GB2198254A - Thermal transfer material and thermal transfer recording method - Google Patents

Description

2198254 THERMAL TRANSFER MATERIAL AND THERMAL TRANSFER RECORDING METHOD

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a thermal transfer material and a thermal transfer recording method for transferring two color-images from a single thermal transfer material onto a recording medium such as plain paper, and more specifically to a thermal transfer material capable of providing clear two-color recorded images free of turbidity, particularly a thermal transfer material suitably used for multi-color recording for providing three or more-color images.

The thermal or heat-sensitive transfer is recording method has recently been widely used because it has general advantages of the thermal recording method such that the apparatus employed is light in weight, compact, free of noise, excellent in operability and adapted to easy maintenance, and also has other advantages such that it does not require acolor-formation type converted paper but provides recorded images with excellent durability.

Further, there is also a commercial demand for a method of obtaining twocolor images while retaining the advantages of the thermal transfer recording method as described above. Accordingly, there have been proposed several techniques for obtaining two-color images.

In order to obtain two-color images on plain paper by the thermal transfer recording method, Japanese Laid-Open Patent Application No. 148591/1981 discloses a two-color type thermal transfer recording element (transfer material) comprising a substrate and two heat-fusible ink layers including a high-melting point ink layer A and a low-melting point ink layer B containing mutually different colorants disposed in this order on the substrate. When a low thermal input energy is applied to the element, only the low-melting point layer B is transferred onto plain paper. On the other hand, when a high thermal input energy is applied to the element, both the heat-fusible ink layers A and B are transferred onto the plain paper. As a result, two-color images can be obtained.

Further, Japanese Laid-Open Patent Application No. 64389/1984 discloses a two-color thermal transfer ink sheet which comprises, on a substrate, an ink layer comprising an ink which melt-exudes at a lower temperature and another ink which is melt-peeled at a higher temperature than the meltexudation temperature.

In the methods using the above-mentioned thermal transfer materials, twocolor recording is effected by changing the energy applied to a thermal head at two levels so as to change the temperature of the ink layers. However, when a high energy is supplied to the ink layers to provide a high temperature, a lower temperature portion is formed at the periphery of a higher temperature portion due to heat diffusion, so that a bordering of a lower temperature color is formed around the higher temperature printed image. Further, when a high energy is supplied to a thermal head, it requires a relatively long time until the thermal head is cooled so that a higher- temperature printed image is liable to be accompanied with a trailing of a lower-temperature color. Further, in any of the above methods, there is a constraint that a relatively low melting material is required for providing an ink to be transferred at a lower temperature, whereby they give rise to problems such as ground soiling and low storability of the thermal transfer material.

As a technique for dissolving the abovementioned problems, our research group has proposed a recording method as disclosed in Japanese Laid-Open Patent Application No. 137789/1986 (U.S. Patent _ Application Serial No. 819,497). In this recording" method, there is employed a thermal transfer material comprising a support and at least a first ink layer and a second ink layer disposed in this order on the support, and after heat is applied to the thermal transfer material, a length of time from the heat application until the separation between the transfer material and a recording medium is so controlled that the second ink layer is selectively, or both the first and second ink layers are, transferred to the recording medium.

our research group has further proposed, as a thermal transfer material for use in such recording method, one as disclosed in Japanese Laid-Open Patent Application No. 295075/1986 and one as disclosed in Japanese LaidOpen Patent Application No. 295079/1986.

Japanese Laid-Open Patent Application No. 295075/1986 discloses a thermal transfer material wherein at least one of a first ink layer and a second ink layer contains a silicone oil Qr a fluorine-containing surfactant so as to promote separation between the first and second ink layers. Japanese Laid-Open Patent Application No. 295079/1986 discloses a thermal transfer material wherein a fine powder layer not meltable under application of a heat energy for recording is disposed between a first ink layer and a second ink layer so as to easily cause separation therebetween. 0 The above-mentioned recording method disclosed in Japanese Laid-open Patent Application No. 137789/ 1986 (U.S. Patent Application Serial No. 819,497), has solved the problems of bordering, trailing, etc., in the prior art. However, this new two-color recording method has not been fully superior to the conventional two-color recording method in respect of latitude of selection of ink layer colors, particularly the color of the first ink layer.

More specifically, where a thermal transfer material comprising a first ink layer and a second ink layer on a support is used in the above-described recording methods inclusive of the conventional twocolor recording method and the above-mentioned new recording method, only the second ink layer is or both the first and second ink layers are transferred onto the recording medium at the time of transfer recording. In this instance, when the first and second ink layers are transferred together, it is inevitable that the color of the second ink layer is mixed into the color of the first ink layer to some extent, so that it is difficult to obtain a beautiful color in this case.

