KR100563240B1 - Biaxially stretched polyester film - Google Patents

Abstract

The present invention relates to a polyester biaxially oriented film widely used as a base film for magnetic recording materials, packaging materials, electrical insulating materials, and various photographic materials because of excellent mechanical properties, electrical properties, dimensional stability, transparency, and heat resistance. In particular, it was devised for the purpose of providing a biaxially oriented polyester film for thermal transfer, which has excellent printability when used as a thermal transfer and has a good processability in a processing process.

The present invention provides a biaxially oriented film containing a specific amount of calcium carbonate particles having a particle size distribution ratio as a large particle, a particle size distribution ratio as a large particle, and silica particles as a small particle, as one method for achieving the above object. Disclosed is a biaxially oriented polyester film for thermal transfer ribbon, wherein SRa is 20 to 50 nm, SRz is 0.6 to 1.5 µm, and MD direction back-variation is 15% or less.

Thermal Transfer Ribbon, Biaxial Orientation, Polyester

Description

 Biaxially Oriented Polyester Film {BIAXIALLY STRETCHED POLYESTER FILM}

The present invention relates to a biaxially oriented polyester film for thermal transfer ribbons excellent in printability and flammability, and excellent in workability without defects such as wrinkles and coating defects during film manufacturing process and ribbon processing.

Polyester biaxially oriented film has excellent mechanical properties, electrical properties, dimensional stability, transparency, heat resistance, etc., so it is widely used as a base film for many applications such as magnetic recording materials, packaging materials, electrical insulating materials, various photographic materials, graphic arts, and the like. In recent years, it has been rapidly growing as a base film for thermal transfer ribbons such as OA and FA.

The thermal transfer ribbon is a melting type in which various pigments are added to a binder such as wax, and the ink layer is melted by heat to be transferred to the transferee, and a dye having sublimability in the binder is added to contact the transferee by heat. There is a sublimation type in which only the dye is transferred to the aqueous layer of the transfer object in the state.

In recent years, the increasing demand of thermal transfer ribbons for barcodes due to increased traffic volume, the increase in demand for high-factor, high-flammability thermal transfer ribbons due to the expansion of digital cameras, etc. The demand for thermal transfer ribbons and thermal transfer ribbon films is on the rise due to the creation of new demand for thermal transfer ribbons and the steady transfer of thermal transfer ribbons for special small prints such as receipts.

In addition, in order to realize cost savings, thermal transfer ribbon processors reduce the thickness of the heat-resistant coating layer or ink layer, and thus the surface structure of the thermal transfer ribbon film has a greater influence on the surface structure of the coating layer. The technique of controlling the surface structure of the transfer ribbon film has become important.

As the film constituting the thermal transfer ribbon, a polyester film that is industrially thin and has excellent mechanical properties and the like has been used. Polyester films used for thermal transfer ribbons having mechanical properties specified (USP 6197430, USP 4675233, USP 6306496), thermal properties specified (JP 10-264337, J 11-321127), surface The definition of roughness characteristics (Japanese Patent Laid-Open No. Hei 10-86543, Japanese Patent Laid-Open No. 2000-108374) and the like have been disclosed, and these techniques have mostly improved the slip resistance of a film or the heat resistance in printing.

However, thermal transfer ribbons made from these films are known to have the following problems.

First, ribbon cutting occurs on the guide roll or the thermal head of the traveling system due to the increase of the transmission speed and the printing energy in the traveling system inside the transfer printer, and foreign matters generated by the cutting are deposited on the thermal head and printed. It is a problem of degrading quality.

Second, in order to solve the above problem, in the case of a ribbon whose surface is smooth, the surface roughness of the film is too flat, resulting in poor workability and wrinkles in the film manufacturing process and the transfer ink coating process of the ribbon manufacturing process. Or poor coating.

In recent years, the use of labels for automotive labels and thermal transfer ribbons for electronic resident card printing requires clearer print quality, less cutting in the traveling system inside the thermal printer as the printing speed increases, and processability should be good. The challenge is to meet the mutually opposite characteristics of the back.

