JP4897950B2 - Polyester film for sublimation type thermal transfer ribbon - Google Patents

Description

  The present invention relates to a polyester film. Specifically, the present invention relates to a polyester film for a sublimation type thermal transfer ribbon which is suitable for printing at high speed and has improved protective layer transfer characteristics.

  Biaxially oriented polyester film has various properties such as mechanical properties, heat resistance, electrical properties, chemical resistance, etc. in a highly balanced manner and is excellent in cost performance. It is widely used as industrial materials such as industrial use. In recent years, in particular, the demand for materials for various printing media has increased. That is, for example, as represented by the use of the sublimation type thermal transfer system, it is possible to realize a high quality image by transferring the dye from the ribbon-like film to the image receiving paper.

  In addition, in order to enable printing in a short time comparable to a conventional silver salt photograph, there is a demand for a material that can cope with high energy and a short time for transferring in a short time.

  However, if the energy per unit time for transfer given from the back side of the ribbon-like film is increased, the base film will be exposed to higher heat, and the deformation of the base film during transfer will cause the sublimation dye to be smooth. Transfer will be hindered and the image will be defective.

  In order to prevent such deformation at the time of transfer, an increase in the strength of the ribbon has been proposed (Patent Document 1). If this method is adopted and only the strength is focused, the longitudinal direction and the width direction are assumed. When the protective layer is transferred after the transfer of each color, which will be described later, isotropic whole surface transfer becomes difficult and anisotropy occurs in the glossiness of the final screen. . Thus, it was impossible to increase the strength of the base film and maintain the isotropic glossiness.

  Furthermore, in order to provide long-term image quality maintenance ("weather resistance" and "light resistance") comparable to conventional silver salt photographs, a protective layer is provided on the transferred image. In general, a protective layer is provided on the ribbon-like film in parallel with the dye layers of the respective colors, and the protective layer is transferred to the image side by heating from the back surface of the substrate.

  However, if the base material of the ribbon for transferring the protective layer is roughened, the protective layer at the interface becomes rough when the base material and the protective layer before transfer are laminated. Becomes the surface of the protective layer after transfer, and the irregularities cause diffused reflection of light, resulting in a decrease in glossiness and a loss of image quality. It is easy to imagine that the surface of the base material is smoothed to increase the glossiness. However, when the surface is smoothed in a thin film, the winding characteristics are drastically reduced due to the handling of the process. Inappropriate.

Japanese Patent Laid-Open No. 11-263077 JP 2003-295612 A

  The present invention has been made in view of the above circumstances, and its solution is to maintain the isotropy of the glossiness of the surface after transfer of the protective layer while realizing an increase in strength suitable for high-speed printing, An object of the present invention is to provide a film for a sublimation type thermal transfer ribbon capable of maintaining high glossiness of the surface after transfer of the protective layer while keeping the surface smoothness from the viewpoint of industrial production to the minimum necessary.

  As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by imparting specific orientation characteristics and surface characteristics to the film, and have completed the present invention.

That is, the gist of the present invention is that the film thickness is 6 μm or less, the 5% elongation strength in the film longitudinal direction is 120 to 145 MPa, the plane orientation degree of the film is 0.165 or more, and the film longitudinal orientation. The degree is 0.070 to 0.091, the absolute value of the difference between the degree of orientation in the film longitudinal direction and the degree of orientation in the width direction is 0.009 to 0.026, and the arithmetic average roughness (Ra) of at least one side is at least. It exists in the polyester film for sublimation type thermal transfer ribbons characterized by being 0.031-0.045 micrometer.

