Patent Application
20080026940
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
The inorganic material aid layer improves transfer of a recording ribbon dye to a recording medium to increase sensitivity of the recording medium. Improvement of the sensitivity is essentially required as the speed of thermal transfer printers increases. In particular, when a recording medium having good whiteness and thermal stability is based on a polyethyleneterephthalate film, the inorganic material aid layer becomes more important.
Transfer of a recording ribbon dye to a recording medium is generally improved by the use of a resin having a low glass transition temperature, Tg, in the dye accepting layer, by introducing additives such as inorganic materials or plasticizers into the dye accepting layer, or by the use of a polypropylene film which can increase the contact area between a recording ribbon and an accepting paper by an exothermic head. However, the resin having a low Tg reduces the stability and the inorganic materials deteriorate the smoothness and produce printing wrinkles and stains. When plasticizers are used, preservation and compatibility with the dye receiving resin are also insufficient.
A polypropylene-based recording material has reduced whiteness and is wrinkled in some recording ribbons during a printing process. Thus, there is a need for a solution other than the conventional methods. In various experiments, when an inorganic material aid layer containing granular materials is interposed between the base layer and the dye accepting layer, transfer of a recording ribbon dye to a recording medium is improved without printing wrinkles and without loss in preservation, thereby increasing the sensitivity of recording medium.
The inorganic material used in the inorganic material aid layer may be selected from the group consisting of silica, alumina, calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium oxide, zinc oxide, zinc carbonate, aluminum silicate, silicic acid, sodium silicate, magnesium silicate and calcium silicate. Silica is preferred.
An inorganic material having a mean particle diameter of 10 μm or greater is most effective. When inorganic materials having a mean particle diameter less than 10 μm are used, the contact area between the recording ribbon and the dye accepting layer does not increase during operation of an exothermic head, and thus the desired effect cannot be obtained.
The inorganic material aid layer includes an organic binder resin together with the inorganic material. For water dispersible inorganic materials, polyvinyl alcohols, polyvinyl pyrrolidones, celluloses including methyl cellulose and hydroxyl propylmethyl cellulose, gelatin, polyethylene oxide, acrylic polymers and the like can be typically used. In addition, polymers such as polyesters and polyurethane or resins such as copolymers in the form of quaternary ammonium are suitable. Examples of a solvent type resin include polyesters resin, polyacrylate resin, polyvinyl acetate resin, polycarbonate resin, polyurethane resin, polyamide resin, and polyvinyl chloride resin used for the dye accepting layer, and a resin having a highly polar bonding.
The inorganic material may be used by dispersing in the organic binder resin. The ratio of the inorganic material to the organic binder resin may be in the range of about 90:10 to 10:90, preferably in the range of about 30:70 to 70:30. When the ratio of the inorganic material to the organic binder resin is less than 10:90, the desired effect cannot be obtained and when the ratio is greater than 90:10, coating adhesion is poor and printing wrinkles and stains are produced.
The inorganic material aid layer includes a brightening agent to increase the whiteness of the recording medium. Examples of the brightening agent include titanium dioxide, calcium carbonate, clay, zinc oxide, and the like. Introduction of the brightening agent into the inorganic material aid layer rather than the dye accepting layer can prevent the brightening agent from reducing the durability of image. Also, an antioxidant, a UV absorbent, a phenol-based additive, and the like, may further introduced into the inorganic material aid layer to improve light resistance.
The inorganic material aid layer may have a coating thickness of about 0.5 to 10 μm, preferably 1 to 5 μm. The inorganic material aid layer may be prepared using all coating methods and a bar or gravure coating method is generally used.
For a base of the thermal transfer recording medium, films such as polyestersulfone, polyimide, cellulose acetate, a copolymer of vinyl alcohol with acetal, or polyethyleneterephthalate, and synthetic papers made of polyethylene, polypropylene or polyesters may be used. When a polypropylene synthetic paper is used as the base, since the synthetic paper itself is easily deformed due to heat, simili interposed between two polypropylene synthetic papers may be used to ensure dimension stability.
The base layer may have a thickness of about 50 to 500 μm. In this case, handling is easy and bending is prevented when forming a coating layer thereon.
A material for the dye accepting layer should have affinity to a dye to be transferred from the thermal transfer recording ribbon, enable diffusion of dye to occur during a transferring process, and provide good preservation to dye after transfer of dye. Examples of such a material include polyester resin, polyacrylate resin, polyvinylacetate resin, polycarbonate resin, polyurethane resin, polyamide resin, polyvinyl chloride resin and resin having a highly polar bonding. In addition to these resins, the dye accepting layer may include fluorine-based compounds, polyethylene wax, silicone oil, and the like, to improve the release property during a transferring process and a surfactant for dispersion thereof.
In the dye accepting layer, titanium dioxide, calcium carbonate, clay, zinc oxide, and the like, may be included to increase whiteness and a fluorescent dye may be included to provide fluorescence. Also, an oxidant or an UV absorbent may be used to improve weather resistance.
The dye accepting layer may have a coating thickness of 0.5 to 10 μm after drying and the whole additives may be 0.1 to 20% with respect to resins.
For a solvent for a coating solution of the dye accepting layer, alcohol, glycol ether, ketone, toluene, dimethyl formaldehyde, ethyl acetate, and the like, may be used in consideration of solubility and workability, with ketone, toluene and dimethylformaldehye being preferred.
