JPH11321130A - Biaxially oriented polyester film for thermal transfer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate film which is hardly wrinkled even when high-energy printing is performed, and is suitable as a support for a melting type and a sublimation type thermal transfer ink ribbon. SOLUTION: The heat shrinkage at 150 ° C. is 4% or less in both the longitudinal direction and the lateral direction of the film, and the film has 7MP.
A thermal transfer method wherein the film has a longitudinal elongation E _MD (%) and a lateral elongation E _TD (%) when heat-treated at 220 ° C. in a state where the stress a is applied, satisfying the following expressions: For biaxially oriented polyester film. [Equation 1] E _MD ² + E _TD ² ≦ 100 ............

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a base film used for a thermal transfer recording medium.

[0002]

2. Description of the Related Art In recent years, thermal transfer printing has been often used for color or full-color (natural color) printing for both sublimation and fusion printing. One is wrinkles (print wrinkles) of the ink ribbon that occur during printing. This print wrinkle is a phenomenon that the base film loses heat due to the heat from the thermal head and wrinkles are generated in the ink ribbon, and this portion is missing printing, which causes the quality of the printed image to be extremely deteriorated. . Conventionally, various improvements have been studied to prevent the occurrence of print wrinkles. However, the increase in printing energy accompanying the recent increase in printing speed is remarkable, and further measures for print wrinkles are required.

[0003]

SUMMARY OF THE INVENTION The present invention provides a substrate film which is hardly wrinkled even when high energy printing is performed, and is suitable as a support for a fusion type and sublimation type thermal transfer ink ribbon. That is the task.

[0004]

The present inventor has solved the above problem.
As a result of intensive studies, polyesters with specific physical properties
The above problems can be solved by using
Find that it can be easily solved and complete the present invention.
Reached. That is, the gist of the present invention is that heat absorption at 150 ° C.
The shrinkage ratio is 4% or less in both the vertical and horizontal directions of the film.
220 ° C. with a stress of 7 MPa applied to the film
Elongation E in the longitudinal direction of the film when heat-treated at_MD(%)
And transverse elongation E _TD(%) Satisfies the following equation
Biaxially oriented polyester film for thermal transfer characterized by the following:
Live in Lum.

[0005]

[Equation 2] E _MD ² + E _TD ² ≦ 100 ............

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The polyester of the polyester film used in the present invention is at least 80 mol% of the repeating unit, preferably 9 mol%.
0 mol% or more refers to ethylene terephthalate, ethylene-2,6-naphthalate, or cyclohexane dimethylene terephthalate. If the ratio is 20 mol% or less, for example, ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1,4
Terephthalic acid as a dicarboxylic acid component, such as diol components such as -butylene glycol, 1,4-cyclohexane dimethylene glycol, and polyalkylene glycol;
A copolyester containing oxycarboxylic acid such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, oxybenzoic acid or the like as a copolymer component may be used. Among these, polyethylene terephthalate is most preferable in consideration of quality and economy.

The polyester film used in the present invention comprises:
If necessary, the composition may contain inorganic particles, organic lubricants, antistatic agents, stabilizers, dyes, pigments, organic polymers, and the like. In particular, to adjust the gloss of the transfer recorded image,
Alternatively, in order to improve the runnability at the time of production of the polyester film or when formed into an ink ribbon, it is preferable to include inorganic particles or organic particles in the polyester film, and to roughen the surface of the polyester film. Has an average surface roughness of 0.03 to 0.2
In particular, when the thickness is set to 0.04 μm, more preferably 0.04 to 0.1 μm, both running property and obtaining a high-definition image can be achieved. Further, in order to recycle the scrap of the film generated during the production, a coating layer component on the film surface may be mixed in the film.

[0008] The polyester film of the present invention needs to be biaxially oriented and then heat-set to form a film. I can't reach it. The thickness of the polyester film is not particularly limited, but a film having a thickness of 1 to 10 μm is preferably used for thermal transfer.

The biaxially oriented polyester film for thermal transfer according to the present invention has a film elongation percentage E _MD (%) and a lateral elongation when heat-treated at 220 ° C. with a stress of 7 MPa applied to the film. The rate E _TD (%) needs to satisfy the following equation.

[0010]

[Equation 3] E _MD ² + E _TD ² ≦ 100 ............

When the sum of squares of the elongation percentage in the longitudinal direction and the elongation percentage in the lateral direction of the film is larger than 100, the ink ribbon using this film as a substrate has a large deformation under high temperature and high stress, and Wrinkling becomes remarkable due to the energy printing. It is preferable to set the sum of squares of the elongation percentage in the longitudinal direction and the elongation percentage in the lateral direction of the formula to 80 or less, more preferably 60 or less, in order to reduce wrinkles.

