JPH0662018B2 - Thermal melt transfer recording medium - Google Patents

Description

The present invention relates to a thermal melt transfer recording medium, and more particularly to a thermal melt transfer recording medium used in a thermal melt transfer recording method using a thermal head employed in computer printers, typewriters, etc.

BACKGROUND ART Conventional thermal melt transfer recording media include, for example,
As disclosed in Japanese Patent Application Laid-Open No. 59-114098 and Japanese Patent Laid-Open No. 60-97888, it has been proposed to provide a wax film layer on the surface of a heat-melt color ink layer to prevent the color ink from transferring to non-printed areas of the receiver, a phenomenon known as background smearing.

However, to prevent soiling of the surface with this conventional two-layer structure, the amount of wax applied must be 3 g/ ^m² or more, preferably 5 g/m².
Approximately 8 g/m ² was required.

However, when such a thick wax layer is provided on the surface of a colored ink layer, a large amount of printing energy is required to melt the wax layer for transfer.

If the ink were to be melted with the same low energy as if it had no surface layer, the transfer to the receiver would not be sufficient, resulting in a decrease in print density. Therefore, if the printing energy is increased, the print would bleed on recording media with a thick wax layer, resulting in a problem of unclear prints.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive melt transfer recording medium which prevents background smearing on the receiver and allows good printing even with low printing energy.

DISCLOSURE OF THE INVENTION The present invention provides a melt transfer recording medium in which a heat-sensitive melt transfer ink layer formed on one side of a support comprises a colored ink layer and a layer formed on the surface of the colored ink layer, the layer containing as its main component a finely crystalline wax having an average particle size of 1 to 5 μm, containing no colorant, and having a coating amount (converted to solids) of 0.1 to 2 g/ ^m2 .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional view showing one embodiment of the thermal melt transfer recording medium of the present invention.

According to the present invention, a layer containing fine crystalline wax as the main component can sufficiently prevent background smearing if it has a thickness of about 0.1 to ² g/m², and therefore high-density, clear printing can be obtained with low printing energy, similar to that achieved without a wax layer.

In other words, the wax layer formed by applying wax in the form of fine crystals of the specific particle size range onto the colored ink layer is bulky, with gaps between the crystal particles, unlike a film. Therefore, even if the wax layer is applied in a small amount, such as 0.1 to 2 g/ ^m² , the apparent thickness of the wax layer is large, completely blocking contact between the colored ink layer and the receiver, thereby sufficiently preventing smearing of the receiver surface. Moreover, because the amount applied is so small, a clear image can be obtained with little printing energy.

As shown in FIG. 1, the thermal melt transfer recording medium of the present invention (hereinafter referred to as the recording medium) comprises a support (1) and a thermal melt transfer ink layer (2).

Suitable materials for the support (1) include resin films having a thickness of 2 to 10 μm, such as polyester film, polycarbonate film, polyamide film, polyimide film, and polyphenylene sulfide film, which have been widely used as base materials for recording media; high-density paper having a thickness of 5 to 25 μm, such as condenser paper, glassine paper, and India paper; and cellophane.

The thermal melt transfer ink layer (2) is composed of a colored ink layer (3) and a layer (hereinafter referred to as crystalline wax layer (4)) formed on the surface of the colored ink layer (3) and containing fine crystalline wax as its main component.

The color ink layer (3) is a conventionally known material obtained by mixing and dispersing a colorant such as a pigment and/or a dye in a wax and/or a heat-melting resin, and optionally a softener such as oil, and is preferably formed on the support (1).
The coating is applied to one side of the sheet in a thickness of about 2 to 7 g/m ² (solid content equivalent).

The crystalline wax layer (4) is formed by applying fine crystalline wax to the surface of the colored ink layer (3), and the amount of application (solid content equivalent) is 0.1 to 2 g/m ² , preferably 0.2
If the coating ^amount is too small,
If the amount is too large, the transfer sensitivity may decrease, both of which are undesirable.

The method of forming the fine crystalline wax is preferably one in which the wax is heated and dissolved in a suitable solvent and then rapidly cooled, or in which a non-solvent for the wax is added after the wax is dissolved to precipitate fine crystals.

The solution containing precipitated wax crystals thus obtained may be used for coating as is, but if it is treated with a dispersing machine or a grinding machine such as an attritor, ball mill or homogenizer to make the wax crystals finer and more uniform, it will be even more effective in preventing background smearing and obtaining clearer printing.

The crystal size of this wax (average particle size measured by the Coulter counter method, the same applies hereinafter) is 1 to 5 μm,
The preferred thickness is 1 to 4 μm. If the wax crystals are larger than this range, the crystalline wax layer (4) will be thick, resulting in insufficient transfer and making it difficult to obtain clear prints. On the other hand, if the wax crystals are smaller than this range, the crystalline wax layer (4) will become more like a film, and unless a large amount is applied, background staining will tend to occur.