For this reason, it has been practiced heretofore to use a bright color in the second ink and a dark color in the first ink so as to enhance the hiding power of the first ink. Actually, where the first ink is in black, it has a fairly good hiding power so that it provides a substantially black image, while it is inevitable that the resultant color is a warm black when the second ink is in red and is a cold black when the second ink is in blue. On the other hand, in case where the first ink is in a dark color other than black, the hiding power is insufficient so that it is further difficult to provide a beautiful color of recorded images.

As a solution to the above problem, it may be conceived to increase the thickness of the first ink layer. If the first ink layer is excessively thick, however, not only a large energy is required for recording but also it is failed to provide a good quality of recorded images because of a lowering in resolution. Accordingly, in the above-mentioned processes where two-color recording is effected by using an ink film comprising a first ink layer and a second ink layer in lamination, recorded images in a beautiful color have not been actually obtained unless the first ink is in black.

Such restriction on the color of the first ink layer provides a serious defect when it is applied to a system where a plurality of thermal transfer materials or ink films each capable of two color recording are used while being switched to effect a multi-color recording. More specifically, even when two ink films are used, only three colors can be obtained if the first inks of both ink films are in black. Further, even when the first ink layers are in colors other than black, there only result in two dark colors close to black, so that little advantage is attained by using two ink films for two-color recording.

Further, when three-color recording is effected by using an ink film capable of two-color recording and an ink film of a single color in combination, it is practically desirable to provide black images which are most frequently used by using a single color ink film which is less expensive and provide bright and clear two-color images by using an ink film for two-color recording. It is however impossible to.provide twocolored images which are both bright and clear by using a conventional ink-film for two color recording, because the first ink layer is inevitably required to be in a dark color.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a thermal transfer material by which twocolor recorded images with good color separation and with respectively clear color tones are given on plain paper through a simple process, by solving the above- mentioned problems involved in the conventional two-color recording method.

As a result of our study, it has been found very effective not to hide the color of the second ink layer to the maximum as in the conventional two-color type thermal transfer material but to positively take advantage of the color of the second ink layer for two-color recording by using a color with a very low hiding power in the first ink layer, in order to provide a clear color tone free of turbidity and somberness.

The thermal transfer material of the present invention is based on the above findings and comprises a support and at least a first ink layer and a second ink layer disposed in the order named on the support, wherein the first ink layer has a yellow color.

Further, thermal transfer recording method according to the present invention comprises:

providing a thermal transfer material (A) comprising a support and at least one ink layer disposed on the support, and a thermal transfer material (B) comprising a support and at least a first ink layer and a second ink layer disposed in the order named on the support, the first ink layer having a yellow color; causing at least one of the thermal transfer materials (A) and (B) to contact a recording medium with its ink layer side; supplying a pattern of energy corresponding to a given image signal to said at least one of the thermal transfer materials (A) and (B); and separating said at least one of the thermal transfer materials (A) and (B) from the recording medium to leave a transferred image in at least one color selected from those colors obtained by combination of the ink layers of said at least one of the thermal transfer materials (A) and (B).

In the above thermal transfer recording method according to the present invention, it is not questioned whether the ink layer of the thermal transfer material (A) or (B) is contacted before or after the application of energy to the thermal transfer material (A) or (B), as far as transferred recorded images can be formed thereby in three or mbre colors.

If the thermal transfer material according to the present invention having the above-mentioned structure is used, even when both the first and second ink layers are transferred onto a recording medium, the color of the lower second ink layer is not incompletely hidden based on the spectral reflection characteristic of the first ink layer but is mixed with the color of the first ink layer according to the subtractive process in a nearly ideal manner to provide a stably clear color.

The thermal transfer material according to the present invention provides particularly clear two-color recorded images when it is provided with a specific relationship in respect of adhesion strength between the ink layers and between the support and the ink layers as described in Japanese Laid-Open Patent Application No. 137789/1986 (U.S. Patent Application Serial No. 819,497). This is presumably for the -10 following reasons.

Thus, when the thermal transfer material of the present invention is constituted to satisfy the adhesion strength relationship which will be supplemented hereinafter, two-color recorded images are provided by control of time for separation from the recording medium after the energy application and not by control of the magnitude of energy applied, so that the first ink layer is transferred so as to well cover the second ink layer and to suppress the material mixing of the first and second ink layers. As a result, the color mixing of the first and second inks according to the additive process (mixing of reflected light rays) is presumably suppressed to a very low level.

These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, wherein like parts are denoted by like reference numerals. In the description appearing hereinafter, "part(s)" and "%" used for describing compositions are by weight unless otherwise noted specifically.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic sectional view across the thickness of an embodiment of the thermal transfer material according to the present invention; Figures 2A and 2B are respectively a schematic sectional view showing a recorded image formed on a recording medium; Figure 3 is a graph showing a variation in adhesion strength between various layers with elapse of time; Figures 4 to 6 respectively show another laminar structure of the thermal transfer material according to the present invention; and Figures 7 and 8 are a schematic sectional view and a schematic perspective view, respectively, illustrating a thermal transfer recording apparatus for two-color recording or four-color recording and a mode of operation thereof using a thermal transfer material according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, a thermal transfer material 1 according to the present invention comprises a support 2, and a first ink layer 3 and a second ink layer 4 disposed in this order on the support.

