JP4918448B2 - Thermal transfer medium - Google Patents

Description

  The present invention relates to a thermal transfer medium, and more particularly to a thermal transfer medium capable of forming a transfer pattern with excellent heat resistance.

  Conventionally, various heat transfer media in consideration of heat resistance have been proposed for printing on heat-resistant tags that are transferred by heating with an iron or the like, or for printing on heat seal portions of packaging substrates. ing. For example, an ink layer in which an ethylene copolymer resin and a styrene-butadiene synthetic rubber are added to increase the heat resistance of the ink layer itself (for example, Patent Document 1), a release layer, and heat resistance protection on a substrate. There are layers in which a layer and an ink layer are formed in this order, and a heat-resistant protective layer is formed of a high melting point resin such as a silicone resin.

  However, in any of the above cases, it is still impossible to form a transfer pattern having sufficient heat resistance. For example, when a tag is formed by thermal transfer, there is a problem that the other fabric is set off. .

  For the purpose of improving such problems, a heat-sensitive transfer medium is provided with a release layer, a heat-resistant protective layer, and an ink layer in this order on a substrate, wherein the heat-resistant protective layer is an isocyanate or an isocyanate-based resin ( For example, a thermal transfer medium comprising an isocyanate and a resin in which a styrene resin, an ethylene-vinyl acetate copolymer, an acrylic resin, an ethylene-acrylic copolymer, or a polyamide resin is combined is proposed. (Patent Document 2).

However, the thermal transfer medium as described above has some improvement in the problem of set-off, but it is still not sufficient, and the heat-resistant protective layer is too high in heat resistance and cannot perform high-speed printing. .
Japanese Patent Laid-Open No. 5-278346 Japanese Patent Laid-Open No. 10-175378

  The present invention has been made in view of the above problems, and provides a thermal transfer medium capable of improving the printing speed and maintaining desired heat resistance (back-off resistance) and scratch resistance. The purpose is to do.

  In order to achieve the above object, the present invention provides a thermal transfer medium in which at least a release layer, a protective layer, and a hot-melt ink layer are provided in this order on a substrate, and the protective layer comprises a polyisocyanate and A thermal transfer medium comprising a one-component thermosetting acrylic resin in a blending ratio (mass ratio) of 50:50 to 80:20 is provided.

  According to the present invention, the protective layer is formed using an ink composition containing polyisocyanate and a one-component thermosetting acrylic resin at a predetermined ratio, whereby heat resistance (back-proof resistance) and scratching are achieved. Therefore, it is possible to provide a thermal transfer medium that does not cause printing defects, printing tailing (printing flow), and printing crushing even when high-speed printing is performed.

  Hereinafter, the thermal transfer medium of the present invention will be described in more detail. In order to develop a thermal transfer medium that has heat resistance and scratch resistance, and that does not generate print defects, print flow, or print collapse even when high-speed printing is performed, the inventors have studied the layer structure of the thermal transfer medium, and also protected it. The material of the ink composition constituting the layer has been studied repeatedly. As a result, it was found that a desired effect can be achieved by forming a protective layer using an ink composition containing polyisocyanate and a one-component thermosetting acrylic resin in a certain ratio, and the present invention has been completed. It was.

  The base material used for the thermal transfer medium of the present invention may be any base material used for conventional thermal transfer media, and specific examples include polyester films. The thickness of the substrate is preferably about 2.5 μm to 9 μm. If the thickness of the substrate is 2.5 μm or more, wrinkles and film breakage are unlikely to occur during production, and if it is 9 μm or less, the transfer of heat during printing can be secured and good printing accuracy can be obtained.

  In addition, a polyester film as a base material that is commercially available for a thermal transfer medium is usually provided with a heat-resistant protective layer for preventing sticking on the surface opposite to the side on which the hot-melt ink layer is provided. Also in the present invention, if possible, it is preferable to use a film provided with such a heat-resistant protective layer as a substrate. Of course, it goes without saying that a heat-resistant protective layer may be provided separately using a base material on which the above-mentioned heat-resistant protective layer is not provided.

