JP2011206964A - Thermal transfer sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal transfer sheet excellent in both the heat resistance and lubricity of a back surface.SOLUTION: The thermal transfer sheet includes a dye layer formed on one side surface of a base material film and a back surface lubricative layer formed on the other side surface. The back surface lubricative layer contains a reaction product of a cellulose-based resin with the weight-average molecular weight of not lower than 60,000 and isocyanate as a binder resin.

Description

  The present invention relates to a thermal transfer sheet used in a thermal transfer printer, and more particularly to a thermal transfer sheet excellent in both heat resistance and slipperiness on the back side.

  In recent years, the use of thermal transfer sheets (ribbons) has been rapidly spreading in order to perform printing or image formation by a printer equipped with a thermal head. Such a thermal transfer sheet usually has a dye layer formed on one side of the base film and a back-sliding layer formed on the other side. In particular, the back side of the thermal transfer sheet in direct contact with the thermal head The back-sliding layer formed in (1) has an important function of ensuring the stability of image formation by imparting heat resistance and slipperiness to the back surface of the thermal transfer sheet.

  In other words, the back slip layer of the thermal transfer sheet may interfere with normal running due to damage or softening of the base film of the thermal transfer sheet due to heat applied from the thermal head, and furthermore, the slipperiness between the thermal head and the thermal transfer sheet. Is provided in order to prevent the problem that the quality of the printed image is deteriorated due to a decrease in the image quality.

  Conventionally, in order to form a back slip layer having such characteristics, it is possible to apply a composition obtained by adding silicone oil or the like as a slipping component to a specific thermoplastic resin or thermosetting resin. Known (Patent Document 1).

  Further, a new improvement technique for improving the characteristics of such a slipping layer has been proposed (Patent Document 2).

Japanese Patent Laid-Open No. 1-222181 JP-A-4-276492

  However, in recent years, there has been a demand for further improvement in print quality and image quality. In particular, from the viewpoint of providing a thermal transfer sheet that can withstand the applied heat of the thermal head and the further advancement of the running speed, the conventional thermal transfer sheet is not necessarily It is not satisfactory enough.

  The present invention has been made in view of the above-described situation in the prior art, and provides a thermal transfer sheet that is further excellent in both heat resistance and slipperiness of the back surface in a thermal transfer sheet that requires improvement in print image quality. It is intended to do.

  In order to achieve the above object, the thermal transfer sheet according to the present invention is a thermal transfer sheet in which a dye layer is formed on one side of a base film and a back slip layer is formed on the other side. The slipping layer comprises a reaction product of a cellulose resin having a weight average molecular weight of 60,000 or more and an isocyanate as a binder resin.

  Furthermore, in the preferable aspect of this invention, the weight average molecular weights of the cellulose resin contained in the said back surface slipping layer are 60,000-200,000.

  In a preferred embodiment of the present invention, the cellulose resin is an ethyl cellulose resin or a cellulose acetate resin.

  The high molecular weight cellulose resin having heat resistance necessary to achieve the above object generally has many hydrophilic resins and has low solubility in organic solvents such as toluene and methyl ethyl ketone.

  In order to achieve the above object, it is necessary to cure the cellulose resin with an isocyanate curing agent to further improve the heat resistance. However, isocyanate-based curing agents cannot be used because they are highly reactive with water and cause the pot life of ink using an aqueous solvent to be shortened. In addition, water-based solvents are harder to dry than organic solvents, and the amount of heat required for the curing reaction in the drying process after ink coating is deprived as the latent heat of vaporization of the solvent, leading to a deterioration in the efficiency of the manufacturing process. There is also.

  Therefore, the present invention selects an ethyl cellulose-based resin and a cellulose acetate-based resin that are highly heat-resistant and soluble in an organic solvent, and can solve the above problems by using this and a back layer using a specific isocyanate curing agent. I found it.

  The “aqueous solvent” refers to a solvent containing water as a main component. As components other than water, for example, alcohols such as methanol, ethanol and propanol, or ketones such as acetone and methyl ethyl ketone, which are not easily phase-separated in the presence of water may be included. good.

  As understood from the results of Examples and Comparative Examples described later, according to the present invention, a thermal transfer sheet excellent in both heat resistance and slipperiness on the back surface can be obtained.

    Hereinafter, preferred embodiments of the thermal transfer sheet of the present invention will be described. The thermal transfer sheet according to the present invention is basically a thermal transfer sheet in which a dye layer is formed on one surface of a base film and a back slip layer is formed on the other surface. A reaction product of a cellulose resin having a weight average molecular weight of about 60,000 or more and an isocyanate is contained as a binder resin.