Hereinafter, the present invention will be described in detail.
The polyester constituting the film of the present invention refers to a polyester having 80% or more of repeating units having an ethylene terephthalate unit or an ethylene-2,6-naphthalate unit. Such a polyester usually undergoes a polycondensation reaction via a transesterification reaction using a lower alkyl ester of an aromatic dicarboxylic acid and a glycol as main starting materials, or a main starting material of an aromatic dicarboxylic acid and a glycol. As a raw material, it is obtained by conducting a polycondensation reaction via an esterification reaction. In order to perform these reactions, a method of adding a metal compound as a catalyst is usually used. For example, compounds such as Ca, Mg, Mn, and Li are generally used as transesterification reaction catalysts, and compounds such as Sb, Ti, Ge, Sn, and Co are used as polycondensation reaction catalysts. Further, the polyester of the present invention may contain other third component without departing from the scope of the present invention.

  As the aromatic dicarboxylic acid component, for example, in addition to terephthalic acid and 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, oxycarboxylic acid (for example, p-oxyethoxybenzoic acid, etc.) ) Etc. can be used. As the glycol component, in addition to ethylene glycol, for example, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like can be used.

  The intrinsic viscosity of the polyester used in the present invention is usually 0.45 or more, preferably 0.50 to 1.0, more preferably 0.52 to 0.80. If the intrinsic viscosity is less than 0.45, there may be a problem that productivity at the time of film production is lowered or the mechanical strength of the film is lowered. On the other hand, it is preferable that the intrinsic viscosity does not exceed 1.0 from the viewpoint of the melt extrusion stability of the polymer.

  The polyester film of the present invention has a thickness of 6 μm or less. 5 μm or less is preferable from the viewpoint of capacity as a final product, and 3 μm or more is more preferable from the viewpoint of winding yield during film production.

  For the purpose of smoothness, the polyester film of the present invention needs to have an arithmetic average roughness (Ra) of at least one side of 0.031 to 0.045 μm, preferably 0.033 to 0.038 μm. The arithmetic average roughness (Ra) will be described in detail in the measurement method item described later. When the arithmetic average roughness (Ra) exceeds 0.045 μm, the glossiness of the image after the transfer of the protective layer is inferior, which is inappropriate. On the other hand, when the arithmetic average roughness (Ra) is less than 0.031 μm, the winding characteristics of the base material are deteriorated, which is inappropriate.

  Of course, the surface opposite to the smooth surface may be roughened from the viewpoint of improving the winding characteristics. In this case, it is preferable to take a laminated structure having a smooth layer and a roughened layer when the polyester is melt extruded.

  Further, in terms of glossiness, the degree of plane orientation needs to be 0.165 or more, and the difference between the degree of orientation in the longitudinal direction and the degree of orientation in the width direction needs to be 0.030 or less. When the degree of plane orientation is less than 0.165, the absolute amount of deformation (elongation or shrinkage) of the film when heat is applied as a substrate increases, and the deformation of the ribbon increases when transferring the protective layer, thereby protecting the film. Peeling at the interface between the layer and the substrate becomes uneven, unevenness is increased, and the gloss of the final image is lowered, which is inappropriate. The degree of plane orientation is preferably 0.167 or more, more preferably 0.170 or more.

  Moreover, when the difference between the degree of orientation in the longitudinal direction and the degree of orientation in the width direction exceeds 0.030, anisotropy occurs in the longitudinal direction and the width direction of deformation of the film when heat is applied as a base material. Anisotropy occurs in the deformation of the ribbon when transferring the protective layer, and anisotropy occurs in the glossiness of the final image. The difference between the degree of orientation in the longitudinal direction and the degree of orientation in the width direction is preferably 0.020 or less, more preferably 0.010 or less.

  Further, the polyester film of the present invention needs to have a 5% elongation strength in the longitudinal direction of 120 to 145 MPa, preferably 130 to 140 MPa for the purpose of smooth transfer during high-speed printing. When the 5% elongation strength in the longitudinal direction is less than 120 MPa, the substrate film is deformed at the time of transfer of each color, and the image is defective, which is inappropriate. When the 5% elongation strength in the longitudinal direction exceeds 145 MPa, as described above, the difference between the orientation degrees in the longitudinal direction and the width direction becomes large, and anisotropy occurs in the glossiness, which is inappropriate.