An object of the present invention is to provide a biaxially oriented polyester film having excellent printability when used in thermal transfer, good processability without producing defects such as wrinkles, coating defects in the production of thermal transfer ribbon film or processing process. To

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention contains 0.01-1.0 weight% of porous inorganic particles with a pore volume of 0.6-2.0 ml / g as an average particle and 13-6.0 micrometers in average particle size, and an average particle diameter is 0.3 as a heavy particle. 0.01 to 1.5% by weight of calcium carbonate particles having a particle size distribution ratio (R) of 1.1 to 4.0 represented by the following formula (1), and 0.01 to 1.5% by weight of the silica particles having an average particle diameter of 0.02 to 1.0 μm. A biaxially oriented film containing -0.5% by weight, wherein the surface roughness SRa is 20 to 50 nm, the SRz is 0.6 to 1.5 µm, and the MD direction back drift rate is 15% or less, biaxially oriented polyester film for thermal transfer ribbons. Initiate.

Hereinafter, the present invention will be described in detail.

The polyester used as the material of the film in the present invention includes a polyester resin unit as well as a blend of other types of polymers and polyesters. If blended, at least 50% by weight is made of polyester resin.

The said polyester resin is a polymer containing the ester group obtained by condensation polymerization of dicarboxylic acid and diol. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, adipic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, bis-, (2-chlorophenoxy) ethane-4, Aliphatic and aromatic dicarboxylic acids such as 4'-dicarboxylic acid can be used. As the diol, for example, ethylene glycol, 1,4-butanediol, diethylene glycol, polyethylene glycol, neopentyl glycol, cyclohexanemethanol and the like can be used.

Two or more types of said dicarboxylic acid and diol may be used, respectively. On the other hand, the intrinsic viscosity of such a polyester is preferably in the range of 0.4 to 2 (more preferably, 0.5 to 1) in the value measured in orthochlorphenol at 25 ° C.

In addition, as the polyester resin, other monomers or polymers may be copolymerized or melt-mixed in two or more kinds of polyester resins within 10 mol% in addition to dicarboxylic acid or diol, and furthermore, the object of the present invention may be impaired. It is also possible to use other kinds of polymers, ultraviolet absorbers, lubricants, pigments, antioxidants, heat stabilizers, flame retardants, antistatic agents and the like.

The biaxially oriented film of the present invention is molded using the above polyester-based resin, and the thickness of the biaxially oriented film is not particularly limited, but is usually 2.0 to 8.0 µm (more preferably 2.5 for thermal transfer ribbons). To 7.0 µm, particularly preferably 2.5 to 6.0 µm). When thickness exceeds 8.0㎛, it takes time for heat conduction

It is not suitable for printing, and if it is less than 2.0 µm, the strength is lowered, resulting in poor workability, and insufficient strength characteristics as a ribbon.

The biaxially oriented film of the present invention contains porous large particles having a pore volume of 0.6 to 1.8 ml / g, more preferably a pore volume of 0.8 to 1.9 ml / g (particularly preferably 1.0 to 1.8 ml / g). By containing a ruler, it becomes possible to satisfy the aptitude at the time of film manufacture and processing, and the abrasion resistance in the running system after manufacture with a ribbon. If the pore volume is less than 0.6 ml / g, the large particles are cut off in the traveling system of the thermal printer during thermal transfer after manufacturing with ribbon, and the printing state is poor, and the film is stretched due to the lack of affinity between the large particles and the resin composition. Since voids are generated and stress is concentrated on these voids during the heat setting process, there is a problem such that the film is broken, which is not preferable. In addition, when the pore volume exceeds 2.0 ml / g, the surface energy of the particles becomes too large, which makes it difficult to disperse the particles, which is undesirable in the step of adding the particles.

