JP2016160403A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film having excellent local heat resistance, print sensitivity, and transportability.SOLUTION: The present invention provides a biaxially oriented polyester film in which a polyester resin constituting the film has a melt viscosity at 280°C of 150-500 [Pa s], and the film thickness is 1-9 μm.SELECTED DRAWING: None

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 and 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 barcode printing because of its excellent cost performance, maintainability, and operability. In recent years, high-definition and high-quality characteristics have been achieved by using color thermal transfer ink. In addition, it is also used in color thermal transfer printers.
In these thermal transfer systems, a thermal transfer ink ribbon in which a thermal transfer layer including a color material such as pigment and dye and a binder such as wax is provided on a polyester film is overlapped with 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 to melt the thermal transfer layer and fusing it on the image receiving sheet.
In thermal transfer ink ribbons, polyester film is required to be thin so that transfer can be easily performed with less energy from the viewpoint of space saving and energy saving of the ribbon, but the polyester is heated locally by the heat of the thermal head. There is a problem of holes in the film. In addition, when the film is made thin, slippage (conveyance) between the thermal head and the polyester film during printing becomes a problem. Therefore, in order to improve local heat resistance and transportability, attempts have been made to alloy a resin that constitutes a polyester film with a high heat resistance resin (Patent Document 1) and to coat the film surface (Patent Document 2). .

JP 2000-309650 A JP-A-7-179077

Even in the methods described in the above-mentioned documents, a certain improvement in local heat resistance and transportability can be obtained. However, in recent years, since the temperature of the thermal head has become higher in order to increase the efficiency of thermal transfer, the method described in the above document does not have sufficient local heat resistance, and is particularly problematic in a thin polyester film. Was remarkable. Also, there are problems with ink applicability, printing sensitivity, and transportability.
This invention solves this problem, and makes it a subject to provide a polyester film with favorable applicability | paintability, local heat resistance, printing sensitivity, and a conveyance property.

In order to solve the above problems, the present invention has the following configuration.
[I] A biaxially oriented polyester film in which the polyester resin constituting the film has a melt viscosity at 280 ° C. of 150 to 500 [Pa · s] and a film thickness of 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 of [I] to [III], in which the polyester resin composition constituting the film contains an antimony element and the content thereof is 100 to 500 ppm with respect to the entire polyester resin composition constituting the film. A biaxially oriented polyester film according to claim 1.
[V] The biaxially oriented polyester film according to any one of [I] to [IV], which is used as a base material for a thermal transfer ribbon.
[VI] The biaxially oriented polyester film according to [V], which is used as a base material for a thermal 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 has good local heat resistance, printing sensitivity, and transportability. Therefore, the film of the present invention can be suitably used for thermal transfer ribbon applications.

Hereinafter, the present invention will be described in detail with specific examples.

  The polyester used in the biaxially oriented polyester film of the present invention has a dicarboxylic acid component and a diol component. In addition, in this specification, a structural component shows 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, methylmalon. Aliphatic dicarboxylic acids such as acid, ethylmalonic acid and the like, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, 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-sodiumsulfoisophthalate 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.

  Examples of the diol component constituting the polyester include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol. Aliphatic diols such as cyclohexanedimethanol, spiroglycol, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9′-bis (4-hydroxy Phenyl) fluorene, diols such as aromatic diols, and those in which a plurality of the above diols are linked. In the present invention, polyethylene terephthalate and polyethylene naphthalate are preferably used as the polyester. More preferably, polyethylene terephthalate is preferable from the viewpoint of applicability such as thickness unevenness.

  The thickness of the biaxially oriented polyester film of the present invention needs to be 1 μm to 9 μm. More preferably, it is 2 micrometers-6 micrometers. When the thickness is less than 1 μm, when the thermal transfer ribbon is formed, the transportability is poor, and printing wrinkles are generated, or holes due to insufficient local heat resistance are generated. On the other hand, when the thickness exceeds 9 μm, the printing sensitivity is lowered when the thermal transfer ribbon is formed, which is not preferable.

