JP2002283450A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film suitable for a base film particularly for a heat-sensitive transfer ribbon having excellent productivity while assuring a transfer image having excellent shape reproducibility and gradability. SOLUTION: The biaxially oriented polyester film formed by a simultaneously biaxially stretching method contains a calcium carbonate having 0.1 to 2 wt.% of a mean article size of 0.5 to 4 μm and an aluminum silicate having 0.05 to 1 wt.% of a mean particle size of 0.1 to 2.0 μm. The polyester film further has a refractive index nz of a thickness direction of 1.495 or more and a value obtained by dividing a heat shrinkage factor (HS) (%) of a longitudinal direction at about 200 deg.C by an F-5 value (N/mm<2> ) (F5) of a longitudinal direction measured at the ambient temperature (at about 23 deg.C) of the film of 0.028 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film formed by a simultaneous biaxial stretching method. More specifically, it is suitable for a thermal transfer ribbon base film which is excellent in productivity without printing unevenness of ink even at high speed and excellent in printing performance without cutting or delamination during the process or in use and excellent in productivity. The present invention relates to a biaxially oriented polyester film formed by an axial stretching method.

[0002]

2. Description of the Related Art As a base film for a thermal transfer printer, a film having a specified surface roughness (Japanese Patent Application Laid-Open No. 62-299).
No. 389) is known. Among the transfer recording methods, the sublimation transfer recording method is increasing in demand as a recording method capable of easily outputting a high-quality full-color image. This sublimation type thermal transfer is a method in which a heat sublimable dye is contained in a binder, and only the dye sublimates by heat and is absorbed by an image receiving layer of a transfer receiving paper to form a gradation image. In this sublimation transfer recording method, in recent years, a higher printing speed has been required. As a method of increasing the speed, a method of efficiently transmitting the heat from the thermal head at the time of printing is effective. For this reason, the base film is required to be thinner. However, in order to meet this demand by simply reducing the thickness of the conventional stretched film, the following problems, for example, in the case of applying a dye ink with the thinning of the film, and workability in the slitting process. There is a new problem that gets worse.

The workability relates to the slipperiness of the film. To improve the workability, a method of giving minute irregularities to the film surface is generally used. Specifically, at the time of polymerization of a thermoplastic polymer which is a raw material of a film with inert particles,
Or, a method of adding after polymerization (external particle addition method), a method of depositing a part or all of a catalyst used at the time of polymerization of a thermoplastic polymer in a polymer in a reaction step (internal particle precipitation method), and the like are known. I have.

However, in the method for producing an ultra-thin film, when the polyester film containing inert particles at the same concentration as that of a normal film is made thinner, the number of inert particles per unit area decreases. However, the space between the inert particles on the film surface is widened, the film surface becomes too flat, and the slipperiness tends to decrease. Therefore, in order to compensate for the decrease in slipperiness due to thinning, it is necessary to increase the concentration of added inert particles or increase the particle size as the film thickness is reduced.

In this case, voids are formed around the interface, that is, around the inert particles due to poor affinity between the inert particles and the thermoplastic polymer, particularly during melt extrusion or drawing at a high draft ratio. As a result of the occurrence of voids, fine particles are easily removed from the obtained film, and not only the shaving powder is generated due to contact with the roller and the process is soiled, but also the breakage is apt to occur, and the productivity is increased. And the stability of the production conditions is lacking. In particular, if coarse particles are present in the slit cross section, tearing may occur from the coarse particles.

As a method of solving such a problem, a biaxially oriented polyester film obtained by a sequential biaxial stretching method is provided with 0.1 to 2% by weight of calcium carbonate having an average particle size of 0.5 to 4 μm and an average particle size of 0.5 to 4 μm. Particle size 0.1-2.0 μm
Japanese Patent Application Laid-Open No. 2000-103874 proposes to contain 0.05 to 1% by weight of aluminum silicate. According to the publication, even during melt extrusion or drawing at a high draft ratio, the affinity between the inert particles and the thermoplastic polymer is improved, so that voids generated around the interface between the two, that is, around the inert particles. It can be suppressed.

[0007]

According to the study of the present inventors, the biaxially oriented polyester in which the above-mentioned voids are suppressed, generates shavings due to contact with a roller, thereby contaminating the process or causing breakage. This problem has been solved, but when used as a transfer material for sublimation-type thermal transfer, the heat of the thermal head deforms the ribbon, which may reduce the reproducibility of images. Was.

Conventionally, means for improving dimensional stability have been employed to suppress the deformation of the ribbon. Specifically, the ribbon is stretched at a higher stretching ratio to make the molecular chains more highly oriented or at a higher temperature. Alternatively, heat crystallization may be performed for a long time to highly crystallize. However, in order to solve this problem, when the molecular chains are oriented to a higher degree or crystallized to a higher degree by the sequential biaxial stretching method, delamination frequently occurs, which causes breakage and product defects. It was found that the productivity was reduced.

Accordingly, an object of the present invention is to solve these problems and secure a transferred image having excellent shape reproducibility and gradation, and at the same time, is excellent in productivity and particularly suitable for a base film for a thermal transfer ribbon. It is to provide a biaxially oriented polyester film.

