor image does not require an additional development step. Moreover, the medium 10 may be handled under normal room light prior to exposure, and the device performing the imaging need not be light tight.

It can be seen that in the imaging medium 10, the diffusion-reducing layer is present only on both sides of the yellow-forming layer 16 and that only this color-forming layer contains a polymer having a glass transition temperature of 50 ° C. See. In the particular color-forming material used in imaging medium 10, the post-imaged diffusion of the magenta and cyan colorants formed in layers 22 and 26, respectively, during imaging the leuco dye formed in layer 16. It is substantially less of a problem than the diffusion of yellow colored materials, and thus in this embodiment of the invention it is yellow that requires the use of polymers having a high glass transition temperature and the provision of a diffusion-reducing layer according to the invention. Only the formation layer. However, in other multicolor imaging media, the invention may be applied to one, two or all three color forming layers to prevent migration of the leuco dye from those layers. May be necessary or desirable.

Example 1 To demonstrate the effect of the glass transition temperature of the color forming layer and the diffusion-reducing subbing and diffusion-reducing layer, a series of experimental media was prepared as shown in the drawings, but as described above, except that ,
Produced without layers 20-26; therefore, these test media produced a monochrome yellow image. Support 12 and color forming layer 1
The composition of 6 is as described above. However, in these experimental media, a coated bubble suppression layer was used in place of the laminated bubble suppression layer 32 described above. To create this coated foam control layer, a water dispersible styrene-acrylic polymer (Jonkryl 538, US 53403 WI) was used on layer 18 instead of adhesive layer 28.
Racine, S.A. C. (Sold by Johnson & Sun, Inc.) and a diffusion barrier layer of about 2 μm thickness was applied. On top of this diffusion barrier layer was applied a bubble suppressor layer containing an ultraviolet absorber; this bubble suppressor layer thus fulfills the functions of both layers 30 and 32 above. This bubble suppression layer is made of 89.5% by weight of polyurethane (Neorezu R-
966, ICI in Wilmington, Massachusetts, USA
Resins US) and 4.7% by weight of nonionic water soluble poly (ethylene oxide) [Polyox N-3000, sold by Union Carbide, Danbury, Conn., USA]. And 4% by weight UV filter (Tinuvin 1
130, sold by Ciba-Geigy, Inc. of Arsdale, NY, USA, and 1.8% by weight of wax lubricant [Michemlube 16
0, sold by Michael Man Chemical Company]
And was applied from an aqueous dispersion. The bubble suppression layer was applied at a coating weight of about 2000 mg / ft ² (21.5 g / m ² ). The composition of the diffusion-reducing basecoat 14 and the diffusion-reducing layer 18 varied; the composition of these two layers was as follows: Medium A : Carboset 526 (Tg 70 ° C) and Neorez R-9000 (US). A 4: 1 (w / w) mixture of polyurethane, Tg <40 ° C., sold by ICI Resins US, Inc. of Wilmington, Mass. Medium B : NeoLes R-9000 and Nalco
1: 1 (wt / wt) mixture of 1060 silica. Medium C : A 10: 1 (w / w) mixture of Jonkryl 538 (Tg 64 ° C.) and Carboset 526.

Each of the three media was then subjected to maximum optical density using an infrared laser to create 40 μm wide lines having an optical density of about 3 separated by a 60 μm wide non-image area. The imaged media had an overall optical density of about 0.4. In the imaged medium, the overall optical density of the imaged medium is increased if diffusion of the yellow coloring material formed during imaging to the non-image areas occurs during storage after imaging. Will. This is because the optical density of the image area does not substantially change, but the optical density of the non-image area increases substantially. Therefore, the total optical transmission densities in blue light of the three imaged media were measured immediately after imaging and again after storage at 45 ° C. for about 1 week; this high temperature storage compared to room temperature storage It can be expected to accelerate the diffusion of. The results are shown in Table 1 below.

[Table 1]

From the data in Table 1, media A and C with the high glass transition temperature diffusion-reducing layer showed no evidence of diffusion after storage, while medium B with the low glass transition temperature storage-diffusion layer preserved. Later showed significant diffusion.

Example 2 To illustrate the effect of using a binder at a low glass transition temperature in the color forming layer, the same as used in Example 1 except that the yellow forming layer is as described above. Estan 5715
(Tg 16 ° C.) to form an imaging medium.
The diffusion-reducing basecoat 14 and diffusion-reducing layer 18 were omitted, but a solvent resistant intermediate layer 20 (compounded as above) was provided over the color-forming layer 16.

After imaging as in Example 1, this medium exhibited a total transmission optical density in blue light of 0.45. After storage after image formation, this density increased to 1.10. This implies the extreme diffusion of color materials experienced by using low glass transition temperature binders in the color forming layer.

