JPH02227290A - Sublimable thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To obtain a sublimable, thermal transfer recording medium which allows highly uniform image to be visualized by forming a dye supply layer consisting of more than two layers and reducing the dye density of a dye supply layer near a dye transfer contributing layer beyond the level of the dye density of a dye supply layer that is near a substrate. CONSTITUTION:A dye supply layer 4 consists of more than two layers and the dye density of a dye supply layer 4a near a dye transfer contributing layer 5 is lower than that of a dye supply layer 4b near a substrate. The dye density of the dye supply layer 4a which is located at the top is higher than that of the dye transfer contributing layer, and the dye density of the dye supply layer 4b which is located at the bottom is assumed to be 10, against which the dye density of the layer 4a is 9 or less. Then independent layers are formed on a substrate by applying the same amount of material in accordance with each prescription for the dye supply layer and the transfer contributing layer under the design of prescribing a material for the dye supply layer and transfer contributing layer. After this, an image- receiving layer is placed together with these independent layers respectively and a constant sublimation temperature is applied to these layers placed together. In this case, an appropriate density gradient or/and further a diffusition factor is provided between the dye supply layer and dye transfer contributing layer so that the relationship between the sublimable transfer amounts is the dye supply layer > the transfer contributing layer.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a sublimation type thermal transfer recording medium.

[Prior art]

Conventionally, two ink layers are formed.

A thermal transfer sheet has been proposed that achieves high sensitivity and maintains storage stability by changing the dye concentration of the outermost ink layer (the dye concentration of the ink layer on the support side) to the dye diffusion coefficient of the outermost ink layer and the dye diffusion coefficient of the ink layer on the support side (Unexamined Japanese Patent Publication No. (See No. 63-47193).

There is also a thermal transfer paper that is used many times by dyeing a base film with 2 to 20 times as much dye as the ink layer and supplying the dye from the base film to the ink layer each time (Japanese Patent Laid-Open No. 176186/1986). reference).

However, these conventional printers still lack sufficient ability to print multiple times. Moreover, in the latter case, since a large amount of dye is present in the base film itself, the strength of the film decreases, and there is a drawback that it cannot be put to practical use as a ribbon.

The present inventors, in Japanese Patent Application No. 63-268204,
The ink layer is made into two layers to separate the functions into a dye supply layer and a dye transfer contributing layer, and particulate dye is present in the dye supply layer to improve the ability to print multiple times.

As a result, although the multi-printing ability was certainly improved, there were cases where the thickness of the dye transfer contributing layer had extremely thick parts and extremely thin parts, that is, there was considerable thickness unevenness in the dye transfer contributing layer. case.

There is a problem in the uniformity of one image due to the density of the transferred image, and there is still room for improvement, and the present invention is a further improvement on this prior invention.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to overcome the conventional drawbacks and provide a sublimation type thermal transfer recording medium that has improved multiple printing characteristics, does not cause shading in transferred image density, and has good image uniformity.

〔composition〕

As a result of intensive research in order to achieve the above object, the present inventors have found that, on a substrate, in order from the substrate side, a dye supply layer consisting of at least an undissolved particulate sublimable dye and an organic binder, and at least A sublimation type thermal transfer recording medium is provided with an ink layer formed by stacking a dye transfer contribution layer consisting of a molecularly dispersed sublimable dye and an organic binder, and the dye supply layer is composed of two or more layers, and the dye It has been found that the above object can be achieved by providing a sublimation type thermal transfer recording medium characterized in that the dye concentration of the dye supply layer close to the transfer contributing layer is lower than the dye concentration of the dye supply layer close to the substrate.

In the sublimation type thermal transfer recording medium of the present invention, the dye supply layer contains at least an undissolved particulate sublimable dye, and the dye transfer contribution layer contains at least a molecularly dispersed sublimable dye.

The present invention is an improvement on the invention of Japanese Patent Application No. 1983-268204 filed by the same applicant.

In other words, by mixing undissolved particulate dye in the dye supply layer and creating an appropriate concentration gradient and/or diffusion coefficient gradient between the dye supply layer and the whole transfer contributing layer, a good number of cycles can be achieved while maintaining the initial gradient each time. Recording becomes possible.