  Suitable applications of the film of the present invention include, for example, a sublimation type thermal transfer system, particularly applications that print at a high speed and require uniform and high gloss.

  Examples of particles present in the polyester to obtain the winding characteristics of the present invention include calcium carbonate, silica, talc, kaolin, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide and the like. Inorganic particles, crosslinked polymer particles, organic particles such as calcium oxalate, and precipitated particles formed at the time of polyester polymerization can be mentioned. Preferred are calcium carbonate, silica, and precipitated particles containing calcium and phosphorus.

For calcium carbonate, (1) the particle size distribution is sharpened and coarse particles (particles that are significantly larger than the average particle size) are easily cut; (2) slipperiness and wear resistance are easily obtained after film formation; (3) It is preferable that particles are not easily broken when an unnecessary portion of a film that does not become a product is remelted and extruded, and the particle size is easily maintained.
Regarding silica, (1) it is preferable to obtain it at a relatively low price than other particles, and so on.

  For precipitated particles containing calcium and phosphorus, (1) it is not necessary to add particles again and it is inexpensive, (2) the deformation of the particles during stretching during film formation is small, and the projection height can be maintained. It is preferable that it exhibits good winding characteristics.

  In order to express the effect of the present invention, it is of course possible to employ a plurality of types of particles represented above. In particular, in order to further improve the slipperiness of the film surface and the winding workability, in addition to the above-exemplified particles, small particles having an average particle size of less than 0.50 μm are used in a range not impairing the gist of the present invention. You can also Preferred as small particles are silica, crosslinked polymer particles, calcium carbonate, and precipitated particles formed during polymerization of the polyester.

  In the production of the polyester containing the additive particles, the particles may be added during the polyester synthesis reaction or directly to the polyester. When added during the synthesis reaction, a method in which the particles are dispersed in ethylene glycol or the like as a slurry and added at any stage of the polyester synthesis is preferable. On the other hand, when added directly to the polyester, a method of adding and mixing to the polyester using a twin-screw kneading extruder as dry particles or as a slurry dispersed in water or an organic solvent having a boiling point of 200 ° C. or less is preferable. . The particles to be added may be subjected to a treatment such as crushing, dispersing, classification, and filtration in advance as necessary.

  As a method for adjusting the content of particles, a master raw material containing particles at a high concentration is prepared by the above-described method, and at the time of film formation, it is diluted with a raw material that does not substantially contain particles, and the particle content is reduced. It is effective to adjust this.

  Further, as additives other than the above-described protrusion forming agent, an antistatic agent, a stabilizer, a lubricant, a crosslinking agent, an antiblocking agent, an antioxidant, a colorant, a light blocking agent, an ultraviolet absorber, etc. May be contained within a range not impairing the effects of the present invention.

Next, the manufacturing method of the film of this invention is demonstrated concretely.
First, a polyester raw material is supplied to an extrusion apparatus. That is, it extrudes as a molten sheet from a slit-shaped die. Next, the molten sheet is rapidly cooled and solidified on the rotary cooling drum so as to have a temperature equal to or lower than the glass transition temperature to obtain a substantially amorphous non-oriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, the electrostatic application adhesion method and / or the liquid application adhesion method are preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the biaxial stretching conditions, the unstretched sheet is first stretched in the first axial direction. The stretching temperature range is usually 70 to 150 ° C., the stretching ratio is usually 2.5 to 6 times, and the stretching can be performed in one step or two or more steps. Next, in the second axis direction, that is, in the direction perpendicular to the first axis direction, the uniaxially oriented film is once cooled below the glass transition point, or pre-heated to a temperature range of, for example, 80 to 150 ° C. without cooling, Further, the film is stretched 2.5 to 5 times, preferably 3.0 to 4.7 times under substantially the same temperature, to obtain a biaxially oriented film. In addition, it is preferable to perform the stretching in the first axial direction in two or more stages because good thickness uniformity can be achieved. In addition, it is possible to re-stretch in the longitudinal direction after lateral stretching, but in any case, the product of the total stretching ratio in the longitudinal direction and the stretching ratio in the width direction should be 16 times or more. = 0.165 or more is preferable to achieve. Also, so-called simultaneous biaxial stretching, in which stretching in the first axial direction and the direction perpendicular thereto, is simultaneously possible.