  As the substrate film, conventionally used substrates are used and are not particularly limited. That is, in addition to polyethylene terephthalate (PET) conventionally used as a base film for a thermal transfer sheet, polycarbonate, polyethylene, polystyrene, polypropylene, polyimide, polyvinyl alcohol film, cellophane, cellulose derivatives such as cellulose acetate, polyethylene film, Resin films such as polyvinyl chloride film, nylon film, polyimide film, and ionomer film can be used. The thickness of a base film is 0.5-50 micrometers normally, Preferably it is the range of 4-7 micrometers.

  As the dye layer, conventionally used dye compositions for sublimation transfer and melt transfer can be used, and are not particularly limited.

  In the present invention, the back slip layer formed on the other surface of the base film, that is, the surface opposite to the surface on which the dye layer is formed (back surface) is composed of a cellulose resin having a weight average molecular weight of about 60,000 or more, isocyanate, These reaction products are included as a binder resin.

  As the cellulose-based resin, an ethylcellulose-based resin or a cellulose acetate-based resin can be suitably used, and among these, ethylcellulose is particularly preferably used. Such an ethyl cellulose is preferably a cellulose ether having an ethoxy group (—CH 2 H 5) partially etherified using ethyl chloride on a replaceable hydroxyl group (—OH) of a cellulose derived from a natural product, for example. 45-49.5) can be used.

  As the cellulose acetate-based resin, cellulose acetate obtained by esterifying cellulose by reacting with acetic acid can be used. Among the cellulose acetates, cellulose diacetate can be used particularly preferably.

  However, in the present invention, it is important to limit the molecular weight (weight average molecular weight) of the cellulose resin to 60,000 or more, and particularly preferably, the molecular weight is limited to a range of 60,000 to 200,000. Preferably, it is desirable to limit the molecular weight to a range of 80,000 to 180,000.

  When the molecular weight of the cellulosic resin is small, particularly when it is less than about 60,000, it cannot sufficiently withstand heat pressing, and it becomes difficult to ensure sufficient heat resistance and lubricity. On the other hand, if the molecular weight of the cellulosic resin is too large, the tendency to be difficult to dissolve increases, which is not preferable. From such a viewpoint, it is desirable to limit the molecular weight to a range of 60,000 to 200,000.

  In addition, the weight average molecular weight in this invention is a weight average molecular weight by polystyrene conversion measured by GPC (developing solvent is THF).

In this invention, the reaction product of the cellulose resin mentioned above and isocyanate is included as binder resin, It is characterized by the above-mentioned. In order to obtain a back-slidable layer containing such a reaction product, usually an equivalent amount of isocyanate is mixed with the prepared cellulose resin to form a coating composition, which is coated on a base film. , A back slipping layer having a predetermined film thickness can be obtained. Usually, the coating amount of the back slipping layer (dry), preferably in the range of 0.1 to 4.0 g / m ^2, more preferably in the range of 0.6~0.7g / m ² is there.

  In the present invention, as the isocyanate, TDI (toluene diisocyanate), MDI (diphenylmethane diisocyanate), NDI (1,5-naphthylene diisocyanate), TODI (tolidine diisocyanate), HDI (hexamethylene diisocyanate), IPDI (isophorone diisocyanate), p-phenylene diisocyanate, XDI (xylylene diisocyanate), hydrogenated HDI, hydrogenated MDI, LDI (lysine diisocyanate), TMXDI (tetramethylxylene diisocyanate), lysine ester triisocyanate, 1,6,11-undecane triisocyanate, 1 , 8-Diisocyanate-4-isocyanate methyloctane, 1,3,6-hexamethylene triisocyanate, bicycloheptant Isocyanates, there may be mentioned TMDI (trimethyl hexamethylene diisocyanate) and the like, but can be used as long as it has an isocyanate group to other be particularly suitably used is toluene diisocyanate.

  The thermal transfer sheet obtained by the present invention is excellent in both heat resistance and slipperiness of the back surface. Therefore, according to the present invention, it is possible to form a good image even under severe printing conditions.

  Hereinafter, the present invention will be described more specifically based on examples of the present invention and comparative examples.

Example 1
On one surface of a PET film (4.5 μm thick), a composition for the back slip layer having the following composition was applied and formed so that the coating thickness after drying was 0.67 g / m ² .