  In the biaxially oriented polyester film of the present invention, the polyester resin constituting the film needs to have a melt viscosity at 280 ° C. of 150 to 500 [Pa · s]. More preferably, it is 180-400 [Pa * s]. The melt viscosity at 280 ° C. of the polyester resin constituting the film is a value determined by a measurement method described later, and serves as an index representing the fluidity of the polyester resin at 280 ° C. When the value is small, it indicates that the fluidity of the polyester resin at 280 ° C. is high, and when the value is large, the fluidity of the polyester resin at 280 ° C. is low. By setting the melt viscosity at 280 ° C. of the polyester resin constituting the film to 150 to 500 [Pa · s], a film having good local heat resistance, printing sensitivity, applicability, and transportability can be obtained.

The reason why this effect is obtained is not limited to any theory, but the present inventors presume as follows.
When the polyester film is used as the base material of the thermal transfer ribbon, a thermal load of about 280 ° C. is locally applied to the polyester film as the base material by the thermal head that has become high temperature when the thermal transfer ribbon is printed. At this time, when the polyester resin constituting the film had a melt viscosity at 280 ° C. of 150 to 500 [Pa · s], the polyester film was subjected to a heat load even when a heat load of about 280 ° C. was locally applied. It is presumed that the polyester resin around the part flows to prevent a hole from being formed in the part subjected to the heat load and the occurrence of defects. 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 heat 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 that the surrounding polyester resin subjected to the heat load cannot flow, and the portion subjected to the heat load Since it cannot be repaired, the portion subjected to the heat load becomes a defect, and the printing sensitivity is lowered. Moreover, since the non-uniformity of extrusion or stretching tends to occur during the production of the polyester film, the non-uniformity of thickness tends to occur, resulting in poor ribbon applicability.

  In order to set the melt viscosity at 280 ° C. within the above range, there are a method for controlling the intrinsic viscosity of the polyester resin used as the film material, a method for controlling the melting point (Tm) of the polyester resin used as the film material, and the like. If the intrinsic viscosity value (IV) of the film raw material is increased and the melting point (Tm) of the polyester resin constituting the film is increased, the melt viscosity at 280 ° C. of the polyester resin constituting the film can be increased. . The IV of the film raw material is preferably 0.7 dl / g or more, more preferably 0.75 dl / g or more, because IV reduction due to heat occurs in the extruder. Furthermore, it is preferable that the temperature control in the extruder is precise. The decrease in IV is likely to occur due to the disorder of temperature control, and it becomes 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 higher and 275 ° C. or lower, more preferably 254 ° C. or higher and 270 ° C. or lower.

  In the biaxially oriented polyester film of the present invention, the amount of carboxyl terminal groups of the polyester resin constituting the film is preferably 5 to 25 [equivalent / t]. More preferably, it is 10-20 [equivalent / t]. If the carboxyl end group amount is less than 5 [equivalent / t], the wettability of the polyester film surface is deteriorated, which may deteriorate the applicability of the ribbon. If it is greater than 25 [equivalent / t], the polyester resin is likely to be deteriorated when subjected to the heat of thermal transfer, and perforation is likely to occur.

  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 SRa is less than 20 nm, the transportability may deteriorate, which is not preferable. If it is larger than 50 nm, the print head cannot be approached and the printing sensitivity may deteriorate, which is not preferable. As a method for setting the surface roughness within the above range, (i) a particle is included in the polyester resin composition constituting the film, (ii) a protrusion is formed on the surface of the film by imprint, (iii) Examples include forming voids in the resin constituting the film and imparting a shape to the film surface by the voids. In the case of a film having a thin film thickness, it is preferable to use the method (i) from the viewpoints of film forming properties and protrusion forming properties.

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

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 system, there are a heat melting type in which a heat-soluble pigment ink is melted and transferred, and a sublimation type in which a sublimable dye ink is sublimated and transferred.
In the thermal melting type thermal transfer system, a thermal load is applied a plurality of times in color printing using a plurality of ink ribbons. Since the polyester film of the present invention is excellent in local heat resistance, it is possible to suppress the occurrence of perforation even when color printing is performed by a thermal melting type thermal transfer method, and as a base material for a thermal melting type thermal transfer ribbon. It can be used suitably.
Further, in the sublimation type thermal transfer system, it is necessary to sublimate the dye with high output and to fix the ink reliably, so that the thermal head tends to become high temperature. Since the polyester film of the present invention is excellent in local heat resistance, even if printing is performed in a sublimation type thermal transfer system, the occurrence of perforation can be suppressed, and therefore it is preferably used as a substrate for a sublimation type thermal transfer ribbon. Can do.