  The film thus obtained is heat-treated for 1 second to 5 minutes under elongation, limited shrinkage, or constant length within 30%. At this time, restretching may be performed in the longitudinal direction, the transverse direction, or both directions in or after the heat treatment step.

By appropriately selecting the above-described stretching conditions and heat treatment conditions, it is necessary that the 5% elongation strength in the longitudinal direction and the difference in orientation degree between the longitudinal direction and the width direction fall within the scope of the present invention.
In addition, in the range which does not inhibit the effect of this invention, according to various end uses, in order to provide adhesiveness with the layer which contacts, a coating layer can be provided in the film surface. In order to impart this adhesion, a polymer (binder polymer) comprising at least one selected from the group consisting of an aqueous polyester polymer and an aqueous acrylic polymer is particularly useful.

  In addition, urea, melamine, guanamine, and acrylamide that are methylolated or alkylolized as a crosslinkable polymer to improve adhesion resistance (blocking resistance), water resistance, solvent resistance, and mechanical strength of the coating layer Compounds, polyamide compounds, epoxy compounds, aziridine compounds, block polyisocyanates, silane coupling agents, titanium coupling agents, zircoaluminate coupling agents, peroxides, thermal and photoreactive vinyl compounds Or a photosensitive resin.

  Further, if necessary, it may contain an antifoaming agent, a coating property improver, a thickener, an antistatic agent, an organic lubricant, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like. .

  As a method of applying the above-mentioned coating liquid to a polyester film, Yuji Harasaki, Tsuji Shoten, published in 1979, reverse roll coater, gravure coater, rod coater, air doctor coater or other coating apparatus shown in "Coating system" Can be used.

  In the present invention, from the viewpoint of cost, in order to provide a coating layer, a so-called in-line coating method in which coating is performed in the film manufacturing process is recommended.

  As a method of coating within the film production process, a coating solution is applied to an unstretched polyester film, and a method of biaxially stretching sequentially or simultaneously, coating to a uniaxially stretched polyester film, and further perpendicular to the previous uniaxial stretching direction. There is a method of stretching in the direction of the above, or a method of applying to a biaxially stretched polyester film and then stretching in the transverse and / or longitudinal direction.

  Since the film of the present invention has a smooth surface and specific characteristics, it can provide high functionality and its industrial value is high.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited by a following example, unless the summary is exceeded. In addition, the evaluation method in an Example is as follows. In Examples and Comparative Examples, “part” means “part by weight”, “%” means “wt%”, and “ppm” means “weight ppm”.

(1) Intrinsic viscosity of polymer [η] (dl / g)
1 g of the polymer was dissolved in 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) and measured at 30 ° C.

(2) Average particle diameter of added particles (d50) (μm)
In an equivalent spherical distribution measured with a centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type) manufactured by Shimadzu Corporation, the particle size of 50% of the integrated volume fraction integrated from the large particle side was taken as the average particle size (d50) of the added particles. .

(3) Average particle diameter of precipitated particles (d50) (μm)
The polyester film containing the precipitated particles was sandwiched between the preparations, melted and cooled, then observed with a microscope, and the image was measured by processing with an image processing apparatus (“Quantime 500+” manufactured by Leica). In its equivalent spherical distribution The particle size with an integrated volume fraction of 50% integrated from the large particle side was defined as the average particle size (d50) of the precipitated particles.

(4) Measurement of the amount of precipitated particles 1.0 liter of o-chlorophenol was added to 100 g of polyester, heated at 120 ° C. for 3 hours, and then centrifuged for 40 minutes using an ultracentrifuge (product of Hitachi Koki “55P-72”). Separation is performed and the resulting particles are vacuum dried at 100 ° C. When the above particles are processed with a scanning differential calorimeter and a melting peak corresponding to the polymer is observed, o-chlorophenol is added to the particles, and after heating and cooling, the centrifugation operation is performed again. And the particle | grains from which the melting peak was no longer recognized are set as precipitation particle | grains. Centrifugation is usually performed twice.

