JPH07314907A - Multiple time printing heat transfer sheet - Google Patents

Abstract

PURPOSE:To provide a multiple time printing heat transfer sheet with which multiple time printing is possible and its preparation. CONSTITUTION:After at least a hot-melt ink layer 3 and a porous layer with a porous structure prepd. by applying a coating liq. wherein a cellulose acetate butyrate resin is dissolved into a mixed solvent of a good solvent and a poor solvent are formed in advance, the porous layer is submerged into the hot-melt ink layer by heating to form a constitution wherein a porous layer ink layer 4 wherein at least a part of the hot-melt ink forming the hot-melt ink layer is held in the porous structure is also provided. In addition, the pore diameter of the fine pores in the porous layer is made 0.5-3mum.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermal transfer sheet,
In particular, the present invention relates to a thermal transfer sheet which is excellent in printing performance for many times.

[0002]

2. Description of the Related Art Conventionally, various thermal transfer sheets have been used for thermal recording in thermal printers, facsimiles and the like. These thermal transfer sheets are obtained by providing a heat-meltable ink layer made of heat-meltable ink on a base material such as a polyester film. However, the ink actually transferred by one printing is small in area. Also, if the heat-meltable ink layer in the printed portion remains without being transferred in the thickness direction, it is possible to re-transfer the heat. However, the thickness of the remaining heat-fusible ink layer decreases each time printing is repeated, and when such a thermal transfer sheet is reused, the print density of the previously used print area gradually decreases, and a sufficient desired print density is obtained. I can't.
Even if a certain degree of print density is obtained, density unevenness in print density occurs between the reuse part and the first print part. Therefore, from such a fact, the usual heat transfer sheet is economically extremely uneconomical because most of the heat-fusible ink is not used and is discarded by one printing use.

Therefore, various proposals have been made for a multi-print thermal transfer sheet which enables multi-printing and can be reused, which has a structure in which a hot-melt ink is held in a porous structure.
It has been tried. For example, JP-A-54-68253
In the publication, a resin component forming a porous structure, a colorant component constituting a hot-melt ink and a solid component solid at room temperature, a solvent for the resin component, and a hot-melt ink dissolved and dispersed. A coating liquid composition consisting of a volatile solvent composition that can be applied to a substrate, and by removing the volatile solvent component by drying, a porous structure due to the resin component is developed, and at the same time, a porous structure is formed within the porous structure. A multi-print thermal transfer sheet is disclosed in which an ink layer having a structure holding a hot-melt ink is formed. Further, Japanese Patent Application Laid-Open No. 55-105579 discloses a multiple-printing thermal transfer sheet having a structure in which a porous structure is formed in advance and a hot melt ink is impregnated to form an ink layer. That is, a resin composition forming a porous structure, a foaming agent component, a coating liquid composition consisting of a solvent component and the like is applied to a substrate, the solvent component is dried, and the porous structure is first expressed by the foaming agent component, Then, a heat-meltable ink is applied to the porous structure to impregnate the porous body with the ink to form an ink layer. In addition, JP-A-60-23489
No. 0 discloses a structure in which a porous structure is formed and then a heat-meltable ink is applied thereon to impregnate the porous structure with the ink to form an ink layer. In the case of Japanese Laid-Open Patent Publication No. 55-105579, it is necessary to impregnate a large amount of ink into the porous structure in order to increase the printing density. It has been disclosed that an adhesive intermediate layer is provided between the base material and the porous structure in order to prevent this from being easily peeled off. In addition, JP-A-60-402
According to Japanese Patent Laid-Open No. 93, a porous structure is formed separately, but the order of formation consists of a resin component, a foaming agent component, a solvent component, etc. which form a porous structure on the heat-meltable ink layer. A configuration is disclosed in which a coating composition is applied, a solvent component is dried, and a foaming agent component is foamed by heating to form a porous layer. With this configuration, the ink penetrates into the porous layer during thermal transfer and further passes through to reach the printing surface.

