JPS6317639B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel thermal transfer recording medium having halftones. More specifically, the present invention relates to a thermal transfer recording medium capable of forming not only solid areas but also halftone halftone areas as a copied image on a copy sheet. Conventionally, as a thermal transfer recording element used in thermal recording devices such as thermal printers and thermal facsimile machines, a thermally transferable heat-melting ink layer is provided on a base material, and the ink layer is stacked so as to face plain paper. 2. Description of the Related Art A thermal transfer recording element is known in which a copy image corresponding to a printing pattern is transferred from the ink layer onto plain paper by printing with a heating body such as a thermal head or a thermal pen on the back surface of a substrate. Unlike conventional thermal paper, such a thermal transfer recording element has the advantage that the printed image is excellent in durability and cannot be easily tampered with because the printed image is formed on plain paper. The printed image transferred to the ink can only be a duplicate image that is completely covered with ink, which is the same as a so-called solid painting, and it is not possible to form an intermediate color.
Therefore, it has the disadvantage that it cannot be used in cases where it is necessary to express shades of color, such as in photographs and graphics. The present invention has been made with the aim of eliminating the above-mentioned drawbacks and providing a new thermal transfer recording medium that can also form half-tone colors. FIG. 1 is a schematic enlarged cross-sectional view showing an embodiment of the recording medium of the present invention, and FIGS. 2 and 3 show the halftone dots and portions of the recording medium shown in FIG. A schematic explanatory diagram showing a state in which a solid portion is formed, and FIGS. 4 and 5 are respectively schematic enlarged sectional views showing other embodiments of the recording medium of the present invention. That is, the recording medium of the present invention, as shown in FIG. and a large number of spot-shaped heat-fusible ink layers B arranged at intervals from each other, and characterized in that the spot-like heat-fusible ink layer B has a lower melting temperature than the hot-fusible ink layer A. That is. In the recording medium of the present invention, when printing is performed from the back side of the base material 1 by the heating element 2 heated to a certain predetermined temperature, only the spot-shaped heat-fusible ink layer B remains as shown in FIG. A copy image corresponding to the printing pattern of the heating element 2 is melt-transferred onto a copy sheet 3 such as plain paper, and halftone dots 4 exhibiting halftones are formed. Furthermore, when the heating body 2 is heated to a temperature higher than the predetermined temperature and printing is performed in the same manner as described above, the heat-fusible ink layers A and B are melted and mixed together as a copy image as shown in FIG. The matching solid area 41 is copy sheet 3
formed on top. However, in the present invention, by changing the temperature of the heating element 2, the copy sheet 3
Desired halftone dot portions 4 and solid portions 41 can be melt-transferred thereon. The halftone dots 4 exhibit halftones similar to the halftone dots formed by gravure printing, letterpress printing, etc. in ordinary printed matter (for example, newspapers, etc.). When the color is black, halftone dots form a gray halftone. Further, the solid portion 41 refers to a state where the copy sheet 3 is completely covered with ink. The base material 1 in the present invention has appropriate heat resistance strength and thermal conductivity of 3.0×10 ^-4 cal/
There are no special restrictions on the material as long as it has excellent heat resistance and thermal conductivity of sec/cm/°C or higher; for example, paper such as plain paper, synthetic paper, laminated paper, polyethylene, polystyrene, etc. Resin films such as polypropylene are preferably used. Further, the thickness of the base material 1 is preferably approximately 60 μm or less in order to obtain good thermal conductivity. The heat-melt ink layer A is formed by hot-melt coating with a composition comprising a thermally conductive substance, a colorant, a binder, a softener, etc., or by solvent coating with a coating liquid in which the composition is dispersed in an appropriate solvent. 3 each formed by
~20g/ ^m2 layer. The spot-shaped hot-fusible ink layer B in the present invention has almost the same composition as the hot-fusible ink layer A, and has a similar color;
It is required to have a melting temperature lower than . This spot-shaped hot-fusible ink layer B is formed by applying hot-fusible ink layer B, which is melted by gravure printing or letterpress printing, onto a hot-fusible ink layer A that has been uniformly coated on the base material 1 in advance at predetermined halftone dots. It is formed by coating in the form of In this way, a large number of spot-shaped hot-fusible ink layers B arranged at intervals are formed on the hot-fusible ink layer A as halftone dots. The spot-like heat-fusible ink layer B has a thickness of 2
The halftone dot area is formed in the shape of a cone, pyramid, truncated cone, truncated pyramid, cylinder, prism, etc. of approximately 20μ and indicates the proportion of the halftone dot area in the unit area. It is preferably formed in a proportion of about 5 to 70%, preferably 30 to 60%. The colorant to be added to the hot-melt ink layers A and B is not particularly limited as long as these ink layers A and B are formed to have similar colors; Pigments and dyes used in the layer are preferably used, and examples of black dyes and pigments include nigrosine base, oil black, graphite, and carbon black. Further, examples of the thermally conductive substance contained in these ink layers A and B include metal powders having good thermal conductivity such as aluminum, copper, tin, and zinc. Such a thermally conductive material promotes the heat conduction effect of melting, softening or sublimating the thermofusible ink layer. In the present invention, heat-fusible ink layers A and B
The binder and softener contained in each of the ink layers A and B must be selected so that a predetermined melting temperature is imparted to each ink layer A and B, respectively. Must be. Therefore, it is preferable that the difference in melting temperature between the hot-melt ink layers A and B is about 10°C or more, especially about 20 to 40°C. When melting and transferring only the heat-melting ink layer B, there is a risk that the heat-melting ink layer A will also be transferred at the same time.
Undesirable. The heat-fusible ink layers A and B are prepared so that their melting temperatures are 70 to 80°C and 50 to 60°C, respectively, and the difference in their melting temperatures is within the above range. Therefore, in the present invention, the binder agents contained in the heat-melting ink layers A and B, respectively, include waxes such as wood wax, beeswax, ceresin wax, spermaceti wax, low molecular weight polyethylene,
It must be determined appropriately from oxidized waxes, ester waxes, etc., taking into account their melting temperatures. In addition, the softener as well as the binder agent,
For example, polyvinyl acetate, polystyrene, styrene-butadiene copolymers, cellulose esters, cellulose ethers, acrylic resins,
It is appropriately determined from petroleum resins, stearic acid, lanolin, vaseline, etc. based on their melting temperatures. These thermally conductive substances, binders, softeners, and colorants are contained in 2 to 30 parts and 5 to 70 parts, respectively, of 100 parts (parts by weight, same hereinafter) of the total amount in both heat-melting ink layers A and B. part, 5 to 35 parts, and 2 to 25 parts. Next, specific formulation examples of each of the heat-melting ink layers A and B obtained in this manner and their respective melting temperatures are shown in the following table.

