JP6543966B2 - Biaxially oriented polyester film - Google Patents

Description

The present invention relates to a biaxially oriented polyester film having good local heat resistance, printing sensitivity and transportability.

Polyester films using polyethylene terephthalate or polyethylene-2,6-naphthalate are excellent in mechanical properties, heat resistance, dimensional stability, chemical resistance, cost performance, etc. It is used. One of them is a thermal transfer ribbon. The thermal transfer recording method is used in fields such as fax and bar code printing because it is excellent in cost performance, maintainability, operability, etc. In recent years, characteristics such as high definition and high image quality can be obtained by using a color thermal transfer ink. In addition, color thermal transfer printers are also used.
In these thermal transfer systems, a thermal transfer ink ribbon provided with a thermal transfer layer containing a coloring material such as pigment and dye and a binder such as wax on a polyester film is superimposed on an image receiving sheet, and a thermal head is used from the back side of the thermal transfer ink ribbon. In this method, an image is formed on the image receiving sheet by applying heat, melting the heat transfer layer and fusing it on the image receiving sheet.
In thermal transfer ink ribbons, it is required to thin the polyester film so that transfer can be easily performed with less energy from the viewpoint of space saving of the ribbon and energy saving, but polyester is locally heated by the heat of the thermal head and polyester There is a problem with holes in the film. In addition, when the film thickness is reduced, the sliding (conveying property) between the thermal head and the polyester film at the time of printing also becomes a problem. Therefore, in order to improve local heat resistance and transportability, attempts have been made to alloy a resin of high heat resistance with a resin constituting a polyester film (Patent Document 1) or to coat the film surface (Patent Document 2). .

JP 2000-309650 A Japanese Patent Application Laid-Open No. 7-179077

Also in the method described in the above-mentioned document, a certain improvement in local heat resistance and transportability can be obtained. However, in recent years, the temperature of the thermal head has become higher in order to increase the efficiency of thermal transfer, so the local heat resistance is not sufficient by the method described in the above document, and the problem is particularly in the case of a thin polyester film. Was remarkable. In addition, the ink application property, the printing sensitivity, and the transportability also have problems.
An object of the present invention is to solve such problems and to provide a polyester film having good coatability, local heat resistance, printing sensitivity and transportability.

In order to solve the above-mentioned subject, the present invention takes the following composition.
[I] A biaxially oriented polyester film wherein the melt viscosity of the polyester resin constituting the film at 280 ° C. is 150 to 500 [Pa · s] and the film thickness is 1 to 9 μm.
[II] The biaxially oriented polyester film according to [I], wherein the amount of terminal carboxyl groups of the polyester resin constituting the film is 5 to 25 equivalent / t.
[III] The biaxially oriented polyester film according to [I] or [II], wherein the surface roughness SRa of at least one surface of the film surface is 20 to 50 nm.
[IV] Any one of [I] to [III] in which the polyester resin composition constituting the film contains antimony and the content thereof is 100 to 500 ppm with respect to the whole polyester resin composition constituting the film Biaxially oriented polyester film according to
[V] The biaxially oriented polyester film according to any one of [I] to [IV], which is used as a substrate of a thermal transfer ribbon.
[VI] The biaxially oriented polyester film according to [V], which is used as a substrate of a heat melting type thermal transfer ribbon.
[VII] A thermal transfer ribbon using the biaxially oriented polyester film according to any one of [I] to [VI].

  The biaxially oriented polyester film of the present invention is excellent in any of local heat resistance, printing sensitivity and transportability. Therefore, the film of the present invention can be suitably used for a thermal transfer ribbon application.

The present invention will be described in detail by way of specific examples.

  The polyester used for the biaxially oriented polyester film of the present invention comprises a dicarboxylic acid component and a diol component. In addition, in this specification, a component shows the thing of the minimum unit which can be obtained by hydrolyzing polyester.