As the support 2 of the thermal transfer material 1, it is possible to use a conventional film or paper as it is, inclusive of films of a plastic having a relatively good heat resistance, such as polyester, polycarbonate, triacetyl cellulose, polyamide, and polyimide; cellophane, parchment paper and capacitor paper. The thickness of the support 2 may preferably be about 1 to 15 pm when a thermal head is used as a heat source for thermal transfer recording but may not be particularly restricted if a heat source such as a laser beam capable of selec- tively heating the thermal transfer ink layer. on the other hand, the first ink layer 3 and the second ink layer 4 on the support 4 may comprise a colorant dispersed in a heat-fusible binder (it is not intended to exclude a case wherein the colorant is dissolved in the binder). In the 3 has a yellow present invention, the first ink layer color by containing a yellow colorant.

Herein, the "yellow color" means not only pure yellow, i.e., a color which absorbs wavelengths of 400 - 500 nm substantially completely and reflects wavelengths of 500 - 600 nm substantially completely but also yellow colors which may contain a tinge of another color to some extent but can be practically regarded as equal to pure yellow in subtractive mixing with another color. More specifically, the yellow color or yellow colorant may preferably be one showing reflection density characteristics observed through color separation filters as will be described hereinbelow.

Thus, a first ink layer 3 containing a yellow colorant is formed in a thickness substantially equal to that used in an actual thermal transfer material (e.g., an ink film) and transferred onto a recording medium such as wood-free paper which is substantially white, i.e., shows densities of 0.05 or less when measured through any of a red filter (R), a green filter (G) and a blue filter (B). The transferred ink image may preferably show densities Dy, D m and D c satisfying the following conditions:

D y > D m + 0.1 and D y > D c + 0.1; more preferably D y > 0.6, D m < 0.45, and D c < 0.25, wherein Dy, D m and D c respectively denote the following:

Dy: Yellow density, i.e., a reflection density measured through a blue filter; D m: A magenta density, i.e., a reflection density measured through a green filter; and D c: A cyan density, i.e., a reflection density measured through a red filter.

For the above density measurement, a McBeth reflection densitometer Model RD 514 or Model RD 517 may be used. These reflection densitometers are provided with Wratten gelatin filters (#47 Blue, #2 Red and #58 Green, available from Eastman Kodak Co.).

Incidentally, the above-mentioned reflection densities may also be measured by preparing a thermal transfer material having only a first ink layer 3 on transparent support 2 (e.g., an ink film not having second ink layer 4) and placing the thermal transfer material on substantially white recording medium such as a wood-free paper as described above showing a density of 0.05 or less when measured through any of 10 the R, G and B filters, and measuring the densities DY, D M and D C of the first ink layer 3 as described above. In this instance, it is preferred that the densities Dy, D M and D C satisfy the same conditions as described above.

The above second ink layer f intermediate f ilm ink layer 3 formed described ink film not having a or density measurement may be an which has been provided with a first by coating according to an ordinary production process and not yet provided with a second ink layer 4; or a residue film remaining after selective transfer of the second ink layer 4 from a completed ink film 4 according to a normal transfer process.

The yellow colorant used in the first ink layer 3 having a yellow color may be selected without particular restriction from known dyes or pigments and may be contained in a proportion of 2 - 500 parts per z parts of a heat-fusible binder resin in the first ink layer 3. Examples of such dyes and pigments which may be used in combination of two or more species as desired may include:

acid dyes, such as C.I. Acid Yellow 1 (C.I.

10316), C.I. Acid Yellow 3 (C.I. 47005), C.I. Acid Yellow 7 (C.I. 56205), C.I. Acid Yellow 11 (C.I.

18820), C.I. Acid Yellow 17 (C.I. 18965), C.I. Acid Yellow 23 (C.I. 19140), C.I. Acid Yellow 2'S (C.I.

18835), C.I. Acid Yellow 29 (C.I. 18900), C.I. Acid Yellow 36 (C.I. 13065), C.I. Acid Yellow 38 (C.I. 25135), C.I. Acid Yellow 40 (C.I. 18950), C.I.

Acid Yellow 42 (C.I. 22910), C.I. Acid Yellow 44 (C.I. 23900), C.I. Acid Yellow 76 (C.I. 18850), C.I.