When aggregates are formed, stress is concentrated on these aggregates during film production, and the film breaks frequently, even if the film is not broken. It is not preferable to cause a problem of degradation. The average particle diameter of the large particles is in the range of 1.3 to 6.0 mu m (more preferably 1.4 to 5.5 mu m, particularly preferably 1.6 to 5.0 mu m). If the particle size is smaller than 1.3 mu m, the surface roughness of the film becomes too low, which causes problems such as wrinkles or coating defects due to deterioration of handleability during the film manufacturing process and processing with ribbons. Greater than 6.0 μm, the surface roughness becomes too high, the number of coarse particles increases, and the pressure of the filter rises too rapidly during the film manufacturing process, requiring frequent replacement of the filter, or increasing the breakage in the stretching process, or thermal The chipping in the traveling system inside the transfer printer is increased, resulting in a deterioration in printing quality. The addition amount of the porous large particles having pores is in the range of 0.01 to 1.0% by weight (more preferably 0.02 to 0.8% by weight, particularly preferably 0.03 to 0.6% by weight). If the added amount is less than 0.01% by weight, the handleability during film production and processing with a ribbon decreases, which causes poor wrinkles, defects such as protrusions and coating defects, and is not preferable. If more, the coarse particles are excessively large, the filter pressure rises rapidly during film production, which requires frequent replacement, which leads to a decrease in productivity and a problem of breaking during drawing of the film. This deterioration causes the particles to be scraped off, and the scraped particles are deposited on the thermal transfer head to degrade the quality of printing, which is undesirable. Examples of the porous large particles having pores include silica, calcium phosphate, and alumina. Among these, precipitated silica and hydroxyapatite calcium phosphate are preferable by the wet method.

The biaxially oriented film of the present invention preferably contains calcium carbonate particles having an average particle diameter of 0.3 to 2.0 µm and a particle size distribution ratio (R) of 1.1 to 4.0 represented by the following formula, in addition to the porous large particles having the pores. Do.

The calcium carbonate particles used as the heavy particles are preferably sufficiently dried, but the water content of the calcium carbonate particles is preferably 5% by weight (more preferably 2% by weight) or less. If the moisture content exceeds 5% by weight, the Ca activity on the surface of the calcium carbonate particles increases, which is not preferable because the calcium carbonate particles agglomerate during the melting of the polyester, or cause the affinity of the particles for polyester. . The calcium carbonate particles used in the heavy particles of the present invention are not limited to the crystal form or the production method, but examples thereof include a calcitic crystal form and a vaterite crystal form. Particularly, the calcium carbonate particles in the form of a vaterite are preferable. . Although it does not specifically limit as a manufacturing method of a calcium carbonate particle, For example, the manufacturing method by reaction of calcium chloride and sodium hydrogencarbonate in the presence of a carbon dioxide gas blowing method, a metathesis method of a salt, and ammonia coexistence is mentioned. For example, carbonic acid gas is blown into a water / methanol mixed suspension of calcium hydroxide, and the carbonation reaction is terminated by setting the temperature of the reaction system to 30 or more before the conductivity of the carbonation reaction system is maximized to prepare a calcium carbonate slurry. Calcium carbonate particles can be obtained in a powder state by powdering the slurry by a dry spray method and performing vacuum drying to obtain a predetermined moisture content.

In the present invention, the particle diameter of the heavy particles is not particularly limited, but the average particle diameter is 0.3 to 2.0 µm (more preferably 0.4 to 2.0 µm, particularly preferably 0.5 to 2.0 µm). If the average particle diameter is less than 0.3 mu m, the ability to form projections is insufficient, and the contact area with the guide roll in the traveling system inside the thermal transfer printer increases, which lowers the wear resistance. The number of protrusions decreases, the number of coarse particles increases, and conversely, wear resistance decreases, which is undesirable. The particle size distribution ratio R of the heavy particles is suitably in the range of 1.1 to 4.0 (more preferably 1.2 to 3.8, particularly preferably 1.3 to 3.7). If the particle size distribution ratio is less than 1.1, there is a problem that it becomes uneconomical because filtration treatment and the like must be performed highly. In addition, when the particle size distribution ratio exceeds 4.0, the formation of fine protrusions of the biaxially oriented film of the present invention becomes insignificant, and the wear resistance is lowered, which causes deterioration of the printability.