[0010]

According to the present invention, an object of the present invention is to prepare calcium carbonate having an average particle size of 0.5 to 4 μm, which is formed by a simultaneous biaxial stretching method, of 0.1 to 2 μm. A biaxially oriented polyester film containing 0.05 to 1% by weight of aluminum silicate having an average particle diameter of 0.1 to 2.0 μm, and a refractive index (nz) in a thickness direction.
Is greater than or equal to 1.495, and the longitudinal heat shrinkage (HS) (%) at 200 ° C. is divided by the longitudinal F-5 value (N / mm ² ) (F5) measured at room temperature (23 ° C.). Value is 0.
This is achieved by a biaxially oriented polyester film which simultaneously has a value of 028 or less.

In a preferred embodiment, the biaxially oriented polyester film of the present invention has a center line average roughness of the film surface of 10 to 40 nm and a space factor of the film of 1 to 19%. The frequency of protrusions having a height of 1.5 μm or more on the surface of the film is 300 to 7
00 pieces / cm ² is that, and in a continuous thickness chart of said film, biaxially oriented polyester was provided that the difference in height between adjacent peak and valley (thickness difference) is less than 8% of the average thickness The film and polyester include a biaxially oriented polyester film containing polyethylene-2,6-naphthalenedicarboxylate as a main component, and can be suitably used as a base film for a thermal transfer ribbon.

[0012]

DETAILED DESCRIPTION OF THE INVENTION [Polyester] As the polyester in the present invention, a polyester containing ethylene-2,6-naphthalenedicarboxylate or ethylene terephthalate as a main component is preferable. Furthermore, the mechanical strength of the film is large, it is possible to produce a relatively thin film, the film is easy to transmit the heat of the thermal head to the sublimation dye, by simultaneous biaxial stretching,
For the reason that tear resistance which is a weak point is improved,
Polyesters containing ethylene-2,6-naphthalenedicarboxylate as a main component are preferred.

The polyester containing ethylene-2,6-naphthalenedicarboxylate as a main component (hereinafter sometimes referred to as polyethylene-2,6-naphthalenedicarboxylate or PEN) includes ethylene-
The polymer containing 2,6-naphthalenedicarboxylate as a repeating unit refers to a polymer of 80 mol% or more, preferably 90 mol% or more, particularly preferably 95 mol% or more. When the PEN is a copolymer,
As the copolymerization component, a compound having two ester-forming functional groups, for example, oxalic acid, adipic acid, phthalic acid, sebacic acid, dodecanedicarboxylic acid, succinic acid, 5-sodium sulfoisophthalic acid, terephthalic acid, isophthalic acid, 2-potassium sulfoterephthalic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, phenylindanedicarboxylic acid, diphenyletherdicarboxylic acid,
Oxycarboxylic acids such as p-oxyethoxybenzoic acid, propylene glycol, 1,2-propanedioxide
1,3-butanediol, 1,4-butanediol
1,1,5-pentaneddiol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-
Cyclohexane dimethanol, 1,4-cyclohexane dimethanol, p-xylylene glycol, ethylene oxide adduct of bisphenol A, ethylene oxide adduct of bisphenol sulfone, triethylene glycol, polyethylene oxide glycol, polytetra Methylene oxide glycol, neopentyl glycol and the like can be mentioned. Of these, copolymerized polyesters having an isophthalic acid component of 1 to 5 mol% are preferred because of their relatively high tear strength.
-A homopoester consisting essentially of naphthalenedicarboxylate is preferred because of its relatively high strength and dimensional stability at high temperatures. Further, the PEN may be one in which a part or all of a hydroxyl group and / or a carboxyl group at a terminal of a molecular chain is blocked by a monofunctional compound such as benzoic acid or methoxypolyalkylene glycol. It may be modified with a very small amount of an ester-forming compound having three or more functions such as glycerin and pentaerythritol within a range where a substantially linear polymer can be obtained.

The above-mentioned PEN is known per se and can be produced by a conventionally known method. However, the transesterification method, that is, an ester-forming derivative of 2,6-naphthalenedicarboxylate (particularly, It is preferable to carry out a transesterification reaction with dimethyl ester) and then to subject the resulting reaction product to a polycondensation reaction at a high temperature and high vacuum to produce a polyester having a desired polymerization degree. At that time, a manganese compound is preferably used as the transesterification catalyst. Examples of the manganese compound include oxides, chlorides, carbonates, and carboxylate salts.
Of these, acetate is particularly preferably used. Also,
It is preferable to add a phosphorus compound at the time when the transesterification reaction is substantially completed to deactivate the transesterification catalyst. As the phosphorus compound, trimethyl phosphate,
Triethyl phosphate, tri-n-butyl phosphate and orthophosphoric acid can be preferably used. Of these, trimethyl phosphate is particularly preferred. Furthermore, an antimony compound is preferably used as the polycondensation catalyst. As the antimony compound, antimony trioxide is particularly preferably used.

The intrinsic viscosity (orthochlorophenol, 35 ° C.) of the polyester is preferably 0.50 to 1.10, more preferably 0.52 to 0.95,
Particularly preferably, it is 0.54 to 0.75. If the intrinsic viscosity is less than 0.50, the tear strength of the formed film may be insufficient, which is not preferable. On the other hand, if the intrinsic viscosity exceeds 1.10, productivity in the raw material production step and the film forming step is impaired, which is not preferable. In the polyester of the present invention, if necessary, an antioxidant, a heat stabilizer, a viscosity modifier, a plasticizer,
Additives such as hue improvement, lubricants and nucleating agents can be added.