In addition, the recording medium according to an embodiment of the present invention may optionally include an undercoating layer between the base layer and the inorganic material aid layer to increase adhesion of these layers, as illustrated in
Examples of the resin useful for the undercoating layer include a polyol resin, polyurethane resin, acrylic resin and vinyl resin and a curing agent, such as polyisocyanates may be generally used in a combination. All of these resins may be used in films based on polyolefin such as polypropylene or polyethylene and polyethyeneterephthalate film.
The undercoating layer may have a thickness of about 0.1 to 5 μm, for example about 0.5 to 2 μm. The undercoating layer may be formed using all coating methods. A bar or gravure coating method is generally used.
The present invention will now be described in greater detail with reference to the following examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.
Polyethyleneterephthalate (thickness: 50 μm; SK, Korea) was deposited to both sides of simili paper (thickness: 100 μm; Hankuk Paper MFG Co., Ltd., Korea). Then, a coating material for an undercoating layer was applied to a surface of the polyethyleneterephthalate layer using a bar coater, and then was dried in an oven (100° C., 1 min) to obtain an undercoating layer having the composition as described below (thickness: about 1 μm).
A coating material for an inorganic material aid layer was applied to the undercoating layer using a bar coater, and then was dried in an oven (110° C., 3 min) to obtain an inorganic material aid layer having the composition as described below (thickness: about 2 μm).
A coating material for a dye accepting layer was applied to the inorganic material aid layer using a bar coater, and then was dried in an oven (110° C., 3 min) to obtain a dye accepting layer having the composition as described below (thickness: about 5 μm).
A recording medium was prepared in the same manner as in Example 1, except that the composition of the inorganic material aid layer was as described below.
A recording medium was prepared in the same manner as in Example 1, except that the composition of the inorganic material aid layer was as described below.
A recording medium was prepared in the same manner as in Example 2, except that the composition of the inorganic material aid layer was as described below.
A recording medium was prepared in the same manner as in Example 1, except that the composition of the dye accepting layer was as described below.
A recording medium was prepared in the same manner as in Example 1, except that the undercoating layer was not formed.
A recording medium was prepared in the same manner as in Example 6, except that the inorganic material aid layer was not formed.
A recording medium was prepared in the same manner as in Example 1, except that the composition of the inorganic material aid layer was as described below.
A recording medium was prepared in the same manner as in Example 1, except that the composition of the inorganic material aid layer was as described below.
A recording medium was prepared in the same manner as in Example 1, except that the composition of the inorganic material aid layer was as described below.
A recording medium was prepared in the same manner as in Example 6, except that the inorganic material aid layer was not formed and the composition of the dye accepting layer was as described below.
A recording medium was prepared in the same manner as in Comparative Example 5, except that the composition of the dye accepting layer was as described below.
A recording medium was prepared in the same manner as in Example 6, except that the inorganic material aid layer was not formed and the composition of the dye accepting layer was as described below.
Evaluation and Results
Sensitivity (Optical Density, Dmax), image wrinkle, and printing stain were evaluated on thermal transfer recording media prepared in Examples 1-6 and Comparative Examples 1-7. The results were listed in Table 1. Image printing was carried out using thermal transfer printers (PD 6000 available from Kodak, U.S.A. and SPP-2040 available from Samsung Electronics, Korea).
Whiteness and light resistance were evaluated on the thermal transfer recording media prepared in Examples 1-6 and Comparative Examples 1-7. The results are listed in Table 2. Image printing was carried out using a thermal transfer printer (SPP-2040, Samsung Electronics, Korea).
It can be seen from the results of Table 1 that when an inorganic material aid layer is interposed between a dye accepting layer and a base of a recording medium, transfer of a recording ribbon dye to the dye accepting layer was increased, thereby increasing the optical density, i.e., sensitivity, of the recording medium. However, when the particle size of the inorganic material is small or the content thereof is low (Comparative Examples 2 and 3), the desired effect is not obtained.
When the inorganic material aid layer is not formed, image stain is produced. Further, excessively high content of the inorganic material rather makes the image stain serious and produces wrinkles (Comparative Example 4). Thus, a proper amount of the inorganic material should be used.
Generally, the brightening agent increases the whiteness of the recording medium compared to when it is not used (Comparative Examples 1-4 in which no brightening agent was used). In the absence of additives such as an UV stabilizer, and the like, the light resistance of the recording medium is reduced (Comparative Example 5). When the brightening agent was used in the dye accepting layer and the inorganic material aid layer and the light resistance promoter was added to each brightening agent-containing layer, the light resistance is improved. The best effect was obtained when the brightening agent was added to the inorganic material aid layer (Comparative Examples 6 and 7). Thus, it can be seen that due to the brightening agent present in the intermediate layer rather than in the top layer and introduction of the inorganic material aid layer, image quality is generally improved and preservation against the outer environment becomes better.
The thermal transfer recording medium according to an embodiment of the present invention has the inorganic material aid layer interposed between the base and the dye accepting layer, which facilitates transfer of the recording ribbon dye. As a result, stain and wrinkle free and clear image quality can be obtained and light resistance can also be improved.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0072249 | Jul 2006 | KR | national |
