JPS62111784A - Ink film for thermal transfer recording - Google Patents

Abstract

PURPOSE:To enable a sufficient color development density to be realized with slight quantity of heat, by a method wherein; in an ink film for thermal transfer recording consisting of a substrate and an ink layer formed thereon and composed of a dye and a binder, a material which vaporizes when thermal transferred to act on the binder in the thermal transfer film and an image receive paper dyeing layer so as to accelerate diffusion of dye vapor is contained in the ink. CONSTITUTION:At least one among compounds shown by a formula is contained in an ink as a material which vaporizes prior to a dye to act on a binder and a dyeing layer and is smaller than the dye in molecular weight and heat of vaporization and cannot react with the dye to produce a complex or salt. The compounds as shown in the formula take identical effects regardless of the variety of the compounds mixed in the ink in the thermal transfer film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] In particular, the present invention relates to a thermal transfer ink film that can be efficiently transferred with a small amount of heat.

[Background of the invention]

Conventionally, a thermal transfer ink film is used, in which ink obtained by dispersing dye in a binder is applied onto a thin heat-resistant sheet such as paper, and heat is heated from the back side with a heat generating head to sublimate only the dye in the ink, resulting in good dyeability. A method has been proposed in which a color image is formed by transferring dye onto an image-receiving paper whose surface is coated with a resin.

The thermal transfer ink film used here increases the color density of the image, produces clear images with high contrast, and reduces the thermal energy from the printer's heat generating head.
In order to extend the life of the heat-generating head, there has been a need to improve the efficiency of sublimation of the dye onto the receiver paper.

In this color copying method, the dye in the ink is heated and sublimated in a short time using a heat-generating head heated to a high temperature of 200 tl' or more, and the dye on the receiving paper is dyed using heat from the hesilica, alumina, metal powder, etc. in the ink. A method has been proposed in which fine inorganic powder with good conductivity is mixed in to improve the efficiency of heat transfer from the heating head to the dye, thereby increasing the sublimation rate of the dye (Japanese Patent Laid-Open No. 79788/1983).

However, in these methods, the amount of inorganic fine powder mixed in is 10 to 100 times the amount of dye, so the dye content in the ink decreases, the total amount of dye vapor is insufficient, and furthermore, the powder prevents the diffusion of dye vapor. Because of this, sufficient color density cannot be obtained. On the other hand, if the amount of ink applied is increased in order to increase the color density, the ink film becomes thicker, resulting in a decrease in heat transfer efficiency, which has the disadvantage that sufficient color density cannot be obtained unless the power applied to the heating head is increased.

[Purpose of the invention]

An object of the present invention is to provide a thermal transfer ink film that can realize sufficient color density with a small amount of heat.

[Summary of the invention]

In order to efficiently transfer the dye from the thermal transfer ink film to the image receiving paper using a small amount of heat, it is necessary to improve not only the rate of heat transfer from the heat generating head to the dye, but also the rate of diffusion of the generated dye vapor.

Since the diffusion rate is proportional to the product of the dye vapor pressure and the diffusion coefficient in the binder or dyed layer of the image receiving paper, it is better to select a material with large values of these values. However, when considering the storage stability of thermal transfer ink films, there are restrictions on the vapor pressure of dyes that can be used and the range of diffusion coefficients of binders or dyed layers. Therefore, we thought that we could achieve our goal if we could increase the diffusion coefficient only during thermal transfer, so we decided to include a substance in the ink that vaporizes during thermal transfer, acts on the binder of the thermal transfer film and the dyed layer of the receiver paper, and promotes the diffusion of dye vapor. Thought.

In general, in polymeric materials such as binders and dyed layers, it is believed that the diffusion coefficient changes significantly after reaching the glass transition temperature (for example, Shigeharu Onogi, "Polymer Materials Chemistry", July 1972, Makoto). Bundo Shinkosha). We believe that if the glass transition temperature is lowered by the action of some kind of substance, the dye diffusion rate will increase and the transfer efficiency can be improved even if the transfer temperature remains the same.
As a result of experimental studies using various compounds, the following points were found.