Acid Yellow 98 (C.I. 14006), and C.I. Acid Yellow 99 (C.I. 13900); basic dyes, such as C.I. Basic Yellow 1 (C.I. 49005), C.I. Basic Yellow 2 (C.I. 41000), and C.I. Basic Yellow 11 (C.I. 48055); direct dyes, such as C.I. Direct Yellow 1 (C.I. 22250), C.I. Direct Yellow 8 (C.I. 13920), C.I. Direct Yellow 11 (C.I. 40000), C.I. Direct Yellow 12 (C.I. 24895), C.I. Direct Yellow 24 (C.I. 22010), C.I. Direct Yellow 26 (C.I. 25300), C.I. Direct Yellow 27 (C.I. 13950), C.I. Direct Yellow 28 (C.I. 19555), C.I. Direct Yellow 33 (C.I. 29020), C.I. Direct Yellow 44 (C.I. 29000), and C.I. Direct Yellow 50 (C.I.

29025); oil-soluble dyes, such as C.I. Solvent Yellow 2 (C.I. 11020), C.I. Solvent Yellow 6 (C.I. 11390), C.I. Solvent Yellow 14 (C.I. 12055), C.I. Solvent Yellow 15 (C.I. 18820), C.I. Solvent Yellow 16 (C.I. 5 12700), C. I. Solvent Yellow 19 (C.I. 13900A), C.I. Solvent Yellow 21 (C.I. 18690), C.I. Solvent Yellow 33 (C.I. 47000), and C.I. Solvent Yellow 56 (C.I. 11021); organic pigment, such as C.I. Pigment Yellow 1 (C.I. 11680), C.I. Pigment Yellow 2 (C.I. 11730), C.I. Pigment Yellow 3 (C.I. 11710), C.I. Pigment Yellow 4 (C.I. 11665), C.I. Pigment Yellow 5 (C.I. 11660), C.I. Pigment Yellow 6 (C.I. 11670), C.I. Pigment Yellow 7 (C.I. 12780), C.I. Pigment Yellow 10 15 (C.I. 12710), C.I. Pigment Yellow 11 (C.I. 10325), C.I. Pigment Yellow 12 (C.I. 21090), C.I. Pigment Yellow 13 (C.I. 21100), C.I. Pigment Yellow 14 (C.I. 21095), C.I. Pigment Yellow 15 (C.I. 21220), C.I. Pigment Yellow 16 (C.I. 20040), C.I. Pigment Yellow 17 (C.I. 21105), C.I. Pigment Yellow 23 (C.I. 60520), and C.I. Pigment Yellow 65 (C.I. 11740); and inorganic pigments, such as Cadmium yellow and chrome yellow.

on the other hand, the colorant used in the second ink layer 4 may be selected without particular restriction from known dyes and pigments used in the fields of printing and recording except for those in black. These colorants may be used singly or in mixture of two or more species in a proportion of 2 - 500 parts per 100 parts of a heat-fusible binder.

Specifically preferred examples of the hues of colorants contained in the second ink layer 4 may include blue which provides green in combination or subtractive mixing with yellow and silver which provides gold in combination with yellow, in respects of providing clear two colors.

Figures 2A and 2B are schematic side sectional views showing typical laminar structures of recorded images formed on recording media by using a thermal transfer material 1 according to the present invention as described above.

Figure 2A shows a recorded image 11a formed on a recording medium 5 by selective transfer of a second ink layer 41. The image 11a when viewed from the above in the figure provides the color (e.g., blue) of the second ink layer 41. Figure 2B shows a recorded image 11b formed by transfer of both the second ink layer 41 and a first ink layer 31 onto a recording medium 5. The image 11b provides a color (e. g., bright and beautiful green) obtained through combination of the color (e.g., blue) of the second ink layer 41 and the color (yellow) of the first ink layer 31 when viewed from the above.

In the case of Figure 2B, if the color of the 18- first ink layer 31 is other than yellow, the color of the second ink layer 41 is incompletely hidden by the first ink layer 31, only a dark, turbid color results. For example, if the second ink layer is in blue and the first ink layer is in green, the transferred image 11 in Figure 2B only provides a dark green color.

The heat-fusible binders constituting the first and second ink layers in combination with colorants as described above may be selected from binders conven- tionally used in thermal transfer inks. Examples of the heat-fusible binders may include waxes including: natural waxes such as whale wax, beeswax, lanolin, carnauba bax, candelilla wax, montan wax and ceresin wax; petroleum waxes such as paraffin wax and microcrystalline wax; synthetic waxes such as oxidized wax, ester wax, low molecular weight polyethylene, Fischer-Tropsch wax and the like; higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and behenic acid; higher alcohols such as stearyl alcohol and behenyl alcohol; esters such as fatty acid esters of sucrose and fatty acid esters of sorbitane; amides such as oleic amide; or resins including: polyolefin resins, polyamide resins, polyester resins, epoxy resins, polyurethane resins, acrylic resins, polyvinyl chloride resins, cellulose resins, polyvinyl alcohol resins, petroleum resins, phenolic resins, polystyrene resins, polyvinyl acetate resins, natural rubber; elastomers such as natural rubber, styrene- butadiene rubber, isoprene rubber, chloroprene rubber; etc.