  Examples of the dicarboxylic acid component constituting the polyester include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid and methylmalon. Aliphatic dicarboxylic acids such as acid, ethyl malonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cycloaliphatic dicarboxylic acids such as cyclohexane dicarboxylic acid, decalin dicarboxylic acid, etc., terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalene Dicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodium sulfoisophthalic acid Acid, fe Toluene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic acid, 9,9'-bis (4-carboxyphenyl) dicarboxylic acids such as fluorene acids and aromatic dicarboxylic acids, or include an ester derivative thereof.

  Further, as a diol component constituting such a polyester, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol Aliphatic diols such as, cycloaliphatic diols such as cyclohexanedimethanol and spiroglycol, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyl Examples thereof include diols such as phenyl) fluorene and aromatic diols, and a series of a plurality of the above-mentioned diols. In the present invention, polyethylene terephthalate and polyethylene naphthalate are preferably used as polyester. More preferably, polyethylene terephthalate is preferable from the viewpoint of coating properties such as thickness unevenness.

  The thickness of the biaxially oriented polyester film of the present invention is required to be 1 μm to 9 μm. More preferably, it is 2 μm to 6 μm. When it is less than 1 μm, when it is formed into a thermal transfer ribbon, it is not preferable because the transportability is poor and the generation of printing wrinkles and the occurrence of perforation due to the local heat resistance shortage are generated. On the other hand, when the thickness exceeds 9 μm, the printing sensitivity is lowered when forming a thermal transfer ribbon, which is not preferable.

  In the biaxially oriented polyester film of the present invention, the melt viscosity of the polyester resin constituting the film at 280 ° C. needs to be 150 to 500 [Pa · s]. More preferably, it is 180-400 [Pa * s]. The melt viscosity of the polyester resin constituting the film at 280 ° C. is a value determined by the measurement method described later, and is an index representing the fluidity of the polyester resin at 280 ° C. The smaller the value, the higher the fluidity of the polyester resin at 280 ° C., and the larger the value, the lower the fluidity of the polyester resin at 280 ° C. By setting the melt viscosity at 280 ° C. of the polyester resin constituting the film to 150 to 500 [Pa · s], it is possible to obtain a film having good local heat resistance, printing sensitivity, coatability and transportability.

The reason why this effect is obtained is not limited to any theory, but the present inventors estimate as follows.
When a polyester film is used as a base of a thermal transfer ribbon, a thermal load of about 280 ° C. is locally applied to the polyester film as a base by the thermal head which has become hot when the thermal transfer ribbon is printed. At this time, when the melt viscosity of the polyester resin constituting the film at 280 ° C. was 150 to 500 [Pa · s], the heat load of about 280 ° C. was locally applied to the polyester film, and the heat load was received. It is presumed that the polyester resin around the part flows to suppress the occurrence of holes or defects in the heat-loaded part. On the other hand, when the melt viscosity is less than 150 [Pa · s], the flowability of the polyester resin is too high, and the portion subjected to the thermal load is easily deformed, and a hole is formed in the polyester film. On the other hand, if the melt viscosity at 280 ° C. is greater than 500 [Pa · s], the melt viscosity is too high, so the surrounding polyester resin that receives the heat load can not flow, and the portion that received the heat load Since it can not be repaired, the printing sensitivity is reduced due to the defect in the portion subjected to the heat load. Moreover, since it is easy to become an extrusion nonuniformity and extending | stretching nonuniformity easily at the time of manufacture of a polyester film, and thickness nonuniformity tends to generate | occur | produce, the coating property of a ribbon deteriorates.

  In order to make melt viscosity in 280 degreeC into the said range, the method of controlling the intrinsic viscosity of the polyester resin used as a film raw material, the method of controlling the melting point (Tm) of the polyester resin used as a film raw material, etc. are mentioned. If the intrinsic viscosity value (IV) of the film material is increased, and if the melting point (Tm) of the polyester resin constituting the film is increased, the melt viscosity of the polyester resin constituting the film can be increased at 280 ° C. . The film material IV is preferably 0.7 dl / g or more, more preferably 0.75 dl / g or more, because the IV decrease due to heat occurs in the extruder. Furthermore, it is preferable that the temperature control in the extruder be precise. Disturbance of temperature control tends to cause a decrease in IV, making it difficult to obtain the melt viscosity of the biaxially oriented polyester of the present invention. The melting point (Tm) of the polyester resin constituting the film is preferably 250 ° C. or more and 275 ° C. or less, more preferably 254 ° C. or more and 270 ° C. or less.

