JPH091947A - Thermal transfer biaxially oriented polyester film - Google Patents

Abstract

PURPOSE: To improve the coating properties and slitting properties by using a biaxially oriented polyester film having a local slack area rate of a specific value or less as a base film of a transfer material for a printer used in a thermal recording system using an electrothermal recorder such as a thermal printer. CONSTITUTION: As a thermal transfer film, a biaxially oriented polyester film having a local slack area rate of 10% or less is used. The polyester uses ethylene glycol as main starting material. The polyester film preferably has centerline mean roughness of one side surface of a range of 0.02 to 1μm. Fine particles inert for the polyester are mixed in any step of the extruding step before forming the film from the polyester manufacturing step. As the inert fine particle, kaolin can be, for example, used. The mean particle size of the inert compound is normally 0.1 to 10μm of equivalent spherical diameter, or preferably selected from a range of 0.3 to 3μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film suitable for heat-sensitive transfer, and more particularly to a biaxially oriented polyester film for heat-sensitive transfer excellent in coating property and slit property. .

[0002]

2. Description of the Related Art Conventionally, various types of recording systems are known, but a thermal recording system using a thermal recording device such as a thermal printer has a high operability, maintainability and cost. It is excellent and widely used. A biaxially oriented film of polyester, particularly polyethylene terephthalate, has been used as the base film of the transfer material for printers because it is excellent in heat resistance, chemical resistance, mechanical properties and the like.
In recent years, regarding this heat-sensitive recording method, a transfer material for a printer has been used for the purpose of reducing the printing energy, speeding up the printing, increasing the fineness of the printing, lengthening the ink ribbon, downsizing the ink ribbon cassette, downsizing the printer, etc. It is required to make the base film thinner.

In order to meet this demand, conventionally known films are not always sufficient, and films having more suitable properties are desired. That is, the base film for heat-sensitive transfer usually has a heat-meltable or sublimable ink layer on one surface and a heat-resistant layer on the other surface.
As the base film becomes thinner, wrinkles are more likely to occur when the ink layer or heat-resistant layer is applied and dried,
This causes problems such as coating stripes and film breakage. Further, the film provided with the ink layer and the heat-resistant layer is slit to a predetermined width and wound up as an ink ribbon, but as the base film becomes thinner, meandering of the film is more likely to occur, which causes ribbon ribbon. The problems of misalignment, wrinkling and breakage occur.

[0004]

Means for Solving the Problems As a result of intensive studies in view of the above problems, the present inventors have found that a film having specific physical properties overcomes the above problems and is useful as a film for thermal transfer. The present invention has been completed.
That is, the gist of the present invention is that the local slack area ratio is 10%.
It exists in the biaxially oriented polyester film characterized by the following.

Hereinafter, the present invention will be described in detail. The polyester referred to in the present invention means an aromatic dicarboxylic acid such as terephthalic acid or 2,6-naphthalenedicarboxylic acid or an ester thereof, and a polyester obtained by using ethylene glycol as a main starting material, but contains other components. It doesn't matter. In this case, the dicarboxylic acid components include terephthalic acid, phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and its isomers, adipic acid,
One or more of sebacic acid and oxycarboxylic acids such as p-oxyethoxybenzoic acid can be used. As the glycol component, one kind or two or more kinds of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used. In any case, the polyester of the present invention refers to a polyester in which 80 mol% or more of repeating structural units have ethylene terephthalate units or ethylene-2,6-naphthalate units.

The biaxially oriented polyester film of the present invention preferably has a center line average roughness (Ra) of at least one surface in the range of 0.02 to 1 μm. When Ra is less than 0.02 μm, slipperiness may be deteriorated, wrinkles may be formed on the film, problems during processing, and sticking of the thermal head may occur. If Ra exceeds 1 μm, the sharpness of the print may be lacked, the sensitivity may be lowered, and the thermal head may be worn. As one of the methods for obtaining a film having such a surface roughness, a metal compound dissolved in the reaction system at the time of polyester production, for example, a phosphorus compound or the like is allowed to act on the metal compound dissolved in the system after the transesterification reaction. There is a method for precipitating fine particles, that is, a so-called precipitated particle method.