  The method for producing a polyester film of the present invention will be described below with reference to examples, but the present invention is not construed as being limited to 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 material in the polymer, the polymer may be filtered with a fiber sintered stainless metal filter. Furthermore, various additives such as compatibilizers, plasticizers, weathering agents, antioxidants, thermal stabilizers, lubricants, antistatic agents, whitening agents, coloring, as long as the effects of the present invention are not impaired. Agents, conductive agents, ultraviolet absorbers, flame retardants, flame retardant aids, pigments and dyes may be added.

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

  For each layer constituting the biaxially oriented polyester film of the present invention, each layer of raw material pellets (and, if necessary, a master batch) is dried under reduced pressure at a temperature of 180 ° C. for 3 hours or more, and then the intrinsic viscosity. Is supplied to an extruder heated to a temperature of 265 to 280 ° C. under a nitrogen stream or reduced pressure so as not to decrease, and is extruded from a slit-shaped 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 scope of the present application, it is preferable to use a cast-in electric heater for temperature control of the cylinder of the extruder, and it is more preferable to perform cooling control with a water cooling jacket. The film is laminated by melt lamination 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 rate fluctuation rate of a casting roll is less than +/- 0.5%. Since the biaxially oriented polyester film of the present invention is very thin as 1 to 9 μm, a large rate of fluctuation in speed is not preferable because the film forming property is deteriorated.

  Next, the unstretched film thus obtained is biaxially stretched. Biaxial stretching method using a longitudinal stretching machine in which several rolls are arranged, stretching in the longitudinal direction using the difference in peripheral speed of the rolls (MD stretching), followed by transverse stretching with a stenter (TD stretching) Will be described.

  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 that cuts the tension and suppresses slipping of the film. In MD stretching, the film running on the stretching roll is pressed by a stretching nip roll with a constant pressure (nip pressure) to sandwich the film and cut the tension. Stretched. The MD stretching temperature is (glass transition temperature (hereinafter referred to as Tg) +5) to (Tg + 50) ° C., and the stretching ratio of MD stretching is 1.2 to 5.0 times. It cools with the cooling roll group of the temperature of 20-50 degreeC after extending | stretching.

Next, stretching in the width direction (TD stretching) is performed using a stenter. The stenter is a device that stretches the film between the clips at both ends while holding the both ends of the film with clips, and is stretched into a preheating zone, a stretching zone, a heat treatment zone, and a cooling zone. The clip temperature is preferably less than 60 ° C. When the clip temperature is 60 ° C. or higher, the biaxially oriented polyester film of the present invention is as thin as 1 to 9 μm, so that the portion gripped by the clip is easily broken and the film forming property may be deteriorated. The stretching ratio of TD stretching is 2.0 to 6.0 times, and the stretching temperature is in the range of (Tg) to (Tg + 50) ° C. After TD stretching, heat setting is performed. In the heat setting treatment, the film is heat-treated in a temperature range of 150 to 240 ° C. while being relaxed under tension or in the width direction. The heat treatment time is in the range of 0.5 to 10 seconds. Then, it cools to 25 degreeC in a cooling zone, a film edge is removed, and the biaxially-oriented polyester film of this invention can be obtained.
[Measurement and evaluation method of characteristics]
(1) Melt viscosity at 280 ° C. The melt viscosity at 280 ° C. was evaluated by the following apparatus based on JIS K7199 (1999). The measurement was made 5 times, and the average was taken as the melt viscosity.
・ Measuring device: Capillograph 1D Toyo Seiki Seisakusho ・ Capillary length: 10 mm
・ Capillary diameter: 1mm
・ Capillary temperature: 280 ℃
Preheating time (time from filling the measurement sample in the capillary to starting measurement): 6 minutes Shear rate: 100 [1 / s]
-Sample amount: 30g
Sample pretreatment: A sample dried at 180 ° C. for 3 hours at a vacuum degree of 0.2 kPa or less was used.