  In the biaxially oriented polyester film of the present invention, the amount of carboxyl end groups of the polyester resin constituting the film is preferably 5 to 25 [equivalent / t]. More preferably, it is 10-20 [equivalent / t]. When the amount of carboxyl end groups is less than 5 [equivalent / t], the wettability of the surface of the polyester film is deteriorated, and the coatability of the ribbon may be deteriorated, which is not preferable. When it is larger than 25 [equivalent / t], the polyester resin is likely to be deteriorated when it receives the heat of thermal transfer, and it may be likely to cause perforation, which is not preferable.

  The biaxially oriented polyester film of the present invention preferably has a surface roughness SRa of at least one surface of 20 to 50 [nm]. More preferably, it is 30-40 [nm]. If the SRa is less than 20 nm, the transportability may deteriorate, which is not preferable. If it is larger than 50 nm, the print head can not be approached and printing sensitivity may be deteriorated, which is not preferable. As a method for setting the surface roughness to the above range, (i) incorporating particles into the polyester resin composition constituting the film, (ii) forming protrusions on the surface of the film by imprint, (iii) A void may be formed in the resin that constitutes the film, and the void may be used to impart a shape to the film surface. In the case of a film having a thin film thickness, it is preferable to use the method (i) from the viewpoint of film forming property and protrusion forming property.

  In the biaxially oriented polyester film of the present invention, the polyester resin composition constituting the film contains antimony, and the content thereof is preferably 100 to 500 ppm. More preferably, it is 150-300 ppm. When the amount of antimony element contained in the polyester resin composition constituting the film is within the above range, the energy transfer by the print head (thermal head) becomes good, the printing sensitivity can be made good, and the local heat resistance Can be good. If the amount of antimony element contained in the polyester resin composition constituting the film is less than 100 ppm, the energy transfer by the print head (thermal head) may be deteriorated to deteriorate the printing sensitivity. If it is more than 500 ppm, the antimony element acts as a catalyst for the thermal decomposition reaction, and the local heat resistance may be deteriorated.

The biaxially oriented polyester film of the present invention is suitably used as a film for a thermal transfer ribbon because it has good coatability, local heat resistance, printing sensitivity and transportability. As a thermal transfer method, there are a heat melting type in which a heat-soluble pigment ink is melted and transferred by heat, and a sublimation type in which a sublimation dye ink is sublimated and transferred.
In the thermal transfer type thermal transfer system, in color printing using a plurality of ink ribbons, a plurality of thermal loads are applied. Since the polyester film of the present invention is excellent in local heat resistance, it can suppress the occurrence of perforation even when color printing is performed by the heat melting type thermal transfer system, and therefore it is used as a substrate of a heat melting type thermal transfer ribbon. It can be used suitably.
In addition, in the sublimation type thermal transfer method, the thermal head tends to have a high temperature because it is necessary to sublimate the dye with high output and fix the ink reliably. Since the polyester film of the present invention is excellent in local heat resistance, it can suppress the occurrence of perforation even if printing is performed in a sublimation type thermal transfer system, and therefore it should be suitably used as a substrate of a sublimation type thermal transfer ribbon. Can.

  The method for producing the polyester film of the present invention will be described below by way of examples, but the present invention is not construed as being limited to only such examples. In order to produce a polyester film, for example, polyester pellets are melted using an extruder, discharged from a die, and then cooled and solidified to form a sheet. At this time, in order to remove the unmelted substance in the polymer, the polymer may be filtered by a fiber sintered stainless metal filter. Furthermore, various additives, for example, compatibilizers, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brighteners, coloring, as long as the effects of the present invention are not impaired. Agents, conductive agents, UV absorbers, flame retardants, flame retardant aids, pigments, dyes and the like may be added.