The above-mentioned heat-fusible binders may be used singly or in mixture of two or more species according to necessity. It is also possible to adjust the properties, such as the super-cooling characteristic, meltviscosity, adhesion strength and hydrophilicity (or hydrophobicity), of the heat- fusible binder by adding thereto a so-called liquid rubber such as polyisobutylene or polybutene and other additives, such as plasticizer, oil agent and surfactant.

The first and second thermal transfer inks may be composed of a heat-fusible binder, a colorant and optional additives as described above so as to provide a melting point or soften. ihg point of preferably 60 180C.

In a preferred embodiment of the thermal transfer material according to the present invention, the adhesion (strength) F 2 between the first ink layer 3 and the second ink layer 4 and the adhesion (strength) F, between the first ink layer 3 and the support 2 have preferably have relative magnitudes which are opposite to each other at a higher temperature and a lower temperature. It is further preferred that the adhesions F 1 and F2 satisfy the relations of F 1 > F2 at a higher temperature and F, < F 2 at a lower temperature as shown in Figure 3. The adhesion (F 2) between the second and first ink layers and the adhesion (F 1) between the first ink layer and the support are evaluated according to relative easiness between the separation between the second and first ink layers, and the separation between the first ink layer and the support, when transfer recording is effected on a recording medium. Such evaluation of the adhesions is not affected by the form of separation between ink layers (e.g., whether or not the separation between the second and first ink layers has occurred strictly at the boundary between these layers, or whether or not some adhesive layer described hereinafter, if any, remains on the thermal transfer material).

The relationships between the adhesions F 1 and F2 as shown in Figure 3 may be realized, in a thermal transfer material having a laminar structure as shown in Figure 1, by using a second ink layer 4 showing a large change in adhesion for a change in temperature (preferably one containing 50 parts or more of a wax component as described above in 100 parts of the total binder component) and by using a first ink layer 3 showing a small change in adhesion for a change in temperature (preferably one containing 50 parts or more of a resin component as described above in 100 parts of the total binder resin).

in order to realize the preferred adhesion as described above more easily, it is possible to provide a first adhesive layer 6 between the support 2 and the first ink layer 3 as shown in Figure 4. The disposition of such a first adhesive layer provides a layer latitude in selection of the material constituting the first ink layer 3 which leads to an advantage in regulation of recorded image quality.

It is also possible to form a second adhesive layer 7 between the first ink layer 3 and the second ink layer 4 as shown in Figure 5. The second adhesive layer 7 is a layer for controlling the adhesion (F 2) between the first and second ink layers. If the second adhesive layer 7 is composed of a material having properties similar to those required of the second ink layer 7 explained with reference to Figure 1, the second ink layer 4 is not necessarily required to satisfy the properties explained with reference to Figure 1. As a result, it becomes possible to compose the second ink layer of a material which can show a large adhesion to the recording medium, e.g., a material similar to one for constituting the first ink layer in the embodiment shown in Figure 1, thus being further advantageous in improving the recorded image quality.

It is further possible to dispose a third adhesive layer 8 on the second ink layer 4 as a layer facing the recording medium as shown in Figure 6. The provision of the third adhesive layer 7 is advantageous', especially when two-color recording is effected on a recording medium with poor surface smoothness.

It is also possible to provide two or more of the above-mentioned first adhesive layer 5, second adhesive layer 6 and third adhesive layer 7 in combination as desired. These adhesive layers are mainly composed of a heat-fusible binder as described above.

In case where the first adhesive layer 6, the second adhesive layer 7 and the third adhesive layer 8 mentioned above are provided, the first ink layer and the second ink layer are free from the above preferred melting point or softening point region of 60 18CC and can even be formed as infusible layers.

In the thermal transfer material 1 of the present invention, the total thickness of the ink layers and adhesive layers, if any, may preferably be20 pm or less, more preferably 1 - 10 pm. Further, each of the first ink layer 3 and the second ink layer 4 may preferably have a thickness in the range of 0.5 - 10 pm, and each of the first adhesive layer 6, the second adhesive layer 7 and the third adhesive layer 8, if any, may preferably have a thickness in the range of 0.1 - 5 pm.

