JPH0715080B2 - Wax for thermal transfer ink - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wax for thermal transfer ink. More specifically, the present invention relates to a wax for thermal transfer ink having improved dispersibility of a colorant.

[Conventional technology]

In recent years, thermal printers and thermal facsimiles have been widely used because of their advantages such as easy handling and low cost.

In such thermal printers and thermal facsimiles,
Usually, a ribbon-shaped or sheet-shaped heat-sensitive transfer type recording medium in which a heat-sensitive transfer ink mainly composed of a wax and a colorant is applied on a substrate is used.

The thermal transfer recording medium is a system in which the thermal transfer ink layer is recorded by being melt-transferred onto plain paper in the form of a printed image by printing with a heating body such as a thermal head, so that the characteristics of the thermal transfer ink, especially The characteristics of the wax, which is its main constituent, have a great influence on the performance of the recording system.

As the wax, conventionally, carnauba wax, montan wax, wood wax, beeswax, ceresin wax,
Natural waxes such as whale wax; synthetic waxes such as petroleum wax, low molecular weight polyethylene, and oxidized wax are used.

[Problems to be solved by the invention]

However, in conventional thermal transfer inks using these waxes, the dispersibility of colorants such as pigments and dyes is not sufficient, so that the color development is poor and a uniform ink layer is formed on the substrate. Was difficult to apply. When the ink layer is non-uniform as described above, there are problems that the image quality is poor and the print density is low.

[Means for solving problems]

The present inventors have conducted intensive studies to provide a wax suitable for a thermal transfer ink while paying attention to the problems of the prior art, and as a result, a specific wax has been identified as an α, β-unsaturated carboxylic acid or an anhydride thereof. The present invention has been completed by finding that it is possible to improve the dispersibility of a coloring agent such as a pigment or a dye without impairing the advantages of the raw material wax by graft-modifying.

That is, the gist of the present invention consists of a wax selected from carnauba wax, candelilla wax, montan wax, microcrystalline wax, and paraffin wax having a melting point of 50 to 100 ° C. and an α, β-unsaturated carboxylic acid and its anhydride. A wax for heat-sensitive transfer ink, comprising a modified wax obtained by grafting an unsaturated carboxylic acid compound selected from the group by radical reaction.

Hereinafter, the present invention will be described in detail.

The raw material wax used in the present invention has a melting point of 50 to 100 ° C., preferably 60 to 90 ° C., more preferably 70 to 90 ° C., selected from carnauba wax, candelilla wax, montan wax, microcrystalline wax, and paraffin wax. It is a wax. If the melting point of this raw wax is too low, blocking resistance is poor and if it is too high, sensitivity is poor. Further, the raw material wax having the above-mentioned specific melting point has only a slight change in the melting point even after graft modification.

The unsaturated carboxylic acid compound used as the grafting agent in the present invention is various α, β-unsaturated carboxylic acids or their anhydrides. Examples of such compounds include acrylic acid, methacrylic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, maleic anhydride, citraconic anhydride, and itaconic anhydride. Among these, maleic anhydride is particularly preferable in terms of graft reactivity and affinity with a colorant.

As a method of grafting the above-mentioned unsaturated carboxylic acid compound to the above-mentioned raw material wax, for example, a known method of graft-adding at a reaction temperature above its decomposition temperature using a radical initiator in the presence or absence of a solvent is used. The method is adopted. No solvent is usually required for the purposes of the present invention.

As the radical initiator, for example, acyl peroxide,
Peresters, dialkyl peroxides, alkyl hydroperoxides and the like are preferable, and among them, dialkyl peroxides are preferable. As a specific example,
-Butyl peroxide.

Each of the wax and the unsaturated carboxylic acid compound may be used alone or in combination of two or more. The use ratio of the wax and the unsaturated carboxylic acid compound is usually 1 to 30 parts by weight with respect to 100 parts by weight of the wax,
It is preferably 3 to 20 parts by weight. The radical initiator is
It is usually 0.01 to 1 with respect to 1 mol of the unsaturated carboxylic acid compound.
Used in the molar range. The reaction temperature is usually 50 to 250 ° C, preferably 150 to 200 ° C. The reaction time is usually
30 minutes to 10 hours. The wax, unsaturated carboxylic acid compound and radical initiator may be added to the reactor all at once and reacted, but first, the wax is charged into the reactor,
It is preferable to add the unsaturated carboxylic acid compound and the radical initiator to the reaction system in several divided portions or continuously at a rate according to the graft addition rate of the reaction system. The target modified wax is obtained by removing the reaction solvent, the unreacted grafting agent and the radical initiator from the reaction product and purifying.

Among the modified waxes obtained by the above method, those having a melting point of 50 to 100 ° C., more preferably 60 to 90 ° C. and a melt viscosity of 1000 cp or less at 100 ° C. are suitable as the thermal transfer ink wax.