[Inert Particles] The biaxially oriented polyester film in the present invention needs to contain both calcium carbonate and aluminum silicate, and fine projections derived from these inert particles are formed on the film surface. Due to its existence, it has excellent workability and an appropriate space factor. If the inert particles are only calcium carbonate, if the workability of the film is to be ensured, the space factor of the film becomes too large,
On the other hand, if the inert particles are only aluminum silicate, large projections cannot be formed, and workability and space factor cannot be compatible.

In the present invention, the calcium carbonate contained in the polyester has an average particle size of 0.5 to 4.0 μm.
m, preferably 0.5 to 2.0 μm. Here, the “average particle size” means the “equivalent spherical diameter” of the particle at a point of 50% by weight of the total measured particles. In addition,
"Equivalent spherical diameter" means the diameter of an imaginary sphere (ideal sphere) having the same volume as a particle, and can be calculated from an electron micrograph of the particle or measurement by a normal sedimentation method. If the average particle size of the calcium carbonate is less than 0.5 μm, when the film is wound on a master roll or a product roll, the air squeezing property is poor (it is difficult for the entrained air to escape), and wrinkles frequently occur or slippage occurs. And the workability in the processing step is reduced. Also,
When the average particle size of calcium carbonate exceeds 4.0 μm, the surface of the film is excessively roughened to increase the space factor, resulting in a decrease in printability and an increase in cutting. The average particle size of calcium carbonate may be larger than the film thickness.

The amount of calcium carbonate added must be 0.1 to 2% by weight in the polyester, and preferably 0.1 to 1% by weight. If the amount of calcium carbonate is less than 0.1% by weight, the air squeezing property when winding the film becomes poor, while if it exceeds 2% by weight, the film surface becomes excessively rough, and the thermal transfer ribbon is used as a thermal transfer ribbon. When printing at high speed, the printing becomes unclear because the heat transfer coefficient of the film is low.

As the calcium carbonate used in the present invention, any one can be employed, and calcite crystals such as precipitated calcium carbonate and the like produced by a chemical method from naturally occurring limestone, chalk (chalk), and limestone, and lime milk Argonite crystals, vaterite crystals obtained by reacting carbon dioxide at a high temperature, and combinations thereof. Heavy calcium carbonate (calcite crystal) obtained by mechanically grinding limestone can also be used.

Next, the aluminum silicate contained in the polyester in the present invention has an average particle size of 0.1%.
-2.0 µm, preferably 0.3-1.2 µm, and its content is 0.05-1 wt%.
If the average particle size of the aluminum silicate is less than 0.1 μm or less than 0.05% by weight, the slipperiness of the film is impaired and the workability is reduced, while the average particle size of the aluminum silicate is 2. If it exceeds 0 μm or if its content exceeds 1% by weight, the film surface becomes rough and the space factor is excessively increased. The aluminum silicate used in the present invention refers to a plate-like aluminosilicate, and any one such as kaolin clay composed of a naturally occurring kaolin mineral can be used. Further, the kaolin clay may have been subjected to a purification treatment such as washing with water.

Incidentally, the biaxially oriented polyester film of the present invention may further contain other fine particles as a third component in addition to the fine particles of calcium carbonate and aluminum silicate. In that case, as the other fine particles, for example, the average particle size falls within the range of the roughness of the above calcium carbonate or aluminum silicate, and is larger than the particle size of the fine particles of calcium carbonate and aluminum silicate contained therein. Small ones are preferred.

The above-mentioned calcium carbonate and aluminum silicate may be added to the polyester before or during the polymerization reaction of the polyester, may be kneaded in an extruder when pelletizing after the polymerization is completed, and may be melt-extruded into a sheet. May be added and dispersed in an extruder. Among them, it is preferable to add them before polymerization because a uniform dispersion state can be easily achieved. As a method of adding calcium carbonate and aluminum silicate to the polyester, a method known per se may be adopted, for example, PE
When N is added before polymerization, it is preferable that calcium carbonate and aluminum silicate are added to ethylene glycol, and the mixture is dispersed in the polymer by ultrasonic vibration or the like.

[Biaxially Oriented Polyester Film] The biaxially oriented polyester film of the present invention needs to have a refractive index (nz) in the thickness direction of 1.495 or more, and the upper limit thereof is at most 1.525. Is preferred. The preferable range of the refractive index in the thickness direction is 1.497 to 1.515.
It is. If the refractive index in the thickness direction is smaller than 1.495,
In particular, in the case of a polyethylene-2,6-naphthalenedicarboxylate film, delamination (lamellar peeling) is likely to occur, and breakage or surface peeling may occur during processing or use. Then, in order to obtain a film that can be used practically while keeping the refractive index (nz) in the thickness direction at 1.495 or more, it is necessary to form a film by a simultaneous biaxial stretching method.

The biaxially oriented polyester film used in the present invention is subjected to a heat shrinkage (hereinafter sometimes referred to as HS) (%) (%) in the machine direction at a temperature of 200 ° C. for 10 minutes, and at room temperature ( The F-5 value (N / mm ² ), which is the load at 5% elongation in the elongation-load curve of the film measured at about 23 ° C.) in the machine direction, has a specific relationship, that is, HS is expressed as F− The value divided by 5 values is 0.028
Or less, preferably 0.026 or less. When the value obtained by dividing the HS by the F-5 value exceeds 0.028, the HS becomes excessively large or the F-5 value becomes excessively small. Shrinkage and wrinkling of the film that is the base material occur, causing color shift and image distortion of the print, and in the latter case, the Young's modulus of the film in the vertical direction is insufficient and the tension applied when starting or stopping printing Elongation deformation occurs in the film, and wrinkles and cuts occur due to tension in the printer. Note that the lower limit of the value obtained by dividing HS by the F-5 value is preferably at least 0.01 from the viewpoint of maintaining the film formability of the film.