[0004]

However, according to the configuration of Japanese Patent Laid-Open No. 54-68253, heat-melting is performed in order to simultaneously form the porous structure and hold the heat-melting ink inside the porous structure. It is possible to retain a large amount of the functional ink, but if the amount is too large, the porous structure does not develop as a structure, and the original purpose of printing many times cannot be achieved. Moreover, since the thermal transfer sheet according to this method simultaneously holds the porous structure and the ink in the structure, the ink is fused to the eyes of the porous structure with a large number of printings and the ink flows out. There is a drawback that the amount is reduced and the print density is reduced. Further, in the structure of Japanese Patent Laid-Open No. 55-105579, since the heat-meltable ink is impregnated into the inside of the porous structure already formed on the substrate in a heat-melted state, it is replaced with air in the porous structure. As a result, it is difficult to sufficiently impregnate a deep part, and as a result that impregnation takes a long time, voids remain in the porous structure, resulting in a decrease or variation in print density. Further, even in the configuration of Japanese Patent Laid-Open No. 60-234890, there is also a problem due to the replacement of air in the porous structure with the heat-meltable ink. Further, in the constitution of JP-A-60-40293, a layer having a porous structure is formed on the heat-meltable ink layer already formed on the substrate, and the heat-meltable ink forms the porous layer at the time of thermal transfer. Although it is a permeation mechanism, since a foaming agent is used to form the porous layer, it is difficult to create a uniform porous diameter, and there are variations in print density, and a large porous diameter is also possible. Has low mechanical strength and has a drawback that the porous layer is destroyed during printing and the entire ink is transferred. Further, after forming the heat-fusible ink layer, a layer having a porous structure is formed by coating a coating liquid comprising a good solvent and a poor solvent on the heat-fusible ink layer, and the heat-meltable ink is heated in the porous layer. A method of infiltrating the ink is also disclosed in Japanese Patent Laid-Open No. 63-128989. According to this method, a homogeneous porous structure can be formed and the above problems can be solved, but the film strength at the time of printing many times, In terms of heat resistance and the like, sufficient performance was not obtained. Therefore, it is an object of the present invention to provide a multi-print thermal transfer sheet which is excellent in multi-print performance and which solves the above drawbacks.

[0005]

In order to solve the above-mentioned problems and to achieve the object, a multi-printing thermal transfer sheet of the present invention comprises:
At least one heat-fusible ink layer on one surface of the substrate,
On top of that, a coating solution prepared by dissolving a cellulose acetate butyrate resin in a mixed solvent consisting of a good solvent and a poor solvent for the resin is used to utilize the difference in evaporation rate between the good solvent and the poor solvent when coating and drying. And forming a porous layer having a porous structure, and then forming a heat-meltable ink layer in the porous layer, wherein at least a part of the heat-meltable ink is permeated by heating. The configuration is characterized by that. In addition, the pore size of the pores of the porous layer is 0.5 to 3
It is also characterized by being μm.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an embodiment of the multi-print thermal transfer sheet of the present invention. In the multi-print thermal transfer sheet 1 of the present invention illustrated in FIG. 1, at least a part of the heat-meltable ink forming the base material 2, the heat-meltable ink layer 3, and the heat-meltable ink layer 3 has a porous structure. The ink layer 5 is composed of the heat-fusible ink layer 3 and the porous ink layer 4. A known slip layer 6 may be provided on the other surface of the base material. Further, although not shown, the slip layer side of the base material may be subjected to known easy adhesion by forming a primer layer or the like for the purpose of improving adhesion between the slip layer and the base material.

As the base material 2 of the multi-print thermal transfer sheet 1 of the present invention, known materials conventionally used for thermal transfer sheets can be used as they are, and other materials can also be used, and there is no particular limitation. Not done. Preferred base materials include, for example, polyester, polypropylene,
Cellophane, cellulose acetate, polycarbonate, polyethylene, polyvinyl chloride, polystyrene, nylon, polyimide, polyvinylidene chloride, polyvinyl alcohol, fluororesin, chlorinated rubber, plastic films such as ionomers, paper such as condenser paper, paraffin paper, non-woven fabric And the like, or a composite base material of them may be used. The thickness of the base material 2 can be changed depending on the material so that its strength and thermal conductivity are appropriate, but its thickness is preferably, for example, 2 to 25 μm. Further, as described above, the back surface of the base material 2 may be provided with the slip layer 6 that prevents thermal fusion with the thermal head and improves the slipperiness.

In order to obtain the multi-print thermal transfer sheet of the present invention, a coating liquid for forming a heat-meltable ink layer, which mainly comprises a colorant component and a binder component that disperses or dissolves the colorant component with respect to the above substrate. To form a heat-meltable ink layer 3, and a porous layer having a porous structure thereon is formed thereon, and then the porous layer is submerged in the heat-meltable ink layer 3, The heat-meltable ink of the heat-meltable ink layer is permeated into the porous layer to form the porous ink layer 4.