However, here, undissolved particulate dye refers to dye that cannot be completely dissolved in the organic binder and precipitates in the form of particles after the ink (organic binder + sublimable dye and 10 solvents) is applied and dried during the formation of the ink layer. This means that even with the same binder and dye, the presence of undissolved particulate dye varies depending on the solvent. The presence or absence of undissolved particulate dye can be easily identified by electron microscopy after the dye supply layer is formed.

The present invention will be described in more detail below with reference to the accompanying drawings. FIG. 1 is an explanatory diagram showing the structure of the sublimation type thermal transfer recording medium of the present invention, in which 1 represents a substrate, 2 represents an ink layer composed of a dye supply layer 4 and a dye transfer contribution layer 5, and 3
6 indicates an image receptor such as paper, and 6 indicates a thermal head.

The feature of the present invention is that among these, the dye supply layer 4 is composed of two or more layers, and the dye supply layer (upper layer) near the dye transfer contribution layer 5
Dye supply layer (lower layer) 4b where the dye concentration of 4a is close to that of substrate 1
The dye concentration is smaller than that of the dye concentration.

The dye concentration of the upper dye supply layer 4a varies depending on the dye concentration of the dye transfer contributing layer and the lower dye supply layer 4b.
Higher than the dye concentration of the dye transfer contribution layer, and assuming that the dye concentration of the lower dye supply layer 4b is 10, the dye concentration is 9 or less, preferably 6.
~8.

By lowering the dye concentration in the upper layer of the dye supply layer, the binder content ratio increases, and as a result, the surface smoothness of the dye supply layer is improved, thereby reducing the concentration caused by uneven thickness of the dye transfer contributing layer. The particle size of the undissolved particle dye that improves unevenness (improves image uniformity) varies depending on the layer thickness of the dye supply layer, but is 0.01 μff1 to 20 μm.
, preferably 1.0 μm to 5 μI.

In addition, the state of the dye in the dye transfer contribution layer is dispersed in a monomolecular state that actually contributes to transfer, which prevents uneven transfer density and prevents the dye from forming between the dye supply layer and the dye transfer contribution layer. This is desirable because it keeps the concentration gradient stable.

In designing the material formulations of the dye supply layer and the transfer contribution layer in the present invention, the dye supply layer and the transfer contribution layer are formed with the same coating amount as a single layer on the substrate, and each is used as a separate image-receiving layer. Create an appropriate concentration gradient and/or diffusion coefficient gradient between the dye supply layer and the dye transfer contribution layer so that when the layers are superimposed and a constant sublimation temperature is applied, the sublimation transfer amount is in the relationship of dye supply layer > transfer contribution layer. Put on.

Next, the thickness of the transfer contribution layer is generally 0.05 to 5 μm.
, preferably 0.1 to 2 μm. The thickness of the dye supply layer, including the upper and lower layers, is generally 0.1~
The layer thickness is 20 μm, preferably 0.5 to 10 μm. The thickness of the upper dye supply layer 4a is the same as that of the lower dye supply layer 4b.
It varies depending on the particle size of the particulate dye inside or the surface roughness of the lower dye supply layer 4b, that is, the degree of unevenness, but it is 0.1 μm.
1 to 3 μm, preferably 0.5 μm to 1.5 μm.

Also, known sublimable dyes, binders, etc. can be used in the transfer contribution layer and dye supply layer of the present invention.

Sublimable dyes are dyes that sublimate or vaporize at temperatures above 60°C, and are mainly used in thermal transfer printing such as disperse dyes and oil-soluble dyes, such as C, 1, Disperse Yellow 1.3. ,8゜9.16,41,54,
60, 77.116, etc., C, 1, Dispersed thread 1, 4, 6, 11, 15, 17, 55, 59, 60,
73.83 etc., C, 1, Disperse Blue 3.1
4,19,26,56,60゜64.72,99,10
8 etc., C, 1, Solvent Yellow such as 77.116, C, I, Solvent Red such as 23.25.27, C, 1, Solvent Blue such as 36.83,105, etc., and one type of these dyes. However, it is also possible to use a mixture of several types.