  Subsequently, the sheet-like material obtained as described above is biaxially stretched in the longitudinal direction and the width direction, and then heat-treated. As a stretching method, sequential biaxial stretching such as stretching in the longitudinal direction followed by stretching in the width direction, simultaneous biaxial stretching in which the longitudinal direction and the width direction are simultaneously stretched using a simultaneous biaxial tenter, etc. The method etc. which combined the sequential biaxial stretching method and the simultaneous biaxial stretching method are included.

  The raw material pellets (and, if necessary, the master batch) of each layer constituting the biaxially oriented polyester film of the present invention are dried under reduced pressure at a temperature of 180 ° C. for 3 hours or more using an extruder. Is fed to an extruder heated to a temperature of 265 to 280 ° C. under a nitrogen stream or under reduced pressure so as not to decrease, extruded from a slit-like T-die, and cooled on a casting roll to obtain an unstretched film. In order to control the melt viscosity of the film within the range of the present invention, it is preferable to use a cast electric heater for temperature control of the cylinder of the extruder, and more preferable to perform cooling control by a water cooling jacket. The film is laminated by using two or more extruders and a manifold or merging block. Moreover, in order to control to the film thickness of this application, it is preferable that the velocity fluctuation rate of a casting roll is less than +/- 0.5%. Since the biaxially oriented polyester film of the present invention is as thin as 1 to 9 μm, if the rate fluctuation rate is large, the film formability is unfavorably deteriorated.

  Next, the unstretched film obtained in this manner is biaxially stretched. Biaxial stretching method in which stretching is performed in the longitudinal direction (MD stretching) using a circumferential velocity difference of rolls using a longitudinal stretching machine in which several rolls are arranged, and then transverse stretching is performed by a stenter (TD stretching) Will be explained.

  First, the unstretched film is MD stretched. The longitudinal stretching machine comprises a preheating roll, a stretching roll, and a cooling roll, and further comprises a nip roll for cutting tension and reducing film slippage. In MD stretching, a film running on a stretching roll is held down by a constant pressure (nip pressure) with a stretching nip roll to cut tension by cutting the film, and the next cooling roll of the stretching roll is rotated with a circumferential speed difference. It is drawn. The MD stretching temperature is (glass transition temperature (hereinafter described as Tg) + 5) to (Tg + 50) ° C, and the stretching ratio of MD stretching is 1.2 to 5.0 times. After drawing, it cools by the cooling roll group of the temperature of 20-50 degreeC.

Next, stretching in the width direction (TD stretching) is performed using a stenter. The stenter is a device for stretching the film by stretching between the clips at both ends while holding the ends of the film with clips, and is divided into a preheating zone, a drawing zone, a heat treatment zone and a cooling zone. The clip temperature is preferably less than 60.degree. When the clip temperature is 60 ° C. or more, the biaxially oriented polyester film of the present invention is as thin as 1 to 9 μm, so the part gripped by the clip may be easily torn and the film forming property may be deteriorated. The stretching ratio in TD stretching is 2.0 to 6.0, and the stretching temperature is in the range of (Tg) to (Tg + 50) ° C. After TD stretching, a heat setting process is performed. The heat setting process is heat-treated in a temperature range of 150 to 240 ° C. while relaxing the film under tension or in the width direction. The heat treatment time is in the range of 0.5 to 10 seconds. Thereafter, the film is cooled to 25 ° C. in the cooling zone, and the film edge can be removed to obtain the biaxially oriented polyester film of the present invention.
[Method of measuring and evaluating characteristics]
(1) Melt viscosity at 280 ° C. Melt viscosity at 280 ° C. was evaluated using the following apparatus in accordance with JIS K7199 (1999). It measured 5 times and made the average melt viscosity.
Measuring device: Capirograph 1D Toyo Seiki Seisakusho Co., Ltd. Capillary length: 10 mm
· Capillary diameter: 1 mm
· Capillary temperature: 280 ° C
Preheating time (time from filling the measurement sample into the capillary to starting measurement): 6 minutes Shear rate: 100 [1 / s]
・ Sample amount: 30 g
Sample pretreatment: dried at 180 ° C. for 3 hours at a degree of vacuum of 0.2 kPa or less.