As the colorant component of the heat-meltable ink layer 3, among known organic or inorganic pigments or dyes, those having good characteristics as a recording material, for example, sufficient printing density, light, Those that do not discolor due to heat, temperature, etc. are preferable. Further, it may be a substance which is colorless when not heated but develops a color when heated, or a substance which develops a color when brought into contact with a material applied to a transfer material. In addition to the colorants forming cyan, magenta, yellow, and black, colorants of various other colors can be used.

As the binder component, various known waxes are mainly used, and if necessary, mineral oil, vegetable oil,
Higher fatty acids such as stearic acid, plasticizers, thermoplastic resins,
What added various additives, such as a filler, is used.

Examples of the wax include microcrystalline wax, ester wax, carnauba wax and paraffin wax. Furthermore, Fischer-Tropsch wax, various low molecular weight polyethylene, wood wax, beeswax, spermaceti wax, ivowa wax, wool wax, shellac wax, candelilla wax, petrolactam,
Partially modified wax, fatty acid ester, fatty acid amide, etc.
Various waxes are used. These waxes facilitate the sinking of the porous layer to the heat-meltable ink layer, and the heat-meltable ink is transferred from the porous layer to the printing surface by a suitable printing energy so that a sufficient print density can be obtained. Melting point is 50 to 90 ° C, and melt viscosity at 100 ° C is 1
It is preferably in the range of 0 to 1000 mPa · s.

If necessary, a thermoplastic resin having a relatively low melting point may be added to the binder component to adjust the fluidity and viscosity of the heat-meltable ink, and the flexibility and adhesiveness to the base material and transfer material. Etc. can be improved. Examples of such a thermoplastic resin include ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid ester copolymer (EEA), polyethylene, polystyrene, polypropylene, polybutene, petroleum resin, vinyl chloride resin,
Vinyl chloride-vinyl acetate copolymer, polyvinyl alcohol, vinylidene chloride resin, methacrylic resin, polyamide, polycarbonate, fluororesin, polyvinyl formal, polyvinyl butyral, acetyl cellulose,
Examples thereof include nitrocellulose, polyvinyl acetate, polyisobutylene, ethyl cellulose, polyacetal and the like, but those having a relatively low softening point conventionally used as a heat-sensitive adhesive, for example, a softening point of 50 to 80 ° C. are preferable. .

Further, in order to impart good heat conductivity and heat melt transferability to the heat meltable ink, a heat conductive substance may be blended as a filler of the binder component. Examples of such fillers include carbonaceous materials such as carbon black, metals such as aluminum, copper, tin oxide, molybdenum disulfide, and metal compounds.

To form the heat-meltable ink layer 3 on the substrate 2, the colorant component and the binder component described above are added,
Further, water, a coating liquid for forming a heat-meltable ink layer in which a solvent component such as an organic solvent is blended and adjusted as necessary, a conventionally known hot melt coat, hot lacquer coat, gravure coat, gravure reverse coat, roll coat, etc. Method. There is also a method of forming using an aqueous or non-aqueous emulsion coating liquid. The thickness of the heat-fusible ink layer varies depending on the number of times printing is set, but
About 30 μm is preferable. If it is less than 5 μm, the printing density after the second printing is lowered, and if it exceeds 30 μm, a large amount of printing energy is required, which is not preferable.

The porous ink layer 4 is a layer in which the above-mentioned heat-meltable ink has penetrated into a porous layer having a porous structure having fine continuous pores, and the heat-meltable ink heated at the time of printing. The ink flows in the fine holes and is transferred to the printed surface, so that the heat-meltable ink is transferred. The resin forming the porous layer is insoluble in the heat-meltable ink, and has heat resistance and physical strength to the extent that structural loss does not occur at the temperature at which the heat-meltable ink undergoes flow transition, Is not retained on the printing surface but is retained and retained on the thermal transfer sheet side. As a result of such a porous structure being formed on the surface of the heat transfer sheet, the heat fusible ink layer initially provided on the substrate is controlled to prevent the transfer of all layers in the thickness direction, and the porous structure is formed. The heat-meltable ink remaining in the structure or as a heat-meltable ink layer below the ink is gradually consumed after each printing, and reprinting with little change in print density is possible.

As a resin for forming such a porous layer, cellulose acetate butyrate resin (CAB) is used.
Is desirable. When expressing a porous structure by the method described below, the cellulose acetate butyrate resin,
It exhibits excellent performance in terms of heat resistance and film strength (fatigue properties) during multiple printing.