  The release layer provided on the substrate needs to be a thin film in order to maintain the heat resistance of the protective layer and the clear print of the hot melt ink layer. The thickness of the release layer is preferably 0.001 to 0.5 μm. If the thickness of the release layer is 0.001 μm or more, the hot-melt ink layer is reliably peeled off during printing. If the thickness of the release layer is 0.5 μm or less, thermal melting does not occur in a wide range during printing, and it is possible to ensure the dot accuracy of printed characters and images, and heat melting to the protective layer Ingredients are difficult to penetrate and the heat resistance of the protective layer is unlikely to deteriorate. The release layer can be provided by a gravure coating method. The thickness of the release layer can be controlled by adjusting the solid content of the ink.

  For the release layer, for example, waxes such as paraffin wax, montan wax, carnauba wax, polyethylene wax and amide wax, and resin release agents such as silicone resin and acrylic resin are used alone or in any desired mixture. Can do.

  The protective layer provided on the release layer needs to have heat resistance enough to withstand the temperature of the thermal head that performs printing, and has a role of maintaining the flatness of the hot-melt ink layer without being distorted by heat. In addition, if the protective layer retains heat resistance more than necessary, heat transfer to the hot melt ink layer will be hindered and the print quality will be deteriorated. Therefore, the protective layer does not cause such deterioration in print quality. It is necessary to have Therefore, it is necessary for the protective layer in the present invention to contain polyisocyanate and one-component thermosetting acrylic resin.

  Thus, if the protective layer contains polyisocyanate and a one-component thermosetting acrylic resin, desired heat resistance can be secured by the polyisocyanate, and a predetermined amount of one-component with respect to the polyisocyanate. By blending the thermosetting acrylic resin, it is possible to improve the thermal responsiveness during high-speed printing while minimizing a decrease in heat resistance.

  Here, the polyisocyanate is not particularly limited and may be any polyisocyanate used in the field of the present invention and other fields. Examples of such polyisocyanates include commercially available products such as Crossnate (trade name) manufactured by Dainichi Seika Kogyo Co., Ltd. and Barnock (trade name) manufactured by Dainippon Ink & Chemicals, Inc. .

  The one-component thermosetting acrylic resin is not particularly limited, and a normal one-component thermosetting acrylic resin can be used. As such one-component thermosetting acrylic resin, for example, UNO-1 (trade name) manufactured by Gifu Serask Manufacturing Co., Ltd. and one-component curable thermolac (trade name) manufactured by Soken Chemical Co., Ltd. And other commercial products.

  The blending ratio (mass ratio) of the polyisocyanate and the one-component thermosetting acrylic resin in the present invention is preferably 50:50 to 80:20. That is, the blending ratio of the one-part thermosetting acrylic resin and the polyisocyanate is substantially the same, or the blending ratio of the polyisocyanate is larger than the one-part thermosetting acrylic resin in the above range. If the one-component thermosetting acrylic resin is 1/2 or less of the polyisocyanate, the heat resistance can be ensured, and the print quality is hardly deteriorated. Moreover, if the one-component thermosetting acrylic resin is 1/4 or more of polyisocyanate, the thermal responsiveness during high-speed printing is unlikely to decrease.

  The thickness of the protective layer is preferably in the range of 0.5 μm to 1.5 μm. If it is 0.5 μm or more, there is no fear of heat resistance failure, and if it is 1.5 μm or less, the problem of cracking is unlikely to occur. The protective layer can be provided by, for example, a gravure coating method.

  A hot-melt ink layer is provided on the protective layer. Conventional pigments and dyes such as carbon black, titanium oxide, iron oxide, ultramarine, lake red, basic base dye, and neozapon dye can be used for the hot-melt ink layer without any particular limitation.