(5) Arithmetic mean roughness Ra (μm)
A film test piece was cut out and Ra was measured and calculated by the following method to obtain an arithmetic average roughness Ra (μm).
It calculated | required as follows using "SE3500" by Kosaka Laboratory. That is, an evaluation length of 2.5 mm was measured using a stylus having a tip radius of 5 μm and a load of 30 mg. The arithmetic average roughness (Ra) was determined according to the description of JIS B 0601-1994. That is, a reference length L is extracted from the roughness curve in the direction of the average line, the x-axis is taken in the direction of the average line of the extracted portion, the y-axis is taken in the direction of the vertical magnification, and the roughness curve is expressed as y = f ( When expressed by x), the value obtained by the following formula is expressed in micrometers (μm). The longitudinal magnification was set to 200,000 times, the cut-off value was set to 0.08 mm, 10 roughness curves were measured, and an average of 10 points of Ra was obtained.

Ra = (1 / L) ∫ 0 L | f (x) | dx

(6) 5% elongation strength in the longitudinal direction (F-5 value)
Ten film test pieces were cut in the longitudinal direction (longitudinal direction). The width of the test piece was 15 mm. Marks with a distance of 50 m are attached to the center of each test piece in the longitudinal direction, and a tensile test is performed using a tensile tester at a gripping interval of 50 mm and a tensile speed of 200 mm / min. The load was measured and calculated by the following formula. The average value of 10 points was defined as 5% elongation strength in the longitudinal direction.
F-5 (MPa) = Load at 5% elongation ÷ 5% elongation strength

(7) Plane orientation degree, longitudinal orientation degree, width direction orientation degree With respect to the cut film specimen, a longitudinal refractive index nMD in the film plane using an Abbe refractometer manufactured by Atago Optical Co., Ltd., the film surface The refractive index nTD in the width direction and the refractive index nα in the thickness direction were measured, and the degree of plane orientation Δp, the degree of orientation Δnp in the longitudinal direction, and the degree of orientation Δnv in the width direction were calculated. The refractive index was measured at 23 ° C. using sodium D line as a light source.

Δp = ((nMD + nTD) / 2) −nα
Δnp = nMD − ((nTD + nα) / 2)
Δnv = nTD − ((nMD + nα) / 2)
Accordingly, the difference between the orientation degree in the longitudinal direction and the orientation degree in the width direction is | Δnp−Δnv | (the absolute value of the difference between the two).

(8) Winding characteristics The following is the non-defective product ratio (ratio of rolls that could be wound without defects such as wrinkles) from a master roll produced by the method described in the examples to a roll of 500 mm width and 35000 m length. Judged by the criteria of.
◎: Good product rate is high and economic efficiency is good ○: Slightly good product rate is lowered, but is economically satisfactory level, good ×: Good product rate is low, economically harmful level, poor

(9) Production of sublimation-type thermal transfer ribbon Unrolled a good roll produced by the method described in (8) above, and coated a back coat layer coating on one side by a gravure coating method. Thereafter, it was stored in an oven at 55 ° C. for 5 days and cured to form a backcoat layer. The coating material for the backcoat layer is 5.0 parts by weight of Denkabutyral # 3000K (manufactured by Denki Kagaku Kogyo Co., Ltd.) as the polyvinyl acetal resin and 0.5 of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) as the isocyanate. Parts by weight, 20 parts by weight of Phosphanol GB520 (manufactured by Toho Chemical Co., Ltd.) as the phosphoric ester, 0.5 parts by weight of Nipsil E-200A (manufactured by Nippon Silica Industry Co., Ltd.) as silica, and methyl ethyl ketone It was prepared by mixing 37 parts by weight and 37 parts by weight of toluene.
Subsequently, the roll-shaped film after the backcoat layer is cured is rewound again, and yellow, yellow, magenta (red), cyan (blue) dyes and images are sequentially formed on the opposite surface of the backcoat layer. The protective layer (overcoat) coating was repeated, applied by gravure coating, and dried.