 The content of the heavy particles is preferably in the range of 0.01 to 1.5% by weight (more preferably 0.02 to 1.2% by weight, particularly preferably 0.03 to 1.0% by weight).

If the content is less than 0.01% by weight, it is not preferable because the effect of improving the wear resistance by the heavy particles is not sufficiently expressed. If the content is more than 1.5% by weight, it is uneconomical because the effect of increasing the wear resistance exceeds the saturation point.

The biaxially oriented film of the present invention has a small particle size of 0.02 to 1.0 μm (more preferably 0.03 to 0.8 μm, particularly preferably 0.04 to 0.6 μm) as small particles other than the porous large particles and the medium particles having the above pores. By containing silica particles having a large number of fine uneven protrusions formed on the surface of the film, the area of contact with the print head in the traveling system is reduced when the printing is made after the ribbon is produced. This reduces the shaving of the surface in contact with the printhead, which is desirable. If the average particle diameter is less than 0.02 μm, the ability to form protrusions is insufficient, and the contact area with the guide roll in the traveling system inside the thermal transfer printer increases, which lowers the wear resistance. The number of protrusions decreases, the number of coarse particles increases, and conversely, wear resistance decreases, which is undesirable. In addition, the content of the small particles is suitably in the range of 0.01 to 0.5% by weight (more preferably 0.02 to 0.4% by weight, particularly preferably 0.03 to 0.3% by weight). If the content is less than 0.01% by weight, it is not preferable because the effect of improving the wear resistance by the small particles is not sufficiently expressed. If the content is more than 0.5% by weight, it is uneconomical because the effect of increasing the wear resistance exceeds the saturation point.

The biaxially oriented film of the present invention may contain nonporous large particles in addition to the porous large particles, the medium particles and the small particles having the above-mentioned pores in terms of printability, wear resistance, aptitude during ribbon processing, and the like. Although it does not specifically limit as a nonporous large particle, The crystal form of delta type, (theta) type, (eta) type, (gamma) type, alumina, zirconia, a silica, etc. are mentioned preferably. Herein, non-porous means a large particle having an average particle size of 1.0 μm or more, which is less than 0.5 ml / g of pore volume and falls below the lower limit of the pore volume proposed in the present patent. In terms of wear resistance, such non-porous large particles are preferably secondary aggregated particles in which primary particles are aggregated. The primary particle size is not particularly limited but is preferably in the range of 5 to 100 nm (more preferably 10 to 80 nm), and the aggregated secondary particle diameter is not particularly limited but is in the range of 1.0 to 4.0 μm (more preferably 1.3 to 3.5 μm). Is preferred. The content is not particularly limited but is preferably in the range of 0.005 to 0.5% by weight, (more preferably 0.01 to 0.3% by weight).

The biaxially stretched film of the present invention is a biaxially stretched film, which is not preferable because of its poor wear resistance as a uniaxial or unstretched film. The degree of such stretching is not particularly limited, but wear resistance is preferable when the elastic modulus, which is a measure of the stretching of the polymer, is 350 kgf / mm 2 or more in both the longitudinal direction and the width direction.

As for the biaxially-oriented film of this invention, the centerline roughness SRa of the surface is 20-50 nm, and 10-point average roughness SRz has the preferable range of 0.6-1.5 micrometers. If the center line average roughness is 20 nm or less, or the 10-point average roughness is less than 0.6 µm, it is not preferable because the sticking phenomenon of fusion to the thermal head during printing occurs, which makes the printing difficult, and the center line average roughness is 50 nm. If the average particle roughness of more than 1.5㎛ more than 1.5㎛

It is not preferable because the number increases, the wear resistance in the traveling system inside the thermal printer becomes worse, the thermal conductivity from the thermal head worsens, and the printing state becomes unclear.

In order to make center line average roughness and 10-point average roughness into the said range, it can achieve by adjusting the average thickness, average particle diameter, and addition amount of the inert particle added to a polyester resin.