However, since this method has a limit in the amount of precipitated particles, it is preferable to employ the so-called additive particle method. The additive particle method is a method in which polyester is blended with inert fine particles in any step from the polyester production step to the extrusion step before film formation, and examples of the inert fine particles include kaolin, talc, and magnesium carbonate. , Calcium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, lithium fluoride, etc. and Ca, Ba,
Examples thereof include, but are not limited to, one or more kinds of metal compounds selected from terephthalates such as Zn and Mn, carbon black, and the like.

The shape of the inert compound may be spherical, lumpy or flat, and its hardness,
There are no particular restrictions on specific gravity, color, etc. The average particle size of the inert compound is usually 0.1 to 10 μm in equivalent spherical diameter.
m, preferably 0.3 to 3 μm. The blending amount with respect to the film is selected from the range of 0.01 to 5% by weight, preferably 0.05 to 3% by weight, and more preferably 0.05 to 2% by weight. Further, various resins and lubricants may be applied for the same purpose, and known methods such as composite of roughened film, promotion of crystallization of film after melt extrusion, sand mat method, chemical treatment method, coating mat method, etc. The method can be applied as appropriate.

Further, the polyester film of the present invention is
The polyester film is a polyester film starting from the above-mentioned polyester and oriented biaxially in both longitudinal and transverse directions. The local slack area ratio measured by the method described below must be 10% or less, preferably 7% or less. If this value exceeds 10%, wrinkles are likely to occur during the coating and drying of the ink layer or the heat-resistant layer, which causes problems such as coating streaks and film breakage. . Also, slit as an ink ribbon,
Ribbing of the ribbon is likely to occur at the time of winding, and this causes problems such as winding deviation, wrinkles and breakage of the ribbon.

In order to reduce the local slack area ratio to 10% or less, for example, in a polyester film manufacturing process, a sheet extruded from a slit-shaped die after melting is cooled and solidified by a casting drum cooled to 30 to 50 ° C. It is preferable to form an unstretched sheet. Furthermore, the degree of plane orientation (ΔP) of the biaxially oriented polyester film obtained by subsequent predetermined stretching and heat treatment is preferably 0.168 or more, preferably 0.170 or more. Also, the faster the production rate, the better. The speed varies depending on the device, but is usually 100 m / min or more, preferably 200 m / min or more. The thickness of the film of the present invention is not particularly limited, but the effect of the present invention is particularly remarkable for a thin film of 10 μm or less, preferably 6 μm or less for thermal transfer.

Next, the production method of the polyester film of the present invention will be specifically described, but the production method is not limited to the following production examples. First, a polyester chip is dried, extruded in a sheet form from a slit-shaped die after melting, and cooled and solidified by a casting drum cooled to 30 to 50 ° C. while closely contacted by an electrostatic contact method to form an unstretched sheet. The sheet is multi-staged and has a high draw ratio in the longitudinal direction at a high temperature in the longitudinal direction.
3. After being stretched to be 5 times, 90-130 ° C., 4.
The film is transversely stretched at 0 to 6.0 times, and then heat treated at 200 to 250 ° C to obtain a biaxially oriented polyester film. In addition, if necessary, a stretching temperature of 95 to
After re-longitudinal stretching at 120 ° C. and a stretching ratio of 1.01 to 2.5 times,
It is possible to obtain a biaxially oriented polyester film by heat treatment, or by subjecting it to transverse stretching and then heat treatment. If necessary, the polyester film may be subjected to corona discharge treatment or coating treatment in the process.