As a method for forming a porous structure, the resin is dissolved in a mixed solvent of a good solvent having good solubility in the resin component and a poor solvent having poor solubility or no solubility. It is formed by applying a coating liquid. In addition, in adjusting the mixed solvent, the good solvent and the poor solvent should be mutually soluble at least within the range of preparation. Further, a solvent having no solubility may be referred to as a non-solvent, but here, a non-solvent in this sense is also referred to as a poor solvent. In general, water is a solvent that is insoluble in a resin other than a specific resin, but the poor solvent here also includes water. Water can also be used as long as it can be dissolved with other good solvent and poor solvent used together with water.

The solvent used in the above method for forming the porous structure is not limited to simply combining the good solvent and the poor solvent, and the good solvent to be combined needs to have a higher evaporation rate than the poor solvent. Because, in the process of applying the coating solution in which the resin is dissolved in the mixed solvent and then drying,
The good solvent evaporates more than the poor solvent from the still undried liquid coating film applied, whereby the resin and the poor solvent are phase-separated, and the poor solvent forms fine droplets. When the solvent is completely evaporated, pores of the same size as the original separated poor solvent liquid remain in the coating film, and a porous structure is developed.

In the case of the cellulose acetate butyrate resin used in the present invention, such a mixed solvent system of a good solvent and a poor solvent specifically uses, for example, the following solvents. Examples of the good solvent include acetone, methyl ethyl ketone, methyl propyl ketone, cyclohexanone, isophorone, methyl acetate, ethyl acetate, tetrahydrofuran, dimethylformamide, diacetone alcohol, methylene chloride and the like. On the other hand, examples of the poor solvent include methyl n-amyl ketone, methyl isoamyl ketone, methyl isobutyl ketone, isobutyl isobutyrate, n-butyl acetate, isobutyl acetate, isopropyl acetate, methanol, ethanol, propanol, isopropyl alcohol, isobutanol, n. -Butanol, toluene and the like.

The mechanism by which a porous structure is formed by applying a coating solution comprising a resin and a good solvent and a poor solvent is that the resin dissolved in the mixed solvent initially has a molecularly homogeneous distribution in the solution. However, as the solubility of the mixed solvent decreases in the drying process described above, the ratio of the interaction between the good solvent and the resin decreases, and the interaction between the resin molecules becomes large in comparison. The resin molecules tend to associate with each other, and the distribution of the resin molecules becomes heterogeneous. There, coacervation occurs, the resin and the poor solvent undergo microphase separation, and the resin gels and becomes non-fluidized. It is considered that when the solvent is completely evaporated, pores of the same size as the original separated poor solvent liquid remain in the coating film, and the voids are connected to form an open cell porous structure having an open structure. .
The compounding ratio of the resin, the good solvent and the poor solvent is appropriately adjusted depending on the interaction strength of these three, the evaporation rate and the difference between the good solvent and the poor solvent, and the target porous structure. is there. However, a process is required in which the resin is microphase-separated with the evaporation of the solvent, and the resin gelates to lose its fluidity, and a porous structure is formed through the gelation. If the amount of the poor solvent is too small, microphase separation does not occur and the resin concentration increases as the solvent evaporates, resulting in incompatibility of the resin, resulting in a glass-like homogeneous coating film, and a porous structure cannot be formed. In addition, since the porous structure having a large porous diameter is formed when the amount of the poor solvent is increased, the thermal transfer amount is increased and the thermal transfer sheet having a high print density can be obtained, but the number of printable times is decreased, and the porous layer Strength decreases. In this way, the compounding amounts of the resin, the good solvent and the poor solvent are adjusted in consideration of the porous diameter, the strength of the porous layer, the number of printings, the printing density and the like.

As described above, the formation and structure of the porous layer are determined by the interaction between the solvents, the interaction between the solvent and the resin molecules, the interaction between the resin molecules, and the relative size of these with respect to time. The change is controlled to control the continuity of pores, the discontinuity, the size of pores, the distribution of pores in the film thickness direction, and the like.