The biaxially oriented polyester film for thermal transfer of the present invention has the above-mentioned properties under high temperature and high stress, and has a heat shrinkage at 150 ° C. in the longitudinal direction and without load. It is necessary to be 4% or less in the horizontal direction. If the shrinkage in either the vertical or horizontal direction exceeds 4%, it will be processed into an ink ribbon.
The heat applied when the back heat-resistant layer or the ink layer is applied to the substrate film greatly shrinks the substrate film, so that uneven coating streaks easily occur on the ink ribbon. 150
The shrinkage ratio at ° C is preferably 3 in both the vertical and horizontal directions.
% Or less, more preferably 2% or less. As the shrinkage decreases, unevenness and streaks of coating are reduced and the film is improved.

The heat-sensitive transfer polyester film of the present invention has a thickness variation of 10 in an arbitrary 15 m long section in the longitudinal direction.
% Is preferable. When the thickness unevenness exceeds 10%, when a high-definition full-color image is printed with an ink ribbon using this as a base film, a difference in color tone due to density fluctuation can be visually recognized, and image quality is impaired. Sometimes. The range of the thickness unevenness is more preferably 7% or less, and if it is 5% or less, it is a level that hardly causes a problem.

The polyester film for thermal transfer of the present invention may have on at least one surface thereof a coating layer which has been coated in a stretching step and then dried to complete orientation crystallization. This coating layer has, for example, an easy-adhesive property as an undercoat of the ink or has a releasability, or an easily-adhesive property as an undercoat of the back heat-resistant layer. It is provided for the purpose of using it as a layer itself.

Next, the method for producing the polyester film of the present invention will be described, but the present invention is not limited to the following production method. The polyester chips are dried by a known means, melt-extruded from a die at a temperature of from melting point to 320 ° C., and cooled and solidified on a casting drum.
At this time, it is preferable to use an electrostatic contact method as a means for holding the film in close contact with the drum. The unstretched film thus obtained is subjected to the next stretching step. In the stretching step, first longitudinal stretching using a roll stretching method,
Next, sequential biaxial stretching in which transverse stretching using a tenter method is performed is preferable. Although the stretching ratio and the stretching temperature vary depending on the composition of the polyester used, taking PET as an example,
In the longitudinal stretching, the film is stretched in one or more stages in the longitudinal direction so that the film temperature becomes 3.0 to 6.0 times in the range of 80 to 120 ° C. At this stage, if necessary, coating with water as a medium can be performed. Thereafter, the film is guided to a tenter, and in the case of PET, stretched 3.0 to 6.0 times in the width direction at 90 to 130 ° C. Next, heat setting is performed at 200 to 240 ° C. for 1 to 30 seconds. After this heat setting, the heat setting temperature is 0 to
Reheat fixation is performed at a temperature lower by 100 ° C. These heat fixation
At the time of reheating fixation, shrink 0.1-5% in the width direction,
Alternatively, the film is stretched by 0.1 to 5% or a combination of both, and then cooled and wound up to obtain a biaxially oriented polyester film.

The biaxially oriented polyester film for thermal transfer of the present invention is provided with a melt type or sublimation type ink layer on one side of the film. These ink layers are provided as an ink layer on a polyester film, for example, by coating or hot-melt coating a known substance containing a coloring material of a pigment or a dye and a polymer binder as main components by a known method. Can be.

Usually, a heat-resistant layer is provided on the surface opposite to the surface on which the ink layer is provided. This heat-resistant layer on the back
This is provided for the purpose of preventing sticking due to heat when coming into contact with the thermal head, and a conventionally known one can be used for this. For example, a material containing a lubricant such as waxes, higher fatty acids and derivatives thereof, a silicon compound, a fluorine compound as a main component, or a material in which inorganic particles, crosslinked organic particles, and fluororesin particles are used in combination with a lubricant, etc. be able to. In addition, the method of applying the heat-resistant layer on the back surface to the polyester film is performed in the process of forming the polyester film,
After applying as a water-soluble or aqueous dispersion, a method of drying, stretching, and heat setting may be used, or an aqueous or organic solvent-based coating may be applied to a polyester film on which orientation crystallization has been completed, and then dried. It is also possible to use a method of providing the same.

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the scope of the invention. In addition, the evaluation method in an Example is as follows. In Examples and Comparative Examples, “parts” means “parts by weight”.