Example 3 The medium used in this example was Medium A described in Example 1.
And C and medium D. Medium D has a diffusion-reducing basecoat and diffusion-reducing layer formed from a mixture of Neoles XR-9637 / Airvol 540 used to form the solvent resistant interlayer 20 in the preferred imaging media described above with reference to the drawings. Medium B described in Example 1 except that
Was the same as

Then all three media are about 3.5
Was imaged to maximum optical density using an infrared laser to form a solid line having a transmission optical density of ∘, adjacent to Dmin (non-image area) having an optical density of about 0.07. If the yellow colored material produced during imaging diffuses into the non-image areas, a gradient of image density will be seen in the non-image areas adjacent to the image lines. Therefore, the transmission optical densities of the three imaged media in blue light were measured at 40, 60 and 80μ from the edge of the image line by a Joyce Leble microdensitometer after storage at room temperature for 6 months. The results of these measurements are shown in Table 2 below.

[Table 2]

From the data in Table 2, the media A and C with the high glass transition temperature diffusion-reducing layer showed no evidence of diffusion after storage, while the medium D with the low glass transition temperature diffusion-reducing layer was preserved. It can be seen that it later showed significant diffusion.

From the above, the present invention is effective in preventing the diffusion of coloring substances formed during image formation, even when the image is stored for a considerable period of time, and is therefore sharp enough not to suffer a substantial loss of sharpness after storage. It can be seen that it makes it possible to obtain a fully resolved image.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a preferred imaging medium of the present invention.

[Explanation of symbols]

 10 Image forming medium 12 Transparent support 14 Diffusion reducing undercoat 16 Yellow forming layer 18 Diffusion reducing layer 20 Solvent resistant intermediate layer 22 Magenta color forming layer 24 Solvent resistant intermediate layer 26 Cyan color forming layer 28 Adhesive layer 30 UV Filter layer 32 Thick, transparent, air bubble suppression layer

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G03C 1/76 351 8910-2H 8/50 8305-2H

Claims (10)

[Claims] 1. The temperature of the color forming layer is equal to or higher than the color forming temperature,
An imaging medium having a color-forming layer comprising a thermally color-forming composition adapted to undergo a color change when raised during a color-forming time, the glass transition temperature of which is at least 50 ° C. A first polymer having a color-forming composition dispersed in the first polymer; further comprising a second polymer in contact with one surface of the color-forming layer. An imaging medium having a glass transition temperature of at least 50 ° C. and essentially free of a color forming composition. 2. A color-forming composition capable of absorbing actinic radiation and a color-forming compound which undergoes a color change when heated above the color-forming temperature during the color-forming time. The image forming medium of claim 1, comprising an absorber capable of generating heat in the color forming layer. 3. The imaging medium of claim 1 or 2 characterized by two diffusion reducing layers in contact with opposite sides of the color forming layer. 4. The imaging medium according to claim 1, wherein the first polymer has a glass transition temperature of at least 75 ° C., preferably at least 95 ° C. 5. Imaging medium according to any one of claims 1 to 4, characterized in that the first polymer is an acrylic polymer, preferably poly (methyl methacrylate). 6. The or each diffusion reducing layer has at least 5 layers.
Imaging medium according to any one of claims 1 to 5, characterized in that it has a glass transition temperature of 5 ° C. 7. Imaging medium according to claim 1, characterized in that the or each diffusion-reducing layer consists of an acrylic polymer, preferably a styrene-acrylic polymer. 8. At least one diffusion-reducing layer has a thickness of at least 1 μm.
An image forming medium according to any one of 1. 9. A support; a first color forming layer located on the support; a diffusion reducing layer located on the first color forming layer; a second color forming layer located on the second diffusion reducing layer. , The second color-forming layer comprises a second color-forming composition adapted to undergo a color change when the temperature of the color-forming layer rises above the second color-forming temperature for a second color-forming time. And the color change experienced by the second color-forming layer is different from the color change experienced by the other color-forming layers; and the glass transition temperature below 50 ° C. interposed between the diffusion-reducing layer and the second color-forming layer. An image forming medium according to any one of claims 1 to 8, further comprising: 10. An image forming medium according to any one of claims 1 to 9 is provided; the color forming layer is imagewise heated above the color forming temperature during the color forming time, whereby a color forming composition is obtained. To undergo a color change in the heated areas to produce colored material in these heated areas, and thereby to form an image; and, for at least about a week, the colored material allows the colored material to reduce the imaging layer and diffusion. Storing without substantially migrating out of the layer; a method of forming and storing images.