JP2644999B2 - Thermal transfer ink - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thermal transfer ink required for a hot-melt transfer printer whose field of use is gradually expanding because it is inexpensive, has low noise, and is easy to handle. About.

[Conventional technology and its problems]

Conventional thermal transfer ink binders are mainly waxes such as paraffin and carnauba, and have extremely low viscosity when melted by heat.Therefore, when printing on thermal transfer paper with good smoothness, glossy clear print unique to thermal transfer is obtained. Was giving. However, as the range of application has been expanded, various required characteristics such as printing on paper having a poorer surface smoothness, printing with printing robustness, printing with high transfer sensitivity, and printing for multiple use have been generated. As the required properties become more advanced, it has been found that conventional inks consisting only of wax are too difficult to cope with, and research on resin-based inks has been advanced in various fields. I have.

Resin expected to print on rough surface paper due to high cohesive strength, resin expected to print on rough surface paper, resin expected to print with high strength and robustness, resin expected to print with high transfer sensitivity amorphous, many with strong adhesive force There are resins and the like that are expected to be used once and the possibility of application to thermal transfer is increasing. However, resins generally have a much higher melt viscosity than waxes, and this tendency is particularly remarkable when made into ink. In the thermal transfer system, the viscosity at the time of melting is an important factor in determining the formation of a transferred image on a transfer paper, and directly affects the printing quality. In the hot melt state, if the viscosity is as low as that of the wax ink, a sufficient contact area can be obtained, and high coverage printing can be achieved. In general, a low viscosity comparable to that of wax cannot be achieved during thermal transfer.

Conventionally, oil (such as butyl cellosolve, spindle oil, etc.) has been used to reduce the viscosity of the high-viscosity resin ink. But the addition of oil
If you have bleed-out or blocking issues on storage,
It was difficult to add an amount sufficient to obtain a sufficient viscosity reducing effect.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, added an appropriate thickener according to the purpose to various heat-meltable resins which could not be used conventionally because of high melt viscosity. The present inventors have found that a thermal transfer ink having excellent printing characteristics can be obtained by adjusting the viscosity by the above method, and have completed the present invention.

That is, the present invention provides a melt viscosity of 10,000 to 1,000,000 cps (120 ° C.
Is a solution-type thermal transfer ink constituted by using a resin of the formula (1) as a base binder, and having a melt viscosity of 1 to 600 cps (120 ° C.) for the purpose of reducing the melt viscosity.
) And partially soluble in the solvent used (100 g at 40 ° C)
At least 1 g of at least one type of thickener selected from higher fatty acids, based on 100 parts by weight of the base resin, and a part of the thickener. It is an object of the present invention to provide a solution type thermal transfer ink characterized in that the insoluble portion is contained in the form of fine particles such as emulsion, slurry, or fine powder.

The thermal transfer ink of the present invention is obtained by adding a viscosity reducing agent composed of a wax in order to reduce the viscosity of a resin-based thermal transfer ink having a relatively high melt viscosity and to use it. To a partially insoluble portion of a wax thinner in the form of fine particles such as emulsions, slurries, and fine powders.

By applying the thermal transfer ink of the present invention onto a substrate using an existing gravure coating machine or the like and drying it, the thermal transfer ink sheet can be used without any consideration of the compatibility of the thickener composed of a high-viscosity resin and wax. Can be obtained.

According to the present invention, any combination of a high-viscosity base resin and a wax-based thinning agent is possible, and any high-viscosity resin can be used as an ink binder for thermal transfer.

The resin as a base binder that can be used in the present invention is a resin having a melt viscosity of 10,000 to 1,000,000 cps (measured at 120 ° C.), for example, a polyester resin, a polyamide resin,
Acrylic resin, polystyrene resin, polystyrene acrylic resin, vinyl chloride resin, polyvinyl butyral resin,
Examples thereof include resins having a melting point in the range of 60 to 120 ° C., such as epoxy resins, ethylene vinyl acetate resins, polyurethane resins, and polycarbonate resins, and mixtures thereof.

The low-viscosity reducing agent that can be used in the present invention has a melt viscosity measured at 120 ° C. of 1 to 600 cps, and is partially soluble in the solvent used (at least 1 g dissolved in 100 g solvent at 40 ° C.)
All of them can be used as long as they are at least one kind selected from waxes. However, a wax having a melt viscosity at 120 ° C. of 1 to 400 cps is more preferable.

Examples of the wax that can be used in the present invention include carnauba wax, candelilla wax, oricure wax,
Natural plant waxes such as sugarcane wax, wood wax, natural animal waxes such as beeswax, whale wax, Chinese wax, wool wax, petroleum waxes such as paraffin wax, microcrystalline wax, oxidized paraffin wax, oxidized microcrystalline wax, and montan wax And mineral waxes such as ozokerite, ceresin, lignite wax, and synthetic waxes such as ketone wax, Fischer-Tropsch wax, caster wax, opal wax, armor wax, and accra wax, and modified waxes thereof.

Solvents usable in the present invention include alcohols such as ethanol and isopropyl alcohol, methyl ethyl ketone,
Any solvent can be used as long as it is a solvent generally used in inks and coatings, such as ketones such as methyl isobutyl ketone, aromatic solvents such as toluene and xylene, and water. If necessary, these solvents may be mixed and used.

To produce a thermal transfer ink sheet using the thermal transfer ink of the present invention, at least one layer of the thermal transfer ink of the present invention is applied in contact with the substrate or a coating layer on the substrate, and may be dried. It can also be used together with other constituent layers such as an overcoat layer or a resistive layer for conducting and heating and a conductive layer.