Thermoplastic or thermosetting resins are used as binders for the dye transfer contributing layer and the dye supplying layer, and among them, resins with relatively high glass transition points or high softening properties include:
For example, vinyl chloride resin, vinyl acetate resin, polyamide, polyethylene, polycarbonate, polystyrene, polypropylene, acrylic resin, phenol resin, polyester, polyurethane, epoxy resin, silicone resin, fluorine resin, butyral resin, melamine resin, natural rubber, synthetic rubber. , polyvinyl alcohol, cellulose resin, etc.

These resins can be used alone, but several types may be mixed or a copolymer may be used.

Furthermore, if a difference is made in the glass transition or softening temperature between the dye transfer contribution layer and the dye supply layer, a resin, natural or synthetic rubber, or even wax with a glass transition temperature of 0°C or less or a softening temperature of 60°C or less is used. are preferable, especially polyethylene oxide, polycaprolactone polyol,
and waxes are useful in practice and are also described above. It is preferable to use a thermoplastic or thermosetting resin in a mixed form with one or more of the above.

The dye 1 degree of the transfer contributing layer is usually 5 to 80%, preferably,
It is about 10 to 60%.

Further, the dye concentration in the dye supply layer is preferably 5 to 80%, but when creating a dye concentration gradient between the dye transfer contribution layer and the dye supply layer, the dye concentration in the dye transfer contribution layer is 1%. .1 to 5 times, preferably 1.5 to 3 times.

Furthermore, as the base sheet, films such as capacitor paper, polyester film, polystyrene film, polysulfone film, polyimide film, polyamide film, etc. are used, and a conventional adhesive layer is provided between the base sheet and the dye supply layer as necessary. etc. may be provided,
Furthermore, a conventional heat-resistant lubricating layer may be provided on the back surface of the base sheet, if necessary.

Up until now, we have described an example in which the dye layer is divided into two layers, but
If an appropriate difference in the amount of dye transfer is created and the functional separation as intended by the present invention can be achieved, it is possible to form the dye layer into a multilayer of two or more layers.

Although the above description has been made with reference to a recording method using a thermal head, the transfer medium of the present invention can also be applied to a recording method in which recording thermal energy is applied by a method other than a thermal head, for example.
It can also be used for methods utilizing Joule heat generated by electrical current in a medium such as a thermal printing plate, a laser beam, or a support and/or an ink layer. Among these, the so-called electrical thermal transfer method, which uses Joule heat generated in the medium, is the most well-known.
6, JP-A-57-14060, JP-A-57-110.4
10, or in many documents such as Japanese Patent Application Laid-Open No. 59-9096.

When used in this current transfer method, polyester, polycarbonate, triacetyl cellulose, and nylon, which have relatively good heat resistance, are used as a support.

Metal powders such as aluminum, copper, iron, B, zinc, nickel, molybdenum, silver, and/or conductive powders such as carbon black are dispersed in resins such as polyimide and aromatic polyamide to change the resistance value to an insulator and a good conductor. It is sufficient to use a support adjusted to be intermediate between the two, or a support prepared by vapor-depositing or sputtering a conductive metal as described above on these supports. The thickness of these supports is desirably about 2 to 15 microns in consideration of Joule heat conduction efficiency.

Further, when used in a laser beam transfer method, a material that absorbs laser beams and generates heat may be selected as the support. For example, a conventional thermal transfer film containing a light absorption heat conversion material such as carbon, or a film in which an absorbing layer is formed on the front and back surfaces of a support is used.

EXAMPLES Hereinafter, the present invention will be explained in more detail based on the following examples, but the present invention is not limited thereto.

Example 1 Three inks for the upper dye supply layer 4a, the lower dye supply layer 4b, and the dye transfer contribution layer 5 having the following compositions were prepared.8.
A sublimation thermal transfer recording medium is formed by coating and drying on a 0 μm polyimide film support 1 so that the lower dye supply layer has a thickness of 3.5 μm, the upper dye supply layer has a thickness of 1.0 μm, and the dye transfer contribution layer has a thickness of 1.0 μm. did.

Solvent Toluene Methyl Ethyl Ketone Example 2 Three kinds of inks for the upper dye supply layer 4a, the lower dye supply layer 4b, and the dye transfer contribution layer 5 having the following compositions were prepared, and 8.
A sublimation type thermal transfer recording medium is formed by coating and drying on a 0 μm polyimide film support 1 so that the lower dye supply layer has a thickness of 3.5 μm, the upper layer dye supply layer has a thickness of 1.0 μm, and the dye transfer contribution layer has a thickness of 1.0 μm. did.