  About yellow (yellow) dye, it apply | coated so that it may become final thickness of 1.0 micrometer, and the coating material is 2.0 parts of macrolex yellow 6G (made by Bayer), and polyvinyl acetoacetal KS-5D (made by Sekisui Chemical Co., Ltd.). Was prepared by mixing 47.5 parts of methyl ethyl ketone and 47.5 parts of toluene.

  About magenta (red) dye, it apply | coated so that it may become final thickness of 1.0 micrometer, and the coating material is 3.0 parts of bimicron VPSN2670 (made by Bayer) and polyvinyl acetoacetal KS-5D (made by Sekisui Chemical Co., Ltd.). It was prepared by mixing 4.0 parts, 46.5 parts of methyl ethyl ketone and 46.5 parts of toluene.

  The cyan (blue) dye was applied to a final thickness of 1.0 μm, and the paint was Kayaset Blue 714 (Nippon Kayaku Co., Ltd.) and polyvinyl acetoacetal KS-5D (Sekisui Chemical Co., Ltd.) Prepared by mixing 4.0 parts of methyl ethyl ketone, 46.0 parts of methyl ethyl ketone, and 46.0 parts of toluene.

  About the coating material for screen protective layers, it apply | coated so that it might become final thickness 2.0micrometer, and a coating material is 20.0 weight part of CAB500-0.5 (made by Eastman Chemical Co.) as cellulose acetate butyrate resin, It was prepared by mixing 40.0 parts by weight of methyl ethyl ketone and 40.0 parts by weight of toluene.

(10) Image production (transfer of each color and transfer of protective layer)
For printing and thermal transfer on the dye receiving layer of photographic paper, a portion of the SVM-25LS ink ribbon, a sublimation type Digital Photo Printer DPP-SV series genuine media manufactured by Sony Corporation, was cut and described in (9) above. The ribbon produced by the method was used by joining together. A digital photo printer manufactured by Sony Corporation was used as a print for evaluation.

(10-1) Production of print unevenness determination image (solid black image) Specifically, first, a black solid image is created using the Adobe software Adope Photo Shop, and the data is printed on the printer. Transfer to DPP-SVM77, use an ink ribbon that replaces the thermal transfer film of the present invention as a part of the SVM-25LS ink ribbon, transfer a black solid image on photographic paper with the thermal transfer head of the printer, The protective layer was solid-transferred onto the image to obtain a black solid final image.

(10-2) Preparation of Glossiness and Glossiness Anisotropy Determination Image (White Solid Image) After a white solid image is transferred and printed on photographic paper in the same manner as (10-1) above The solid image of the protective layer was transferred onto the image to obtain a solid white final image.

(11) Print unevenness (defects)
Defects on the surface of the final image produced by the method described in (10-1) above were visually observed. In other words, when the ribbon is wrinkled during the transfer of each color, the color of the wrinkle portion is not transferred, and the final color is not black (= combination of yellow + red + blue), but becomes another color. Can be judged. The print unevenness was determined according to the following criteria.
◎: Print unevenness is not recognized at all, excellent ○: Print unevenness is slightly recognized, but is a level that is practically satisfactory, and good ×: Print unevenness is a level that cannot be practically used, and is poor

(12) Glossiness and anisotropy of glossiness Transfer the glossiness of the surface of the final image (solid white) produced by the method described in (10-2) above using Gloss Meter VG2000 (NIPPON DENSHOKU). The 20 ° Gloss was measured in a direction corresponding to the longitudinal direction of the ribbon, and the glossiness was determined according to the following criteria.
-Glossiness ◎: Gloss is sufficient and excellent ○: Gloss is slightly lowered, but it is a level that does not cause a problem in practical use, Good ×: Gloss is insufficient, cannot be used practically, and is poor

  The gloss anisotropy was determined by visually checking the surface of the final image in the direction corresponding to the longitudinal direction and the width direction of the ribbon, and by the following criteria.