[Table] *The melting point is that of the paraffin wax used.
In the present invention, as shown in FIG. 4, a release layer 5 is provided between the heat-fusible ink layers A and B, so that the heat-fusible ink layer B is peeled off from the hot-fusible ink layer A during melt transfer. You can make it easier. Such a release layer may include, for example, a wax-like material with low mechanical strength [e.g., paraffin wax (melting point 48-63°C), stearic acid, cetyl alcohol,
Waxes such as low molecular weight polyethylene, higher fatty acids, higher alcohols, etc.] or substances with excellent release properties (e.g. silicone resins, fluorine resins, etc.)
A layer of 0.3 to 3 microns thick is preferably made of a material such as Sielatsuk etc. Further, as shown in FIG. 5, the present invention provides hot-melt ink layers A and B as described above on one side of the base material 1, and a solid or semi-solid acid and ink layer on the other side of the base material 1. A thermosensitive coloring layer 6 containing an integral layer of a dye precursor that develops color by reacting with an acid.
and the thermosensitive coloring layer 6 is configured to adjust the tone of the color developed by the coloring reaction according to the respective melting temperatures of the thermofusible ink layers A and B. It also provides. As shown in FIGS. 1 to 3 or 4, such recording elements are different from each other on the copy sheet 3 by the hot-melt ink layers A and B and, if necessary, the release layer 5 provided between them. At the same time as the color copy images 4 or 41 are formed, the heat-sensitive color forming layer 6 on the upper surface of the base material
A printed image (not shown) having a tone corresponding to 1 is formed. The heat-sensitive coloring layer 6 has a layer of about 10 μm in which an organic or inorganic acid that is solid or semi-solid at room temperature and a dye precursor that develops color by reacting with the acid are uniformly dispersed and fixed together using a suitable binder agent. The layers are as follows. It is preferable that the dye precursor is configured so that the color exhibited by the coloring reaction is approximately the same as the color of each coloring material contained in the heat-melting ink layers A and B. When the dye precursor exhibits a dark color such as black or blue, the dye precursor may be, for example, crystal violet lactone, 3,7
-bisdiethylaminofluorane, 4,4'-bisdimethylaminopiperazine hydrol, etc., and when it exhibits a light red color, for example, 4-hydroxy-4'-dimethylaminotriphenylmethane lactone. , 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, and the like. Examples of the organic or inorganic acids include benzoic acid, tartaric acid, citric acid, salicylic acid, stearic acid, gallic acid, bisphenol A, naphthoic acid, pyrophosphoric acid, and metaphosphoric acid. When the recording medium of the present invention thus obtained is printed at different temperatures by the heating body 2,
It is possible to form halftone dots and solid areas 41 on the copy sheet in accordance with each temperature, and it is extremely clear compared to conventional recording media that can only form copied images consisting of solid areas only. be.

[Brief explanation of the drawing]

FIG. 1 is a schematic enlarged cross-sectional view showing one embodiment of the recording medium of the present invention, and FIGS. 2 and 3 show how halftone dots and solid areas are formed by heat applied from a heating element, respectively. The schematic explanatory drawings shown in FIGS. 4 and 5 are schematic sectional views showing other embodiments of the recording element of the present invention, respectively. (Main symbols in the drawings) 1: Base material, A: Hot-fusible ink layer, B: Spot-shaped hot-fusible ink layer,
4: Halftone area, 41: Solid area.

Claims (1)

[Scope of Claims] 1. A base material, a heat-fusible ink layer A uniformly applied on the base material, and a plurality of dots arranged at intervals on the ink layer A in the form of halftone dots. The spot-like hot-fusible ink layer B is composed of the hot-fusible spot-like ink layer B, and the spot-like hot-fusible ink layer B is
A thermal transfer recording medium having halftones characterized by having a melting temperature lower than . 2. The recording medium according to claim 1, wherein the hot-fusible ink layer A and the spot-like hot-fusible ink layer B are inks having similar colors.