  Examples of the binder component of the hot-melt ink layer include waxes such as polyethylene wax, microcrystalline wax and carnauba wax, and heat such as vinyl chloride polymer, polyester resin, ethylene-vinyl acetate copolymer and terpene resin. Ingredients that have been conventionally used for forming hot-melt ink layers such as plastic resins, thermosetting acrylic resins, unsaturated polyester resins, epoxy resins, polyamide resins and silicone resins, and other UV curable resins Can be used without restriction.

  On the hot-melt ink layer, for example, an acrylic resin, a vinyl resin, a urethane resin, and waxes are used alone or in any mixture, and bonded according to the type of the image receiving object to be printed. A layer may be provided. Depending on the surface condition and material of the image-receiving member, if the adhesive layer is too thin, good adhesion of printed characters and images cannot be obtained. If the adhesive layer is too thick, the adhesive component moves due to the heat of the thermal head. As a result, the flatness of the hot-melt ink layer is deteriorated and the printing accuracy is deteriorated. As long as the adhesive layer can maintain adhesion to the image receiving member, the thinner the adhesive layer, the more securely the flatness of the hot-melt ink layer can be maintained, and clearer characters and images can be obtained. The thickness of the adhesive layer is appropriately selected according to the type and surface state of the image receiving member, but is usually in the range of 0.1 to 5 μm.

  In addition, the adhesive layer has a purpose of preventing wrinkling when winding the thermal transfer medium, preventing sticking of the thermal transfer medium when stored in a roll shape, and improving the adhesion with the image receiving member by roughening the adhesive surface. Therefore, it is desirable to add a fine powder slip agent. Examples of the fine powder slip agent include powders of inorganic materials such as silica and talc, and organic fillers such as resin beads. The slip agent is desirably contained in the adhesive layer in an amount of 2 to 30% by mass. If the addition amount of the slip agent is 2% by mass or more, the thermal transfer medium is slippery and easy to process and store, and if it is 30% by mass or less, the components involved in the adhesion are not reduced and the adhesive force is secured. be able to. The adhesive layer can be provided by, for example, a reverse coating method.

  The total thickness of the transfer layer (including a release layer, a protective layer, a hot-melt ink layer, and if necessary, other layers such as an adhesive layer) in which each layer is sequentially provided on the substrate in this way is the thickness of the substrate. Or less. When the thickness of the transfer layer exceeds the thickness of the substrate, it is difficult to maintain a good balance between the degree of heat transfer during printing and the time, and the printing accuracy is reduced.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In Examples and Comparative Examples, “part” is based on mass unless otherwise specified. Moreover, the amount of components other than the solvent is all in terms of solid content.

Example 1
On one surface of a 5.6 μm-thick polyethylene terephthalate film (manufactured by Mitsubishi Chemical Polyester Film Co., Ltd.), which is a base material, a coating liquid having the following composition (I) is dried and the coating amount is 0.3 g / m ² It was applied using a gravure coater and dried to form a heat-resistant protective layer.
Composition (I):
Silicone resin 10 parts Toluene 45 parts Methyl ethyl ketone (MEK) 45 parts

On the other surface of the polyethylene terephthalate film, a coating liquid having the following composition (II) was applied using a gravure coater so that the coating amount after drying was 0.5 g / m ^2, and dried to form a release layer. .
Composition (II):
Polyethylene wax 9 parts Ethylene-vinyl acetate copolymer 1 part Toluene 10 parts

On this release layer, a coating solution having the following composition (III) was applied using a gravure coater so that the coating amount after drying was 1.0 g / m ² , dried and then cured at 130 ° C. for 30 minutes. To form a protective layer.
Composition (III):
7 parts of polyisocyanate (Crosnate D-70 (trade name) manufactured by Dainichi Seika Kogyo Co., Ltd.)
Three-part one-part thermosetting acrylic resin (UNO-1 (trade name) manufactured by Gifu Seratsuk Factory)
30 parts of MEK