The wax crystal-containing liquid prepared as described above is applied to the surface of a colored ink layer (3) previously formed on a support (1) by a typical coating method, and heated to a temperature that does not dissolve the wax to remove the solvent, thereby forming a crystalline wax layer (4) on the surface of the colored ink layer (3).

This application method may be a conventionally known method such as a Mayer bar method, a gravure coating method, or a reverse coater.

Examples of waxes that can be used in the present invention include vegetable waxes such as candelilla wax, carnauba wax, rice wax, and Japan wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as montan wax; petroleum waxes such as paraffin wax and microcrystalline wax; higher fatty acids such as palmitic acid, stearic acid, and behenic acid; higher alcohols such as palmityl alcohol, stearyl alcohol, and behenyl alcohol; higher fatty acid esters such as methyl stearate, cetyl stearate, and myricyl palmitate; amide waxes such as stearamide and palmitamide; polyethylene wax; coal-based wax; and synthetic waxes such as Fischer-Tropsch wax, which can be used alone or in combination.

Thus, the term "wax" as used in the present invention is a concept that includes not only the original wax but also wax-like substances.

Furthermore, if necessary, in order to improve the adhesion to the colored ink layer (3), a heat-melting resin having a softening point of about 40 to 120°C may be added in an amount of 1 part by weight (parts by weight, the same applies hereinafter) to 100 parts by weight of the wax.
If the amount of the heat-melting resin mixed is too large, fine crystals of the wax may not be formed or the transfer sensitivity may be reduced, which is not preferable.

The heat-melting resin may be rosin or a derivative thereof,
Polyamide resins, acrylic resins, phenolic resins, xylene resins, cellulose resins, vinyl acetate resins, butyral resins, etc. can be used alone or in combination.

If necessary, in order to adjust the strength of the crystalline wax layer (4), white pigments or extender pigments such as silica, alumina, titanium oxide, zinc oxide, calcium carbonate, barium carbonate, etc. may be added as additives in an amount of 5 to 100 parts per 100 parts of wax.
If the amount of the additive is too large, fine wax crystals may not be formed or the crystalline wax layer 4 may become too brittle, which is undesirable.

Examples of solvents that can dissolve the wax include toluene, benzene, xylene, ethyl acetate, methyl ethyl ketone, tetrahydrofuran, and acetone, and an appropriate solvent can be selected depending on the type of wax.

Non-solvents for wax include water, alcohols (methanol, ethanol, isopropanol, butanol, etc.), ethyl acetate, n-heptane, n-pentane,
Examples include cyclohexane and dioxane, and an appropriate one can be selected depending on the type of wax.

It should be noted that the above solvents and non-solvents may be solvents or non-solvents depending on the type of wax, and therefore the above descriptions are merely examples.

When printing using the recording medium of the present invention, paper is generally used as a receiver. However, when using the recording medium of the present invention, an overhead projector (hereinafter referred to as
It was discovered that clear printing without background staining could be obtained on resin film for use with overhead projectors (OHPs).

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described with reference to examples and comparative examples.

Example 1 Polyethylene terephthalate film (1) with a thickness of 6 μm
The surface is coated with a colored ink of the composition below at a rate of 3.5g/ ^m².
The ink was applied using a hot melt coater so that the ink layer (3) was formed. Composition of the ink layer : Paraffin wax 155F 12 parts, Carnauba wax 3 parts, Ethylene-vinyl acetate copolymer 2 parts, Carbon black 3 parts. On the other hand, 1 part of oxidized wax (trade name "PO Wax H-10", manufactured by Nippon Oil Corporation) was dissolved in 2 parts of toluene heated to 80°C, and then 7 parts of isopropanol was added at a temperature of 50°C or higher to form fine crystals (size 1000 nm) of the oxidized wax.
A suspension containing precipitated particles (1.5 μm) was obtained.

This suspension was applied to the surface of the colored ink layer (3) using a Mayer bar so that the amount of coating after drying was 0.7 g/ ^m2 .
The solvent was then substantially completely removed by treating the coated film in a hot air dryer at 0°C for 20 seconds to form a crystalline wax layer (4).

The sample thus obtained was used to print at room temperature in a thermal transfer print word processor WD-200 manufactured by Sharp Corporation, using electronic copying paper (trade name "Xerox M" manufactured by Fuji Xerox Co., Ltd.) as a receiver. The density of the print image formed on the receiver, measured with a Macbeth densitometer RD514, showed an 0D value of about 1.1, and a clear print without bleeding was obtained.

Furthermore, there was no evidence of color ink being transferred to any area other than the designated image forming area, and so-called background staining did not occur.

Comparative Examples 1 to 5 A crystalline wax layer was formed on the surface of a colored ink layer in the same manner as in Example 1, except that the average particle size of the wax microcrystals and the amount of application were changed as shown in Table 1. In Comparative Example 5, no wax layer was formed on the colored ink layer (blank).

A printing test was carried out on each of the obtained samples in the same manner as in Example 1. The results are shown in Example 1 and Example 2 below.
The results of steps 1 to 3 are shown in Table 1. The print density and background scumming shown in Table 1 were evaluated according to the following criteria.