The biaxially oriented polyester film obtained by the above operation has a tensile elastic modulus in the machine direction and the transverse direction of 5
00kg / mm ² or more, F5 value in the longitudinal and transverse directions 10-15 kg / mm ^2, the longitudinal and transverse direction of the heat shrinkage ratio is preferably 1% or less. Tensile elastic modulus is 500
If it is less than kg / mm ² , the film tends to be weak and wrinkles tend to occur during processing. F5 value is 10kg
If it is less than / mm ² , the film tends to stretch and it is difficult for the film to elastically recover, and there is a possibility that the ribbon may become thick due to plastic deformation during printing. Also, the F5 value is 15 kg /
If it exceeds mm ² , shrinkage due to heat of the thermal head at the time of printing becomes large and clear printing becomes impossible. If the heat shrinkage exceeds 1%, wrinkles during processing and unclear printing tend to occur. Further, the intrinsic viscosity of the film is 0.58 or more, preferably 0.63 or more. If the intrinsic viscosity is less than 0.58, sticking and perforation are likely to occur due to heat of the thermal head during printing.

Next, a transfer ink layer is formed on the biaxially oriented polyester film of the present invention obtained as described above. At that time, if necessary, pretreatment such as corona discharge treatment or undercoating may be performed. The transfer ink of the present invention is not particularly limited, and known ones can be used. Specifically, it contains a binder component, a coloring component, etc. as a main component, and if necessary, a softening agent, a flexible agent, a melting point adjusting agent,
You may mix a smoothing agent, a dispersing agent, etc. as an additive component.

Specific examples of the above main components include paraffin wax, carnauba wax, as a binder component,
Well-known waxes such as ester wax and various low melting point polymers are useful, and carbon black and various organic and inorganic pigments or dyes are useful as the colorant component. The ink also includes sublimable ink. As a method for providing the transfer ink layer on one side of the film of the present invention, known methods, for example, hot melt coating, gravure with a solvent added, reverse, using a solution coating method such as a slit die method and the like it can. It is desirable to provide a known anti-fusing layer on the side of the film where the transfer ink layer is not provided in order to prevent sticking of the thermal head.

[0015]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The evaluation method used in the present invention is as follows. (1) Local slack area ratio A constant tension, constant speed unwinding and winding device for a film provided with a tension adjusting mechanism, at least two parallel rolls, a visible light irradiation lamp and a reflection projection screen is used. A film roll slit into a predetermined width and length is attached to the unwinding part of the above device, the film is unwound, passed between two parallel rolls with an interval, and then wound. At that time, the tension applied to the film between the two parallel rolls was adjusted to 1.82 kg / mmm ² per film cross-sectional area and the speed of the film was 10 m / min, and the film was irradiated with visible light. The reflected light from the film is projected on the projection screen.
The local slack is the local slack of the film (the part with poor flatness), and when the above device is used, the visible light radiated to that part is not reflected normally but becomes a black shadow on the reflective projection screen. Appears. The film is run for a specified length, during which the black shadow with a length of 1 m or more in the longitudinal direction of the film, that is, the number and area of local slack is measured visually or by image processing, and the local slack area is calculated from the following formula. Calculate the rate.

[0016]

[Equation 1] It should be noted that minute local slack with a length of less than 1 m does not affect the workability as a thermal transfer ribbon even if it exists in the film, and therefore is not measured.

(2) Wrinkle film tension 1.82 kg / mm ² , film speed 12
Under a condition of 0 m / min and a drying temperature of 100 ° C., a heat-resistant layer made of a silicone-modified urethane resin and having a thickness of 0.3 μm is provided on one surface of the film by a bar coating method. Then, under the conditions of a film tension of 1.82 kg / mm ² , a film speed of 80 m / min, and a drying temperature of 70 to 50 ° C., ethylene was formed on the film surface opposite to the surface provided with the heat-resistant layer by the gravure coating method.
60 parts of vinyl acetate copolymer, 25 parts of carbon black,
An ink layer having a coating amount of 1.6 g / m ² comprising 15 parts of hydrogenated rosin is provided. The condition of wrinkles occurring on the film in the above process is evaluated in the following three stages. ○: No wrinkles are generated in the process and there is no problem. △: Slight wrinkles are generated in the process, but disappears immediately. ×: Continuous creases are generated in the process and processing is impossible.

