JP5929382B2 - Thermal transfer recording medium - Google Patents

Description

  The present invention relates to a heat transfer type thermal transfer recording medium.

In thermal melt transfer recording, a thermal transfer ink sheet (thermal transfer recording medium) is heated using thermal energy controlled by an electrical signal from a laser, thermal head, or the like, and the molten ink is transferred onto a transfer target image. Is recorded. As one of the methods, a thermal transfer recording medium in which an ink layer composed of a heat-meltable substance mainly composed of wax and a colorant such as a dye or pigment is provided on a support is used, and the ink layer is transferred during transfer. A method is known in which heating is performed in accordance with print information, and melted and transferred to a transfer medium such as recording paper.
Such thermal transfer recording methods are widely used in various fields. For example, barcodes, product names, prices, serial numbers, etc. are printed on packing materials or label stickers for display, etc. We are managing.

Carnauba wax is suitably used as the wax in order to record clear images on these various transferred materials. Carnauba wax is a hard wax with excellent frictional resistance, low melting point and excellent sensitivity characteristics, and also has advantages such as sharp thermal characteristics and low melt viscosity, leading to excellent printing characteristics. It is used for the purpose of forming a transfer image having excellent properties and lubricity (Patent Document 1).
However, when the outermost surface is composed of an ink layer containing a colorant, for example, when a printer with a high thermal head pressure is used, the ink surface and the receiver are likely to be rubbed and contaminated, which may be a problem in display applications. Many.

Therefore, in order to solve this problem, a method has been proposed in which an over layer mainly composed of a hot-melt material having an elongation rate of 5% or less at 40 to 60 ° C. is provided on the ink layer (Patent Document 2). . According to this method, the thermal transfer recording medium is formed with an over layer using a high-hardness wax, or a polymer having a high Tg (glass transition point) or high molecular weight. However, in the case of a high-hardness wax, the scratch strength is inferior. Therefore, although it has a certain level of resistance against surface contact and line contact, the printed image is relatively easily lost due to scratching by a sharp edge. In addition, when a high Tg or high molecular weight polymer is used, a void (disappearance of an image) occurs in a transfer paper having a poor surface smoothness.
Further, in order to improve the fixability to the transfer paper, a method of containing a styrene resin having a number average molecular weight of about several hundred to several thousand, and further a tackifier (so-called tackifier) such as a terpene resin or a rosin ester. (Patent Documents 3 and 4), however, this method tends to cause a phenomenon in which ink that should not be originally printed is transferred to the rear end portion of the printed image due to the residual heat or heat accumulation of the thermal head. There was a difficulty. Moreover, since tackiness appears, blocking resistance may be reduced.

  As described above, the prior art has various problems. Therefore, the present invention solves these problems, enables high-quality recording even on a transfer paper having a poor surface smoothness, and is free from rubbing stains on the transfer paper. Another object of the present invention is to provide a thermal transfer recording medium of a thermal melting type having excellent scratch resistance of images.

The above problem is solved by the following invention 1).
1) In the thermal transfer recording medium having a release layer mainly composed of a wax on a support, an ink layer containing a wax and a colorant, and an over layer mainly composed of a wax and a resin on the support layer, A thermal transfer recording medium, wherein the resin is a styrene acrylate copolymer having a number average molecular weight of 1500 to 5000 .

  According to the present invention, it is possible to perform recording with high image quality even on a transfer paper having a poor surface smoothness, there is no rubbing stain of the ink on the transfer paper, and the scratch resistance of the image is improved. An excellent heat-melting type thermal transfer recording medium can be provided.

Hereinafter, the present invention 1) will be described in detail. The embodiment of the present invention 1) includes the following inventions 2) to 3 ), and these will be described together.
2 ) The thermal transfer recording medium according to 1 ), wherein Tg of the styrene acrylate copolymer is 55 to 70 ° C.
3 ) The thermal transfer recording medium according to 1) or 2) , wherein the styrene acrylate copolymer is contained in an over layer in an amount of 20 to 30% by weight.