・ Glossiness anisotropy ◎: Glossiness anisotropy is not recognized, excellent ○: Glossiness anisotropy is slightly recognized, but at a practically satisfactory level, good: Glossiness Anisotropy is large, unusable for practical use, and poor

(Polyester raw material a)
86 parts of terephthalic acid and 70 parts of ethylene glycol were placed in a reactor, and an esterification reaction was carried out at about 250 ° C. under a pressure of 0.5 kg / mm ² for 4 hours. Next, 0.015 part of antimony trioxide, silica particles having an average particle diameter of 2.2 μm, and 0.01 part of phosphoric acid were added. While gradually raising the temperature from 250 ° C. to 285 ° C., the pressure was gradually reduced from normal pressure to 0.5 mmHg. After 4 hours, the polycondensation reaction was stopped to obtain a polyester (a) having an intrinsic viscosity of 0.66. This polyester (a) contained 0.50% by weight of silica particles.

(Polyester raw material b)
A polyester (b) having an intrinsic viscosity of 0.66 was obtained in exactly the same manner as the polyester a, except that in the polyester raw material a, crosslinked polymer particles having an average particle size of 0.3 μm were added instead of silica particles. This polyester b contained 0.20% by weight of crosslinked polymer particles.

(Polyester raw material c)
A polyester for dilution (c) having an intrinsic viscosity of 0.66 was obtained in the same manner as for the polyester a except that no silica particles were added to the polyester raw material a.

(Polyester raw material d)
A polyester (d) having an intrinsic viscosity of 0.66 was obtained in the same manner as for the polyester a except that calcium carbonate particles having an average particle diameter of 1.8 μm were added in place of the silica particles in the polyester raw material a. This polyester d contained 0.50% by weight of calcium carbonate particles.

(Polyester raw material e)
100 parts of dimethyl terephthalate, 70 parts of ethylene glycol and 0.11 part of calcium acetate monohydrate are placed in a reactor and heated for heating and distilled off to conduct transesterification, which takes 4 hours from the start of the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, a solution obtained by uniformly dissolving 0.124 part of triethyl phosphite and 0.54 part of triethyl phosphate in ethylene glycol is added to the reaction mixture, and then 0.04 part of antimony trioxide is added, and then 10 minutes are added. In short, it reached 236 ° C. From this point, the pressure in the system is gradually reduced, and the temperature in the system is 265 ° C. and the pressure is 300 mmHg 80 minutes after the addition of antimony trioxide. Thereafter, the temperature is gradually raised and reduced and finally 285 ° C. and 1 mmHg or less. did. After 4 hours, the inside of the system was returned to normal pressure and the polymer was discharged to form a chip to obtain a polyester (e) having an intrinsic viscosity of 0.66. In this polyester (e), a large number of uniform and fine precipitated particles were observed, and the average particle size was 1.8 μm. When the amount of the precipitated particles was measured according to the method described, it was 0.4% by weight based on the polyester.

Example 1:
Polyester (a), polyester (b) and polyester (c) are mixed and contain 0.05% silica particles having an average particle size of 2.2 μm and 0.02% crosslinked polymer particles having an average particle size of 0.3 μm. Used as raw material. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.70 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.67 times at 75 ° C. Then, it led to the tenter, stretched 4.35 times at 110 ° C. in the transverse direction, and heat-treated at 232 ° C. to obtain a biaxially stretched polyester film (master roll) having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

Example 2:
Polyester (c) and polyester (d) were mixed to obtain a raw material containing 0.15% calcium carbonate particles having an average particle diameter of 1.8 μm. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.70 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.59 times at 75 ° C. Then, it led to the tenter and stretched 4.35 times at 110 degreeC to the horizontal direction, heat-processed at 230 degreeC, and obtained the 4.5 micrometer-thick biaxially stretched polyester film (master roll). While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