In order to reduce the HS, it is preferable to increase the heat setting temperature. In particular, in the case of a simultaneous biaxial stretching machine capable of imparting longitudinal relaxation during heat setting, it is preferable to use the same. On the other hand, in order to increase the F-5 value, it is preferable to increase the stretching ratio in the longitudinal direction. Preferred HS
Is in the range of 0-7%. Further, the F-5 value is preferably at least 10 N / mm ² , more preferably 1 N / mm ^2.
It is preferably in the range of 0 to 25 N / mm ² . Simultaneous biaxial stretching is necessary to make these HS and F-5 values compatible with the refractive index in the thickness direction.
It is preferable to simultaneously biaxially stretch EN to obtain a biaxially oriented polyester film.

The thickness of the biaxially oriented polyester film of the present invention is preferably 0.5 to 10 μm. When the thickness exceeds 10 μm, it takes time for heat conduction at the time of printing, which is not suitable for high-speed printing. On the other hand, when the thickness is less than 0.5 μm, the workability is poor due to low tension, and the strength required for the ribbon cannot be secured.

The biaxially oriented polyester film of the present invention has fine projections caused by the above-mentioned calcium carbonate and aluminum silicate on its surface, and its preferred surface shape will be described below. The center line average roughness of the surface of the biaxially oriented polyester film (R
a) is preferably in the range of 10 to 40 nm.
If the center line average roughness of the film surface is less than 10 nm, sufficient slip properties may not be obtained, and winding may be difficult. On the other hand, when the center line average roughness is larger than 40 nm, when high-speed printing is performed by a thermal transfer printer, the heat transfer coefficient is poor and the printing may be unclear.

The frequency of protrusions having a height of 1.5 μm or more on the surface of the biaxially oriented polyester film in the present invention is as follows:
It is preferable that the number be in the range of 300 to 700 / cm ² . The frequency of the protrusions having a height of 1.5 μm or more is 300 / c.
If it is less than m ² , the gap between the projections is widened and the film surface is flattened, and the film tends to be poor in slipperiness. On the other hand,
The frequency of the projections having a height of 1.5 μm or more is 700 / cm ²
If it exceeds, the film surface becomes excessively rough, and in some cases, due to voids generated around the contained fine particles, breakage during film formation and breakage during stretch film formation may occur frequently.

The space factor of the biaxially oriented polyester film in the present invention is preferably in the range of 1 to 19%. If the space factor is less than 1%, the slipperiness and workability (handling properties) of the film are likely to be insufficient, while if it exceeds 19%, the surface becomes excessively rough and may cause breakage in some cases. There is.

The continuous thickness chart obtained by continuously measuring the thickness of the biaxially oriented polyester film in the present invention shows that the difference between the heights of adjacent peaks and valleys (thickness difference) is an average in both the longitudinal and width directions. It is preferable that the thickness is 8% or less, preferably 5% or less, more preferably 3% or less of the thickness.
If the thickness difference exceeds 8% of the average thickness, the amount of heat transfer received from the thermal head of the printer fluctuates due to the thickness difference, which may cause printing unevenness. Further, in the continuous thickness chart, the interval between the peaks and the valleys is preferably 10 cm or more from the viewpoint of suppressing print unevenness. Furthermore, in the continuous thickness chart, the thickness unevenness (a value obtained by dividing the maximum thickness difference obtained by subtracting the minimum thickness from the maximum thickness by the average thickness) is preferably 10% or less, more preferably 8% or less. When the thickness unevenness is 10% or less, a film having an extremely uniform thickness is obtained, and an excellent effect that no unevenness is generated when applying an easy-to-use agent and no unevenness is generated when a dye is applied is achieved. it can.

The biaxially oriented polyester of the present invention has an AC volume resistivity in a molten state of at most 60.
It is preferably × 10 ⁸ Ωcm. When the AC volume resistivity is at most 60 × 10 ⁸ Ωcm, a sufficient amount of electric charge can be imparted to bring the molten polyester extruded from the melt extruder into close contact with the cooling drum during film formation, and the thickness of the film is reduced. A stable film formation can be secured without lowering the uniformity.
To achieve such an AC volume resistivity, it is preferable to add a quaternary phosphonium salt of sulfonic acid to the polyester.

[Method of forming biaxially oriented polyester film]
The biaxially oriented polyester film in the present invention needs to be manufactured by a simultaneous biaxial stretching method. As a longitudinal stretching mechanism of the simultaneous biaxial stretching machine, there are a conventional type of a screw type in which a clip is placed on a groove of a screw to increase a clip interval, and a pantograph type in which a pantograph is used to increase a clip interval. They are,
There are problems such as a low film-forming speed and difficulty in changing conditions such as a draw ratio. However, when such equipment is already possessed, it can be used for producing the biaxially oriented polyester film. On the other hand, in recent years, a simultaneous biaxial tenter of a linear motor type has been developed, and has attracted attention due to its high film forming speed. The simultaneous biaxial stretching of the linear motor system can solve these problems at once. Therefore, when a new simultaneous biaxial stretching machine is introduced, it is preferable to use equipment of this type. Also, simultaneous biaxial stretching does not use a longitudinal stretching roller as in sequential biaxial stretching, and thus has the advantage of reducing scratches on the film surface. Others
In the sequential biaxial stretching, the surface of the benzene ring or naphthalene ring of the polyester tends to be parallel to the film surface, the refractive index nz in the thickness direction decreases, the tear propagation resistance decreases,
Although delamination is easy, this is improved by simultaneous biaxial stretching. In the structure that can relax vertically in the heat setting area,
The heat shrinkage (HS) in the vertical direction at 200 ° C. can be further reduced. Since these characteristics match the required characteristics of the thermal transfer ribbon, it is necessary to perform simultaneous biaxial stretching in the present invention.