(2) Intrinsic Viscosity A polyester composition is dissolved in 100 ml of orthochlorophenol (solution concentration C = 1.2 g / dl), and the viscosity of the solution at 25 ° C. is measured using an Ostwald viscometer. Similarly, the viscosity of the solvent is measured. Using the obtained solution viscosity and solvent viscosity, [η] (dl / g) is calculated according to the following equation (c), and the obtained value is taken as the intrinsic viscosity (IV).
(C) spsp / C = [η] + K [η] ² · C
(Here, sp sp = (solution viscosity (dl / g) / solvent viscosity (dl / g)-1, K is a Huggins constant (0.343)).

(3) Amount of terminal carboxyl group (described as COOH amount in the table)
It measures according to the following conditions according to the method of Maulice (document M. J. Maulice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)). 2 g of a polyester composition is dissolved in 50 mL of o-cresol / chloroform (weight ratio 7/3) at a temperature of 150 ° C., titrated with a 0.05 N KOH / methanol solution, and the amount of terminal carboxyl groups is measured. It shows by the value of / polyester 1t. In addition, the indicator at the time of titration uses the phenol red, and let the point which changed from yellow green into pink as the end point of titration.

(4) Surface roughness SRa [nm]
The surface morphology of the polyester film is measured under the following conditions in accordance with JIS-B0601 (1994) using a high-resolution fine-shape measuring instrument (three-dimensional surface roughness meter) of the stylus method.
・ Measurement device: Three-dimensional fine shape measurement device (Model ET-4000A) Co., Ltd. Kosaka Laboratory Ltd. ・ Analyzer: Three-dimensional surface roughness analysis system (Model TDA-31)
-Tactile needle: Tip radius 0.5 μmR, diameter 2 μm, made of diamond-Needle pressure: 100 μN
・ Measurement direction: After measuring the film longitudinal direction and film width direction once each ・ Average length of X measurement: 1.0 mm
・ X feed rate: 0.1 mm / s (measurement speed)
・ Y feed pitch: 5μm (measurement interval)
・ Y number of lines: 81 (number of measurements)
・ Z magnification: 20 times (longitudinal magnification)
・ Low-pass cutoff: 0.20 mm (waviness cutoff value)
High frequency cutoff: R + W mm (roughness cutoff value) R + W means that no cutoff is performed.
· Filter method: Gaussian space type · Leveling: Yes (tilt correction)
・ Reference area: 1 mm ² .

(5) Element content The content of the metal element of the polyester resin composition constituting the film is determined by atomic absorption spectrometry (manufactured by Koridate Seisakusho: polarized Zeeman atomic absorptiometer 180-80, frame: acetylene-air) went.

(6) Thickness of film (μm)
The film thickness was measured at arbitrary five places in a state where ten sheets of the film were stacked, using a dial gauge and according to JIS K 7130 (1992) A-2. The average value was divided by 10 to obtain the film thickness.

(7) Coatability A coating solution of the following composition (i) is coated on one surface of the biaxially oriented polyester film of the present invention using a direct gravure coater so that the coating amount is 0.3 g / m ^2, and dried The heat-resistant protective layer was formed.
Composition (i)
Silicone resin: 10 parts Toluene: 45 parts MEK: 45 parts
A coating solution of the following composition (ii) was coated on the other surface of the biaxially oriented polyester film using a direct gravure coater so that the coating amount was 0.5 g / m ^2, and dried to form a release layer. .
Composition (ii)
Polyethylene wax: 9 parts Ethylene-vinyl acetate copolymer: 1 part Toluene: 10 parts A coating solution of the following composition (iii) on this release layer was coated by a direct gravure coater so that the coating amount would be 1.0 g / m ² The coating was applied and dried to form a hot-melt ink layer to obtain a thermal transfer ribbon.
Composition (iii)
Carnauba wax: 10 parts Terpene phenol resin: 30 parts Carbon black: 10 parts Toluene: 100 parts The coatability of the obtained thermal transfer ribbon was evaluated based on the following criteria.
The thermal transfer ribbon having a width of 1 m and a length of 20 m was observed in a dark room using reflected light from a three-wavelength fluorescent lamp as a light source, and the number of coating defects was counted. The coating defects as used herein refer to "coating stripes" in which there are portions which are not coated in a stripe shape in the longitudinal direction of the film and "coating omissions" in which coating unevenness is formed in a crater shape. The coating streaks were counted on those which can be visually confirmed, and the coating omissions were counted on those having a diameter of 5 mm or more. A was the best, and C or more passed.
A: less than 5 B: 5 or more and less than 10
C: 10 or more and less than 30
D: 30 or more.