Thus, an intermediate product of a thermal transfer sheet is obtained in which a porous layer having a porous structure composed of open cells is formed on the heat-meltable ink layer formed on the substrate.
The porous layer is then allowed to settle within the hot melt ink layer. To settle the heat transfer sheet, the heat-meltable ink layer is melted and fluidized by heating or the like, and the heat-meltable ink permeates into the porous layer by a capillary phenomenon or the like so that the heat-meltable ink layer is melted. Let the layers get in. At this time, an appropriate pressure may be applied to the layer between the porous layer and the heat-meltable ink layer so that the subsidence can be performed more quickly. In addition,
If the porous layer settles under the heat-fusible ink layer, that is, even inside, it does not achieve the purpose of its transfer control, but such a phenomenon does not occur as long as it sinks due to the capillary phenomenon.

In this way, a porous ink layer containing a heat-meltable ink in the porous layer is obtained. The thickness of the porous ink layer is appropriately adjusted depending on the porosity and the like.
It is preferably about 5 to 4.0 μm. If it is too thin, the physical strength of the porous ink layer will decrease, and if it is too thick, a large amount of printing energy will be required and the printing density will decrease. Further, the size of the pores into which the heat-meltable ink enters is 0.5 to 3 μm.
A value of m is preferable because the amount of transferred ink can be made uniform. If the pore size is too small, the amount of transfer due to the outflow of ink will decrease and the printing density will decrease, while if it is too large, the number of times of printing will decrease and the physical strength of the porous ink layer will decrease, which is not preferable.

Finally, needless to say, the multi-print thermal transfer sheet of the present invention can be applied as color printing, and a multi-color multi-print thermal transfer sheet is also an embodiment of the present invention. Further, the thermal transfer printer can be applied to either a line type or a serial type.

[0025]

As described above, in the multi-time printing thermal transfer sheet of the present invention, after forming the heat-meltable ink layer on one surface of the substrate, the porous layer having the porous structure is formed thereon, Next, the porous layer is allowed to sink into the hot-melt ink layer, thereby allowing the hot-melt ink to enter the porous structure from the lower side of the porous layer. As a result, the entry of the heat-meltable ink into the porous structure occurs from the back surface side of the porous layer, and the air in the porous structure escapes to the front surface side without obstruction. Can be degassed quickly and easily, and the inside of the porous structure is sufficiently filled with the hot-melt ink. A porous ink layer free of residual air is obtained. In order to form a porous structure, the resin and a good solvent and a poor solvent for the resin are formed by coating with a coating liquid.
By properly adjusting these components, blending ratio, and coating conditions,
The porous structure is freely controllable, so that a homogeneous and desirable porous structure is formed. In particular, by forming a porous structure with a cellulose acetate butyrate resin, a desirable porous structure having excellent heat resistance and film strength (mechanical strength, fatigue property) after printing many times can be obtained.
Further, by limiting the pore size of the pores of the porous layer to a specific range, the ink transfer amount becomes constant. By the porous ink layer thus obtained, the transfer amount control for gradually transferring the transfer amount of the heat-meltable ink to the printing surface is performed. In addition, since the heat-meltable ink layer in which the heat-meltable ink is sufficiently stored is located below the porous ink layer, the heat-meltable ink consumed for printing inside the porous ink layer is replenished from the bottom. As a result, continuous printing can be performed many times.

Next, the multi-print thermal transfer sheet of the present invention will be described more specifically with reference to Examples and Comparative Examples. In addition,
In the text, parts or ratios are based on weight unless otherwise specified.

Example 1 A polyethylene terephthalate film having a thickness of 4.5 μm was used as a base material, and a coating liquid for forming a heat-meltable ink layer having the following composition was formed on one surface of the film with a roll coater to a thickness of 6 g / m ² . And a coating solution for forming a porous layer having the following composition with a gravure coater, and the solvent component is dried at a temperature of 80 ° C. to a thickness of 2 μm.
(0.5 g / m ² ), a porous layer having a pore size of 0.5 to 25 μm is formed, and the porous layer is dropped into the heat-meltable ink layer by continuing heating at 80 ° C. A multi-time printed thermal transfer sheet of the present invention was obtained as a porous ink layer containing ink. Coating liquid for forming heat-fusible ink layer A coating liquid having the following composition was dispersed in a sand mill for 2 hours while heating at 120 ° C. Carnauba wax 10 parts Paraffin wax (HNP-3 manufactured by Nippon Seiro Co., Ltd.) 65 parts Ethylene / vinyl acetate copolymer 10 parts (Evaflex 410 manufactured by DuPont) Carbon black 15 parts Coating liquid for forming a porous layer Cellulose acetate butyrate resin 5 parts Solvent (acetone: n-butanol = 1: 1.25) 95 parts