The simultaneous biaxial stretching referred to in the present invention is to simultaneously orient the film in the machine direction and the transverse direction. The film is conveyed while holding both ends of the film with clips using a simultaneous biaxial stretching machine. Refers to the operation of stretching in the vertical and horizontal directions. Here, the longitudinal direction of the film is the longitudinal direction of the film, and the lateral direction is the width direction of the film. Of course, it is sufficient if there is a portion where the stretching in the longitudinal direction and the stretching in the transverse direction are simultaneously stretched temporally.Therefore, after stretching in the transverse direction or the longitudinal direction independently first, the longitudinal direction and the transverse direction are combined. A method of simultaneous stretching, a method of further stretching independently in the horizontal or vertical direction after simultaneous biaxial stretching, and the like are also included in the scope of the present invention.

In order to produce the polyester film of the present invention, after the polyester contains predetermined inert fine particles, for example, at a normal extrusion temperature, that is, at a temperature not lower than the melting point (hereinafter referred to as Tm) and not higher than (Tm + 70 ° C.). The melt-extruded film-like melt is quenched on the surface of a rotary cooling drum to obtain an unstretched film having an intrinsic viscosity of 0.40 to 0.90 dl / g. In the case of PEN, for example, drying is performed at 170 ° C.
For about an hour, the extrusion temperature is around 300 ° C., and the surface temperature of the cooling drum is about 60 ° C. In order to increase the adhesion between the film melt and the rotary cooling drum in this step, an electrostatic adhesion method for imparting an electrostatic charge to the film melt has been known. The above-mentioned electrostatic adhesion may be insufficient due to the high electric resistance of the melt of the polyester. However, as a countermeasure, in the present invention, the polyester is added to the polyester in an amount of 0.05 to 40 mmol% of sulfonic acid based on the total carboxylic acid component. It is preferred to include a quaternary phosphonium.

Next, this unstretched film was guided to a simultaneous biaxial stretching machine by gripping both ends of the film with clips, and was subjected to (Tg-10 of polyester) to
(Tg + 70), heated to one stage or two or more stages for simultaneous biaxial stretching at an area magnification of 10 to 40 times, and then (melting point Tm-120 of polyester) to
In a temperature range of (Tm-10) C, simultaneous biaxial stretching is performed at an area magnification of 2 to 5 times in one step or in two or more steps. Subsequently, after performing fixed-length heat setting in a temperature range of (Tm-70) to (Tm) ° C., in a cooling process from the heat setting, preferably in a vertical and horizontal direction in a temperature range of 100 to 200 ° C. Preferably, the relaxation treatment is performed in the range of 1 to 10% in each direction. In the case of PEN, the preheating temperature is about 140 ° C,
The stretching temperature is preferably about 145 ° C, and the heat setting temperature is preferably about 235 ° C. Thereafter, the film is cooled and wound up to room temperature, while being subjected to relaxation treatment in the vertical and horizontal directions if necessary, to obtain the desired simultaneous biaxial polyester film.

In the present invention, a process before or after simultaneous biaxial stretching is performed in order to impart surface characteristics of the film, for example, to impart easy adhesion, easy slipping, releasing property, and antistatic property. It is also preferable to coat a coating agent on the surface of the polyester film.

For example, when the biaxially oriented polyester film of the present invention is used for a thermal transfer ribbon, the surface of the polyester film to which the ink layer is applied is coated with a polyester modified with urethane, polyester, acrylic or vinyl resin. It is preferable to have a coating layer made of at least one water-soluble or water-dispersible resin selected from the group consisting of: This coating layer is useful for enhancing the adhesion between the ink layer composed of the sublimable dye and the resin binder and the polyester film.

[Thermal Transfer Ink Layer] When the biaxially oriented polyester film of the present invention is used for a thermal transfer ribbon, the thermal transfer ink layer is not particularly limited, and a known one can be used. That is, a binder component,
It is composed of a coloring component or the like as a main component, and an appropriate amount of a softener, a plasticizer, a dispersant, or the like added as necessary. Specific examples of the main component include, as binder components, known waxes such as carnauba wax and paraffin wax, celluloses, polyvinyl alcohols, polyvinyl alcohol partially acetalized products, polyamides, and various high-melting polymer materials. As the coloring agent, carbon black is mainly used, and other various dyes or organic or inorganic pigments are used. Further, the thermal transfer ink layer may contain a sublimable dye. Various disperse dyes and basic dyes can be used as the sublimable dye.

As a method for providing the thermal transfer ink layer on the surface of the biaxially oriented polyester film (if the adhesive layer is provided, the surface of the adhesive layer), a known method, for example, hot melt coating, solvent A solution coating method such as a gravure, reverse, or slit die method can be used in the state where it is added.