(8) Local heat resistance, printing sensitivity The thermal transfer ribbon obtained in the above (7) was subjected to energy using a thermal transfer printer (Seiko Electronics Co., Ltd. high definition printer Color Printer 2 software “PALMIX” with 8 gradations) The image was printed at level 20 and evaluated according to the following criteria. A was the best, and C or more passed.
・ Local heat resistance (hole number)
The thermal transfer ribbon after printing was visually confirmed, and the number of holes was evaluated.

A: 5 pcs / 100 mm ^{2 or} less B: 5 to 10 pcs / 100 mm ^{2 or} less C: 10 to 30 pcs / 100 mm ² less than D: 30 pcs / 100 mm ² or more print sensitivity energy level is lowered to obtain a print The images were visually judged and evaluated.

A: energy level less than 10 with no image quality unevenness B: energy level with 10 or more and less than 15 without image quality unevenness C: energy level with 15 or more but less than 20 without image quality unevenness D: energy level with 20 or more image quality unevenness.

(9) Transportability The thermal transfer ribbon obtained in (7) above was subjected to 10 m printing in the same manner as in (7) above, and evaluated according to the following criteria. A was the best, and C or more passed.
A: Less than 3 wrinkles are generated per 20 cm of ribbon B: 3 or more and less than 5 wrinkles are generated per 20 cm of ribbon (practicable)
C: 5 or more and less than 10 wrinkles occur per 20 cm of ribbon (practical use possible)
D: Ribbon transport failure is observed or wrinkles of 10 or more per 20 cm of ribbon occur (there is a problem in practical use)

EXAMPLES Hereinafter, the present invention will be described by way of examples, but the present invention is not necessarily limited thereto.
In addition, in the following, Examples 4, 14, 16 to 20 shall be read as Reference Examples 4, 14, 16 to 20.

  [Production of PET] 100 parts by mass of dimethyl terephthalate, 57.5 parts by mass of ethylene glycol, 0.03 parts by mass of magnesium acetate dihydrate, 0.03 parts by mass of antimony trioxide were melted at 150 ° C. under a nitrogen atmosphere . The melt was heated to 230 ° C. over 3 hours with stirring to distill off methanol and complete the transesterification reaction. After completion of the transesterification reaction, an ethylene glycol solution (pH 5.0) in which 0.005 parts by mass of phosphoric acid was dissolved in 0.5 parts by mass of ethylene glycol was added. The intrinsic viscosity of the polyester composition at this time was less than 0.2. Thereafter, the polymerization reaction was carried out at a final temperature of 285 ° C. under a vacuum of 0.1 Torr to obtain a polyethylene terephthalate having an intrinsic viscosity of 0.52 and a terminal carboxyl group content of 15 equivalent / ton. The obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours. Thereafter, solid phase polymerization at 220 ° C. under a vacuum degree of 0.3 Torr for 8 hours was carried out to obtain a polyethylene terephthalate (PET chip-1) having an intrinsic viscosity of 0.80 and a terminal carboxyl group amount of 10 equivalent / ton. The glass transition temperature of the obtained PET chip-1 was 82 ° C, and the melting point thereof was 255 ° C.

Example 1
PET chip 1 and silica having an average particle diameter of 2 μm were mixed, and the mixture was melt-kneaded to prepare master pellet-2. Here, the concentration of silica in master pellet 2 is 2% by mass.