The thermal transfer material according to the present invention may be obtained by forming the respective layers by mixing the materials constituting the respective layers and an organic solvent selected from those including hydrocarbon solvents, such as hexane, toluene and xylene; alcohol solvents, such as methanol, ethanol, and isopropanol; ether solvents, such as diethyl ether, tetrahydrofuran, and diethylene glycol diethyl ether; and ester solvents, such as ethyl acetate and butyl acetate capable of dissolving the binders for the respective layers, and applying the thus formed coating liquids successively on the support. Alternatively, the so-called hot-melt coating method may be adopted, including the steps of blending, hot-melting and applying the materials in a molten state for the respective layers. The materials for the respective layers may be formed into aqueous emulsions by the addition of a dispersant such as a surfactant, and the aqueous emulsions may be appliedto form the respective layers. Further, the respective layers of the transfer material may also be formed by using the above mentioned coating methods in combination, i.e., by using different methods for the respective layers.

Now, a method of two-color recording effected by using the thermal transfer material of the present invention will be explained with reference to a preferred embodiment wherein a thermal head is used as a most typical heat source, and there is used a thermal transfer material (1) having a laminar structure as shown in Figure 1 and showing changes with time after energy application as shown in Figure 3, i.e., an adhesion F 1 with a relatively small change for a temperature change between the support 2 and the first ink layer 3 and an adhesion F 2 with a relatively large change for a temperature change between the first ink layer 3 and the second ink layer 4.

More specifically, a system as schematically shown in Figure 7 may preferably be used. Referring to Figure 7, a thermal transfer material 1 wound off from a supplying core 9a and wound up by a take-up core 9b between which, at a heat-applying position, it is pressed against a recording medium 5 supported by a platen 12 by means of a thermal head 10 so-that the second ink layer thereof contacts the recording medium and simultaneously a pattern of heat is applied to the thermal transfer material 1 from the thermal head 10. If the thermal transfer material 1 is peeled from the recording medium 5 at the rear end 10a of the thermal head 10 immediately after the heat application, only the second ink layer is transferred to the recording medium 5 because F 1 > F 2 On the other hand, when a peeling-control member 13 is moved in the directions of an arrow A to a position 13a indicated by dashed lines, the thermal transfer material 1 and the recording medium 5 are pressed against each other, a pattern of heat is supplied from the thermal head, and the thermal transfer material 1 is peeled from the recording medium 5 at the position 13a of the control member 13, both the first and second ink layers are transferred to the recording medium 5 because F 1 < F2 Among the members shown in Figure 7, the thermal transfer material 1, the supplying core 9a, the take-up core 9b, the thermal head 10, and the peeling-control member 13 are housed in a carriage 14 and moved in the direction of an arrow B. The thermal transfer material accordina to the present invention may suitably be loaded also on an apparatus as shown in Figure 8, a schematic perspec tive view, wherein two thermal transfer materials can be loaded in parallel.

Next, a thermal transfer recording method according to the present invention will be explained based on Figure 8.

Referring to Figure 8, a pair of ribbon cartridges 15a and 15b each housing one thermal transfer material 1 in the form of a ribbon are superposed with one on the other on a movable mount 16 capable of moving up and down in the direction of an arrow C, i.e., away and toward a carriage 14. When the movable mount 16 is in its lower position as shown in the figure, the ribbon cartridge 15a is used for recording. When the movable mount 16 is in its upper position a little away from the carriage 14, the ribbon cartridge 15b is used for recording.

In the recording operation, a thermal head 10 is pressed against a recording medium 5 supported by a platen 12 by the medium of a thermal transfer material 1, whereby the thermal transfer material 1 is heated in a pattern and simultaneously the carriage 14 is moved in the direction of an arrow B. In order to transfer only the second ink layer onto the recording medium 5, a peeling-control member 13 is left away from the recording medium 5 so that the thermal transfer material 1 is separated from the recording medium 5 immediately after the thermal transfer material 1 has passed through the thermal head 10. On the other hand, in order to transfer both the first ink layer and the second ink layer, the peeling-control member 13 and the thermal head 10 are together pressed against the recording medium 5 by the medium of the thermal transfer material 1 The above operation is effected by using the thermal transfer material 1 respectively encased in the ribbon cartridges 15a and 15b for conducting two-color recording respectively, whereby recording of totally four-color clear images may be effected.

In the above-explained embodiment of the recording method, two thermal transfer materials respectively according to the present invention are used. In the thermal transfer recording method of the present invention, however, it is sufficient if at least one of two or more thermal transfer materials used is in the form of a two-color thermal transfer material 1 Ithermal transfer material according to the invention) as described above, another themal transfer material can have any ink layer structure (a single layer or plural layers) or any color (bright or dark).

The two-color thermal transfer material 1 can provide two-color recorded images in two bright colors. Accordingly, even when another thermal transfer material having a single black ink layer is used, it is possible to provide clear three- color recorded images in combination of bright, bright and black colors.