[0019] (1) 7 MPa under stress, the one end of the elongation film at 220 ° C., a film sectional area 1 mm ² per 7.
In a state where the weight was hung so as to be 0 N, heat treatment was performed for 3 minutes in a hot-air circulation oven maintained at 220 ° C., and the length of the sample before and after the heat treatment was measured. At this time, the elongation was calculated by the following equation.

[0020]

Elongation (%) = 100 × change in sample length before and after heat treatment / sample length before heat treatment

(2) Heat shrinkage at 150 ° C. under no stress In a state where no stress is applied to the film, heat treatment is performed for 3 minutes in a hot air circulating oven maintained at 150 ° C. Was measured. At this time, the elongation was calculated by the following equation.

[0022]

## EQU5 ## Shrinkage (%) = 100 × change in sample length before and after heat treatment / sample length before heat treatment

(3) Unevenness of Film Thickness A continuous film thickness measuring device (using an electronic micrometer) manufactured by Anritsu Co., Ltd. randomly extracted 20 points in a longitudinal direction of a 15-m long section of a biaxially oriented film. The maximum thickness (μm) and minimum thickness (μm) for each sample
m) is measured, and thickness unevenness is calculated from the average thickness (μm) in that section according to the following formula.
The thickness unevenness of the sample was determined.

[0024]

[Equation 6] Thickness unevenness (%) = ｛(maximum thickness−minimum thickness) /
(Average thickness)｝ × 100

The average thickness used here is a value calculated from the measured area, weight and density of the sample. At this time, the density was 1.397 for polyethylene terephthalate, 1.354 for polyethylene naphthalate,
Polycyclohexane dimethylene terephthalate is 1.2
70 was used uniformly. (5) Intrinsic Viscosity of Polyester Film The intrinsic viscosity of the polyester film was measured at a temperature of 30 ° C. by dissolving in a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio).

(6) Center line average roughness (Ra) This was performed according to the method described in JIS B0601-1976. For measurement, Kosaka Laboratory Co., Ltd. surface roughness meter SE-3
F was used. The center line average roughness is determined under the conditions of a stylus diameter of 2 μm, a stylus weight of 30 mg, a cutoff value of 0.08 mm, and a measurement length of 2.5 mm. Do this at 12 measurement points,
Among these, the maximum value and the minimum value were respectively cut, and the average value of 10 points was obtained and defined as Ra. (7) Suitability of Ink Ribbon Processing and Degree of Print Wrinkling On one side of the polyester film, a coating agent having the following composition as a back heat-resistant layer is applied by a gravure coater so that the thickness after drying becomes 0.2 μm. It was dried by blowing hot air at 80 ° C.

Backside heat-resistant layer composition Amino-modified silicone / epoxy-modified silicone / ethanol / isopropanol = 4/3/43/50 (weight ratio) Then, on the opposite side of the backside heat-resistant layer, a molten ink having the following composition was applied with a thickness of 3 μm. Then, an ink layer was formed by hot melt coating so as to obtain an ink ribbon, and the ink ribbon was cut.

Composition of molten ink Carnauba wax: 30 parts Paraffin wax: 45 parts Ethylene / vinyl acetate copolymer: 5 parts Carbon black: 20 parts Visual inspection of the ink ribbon as to whether or not the ink ribbon was processed normally by processing. Investigated and judged.

The prepared ink ribbon was incorporated into a FAX machine (model name: FAX-1350M) manufactured by Brother Industries, Ltd., and black solid printing was performed on the entire surface of the A4 size sheet at the maximum printing density. The degree of print wrinkles was determined using the following criteria.

[0030]

[Table 1] Ａ Rank AA Wrinkles and missing prints occurred at all Not Rank A Print wrinkles and print omissions are so small that they can be ignored. Occurs 発 生

Example 1 Polyethylene terephthalate containing 0.2% of silica particles having an average particle size of 1.0 μm and having an intrinsic viscosity of 0.60 was dried by a conventional method, and then melt-extruded at 290 ° C. An unstretched film was formed on a cast drum while using the electrostatic adhesion method. The unstretched film was guided to a roll stretching apparatus, stretched 2.7 times in the longitudinal direction at 98 ° C., and further stretched 1.68 times in the longitudinal direction at 85 ° C. Next, the film is stretched 4.5 times in the transverse direction at 105 ° C. by a tenter method, and further stretched by 2% in the heat-fixing zone of the tenter for 22%.
After heat-setting at 0 ° C. for 3 seconds, a 5% relaxation treatment was performed at 200 ° C. in the width direction to obtain a biaxially oriented polyester film having a thickness of 4.5 μm. The thickness unevenness of this film in the vertical direction was 6%.