Example 3:
Polyester (a) and polyester (c) were mixed to obtain a raw material containing 0.08% silica particles having an average particle size of 2.2 μm. This mixed raw material was dried by a conventional method and supplied to an extruder, and a biaxially stretched polyester film (master roll) having a thickness of 4.5 μm was obtained in exactly the same manner as in Example 2. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

Example 4:
Polyester (a) and polyester (c) were mixed to obtain a raw material containing 0.05% of silica particles having an average particle size of 2.2 μm. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.90 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.54 times at 75 ° C. Then, it led to the tenter and stretched 4.35 times at 110 degreeC to the horizontal direction, heat-processed at 230 degreeC, and obtained the 4.5 micrometer-thick biaxially stretched polyester film (master roll). While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

Example 5:
Polyester (c) and polyester (e) were mixed to obtain a raw material containing 0.12% of precipitated particles having an average particle diameter of 1.8 μm. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.90 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched 1.50 times at 75 ° C. Then, it led to the tenter and stretched 4.35 times at 110 degreeC to the horizontal direction, heat-processed at 230 degreeC, and obtained the 4.5 micrometer-thick biaxially stretched polyester film (master roll). While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

Comparative Example 1:
Polyester (a) and polyester (c) were mixed to obtain a raw material containing 0.30% silica particles having an average particle size of 2.2 μm. This mixed raw material was dried by a conventional method and supplied to an extruder, and a biaxially stretched polyester film (master roll) having a thickness of 4.5 μm was obtained in exactly the same manner as in Example 5. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

Comparative Example 2:
Polyester (c) and polyester (d) were mixed to obtain a raw material containing 0.03% calcium carbonate particles having an average particle diameter of 1.8 μm. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched by 2.70 times at 90 ° C. in the longitudinal direction using a roll stretching method, and further stretched by 1.40 times at 75 ° C. Then, it led to the tenter and stretched 4.35 times at 110 degreeC to the horizontal direction, heat-processed at 230 degreeC, and obtained the 4.5 micrometer-thick biaxially stretched polyester film (master roll). While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

Comparative Example 3:
Polyester (c) and polyester (e) were mixed to obtain a raw material containing 0.12% of precipitated particles having an average particle diameter of 1.8 μm. The mixed raw material was dried by a conventional method, supplied to an extruder, melted at 290 ° C., extruded into a sheet, and rapidly cooled on a cooling roll using an electrostatic application adhesion method to obtain an amorphous sheet. The obtained sheet was stretched 2.70 times at 90 ° C. in the longitudinal direction by using a roll stretching method, and further stretched 1.72 times at 75 ° C. Thereafter, the film was guided to a tenter, stretched 4.10 times in the transverse direction at 110 ° C., and heat treated at 217 ° C. to obtain a biaxially stretched polyester film (master roll) having a thickness of 4.5 μm. While being trimmed to a width of 500 mm from this master roll, the film was wound into a roll at a total length of 35000 m and a speed of 250 m / min on a 6-inch inner diameter core to obtain a roll film.

  The results obtained for Examples 1 to 5 and Comparative Examples 1 to 3 are summarized in Tables 1 to 3 below.

  The film of the present invention can be suitably used, for example, as a base film for a sublimation type thermal transfer ribbon.

Claims (1)

The film thickness is 6 μm or less, the 5% elongation strength in the film longitudinal direction is 120 to 145 MPa, the plane orientation degree of the film is 0.165 or more, and the orientation degree in the film longitudinal direction is 0.070 to 0.00. 091, the absolute value of the difference between the degree of orientation in the film longitudinal direction and the degree of orientation in the width direction is 0.009 to 0.026, and the arithmetic average roughness (Ra) of at least one side is 0.031 to 0.045 μm. A polyester film for a sublimation type thermal transfer ribbon, characterized in that there is.