The present invention is also advantageous in producing thermal transfer materials with many recording colors. For example, in order to produce thermal transfer materials for providing recorded images in four colors of silver, gold, blue and green, it has been conventionally required to prepare coating liquids in the four colors and separately applying the four coating liquids on different supports thereby to -28 provide four thermal transfer materials. In contrast thereto, according to-the present invention, it is possible to prepare totally three coating liquids including one for a first ink layer 3 in yellow, and two for second ink layers in silver and blue, and apply yellow and silver inks successively on a substrate and yellow and blue inks successively on another substrate, thereby to prepare two thermal transfer materials which can provide four-color images in silver, gold, blue and green. Further, in respect of process for producing plural types of two-color thermal transfer materials, the present invention provides an advantage that common production steps are adopted up to the coating step of the first ink layers for the plural-types of thermal transfer materials, because a yellow ink is commonly used as the first inks.

As described above, the present invention provides a thermal transfer material comprising a support and at least a first ink layer and a second ink layer on the support wherein the first ink layer has a yellow color, and a multi-color thermal transfer recording method.

By using the thermal transfer material according to the present invention, recorded images in clear two colors are formed on plain paper, etc., only by applying a pattern of energy to the thermal transfer material superposed with a recording methed and separatirig them while changing the time after the energy application.

Hereinbelow, the present invention will be explained more specifically while referring to specific examples of practice. Incidentally, the melt viscosity of a sample was measured by means of a rotational viscometer (Etype), and the numberaverage molecular weight Mn of a sample such as oxidized polyethylene was measured in the following manner. [Molecular Weight Measurement] The VPO method (Vapor Pressure Osmometry Method) is used. A sample of oxidized polyethylene is dissolved in a solvent such as benzene at various concentrations (C) in the range of 0.2 to 1.0 g/100 ml to prepare several solutions. The osmotic pressure WC) of each solution is measured and plotted versus the concentration to prepare a concentration (C)- osmotic pressure (7/C) curve, which is extrapolated to obtain the osmotic pressure at the infinite dilution (Tr/C) 01 From the equation of WC)O = RT/Mn, the number-average molecular weight Mn of the sample is derived.

Example 1 <Coating liquid A> oxidized polyethylene aqueous diepersion 80 parts (Mn=4000, melt viscosity = 5xiO 2 mPa-S at 1400C) Acrylic resin aqueous dispersion 20 parts (melt viscosity = 5x1O 4 mPa-S at 1500C) (The amounts and softening points of aqueous dispersions for providing a coating liquid in this example and the other examples are all expressed based on their solid contents.) The above components were sufficiently mixed to prepare a coating liquid A. The coating liquid A was applied on a 6 p-thick PET (polyethylene tere- phthalate) film and dried at 60'C to form a 1 p-thick first adhesive layer.

<Coating liquid B> Acrylic resin aqueous dispersion (melt viscosity = 5x1O 4 mPa-S at 1500C) Hansa Yellow G aqueous dispersion parts parts (C.I. Pigment Yellow 1 (C.I. 11680)) The above components were sufficiently mixed to prepare a coating liquid B, which was applied on the above-prepared first adhesive layer and dried at 25 WC to form a 2 pm-thick first ink layer.

<Coating liquid C> Carnauba wax aqueous dispersion (melt viscosity = 1x101 mPa-S at 130'C) The above coating liquid C was applied on the above-prepared first ink layer and dried at 60'C to form a 1 Um-thick second adhesive layer. <Coating liquid D> oxidized polyethylene aqueous dispersion 55 parts (Mn=2000,.melt -Viscosity = 2x1O 2 mPa-S at 140C) Ethylene-vinyl acetate resin aqueous dispersion 25 parts (melt viscosity = 1x1O 5 mPa-S at 1500C) Phthalocyanine blue aqueous dispersion 20 parts The above components were sufficiently mixed to prepare a coating liquid D, which was then applied on the above-prepared second adhesive layer and dried at 800C to form a 2 pm-thick second ink layer, whereby a thermal transfer material M was obtained.

Then, the above thermal transfer material-(I) was cut into a 6 mm-wide ribbon and used for recording by means of a thermal transfer recording apparatus for an English typewriter (Typestar 6, mfd. by Canon K.K.) Referring to Figure 7, as a thermal head 10, one prepared by Rohm K.K., having a length from the center of the heat generating part (not shown) to the trailing end 10a of 350 pm was used. A carriage loading the thermal head 10 and the ink ribbon (thermal transfer material) 1 was moved in the direction of an arrow B, at a moving velocity of 50 mm/sec.

In this manner, a pattern of heat was applied for a pulse duration of 0.7 msec from the thermal head 10 to the thermal transfer material 1, and about 5 msec thereafter, the thermal transfer material 1 was peeled from the recording medium 5 (wood-free paper having a Bekk's smoothness of 200 sec) as a rapid peeling mode, whereby a clear blue recorded image 11a (Figure 2A) due to transfer of the second ink layer was formed on the recording medium.

on the other hand, in order to delay the time of the peeling, a control member 13 for controlling the peeling was disposed at about 5 mm. (i.e., Z = 5 mm as shown in Figure 7) after the trailing end 10a of the thermal head (i.e., downstream side of the trailing end 10a with respect to the moving direction of the thermal transfer material 1) and moved toward the recording medium, and the thermal transfer material 1 was peeled from the recording medium 5 about 100 msec after pattern heat-application from the thermal head 10 to the thermal transfer material 1 in the above described manner, whereby a clear green recorded image 11b (Figure 2B) due to transfer of the first and second ink layers was formed.