The biaxially oriented film of the present invention needs to have a thickness variation in the longitudinal direction of 15% or less (more preferably 13% or less). If the thickness variation rate is more than 15%, wrinkles or poor coating occur easily when processing into a ribbon, which is not preferable. In order to make the thickness change rate of a longitudinal direction into the said range, it can achieve by adjusting the shaping | molding conditions at the time of manufacturing an unstretched film, the drawing temperature in a longitudinal drawing process, and a draw ratio. Among these, in particular, the molding conditions in manufacturing the unstretched film are important, and it is important to set the distance between the polymer sheet discharged from the die on the slit and the wire electrode applying the voltage in an appropriate range. In other words, if the distance is too long for the distance between the wire electrode and the cooling drum surface, the potential gradient formed between the wire electrode and the cooling drum is lowered so that sufficient charge is not discharged from the wire electrode.

The force decreases, so that sufficient adhesion cannot be obtained on the cooling drum, which leads to an increase in the degree of backlash. On the contrary, if the distance is too short, the potential gradient becomes excessive, resulting in a breakdown of the polymer sheet, which causes a problem of discharge. In addition, the position in the direction in which the polymer sheet of the wire electrode is drawn is more than the point where the molten polymer sheet discharged from the die lands on the surface of the cooling drum.

If the wire electrode is installed on the upstream side, the coulomb repulsive force acting between the polymer sheet and the wire electrode and the vibration of the peripheral device are combined to cause the polymer sheet to shake, thereby increasing the rearward fluctuation rate. On the contrary, if it is provided downstream from the landing point, the cooling drum side surface of the polymer sheet is already cooled to some extent, and the polymer sheet is not sufficiently adhered to the cooling drum.

As a method of incorporating the particles into the polyester, it may be added at any stage of the polyester production process or the molding process, but immediately before the polycondensation reaction to obtain a polymer having a film forming ability in a reduced pressure or inert air stream, a relatively low molecular weight intermediate. Or it is preferable to add initially, from the point of dispersibility with respect to the obtained polyester resin, and prevention of coloring of a polymer. Addition of slurry to diol ethylene glycol

It is preferable to disperse | distribute and to superpose | polymerize this ethylene glycol with the predetermined dicarboxylic acid component. Of course, the water slurry of the particles is directly mixed with a predetermined polyester pellet, kneaded in polyester using a vented twin screw extruder to prepare a masterbatch, diluted with other polyester, and the content in the film. It may be adjusted.

The pellet containing the predetermined amount of particles is then dried as necessary, and then extruded from a known slit-like die into a sheet to be solidified on a casting roll to produce an unstretched film. Subsequently, this unstretched film is biaxially stretched in the longitudinal direction and the transverse direction to make it biaxially oriented. As the stretching method, it is possible to use a sequential biaxial stretching method or a simultaneous biaxial stretching method. However, the longitudinal stretching is divided into two or more stages using the sequential biaxial stretching method, which is first performed in the longitudinal direction and then in the width direction, and the longitudinal stretching temperature is 80 to 150 캜, the longitudinal stretching ratio is 3.0 to 6.5 times and the longitudinal stretching speed. The range of 5,000-50,000% / min is preferable. As the stretching method in the width direction, a method using a stenter is preferable, the stretching temperature is preferably 80 to 160 ° C., the stretching ratio in the width direction is 3.5 to 6.0 times, and the stretching speed in the width direction is preferably in the range of 1,000 to 20,000% / min. . Subsequently, the stretched film is heat-treated. In this case, the heat treatment temperature is preferably in the range of 200 to 245 캜, and the heat treatment time is in the range of 0.5 to 30 seconds.