Furthermore, a coating liquid having the following composition (IV) was applied onto the protective layer using a gravure coater so that the coating amount after drying was 1.0 / m ² and dried to form a hot-melt ink layer. .
Composition (IV):
10 parts of ethylene-vinyl acetate copolymer (Evaflex 250 (trade name) manufactured by Mitsui DuPont Chemical Co., Ltd.)
30 parts of terpene phenol resin (YS Polyester T115 (trade name) manufactured by Yasuhara Chemical Co., Ltd.)
Carbon black 10 parts Toluene 100 parts

<< Examples 2 to 4 >>
A thermal transfer medium of the present invention was obtained in the same manner as in Example 1 except that the blending ratio of the polyisocyanate constituting the protective layer and the one-component thermosetting acrylic resin in Example 1 was changed to the values shown in Table 1. .

<< Comparative Examples 1 and 2 >>
A thermal transfer medium for comparison was obtained in the same manner as in Example 1 except that the blending ratio of the polyisocyanate constituting the protective layer and the one-component thermosetting acrylic resin in Example 1 was changed to the values shown in Table 1. .

<< Comparative Example 3 >>
A comparative thermal transfer medium was obtained in the same manner as in Example 1 except that the coating liquid having the following composition (V) was used as the protective layer.
Two-part thermosetting acrylic resin 60 parts (Acridic A-810 (trade name) manufactured by Dainippon Ink & Chemicals, Inc.)
3 parts of polyisocyanate (curing agent) (Bernock D-800 (trade name) manufactured by Dainippon Ink and Chemicals, Inc.) Nitrocellulose 11 parts MEK 360 parts

[Evaluation test]
With respect to the thermal transfer medium of the present invention obtained in Examples 1 to 4 and the comparative thermal transfer medium obtained in Comparative Examples 1 to 3, the polypropylene packaging material was moved on the conveyor at respective speeds of 5 m / min and 25 m / min. While moving, printing was performed using a thermal transfer printer (SmartDate-3c (product name) manufactured by EDM) to form a print pattern on a polypropylene packaging material to obtain a print sample. The obtained print samples were evaluated by the following methods from the viewpoints of print quality, scratch resistance and heat resistance.

(1) Print quality The obtained print samples were evaluated by visually confirming the absence of printing, the printing flow, and the presence or absence of printing crushing. The evaluation criteria were as follows. The evaluation results are shown in Table 2.
◯: Printing failure, printing flow, and printing crushing were not confirmed.
Δ: Although there was no problem in practical use, some printing defects, printing flow, and printing crushing were confirmed.
X: Severe printing defect, printing flow, and printing crushing were confirmed.

(2) Friction property A steel ball having a diameter of 10.9 mm attached to the tip of a friction element of a fretting tester (electric lock meter No. 416-TMI manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS L 0823 It was brought into contact with the surface of the printing surface and slid back and forth on the surface with a terminal load of the load lever of 88.2 kPa. The change in the printing state during the reciprocation of the steel ball 30 times was visually observed. Evaluation was made according to the following evaluation criteria. The evaluation results are shown in Table 2.
A: There was no problem in printing.
○: There was no problem in printing, but there was a trace of rubbing.
(Triangle | delta): Although printing was legible, it was scraped off by abrasion and became thin.
×: Unreadable print.

(3) Heat resistance (offset resistance)
An iron at 150 ° C. was pressed from the top of the printed part for 2 seconds at a pressure of 0.2 MPa, and the presence or absence of smudges in the part heated by the iron was confirmed.
○: No stain due to hot melt ink ×: There is stain due to hot melt ink

  The thermal transfer medium according to the present invention can be suitably used for printing characters and images at high speed.

Claims (1)

A thermal transfer medium in which at least a release layer, a protective layer, and a hot-melt ink layer are provided in this order on a substrate,
The thermal transfer medium, wherein the protective layer contains polyisocyanate and a one-component thermosetting acrylic resin in a blending ratio (mass ratio) of 50:50 to 80:20.