[Fusion Prevention Layer] The biaxially oriented polyester film used for the thermal transfer ribbon is provided on one side of the biaxially oriented polyester film on which the thermal transfer ink layer is not provided, in order to prevent sticking of the thermal head portion. For example, a conventionally known or used anti-fusing layer can be provided. Further, it is preferable to form a fusion layer containing a polyurethane obtained from a polyol (for example, polyalcohol) and a polyisocyanate compound, and a phosphate-based compound as a surfactant. As the polyol forming the polyurethane, for example, polyvinyl butyral resin having a hydroxyl group,
Polyesters, polyether resins, polybutadiene resins, acrylic polyols, nitrocellulose resins, cellulose acetate resins, cellulose acetate resins, and polyalcohols such as urethane and epoxy prepolymers can be preferably used. Further, the provision of the anti-fusing layer may be performed on the unstretched film or may be performed after the film is once wound as a biaxially oriented film. By doing so, after processing into a thermal transfer ribbon,
This is preferable because the thermal history applied to the film base from the thermal head can be reduced.

[0041]

EXAMPLES The present invention will be further described below with reference to examples. Incidentally, various physical property values and characteristics in the present invention,
It is measured and defined as follows. In the examples, “parts” means parts by weight. (1) Average particle size of particles CP-50 type centrifugal particle size analyzer (Centrifuga 1) manufactured by Shimadzu Corporation
The measurement was carried out using a Particle Size Analyzer. The particle size corresponding to 50% by mass was read from the integrated curve of the particles of each particle size calculated based on the obtained centrifugal sedimentation curve and the residual amount, and this value was defined as the above average particle size (Book “particle size”). Measurement Techniques ", published by Nikkan Kogyo Shimbun, 1975, pp. 242 to 247).

(2) Particle Size of Particles in Film A small piece of the sample film was fixed on a sample table for a scanning electron microscope, and a sputter device (JIS-JIS) manufactured by JEOL Ltd. was used.
Using a 1100 type ion sputtering apparatus), the film surface was exposed to 0.25 mm under a vacuum of 1 × 10 ⁻³ torr.
Ion etching was performed for 10 minutes under the conditions of kV and 1.25 mA, and gold sputtering was performed using the same apparatus. Then, the sample film is scanned with a scanning electron microscope for 1-3.
Observation was performed at 10,000 times, and the area equivalent particle diameter (Di) of at least 100 particles was obtained with Luzex 500 manufactured by Nippon Regulator Co., Ltd. Area equivalent represented by the following formula (Di)
Was defined as the average particle size (D).

[0043]

(Equation 1)

(3) Film Thickness and Thickness Variation An electronic micrometer (K-312A) manufactured by Anritsu Corporation
5 m each in the machine direction and the transverse direction of the sample film under the conditions of a needle pressure of 30 g and a running speed of 25 mm / sec.
And the thickness was measured over a length of 1 m to obtain a continuous thickness chart. From this chart, the maximum and minimum thickness,
And the difference in thickness between adjacent peaks and valleys was read. Next, the same sample was measured for width (cm), length (cm), weight (g), and density (g / Cm), and the average thickness (μm) was calculated by the following equation (1). Then, the ratio of the difference between the maximum thickness and the minimum thickness to the average thickness is calculated by the following formula (2) to obtain a thickness unevenness, and the ratio of the difference between the thicknesses of adjacent peaks and valleys to the average thickness is calculated by the following formula (3). Calculated.

[0045]

(Equation 2)

[0046]

(Equation 3)

[0047]

(Equation 4)

(4) Surface Roughness (Center Line Average Roughness, Ra) A surface roughness meter (Tokyo Seimitsu Co., Ltd.)
The center line average roughness was measured by Surfcom 111A), and the average value thereof was calculated as the surface roughness.

(5) Space Factor (SF) A sample film was placed in a square of 10 cm square (area 100 c
cut into m ^2), the weight w (g) and density d (g / cm ³⁾ from the gravimetric method the thickness of the cut sample film t1
(Μm). In addition, the 10 cut out as described above is used.
Ten sample films of cm square were stacked, and the thickness t2 (μm) of one sample film obtained using a micrometer was obtained and calculated by the following equation.

[0050]

(Equation 5)

(6) Number of protrusions having a height of 1.5 μm or more NIKON two-beam microscope OPTIPHOTO (wavelength λ =
546 nm), the height of the protrusions was calculated using the fact that the interference fringes were 2 / λ, and the protrusions having a height of 1.5 μm or more per cm ² were counted. This was performed on each of the front and back surfaces of the sample film, and the average value thereof was calculated to obtain the number of protrusions having a height of 1.5 μm or more.

(7) Refractive index (nz) in the thickness direction An Abbe refractometer (manufactured by Atago Co., Ltd.) was used.
Using a-D line, the refractive index in the film thickness direction is measured at 25 ° C.

(8) Heat Shrinkage A 30 cm square sample film whose exact length was measured in advance was suspended in an oven set at a temperature of 200 ° C., and held for 10 minutes under no load. After taking out and returning to room temperature, a change in the dimension is measured. The heat shrinkage is defined by the following equation.

[0054]

(Equation 6)

Here, L _{0 is} the length of the film before the heat treatment, L is the length of the film after the heat treatment in the same direction, and the heat shrinkage is 10 samples in the longitudinal (longitudinal) direction of the film. The average value was obtained by sampling.