In the case of the relaxation treatment, the treatment is performed from the heat treatment until it is wound on the roll. In the lateral relaxation treatment, the width of the stenter is reduced between the heat treatment zone and the cooling zone by 0 to the width direction of the film. The relaxation treatment of ˜10% is preferable, and the longitudinal relaxation treatment is performed by cutting both ends of the film and lowering the take-out speed than the feed rate of the film under the temperature conditions of Tg or more and below the melting temperature of the film. Method, a method of heating with an infrared heater between two conveying rolls having different speeds, or a method of lowering the speed of the roll after the heating zone lower than the speed of the roll before the heating zone while passing the heating zone by the heating oven or the infrared heater. Although any method may be used, it is preferable to perform the relaxation treatment at a reduction ratio of the take-out speed to 0 to 5% compared to the speed on the supply side. The.

Moreover, the polyester composition which comprises the film of this invention may contain a part of the composition collect | recovered by recycling. The recycled composition refers to a polyester composition composed of trimming parts, quality non-conforming products or waste products generated in the film manufacturing process.

In the film for thermal transfer ribbon of the present invention, a transfer ink layer of a molten or sublimation type is coated on one side of a biaxially oriented film made of a polyester composition. Such a transfer ink layer can be applied as a transfer ink layer on a polyester film by applying or hot-melting a known composition having a known composition mainly composed of a pigment or dye colorant and a binder made of a polymer compound. Although it does not specifically limit about the thickness of a transfer ink layer, It is preferable to set it as 2 micrometers or less. If it exceeds 2 μm, there may be a problem that the remodelability is insufficient. By setting the thickness to 2 µm or less, for example, four or more sets of modified expressions can be easily performed. In addition, a heat resistant layer is applied on the opposite side of the transfer ink layer. The heat resistant layer is provided for the purpose of preventing sticking due to heat when contacted with the heat sensitive head, and known ones known in the art can be used here. As a typical heat-resistant coating layer, various waxes, cellulose resins, modified acrylic resins such as acrylic silicone, butyral resins, silicone resins, imide resins, silicone oils, various mineral oils, phosphoric acid compounds and the like can be used. In addition, various organic particles and inorganic particles may be added to the heat-resistant coating layer. The thickness of the heat-resistant coating layer is not particularly limited, but is preferably in the range of 0.01 to 1.0 µm, particularly 0.02 to 0.3 µm, in terms of thermal head contamination and heat resistance. In addition, the method of coating is not particularly limited, but may be dried or stretched after a predetermined coating is applied to a uniaxially or unstretched film.

You may apply | coat and dry to the film which performed the process. Representative coating methods include a gravure method, a reverse method, a metering bar method, a die coating method, a gap coating method and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, wherein the characteristic values were measured and evaluated using the following measurement methods and evaluation criteria.

(1) Average particle size and particle size distribution ratio

It was measured using a CP-50 type Centrifugal Particle Size Analyser manufactured by Shimadzu Corporation. The particle size equivalent to 50 weight% was grasped | ascertained by the Cumulative curve of each particle size particle and its abundance computed based on the obtained centrifugal sedimentation curve, and this value was made into the said average particle diameter. The particle size distribution ratio was calculated based on the centrifugal sedimentation curve obtained in the measurement of the average particle diameter, and was calculated by calculating a Cumulative curve of each particle size and its abundance.The cumulative weight of the particles and the cumulative weight of the particles were 25% by weight. By grasping the particle size corresponding to 75% by weight, the former value was divided by the latter value, and the particle size distribution ratio R of each particle was calculated.

(2) working volume

Using a high-speed specific surface area manufactured by Shimadzu Corporation and a pore distribution measuring device, Asappu 2400, the pore volume between 17 and 3000 mm in pore diameter was calculated by BJH method by nitrogen adsorption desorption.

(3) Surface roughness SRa, SRz

It measured according to DIN-4768. Using a 5 micrometer R needle, it measured by 2.5 mm of measurement length, 40 scanning volumes, and 0.25 mm of cutoff values. Four repeated measurements of the same sample were made as the average of the three remaining data except for the largest one.