Example 3 Three inks for the upper dye supply layer 4a, the lower dye supply layer 4b, and the dye transfer contribution layer 5 having the following compositions were prepared.8.
A sublimation thermal transfer recording medium was formed by coating and drying on a 0 μm polyimide film support 1 such that the lower dye supply layer had a thickness of 3.0 μm, the upper dye supply layer had a thickness of 1.5 μm, and the dye transfer contributing layer had a thickness of 1.0 μm. .

Sublimable dye Macrolex-Yellow 6G 10 parts by weight
6 parts by weight 4 parts by weight Sublimable dye solvent Toluene Methyl ethyl ketone Butanol Ethanol Solvent Toluene 95 95 95 Methyl ethyl ketone 95 95 95 Example 4 Three types of upper dye supply layer 4a, lower dye supply layer 4b and dye transfer contributing layer having the following compositions 8. Prepare ink for 5.
A sublimation type thermal transfer recording medium is formed by coating and drying on a 0 μm polyimide film support 1 so that the lower dye supply layer has a thickness of 3.5 μm, the upper layer dye supply layer has a thickness of 1.0 μm, and the dye transfer contribution layer has a thickness of 1.0 μm. did.

Sublimable dye (manufactured by Bayer AG) Binder polymer solvent toluene 95 95 95 Methyl ethyl ketone 95 95 95 Note that in Example 1, after the dye supply layer was formed.

Before forming the dye transfer contribution layer, the surface of the dye supply layer was examined using a scanning electron microscope S-310A (manufactured by Hitachi, Ltd.) at 200 nm.
When observing wA at 0x magnification, it was confirmed that in Example 1, most of the undissolved particulate dye was surrounded by the binder material, and the surface smoothness of the dye supply layer was improved by the binder material. .

Regarding the sublimation type thermal transfer media of Examples 1 to 4 above, the first
As shown in the figure, an image receiving paper from Hitachi Video Printer VY-50 supply VY-3100, which is an image receiving paper for sublimation type thermal transfer recording, is used as an image receptor 3, and a thermal head 6 is used as printing conditions with an applied power of 455 mW/ As a result of printing multiple times using the same dots, the results shown in Table 1 were obtained. However, the print density (optical density) was evaluated using a Macbeth densitometer RD-914. Furthermore, 1 degree unevenness was evaluated visually. As can be seen from the results shown in Table 1, by improving the irregularities on the surface of the supply layer, the surface of the ink layer becomes smooth, and a decrease in recording density due to white spots etc. when the number of recordings is n=1 can be prevented. Furthermore, since the thickness of the layer contributing to dye transfer becomes uniform, density unevenness is improved.

Table 1 (However, since the density unevenness in Example 2 cannot be evaluated visually alone, the image receptor was uniformly colored cyan and the image was transferred onto the image receptor for evaluation.

In addition, density unevenness was evaluated based on the following criteria with n=1 being the most common.

0 Virtually no by visual inspection Δ Slightly present) [Effect] By lowering the dye concentration of the supply layer in the upper layer, the ability to print multiple times is not deteriorated (because the lower layer has a large amount of undissolved particulate dye), and By improving the surface smoothness of the supply layer (by increasing the binder content ratio in the upper layer), the smoothness of the ink layer surface is improved, the density drop at n=1 is improved, and the thickness of the layer contributing to dye transfer is increased. By making it uniform, density unevenness is also improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the structure of the sublimation type heat-sensitive transfer material of the present invention. 1...Substrate 2...Ink layer 3...Image receptor 4...Dye supply layer 5...Dye transfer contributing layer 6...Thermal head

Claims (1)

[Claims] 1. On the substrate, in order from the substrate side, a dye supply layer consisting of at least an undissolved particulate sublimable dye and an organic binder, and at least a molecularly dispersed sublimable dye and an organic binder. A sublimation type thermal transfer recording medium provided with an ink layer formed by laminating dye transfer contributing layers, where the dye supply layer consists of two or more layers, and the dye concentration of the dye supply layer close to the dye transfer contributing layer is close to that of the substrate. A sublimation type thermal transfer recording medium characterized in that the dye concentration is lower than that of a dye supply layer.