(Composition for back slip layer)
Etocel STD45 (Nihon Kasei Co., Ltd.) 5% solution 30g
Barnock D-750-45 (manufactured by DIC) 3.57g
sz-pf (manufactured by Sakai Chemical) 0.3 g

Details of each of the above components are as follows.
Etocel STD45: Ethyl cellulose having a weight average molecular weight of about 140,000 (the number of hydroxyl groups is about 1.5 per repeating unit). Diluted with methyl ethyl ketone for blending Vernock: Isocyanate, etose amount and equivalent sz-pf: Zinc stearate

  Methyl ethyl ketone was used as a diluent solvent for etosel STD45.

  The film coated with the back slip layer was combined with a thermal transfer image-receiving sheet for a sublimation printer CP9000D manufactured by Mitsubishi Electric Corporation. The frictional force during printing was measured under the following conditions, and the following evaluation was performed. In addition, the thermal transfer printer with a frictional force measurement function described in JP-A-2003-300368 was used for printing and measuring the frictional force.

Thermal head: Toshiba Hokuto Electronics thermal head, head resistance 5020Ω, resolution 300 dpi (dots per inch)
Line speed: 1 ms / Line (Resolution in the paper transport direction is 300 lpi (line per inch))
Pulse duty: 90%
Applied voltage: 26.5V
Printing pressure: 40N
Print image: gradation image with a width of 1388 pixels x length of 1024 pixels and a gradation of 0 to 255 (one pixel corresponds to one dot, the print start position is 0 gradation)

  The 255 gradation corresponds to the gradation value for obtaining the highest print density, and the lower the numerical value, the lower the print density.

(result)
The frictional force between the thermal head and the back surface was within the range of about 20 to 27 N until the gradation of the printed image was close to 0 to 210, indicating stable friction characteristics.

  Furthermore, the heat resistance was satisfactory with no abnormalities such as film tearing during printing.

Example 2
On one surface of a PET film (4.5 μm thick), a composition for the back slip layer having the following composition was applied and formed so that the coating thickness after drying was 0.67 g / m ² .

(Composition for back slip layer)
Etoseru STD200 (Nihon Kasei Co., Ltd.) 5% solution 30g
Barnock D-750-45 (manufactured by DIC) 3.57g
sz-pf (manufactured by Sakai Chemical) 0.3 g

Details of each of the above components are as follows.
Etocel STD200: Ethyl cellulose having a weight average molecular weight of about 190,000 (the number of hydroxyl groups is about 1.5 per repeating unit)
Burnock: amount of isocyanate and etose and equivalent sz-pf: zinc stearate

  Evaluation was performed in the same manner as in Example 1.

(result)
The frictional force between the thermal head and the back surface was within the range of about 20 to 27 N until the gradation of the printed image was close to 0 to 210, indicating stable friction characteristics.

  Furthermore, the heat resistance was satisfactory with no abnormalities such as tearing of the film during printing.

Comparative Example 1
On one surface of a PET film (4.5 μm thick), a composition for the back slip layer having the following composition was applied and formed so that the coating thickness after drying was 0.67 g / m ² .

(Composition for back slip layer)
Etocel STD7 (Nihon Kasei Co., Ltd.) 5% solution 30g
Barnock D-750-45 (manufactured by DIC) 3.57g
sz-pf (manufactured by Sakai Chemical) 0.3 g

Details of each of the above components are as follows.
Etocel STD7: Ethyl cellulose having a weight average molecular weight of about 55000 (the number of hydroxyl groups is about 1.5 per repeating unit)
Burnock: amount of isocyanate and etose and equivalent sz-pf: zinc stearate

  Evaluation was performed in the same manner as in Example 1.

(result)
The frictional force suddenly changes between the gradation 25 and 80 to 110 of the printed image, and the frictional force between the thermal head and the back surface is in the range of 18 to 40 N between the gradations 40 to 210 of the printed image. The friction characteristics were unstable.

  Furthermore, regarding the heat resistance, there was a sticking mark on the back surface of the film after printing, and the heat resistance was insufficient. This sticking portion was a portion where the frictional force changed rapidly.

Claims (3)

In the thermal transfer sheet in which the dye layer is formed on one surface of the base film and the back slip layer is formed on the other surface,
The thermal transfer sheet, wherein the back sliding layer comprises a reaction product of a cellulose resin having a weight average molecular weight of 60,000 or more and an isocyanate as a binder resin.   The thermal transfer sheet according to claim 1, wherein the cellulose resin contained in the back slip layer has a weight average molecular weight of 60,000 to 200,000.   The thermal transfer sheet according to claim 1 or 2, wherein the cellulose resin is an ethyl cellulose resin or a cellulose acetate resin.