By further reacting the modified wax with amines,
It is also effective to partially introduce an amide bond or an imide bond for modification. In this case, dispersibility, heat resistance, etc. are improved. Examples of the amines include butylamine,
Alkylamines such as octylamine, laurylamine and stearylamine; aromatic amines such as aniline and naphthylamine. The reaction between the modified wax and amines is carried out, for example, by mixing the two and heating them at 160 to 250 ° C. for dehydration reaction.

The modified wax obtained as described above probably has a polar group derived from an α, β-unsaturated carboxylic acid or an anhydride thereof in the wax molecule, and thus is well compatible with colorants such as pigments and dyes. It is considered that the colorant has an excellent effect of uniformly dispersing it in the form of fine particles in the wax, the color developability is good, and the melt viscosity of the ink is low.

The wax for heat-sensitive transfer ink of the present invention, which comprises the modified wax, is preferably used as a wax component of the heat-sensitive transfer ink. That is, similar to the conventionally used waxes, it can be used as a heat-sensitive transfer ink by blending a colorant and an appropriate softening agent, resin and the like. At this time, conventionally used waxes may be appropriately used in combination within a range that does not impair the properties of the wax of the present invention. In that case, it is usually preferable that the modified wax of the present invention is contained in the thermal transfer ink in an amount of 10% by weight or more, and more preferably 20% by weight or more, though it depends on the purpose.

〔Example〕

Next, specific embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Production Example 1 (Invention) Paraffin wax (manufactured by Nippon Seiro Co., Ltd .; HNP-10, melting point)
(78 ° C) 1000 g was charged into a reactor, and after nitrogen gas was sufficiently replaced, it was heated to 170 ° C and 100 g of maleic anhydride and di-
30 g of t-butyl peroxide was added over 3 hours while paying attention to the exotherm, and the grafting reaction was carried out. After the addition was completed, the temperature was maintained at 170 ° C. for 1 hour to complete the reaction. At this time, the reaction rate of maleic anhydride was almost 100%. Then, the decomposition product of di-t-butyl peroxide was removed under reduced pressure to obtain 1100 g of a reaction product. Table 1 shows the physical properties of the product.
Shown in.

Production Examples 2 to 6 (Invention) Modified waxes were produced in the same manner as in Production Example 1 except that the charging composition was as shown in Table 1. Table showing their physical properties
1 is also shown.

In the case of Production Example 6, since a small amount of a viscous resinous material was separated at the bottom of the reactor after the reaction was completed, a uniform upper layer was separated to obtain a reaction product.

Test Example 1 (Dispersibility) Using the modified waxes shown in Table-1, hot melt dispersion was performed with the compositions shown in Table-2 to evaluate the dispersibility. The dispersibility of the dispersion was evaluated by hot-coating the dispersion on a slide glass and observing the dispersed state of the pigment and the size of the dispersed particles with an optical microscope. The melt viscosity of the dispersion was measured at 100 ° C. If the wax is well compatible with the pigment and the dispersibility is good, the viscosity becomes low.

As a comparative example, the dispersibility was similarly evaluated using the raw wax.

The results are shown in Table-2.

Use Example 1 A thermal transfer ink prepared by the composition shown in Table 3 was formed to a thickness of 6 μm.
m polyethylene terephthalate film was hot-melt coated using a wire bar to obtain a thermal transfer recording sheet having an ink layer thickness of 3 to 4 μm.

With respect to the obtained coated sheet, the coatability of the ink was evaluated by the coating unevenness on the coated surface.

Further, the coated sheet was mounted on a thermal printer (a prototype equipped with a thin film line thermal head with a heating element density of 8 dots / mm) and printed. The print quality was evaluated by the ink removal property from the coated sheet and the print density.

The results are shown in Table-3.

[Advantages of the Invention] The wax for heat-sensitive transfer ink of the present invention has high dispersibility of colorants such as pigments and dyes, so that the colorants can be extremely stably and uniformly dispersed at a high concentration, and extremely clear printing can be performed. You can get a statue.

Also, since the melt viscosity of the ink is low, workability during melting,
Good coatability on the substrate.

Further, since it has a good hue, it can be used not only for black ink but also for color ink.

Furthermore, since a raw material wax having desired physical properties as a thermal transfer ink can be selected and modified depending on the purpose, the range of composition design of the thermal transfer ink can be widened.

Claims (4)

[Claims] 1. A wax selected from carnauba wax, candelilla wax, montan wax, microcrystalline wax, and paraffin wax having a melting point of 50 to 100 ° C., which is selected from the group consisting of α, β-unsaturated carboxylic acids and their anhydrides. A wax for heat-sensitive transfer ink, comprising a modified wax obtained by grafting a selected unsaturated carboxylic acid compound by a radical reaction. 2. The wax for heat-sensitive transfer ink according to claim 1, wherein the melting point of the modified wax is from 50 to 10
Melt viscosity at 0 ° C and 100 ° C is 1000 cP or less. 3. The wax for heat-sensitive transfer ink according to claim 1 or 2, wherein the unsaturated carboxylic acid compound is maleic anhydride. 4. The wax for thermal transfer ink according to any one of claims 1 to 3, wherein the raw material wax is paraffin wax or carnauba wax having a melting point of 60 to 90 ° C. What to do.