The ink for thermal transfer of the present invention is usually applied onto a substrate by a coating machine or a printing machine. At that time, if the added viscosity reducing agent is completely insoluble in the solvent used, the interaction between the precipitated particles becomes stronger, the structural viscosity increases, the coating is released from the gravure at the time of coating and printing, and the leveling is performed immediately after coating. Is a problem, and it is difficult to obtain a clean coating surface. However, in the present invention, since the added viscosity reducing agent is partially soluble in the solvent used, the structural viscosity can be suppressed, and as a result, good coating properties and printability can be achieved.

〔Example〕

Hereinafter, the effectiveness of the present invention will be illustrated by examples, but the present invention is not limited to these examples.

Example 1 Polyester resin having a softening point of 90 ° C. (melt viscosity at 120 ° C. 2
A solvent-based thermal transfer ink composed mainly of 3000 cps) and having the following composition ratio was prepared.

Separately, a carnauba wax slurry solution using toluene was prepared. This may be a slurry prepared by completely dissolving carnauba wax in hot toluene and then cooling it, or a slurry prepared by adding carnauba wax fine powder to toluene and then dispersing as necessary.

Further, a slurry was added to the ink to prepare ink to ink.

These inks were applied on a 3.5 μm polyethylene terephthalate (PET) film and dried to prepare a thermal transfer ink sheet.

Printing evaluation was performed on the obtained thermal transfer ink sheet using a commercially available thermal transfer printer. The evaluation results are summarized in Table 1. As the addition amount of the carnauba wax slurry increases, the viscosity reduction effect occurs, and the transfer rate and the transfer rate are almost the same as those of the wax ink while maintaining the characteristics of the resin such as the robustness.
It can be seen that a thermal transfer image having a resolution can be obtained.

Comparative Example 1 A thermal transfer image was obtained using the ink of Example 1 under the same conditions as in Example 1.

Table 1 shows the detailed printing results. In this case, since the ink had an extremely high viscosity, sufficient transfer was not obtained, and a transferred image having a low coverage was obtained.

Example 2 Polyamide resin having a softening point of 86 ° C (melt viscosity at 120 ° C of 175)
00), polystyrene acrylic resin with a softening point of 102 ° C (120 ° C
Example 1 was prepared using a solvent-based ink composed mainly of a polystyrene resin having a softening point of 78 ° C. (melt viscosity of 50,000 at 120 ° C.) or a polystyrene resin having a softening point of 78 ° C. (solvent: toluene / methyl ethyl ketone = 1/1). A 1: 1 mixed slurry of polyethylene wax (melt viscosity at 120 ° C. 30 cps) and carnauba wax prepared in the same manner as in Example 1 in a resin-to-resin ratio of 10,2
The inks were adjusted by adding 0, 30, 40, 50% and 150%.

When the same printing evaluation as in Example 1 was performed, the results shown in Table 2 were obtained, and it was confirmed that there was a clear viscosity reducing effect.

Example 3 Paraffin wax having a melting point of 105 ° C. (melt viscosity at 120 ° C.)
A slurry was prepared in toluene using 23 cps) and added to the polyester resin described in Example 1 at a resin weight ratio of 30% to prepare an ink. When the same printing evaluation as in Example 1 was performed, the results shown in Table 3 were obtained.

As is clear from Table 3, an ink having a sufficient viscosity reducing effect and having good printing characteristics was prepared. As described above, it was found that even a high melting point wax having a melting point exceeding 100 ° C. exhibited a viscosity reducing effect if the melt viscosity was low.

Example 4 Polyamide resin having a softening point of 106 ° C. (melt viscosity at 120 ° C. 12
0000 cps) was emulsified in a usual manner to prepare an emulsion ink. Separately, denatured microcrystalline wax having a melting point of 87 ° C. (melt viscosity at 120 ° C. 4 cps) is emulsified with a commonly used emulsifier to prepare a similar emulsion. It was created. When the same printing evaluation as in Example 1 was performed, the results shown in Table 3 were obtained.

As is clear from Table 3, an emulsion ink having good printing characteristics was prepared.

Comparative Example 2 An ink was prepared by adding a polyester resin having a melting point of 78 ° C. (melt viscosity at 120 ° C., 2300 cps) to the resin ink used in Example 1 at a ratio of 30% to the resin. When the same printing evaluation as in Example 1 was performed, the results shown in Table 3 were obtained.

As is evident from Table 3, although a slight decrease in viscosity was observed, no viscosity-reducing effect was exhibited to give good printing characteristics. As described above, it has been proved that even a low melting point resin having a melt viscosity outside the range of the present invention has a remarkably low effect.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-37472 (JP, A) JP-A-61-51386 (JP, A) JP-A-63-89386 (JP, A) JP-A-61-37386 68290 (JP, A) JP-A-60-166485 (JP, A)

Claims (1)

(57) [Claims] 1. A solution type thermal transfer ink comprising a resin having a melt viscosity of 10,000 to 1,000,000 cps (measured at 120 ° C.) as a base binder. At least one kind of viscosity reducing agent selected from waxes having a viscosity of 1 to 600 cps (measured at 120 ° C) and being partially soluble in the solvent used (at least 1 g soluble in 100 g solvent at 40 ° C) 20 to 120 parts by weight with respect to 100 parts by weight of the base resin, and a partially insoluble portion of the thickener is contained in the form of fine particles such as an emulsion, a slurry, or a fine powder. For ink.