Print density: ◯: 0D value is 0.9 or more; Δ: 0D value is 0.6 or more but less than 0.9; ×: 0D value is less than 0.6; Background staining: ◯: No colored ink adheres to the receiving paper except in the printed area.

×...Colored ink is attached to areas other than the printed area.

Comparative Example 6 P0 wax H-10 was applied to the surface of the colored ink layer (3) formed in the same manner as in Example 1 by hot melt coating.
The coating was applied in an amount of 1.0 g/m ² to form a film-like wax layer on the surface of the colored ink layer (3).

A printing test was carried out using this sample in the same manner as in Example 1. As a result, background smearing frequently occurred, and the printing density was 0.95.

Comparative Example 7 PO wax H-10 was applied to the surface of the colored ink layer (3) formed in the same manner as in Example 1 by hot melt coating.
The coating was applied in an amount of 3.0 g/m ² to form a film-like wax layer on the surface of the colored ink layer (3).

A printing test was carried out using this sample in the same manner as in Example 1. As a result, no background smearing occurred, but the print density was light at 0.5.

Comparative Examples 8 and 9 A film-like wax layer was formed on the surface of the colored ink layer in the same manner as in Comparative Example 6, except that the amount of wax applied was changed as shown in Table 2.

A printing test was carried out on each of the obtained samples in the same manner as in Example 1. The results are shown in Table 2 together with the results of Comparative Examples 6 and 7. The evaluation criteria shown in Table 2 are the same as those described above.

Example 2 A crystalline wax layer (4) was formed on the surface of a colored ink layer (3) formed in the same manner as in Example 1, by the following method.

One part of candelilla wax and one part of carnauba wax were dissolved in 6 parts of toluene heated to 80°C, and then 12 parts of methanol was added while the temperature was kept above 50°C to obtain a suspension containing fine crystals of the wax. This was then pulverized for about 30 minutes in an attritor filled with glass balls.

The suspension thus pulverized (wax crystal size: 3.6 μm) was applied to the surface of the colored ink layer (3) using a Mayer bar so that the coating amount after drying would be 1.0 g/ ^m2 , and the coating was treated in a hot air dryer at 60°C for 20 seconds to substantially completely remove the solvent, thereby forming a crystalline wax layer (4).

Using the sample thus obtained, a printing test was carried out in the same manner as in Example 1. As a result, no background smearing occurred and clear printing with a printing density of 1.0 was obtained.

Example 3 A crystalline wax layer (4) was formed on the surface of a colored ink layer (3) formed in the same manner as in Example 1, by the following method.

4 parts of candelilla wax was heated to 70°C in toluene (7 parts)
After dissolving the wax in 25 parts of methanol, the temperature was increased to 50° C. or higher, and a suspension was obtained in which fine crystals (2.5 μm in size) of the wax were precipitated.

This suspension was mixed with polyvinyl alcohol (trade name "UMR-10L
4 parts of a resin solution prepared by dissolving 1 part of "" (Unitika Chemical Co., Ltd.) in 9 parts of methanol was added and the mixture was homogenized using a homogenizer.
Stirred for 10 minutes.

The suspension containing the resin is then applied to the color ink layer.
The surface of (3) was coated with a Mayer bar so that the coating amount after drying was 0.3 g/ ^m² , and the coating was treated in a hot air dryer at 60°C for 20 seconds to substantially completely remove the solvent, forming a crystalline wax layer (4).

Using the sample thus obtained, a printing test was carried out in the same manner as in Example 1. As a result, no background staining occurred and clear printing with a printing density of 1.1 was obtained.

Example 4 Using each of the recording media obtained in Examples 1 to 3, an OHP film was printed on an OHP film printer (No. 842, manufactured by Kyocera Corporation).
P film (product name "Xerox Film", Fuji Xerox
When printing was performed on a paper made by Epson Corporation, clear printing was obtained, especially in the fine lines, and no background smearing occurred.

Comparative Example 10 When printing was performed on an OHP film in the same manner as in Example 4 using the recording medium obtained in Comparative Example 7, there was no background smearing, but the printing, particularly in the fine line portions, was unclear and the result was not suitable for practical use.

Comparative Example 11 In Example 1, a crystalline wax layer was formed on the colored ink layer (3).
A recording medium without (4) was prepared and used to print on an OHP film in the same manner as in Example 4, but the printing was unclear, particularly in the fine line portions.

Continued from the front page (56) References: JP 59-114098 (JP, A) JP 60-97888 (JP, A) JP 59-24693 (JP, A) JP 60-61290 (JP, A)

Claims (1)

[Claims] [Claim 1] A thermal melt transfer recording medium in which a thermal melt transfer ink layer formed on one side of a support comprises a colored ink layer and a layer formed on the surface of the colored ink layer, the layer having a coating amount (solids equivalent) of 0.1 to 2 g/ ^m2 and consisting primarily of finely crystalline wax with an average particle size of 1 to 5 μm, containing no colorant.