(3) Slitting property Film tension 1.82 kg / mm ² , film speed 10
Under the condition of 0 m / min, the film provided with the heat resistant layer and the ink layer is slit into a ribbon shape having a width of 5 mm and a length of 300 m. At this time, the slitting property of the ribbon is evaluated according to the following three grades. ○… Slits and winding up are good, and there is no problem. △… Slightly meandering, but there is no winding deviation. ×… Rolling deviation and wrinkling occur. (4) Surface orientation (ΔP) Abbe refractometer manufactured by Atago Optical Co. The maximum value nγ of the refractive index in the film plane, and the refractive index nβ in the direction perpendicular thereto,
And the refractive index nα of the film in the thickness direction was measured, and the degree of plane orientation was calculated from the following equation. In addition, the measurement of the refractive index was performed at 23 ° C. using a sodium D line.

[0019]

[Equation 2]

(5) Tensile Modulus Tensile Testing Machine Intesco Model 200 manufactured by Intesco Corporation
Using the 1 type, a sample film having a length of 300 mm and a width of 20 mm was pulled at a strain rate of 10% / min in a room controlled at a temperature of 23 ° C. and a humidity of 50% RH, and the first linear portion of the tensile stress-strain curve was drawn. Is calculated by the following formula.

[0021]

(Equation 3) (In the above formula, E is the tensile elastic modulus (kg / mm ² ), Δσ is the stress difference due to the original average cross-sectional area between two points on the straight line, and Δε is the strain difference between the same two points.)

(6) F5 value Intesco model tensile tester Intesco model 200
A sample film having a length of 50 mm and a width of 15 mm was pulled at a speed of 200 mm / min in a room adjusted to a temperature of 23 ° C. and a humidity of 50% RH using the 1 type, and the strength at 5% elongation was defined as F5 value.

(7) Heat Shrinkage Rate Heat treatment was performed in an atmosphere of 100 ° C. for 3 minutes in a non-tensioned state, and the lengths of the samples before and after the heat treatment were measured to calculate by the following formula.

[0024]

(Equation 4)

(8) Surface roughness (Ra) The center line average roughness Ra (μm) is defined as the surface roughness.
It was determined as follows using a surface roughness measuring instrument (SE-3F) manufactured by Kosaka Laboratory Ltd. That is, the reference length L (2.5 mm) from the sectional curve of the film in the direction of the center line
When the roughness curve y = f (x) is expressed with the center line X axis of this extracted portion and the direction of the vertical magnification as the Y axis, the value given by the following formula is expressed as (μm). . The center line average roughness was represented by the average value of the center line average roughness of the extracted portions obtained from the 10 section curves obtained from the surface of the sample film. The tip radius of the stylus was 5 μm, the load was 30 mg, and the cutoff value was 0.08.
mm.

[0026]

(Equation 5) (9) Intrinsic viscosity 1 g of polymer is phenol / tetrachloroethane = 50
/ 50 (weight ratio) in 100 ml of a mixed solvent.
It was measured at 0 ° C.

Example 1 Polyethylene terephthalate containing 0.7% by weight of silicon dioxide having an average particle diameter of 1.3 μm was dried, melted at 308 ° C., and extruded into a sheet from a T-shaped die at a speed of 60 m /
It was brought into close contact with a casting drum set at 43 ° C., which was rotated for a minute, by an electrostatic contact method, and cooled and solidified to obtain an amorphous unstretched sheet. Subsequently, the film was stretched in the machine direction at a temperature of 101 ° C. to 2.7 times, and further at 80 ° C. to a ratio of 1.59 times.
And stretched 4.62 times. Further, heat treatment was performed at 235 ° C. to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 2.5 μm and an intrinsic viscosity of 0.65. A heat-resistant layer and an ink layer were provided on the obtained film, and further slit into a ribbon shape to evaluate workability. The obtained results are shown in Table 1 below together with those of other examples and comparative examples.