The above recorded images 11a and 11b both showed good image qualities.

Example 2 <Coading liquid E> oxidized polyethylene aqueous dispersion (Mn=2000, melt viscosity = 2xl 02 mPa-S at 140C) Ethylene-vinyl acetate resin aqueous dispersion (melt viscosity = 1x1O 5 mPa-S at 150C) Flaky aluminum powder parts parts parts (average particle size = 10 pm, average thickness = 0.3 pm) The above ingredients were sufficeintly mixed to prepare a coating liquid E.

is A thermal transfer material (II) was prepared in the same manner as in Example 1 except that the coating liquid E was used in place of the coating liquid D to form a second ink layer.

Transfer recording was effected in the same manner as in Example 1 by using the thermal transfer material (II). As a result, a clear silver image 11a was formed in a rapid peeling mode (about 7 msec), while a clear gold image 11b was formed in a delayed peeling mode (about 100 msec). Both images were good in image quality. Comparative Example 1 A thermal transfer material (III) was prepared in the same manner as in Example 1 except that a coating liquid F obtained by sufficiently mixing the following ingredients was used in place of the coating liquid B to form a first ink layer.

<Coating liquid F> Acrylic resin aqueous dispersion 60 parts (melt viscosity = 5xjO 4 mPa-S at 1500C) Red azo pigment aqueous dispersion 40 parts Transfer recording was effected in the same manner as in Example 1 by using the thermal transfer material (III). As a result, a clear blue image 11a was formed in a rapid peeling mode similarly as in Example 1, whereas only a somber dark violet image was obtained in a delayed peeling mode and it was not sufficiently differentiated from the above blue image.

Claims (13)

1. A thermal transfer material comprising a support and at least a first ink layer and a second ink layer disposed in the order named on the support, 5 wherein the first ink layer has a yellow color.

2. A material according to Claim 1, wherein th first ink layer, when transferred alone onto a substantially white recording medium, provides densities Dy, DM and DC satisfying the following conditions:

D Y > D N + 0.1 and D Y > D c + 0.1, wherein D Y denotes a reflection density measured through a blue filter, D m a reflection density measured through a green filter, and D c a reflection density measured through a red f ilter.

2

3. A material according to Claim 2, wherein th densities Dy. D m and D c satisfy the following 0 conditions:

D Y > 0.6, D m < 0.45 and D c < 0.25.

4. A material according to Claim 1, wherein said second ink layer contains a blue colorant.

5. A material according to Claim 1, wherein said second ink layer contains a silver colorant.

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6. A material according to Claim 1, wherein the adhesion strength F 1 between the support and the first ink layer and the adhesion strength F 2 between the first and second ink layers satisfy the relations of F 1 > F 2 at a higher temperature and F, < F 2 at a lower temperature.

7. A material according to Claim 6, wherein a first adhesive layer is disposed between the support 10 and the first ink layer.

8. A material according to Claim 6, wherein a second adhesive layer is disposed between the first and second ink layers.

is

9. A material according to Claim 6, wherein a third adhesive layer is disposed on the second ink layer.

10. A thermal transfer recording method, comprising:

providing a thermal transfer material (A) comprising a support and at least one ink layer disposed on the support, and a thermal transfer material (B) comprising a support and at least a first ink layer and a second ink layer disposed in the order named on the support, the first ink layer having a yellow color; causing at least one of the thermal transfer materials (A) and (B) to contact a recording medium with its ink layer side; supplying a pattern of energy corresponding to a-given image signal to said at least one of the - thermal transfer material (A) and (B); and separating said at least"one of the thermal transfer materials (A) and (B) from the recording medium to leave a transferred image in at least one color selected from those colors obtained by combination of the ink layers of said at least one of the thermal transfer materials (A) and (B).

11. A method according to Claim 10, wherein said thermal transfer material (A) also comprises at least a first ink layer and a second ink layer disposed in the order named on the support, and the first ink layer has a yellow color.

12. A thermal transfer material, substantially as described with reference to the drawings, or as described in any of the Examples.

13. A thermal transfer recording method, substantially as described with reference to the drawings, or as described in any of the Examples.

1 Published 1988 at The Patent Office, State House, 6671 High Holborn, London WCIR 4T.P. Further copies may be obtained from The Patent Office. Sales Branch. St Mary Cray. Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Crky, Kent. Con. 1/87.