Example 2 A multi-print thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the coating composition for forming a porous layer had the following composition. Coating liquid for forming a porous layer Cellulose acetate butyrate resin 5 parts Solvent (acetone: ethanol = 1: 1.5) 95 parts

Example 3 A multi-print thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the coating composition for forming a porous layer had the following composition. Coating liquid for forming a porous layer Cellulose acetate butyrate resin 5 parts Solvent (methyl ethyl ketone: n-propanol = 1: 1.2) 95 parts

Example 4 A multi-print thermal transfer sheet of the present invention was obtained in the same manner as in Example 1 except that the coating composition for forming a porous layer had the following composition. Coating liquid for forming a porous layer Cellulose acetate butyrate resin 5 parts Solvent (methyl ethyl ketone: n-butanol = 1: 1.2) 95 parts

Comparative Example 1 A porous ink layer-forming coating solution having the following composition was applied on one surface of the same substrate as in Example 1 by a gravure coater to a thickness of 6.5 μm to give a porous film. A multi-time printing thermal transfer sheet having a porous ink layer having the structure and the retention of the heat-meltable ink inside thereof was obtained. Coating liquid for forming porous ink layer Carnauba wax 10 parts Paraffin wax (HNP-3 manufactured by Nippon Seiro Co., Ltd.) 65 parts Ethylene / vinyl acetate copolymer 10 parts (Evaflex 410 manufactured by DuPont) Carbon black 15 Part Cellulose acetate butyrate resin 6 parts Solvent (methyl ethyl ketone: toluene = 2: 1) 24 parts As a result of the printing test, the printing density of this multi-time printing thermal transfer sheet was drastically reduced.

Comparative Example 2 The order of applying the heat-fusible ink layer forming coating solution and the porous layer forming coating solution used in Example 1 was reversed on one surface of the same substrate as in Example 1. First, a porous layer having a thickness of 2 μm is first formed on the substrate, and then a heat-meltable ink layer having a thickness of 6 μm before permeation is applied on the porous layer, followed by heating at 80 ° C. for 3 minutes. Then, the heat-meltable ink was submerged in the porous layer to obtain a printed thermal transfer sheet many times. This multi-print thermal transfer sheet had a high print density at the first time, probably because the heat-meltable ink layer did not sink sufficiently, but the print density after that was low and the print density was inferior in uniformity.

Comparative Example 3 A multi-time printing thermal transfer sheet was obtained in the same manner as in Example 1 except that the coating composition for forming a porous layer had the following composition. Coating liquid for forming a porous layer Cellulose acetate propionate resin 5 parts Solvent (methyl ethyl ketone: water = 9: 1) 95 parts This thermal transfer sheet tears the porous film by printing 3 to 4 times,
All the transfer occurred and the print density suddenly dropped.

Using the multi-print thermal transfer sheets of the above-mentioned Examples and Comparative Examples, a print test was conducted at the same location under the following conditions, and the print density was measured for each number of prints to obtain the results shown in Table 1. Printing conditions Equipment: Test printer equipped with a thin film thermal head Printing energy: 0.6 mJ / dot Transfer paper: Fine paper (Beck smoothness 80 seconds)

[0035]

[Table 1]

[0036]

EFFECT OF THE INVENTION Since the multi-print thermal transfer sheet of the present invention is constructed as described above, the porous structure of the porous ink layer is excellent in mechanical strength and the porous structure collapses or breaks during printing. It is possible to obtain a uniform print density without any transfer, and with excellent homogeneity of the porous structure. Further, even if the printing is repeated, the number of times the high-density printing density is maintained is long, and excellent economic efficiency is exhibited.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a multi-print thermal transfer sheet of the present invention.

[Explanation of symbols]

 1 Multi-time thermal transfer sheet 2 Base material 3 Heat-meltable ink layer 4 Porous ink layer 5 Ink layer 6 Slip layer

Claims (2)

[Claims] 1. A coating liquid comprising at least a heat-fusible ink layer on one surface of a base material, and a cellulose acetate butyrate resin dissolved thereon in a mixed solvent comprising a good solvent and a poor solvent for the resin. After forming a porous layer having a porous structure by utilizing the difference in evaporation rate between a good solvent and a poor solvent when coating and drying, heat for forming the heat-meltable ink layer in the porous layer A multi-print thermal transfer sheet comprising: a porous ink layer in which at least a part of the fusible ink is permeated by heating. 2. The pore size of the pores of the porous layer is 0.5 to 3 μm.
The multi-print thermal transfer sheet according to claim 1, wherein