  Next, this master pellet-2 (10 parts by mass) and PET chip-1 (90 parts by mass) were mixed, and these mixtures were dried under reduced pressure at 180 ° C. for 3 hours. The temperature was supplied to an extruder E whose cylinder was heated to 282 ° C. using a cast electric heater and a water cooling jacket for temperature control, and was introduced into a T die cap.

Next, the melt of PET chip-1 and masterbatch-2 is extruded into a sheet form from the inside of the T die cap to form a molten single-layer sheet, and the cast drum is cooled at a surface temperature of 25.degree. The contact cooling and solidification were carried out while applying a charge to prepare an unstretched film. Then, after preheating the obtained unstretched film with heated rolls, tension is cut using a silicon stretching roll and a nip roll, and 3.5-fold MD stretching is performed at a temperature of 90 ° C. in the longitudinal direction. Then, it cooled by the roll group of temperature of 25 degreeC, and obtained the uniaxially stretched film. While holding the both ends of the obtained uniaxially stretched film with a clip cooled to 60 ° C. or less, it is led to a preheating zone at a temperature of 80 ° C. in a tenter, and is continuously orthogonal to the longitudinal direction in a heating zone at a temperature of 90 ° C. The film was stretched 3.7 times in the width direction (TD direction). Subsequently, heat treatment was performed at a temperature of 232 ° C. for 5 seconds in a heat treatment zone in the tenter, and relaxation treatment was further performed at a temperature of 232 ° C. in the 4% width direction. Next, after being uniformly cooled in the cooling zone, the film was wound up to obtain a biaxially oriented polyester film. Properties of the obtained film are shown in the table. It was a film excellent in all of coating property, local heat resistance, printing sensitivity and transportability.
(Examples 2 to 3)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the film thickness was changed as shown in Table 1.
(Examples 4 to 5)
Example 5 is the same as Example 1 except that a polyester resin having an intrinsic viscosity of 1.4 is used in Example 5 except that a polyester resin having an intrinsic viscosity of 0.67 is used as PET chip-1 A biaxially stretched polyester film was obtained.
(Examples 6 to 9)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that a film raw material having the amount of terminal carboxyl group described in Table 1 was used.
(Examples 10 to 13)
The average particle diameter of the particles contained in the master pellet 2 is 1.3 μm in Example 10, 1.5 μm in Example 11, 2.5 μm in Example 12, and 2.7 μm in Example 13. A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the surface roughness was changed.
(Examples 14 to 20)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the metal element and the content contained in the polyester resin composition constituting the film were changed as shown in Table 1.
(Example 21)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that a PEN chip having an intrinsic viscosity of 0.58, a terminal carboxyl group content of 15 equivalents / t, and a melting point of 264 ° C. was used instead of PET chip-1. .
(Comparative Examples 1 and 2)
A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the film thickness was changed as shown in Table 1.
(Comparative examples 3 to 4)
Example 4 is the same as Example 1 except that a polyester resin having an intrinsic viscosity of 1.5 is used in Example 5 except that a polyester resin having an intrinsic viscosity of 0.65 is used as PET chip-1 A biaxially stretched polyester film was obtained.

The biaxially oriented polyester film of the present invention has good coatability, local heat resistance, printing sensitivity and transportability. Therefore, it is suitably used as a film for thermal transfer ribbons.

Claims (5)

Film a melt viscosity of 280 ° C. of the polyester resin constituting the the 200 ~500 [Pa · s], Ri film thickness 1~9μm der, polyester resin composition constituting the film contains antimony element cage, polyester is 100~300ppm to the whole resin composition, biaxially oriented polyester film that is used as the substrate of the thermal transfer ribbon constituting the content of the film. The biaxially oriented polyester film according to claim 1, wherein the amount of terminal carboxyl groups of the polyester resin constituting the film is 5 to 25 equivalents / t. The biaxially oriented polyester film according to claim 1 or 2, wherein the surface roughness SRa of at least one surface of the film surface is 20 to 50 nm. The biaxially oriented polyester film according to any one of claims 1 to 3, which is used as a substrate of a heat melting type thermal transfer ribbon. A thermal transfer ribbon using the biaxially oriented polyester film according to any one of claims 1 to 4 .