The thermal transfer recording medium of the present invention is characterized by containing a styrene acrylate copolymer as an overlayer resin mainly composed of wax and resin. Here, the main component means that it is composed of wax and resin, excluding auxiliary components to be blended as necessary.
Examples of the acrylate monomer constituting the styrene acrylate copolymer include methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, lauryl alkylate, hydroxyethyl acrylate, cyclohexyl alkylate, and 2-ethoxyethyl. Examples include alkylate and ethyl carbitol acrylate.
The number average molecular weight of styrene-acrylic acid ester copolymer, shall be the 1 500-5000. The Tg is preferably 50 to 85 ° C, more preferably 55 to 70 ° C. If the number average molecular weight is 5000 or less, the sensitivity does not decrease. Further, if the Tg is less than 50 ° C., the printed image may be blurred and thickened, and if it exceeds 85 ° C., transfer defects such as missing / missing dots due to insufficient transfer may occur.

  The content of the styrene acrylate copolymer in the over layer is preferably about 15 to 35% by mass, and more preferably 20 to 30% by mass. If it is less than 15% by mass, the effect of improving the scratch resistance may not be obtained, and if it exceeds 35% by mass, the sensitivity may be lowered.

The wax used for the over layer is vegetable wax such as rice wax, wax, candelilla wax, carnauba wax, animal wax such as lanolin, beeswax, shellac wax, mineral wax such as montan wax, paraffin wax. And synthetic waxes such as microcrystalline wax, oxidized paraffin wax, chlorinated paraffin wax, ricinoleic acid amide, lauric acid amide, oleic acid amide, polyethylene wax, and polyethylene oxide wax. What is necessary is just to select suitably according to the sensitivity at the time of print image formation required among these, and the heat-resistant abrasion property of a print image.
The content of the wax in the over layer is preferably about 65 to 85% by mass.
The over layer has a thickness of 0.3 to 2 μm, preferably about 0.5 to 1.2 μm.

The ink layer contains a wax and a colorant, and optionally contains various additives such as a dispersant and an antistatic agent.
As the colorant, organic or inorganic pigments and dyes generally used in this type of thermal transfer recording medium can be used. 10-50 mass% is suitable for the content rate of the coloring agent in an ink layer. If it is less than 10% by mass, the image density may be insufficient, and if it exceeds 50% by mass, transfer failure or image fixability may be deteriorated.
As the wax for the ink layer, the same material as that for the over layer can be appropriately selected and used. The content of the wax in the ink layer is appropriately 50 to 90% by mass.
The film thickness of the ink layer is 1 to 3 μm, preferably about 1 to 2 μm.

The support is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include various plastic films such as polyethylene terephthalate, polyester, polycarbonate, polyimide, polyamide, polystyrene, polysulfone, polypropylene, polyethylene, and cellulose acetate. It is done. Among these, a polyethylene terephthalate film is preferable in terms of excellent strength, heat resistance, and thermal conductivity of the thermal transfer recording medium itself.
The thickness of the support is not particularly limited and can be appropriately selected according to the purpose, but is preferably 3 to 10 μm.

In the thermal transfer recording medium of the present invention, it is preferable to provide a back layer on the surface opposite to each of the layers as viewed from the support (the surface opposite to the surface on which the ink layer is formed). Since heat is directly applied to the opposite surface in accordance with the image by a thermal head or the like during transfer, the back layer needs to be resistant to high heat and to friction with the thermal head or the like.
Suitable materials for the back layer include silicon-modified urethane resin, silicon-modified acrylic resin, silicone resin, silicone rubber, fluorine resin, polyimide resin, epoxy resin, phenol resin, melamine resin, nitrocellulose and the like.
In addition, inorganic fine particles such as talc, silica, and organopolysiloxane, a lubricant, and the like can be added to the back layer as necessary.
The thickness of the back layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.01 to 1.0 μm.

A release layer mainly composed of wax is provided between the support and the ink layer. Here, the main component means that it is composed only of wax, excluding auxiliary components to be blended as necessary.
The release layer has a function of improving the peelability between the support and the ink layer at the time of printing. When heated by a thermal head, the release layer melts into a low-viscosity liquid. The ink layer can be easily cut near the interface.
The wax used for the release layer may be appropriately selected from the same materials as those for the over layer, but preferably has a melting point or softening point of 70 to 120 ° C.
Further, rubbers such as butadiene rubber and nitrile rubber may be added in order to prevent the ink layer from being lost from the support by providing the release layer with flexibility and forming a flexible layer. Similarly, it is possible to add resins having strong adhesiveness, and preferable materials include ethylene vinyl acetate copolymer.