(2) Intrinsic viscosity The 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 by the following equation (c), and the obtained value is used as the intrinsic viscosity (IV).
(C) ηsp / C = [η] + K [η] ² · C
(Where ηsp = (solution viscosity (dl / g) / solvent viscosity (dl / g)) − 1, K is a Huggins constant (assuming 0.343)).

(3) Terminal carboxyl group amount (in the table, described as COOH amount)
The measurement is carried out under the following conditions in accordance with the method of Malice (document MJ Malice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960)). 2 g of the polyester composition was dissolved in 50 mL of o-cresol / chloroform (weight ratio 7/3) at a temperature of 150 ° C., titrated with a 0.05N KOH / methanol solution, the amount of terminal carboxyl groups was measured, eq. / Indicated by the value of polyester 1t. In addition, the indicator at the time of titration uses phenol red, and the place where it changed from yellowish green to light red is set 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-definition fine shape measuring instrument (three-dimensional surface roughness meter) of the stylus method.
・ Measuring device: 3D fine shape measuring instrument (model ET-4000A), manufactured by Kosaka Laboratory Ltd./Analyzing equipment: 3D surface roughness analysis system (model TDA-31)
-Stylus: Tip radius 0.5 μm R, diameter 2 μm, made of diamond • Needle pressure: 100 μN
・ Measurement direction: film longitudinal direction and film width direction average after each measurement ・ X measurement length: 1.0 mm
-X feed speed: 0.1 mm / s (measurement speed)
・ Y feed pitch: 5μm (measurement interval)
-Number of Y lines: 81 (measured number)
・ Z magnification: 20 times (vertical magnification)
・ Low frequency cut-off: 0.20mm (swell cut-off value)
High frequency cut-off: R + Wmm (roughness cut-off value) R + W means not cut off.
-Filter method: Gaussian space type-Leveling: Available (tilt correction)
- reference area: ^1mm 2.

(5) Element content The content of the metal element in the polyester resin composition constituting the film is determined by atomic absorption spectrometry (manufactured by Sasatsu Seisakusho: Polarized Zeeman atomic absorption photometer 180-80. Frame: acetylene-air). went.

(6) Film thickness (μm)
The film thickness was measured at any five locations using a dial gauge in accordance with JIS K7130 (1992) A-2 method with 10 films stacked. The average value was divided by 10 to obtain the film thickness.

(7) Coating property A coating liquid of the following composition (i) is applied to 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. To form a heat-resistant protective layer.
Composition (i)
Silicone resin: 10 parts Toluene: 45 parts MEK: 45 parts
A coating liquid having the following composition (ii) was applied to 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 Apply a coating liquid of the following composition (iii) on this release layer with a direct gravure coater so that the coating amount is 1.0 g / m ^2. It was applied and dried to form a heat-meltable 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 applicability of the obtained thermal transfer ribbon was evaluated according to the following criteria.
A thermal transfer ribbon having a width of 1 m and a length of 20 m was observed with reflected light using a three-wavelength fluorescent lamp as a light source in a dark room, and the number of coating defects was counted. The term “coating defects” used herein refers to “coating stripes” where there are portions that are not applied in the form of stripes in the longitudinal direction of the film, and “coating defects” in which uneven application occurs in the form of craters. The coating streaks were counted for those that could be visually confirmed, and the coating omission was counted for those having a diameter of 5 mm or more. A was the best, and C or higher was accepted.
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) is energized by using a thermal transfer printer (Seiko Denshi Kogyo Co., Ltd. high-definition printer Color Printer 2 8 gradation software "PALMIX"). Printing was performed at level 20 and evaluated according to the following criteria. A was the best, and C or higher was accepted.
・ Local heat resistance (number of holes)
The thermal transfer ribbon after printing was visually confirmed to evaluate the number of holes.

A: Less than 5 pieces / 100 mm ² B: 5-10 pieces / 100 mm ^{2 or} less C: 10-30 pieces / 100 mm ^{2 or} less D: 30 pieces / 100 mm ² or more The image was visually judged and evaluated.

A: No image quality unevenness even when energy level is less than 10 B: No image quality unevenness even if energy level is 10 or more and less than 15 C: No image quality unevenness even if energy level is 15 or more and less than 20 D: Image quality unevenness even if energy level is 20 or more.