Example 2 A biaxially stretched film was obtained in the same manner as in Example 1 except that the rotating speed of the casting drum was changed. That is, it was cooled and solidified by a casting drum rotating at a speed of 55 m / min. Next, the processability was evaluated in the same manner as in Example 1 using the obtained film. Example 3 Polyethylene terephthalate containing 0.7% by weight of silicon dioxide having an average particle diameter of 1.3 μm was dried, melted at 308 ° C., and extruded into a sheet through a T-type die at a speed of 52 m /
It was brought into close contact with a casting drum set at 43 ° C., which was rotated for a minute, by an electrostatic contact method, and cooled and solidified to obtain an amorphous unstretched sheet. Subsequently, the film was stretched in the longitudinal direction by 2.7 times at 95 ° C., further by 1.59 times at 80 ° C., and then in the transverse direction by 4.55 times at 110 ° C. Further heat treatment at 235 ℃,
A biaxially oriented polyethylene terephthalate film having a thickness of 2.5 μm and an intrinsic viscosity of 0.65 was obtained. Next, the processability was evaluated in the same manner as in Example 1 using the obtained film.

Example 4 Polyethylene terephthalate containing 0.7% by weight of silicon dioxide having an average particle diameter of 1.3 μm was dried, melted at 308 ° C. and extruded into a sheet form from a T-type die at a speed of 52 m /
It was brought into close contact with a casting drum set at 43 ° C., which was rotated for a minute, by an electrostatic contact method, and cooled and solidified to obtain an amorphous unstretched sheet. Subsequently, it was stretched 2.5 times at 101 ° C in the longitudinal direction and 1.76 times at 88 ° C, and then 100 ° C in the transverse direction.
Was stretched 4.25 times. Further, heat treatment was performed at 236 ° C. to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 2.5 μm and an intrinsic viscosity of 0.65. Next, the processability was evaluated in the same manner as in Example 1 using the obtained film.

Example 5 Polyethylene terephthalate containing 0.7% by weight of silicon dioxide having an average particle diameter of 1.3 μm was dried, melted at 308 ° C. and extruded into a sheet form from a T-type die at a speed of 60 m /
It was brought into close contact with a casting drum set at 43 ° C., which was rotated for a minute, by an electrostatic contact method, and cooled and solidified to obtain an amorphous unstretched sheet. Subsequently, after stretching 3.5 times in the longitudinal direction at 95 ° C., it was stretched 4.0 times in the transverse direction at 110 ° C. Further, heat treatment was performed at 235 ° C. to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 2.5 μm and an intrinsic viscosity of 0.65. Next, the processability was evaluated in the same manner as in Example 1 using the obtained film.

Comparative Example 1 Polyethylene terephthalate containing 0.7% by weight of silicon dioxide having an average particle diameter of 1.3 μm was dried, melted at 308 ° C. and extruded into a sheet form from a T-type die at a speed of 44 m /
It was brought into close contact with a casting drum set at 38 ° C., which was rotated for a minute, by an electrostatic contact method, and cooled and solidified to obtain an amorphous unstretched sheet. Subsequently, the film was stretched in the machine direction at a temperature of 102 ° C by 2.7 times and further at 90 ° C by 1.67 times, and then stretched in a transverse direction at 110 ° C.
Was stretched 4.55 times. Further, heat treatment was performed at 235 ° C. to obtain a biaxially oriented polyethylene terephthalate film having a thickness of 2.5 μm and an intrinsic viscosity of 0.65. Next, the processability was evaluated in the same manner as in Example 1 using the obtained film. As is clear from the results of Table 1, the films of Examples 1 to 5 satisfying the requirements of the present invention have excellent properties for thermal transfer, whereas Comparative Example 1 having a large local slack area ratio is an ink. Poor coatability and slitability.

[0032]

[Table 1]

[0033]

INDUSTRIAL APPLICABILITY The biaxially oriented polyester film for heat-sensitive transfer of the present invention has excellent ink coating properties and slit properties, and its industrial value is high.

Claims (1)

[Claims] 1. A biaxially oriented polyester film for thermal transfer, which has a local slack area ratio of 10% or less.