  In producing the thermal transfer recording medium of the present invention, the coating liquid for each layer is coated on a support using a bar coater or a gravure coater. The coating film thickness of each layer may be appropriately determined according to the purpose of use of the thermal transfer recording medium, and is selected from each film thickness range described above.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not limited by these Examples. “Part” and “%” are based on mass unless otherwise specified.

Example 1
-Production of thermal transfer recording media-
<Preparation of carnauba wax aqueous dispersion for overlayer coating solution>
Carnauba wax: 36 parts by weight, nonionic surfactant: 4 parts by weight, water: 50 parts by weight, isopropyl alcohol: 10 parts by weight are mixed and dispersed with a ball mill until the volume average particle size is 0.2 μm. A carnauba wax aqueous dispersion was obtained.

<Preparation of overlayer coating solution>
The following materials were mixed to obtain an overlayer coating solution.
-Carnauba wax aqueous dispersion: 80 parts-Styrene acrylate copolymer: 20 parts (JONCRYL 52J Tg manufactured by BASF: 56 ° C, number average molecular weight: 1700)

<Preparation of carbon black aqueous dispersion for ink layer coating liquid>
Carbon black: 21 parts by weight, acrylic resin: 9 parts by weight, monoethylene glycol: 10 parts by weight, water: 60 parts by weight are mixed and dispersed with a ball mill to a median particle size of 0.2 μm. Got

<Preparation of ink layer coating liquid>
The following materials were mixed to obtain an ink layer coating solution.
-Carbon black aqueous dispersion: 20 parts-Carnauba wax emulsion: 80 parts (SELOSOL R-586 manufactured by Chukyo Yushi Co., Ltd.)

<Preparation of release layer coating solution>
The following materials were mixed and dispersed until the average particle size became 2.5 μm to obtain a release layer coating solution.
Carnauba wax: 18 parts Low molecular weight ethylene vinyl acetate copolymer (weight average molecular weight 2100, vinyl acetate ratio 21% by weight, EV150, Mitsui-DuPont Polychemicals): 2 parts Toluene: 60 parts Methyl ethyl ketone: 20 parts

<Preparation of coating solution for back layer>
The following materials were mixed to obtain a back layer coating solution.
Silicone rubber (solid content 30%, KS779H manufactured by Shin-Etsu Chemical Co., Ltd.): 16.8 parts Chloroplatinic acid catalyst (CPL-8 manufactured by Shin-Etsu Chemical Co., Ltd.): 0.2 parts Toluene: 83 parts

<Coating of each layer>
The back layer coating solution was applied to one side of a support made of a polyester film having a thickness of 4.5 μm and dried at 80 ° C. for 10 seconds to form a back layer having a thickness of 0.02 μm.
Next, the release layer coating liquid is applied to the surface of the support opposite to the surface on which the back layer is formed, and dried at 40 ° C. for 10 seconds to form a release layer having a thickness of 1.5 μm. Formed.
Next, the ink layer coating solution was applied onto the release layer and dried at 70 ° C. for 10 seconds to form an ink layer having a thickness of 1.5 μm.
Further, the overlayer coating solution was applied onto the ink layer and dried at 70 ° C. for 10 seconds to form an overlayer having a thickness of 0.5 μm, thereby obtaining a thermal transfer recording medium.

(Examples 2 , 6, 8 to 11, Reference Examples 3 to 5, 7, Comparative Examples 1 to 4)
A thermal transfer recording medium was produced in the same manner as in Example 1 except that the material composition of the over layer was changed as shown in each column of Examples and Comparative Examples in Table 1.
The details of the resin in the table are as follows.
Example 2 and Example 9:
BASF JONCRYL 586 Tg 60 ° C, number average molecular weight 4600
Reference example 3:
BASF JONCRYL 611 Tg 50 ° C., number average molecular weight 8100
Reference example 4:
BASF JONCRYL 501J Tg65 ° C, number average molecular weight 12000
Reference example 5:
JONCRYL 683 Tg75 ° C., number average molecular weight 8000, manufactured by BASF
Example 6:
BASF JONCRYL 57J Tg 67 ° C, number average molecular weight 4900
Reference example 7:
BASF JONCRYL 60J Tg85 ° C, number average molecular weight 8500
-Example 8, Example 10, Example 11
BASF JONCRYL 52J Tg: 56 ° C., number average molecular weight: 1700
Comparative Example 2: YS Polyster 115 manufactured by Yasuhara Chemical Co., Ltd.
Comparative Example 3: Mitsui Chemicals FTR8120