(9) Transportability The thermal transfer ribbon obtained in (7) above was printed 10 m in the same manner as in (7) above, and evaluated according to the following criteria. A was the best, and C or higher was accepted.
A: Less than 3 wrinkles generated per 20 cm of ribbon B: 3 or more wrinkles generated per 20 cm of ribbon (practical)
C: Wrinkles of 5 or more and less than 10 are generated per 20 cm of ribbon (practical)
D: Ribbon conveyance failure is observed, or 10 or more wrinkles are generated per 20 cm of ribbon (practically problematic)

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

  [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 and 0.03 parts by mass of antimony trioxide were melted at 150 ° C. in a nitrogen atmosphere. . While stirring this melt, the temperature was raised to 230 ° C. over 3 hours to distill methanol, and the transesterification reaction was completed. 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 performed at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr to obtain polyethylene terephthalate having an intrinsic viscosity of 0.52 and a terminal carboxyl group amount of 15 equivalents / ton. The obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours. Thereafter, solid-state polymerization was performed at 220 ° C. and a vacuum degree of 0.3 Torr for 8 hours to obtain polyethylene terephthalate (PET chip-1) having an intrinsic viscosity of 0.80 and a terminal carboxyl group amount of 10 equivalents / ton. The obtained PET chip-1 had a glass transition temperature of 82 ° C. and a melting point of 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 density | concentration of the silica in the master pellet-2 is 2 mass%.

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

Next, the melt of PET chip-1 and masterbatch-2 is extruded from the inside of the T die die into a sheet to form a molten single layer sheet, which is statically placed on a cast drum having a surface temperature of 25 ° C. and a speed fluctuation rate of ± 0.2%. An unstretched film was produced by tightly cooling and solidifying while applying an electric charge. Subsequently, after preheating the obtained unstretched film with a heated roll group, the tension is cut by using a silicon-made stretching roll and a nip roll, and 3.5 times MD stretching is performed at a temperature of 90 ° C. in the longitudinal direction. Then, it was cooled with a roll group having a temperature of 25 ° C. to obtain a uniaxially stretched film. The resulting uniaxially stretched film is held at both ends of the uniaxially stretched film with a clip cooled to 60 ° C. or lower and led to a preheating zone at a temperature of 80 ° C. in the tenter. The film was stretched 3.7 times in the width direction (TD direction). Subsequently, a heat treatment was performed at a temperature of 232 ° C. for 5 seconds in a heat treatment zone in the tenter, and a relaxation treatment was further performed in the 4% width direction at a temperature of 232 ° C. Subsequently, the film was gradually cooled in a cooling zone and wound up to obtain a biaxially oriented polyester film. The 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 2-3)
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)
In Example 4, except that a polyester resin having an intrinsic viscosity of 0.67 was used as PET chip-1, Example 5 was carried out in the same manner as in Example 1 except that a polyester resin having an intrinsic viscosity of 1.4 was used. 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 the film raw material having the terminal carboxyl group amount shown in Table 1 was used.
(Examples 10 to 13)
The average particle size of the particles contained in Master Pellet-2 is 1.3 μm in Example 10, 1.5 μm in Example 11, 2.5 μm in Example 12, 2.7 μm in Example 13, and listed in Table 1. 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 amount of 15 equivalent / t, and a melting point of 264 ° C. was used instead of the PET chip-1. .
(Comparative Examples 1-2)
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 3-4)
In Example 4, except that a polyester resin having an intrinsic viscosity of 0.65 was used as PET chip-1, in Example 5, a polyester resin having an intrinsic viscosity of 1.5 was used. A biaxially stretched polyester film was obtained.

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

Claims (7)

The biaxially oriented polyester film whose melt viscosity of 280 degreeC of the polyester resin which comprises a film is 150-500 [Pa * s], and film thickness is 1-9 micrometers. 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 equivalent / 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 polyester resin composition constituting the film contains an antimony element, and the content thereof is 100 to 500 ppm with respect to the entire polyester resin composition constituting the film. Axial-oriented polyester film. The biaxially oriented polyester film according to any one of claims 1 to 4, which is used as a base material for a thermal transfer ribbon. The biaxially oriented polyester film according to claim 5, which is used as a base material for a heat melting type thermal transfer ribbon. A thermal transfer ribbon using the biaxially oriented polyester film according to claim 1.