(4) thickening rate

The film thus prepared was sampled in a width of 5 cm in the longitudinal direction, set in a film traveling device, and then continuously run over 5 meters, and the film thickness was measured using an Anritsu film thickness gauge KG601A. From the recording chart, (maximum thick-minimum thick) / average thick x 100 (%) was expressed as the longitudinal fluctuation rate in the longitudinal direction.

(5) factor

Using a high-precision printer manufactured by Seiko Electronics Co., Ltd. as a thermal transfer printer, the sharpness of the print was observed by visual observation and 100-fold stereoscopic microscope. As shown in Table 1 below, a case in which the printed character had no defects such as scratching, elongation, deformation, and no unnecessary factor in the portion other than the printed factor was O.

Although no defects or unnecessary factors were identified visually, the case where it was confirmed by △, the naked eye, and the 100-times microscope was × as the case where it was confirmed by the 100-time stereoscopic microscope.

TABLE 1

 (6) Aptitude at the time of thermal ribbon processing

After applying the following coating liquid as a heat-resistant layer on one side of the biaxially oriented film using a metering bar method so that the coating thickness after drying was 0.2 μm, the solvent was applied under conditions of a film tension of 20 MPa, a heating temperature of 130 ° C., and a heating time of 15 seconds. Drying and crosslinking were carried out.

 (Composition of Heat Resistant Layer)

Polyacrylic acid ester: 13.4 wt%

Amino modified silicone: 6.5 wt%

Isocyanate: 0.1 wt%

Toluene: 35.0 wt%

Methyl ethyl ketone: 45.0 wt%

Subsequently, the transfer ink of the following composition was applied to the opposite surface of the heat resistant layer using a gravure coater so that the coating thickness was 1.5 μm, and then the film was dried under conditions of 20 MPa, heating temperature of 110 ° C., and heating time of 12 seconds. It was.

 (Composition of Transfer Ink)

Ethylene Vinyl Acetate Copolymer: 28 wt%

Water-based rosin wax: 7 wt%

Carbon Black: 15 wt%

Toluene: 47 wt%

Ethylene Glycol Monomethyl Ether: 3 wt%

In processing the ribbon, whether or not it can be processed normally was observed in the process, or the processed ribbon was visually examined and classified as follows.

 0: No wrinkles occur at all in the process, and coating defects do not occur, △: Fine wrinkles occur in the process, but do not lead to poor coating, ×: wrinkles are severely generated and coating defects are also generated in the process. Occurs.

(7) abrasion resistance of film

The film was cut into a 1/2 inch wide tape, and a guide pin (surface) made of SUS material was used using a tape running tester (TBT300D / H manufactured by Yokohama Systems) under an environment of temperature of 20 ° C and a relative humidity of 60%. Roughness Ra: 0.1㎛) Drive and rub on the top (driving speed 50mpm, guide pin contact angle 60 °, unwinding tension 50 grams). Evaluation was made based on the criteria.

  0: no visible wear, Δ: less than 1/10 of the apparent contact area between the pin and the film, x: 1/10 or more

<Example 1>

(A) Preparation of Polyester Resin Composition

10 parts by weight of porous silica particles having an average particle diameter of 2.5 μm and a pore volume of 1.6 ml / g and 90 parts by weight of ethylene glycol were mixed and stirred at high temperature for 3 hours at room temperature to obtain a porous silica particle / ethylene glycol slurry (a).

10 parts by weight of synthetic calcium carbonate particles having an average particle diameter of 0.5 mu m and a particle size distribution ratio of 2.7 and 90 parts by weight of ethylene glycol were mixed and stirred at high temperature for 3 hours at room temperature to obtain calcium carbonate particles / ethylene glycol slurry (b).

10 parts by weight of silica particles having an average particle diameter of 0.08 μm and 90 parts by weight of ethylene glycol were mixed and stirred at high speed for 3 hours at room temperature to obtain silica particles / ethylene glycol slurry (c).