Regarding the thermal transfer recording media of Examples 1 , 2 , 6, 8 to 11, Reference Examples 3 to 5, and 7 and Comparative Examples 1 to 4, the material to be transferred, the sensitivity, the fineness, and the scratch strength are as follows. Was evaluated. The results are shown in Table 2.

[Stain to be transferred]
Printing was performed on each thermal transfer recording medium under the following conditions, and the transfer-substance contamination was evaluated according to the following criteria.
-Printer: Thermal transfer printer ("M4800RV"; manufactured by SATO)
Head density: 8 dots / inch Printing speed: 6 inches / sec
・ Printing energy: Memory 2 (standard)
-Transfer object: YUPO SG90 (manufactured by Lintec)

-Evaluation criteria-
◯: There is no rubbing dirt other than the printed part.
X: There is rubbing dirt other than the printed part.

[Low smooth paper transfer]
Printing was performed on each thermal transfer recording medium under the following conditions, and the degree of character transfer was evaluated according to the following criteria.
-Printer: Thermal transfer printer ("M4800RV"; manufactured by SATO)
Head density: 8 dots / inch Printing speed: 6 inches / sec
・ Printing energy: Memory 2 (standard)
-Transfer object: N mat 55 (manufactured by Oji Tuck)
・ Printing pattern: Size 1.5mm square, Mincho, Alphabet

-Evaluation criteria-
○: There is no blur or chipping and it is legible.
Δ: Slightly chipped or chipped, but legible.
×: Scratch, chipping, and unreadable.

[Definition]
Printing was performed on each thermal transfer recording medium under the following conditions, and the ANSI (American Standards Association) grade of the barcode (code 39) was measured with a barcode verifier (QC600) and evaluated according to the following criteria.
-Printer: Thermal transfer printer ("M4800RV"; manufactured by SATO)
Head density: 8 dots / inch Printing speed: 6 inches / sec
・ Printing energy: Memory 2
-Transfer object: N mat 55 (manufactured by Oji Tuck)
・ Printing pattern: Narrow bar (thin line) / wide bar (thick line) is a bar code (Code 39) made up of 2 dot width / 6 dot width lines, and arranged in parallel to the printing direction. code

-Evaluation criteria-
○: ANSI Grade A
Δ: ANSI grade B
×: ANSI grade C or lower

[Scratch strength]
Printing on each thermal transfer recording medium under the following conditions, using a lab tester with a bar code, the pen scanner (tip: glass sphere) begins to destroy the image under a 200 g load (cannot be read with a pen scanner) The number of times was read and evaluated according to the following criteria.
-Printer: Thermal transfer printer ("M4800RV"; manufactured by SATO)
Head density: 8 dots / inch Printing speed: 6 inches / sec
・ Printing energy: Memory 2
-Transfer object: Cast coated paper (manufactured by Lintec)
・ Print pattern: Narrow bar (thin line) / wide bar (thick line) is a bar code (Code 39) composed of lines of 2 dots width / 6 dots width, respectively, and arranged at right angles to the print direction. code

-Evaluation criteria-
◎: 121 times or more ○: 81 to 120 times △: 41 to 80 times ×: 40 times or less

JP-A-9-156240 Japanese Patent No. 3219300 JP-A-2-141290 Japanese Patent Laid-Open No. 11-180044

Claims (3)

In a thermal transfer recording medium having a release layer mainly composed of a wax on a support, an ink layer containing a wax and a colorant on the support, and an over layer mainly composed of a wax and a resin on the support layer, the resin is A thermal transfer recording medium, which is a styrene acrylate copolymer having a number average molecular weight of 1500 to 5000 . The thermal transfer recording medium according to claim 1, wherein the styrene acrylate copolymer has a Tg of 55 to 70 ° C. The thermal transfer recording medium according to claim 1 or 2, characterized in that the styrene-acrylic acid ester copolymer, containing 20 to 30 wt% in the over layer.