In order to produce such an effect, it must be a substance that at least evaporates before the dye and acts on the binder and dyed layer. For this purpose, a substance having a smaller molecular weight than the dye is preferable. However, a material with a large heat of vaporization is preferable because it lowers the ink temperature during transfer and reduces the amount of dye vapor. Also, substances that react with dyes to form complex compounds or salts to change the hue are also unsuitable.

It has been found through experiments that the substance shown in the following chemical formula (I) is suitable as a substance that satisfies these conditions.

(In the formula, R1, R1, is a straight chain or branched alkyl group or alkoxy group having 6 or less carbon atoms, a hydrogen atom, a hydroxyl group, a nitro group, a halogen atom, a phenyl group, a carboxy group, an alkyloxycarbonyl group) , carbamoyl group, cyan group, iso7ano group, formyl group, amino group,
Indicates an acetonyl group, a propionyl group, and a phenanyl group.

) (I) The effects exerted by these compounds shown by formula (I) are the same whether they are mixed alone into the ink of the thermal transfer film or when a plurality of compounds are mixed into the ink. (I)
There is a limit on the amount of the compound shown in the formula mixed into the ink (although there is no limit,
The practical upper limit is the amount of ink that causes stickiness on the surface of the ink.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in more detail based on Examples.
The present invention is not limited to these examples.

For the test residue, 0.5 mt of ink of each formulation was coated on a base film (6 μm thick polyethylene terephthalate (PET) film) using a percoater in a size of 10 x 15 crn, and then dried at room temperature to prepare a thermal transfer ink film.

Comparative Example 1 Composition Weight sublimable dye (
BA8F' M430) 2. i Polyamide resin (Henkel Nippon Parsalon) λO1 toluene
9.0g isopropanol
9.0.9 Examples 1 to 1° Additives shown in Table 2 were added to s and oy of the ink of the comparative example to prepare inks of the present invention. A thermal transfer ink film was prepared in the same manner as in the comparative example.

Thermal transfer ink films produced in Table 1 Comparative Examples and Examples 1 to 10 were printed on a thermal printer (heating head resistor 21
0 Ω and head applied pressure of 7.0 OV), the head energization time was set to 0 to 2 Qms, and the input thermal energy was varied to print on image-receiving paper. Next, the reflected color density of this receiver paper was measured using a Macbeth type total densitometer, and the color density characteristics shown in Table 2 were obtained. It is clear from Table 2 that all of the thermal transfer ink films produced in Examples 1 to 10 develop colors at higher densities than those of the comparative examples, provided that the electricity supply time to the heating head is the same. That is, according to the present invention, the efficiency of dye transfer from the thermal transfer ink film to the image receiving paper is improved, and the color density is increased.

〔Effect of the invention〕

According to the present invention, if the thermal energy input to the thermal transfer film is the same, the color density of the image-receiving paper is improved, and conversely, when the color density of the image-receiving paper is the same, the thermal energy input to the thermal transfer film can be reduced. effective.

Claims (1)

[Claims] 1. An ink film for thermal transfer recording in which an ink layer consisting of a dye and a binder is provided on a base material, wherein the ink layer contains at least one compound represented by the following chemical formula (I). An ink film for thermal transfer recording that is characterized by: ▲There are mathematical formulas, chemical formulas, tables, etc.▼…………(I) (However, R_1, R_2, R_3 are straight-chain alkyl groups with 6 or less carbon atoms, branched alkyl groups, alkoxy groups, hydrogen atoms, hydroxyl groups, Nitro group, halogen atom, phenyl group, carboxy group, alkyloxycarbonyl group, carbamoyl group, cyano group, isocyano group, formyl group, amino group,
Indicates an acetonyl group, a propionyl group, and a phenacyl group. )