(9) F-5 value tensile tester (ORIENTENCE TENSILON T)
Using a C-100 type), in a room adjusted to a temperature of 23 ° C. and a relative humidity of 50%, a film test piece cut out into a strip shape (length 150 mm × width 10 mm) along the longitudinal direction of the sample film, It was fixed between chucks having an interval of 100 mm. Then, the film test piece is pulled at a pulling rate of 100 mm / min to obtain a load-elongation curve (stress-strain curve) on the chart. A load value at 5% elongation is determined from this load elongation curve, and this is defined as an F-5 value.

(10) Delamination resistance (fold delamination whitening ratio) A sample film was cut into a square (80 mm x 80 mm) and folded into two pieces by hand so that opposing sides could overlap lightly. . The two-folded sample film was sandwiched between a pair of flat metal plates and pressed with a press at a predetermined pressure P1 (kgf / cm ² ) for 20 seconds.
Next, the fold of the two-fold sample film taken out from between the metal plates was stretched out by hand, returned to the original flat state, and again,
20 at pressure P1 (kgf / cm ² )
Pressed for seconds. Thereafter, the sample film sample is taken out from between the metal plates, and the length (mm) of the whitened portion appearing on the fold is measured with a microscope. In addition, the measurement of the length of the whitened portion was performed by using six different press pressures P1 (1, 2, 3, 3).
4, 5, 6 (kgf / cm ² )), respectively, using fresh film samples. Then, the average value of the total length (mm) of the whitened portion at each press pressure is obtained, and the ratio of the average value to the total length (80 mm) of the fold is defined as the fold delamination whitening ratio. It is used as an index indicating the likelihood of occurrence of delamination. The smaller the value of the fold delamination whitening ratio, the better the delamination resistance.

(11) Film-forming properties The degree of the film-forming state up to the time when the formed base film is slit into a predetermined width is observed and evaluated according to the following criteria. Rank A: An extremely stable slit having a frequency of occurrence of cutting or wrinkling of 0 to 1 time / day and a film forming property capable of winding. Rank B: Stable slits with a frequency of occurrence of cuts or wrinkles of 2 to 4 times / day and film formability capable of winding up. Rank C: Stable slits with a frequency of cuts or wrinkles of 5 to 7 times / day and film forming properties at a level that cannot be rolled up. Rank D: The frequency of occurrence of cuts or wrinkles is 8 times / day or more, and stable slits in which extremely large wrinkles are generated and film forming properties in which winding is not expected.

(12) Printability Images were printed on an image receiving sheet VY-200 (standard paper manufactured by Hitachi, Ltd.) using a printer Hitachi VY-200 (manufactured by Hitachi, Ltd.) so that the optical density became maximum. With respect to the produced thermal transfer ribbon, printability and wrinkles generated in the ribbon were evaluated according to the following criteria. ：: Clear printing is possible Δ: Printing density is not uniform ×: Ribbon is wrinkled and printing is disturbed.

Example 1 0.03 parts of manganese acetate tetrahydrate was added to a mixture of 100 parts by weight of dimethyl 2,6-naphthalenedicarboxylate and 60 parts of ethylene glycol, and the mixture was gradually heated from 150 ° C. to 240 ° C. The transesterification reaction was performed while raising the temperature. On the way, when the reaction temperature reached 170 ° C., 0.024 part of antimony trioxide was added, and calcium carbonate particles having an average particle size of 1.5 μm and aluminum silicate particles having an average particle size of 0.8 μm were separately added to the film. The content was added so that the content was 0.3% by weight and 0.2% by weight. Then, when the temperature reached 220 ° C., 0.021 parts of 3,5-dicarboxybenzenesulfonic acid tetrabutylphosphonium salt (1 mmol% Was added). Subsequently, a transesterification reaction was performed, and after the transesterification reaction was completed, 0.023 parts of trimethyl phosphate was added. Thereafter, the reaction product was transferred to a polymerization reactor, and the temperature was raised to 290 ° C.
A polycondensation reaction was carried out under a high vacuum of 0.2 mmHg or less to obtain polyethylene-2,6-naphthalenedicarboxylate having an intrinsic viscosity of 0.61 dl / g measured with an o-chlorophenol solution at 25 ° C.

This polyethylene-2,6-naphthalenedicarboxylate was melt-extruded in the form of a sheet using an extruder and a T-die, and was then applied to a water-cooled casting drum.
It was adhered at a speed of 5 m / min and solidified by cooling to obtain an unstretched film. On the surface of the unstretched film to which the ink layer was to be applied, a coating agent 1 having the following composition was applied by a gravure coater so that the coating thickness after drying was 0.1 μm as an easy adhesion layer. The unstretched film was introduced into a simultaneous biaxial stretching machine, preheated at 140 ° C, and then 5.4 mm in the longitudinal direction at 145 ° C.
It was simultaneously stretched while holding it with a 4.0-fold clip in the transverse direction. Thereafter, the resultant was heat-set at 200, 230 and 235 ° C. for 2 seconds in the first, second and third heat-setting zones, respectively, to obtain a biaxially oriented film having a thickness of 3.5 μm.

Composition of Coating Material 1 (Acrylic Resin + Polyester Resin + Epoxy Resin) The composition of the coating material 1 is as follows. The acrylic resin is composed of 65% by mole of methyl methacrylate / 28% by mole of ethyl acrylate / 2% by mole of 2-hydroxyethyl methacrylate / 5% by mole of N-methylolacrylamide, and has a solid content of 42% by weight. 35 mol% of terephthalic acid / 13 mol% of isophthalic acid / 5 mol% of 5-sodium sulfoisophthalic acid, ethylene glycol 45 mol% / diethylene glycol 5 mol% as glycol component
42% by weight on a solid basis; N, N, N ', N',-tetraglycidyl-m-xylylenediamine as an epoxy-based crosslinking agent is 6% by weight on a solid basis; 10% by weight of lauryl polyoxyethylene as a solid content weight agent. Table 1 shows the properties of the obtained biaxially oriented polyester film.

