Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2001-08-06
2003-03-25
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S423700, C428S480000, C428S483000, C428S910000
Reexamination Certificate
active
06537657
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a biaxially oriented polyester film for a thermal transfer ribbon. More specifically, this invention relates to a biaxially oriented film for a thermal transfer ribbon excellent in productivity [concretely, capable of increasing film forming speed (high speed film-forming performance), free from drop-out of particles from film in film forming process (abrasion resistance), free from breakage of film on slitting (slitting property)], and having excellent printing performance with no uneven transfer even in the case of high speed printing when it is used as a thermal transfer ribbon.
BACKGROUND ART
A thermal transfer recording system is a system for printing images and letters by transferring thermal ink contained in a thermal transfer ribbon by the heat generated from a thermal head to an image receiving paper. It has been popularized because of little printing sound and easiness in color printing.
Regarding the type of the thermal transfer recording, two types, i.e. heat melt type and sublimation type are practically used now. Out of them, the sublimation-type thermal transfer recording system is rapidly being popularized recent years as a recording system which can easily output high-quality full color images. The sublimation-type thermal transfer recording system has the following feature: a thermal transfer ribbon is constituted by laminating a layer of a thermal transfer ink having a composition consisting of a heat-sublimable dye dispersed in a binder on the surface of a base film; the obtained thermal transfer ribbon is laid on a transfer-receiving material (printing paper, film or the like); a thermal head is brought into contact with the thermal transfer ribbon to give heat energy to it; thereby, only the heat-sublimable dye at a heated position is sublimed; the sublimed dye is transferred to the image-receiving surface of the transfer-receiving material; and as a result, images and letters are printed.
Recently, it is required with the needs of speeding-up of printing to raise the thermal head temperature on printing and decrease the thickness of a thermal transfer ribbon, in other words, to reduce the thickness of film for the thermal transfer ribbon, in order to efficiently transmit heat from the thermal head to the thermal transfer ribbon.
However, the thinning of a film for thermal transfer ribbons is accompanied by the following problems.
Firstly, it becomes difficult to produce a film at high speed.
As a base film for thermal transfer ribbons, a biaxially oriented polyester film having excellent heat resistance, mechanical property and dimensional stability is used. As the polyester constituting the biaxially oriented polyester film, polyethylene terephthalate (hereafter, it is abbreviated as PET) and polyethylene-2,6-naphthalate (hereafter, it is abbreviated as PEN) are mainly used.
The biaxially oriented films like this are produced mainly by a consecutively biaxially stretching method. The consecutively biaxially stretching method is a process that molten polyester polymer is extruded from a die by an extruder into a sheet-shaped molten product, it is quenched on the surface of a rotary cooling drum, subsequently it is stretched in the longitudinal direction and the transverse direction, and further it is optionally subjected to a heat-setting treatment and a heat-relaxation treatment.
It is desirable that film forming can be carried out stably with a reduced breakage frequency to economically produce film in such a production method. Further, it is desired that surface faults are reduced and thickness homogeneity is increased in an obtained film. For that, it is necessary to increase the closeness of the above-mentioned film-shaped molten product to the surface of the rotary cooling drum. As the method for increasing the closeness, a method (called an electrostatic casting method) is known, that is, a wire-shaped electrode is placed in a vicinity of the extruding die and the rotary cooling drum to apply static charge on the surface of the film-shaped molten product, and the film-shaped molten product is quenched while it is brought into close contact with the surface of the rotary cooling drum.
However, having a larger molten electric resistance than PET, PEN has various more difficulties than the case of PET in a production of a thin PEN film for a base film of thermal transfer ribbons by electrostatic casting method. That is, when a PEN film is formed, the quantity of electrostatic charge to the surface of a film-shaped product per unit area becomes low due to thin thickness of the film-shaped molten product in the stage of electrostatic casting and further large molten electric resistance of PEN. Resultingly, the closeness between the film-shaped molten product and the surface of the rotary cooling drum is insufficient, and this causes troubles of inducing pin-shaped faults on the surface of a film, lowering of homogeneity of film thickness, and film breakage in an extreme case.
The second problem is the breakage of film during slitting.
Since a PEN film has a lower tear resistance than a PEN film, the PEN film is apt to break during slitting. The breakage of the PEN film is extreme when the film is thin. For example, a problem arises when a stretched film is slit or a thermo transfer ribbon is slit to get a product in the process of film production.
The third problem is the dropping-out of particles from film during film forming.
In polyester film, inert particles are commonly added to the polyester polymer to improve workability in a finishing process with the object of imparting slipperiness to film. However, when a film to be produced from an inert particle-added polymer is thin, the number of inert particles per unit area is decreased, the spaces between fine particles existing on the surface are widened, the film surface becomes too flat, and the slipperiness of the film tends to decrease. Therefore, in order to make up the decrease in slipperiness with decreasing thickness of the film, it is required that the concentration of added inert fine particles is increased, or the average particle diameter of the inert fine particles are increased with the decreasing thickness of the film.
In this case, the following problems occur: a great number of voids are generated on interfaces around the inert inorganic fine particles due to the lack of affinity between the inert fine particles and polyester polymer especially during melt extrusion or drawing with a high draw ratio, and as a result of the generation of voids, fine particles are apt to drop out from the obtained film, and abrasion dusts are generated by the contact with a roll to dirt the manufacturing process.
As the base film like this, a polyester film having a specified surface roughness is disclosed by JP-A 62-299389 (JP-A means Japanese unexamined patent publication), but this film cannot solve the above-mentioned problems.
Further, in a sublimation-type thermal transfer system, a heat-sublimable dye exists in a binder, only the dye sublimes by heat, and it is absorbed into an image receiving layer of a transfer-receiving paper to form a toning image. In order to allow only the dye to sublime, high adhesivity between the ink layer and the base material is required, and further it is necessary that environmental change nor time passage does not decrease the adhesivity. When the adhesivity is insufficient, it causes a trouble that whole of the ink layer is transferred to the transfer-receiving paper and toning is extremely lost. Since a polyester film generally has high crystalline orientation, the adhesivity between the film and an ink layer or the like is poor, and so it is hard for an ink layer to be closely adhered if it is directly applied on the polyester film. Hence, methods of applying a physical or chemical treatment on the surface of a film to increase the adhesivity to an ink layer conventionally have been proposed, but these conventional methods do not give sufficient adhesivity.
DISCLOSURE OF THE INVENTION
The object of the
Furuya Koji
Watanabe Shinya
Chen Vivian
Teijin Limited
LandOfFree
Biaxially oriented polyester film for thermal transfer ribbon does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Biaxially oriented polyester film for thermal transfer ribbon, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Biaxially oriented polyester film for thermal transfer ribbon will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3039207