The evaluation results of the obtained polyester film are shown in Table 1 below, and since the amount of elongation under high temperature and high stress is small, the occurrence of wrinkles in printing is small. In addition, since the shrinkage ratio under no stress is small, the film deformation at the time of providing the ink layer and the back heat resistant layer was small, and the workability to the ink ribbon was also good.

Example 2 Polyethylene naphthalate having an intrinsic viscosity of 0.55 and containing 0.2% of silica particles having an average particle size of 1.0 μm was dried in a conventional manner, and then melt-extruded at 310 ° C. An unstretched film was prepared on a cast drum while using the adhesion method. The unstretched film was guided to a roll stretching apparatus, stretched 2.7 times in the longitudinal direction at 130 ° C., and further stretched 1.8 times in the longitudinal direction at 123 ° C. Subsequently, the film is stretched 5.0 times in the transverse direction at 135 ° C. by a tenter method, and further stretched by 2% in a heat fixing zone of the tenter while performing 22% tentering.
After heat-setting at 0 ° C. for 3 seconds, a 5% relaxation treatment was performed at 200 ° C. in the width direction to obtain a biaxially oriented polyester film having a thickness of 4.5 μm. The thickness unevenness of this film in the longitudinal direction was 5%.

The evaluation results of the obtained polyester film are shown in Table 1. The amount of elongation under high temperature and high stress is small, so that the occurrence of print wrinkles during printing is small. In addition, since the shrinkage ratio under no stress is small, the film deformation at the time of providing the ink layer and the back heat resistant layer was small, and the workability to the ink ribbon was also good.

Comparative Example 1 Casting, longitudinal stretching and transverse stretching of the polyester performed in Example 1 were performed in exactly the same manner. The heat setting is performed after heat setting at 220 ° C. for 3 seconds without tentering.
A 5% relaxation treatment was performed in the width direction at 5 ° C. to obtain a biaxially oriented polyester film having a thickness of 4.5 μm. The thickness unevenness in the longitudinal direction of the obtained film was 5%. The evaluation results of the obtained polyester film are shown in Table 1. Since the elongation amount under high temperature and high stress was out of the range of the present invention, wrinkles occurred in high energy printing. The film deformation during application of the ink layer and the back heat-resistant layer was small, and the workability to the ink ribbon was good.

Comparative Example 2 Casting, longitudinal stretching and transverse stretching of the polyester in Example 1 were carried out in exactly the same manner. In the heat setting, a biaxially oriented polyester film having a thickness of 4.5 μm was obtained without performing relaxation treatment after performing heat setting at 220 ° C. for 3 seconds while performing tentering of 2%. The thickness unevenness of this film in the longitudinal direction was 5%. The obtained polyester film has a large shrinkage at 150 ° C. and is out of the range of the present invention, so that the shrinkage during the processing of the ink ribbon is remarkable, and wrinkles and unevenness are generated in the ink. The ribbon could not be created.

Comparative Example 3 After casting was performed in exactly the same manner as in Example 1,
The film was stretched 2.5 times in the longitudinal direction at 98 ° C. by a roll stretching device, and further stretched 1.5 times in the longitudinal direction at 85 ° C. Thereafter, transverse stretching and heat fixing were performed in exactly the same manner as in Example 1 to obtain a biaxially oriented polyester film having a thickness of 4.5 μm. The thickness unevenness of this film in the vertical direction was 9%. The evaluation results of the obtained polyester film are shown in Table 1. The elongation amount under high temperature and high stress is out of the range of the present invention.
Print wrinkles occurred with high energy printing. The film deformation during application of the ink layer and the back heat-resistant layer was small, and the workability to the ink ribbon was good.

[0038]

[Table 2]

[0039]

According to the biaxially oriented polyester film for thermal transfer of the present invention, when an ink ribbon is prepared by using this as a support, the elongation under high temperature and high stress is small, so that printing can be performed even when high energy printing is performed. It has the characteristic of hardly causing wrinkles, and is suitable as a support for a fusion-type or sublimation-type ink ribbon for thermal transfer, and its industrial value is high.

Claims (1)

[Claims] 1. The film has a heat shrinkage at 150 ° C. of 4% or less in both the longitudinal and transverse directions of the film,
A thermal transfer method wherein the film has a longitudinal elongation E _MD (%) and a lateral elongation E _TD (%) when heat-treated at 220 ° C. in a state where the stress a is applied, satisfying the following expressions: For biaxially oriented polyester film. [Equation 1] E _MD ² + E _TD ² ≦ 100 ............