Next, a coating agent 2 having the following composition was used as an anti-fusing layer, and the surface of the biaxially oriented film opposite to the surface on which the easy-adhesion layer was formed was gravure so that the coating thickness after drying was 0.5 μm. A transfer ink having the following composition was coated with a gravure coater on the above-mentioned easy-adhesion layer so that the coating film thickness after drying was 1.0 μm, thereby producing a heat-sensitive transfer ribbon. Composition of coating agent 2-Acrylic ester 14.0% by weight-Amino-modified silicone 5.9% by weight-Isocyanate 0.1% by weight-Water 80.0% by weight Composition of thermal transfer ink-Magenta dye (MSRedG) 3.5 % By weight Polyvinyl acetoacetal resin 3.5% by weight Methyl ethyl ketone 46.5% by weight Toluene 46.5% by weight Table 1 shows the properties of the obtained thermal transfer ribbon.

Example 2 The inert particles were changed to those shown in Table 1, the stretching temperature was 140 ° C., and the longitudinal stretching ratio was 5.1.
The same operation as in Example 1 was repeated except that the draw ratio and the transverse stretching ratio were changed to 3.8 times. Table 1 shows the properties of the obtained biaxially oriented polyester film and thermal transfer ribbon.

Comparative Example 1 The same procedure as in Example 1 was carried out until an unstretched film was prepared.
, And then stretched 5.4 times in the longitudinal direction between high and low speed rollers. The coating 1 described in Example 1 was dried on the side to which the ink layer was applied as an easy-adhesion layer so that the coating thickness after drying was 0. Coating was performed with a gravure coater so that the thickness became 1 μm. Then, while holding it with a clip at a temperature of 145 ° C. with a horizontal stretching machine, 4.
The film was stretched 0 times and then heat-set at 235 ° C. for 3 seconds in a heat-setting zone to obtain a 3.5 μm-thick biaxially oriented polyester film. The obtained biaxially oriented polyester had a slightly large value of (HS / F5) and slightly poor printability, a low refractive index nz in the thickness direction, and poor delamination. The obtained biaxially oriented polyester was used as a thermal transfer ribbon by repeating the same operation as in Example 1. Table 1 shows the properties of the obtained biaxially oriented polyester film and thermal transfer ribbon.

Comparative Example 2 The same operation as in Example 1 was repeated, except that the inert particles were changed to those shown in Table 1. Table 1 shows the properties of the obtained biaxially oriented polyester film and thermal transfer ribbon.

[0067]

[Table 1]

In Table 1, PEN is polyethylene-2,6-naphthalenedicarboxylate, and HS is 20.
Thermal shrinkage (%) when treated at 0 ° C. for 10 minutes, F5 is the F-5 value (N / mm ² ) in the longitudinal direction measured at 23 ° C., and the number of coarse protrusions is the number of protrusions having a height of 1.5 μm or more. , Nz is the refractive index in the thickness direction of the film.

[0069]

According to the present invention, polyester having high mechanical strength and capable of reducing thickness, especially polyethylene-2,
It is possible to provide a film suitable for a base film of a thermal transfer ribbon, which utilizes the thermal dimensional stability of a 6-naphthalene dicarboxylate film at a high temperature and improves the delamination resistance which is a disadvantage.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 3/34 B29K 67:00 C08L 67/02 B29L 7:00 // B29K 67:00 B41M 5/26 B B29L 7:00 101A F term (reference) 2H111 AA01 AA26 AA27 BB06 BB08 4F071 AA45 AA46 AB21 AB26 AD06 AF31Y AF61Y AH16 BB02 BB06 BB08 BC01 BC14 BC15 BC16 4F210 AA24 AA26 AB16 AG01 AH81 QA00Q07QA18QA01QA00

Claims (4)

[Claims] 1. A method in which calcium carbonate having an average particle size of 0.5 to 4 μm, which is formed by a simultaneous biaxial stretching method, has a thickness of 0.1 to 2 μm.
A biaxially oriented polyester film containing 0.05% to 1% by weight of aluminum silicate having an average particle size of 0.1 to 2.0 μm and a refractive index (nz) in the thickness direction of 1.495 or more. ,
And the longitudinal heat shrinkage (HS) at 200 ° C. (%)
Was measured at 23 ° C. in the vertical direction (N / mm ² ).
A biaxially oriented polyester film, wherein the value obtained by dividing by (F5) is 0.028 or less. 2. The following (1) to (4) (1) the center line average roughness of the film surface is 10 to 40 n
m; (2) the space factor of the film is 1 to 19%; (3) the frequency of protrusions having a height of 1.5 μm or more on the surface of the film is 300 to 700 / c.
It is m ^2; and, (4) in a continuous thickness chart of the film, the difference in height between adjacent peaks and valleys (thickness difference)
Is at most 8% of an average thickness. 3. Polyester is polyethylene-2,6-
2. The method according to claim 1, which comprises naphthalene dicarboxylate as a main component.
2. The biaxially oriented polyester film according to 1. 4. The thermal transfer ribbon according to claim 1, which is used for a thermal transfer ribbon.
3. The biaxially oriented polyester film according to any one of 3.