Meanwhile, slurry (a) prepared in advance of the reaction product after adding 0.06 parts of magnesium acetate as a catalyst to 100 parts by weight of dimethyl terephthalate and 64 parts by weight of ethylene glycol as a catalyst and performing a transesterification reaction while gradually raising the temperature from 150 ° C to 240 ° C. After adding (b) and (c) to the addition amounts of Table 2, 0.03 parts by weight of antimony trioxide as a polycondensation catalyst and 0.04 parts by weight of trimethyl phosphate were added, and a polycondensation reaction was carried out to obtain a polyethylene terephthalate composition having an intrinsic viscosity of 0.625. .

(B) Preparation of Biaxially Oriented Polyester Film

The polyester resin obtained in A was vacuum-dried at 160 degreeC and 3 torr for 6 hours. The polymer was fed to an extruder and melted and extruded at 285 ° C to form a sheet from a slit die on a cooling drum having a surface temperature of 28 ° C. At this time, the gap between the die and the cooling drum is set to 27 mm, the vertical distance between the cooling drum and the wire electrode is 4 mm and the horizontal distance between the wire electrodes from the die vertical direction is 52 mm, while the sheet is brought into close contact with the drum surface. The DC voltage was 8.5 kV and cooled and solidified at a speed of 45 m / min to obtain an undrawn sheet. The unstretched sheet was stretched in the longitudinal direction by 1.7 times at 121 ° C., 1.4 times at 120 ° C., and 2.1 times at 115 ° C., and the resulting uniaxially stretched film was sent to the stenter and stretched in the transverse direction at 125 ° C. and 3.9 times, after stretching. Heat treatment was performed at 230 ° C. and 3.8% relaxation treatment was performed in the transverse direction. As a result, a biaxially oriented film having a thickness of 4.6 µm was obtained.

(C) Measurement and evaluation of physical properties

With respect to the biaxially oriented film obtained above, surface roughness SRa, SRz, back drift rate, and abrasion resistance were evaluated, and the evaluation results are shown in Table 2. Subsequently, a heat-resistant layer and a transfer ink layer were applied to one side and the opposite side of the obtained biaxially oriented film as described above to prepare a transfer ribbon, and then the printability and aptitude during ribbon processing were evaluated.

Indicated.

<Examples 2-7, Comparative Examples 1-6, Comparative Examples 8-9>

As shown in Table 2 and Table 3, the film was prepared by changing the type, average particle size, and amount of the porous large particles, the medium particles, the small particles, and the non-porous large particles, and the physical properties thereof were measured and evaluated, and are shown in Tables 2 and 3. .

<Comparative Example 7>

The distance between the die and the cooling drum was 18 mm, and the distance between the electrode wires was 42 mm from the straight line parallel to the die discharge part. Was measured and evaluated and shown in Table 3.

TABLE 2

TABLE 3

ㅍ

ㅍ

As can be seen from the above examples and comparative examples, the biaxially oriented film according to the present invention contains particles having an appropriate size and shape, thereby making the surface roughness and back drift rate of the film within a specific range, thereby providing excellent wear resistance, printability and processability. It is excellent and is particularly suitable for thermal ribbons.

Claims (3)

As large particles, it contains 0.01 to 1.0% by weight of porous inorganic particles having a pore volume of 0.6 to 1.8 ml / g and an average particle diameter of 2.0 to 4.5 µm, and an average particle diameter of 1.0 to 2.0 as heavy particles. 0.01 to 1.5% by weight of calcium carbonate particles having a particle size distribution ratio (R) of 1.1 to 4.0 represented by the following formula, and 0.01 to 0.5% by weight of silica particles having an average particle diameter of 0.4 to 1.0 μm as small particles. As a biaxially stretched film, surface roughness SRa is 20-50 nm, SRz is 0.6-1.5 micrometers, and MD direction back-shifting rate is 15% or less, The biaxially-oriented polyester film for thermal transfer ribbons characterized by the above-mentioned.

The biaxially oriented polyester film for thermal transfer ribbons according to claim 1, wherein the porous inorganic particles are porous silica obtained by a wet method. The biaxially oriented polyester film for thermal transfer ribbon according to claim 1, wherein the thermal transfer ink layer has a thickness of 2.0 µm or less.