Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2000-05-10
2001-10-16
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S323000, C428S328000, C428S330000, C428S331000, C428S423700, C428S480000, C428S483000, C428S690000, C428S690000, C428S910000, C427S384000, C427S385500, C427S393500
Reexamination Certificate
active
06303210
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a biaxially oriented polyester film for a thermal transfer ribbon, a laminated film composed thereof and its production process. More particularly it relates to a biaxially oriented polyester film for a thermal transfer ribbon having excellent productivity (concretely, increased film-forming speed, decreased breaking frequency of film in film-forming process and improved yield from stock film) and giving a ribbon for thermal transfer printer having excellent printing performance and free from the troubles of thin ink spot even in the case of high-speed printing and creasing of the ribbon caused by the friction with a head, a laminated film having an adhesiveness improving layer on the above biaxially oriented polyester film and having excellent adhesivity to a thermal transfer ink layer, and a process for the production of the biaxially oriented polyester film.
BACKGROUND ARTS
Thermal transfer recording is a process to print an image and letter by the transfer of a thermal ink included in a thermal transfer ribbon to an image-receiving paper by the heat generated by a thermal head and is being popularized owing to low printing noise and easy color printing ability.
Two types of the thermal transfer recording, i.e. hot-melt type and sublimation type, have been put into practice, and the sublimation-type thermal transfer recording process has rapidly been spreading recently as a recording process enabling easy output of a full-color image having high picture quality. The sublimation-type thermal transfer process is a process using a thermal transfer ribbon produced by coating a surface of a base film with a thermal transfer ink having a composition containing a heat-sublimable dye dispersed in a binder, laying the ribbon on a printing object, contacting a thermal head with the thermal transfer ribbon to apply thermal energy to the ribbon to effect the sublimation of the heat-sublimable dye exclusively at the heated part and the transfer of the sublimed dye to the image-receiving face of the transfer object (printing paper, film, etc.) to print an image or letter.
According to the recent requirement for increasing the printing speed, the increase in the temperature of the thermal head in printing and the thinning of the thermal transfer ribbon are required for the efficient transfer of heat from the thermal head to the thermal transfer ribbon.
However, the thermal deformation of the base film of the thermal transfer ribbon becomes nonnegligible by the increase of the thermal head temperature in printing to cause the problems of the unclear printed image and the generation of crease of the thermal transfer ribbon and, in extreme case, the printing becomes completely impossible.
It is necessary to decrease the thickness of the base film of the thermal transfer ribbon for the thinning of the transfer ribbon. A biaxially drawn polyester film having excellent heat-resistance and mechanical properties is used as the base film. However, the workability in the ink layer application process and the slitting process becomes poor by merely decreasing the thickness of conventional polyester film.
The above workability depends upon the slipperiness of the film surface, and it is generally known that the slipperiness of a polyester film can be improved by forming minute irregularity on the film surface. Examples of known process for the application of irregularity are the addition of inert particles during or after the polymerization of a thermoplastic polymer to be used as a raw material for the film (external particle addition method) and the separation of a part or total of the catalyst, etc., used in the polymerization of a thermoplastic polymer during the reaction process to precipitate the separated particles in the polymer (internal particle precipitation method).
However, when a polymer incorporated with inert particles is formed to a film while keeping the concentration of the particles at a constant level in the process for the production of an ultrathin film which is an object of the present invention, the number of the inert particles per unit area decreases, the distance between protrusions on the film surface originated from the particles increases and the slipperiness of the film becomes poor owing to excessive flattening of the film surface. Accordingly, the more the film thickness decreases, the more the addition concentration or the particle diameter of the inert particles should be increased to compensate the lowering of the slipperiness caused by the decrease of the film thickness.
When the diameter of the inert particle is increased, voids are frequently generated on the interface, i.e. around the inert particle owing to the poor affinity of the inert particle and the thermoplastic polymer especially in the melt-extrusion or drawing at a high drafting ratio, resulting in the occurrence of problems of remarkable lowering of the mechanical properties (e.g. mechanical strength) of the produced film and the increase in the breakage frequency in the production of the film to lower the productivity of the film.
A polyester film having restricted surface roughness is proposed as such base film in JP A62-299389, however, the above two problems cannot be solved by such film.
In the sublimation-type thermal transfer process, the sublimable dye is present in a binder, only the dye is sublimed with heat and the sublimed dye is absorbed in the image-receiving layer of the transfer object paper to form a graded image on the paper. For subliming exclusively the dye, high adhesivity is necessary between the ink layer and the substrate film and the adhesivity is required to be resistant to the lowering with environmental change and aging. When the adhesivity is insufficient, the whole ink layer is transferred to the transfer object paper to cause remarkable deterioration of the gradation. Since a polyester film generally has high crystal orientation, it has poor adhesivity to ink layer, etc., and good adhesion is difficult to attain by the direct application of an ink layer to the film. To solve the problem, applications of physical and chemical treatments to the film surface for increasing the adhesivity to the film have been proposed, however, sufficient adhesivity cannot be attained by these methods.
It is desirable to increase the productivity of a film for providing the film at a low cost, and the improvement on the productivity has the following problems.
The first problem is as follows. A biaxially oriented polyester film is produced usually by extruding a polyester polymer through an extrusion nozzle in molten state, the molten film is quenched on the surface of a rotating chill drum to form an undrawn film and the film is biaxially drawn in longitudinal and lateral directions. In this case, the contact between the molten film and the surface of the rotating chill roll should be increased to eliminate the surface defect and improve the thickness uniformity of the film. A known method for increasing the contact is the installation of a wire electrode on the extrusion nozzle and the surface of the rotating chill drum to deposit electrostatic charge on the surface of the molten film and the quenching of the molten film by closely contacting the film with the surface of the chill drum (hereinafter called as electrostatic casting method). Since the electric resistance of a molten polyester is high in general, the quantity of electrostatic charge on unit area of undrawn film surface becomes small to lower the contact of the molten film to the chill drum surface and increase the film breakage frequency by the generation of pinholes on the film surface and the occurrence of uneven film thickness. The above problem becomes sensible especially in a thin film such as a base film for thermal transfer ribbon.
The second problem is described as follows. The polyester film to be used as a base film is produced generally by forming a stock film having a width larger than that of the product film, cutting both edges and slitting to a prescribed widt
Furuya Koji
Kawai Shinichi
Suzuki Kenji
Watanabe Shinya
Chen Vivian
Sughrue Mion Zinn Macpeak & Seas, PLLC
Teijin Limited
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